A REVIEW OF SYNCHRONIZATION OF ESTRUS IN POSTPARTUM … · 2017-10-30 · estrous synchronization agent. The percentage of MGA-treated females in estrus in a 6-d period following

A REVIEW OF SYNCHRONIZATION OF ESTRUS IN POSTPARTUM CATTLE’

is

K. G. Odde

Colorado State University2, Fort Collins 80523

ABSTRACT

Estrus has been synchronized in cattle with progestogens, prostaglandins (prostaglandin F2a and its analogues), progestogen-estrogen combinations and progestogen-prostaglandin combinations. Progestogens administered for 14 to 20 d are effective in synchronizing estrus; however, fertility at the synchronized estrus is subnormal. Duration of progestogen treatment can be reduced by combining it with an estrogen. Syncro-Mate B is a progestogen-estrogen combination that results in a tightly synchronized estrous response. Prostaglandins can be used in double- or single-injection programs. Fertility of the estrus after prostaglandin treatment is similar to that of controls. Estrus also has been synchronized effectively by combining a 5- to 9 d progestogen treatment with prostaglandin at or near the end of treatment. When prostaglandin is used alone, cattle in the late stages of the luteal phase (d 11 to 15 of the estrous cycle) at the time of prostaglandin injection have a higher estrous response and may be more fertile than those injected with prostaglandin in the early part (d 6 to 9) of the luteal phase. More recently, a 14-d progestogen treatment has been combined with a prostaglandin injection given 16 to 18 d after progestogen withdrawal. This system places cattle in the late luteal phase of the estrous cycle at the time of prostaglandin injection and has resulted in an estrus with greater fertility than that immediately following progestogen treatment. (Key Words: Estrous Synchronization, Beef Cattle, Progestogens, Prostaglandins.)

J. h i m . Sci. 1990. 68317-830

lntroductlon

Less than 5% of the national beef cow herd inseminated artificially each year, primarily

because most beef cows are maintained in range environments and artificial insemination programs require extensive labor and management skill. Synchronization of estrus facilitates the use of genetically superior sires through artificial insemination. The economic value of estrous synchronization and artificial insemination varies geatly, depending on management and environmental conditions. Factors important in determining economic value include

’Colorado State Univ. Agric. Exp. Sta Res. Publ. (Pro- JCCI 605) . Resented at a symposium titled “Postpartum Rebreediig in Cattle” at the ASAS 80th Annu. Mtg.. New Bnmswick. NJ.

*~cpt . of ~nim. Sci. Received January 3. 1989. Accepted May 24,1989.

costs of labor, drugs for estrous synchronization and semen, and natural service bull costs (Pace, 1985). Estrous synchronization also may enhance efficiency by allowing for a shortened breeding and calving season. Be- cause the cow has a 21-d estrous cycle, cows could have three opportunities to be bred in a 45-d breeding season with synchronization of estrus at the beginning of the breeding season, whereas a 63d breeding season would be required for three breeding opportunities without synchronization of estrus. Cows that calve early during the calving season have heavier calves at weaning and longer postpartum periods for rebreeding (Dunn and Kaltenbach, 1979). However, appropriate nutritional management of cows is critical in attaining a short calving season.

Synchronization of estrus implies the ma- nipulation of the estrous cycle or induction of estrus to bring a large percentage of a group of females into estrus at a predetermined time.

817

818 ODDE

TABLE 1. SUMMARY OF SELECTED REFERENCES ON THE USE OF PROGESTOGENS FOR SYNCHRONlZATlON OF ESTRUS IN CATTLE

Reference

Christian and Ca3ida, 1948 Ulberg et al., 1951 Wiltbank et al., 1965 Roche, 1974a Sreenan, 1975 Sreenan and Mulvehil, 1975 Roche, 1975 Roche, 1976 Roche and Ireland, 1981 Folman et al.. 1981 Smith et al., 1984 Sprott et al., 1984

Method

Progesterone, b l y injection

Rogesterone. via intravaginal spooge pessaries

Progesterone-releasing intravagmal devices (PRID)

6-methyl-17 acetoxy-progesterone (MAP), orally

6-chloro-6-dehydro-17-acetoxyprogesterone (CAP), orally

Dihydroxyprogesterone acetophenide (DHPA), orally

Melengestrol acetate (MGA), orally

Hansel et al., 1966 Dhindsa et al., 1967 Hacken et al.. 1972 Hansel et al.. 1966 Wagner et al.. 1968 G w e n , 1975 Fulton et al., 1978 Wiltbank et al.. 1967 Wiltbank and Kasson. 1967 Zimbelman and Smith, 1966 Roussel and Beatty. 1969 DeBois and Bierschwal, 1970 Zimbelman et al., 1970 Hill et al., 1971

Females may be “inseminated according to estrus,” which means that cows will be observed for signs of estrus and inseminated approximately 12 h after observed estrus. Alternatively, cows may not be observed for signs of estrus but instead may be inseminated at a fixed, predetermined time. This procedure is referred to as timed breeding, breeding by appointment or mass mating.

Ideally, an estrous synchronization system should elicit a fertile, tightly synchronized estrous response in a high percentage of treated females. Methods of evaluating synchronization systems include estrous response (percentage of females showing estrus of those treated), synchronized conception rate (percentage of females conceiving of those inseminated), synchronized pregnancy rate (percentage of females conceiving of the total treated), and pregnancy rate at various stages of the breeding season. Distribution of estrus or

b e upjohn CO., K~LUIUAJO. MI.

degree of synchrony is important when evaluating a system’s potential for timed breeding.

The purpose of this paper is to review methods of synchronizing estrus in the postpartum beef cow. Factors influencing success of synchronization programs also will be discussed.

Progestogens

Progestogens suppress estrus in cattle and have been used widely to alter the estrous cycle. Several progestogens have been investi- gated; these are summarized in Table 1.

One of the more widely used progestogens is melengestrol acetate3 (MGA), which sup- presses estrus when administered orally (Zim- belman and Smith, 1966; Roussel and Beatty, 1969; DeBois and Bierschwal, 1970; Randel et al., 1972). Melengestrol acetate, when administered orally, is 300 to 900 times more potent than 6-methyl- 17 acetoxy-progesterone (MAP), and providing .5 mg/(head.d) sup- pressed estrus and ovulation in nearly all animals (Zimbelman and Smith, 1966). The

SYNCHRONIZATION OF ESTRUS IN CATTLE 819

level of MGA fed is related to the time of estrus following MGA withdrawal; cattle receiving lower levels of MGA showed estrus sooner than those fed higher levels of MGA (Zimbelman and Smith, 1966; Hill et al., 1971; Randel et al., 1972). Zimbelman et al. (1970) reviewed 24 studies that addressed the effectiveness of MGA fed for 10 to 18 d as an estrous synchronization agent. The percentage of MGA-treated females in estrus in a 6-d period following treatment was similar to the percentage of controls in estrus in a 20-d period. However, the first-service conception rate was 14% lower for MGA-treated females than for controls. This reduced conception rate was temporary and was confined to breeding at estrus occurring within about 10 d after MGA withdrawal.

