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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
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
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