Growth performance of lambs fed mixed diets containing halophyte ingredients

ANIMAL FEED SCIENCE AND TECHNOLOGY

ELSEVIER Animal Feed Science Technology 63 ( 1996) 137- 148

Growth performance of lambs fed mixed diets containing halophyte ingredients

R.S. Swingle a, E.P. Glenn b7*, V. Squires ’ a Department of Animal Science, University of Arizona, Tucson, AZ, USA

b Environmental Research Laboratory, University of Arizona, 2601 E. Airport Drive, Tucson, AZ 85706-6985, USA

’ Roseworthy Campus, University of Adelaide, Adelaide, SA,# Australia

Accepted 7 March 1996

Abstract

The growth rates of lambs fed on diets containing halophyte components were assessed in two trials of 84days duration each, from weaning to slaughter weight. Three halophyte forages, Atriplex barclayana, Suaeda esteroa and Salicornia bigelouii straw, were compared with Cyn- odon dactylon hay at 30% of the diet. Halophyte forages were much higher in mineral content than Cynodon hay (24-34% vs. 5%). The trials also compared Salicornia seed meal with cottonseed meal at 10% inclusion. All diets were high in concentrate (70%) and contained 12515% protein. Dry matter intake was higher for lambs fed diets containing halophyte forages than for lambs fed on the grass control diet. Because of the increased intake, halophyte-fed lambs were able to gain at the same rate as the control lambs, but, as expected, feed efficiency was lower and water intake was higher. Carcass merit of all lambs was excellent and was not affected by the inclusion of halophyte forages in the diet. In one trial an additional control tmatment was included in which Cynodon hay was supplemented with NaCl to attempt to isolate the effect of excess salt on feed intake and growth. However, the simulated halophyte diet (Cynodon + NaCl) supported lower weight gains and intake rates than the control or natural halophyte diets, showing that the form in which salts are present in halophyte forages is important to their acceptability to animals. It is concluded that halophytes could become important feed resources at moderate inclusion levels wherever production of these plants can be justified agronomically.

Keywords: Atriplex; Salicornia; Suaeda; Halopbytes; Digestibility; Lamb performance

* Corresponding author.

0377~8401/%/$15.00 Copyright 0 1996 Elsevier Science B.V. All rights reserved. PII SO377-8401(96)01018-8

138 R.S. Swingle et al./Animal Feed Science Technology 63 (1996) 137-148

1. Introduction

In many areas of the world, native and introduced halophytes are important forage resources, especially for sustaining grazing livestock when other feeds are scarce (Squires and Ayoub, 1994). However, until relatively recently little attention was given to the possibility that halophyte ingredients could be useful in mixed feeds for livestock (Glenn et al., 1992; Riley et al., 1994). The feasibility of this approach depended first on developing the concept of growing halophytes as irrigated crops (Glenn and O’Leary, 1985; Glenn et al., 1991; Glenn and Watson, 1993; Miyamoto et al., 1994). Halophyte forages, grains, oilseeds and the various by-products could become available in larger quantities for use as livestock feeds if efforts to develop irrigated halophytes in USA, the Arabian Gulf and Mexico continue to be successful (Glenn and Watson, 1993; Riley and Abdal, 1993).

The general nutritional characteristics of halophyte forages have been well defined (reviewed by Gihad and El Shaer (1994)). Nutrient composition varies by species, plant part, stage of maturity and salinity of the irrigation source. Halophytes usually contain sufficient crude protein and (or) carbohydrate components to have significant nutritional potential. However, the typically high content of minerals (much of which is NaCl) compromises the usefulness of halophyte forages (Benjamin et al., 1992). Concern has been also been expressed that animals fed on halophyte forages might have lower meat quality than animals on conventional forages (Gihad and El Shaer, 1994). Incorporation of halophyte feedstuffs into mixed diets would minimize potential adverse effects of the high salt content and would probably yield higher economic returns than would be possible from direct grazing of halophyte resources (Swingle et al., 1994).