Fertility also is reduced after long-term administration of MAP (Hansel et al., 1961), 6-chloro-6-dehydro-17-acetoxy progesterone (CAP; Hansel et al., 1966) and dihydroxyprogesterone acetophenide (DHPA; Wiltbank et al., 1967).

The mechanism responsible for reduced fertility following extended progestogen treatment is not well established. Altered follicular growth and an increase in the number of atretic follicles after MGA treatment may contribute to reduced fertility (Guthrie et al., 1970; b o n d et al., 1971). Sperm transport is reduced following insemination after progestogen treatment in the ewe (Hawk, 1971), and fertilization rate is reduced following MGA treatment (Hill et al., 1971; Reed and Rich, 1972; Wordinger et al., 1976). Wishart and Young (1974) reported that cleavage rates were retarded in females exposed to progestogens. Perhaps the reduced fertility observed after progestogen treatment is due to a combination of these and other factors.

Progestogen-Estrogen Combinations

Treatment of cattle with progestogens for less than 14 d was reported not to reduce conception rate (Wiltbank and Kasson, 1968; Roche, 1974a. 1976). However, for these short-term progestogen systems to be effective in synchronizing estrus, a luteolytic agent must be incorporated.

4CEVA Laboratories, Inc., Overland Park, KS.

Estrogens are luteolytic when administered to cattle during the early part of the estrous cycle (Wiltbank et al., 1961). Thimonier et al. (1975) treated cows with an injection of estradiol valerate followed by a norgestomet implant and reported that implanting for 13 or 15 d reduced fertility compared with implanting for 7 or 9 d. Wiltbank and Gonzalez- Padilla (1975) reported that a 9-d implant containing 6 mg norgestomet plus an injection of 5 mg of estradiol valerate and 3 mg of norgestomet given at the time of implant insertion successfully synchronized estrus and also induced estrus in noncycling beef heifers. This treatment now is commercially available as Syncro-Mate B4 and is approved by the Food and Drug Administration (FDA) for synchronization of estrus in dairy and beef heifers and postpartum beef cows.

Studies evaluating the effectiveness of Syncro-Mate B are summarized in Table 2. Clearly, Syncro-Mate B treatment results in a high percentage of cattle showing estrus soon after treatment. The range of females showing estrus after Syncro-Mate B treatment was 77 to loo%, with values being greater than 90% in most trials. The fertility of this estrus, however, was variable. First-service conception rate ranged from 33 to 68%. The differences in conception rate across trials may be due in part to level of cyclicity. Although first-service conception rate is not available in the study reported by Mares et al. (1977), 5-d pregnancy rate was lower in herds in which less than 50% of the cows were cycling prior to treatment compared with herds in which greater than 50% of the cows were cycling. This likely is due to a lower first-service conception rate in herds in which cycling was poor, because Syncro-Mate B usually results in a high estrous response. Brink and Kiracofe (1988) reported a 30% conception rate in postpartum cows known to be anestrous at treatment. Similarly, Brown et al. (1988) reported a 30% conception rate in noncycling heifers treated with Syncro-Mate B vs a 48% conception rate in cycling heifers. In some studies, however, conception rate has been quite high after treatment of anestrous females with Syncro- Mate B (Wiltbank and Gonzalez-Padilla, 1975; Miksch et al., 1978).

Luteal dysfunction may be one cause of reduced fertility in catlle treated with Syncro- Mate B (King et al., 1986; Favero et al., 1988). This may be due to insufficient LH production

820 ODDE

TABLE 2 SUMMARY OF SELECTED REFERENCES ON THE USE OF SYNCRO-MATE B FOR SYNCHRONIZATION OF ESTRUS IN CATTLE

Mares et al., 1977 (total number = 2,332)

Miksch et al., 1978

Kaltenbach a n d m 1979

5 d Fust-service 5-d Pregnancy Estrus conception Pregnancy rate

Animal rate, rate rate, 25 to 28 d. Reference t Y F Trial Treatment' No. % % % %

Wiltbank and Prepubaal I SMB-E 16 94 57 50 Gonzala-Padilla, beef Control 14 0 0 1975 heifers

II SMB-E n 79 56 43 Control 81 6 4

Yearling I SMB-E 78 100 33 33 60 heifers ConUOl 77 27 54 14 60

I1 SMB-E 98 98 63 63 80 COnUOl 95 27 63 10 74

111 SMB-E 56 98 56 55 71 Control 53 28 60 15 64

IV SMB-E 39 85 38 31 51 Control 39 10 63 5 51

V SMB-E 99 96 49 43 56 Control 99 26 45 15 50

VI SMB-E 99 96 45 43 56 COnUOl 99 26 45 15 50

VI1 SMB-E 97 77 40 30 38 COnUOl 89 16 52 4 26

beef cows SMB-T 51 66 >50% control 12 56 cycling

Postpartum I SMB-E 16 32 beef cows SMB-T 26 41 40% COnaOl 3 17 cycling

Puberal 1 SMB-E 44 93 39 36 64 beef SMB-T 44 89 39 39 73 heifers COnUOl 29 38 56 16 62

II SMB-E 23 100 39 39 74 SMB-T 21 86 62 62 61 Control 21 33 62 28 67

III SMB-E 50 94 34 32 64 COnUOl 48 25 72 18 58

Cycling I SMB-E 77 93 68 64 82 Ptp- COnUOl 71 25 84 20 83

Postpartum I SMB-E 39 59

cows A n t s t r o u ~ I SMB-E 33 82 60 48 70 Postp- Control 38 13 69 8 58 wws

POS~PWNIII I SBM-T-CR48 70 51 beef cows SMB-T-CR24 69 43

II SMB-T-CR48 92 SMB-T-CR24 93

41 33

(cortlinued)

SYNCHRONIZATION OF ESTRUS IN CATTLE 82 1

TABLE 2. (Continued) SUMMARY OF SELECIED REFERENCES ON THE USE OF SYNCRO-MATE B FOR SYNCHRONIZATION OF ESTRUS IN CATTLE

~

5 d First-service 5-d Pregnancy Estrus conception Pregnancy rate

Anunal rate, rate rate, 25 lo 28 d, Reference w Trial Treatmenta No. 8 w 6 %

Kaltenbach Postpartum 111 SMB-T-CR48 154 42 and Dunn, beef cows SMB-T-CR24 146 51 1979

IV SMB-T-CR48 62 47 SMB-T-CR24 60 47

V SMB-T-CR48 95 45 SMB-T-CR24 84 55

Peterson et al.. Postpartum I SMB-T 126 37 75 1979 beef cows SMB-T-CR48 131 54 86

Control 91 60 11 SMB-T-CR48600 45 63

SMB-T-CR24 600 49 65 Control 288 53

Kiscr et al., Po~tpartum I SMB-T 97 23 32 59 1980 beef cows SMB-T-CR24 43 40 28 5 8

SMB-T-CR48 103 I1 46 72 Spitzer et al., Virgin I SMB-E 114 98 48 47 70

1981 beef heifers Control 110 26 70 22 71 11 SMB-E 54 83 35 30 56

SMB-T 41 45 45 74 Control 45 44 58 22 69

Ul SMB-E 48 100 63 63 73 SMB-T 98 52 52 70 control 53 40 49 21 60

IV SMB-E 56 91 56 52 73 SMB-T 195 62 62 83 Control 68 25 15 19 69

following implant removal (Hixon et al., 1981).

