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Reproductive Performance of Crossbred and Straightbred Cattle on Different Pasture Programs in Florida¹

Florida Agricultural Experiment Station³

Abstract

A study was made of 3,994 pasture matings in beef cattle at the Florida Range Cattle Experiment Station from 1944 to 1958. There were three groups of straightbred cattle, including Brahman, Shorthorn and grade Shorthorn. There were nine crossbred and mixed groups classified on the basis of breed of sire to which mated and breed composition of cow. Six different pasture programs were represented. Other variables included lactation status of the dam during the breeding season, age of cow at calving and year. The data were analyzed by the method of fitting constants. Due to significant interactions, constants were obtained from within-lactation status analyses also. Weaning percent and preweaning death loss are the dependent variables reported.

Lactation status exerted the greatest influence with lactating and non-lactating cows having calving rates of 63% and 84%, respectively. There were highly significant interactions of lactation status with pasture, year and breed group.

Overall weaning rate for pastures varied from 64% in all native range to 78% in improved pasture with supplemental feed. Non-lactating cows had weaning rates similar on all pastures with a slight advantage for pasture programs containing native range. For lactating cows, however, there was a marked advantage in weaning rate for cows on improved pasture compared to native range.

Age of cow had a pronounced effect in both lactating and non-lactating cows. Lowest reproduction rates occurred in 2- and 3-year-old cows increasing to a peak at 6 or 7 years after which non-lactating cows remained nearly constant to 18 years while lactating cows declined slightly. A significant interaction of age and lactation status resulted because the lowered reproduction of young cows was more pronounced in lactating than in non-lactating cows.

A significant breed by lactation status interaction resulted because non-lactating cows of all breed groups performed at nearly the same levels while lactating cows showed wide breed differences in weaning percent with deviations from the mean ranging from –19% to 18%. Within-group comparisons showed an apparent effect of breed-of-sire on weaning percent with crossbred bulls ranking lowest, Brahman next, and British breed bulls highest. Among females included in a Brahman-Shorthorn crossbreeding comparison, the deviations from the mean for cows classified on proportion of blood were –6.7% for purebreds, –2.9% for 3/4 bloods and 14.2%, for F₁ females. Grade Shorthorns were an exception to generally poor performance of straightbreds with a deviation of 12% compared to –10% for purebred Shorthorns.

¹ Florida Agricultural Experiment Station Journal Series No. 1284.

² Present address: Iberia Livestock Experiment Station, Jeanerette, Louisiana.

³ This work was part of the S-10 Beef Cattle Breeding Project, which is cooperative between Southern State Experiment Stations and the U.S.D.A.