This paper tests the potential of three halophyte species that can be grown on highly saline water (Glenn and O’Leary, 1985; Glenn et al., 1991, Glenn et al., 1994a, Glenn et al., 1994b; Nerd and Pastemak, 1992) as feed for small ruminants. Forages from Sulicornia bigelovii Torr., Atriplex barcluyunu ssp. sonorue Hall and Clements and Suuedu esteroru Ferr. and Whitmore were compared with common bermuda grass hay (Cynodon ductylon (L.) Pers.) for their ability to support weight gain of sheep in high-energy diets. The effect of excess salt on weight gain and feed consumption was tested by including a bermuda grass control diet that contained salt levels equal to those of halophyte diets. Halophyte seed meal has a much lower salt content than the forage (Glenn et al., 1991) but has not previously been tested in ruminant diets. S. bigelovii seed meal was compared with cottonseed meal as a protein supplement.

2. Materials and methods

2.1. Hulophyte ingredients

A. burcluyunu is a perennial halophyte shrub native to coastal deserts in northern Mexico which has been grown on seawater in Mexico (Glenn and O’Leary, 1985) and Israel (Nerd and Pastemak, 1992). Forage evaluated in Trial 1 was hand-harvested from a natural stand growing on saline soil near Puerto Penasco, Mexico. Plants were harvested at the flowering stage, when the leafstem ratio was high (approximately 2: 1).

R.S. Swingle et al./Animal Feed Science Technology 63 (1996) 137-148 139

S. bigelovii is an annual, succulent halophyte native to salt marshes in northern Mexico. It is under investigation as a potential oilseed crop for production using direct seawater irrigation (Glenn et al., 1991). The forage evaluated in Trials 1 and 2, and the oilseed meal evaluated in Trial 1, were from crops grown in seawater-irrigated plots at Puerto Penasco, Mexico. Forage (straw> was that portion of the harvested material left after threshing and recovery of seeds. Seed meal was the residue remaining after oil extraction by a commercial processor (Desert Whale, Inc., Tucson, AZ) using a steam-heated press.

S. e~feroa is another succulent halophyte native to marshes of western North America (Mason, 1957). The forage evaluated in Trial 2 was the entire aerial portion of plants which were grown in seawater-irrigated plots at Puerto Penasco, Mexico (Glenn et al., 1994a). Leafistem ratios were not determined for the succulent forages (5. bigelouii is leafless).

2.2. Growth and digestion trials

2.2.1. General In each of two 84day growth trials, wether lambs were blocked by weight and

randomly assigned from within weight blocks to four treatment groups of six lambs each. Lambs were housed in individual pens (2.5 m X 5 m> which had concrete floors and were partly covered (2.5 m X 2.5 m). Lambs were individually fed to appetite once daily at approximately 06:OOh. Orts were removed and weighed before each feeding. The amount of fresh diet offered was adjusted as needed to allow each lamb to achieve the maximum intake consistent with minimal sorting of diet ingredients torts less than 5%). Fresh drinking water was available at all times. At the beginning and end of each trial, lambs were weighed individually before the morning feeding, but without other restriction of feed or water. Dry matter content of diets and orts was determined weekly to convert feed consumed to a dry matter basis.

Forages were included as 30% of diet dry matter. Halophyte forages were compared with Cynodon dactylon (L.) Pers. (common bermuda grass) hay obtained from a local commercial source. All forages were sun-cured, and were chopped in a rotary type mill fitted with a screen having rectangular 3.8 m X 7.6cm openings, before mixing with other diet ingredients. Diets within a trial were formulated to have the same concentrations of crude protein (13.4% in Trial 1 and 13.0% in Trial 21, Ca and P.

Diet digestibilities were determined from 5 day total feces collections conducted either after (Trial 1) or during the last week (Trial 2) of the growth trial. For at least 2days before, and for the duration of the collection period, feed offered to each lamb was restricted to 95% of the observed dry matter intake the previous week, and the daily allowance was offered in equal portions at approximately 06:OO and 18:OO h. Rather than using metabolic cages or attaching collection bags to animals, feces were collected from the pen floors, to minimize disturbance to animals so they would continue their normal feeding habits through the digestion trial. Lambs were placed in alternate pens (one empty pen between lambs) for this portion of the study to prevent mixing of feces between blocks. Pens were continuously patrolled and feces were removed as deposited or at least every 2 h during daylight hours to minimize trampling or contamination with


urine. After the first collection of feces each morning before the first feeding, each pen floor was thoroughly washed using a high-pressure hose to maintain a clean collection surface throughout the digestion trials.