Stage of the estrous cycle at the beginning of treatment also may influence conception rate after Syncro-Mate B. Brink and Kiracofe (1988) reported a 47% conception rate for heifers that were on d 11 or less of the estrous cycle compared with a 37% conception rate for heifers that were on d 12 or greater of the estrous cycle at the beginning of treatment. This reduced conception rate for heifers late in the estrous cycle may be due to progestogen (natural progesterone plus norgestomet) exposure. Long-term progestogen treatment has been shown to reduce conception rate.

Body condition of beef cattle influences conception rate after Syncro-Mate B treatment. Thin cattle have longer postpartum intervals to estrus (DUM and Kaltenbach, 1979) and therefore are more likely to be noncycling at the time of treatment, resulting in reduced

conception rates. However, Andersen et al. (1 987) reported that synchronized pregnancy rate was reduced in beef heifers that were greater than condition score 6, suggesting that having cattle too fat also may be demmental.

Pregnancy rates after 5 d were greater in five of six mals (Table 2) for cattle inseminated at a fixed time (usually 48 to 54 h after implant removal) following Syncro-Mate B treatment compared with cattle inseminated according to esuus. Timed insemination has the advantage of reducing labor and management for detection of estrus and cattle handling. Pregnancy rates at 25 to 28 d of the breeding season were higher for females treated with Syncro-Mate B than for control females in most mals.

Separation of calves from their dams from the time of implant removal until breeding is the label-recommended usage for Syncro-Mate B in suckled beef cows. Calf removal im-

822 ODDE

proved the estrous response (Dowling et al., 1977) and synchronized pregnancy rate in time-bred cows (Kiser et al., 1980). However, Pace and Sullivan (1980) reported no advantage in pregnancy rate for cows treated with Syncro-Mate B with calf removal compared with no calf removal in a study utilizing 2,015 postpartum beef cows from 10 ranches. Simi- larly, Brown et al. (1986) showed no advantage for calf removal compared with no calf removal after Syncro-Mate B treatment. Cows in both these studies were bred according to estrus; this may explain some of the difference between these studies and that of Kiser et al. (1980). Additionally, Kiser et al. (1980) stated that the benefit of calf removal was reduced in herds in adequate body condition.

A combination of injecting estradiol valerate and progesterone followed by a 12-d application of progesterone-releasing intravaginal devices (PRID) also is effective at synchronizing estrus in cows (Sprott et al., 1984).

Prostaglandin F2a and Analogues

The luteolytic properties of prostaglandin Fza and its analogues are well established (Lauderdale, 1972; Louis et al., 1972; Rowson et al., 1972; Roche, 1974b; Hafs and Manns, 1975; Jackson et al., 1979; Herschler, 1983; Maffeo et al., 1983). Because these compounds cause luteolysis, they can be used to synchro- nize estrus in cattle.

There are three prostaglandin products that are approved by FDA for synchronization of estrus in cattle in the U.S. These are PGFh or Lutalyd, cloprostenol or Estrumate6, and fenprostalene or Bovilene7. Label-approved dosages for each of the products are PGF2a, 25 mg; cloprostenol, 500 pg; and fenprostalene, 1 mg.

In general, PGFza and its analogues are ineffective in causing luteolysis in the early stage of the estrous cycle (Lauderdale, 1972; Rowson et al., 1972; Jackson et al., 1979; Battista et al., 1984; Kiracofe et al., 1985). Estrous synchronization systems using prosta-

h e Upjohn CO., K ~ ~ ~ G X X , MI. %lobay Corporation, Shawnee, KS. 7Syntex Animal Health Inc., West Des Moines, L4.

glandins were developed to circumvent this problem.

One method of synchronizing estrus with prostaglandins alone is to give two injections, 10 to 12 d apart. If cattle are dismbuted equally across the day of the estrous cycle, approximately 70% of the cycling cattle should show estrus after the first injection. These cattle and the remainder of the cycling cattle should be at a stage of the estrous cycle to respond to the second injection. This system has k e n evaluated in several studies (Table 3). Lauderdale (1979) evaluated the two-injection system in 24 herds of lactating beef cows and 22 herds of beef heifers. Pregnancy rate after 5 d was similar for cattle that were bred by estrus or time bred 80 h after the second injection and was greater for both treated groups than for controls. Synchronized concep tion rate was similar for treated cattle bred by estrus and controls. Other studies have shown that fertility following PGF2, is similar to controls (Roche, 1974k Hafs and Manns, 1975). Interval to estrus after PGF2, is shorter for heifers than for cows (King et al., 1982) and time-breeding heifers at 80 h after the second injection may be too late, thus reducing conception rate (Burfening et al., 1978).

Burfening et al. (1978) reported that among cattle known to be cycling prior to a two- injection system, only 71% showed estrus following the second injection. This may be due to an effect of stage of estrous cycle. Research with beef heifers has shown that stage of the estrous cycle within the luteal phase when prostaglandin is given affects the proportion of cattle showing estrus and the time interval from prostaglandin injection to the onset of estrus (King et al., 1982). Cattle injected during d 10 to 15 of the estrous cycle had a greater estrous response (percentage of females showing estrus following treatment) and showed estrus later than cattle injected d 5 to 9 of the estrous cycle. Similar results have been reported in lactating dauy cows (Macmil- Ian, 1983; Macmillan and Henderson, 1984) and stage of the estrous cycle at the time of prostaglandin injection influences interval to estrus in dairy heifers (Johnson, 1978; Refsal and Seguin, 1980; Stevenson et al., 1984). Furthermore, conception rate may be higher following late luteal phase injections compared with early luteal phase injections (Watts and Fuquay, 1985). However, Stevenson et al. (1984) reported no difference in conception


TABLE 3. SUMMARY OF SELECTED REFERENCES ON THE USE OF PROSTAGLANDIN Fza IN CATTLE

5-d First-service Animal ~strus conception hem an^^ rate* %

No. rate. % rate5d, % 5 d 9 d 24d Reference rype Treaunent

Lauderdale, 1979

Moody. 1979

Lauderdale et al.. 1980

Lauderdale et al.. 1980

Lauderdale et al., 1980

DeSilva et al., 1984

Lactating beef cows (24 herds)

heifers (22 herds)

beef cows

Beef cows (12 herds, 1,600 cows)

heifers (5 herds, 700 heifers)

Beef cows (38 herds, 5m cows)

Becf

Lactating

Beef

Becf heifm (18 herds, 2,700 heifers)

Beef cows (3 herds, 500 cows)

heifers (3 herds, 880 heifers)

