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U. S. Department of Agiculture and Louisiana Agricultural Experiment Station, Jeanerette 70544
Abstract
A three-year study was conducted to determine factors influencing estrus and pregnancy rate from mating Angus (A) and Brahman (B) sires to A, B, Brangus (BR) and Africander-Angus (AF) cows; Brangus sires to BR cows and AF sires to AF cows. All heifers were placed in the breeding pastures as 2-year-olds and had a 6.8% lower (P<.05) pregnancy rate after two services and became pregnant 4.2 days later (P<.01) than older cows. Three-year-old lactating cows had a 15.1-day longer (P<.01) interval from calving to first estrus, a 10.6-day longer (P<.05) interval from calving to pregnancy and a 10.9% lower (P<.05) pregnancy rate than older lactating cows.
Breeds differed (P<.05) in percentage of cows showing estrus. Straightbred A and AF matings were similar (P>.05) for all factors studied except pregnancy date. Both breeds conceived earlier (P<.05 to P<.01) and were superior to B (P<.05 to P<.01) in pregnancy rate at first service and at 75 days. Straightbred Brangus matings were intermediate between the Angus and Brahman in pregnancy date and pregnancy rate at first service but were similar (P>.05) to the Brahman in pregnancy rate for 75 days. Cows bred to A sires had higher pregnancy rates at first service (P<.05), for two services (P<.05 to P<.01) for 75 days (P<.05) and became pregnant earlier (P<.01) than cows bred to B sires.
Due to low reproductive performance of the B, the A x B and B x A crossbreds exceeded the purebred A and B average by 9.2% for pregnancy rate at first service, 2.4% for pregnancy rate for two services, 7.5% for services required for conception and 2.9% for pregnancy rate for 7 5-days.
1 Published with the approval of the Director for the Louisiana Agricultural Experiment Station, cooperative with USDA, Science and Education Administration, Federal Research and the Southern Regional Beef Cattle Breeding Project S-10.
2 Iberia Livestock Experiment Station, USDA, SEA, FR. Present address: Livestock and Range Research Station. USDA,SEA, Miles City, MT 59301
3 Iberia Livestock Experiment Station, Louisiana Agricultural Experiment Station, Jeanerette 70544 (Retired.)
4 Graduate Assistant, Animal Science Department, Louisiana State University, Baton Rouge 70803.
5 Professor of Experiment Statistics, Louisiana State University, Baton Rouge 70803.
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