The total daily feces output of each lamb was weighed after removing by hand any contaminating materials such as wool or uneaten feed that may have been collected with the feces. An aliquot (at least 10%) of daily feces from each lamb was dried for 48 h in a forced-air oven at 50°C. Feces that appeared to have been trampled or sprayed with urine were excluded from the aliquot. At the conclusion of collection periods, dried fecal aliquots were cornposited by lamb and ground to pass a 1 mm screen using a Wiley mill. Samples of forages obtained at intervals during the growth and digestion trials, samples of mixed diets fed and orts, if any, left by each lamb during the digestion trials were prepared for analysis in the same manner as fecal samples. Water intake by each lamb was determined daily during the 5 days of fecal collection.

Final dry matter, ash and nitrogen were determined on all samples using Association of Official Analytical Chemists (1980) methods. Neutral detergent fiber was determined by the method of Robertson and Van Soest (1977), acid detergent fiber as described by Goering and Van Soest (19701, and chloroform-methanol-hydrochloric acid (CMH) lipids by the method of Marchello et al. (1971). Permanganate lignin was determined in forages and seed meals according to the method of Goering and Van Soest (19701, and Na and K by atomic absorption spectrophotometry. At the end of each trial, lambs were slaughtered and the carcasses processed and evaluated by the staff of the University of Arizona Department of Animal Sciences Meats Laboratory.

Data for both experiments were analyzed as a randomized complete block design using a general least-squares model with provision for missing replicates. When treatment (diet) effects were significant at P < 0.05, means were separated using Tukey’s Honest Significant Difference test (Wilkinson et al., 1992).

2.2.2. Trial 1 Twenty-four Suffolk X Rambouillet wethers (mean initial weight, 30.3 kg) from the

University of Arizona sheep flock were used. Diets were: (I) control-Cynodon forage with cottonseed meal; (II), Atriplex forage with cottonseed meal; (III) Salicornia forage with cottonseed meal; (IV) Cynodon hay with Salicornia seed meal. Cottonseed meal obtained from a commercial source was used to make Diets I, II and III isonitrogenous with Diet IV, which contained 10% Salicornia seed meal (see Table 2, below). Salicornia meal was received from the processor in the form of flakes, which were incorporated into Diet IV without further processing. The growth trial was conducted from 17 February to 11 May 1993.

2.2.3. Trial 2 Twenty-four Rambouillet wethers (mean initial weight, 30.9 kg) purchased from a

commercial source were used. Diets were: (I) control-Cynodon forage; (II) Salicornia forage; (III) Suaeda forage; (IV) synthetic halophyte-Cynodon forage + NaCl to give approximately the same ash content as the natural halophyte forages. The growth trial was conducted from 9 September to 25 November 1993. One animal was lost from Trial 1 and two from Trial 2 during the experiment.


3. Results

3.1. Meals and test diets

Compared with Cynodon hay (Table 11, halophyte forages contained much higher percentages of total ash (23.G34.1% of dry matter vs. 8.8-10.8%) and Na (4.1-11.3% vs. 0.05%). Although Atriplex, Salicornia and Suaeda forages contained moderate concentrations of crude protein, they each contained less protein than Cynodon (7.1- 10.2% of dry matter vs. 12.3-12.6%), necessitating higher levels of cottonseed meal supplementation to produce isonitrogenous diets (Tables 2 and 3). Cell-wall content was higher in Cynodon hay than in halophyte forages. Lignification of cell walls was considerably higher (42% of acid detergent fiber) for Atriplex than for Cynodon, Salicornia and Suaeah (23-26% of acid detergent fiber); Atriplex are woody shrubs. Although diets were designed to be isonitrogenous, there was some variability among treatments in actual protein levels (range 12.5-15%) determined by analysis during the digestion trials.