Lactating beef cows

Beef

Control 67 1 PGFza-2-E* 531

Control 683 PGFza-2-E 462

Control 638 AI4d

Control PGF2a-l-Ed

PGF2a-2TSOb 642

PGFza-2T80 469

PGF2,-1-EC 637

Control PGF2cl -Ed

Control A14d

Control A14d

PGF2a- 1-E'

PGF2a-1 -EC

Conuol PGF2,-1 -Ed PGF2y2-E' Control PGF2,-1-@ PGFZ~-~-E '

PGFza2-CRle 133 PGFz ,~ -CRI&~~ 125 PGFk2-CR2g 140 PGFza2 156 cows bred by esvus. t h e bred at 80 to 90 h if not

11 68 47 61

13 50 66 55

38 58 46 42

11 34 35 9

38 36

17

32 14 30

12 28

26

39 24

45

16 36 46 7

17 22

36 34 23 34

48 55 49 53 56 51

56 60

49 55

54

56 55

56

48 58 60 37 40 38

53 57 46 56

in estrus)

'PGFza-2-E = two injections of PGFza given 10 to 12 d apart and cattle were bred according to esms following the

bpcFk-2-T80 = two injections of F'GFk given 10 to 12 d apart and cattle were time bred at 80 h after the second

CA14d-PGFk-l-E=cattle wereobservedforescrusandbredfor4d.thencaalenotdetectedinesuus wereinjected with

dpcFk-1-E = single injection of PGF2a and cattle were bred according io estrus. -1 = calves were removed for 48 h after the first injection of a two-injection program. 'CRlBr2 =calves were removed for 48 h after both injections of a tweinjection program. k R 2 = calves were removed for 48 h after the second injection of a two-injection program.

seumd injection.

injection.

PGFza and bred according to esms.

824 ODDE

rate for heifers injected during the early luteal phase compared with the late luteal phase and bred at estrus. Cattle that show estrus after the first injection of a two-injection system usually are on d 6 to 9 of the estrous cycle at second injection. These cattle may have a reduced estrous response; this may explain partially some of the results with the two-injection system.

Attempts have been made to improve the effectiveness of the two-injection system by adding a calf removal treatment (DeSilva et al., 1984). Removal of calves for 48 h either immediately after the first injection, the second injection, or after both injections did not improve 5- or 24-d pregnancy rate for any of the calf removal groups compared with the two-injection system without calf removal. Peters et al. (1977) increased estrous response by injecting estradiol benzoate 48 h after the second injection of PGF2a; however, conception and pregnancy rates were not improved.

Prostaglandins also have been used in single-injection programs. One of the more popular methods of using prostaglandin has been to detect estrus and artificially inseminate cattle for 4 d. inject those that have not been detected in estrus on d 5 , and continue observation for estrus and then breed from d 5 through 9. This system increases pregnancy rate of cows or heifers through 9 d of breeding compared with controls (Moody, 1979; Lau- derdale et al., 1980). This system requires more labor for detection of estrus and artificial insemination but requires less prostaglandin than the two-injection, breed by estrus program and requires less prostaglandin and semen than the two-injection, time breed program. Another single-injection system that has been used is to inject prostaglandin and breed at detected estrus for 5 d. This system increases 5-d pregnancy rate compared with controls (Lauderdale et al., 1980).

Analogues of PGF2, cause luteolysis of the mature corpus luteum in cattle. Cloprostenol has been used effectively for synchronizing estrus in cattle (Johnson, 1978; Jackson et al., 1979; Roche and Prendiville, 1979; Hardin et al.. 1980; Refsal and Seguin, 1980 Jackson et al., 1983; Seguin et al., 1983) as has fenprostalene (Herschler, 1983) and alfaprostol (Jochle et al., 1982; Schilling et id., 1982; Maffeo et al., 1983; Kiracofe et al., 1985; Hansen et al., 1987). Little information is available in the scientific literature on direct comparisons among the prostaglandins.

Progestogen-Prostaglandin Combinations

Instead of administering an estrogen at the beginning of a progestogen treatment to reduce the length of progestogen exposure, a prostaglandin may be administered at or near the end of a progestogen treatment (Table 4). This approach was first taken by Heersche et al. (1974) and Wishart (1974). They combined a norgestomet implant with an injection of PGF2a before or at implant removal. At the end of the implant period, cattle should either have a corpus luteum that is susceptible to regression by prostaglandin or have undergone natural corpus luteum regression already. Therefore, cattle should show estrus soon after implant removal and prostaglandin injection.

When beef heifers were treated with a 7-d norgestomet implant and injected with PGF2a on d 6 or 7 after implantation, 93% showed estrus within 5 d and 62% of these conceived, which was similar to a 60% fxst- service conception rate for controls (Heersche et al., 1979). Combined with an injection of alfaprostol at implant removal, a 9-d norgestomet implant was as effective as Syncro-Mate B in postpartum beef cows (Bed et al., 1984; Brown et al., 1986). Whittier et aI. (1986) reported that a 7-d norgestomet implant with alfaprostol on d 7 resulted in conception and pregnancy rates similar to those obtained with Syncro-Mate B; however, the degree of synchrony was better for heifers treated with Syncro-Mate B.

A tighter synchrony of estrus, which is important for timed insemination, can be attained by injecting prostaglandin 2 d prior to norgestomet implant removal (Odde et al., 1984). However, this requires an additional day of cattle handling. This concept also has been used by Bed (1983) and Smith et al. (1984), who applied a PRID for 7 d and injected PGF2a on d 6. In both studies, synchronized pregnancy rate was greater for the PRID-PGFza group than for cattle treated with two injections of PGF2a 11 d apart.

A short-term feeding of MGA was combined with an injection of PGF2, at the end of MGA feeding (Beal and Good, 1986). This system induced cycling successfully in some noncycling cows. However, fertility of the estrus after treatment in cattle known to be cycling prior to this treatment was reduced relative to controls (Bed et al., 1988). This reduced fertility was present in cattle that were


greater than d 13 of the estrous cycle at the progestogen treatment may lower fertility, beginning of treatment. This day of cycle even though the progestogen treatment is 9 d effect was similar to that reported for Syncro- or less. Mate B (Brink and Kiracofe, 1988) and again To overcome the potential problem of suggests that breeding immediately following reduced fertility when breeding following a

TABLE 4. SUMMARY OF SELECTED REFERENCES ON THE USE OF PROGESTOGEN-PROSTAGLANDIN COMBINATIONS FOR SYNCHRONIZATION OF ESTRUS IN CATTLE

