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Factors Influencing Gestation Length, Birth Weight and Calf Survival of Angus, Zebu and Zebu Cross Beef Cattle¹

US Department of Agriculture and Louisiana Agricultural Experiment Station, Jeanerette 70544

Abstract

Day of birth in a calendar year (DB), gestation length (GL), birth weight (BW) and survival rate of calves (SR) were recorded for 4 years for single-sire matings of (1) Angus (A) and Brahman (B) sires to A, B, Brangus (BR) and Africander-Angus (AF) dams; (2) BR sires to BR dams, and (3) AF sires to AF dams, a total of four straightbred and six crossbred breed groups. Sex (S) differences were found for GL, BW and SR (P<.05 to P<.01), but not for DB (P>.05). Age of dam had no effect on GL but influenced DB (P<.01), BW (P<.01) and SR (P<.05). Precalving weight of the dam influenced BW (P<.01) but not GL. Birth weight was influenced by GL (P<.01). Differences among breed groups were found for all traits. Purebred A had the shortest GL and the earliest BD, while purebred B had the longest GL, the latest BD, the lightest BW and the lowest SR of any of the breed groups. The BR and AF had higher BW but were generally intermediate to the A and B in other traits. Combined breed of sire and dam effects accounted for most of the breed differences. The response and percentage heterosis obtained for such traits as DB and SR depended upon characteristics of the breeds involved and environmental factors such as date of breeding season and weather at calving. Heterosis calculated as a percentage of the A and B average was not significant for DB or GL but was 15% for BW and 14% for SR.

¹ Published with the approval of the Director for the Louisiana Agr. Exp. Sta., cooperative with USDA, SEA, AR, and the Southern Regional Beef Cattle Breeding Project S-10.

² Iberia Livestock Exp. Sta., USDA, SEA, AR. Present address: Livestock and Range Research Station, USDA, SEA, AR, Miles City, MT 59301.

³ Iberia Livestock Exp. Sta., Louisiana Agr. Exp. Sta., Jeanerette 70544 (retired).

³ Anim. Sci. Dept., Louisiana State Univ., Baton Rouge 70803.

⁵ Louisiana State Univ., Baton Rouge 70803.

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