Total ash and Na concentrations were lower in Salicornia seed meal than in the forage, but Salicornia seed meal contained higher concentrations of both ash (14.3% vs. 8.4%) and Na (1.8% vs. 0.08%) than cottonseed meal. Crude protein concentration was lower (35.8% vs. 44.2% of dry matter) and lipid content higher (13.2% vs. 7.0%) in Salicornia seed meal than in cottonseed meal.

3.1.1. Trial I Mean dry matter intake exceeded 3% of body weight for all treatment groups (Table

31, and was higher for lambs fed diets containing 30% of halophyte forages than for those fed diets with Cynodon hay. The highest dry matter intake was by lambs fed the diet containing Salicornia forage. Intakes by lambs fed diets containing Cynodon hay with either cottonseed meal or Salicornia meal were similar.

Daily gains, which averaged 0.24 kg day - ’ , did not differ among diets. Because of their higher dry matter intakes, lambs fed diets containing halophyte forage had poorer feed efficiencies than those fed Cynodon hay. Feed efficiencies were not different for

Table 1 Chemical composition of diet ingredients (% of dry matter)

Item CP Ash Na K NDF ADF KMnO, lignin CMH lipid

Trial 1 Cyrwdon hay Atriplex forage Salicornia straw Cottonseed meal Salicornia seed meal

Trial 2 Cyrwdon hay Salicomia straw Suaeda forage

12.3 8.8 0.1 1.5 62.7 26.1 6.4 5.3 10.2 23.8 4.1 1.8 46.9 27.0 11.4 4.0 7.1 33.1 11.3 1.3 41.3 20.9 5.4 6.8

44.2 8.4 0.1 1.5 29.1 17.2 7.9 7.0 35.8 14.3 1.8 1.8 17.7 12.9 11.9 13.2

12.6 10.8 nd nd 64.0 31.3 3.7 6.8 6.5 25.2 7.6 1.0 48.3 27.2 3.9 7.0 7.6 34.1 10.2 1.4 36.0 19.4 4.5 4.6


Table 2 Diet composition, per cent of dry matter, Trial I a

Item Diet

1 Cyn0don

hay

II Atriplex forage

III Salicornia straw

IV Salicornia seed meal

Atriplex forage Cynodon hay Salicornia straw Sorghum grain, dry rolled Cottonseed meal Salicornia meal Animal fat Cane molasses Limestone NaCI Mono-, di-calcium phosphate Total Determined analysis (%b) b

CP Ash NDF ADF CMH lipid

30.00

55.85 53.85 7.00 9.80

1.00 5.00 0.80 0.25

100.00

12.5 13.0 15.0 13.0 6.1 11.3 13.3 6.3

28.5 25.3 22.4 28.6 13.2 14.2 11.6 13.6 6.8 5.6 8.6 6.4

30.00

1 .oo 1 .OO 5.00 5.00 0.30 0.65

0.05 100.00

30.00 51.50 11.80

100.00

30.00

53.20

10.00 1.00 5.00 0.80

100.00

a All diets were supplemented with vitamin A, 3300IUkg-‘. b Laboratory values determined on diets fed during the digestion trial.

Table 3 Diet comoosition. oer cent of drv matter. Trial 2 a

Item Diet

I Cynodon II Salicornia III Suaeda IV Cynodon

hay straw forage hay + NaCl

Cynodon hay 30.00 22.00 Salicornia straw 30.00 Suaeda forage 30.00 Sorghum grain, dry rolled 58.35 54.15 54.00 55.40 Cottonseed meal 4.50 9.10 8.90 7.60 Animal fat 1.00 1.00 1.00 1.00 Cane molasses 5.00 5.00 5.00 5.00 Limestone 0.75 0.65 1.00 0.90 NaCl 0.25 Mono-, di-calcium phosphate 0.15 0.10 0.10 0.10 Total 100.00 100.00 100.00 100.00 Determined analysis (Or,) b

CP 13.2 12.6 13.4 13.1 Ash 5.8 10.3 9.1 12.1 NDF 31.0 32.4 30.8 27.0 ADF 14.1 16.8 14.4 12.6 CMH lipid 6.4 6.7 6.4 6.0

a All diets were supplemented with vitamin A, 33001Ukg-‘. b Laboratory values determined on diets fed during the digestion trial.