Reference Animal type Treatment No. 5 to 7 d, 8 rate, % 5 to 7 d 25 to 30 d

Hecrsche et al., 1979

Bed, 1983

smith et al., 1984

Brown et al., 1986

Whinier et al., 1986

&al and Good, 1986

Bed and Good. 1986

Bed et al.. 1988

Brown et al.. 1988

Cycling beef heifers

Lactating k f cows

Dairy heifers

POsCpartum beef COWS

Beef heifers

Cycling Pap- beef cows

AneStroUS Pap- beef cows

Cycling beef cows and heifers

Beef heifers

7-d Norgestomet implant plus PGF2, d 6 or 7-EP

Control 7 d PRIDb-PGF2,

ffiFb-2-E' Control 7 d PRID-F'GFk

on d 6-E

on d 6 - W d PGFZ~-~-TBOC Conuol SMBf-E SMB-CRg-E 9 d Norgestomet

implant- Alfaprostol d 9-E

9-d Norgestomet implant- Alfaprostol d 9-CR-E

SMB-E 7 d Norgestomet

implant- Alfaprostol d 7-E

5 d MGAh-PGF2, d 5-E

7 d MGA-PGF2, d 7-E

9 d MGA-PGFb d 9-E

5-d MGA-PGF2, d 5-E ~~

7-d MGA-PGFza

9 d MGF-PGF2, d 7-E

d 9-E 7 d MGA-PGF2a d 7-E

Control

SMB-E 14d MGA-PGFk 16-18 d late?-E

28 1 47

26 24 28

93 90 91

118 125

120

117 88

89

51

55

61

83

86

76

138 125

153

157

93

63 28 10

81 87

76

87 98

94

62

80

77

57

69

60

72 34

90

83

62 60

66 52 73 53 5 1

42

54 60

62

46

53

52

66

43

44

55 73

41

69

49 53 28 52 10 56

42 45

32

47 59

58

25

42

39

32

29

27

40 24

37

57 (continued)

826 ODDE

TABLE 4. (Continued) SUMMARY OF SELECTED REFERENCES ON THE USE OF PROGESTOGEN-PROSTAGLANDIN COMBINATIONS FOR SYNCHRONIZATION OF ESTRUS IN CATTLE

Estrus First-service rate conception Pregnancy rate. 9%

Reference Animal type Treatment No. 5 to 7 d, 8 rue, 8 5 to 7 d 25 to 30 d

King et al., Lactating SMB-E 168 79 65 49 61 1988 beef cows 14d Norgeaomet

implant- AI faprostol

16 d later-E 172 64 75 51 17 Control 166 27 57 16 I 3

1988 heifers on d 7-E 64 56 42 32 68

17 d later-E 65 75 65 55 84 Control 64 17 45 15 68

Mauck et al.. Beef 7-d MGA-PGFz,

14d MGA-PGFk

'E = bred according to estrus. %'RID = progesterone-releasing intravaginal device. '?GFza-2-E = two injections of PGFh given 1 1 d apart and cattle were bred according to estrus. d.rW = cattle were time bred 84 h after PGFz, injection. fSMEl = Synchro-Mate B. WR = calf removal for 48 h following implant removal. h~~~ = melengesuol acetate. i14d MGA-PGFz, 16-18 dlater = melegestrol acetate was fed for 14 d and PGFh was injected 16 to 18 d after Lhc last

day of MGA feeding.

progestogen treatment (Miksch et al., 1978; Bed et al., 1988) and to take advantage of the fact that PGF2a is more effective during the late luteal phase (d 10 to 15) than during the early luteal phase (King et al., 1982; Tanabe and Hann, 1984; Watts and Fuquay, 1985), Brown et al. (1988) developed a system in which MGA was fed for 14 d and PGF2, was administered 16 to 18 d after the last day of MGA feeding. This system was designed to place cattle in the late luteal phase of the estrous cycle at the time of PGF2a administration. This system was compared to Syncro- Mate B (Brown et al., 1988) and to a 7-d MGA treatment with PGF2, given on d 7 in beef heifers (Mauck et al., 1988). The 14-d MGA treatment with PGF2a given on d 17 after the last day of MGA feeding resulted in greater synchronized conception and pregnancy rates. Although degree of synchrony (percentage in esms in peak 24-h period) was similar between this system and Syncro-Mate B, these systems have not been compared in cattle that were inseminated at a predetermined, fixed time.

Applying this concept to postpartum cows, King et al. (1988) administered a norgestomet implant for 14 d and injected alfaprostol 16 d after implant removal. This system was com-

pared to Syncro-Mate B. Although esmous response was greater for cows treated with Syncro-Mate B, synchronized conception rate was greater for the norgestomet-alfaprostol group, with synchronized pregnancy rate through 5 d of breeding being similar for the two groups. Yelich et al. (1988) evaluated the 14-d MGA treatment with PGF2, given 17 d after the last MGA feeding in postpartum cows. They reported that synchronized pregnancy rate was high (61%) for cows with a condition score of 5 or greater (Richards et al., 1986) compared with 19% for cows with a condition score of 4 or less, suggesting that this system was effective in postpartum cows for which body condition was at least moder- ate.

Management Factors Affecting Estrous Synchronization

Criteria used by cattle producers to evaluate estrous synchronization programs are not lim- ited to reproductive results. Cost and ease of application also are important. Reproductive results will depend on the synchronization program, the cattle (cyclicity level and fertility, nutritional status, genotype, docility), semen fertility, AI technician capability, and estrous


detection ability (if not breeding at a predetermined fixed time). Cost depends on which product and which synchronization program is used. Ease of application depends on the synchronization program, cattle handling facil- ities and docility of the cattle. The relative importance of each factor varies greatly for different producers. For example, in some situations, estrous synchronization with artificial insemination is impossible unless timed insemination can be used. Conversely, for some producers, detection of estrus can be accomplished with little difficulty and a tightly synchronized estrus allowing for timed insemination is not critical.

A frequent concern expressed by producers is that estrous-synchronized cows may all calve at once and calf losses may be high if weather conditions are poor. However, cows that conceive to a synchronized estrus have normal variation in gestation length, and less than 20% would be expected to calve on the peak day in the calving season (Odde et al., 1987).

Beef heifers frequently are maintained in a more confined environment than cows are and therefore may be more likely candidates for synchronization of estrus and artificial insemination. In cows or heifers, the factor most limiting the success of the synchronization program is percentage cycling. Percentage cycling at the beginning of the breeding season in heifers is influenced largely by age and nutrition, whereas in beef cows it is influenced by calving date, nutrition and suckling. With appropriate nutritional management, several synchronization programs can be used successfully in both cows and heifers.

Implications

Developments in estrous synchronization of cattle over the last 40 yr are reviewed in this paper. The development and subsequent commercial availability in the U.S. of prostaglandin PGF2, and its analogues (Lutalyse; Estrumate; Bovilene) and Syncro-Mate B have facilitated use of artificial insemination in many cattle operations. These products also have been helpful in increasing pregnancy rate at fixed times of the breeding season. Recent developments in progestogen-prostaglandin combinations may result in additional useful estrous synchronization programs for producers.

Literature Cited

Andersen. K. J.. J . S . Brinks. D. G. LeFever, W. C. Asbury. D. W. Schafer and J. L. Moon. 1987. Reproductive performance of Angus heifers. Colorado State Univ. Beef Program Rep., p 71. Fori Collins.

