G.D. Fike 1 , M.E. King 1 , L.R. Corah 1 and W.D. Busby 2 1 Certified Angus Beef LLC

Effect of Time of Birth Within the Spring Calving Season on

Performance and Carcass Traits of Beef Calves Fed in the Iowa

Tri-County Steer Carcass Futurity

G.D. Fike1, M.E. King1, L.R. Corah1 and W.D. Busby2

1Certified Angus Beef LLC2Iowa Tri-County Steer Carcass Futurity

2010 Annual ASAS Meeting

Introduction and Background• Larson, et al., (2010)

found that calves born during the first 21 d calving period had greater HCW, marbling scores and greater % grading premium Choice and higher carcass values than calves born in the 2nd or 3rd 21 d intervals; however, no differences were found in ADG

Objectives• Does age of calf and

time of birth within the calving season affect:– Feedlot performance– Marbling score and,

ultimately, USDA quality grade

– Certified Angus Beef ® (CAB®) acceptance rate

Materials and Methods• Data were analyzed on 1,369 calves from a

single, central Missouri ranch for a six-year period (2002-2007)

• Genetics were Angus/Simmental-based, rotating sires among different years

• All cattle were fed a common dietary energy level and administered similar health and implant treatments in a southwest Iowa feedlot

• All cattle were weighed, sorted, vaccinated, implanted, disposition scored and body conditioned scored within 4 days of arrival

Materials and Methods• Calves were sorted and harvested when visually

determined to have one cm of fat cover• Only cattle with full, detailed carcass and

performance information were included in the study

• Calves were divided into four sequence groups:– Early – born d 1-21 of calving season (E)– Mid-early – born d 22-42 (ME)– Mid-late – born d 43-63 (ML) and– Late – born d>63 (L)

Materials and Methods• Statistical analyses:

– Continuous outcomes were quantified using one-way analysis of variance (ANOVA)

– For rate analyses, Chi-square was employed

Percent Angus of the Calf by Birth Sequence Within the

Spring Calving Seasona

abcMeans with unlike superscripts differ (P<0.05)

Disposition Score1 of the Calf by Birth Sequence Within the

Spring Calving Season

a

abMeans with unlike superscripts differ (P<0.05)

1Disposition score: 1=docile; 6=very aggressive

Feedlot Delivery Weight, Adjusted Final Weight, Harvest Age and HCW by Birth Sequence Within

the Spring Calving Season

VariableBirth Sequence

E ME ML LDelivery Wt., kg 328.2a 321.7b 310.8c 291.4d

Adjusted Final Wt., kg 554.2a 550.7ab 552.8ab 538.6b

ADG, kg/d 1.46a 1.49ab 1.53b 1.51ab

Harvest Age, d 476.5a 463.8b 448.3c 435.2d

HCW, kg 341.1a 338.4ab 342.1ab 332.5b

abcdMeans within a row with unlike superscripts differ (P<0.05)

Carcass Merit by Birth Sequence Within the Spring

Calving Season

VariableBirth Sequence

E ME ML LFat Thickness, cm 1.00a 1.02ab 1.07b 1.05ab

REA, sq. cm. 84.13 84.26 84.13 82.77MS1 459.3a 453.7a 436.0b 430.0b

Calculated YG 2.59 2.59 2.69 2.65Carcass Value, $/hd

$1046.88a

$1035.93ab

$1035.63ab

$1006.61b

a bMeans within a row with unlike superscripts differ (P<0.05)1Marbling score: 400=Small0; 500=Modest0

Quality Grade by Birth Sequence Within the Spring

Calving Season

USDA Quality Grade

Birth Sequence

E ME ML LChi-

SquareP value

Prime 0.53% 0.78% 0.00% 0.00% 0.3915CAB® 28.60% 24.37% 16.28% 11.24% <.0001All Choice 85.05% 83.63% 76.88% 77.89% 0.0087Select 13.88% 14.81% 23.12% 21.05% 0.0043Standard 0.53% 0.78% 0.00% 1.05% 0.9695

Conclusions• The oldest calves were/had:

– Heavier at feedlot delivery – Heavier at harvest and greater HCW– Greater marbling scores– Higher percentage of calves grading USDA

Choice and CAB®

– Greater carcass value per heado Than their latest born counterparts