Table 4 Growth oerformance. Trial 1

Item Diet

I Cynodon II Atriplex III Salicornia IV Salicornia SEM

hay forage forage seed meal

Lambs, n 6 6 6 6 Live weight (kg)

Initial 30.5 30.5 30.1 29.9 0.53 Final 50.5 50.0 51.1 52.1 1.34

Daily DM intake kg 1.30 a l&b 1.67 ’ 1.33 a 0.07 %ofBW 3.2 a 3.6 b 4.1 c 3.3 a 0.13

Daily OM intake kg 1.21 1.28 1.45 1.25 0.07 %ofBW 3.0 a 3.2 ab 3.6 b 3.1 ab 0.14

Daily gain (kg) 0.24 0.23 0.25 0.27 0.015 Efficiency

Gain:DMI 0.19 a 0.16 b 0.15 b 0.20 a 0.005 Gain:OMI 0.20 ab 0.18 b 0.17 b 0.21 ac 0.006

ab~c Means within the same row without a common letter in the superscript.

lambs fed Atriplex or Salicornia forages or for those fed cottonseed or Salicornia meals.

There were few differences in apparent digestibility coefficients among diets (Table 41. Digestibilities of organic matter, neutral and acid detergent fibers tended to be lower for halophyte forage diets than for Cynodon diets and were lowest for the Salicornia forage diet. The higher intake for this diet might have contributed to the lower digestion coefficients. Except for lipid digestibility, which tended to be lower for the Salicornia seed meal diet, source of supplemental protein did not influence digestibility of Cynodon-based diets. Because of their higher ash content and (or) lower digestibility of organic matter, halophyte forage diets contained less digestible organic matter than Cynodon diets.

Lambs fed diets containing halophyte forages consumed up to 110% more water per day and 50% more water per kilogram of dry matter intake than those fed the diets with Cynodon hay (Table 5). Because lambs fed halophyte forages also had higher ash intakes, differences in water intake among treatments were smaller when expressed per kilogram of ash intake.

The only carcass parameter to be affected by treatment was dressing percentage, which was slightly, but consistently, higher for lambs fed halophyte forage diets (Table 6). This observation was somewhat surprising, as the higher dry matter and water intakes by lambs fed diets containing halophyte forages might more logically have decreased dressing percentage.

3.1.2. Trial 2 In the second trial Suaeda forage was compared with Salicornia and Cynodon

forages, and an ‘artificial halophyte’ forage was created by adding NaCl to Cynodon hay


Table 5 Dry matter, ash and water intakes and apparent digestibility coefficients, Trial 1

Item Diet

1 Cynodon

hay

II Atriplex forage

III Salicornia straw

IV Salicornia seed meal

SEM

Lambs, n Intake

DM (kgday-‘) Ash (kg day - ’ ) Water (1 day- ’ )

kg-’ DMI kg-’ ash

Apparent digestibility (%I DM OM CP NDF ADF CMH lipids

6 5 6 6

1.46 a 1.69 a 1.91 b 1.53 a 0.09 a 0.19 b 0.25 ’ 0.10 a 7.1 a 10.6 b 13.2 b 6.3 a 4.9 a 6.3 b 6.9 b 4.1 a 78.9 a 55.8 ab 52.8 b 63.0 ab

0.187

0.19, 0.88 8.32

74.3 73.5 72.0 75.4 a 74.6 a 71.0 b 58.3 63.9 61.1 56.1 a 51.2 a 40.7 b 55.1 a 44.6 b 36.1 ’ 68.4 ab 65.8 ab 71.1 a

74.0 1.29 75.3 a 1.55 60.1 1.83 55.1 a 3.64 53.9 a 4.17 63.4 b 2.30

ab,c Means within the same row without a common letter in the superscript.