Battista, P. J., C. E. Rexroad. Jr. and W. F. Williams. 1984. Effects of progesterone administered to dairy heifers on sensitivity of corpora lutea to F'GF2, and on plasma LH concentration. Theriogenology 22:47.

Beal. W. E. 1983. A note on synchronization of oestrus in postpartum cows with prostaglandin F2, and a progesterone releasing device. Anim. Prod. 37:305.

Beal. W. E.. J. R. Chenault, M. L. Day and L. R. Corah. 1988. Variation in conception rates following synchronization of estrus with melengestrol acetate and prostaglandin F2,. J. Anim. Sci. 66599.

Beal, W. E. and G. A. Good. 1986. Synchronization of estrus in postpartun beef cows with melengestrol acetate and prostaglandin Fa,. J. Anim. Sci. 63:343.

Bed. W. E., G. A. Good and L. A. Peterson. 1984. Estrus synchronization and pregnancy rates in cyclic and noncyclic beef cows and heifers treated with Syncro- Mate B or norgestomet and alfaprostol. Theriogenol- ogy 2259.

Brink, J. T. and G. H. Kiracofe. 1988. Effect of estrous cycle stage at Syncro-Mate B treatment on conception and time to e m s in cattle. Theriogenology 29513.

Brown, L. N., K. G. Odde, M. E. King, D. E. LeFever and C. J. Neubauer. 1988. Comparison of MGA-PGF2, to Syncro-Mate B for estrous synchronization in beef heifers. Theriogenology 30: 1,

Brown, L. N.. K. G. Odde, D. G. LeFever, M. E. King and C. J. Neubauer. 1986. Norgestomet-Alfaprostol or Syn- cro-Mate B for estrus synchronization in beef cows. J. Anim. Sci. (Suppl. 1):383 (Abstr.).

Burfening. P. J., D. C. Anderson, R. A. Kinkie, J. Williams and R. L. Friedrich. 1978. Synchronization of estrus with PGF2, in beef cattle. J. A n n . Sci. 4 7 9 9 .

Chnstian, R. E. and L. E. Casida. 1948. The effects of progesterone in altering the estrous cycle of the cow. J. Anim. Sci. 7 : W (Abstr.).

DeBois, C.H.W. and C. J. Bierschwal, Jr. 1970. Estrous cycle synchronization in dairy cattle given a 14-day treatment of melengestrol acetate. Am. J. Vet. Res. 31:1545.

DeSilva, M., T. G. Dunn and C. C. Kaltenbach. 1984. Estrous response and pregnancy rates following calf removal in beef cows treated with prostaglandin F2u Theriogenology 212335.

Dhindsa. D. S., A. S . Hoversland and E. P. Smith. 1967. Estrous control and calving performance in beef cattle fed 6-methyl-17-acetoxy-progesterone under ranch conditions. J. Anim. Sci. 26:167.

Dowling, D. W., J. E. Pexton and P. T. Fagerlin. 1977. Methods of bovine estrus control: Calf separation and 7- vs. 9-day treatments. J. Anim. Sci. 45(Suppl. 1):151 (Abstr.).

Dunn. T. G . and C. C. Kaltenbach. 1980. Nutrition and the postpartum interval of the ewe, sow and cow. J. Anim. Sci. Sl(Supp1. 2):29.

Favero. R. I., D. B. Faulkner and D. J. Kesler. 1988. Estrous synchronization in beef females with Syncro-Mate 8: Efficacy and factors that restrict optimal pregnancy rates. Theriogenology 29:245.

Folman, Y., S. R. McPhee and 1. A. Cummin. 1981. The effect of Estrumate followed by progesterone coils on oestrus synchronization and conception of postpanun beef and dairy cows. Anim. Reprod. Sci. 4:117.

Fulton, R.. L. Ball and J. N. Wiltbank. 1978. Synchroniza- tion of estrus following 7 or 9 day treatment with

828 ODDE

chlormadinone acetate (CAP). Theriogenology 10:73. Grunert, E. 1975. Fertility of estrus synchronized dauy

heifers treated with CAP alone or in combination with estradiol benzoate, hCG, or GnRH. Ann. Biol. Anim. Biochim. Bicphys. 15:273.

Guthrie, H. D., D. R. b o n d , D. M. Henricks and J. F. Dickey. 1970. Ovarian follicular changes in heifers mated with melengesml acetate. I. Reprod. F d l . 2 2 363.

Hacken, A. J.. R. J. Schcchter. W. C. Hobson. W. Hanscl and P. J. Ross. 1972. Luteinizing hormone and estrogen during synchronization. J. Anim. Sci. 35:244 (Abstr.).

Hafs. H. D. and J. G. Manns. 1975. Onset of oesm and fertility of dairy heifers and suckled beef cows treated with prostaglandin F h Anim. Prod. 21:13.

Haasel, W., L. E. Donaldson. W. C. Wagner and M. A. Bnmner. 1966. A comparison of estrous cycle synchronization methods in beef cattle under feedlot conditions. J. h i m . Sci. 25:497.

Hausel, W.. P. V. Malven and D. L. Black. 1961. Estrous cycle regulation in the bovine. J. Anim. Sci. 20621.

Hansen. T. R., R. D. Randcl and L. A. Peterson. 1987. Bovine corpus luteum regression and e m s response following treatment with alfaprostol. J. Anim. Sci. 64: 1280.

Hardin. D. R.. A. C. Warnick and M. J. Fields. 1980. Artiicial insemination of subtropical commercial beef cattle following synchronization with cloprostenol (IC1 80996): II Estrous response. Theriogenology 14: 259.

Hawk.H.W. 1971. Spermdestructioninthesheepvagina. J. Anim. Sci. 33255 (Abstr.).

Heersche, G.. Jr., G. H. Kiracofe. R. C. DeBenedetti. S. Wen and R. M. McKee. 1979. Synchronization of esuus in beef heifers with a norgcstomet implant and prostaglandin-Fk. Theriogenology 11:197.

Heersche, G.. Jr.. G. H. Kiracofe. R. M. McKee, D. L. Davis and G. R. Brower. 1974. Control of estrus in heifers with P G F z ~ and Syncro-Mate B. J. Anim. Sci. 38:225 ( A m . ) .

Herschler. R. C. 1983. Estrus synchronization and conception rates in k f heifers using fenprostalene in both single- and double-injection programs. Agri-Practice 4:28.

Hill. I. R., D. R. Lamond, D. M. Henricks, J. F. hckey and G. D. Niswender. 1971. The effect of melengestrol acetate (MGA) on ovarian function and fertilization in beef heifers. Biol. Reprod. 4:16.

Hixoa. D. L.. D. J. Kes1er.T. R. Troxel, D. L. Vincent and B. S. Wiseman. 1981. Reproductive hormone secretions and first service conception rate subsequeni to ovulation conwol with Syncro-Mate B. Theriogenol- ogy 16219.

Jackson, P. S., R. J. Esslemont and J. H. Bailie. 1983. Subsequent fenility following cloprostenol induced lutcolysis in the bovine. Vet. Rec. 112:153.

