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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


• 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)


• 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

Variable

Birth Sequence

E ME ML L

Delivery 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

Variable

Birth Sequence

E ME ML L

Fat Thickness, cm

1.00a 1.02ab 1.07b 1.05ab

REA, sq. cm. 84.13 84.26 84.13 82.77

MS1 459.3a 453.7a 436.0b 430.0b

Calculated YG 2.59 2.59 2.69 2.65

Carcass 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% 0.3915

CAB® 28.60% 24.37% 16.28% 11.24% <.0001

All Choice 85.05% 83.63% 76.88% 77.89% 0.0087

Select 13.88% 14.81% 23.12% 21.05% 0.0043

Standard 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