(Table 6). The Rambouillet animals used in the second trail had a similar range of feed intake (3.1-4.2% body weight) but lower weight gain (0.13-0.19 kgday-’ ) and feed efficiency (0.12-0.14 kg kg-’ > than the Suffolk X Rambouillet wethers used in the first trial (Table 7). Lambs fed natural halophyte forages had higher feed intake than lambs

Table 6 Carcass characteristics, Trial 1

Item Diet

I Cynodon

hay II Atriplex forage

III Salicorniu straw

IV Scdicorniu seed meal

SEM

Lambs, n Hot carcass wt. (kg) Dressing 8 ’ Fat thickness (cm)

Actual Adjusted ’

KPH fat (%) 3 USDA Quality Grade 4 USDA Yield Grade 5

6 6 6 6 26.7 27.4 28.3 26.5 0.90 51.4’ 52.5 b 52.3 b 49.2 a 0.76

0.10 0.10 0.11 0.08 0.013 0.12 0.13 0.14 0.11 0.018 2.1 3.0 2.3 2.6 0.37 4.93 5.07 5.15 5.03 0.216 3.5 3.7 3.9 3.3 0.46

’ (Hot carcass weight/final live weight)X 100. * Actual fat thickness, cm + (((%KPH - 1.0)/2)X 0.1). 3 Kidney, pelvic and heart fat, percentage of carcass weight. 4 Coded: 4.00, Choicem; 4.50, Choice5’; 5.00, Primem; etc. ’ (Adjusted fat thickness, cm X 2.54)+ 0.4. a’ Means within the same row without a common letter in the superscript.

R.S. Swingle et al./Animal Feed Science Technology 63 (19%) 137-148 145

Table I Growth oerfonnance. Trial 2

Item Diet

I Cynodon 11 Salicornia III Suaeda IV Cynodon SEM hay StraW forage hay + NaCl

Lambs, n 5 6 6 5 Live weight (kg)

Initial 30.1 30.5 32.2 30.8 0.72 Final 44.7 45.9 46.6 42.1 0.80

Daily DM intake kg 1.21 a 1.51 b 1.62 b 1.14 a 0.12 %ofBW 3.2 a 3.9 b 4.2 b 3.1= 0.22

Daily OM intake kg 1.14a 1.35 ab 1.38 b 0.99 ac 0.055 %ofBW 3.1 3.5 3.6 2.7 0.087

Daily gain (kg) 0.17 * 0.18 ab 0.19 B 0.13 b 0.010 Efficiency

Gain:DMI 0.14 0.12 0.12 0.12 0.009 Gain:OMI 0.15 0.13 0.14 0.14 0.010

4b Means within the same row without a common letter in the superscript.

fed Cynodon hay, similar to the results of Trial 1, but animals fed the artificial halophyte had the lowest rates of feed intake and weight gain. The form in which NaCl is incorporated into a diet turned out to be important in determining its acceptability to the lambs. Lambs had similar feed efficiencies on all diets.

Table 8 Dry matter, ash and water intakes and apparent digestibility coefficients, Trial 2

Item Diet

I Cyrwdon

hay II Salicornia straw

III Suaeda forage

IV Cynodon hay + NaCl

SEM

Lambs, n Intake DM, kgday-’ Ash, kgday- ’ Water, lday-’ lkg-’ DMI ?lkg-’ ash Apparent digestibility, DM OM CP NDF ADF CMH-lipids

5 6 6 5

1.24 a 0.07 a 2.3 = 1.8 a 34.2

% 72.0 73.6 62.1 a 58.8 a 53.4 a 10.5

1.43 b 1.50 b 1.12 a 0.14 0.14b 0.12 b 0.12 b 0.02 4.6 b 4.4 b 4.2 = 0.61 3.1 bc 3.0 b 3.8 ’ 0.17 32.6 36.4 36.4 8.32

69.2 70.3 78.3 2.67 69.6 71.2 78.4 2.18 61.2 a 65.3 *b 68.7 b 2.11 47.6 b 48.4 b 55.6 a 3.60 42.0 b 36.2 b 55.6 a 4.7 1 67.3 70.4 68.0 2.06

Pb Means within the same row without a common letter in the superscript.


Digestibility of dry matter and organic matter did not differ significantly (P < 0.05) among treatments but fiber digestibility was lower for the halophyte compared with the Cynodon diets (Table 8). Lambs fed the artificial halophyte diet had higher crude protein digestibility than lambs on Cynodon control or Sulicomiu diets. As in Trial 1, lambs on the halophyte diets (including the artificial halophyte) consumed more water per kilogram of feed intake than lambs on Cynodon hay without added NaCl, but water consumption per kilogram of ash intake was similar among treatments (Table 8). Water intakes in this trial ranged from 2.3 to 4.6 1 day - ’ ; this is lower than the range reported in Trial 1 (6.3-13.21 day-‘), which was in spring when ambient temperature was higher. The impact of seasonal variation in water intakes was as high as the effect of feeding halophyte ingredients in the diets.