Jackson, P. S.. C. T. Johnson, B. J. Furr and J. F. Beattie. 1979. Influence of stage of oestrus cycle on time of 0esuusfoUowing cloprostenol treatment in the bovine. Theriogenology 12: 153.

Jochle, W.. D. Kuzmanov and J. Vujosevic. 1982. Estrous cycle synchronization in dairy heifers with the prostaglandin analog alfaprosml (I). Theriogenology 18:215.

Johnson, C. T. 1978. Time to onset of oestrus after the injection of heifers with cloprostenol. Vet Rec. 103: 204.

Kaltenbach, C. C. and T. G. Dunn. 1979. Effect of 24- vs 48-hr calf removal in progestogen synchronized beef cows. I. Anim. Sci. 49(Suppl. 1):307 (Abstr.).

King, M. E., G. H. Kiracofe, J. S. Stevenson and R. R. Schalles. 1982. Effect of stage of the estrow cycle on interval to e s m after P G F k in beef cattle. Theriogen- ology 18191.

King, M. E., K. G. Odde, M. D. Holland, H. S. Mauck and D. G. LeFever. 1988. Synchronization of estrus in beef cows with Norgestomet-Alfaprostol or Syncro-Mate B. Theriogenology 30:785.

King. M. E., K. G. Odde, D. G. LeFever, L. N. Brown and C. J. Neubauer. 1986. Synchronization of estrus in embryo transfer recipients receiving demi-embryos withsyncro-Mate B or Estrumate. Theriogenology 26: 221.

Kiracofe, G. H.. L. E. Keay and K. G. Odde. 1985. Synchronization of estrus in cyclic beef heifers with the prostaglandin analog alfaprostol. Theriogenology 24:737.

Kiser, T. E., S. E. Dunlap, L. L. Benyshek and S. E. Mares. 1980. The effect of calf removal on estrous response and pregnancy rate of beef cows after Syncro-Mate B treatment. Theriogenology 13:381.

Lamond. D. R.. J. F. Dickey, D. M. Henricks, J. R. Hill, Jr. and T. M. Leland. 1971. Effect of progestin on the bovine ovary. J. Anim. Sci. 33:77.

Lauderdale, 1. W. 1972. Effects of FGF2a on pregnancy and estrous cycle of cattle. J. Anim. Sci. 35246 (Abstr.).

Lauderdale, J. W. 1979. Efficacy of Lutalyse sterile solution. In: J. W. Lauderdale and J. H. Sokolowski (Ed.) Procecdigs of the Lutalyse Symposium. pp 17-32. Upjohn Co., Kalamazoo. MI.

Lauderdale. J. W., J. F. McAllister, E. L. Moody and D. D. Kratzer. 1980. Pregnancy rate in beef cattle injected once with PGFk. J. Anim. Sci. 51(Suppl. 1):296 (AbStL).

Louis. T. M.. H. D. Hafs and D. A. Morrow. 1972. Estrus and ovulation after uterine prostaglandin Fzu in cows. J. Anim. Sci. 35:247 (Abstr.).

Macmillan, K. L. 1983. Prostaglandin responses in dairy herd breeding programmes. N.Z. Vet. 1. 31:llO.

Macmillan, K. L. and H. V. Henderson. 1984. Analyses of the variation in the interval from an injection of prostaglandin F2a to oesttus as a method of studying patterns of follicle development during dioestrus in dairy cows. Anim. Reprod. Sci. 6:245.

Maffeo, G.. R. Ballabio, V. Olgiati and F. Guidobono. 1983. Induction of estrus in cows by a new analogue of PGFza (alfaprostol). Prostaglandins 25541.

Mares, S. E., L. A. Peterson, E. A. Henderson and M. E. Davenport. 1977. Fertility of beef herds inseminated by estrus or by time following Syncro-Mate B (SMB) treatment. J. Anim. Sci. 45(Suppl. 1):185 (Abstr.).

Mauck, H. S., M. D. Holland, M. E. King, D. G. LeFever and K. G. Odde. 1988. Effectiveness of two MGA-PGF2, combinations for estrous synchronization of beef heifers. Proceedings, Western Section Am. Soc. Anim. Sci. 39:283.

MiLsch, E. D., D. G. LeFever. G. Mukembo, J. C. Spitzer and J. N. Wiltbank. 1978. Synchronization of estrus in beefcatlle. 11. Effect of an injection of norgestomet and an estrogen in conjunction with a norgestomet implant in heifers and cows. Theriogenology 10:201.

Moody, E. L. 1979. Studies on Lutalyse use programs for estrus control. In: J. W. Lauderdale and 1. H. Sokolowski (Ed.) Proceedings of the Lutalyse Sympo-

SYNCHRONIZATION OF ESTRUS IN CAl’TLE 829

sium. pp 33-52. Upjohn Co.. Kalamazoo. MI. W e . K. G.. D. G. LeFever, R. S. Anderson and R. E.

Taylor. 1984. Estrous synchronization with norgestomet and alfaprostol. Colorado State Univ. Beef Rogram Rep. p. 34. Fort Collins.

Odde, K. G.. D. G. LeFever. H. S. Mauck and R. E. Taylor. 1987. Calving disvibution of estrous synchronized beef cows. Colorado State Univ. Beef Program Rep. p 89. Fort Collins.

Pace, M. M. 1985. What makes A.I. and synchronization more profitable? Proc. Annu. Conf. N d . Assoc. Anim. Breed. p 20. Denver. CO.

Pace, M. M. and J. J. Sullivan. 1980. Effect of Syncro-Mate B (SMB) and calf separation on beef cattle estrus and pregnancy rates. J. h i m . Sci. Sl(Supp1. 1):312 (Abstr.).

Peters, J. B., 1. A. Welch, J. W. Lauderdale and E. K. Loskeep. 1977. Synchronization of estrus in beef cattle with P G F h and estradiol benzoate. J. Anim. Sci. 45: 230.

Peterson. L. A., S. F. Mares, E. A. Henderson and M. E. Davenport. 1979. Effect of calf separation time on pregnancy rates of cows synchronized with SYNCRO- MATE B (SMB). 1. Anim. Sci. 49 (Suppl. 1):326 (Ak.).

Randel, R. D., C. J. Callahan. R. E. Erb, H. A. Gawerick and B. L. Brown. 1972. Effect of melengesuol acetate on plasna progesterone, luteinizing hormone and total corticoids in dairy heifas. J. Anirn. Sci. 35:389.

Reed, 1. D. and T. D. Rich. 1972. Influence of MGA on cow faility. J. Anim. Sci. 35:1123 (Abstr.).

Refsal, K. R. and B. E. Seguin. 1980. Effect of stage of diestrus and number of cloproaenol (IC1 80,996) injections on intervals to e s m , LH peak and ovulation in heifers. ‘Iheriogenology 14:37.

Richards, M. W.. J. C. Spitztr and M. B. Warner. 1986. Effect of varying levels of postpartum nutrition and body condition at calving on subsequent reproductive performance in beef cattle. J. Anim. Sci. 62:300.

Roche, J. F. 1974a. Effect of short term progesterone treatment on oestlus responsc and fertility in heifers. J. Reprod. Fertil. 40:433.

Roche. J. F. 1978. Synchronization of oestrus and fertility following artificial insemination in heifers given prostaglandin Fza J. Reprod. Fertil. 37:135.

Roche, J. F. 1975. Synchronizatim of oesuus in cows using intravaginal silastic coils containing progesterone. Ann. Biol. A n i . Biochim. Biophys. 15:301.

Roche, J. F. 1976. Calving rate of cows following insemination after a 12-day treatment with silastic coils impregnated with proptenme. J. Anim. Sci. 43: 164.

Roche, J. F. and J. J. Ireland. 1981. Effect of exogenous progesterone on time of occurrence of the LH surge in heifers. J. Anim. Sci. 52580.

Roche. J. F. and D. J. Prendiville. 1979. Control of estrus in dairy cows with a synthetic analogue of prostaglandin Fza Theriogcnology 1153.

Roussel, J. D. and J. F. Batty. 1%9. Effects of melengesuol acetate on synchronization of estrus. subsequent fertility, and milk constituents of lactating dairy cows. J. Dairy Sci. 52:2020.

Rowson, L.E.A., R. Tervit and A. Brand. 1972. The use of prostaglandin for synchronization of oestrus in cattle. J. Reprod. Fenil. 29145.

Schilling, E., W. Jochle and D. Smidt. 1982. Estrous cycle synchronization in dairy heifers with the prostaglandin

analog alfaprostol (11). Theriogenology 18:413. S e w , B. E., D. J. Tate and D. E. Otterby. 1983. Use of

cloprostenol in a reproductive management system for dairy cattle. J. Am. Vet. Med. Assoc. 183533.

Smith, R. D., A. J. Pornerantz, W. E. Bed, J. P. McCann, T. E. Pilbeam and W. Hansel. 1984. Insemination of Holstein heifers at a preset time after estrous cycle synchronization using progesterone and prostaglandin. J. Anim. Sci. 58:792.

Spitzer, J. C., S. E. Mares and L. A. Peterson. 1981. Pregnancy rate among beef heifers from timed insemination following synchronization with a progestin treatment. J. Anim. Sci. 53:l.

Sproa. L. R., J. N. Wiltbank, W. N. Songster and S. Webel. 1984. Estrus and ovulation in beef cows following use of progesterone-releasing devices, progesterone and eswadiol valerate. Theriogenology 21 :349.

Srecnan. J. M. 1975. Effect of long- and short-term intravaginal progestagen treatments on synchroniza- tionof 0esuu.s and fertility in heifers. 1. Reprod. Fertil. 45:479.

Sreenan, J. M. and P. Mulvehill. 1975. The application of long- and short-term progestagen treatments for oestrus cycle conuol in heifers. J. Reprod. Fenil. 45: 367.

Stevenson. J. S., M. K. Schmidt and E. P. Call. 1984. Stage of estrous cycle, time of insemination, and seasonal effects on estrus and fertility of Holstein heifers after prostaglandin Fzu J. Dairy Sci. 67:1798.

Tanabe. T. Y. and R. C. Hann. 1984. Synchronized estrus and subsequent conception in dairy heifers treated with prostaglandin F k I. Influence of stage of cycle at treatment. J. Anim. Sci. 58:805.

’Ihimonier, J., D. Chupin and I. Pelot. 1975. The control of reproduction in the nursing cow with a progestagen short-term treatment. Ann. Biol. Anim. Biochim. Biophys. 15:263.

Ulbcrg, L. C., R. E. Christian and L. E. Casida. 1951. Ovarian response in heifers to progesterone injections. J. Anim. Sci. 10:752.

Wagner, J. F., E. L. Veenhuizen, R. P. Gregory and L. V. Tonkinson. 1%8. Fertility in the beef heifer following treatment with 6-chloro-A6-17 acetoxyprogesterone. J. Anim. Sci. 27:1627.

Watts, T. L. and J. W. Fuquay. 1985. Response and fertility of dairy heifers following injection with prostaglandin Fza during early. middle and late d i e m s . Theriogen- ology 23:655.

Whinier. J. C., G. H. Deutscher and D. C. Clanton. 1986. Progestin and prostaglandin for estrous synchronization in beef heifers. J. Anim. Sci. 63:700.

Wiltbank, J. N. andE. Gonzalez-Padilla. 1975. Synchroniza- tion and induction of estrus in heifers with a progestagen and estrogen. Ann. Biol. Anim. Biochim. Biophys. 15:255.

Wiltbank, J. N., J. E. Ingalls and W. W. Rowden. 1961. Effects of various forms and levels of estrogens alone or in combination with gonadotrophins on the estrous cycle of beef heifers. J. Anim. Sci. 20:341.

Wiltbank. J. N. and C. W. Kasson. 1%8. Synchronization of esms in cattle with an oral progestational agent and an injection of an estrogen. J. A n i . Sci. 27:113.

Wiltbank, J . N., R. P. Shumway, W. R. Parker and D. R. Zimmerman. 1967. Duration of estrus, time of ovulation and fertilization rate in beef heifers synchronized with dihydroxyprogesterone acetophenide. 1. h m . Sci. 26:764.

Wiltbank, J. N., D. R. Zimmerman, J. E. Ingalls and W. W.

830 ODDE

Rowden. 1%5. Use of progestational compounds alone or in combination with an estrogen for synchronization of e m . J. h i m . Sci. 24:990.

Wishart, D. E 1974. Synchronisation of oestrus in cattle using a potent progestin (SC21009) and PGFh.

Wishart, D. F. and 1. M. Young. 1974. Artificial insemination of progestin (SC21009) mated cattle at peckter- mined times. Vet. Rcc. 95503.

Wordings. R. I., J. F. Dickey and J. R. Hill, Jr. 1976. Influence of a progestogen on carbohydrate histo- chemical and histologic features of the ampulla of the bovine ut& tube. Am. J. Vet. Res. 37901.

Theriogenology 1:m.

Yelich, J. V.. H.S. Mauck, M. D. Holland, M. E. King and K. G. M e . 1988. Synchronization of estrus in suckled beef cows with melengesuol acetate (MGA) and PGFza. Proc., Western Section Am. SOC. Anim. Sci. 39302.

Zimbleman, R. G., J. W. Lauderdale. 1. H. Sokolowski and T. G. Schalk. 1970. Safety and pharmacologic evaluations of melengestrol acetate in cattle and other animals: areview. J. Am. Vet. Med. Assoc. 157:1528.

Zimblcman. R. G. and L. W. Smith. 1966. Control of ovulation in cattle with melengestrol acetate. I. Effect of dosage and route of administration. J. Reprod. Fenil. 11:185.

A REVIEW OF SYNCHRONIZATION OF ESTRUS IN POSTPARTUM … · 2017-10-30 · estrous synchronization agent. The percentage of MGA-treated females in estrus in a 6-d period following

Documents