Carcass characteristics were similar among treatments; dressing percentage was not higher for lambs on halophyte diets, unlike the results from Trial 1.

4. Discussion

Halophyte forages were much higher in mineral content, lower in crude protein, and had lower fiber digestibility than Cynudon hay. These differences are characteristic of halophyte forages compared with grass forages (Wilson, 1966; Gihad, 1993; Gihad and El Shaer, 1994). Nevertheless, at 30% inclusion halophyte forages supported the same weight gain of lambs as Cynodon hay, and organic matter digestibility was high. The results were similar to those obtained when goats were fed halophytes at 30-50% of the total diet (Glenn et al., 1992; Nawaz et al., 1994).

The lambs in this study were able to increase their feed intake to compensate for the lower organic matter content of the natural halophyte forages compared with Cynodon hay. By contrast, lambs did not increase their intake of the artificial halophyte (Cynodun + NaCl) but actually consumed less of this diet than any other diet, with the result that these lambs had the lowest rates of weight gain, These results showed that the form in which NaCl is presented to the animals is important to how much they will consume. In halophytes, salt is infused throughout the stem and leaf tissues and the animals were unable to sort the feed to avoid the salt. In the artificial halophyte diet the salt was separate from the forage component and the animals tended to avoid the fine fraction in their feed, which contained meal and grain as well as salt, so that their overall feed intake was reduced.

Halophyte forages have produced less positive results when included as the sole dietary component or with just an energy supplement. In an in vivo digestibility trial with sheep, Atriplex barclayana had an apparent digestibility of 59% and 56% for dry matter and organic matter, respectively (Benjamin et al., 1992). It was concluded that at high inclusion levels the high salt concentrations in the leaves and stem markedly lowers its potential as a fodder plant. The inclusion rate of the halophyte forage was well in excess of those likely to be used in mixed rations for fattening livestock and underesti- mates the potential value of halophytes at lower inclusion rates, as gastrointestinal fill limits intake on low-energy diets and sheep cannot compensate for the high ash content by eating more forage.


The extra water required to handle the additional salts may present a problem in some situations. However, in arid regions where forage crops must be irrigated, many times more water is required to grow the forage crop than is required by the animals that eat the crop. If saline water can be used for irrigation of the crop, the net saving of fresh water is substantial even if the water requirement of the livestock is higher. In such cases, the salts contributed by the moderate level of halophyte component can be considered as unimportant provided that ample quantities of fresh drinking water are available to flush out the excess salts. The halophyte forages did not lower carcass quality in these experiments, despite concerns to the contrary (Gihad and El Shaer, 1994), nor did it produce health problems for the animals.

The results also showed that Salicorniu seed meal, a byproduct of seawater-irrigated oilseed crops, may be used to replace cottonseed meal in mixed rations. The experiment did not include a negative control (a diet without seed meal) so the potential of the animals for a positive response was unknown; however, they did not exhibit the negative response that this level of Sulicornia meal produced in poultry owing to its saponin content (Glenn et al., 1991). It is concluded that halophyte forages and seed products could become important feed resources for small ruminant production wherever production of these unique plants can be justified agronomically (Glenn and Watson, 1993).

Acknowledgements

Part funding was made available by Halophyte Enterprises, Inc., the Electric Power Research Institute and the State of Arizona. The input of Dr. J.J. Riley is gratefully acknowledged, as is the assistance provided by David Moore. Jorge Aquino and Mario Tarrazon, graduate students in the Department of Animal Science, University of Arizona, provided technical assistance. Special thanks are due to the University of Arizona Meat Science Laboratory. Sue Moodie also gave valuable technical assistance. The University of Adelaide provided a period of sabbatical leave for one of us (V.R.S.).

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Growth performance of lambs fed mixed diets containing halophyte ingredients

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