Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 11, 1997
Publication Date: N/A
Interpretive Summary: An important element in optimizing cow-calf production is the selection of the breed of cow that matches the producers environment and management style. The overall efficiency of a production system may be increased if inputs are decreased and subsequent performance is maintained. Development of heifers represent a substantial input cost to the production system. In this study, it was found that heat-tolerant cattle differ in their post-weaning growth rates and that expression of puberty differs with breeds. Pregnancy rates were not different when adequate forage was available during breeding. Reducing harvested feed fed to heifers will slow growth; however, heifers gain more of their mature weight on grazed forages while maintaining equal reproductive performance. This study typifies the growth patterns and reproductive performance of heifers at two levels of nutrition to allow selection of breeds appropriate for different production systems and gives an alternative approach to raising heifers that reduces harvested feed inputs and increase utilization of grazed forage.
Technical Abstract: Heifers from seven breeds of sires (Hereford, Angus, Belgian Blue, Piedmontese, Brahman, Boran, and Tuli) were evaluated by breeding to Angus, Hereford, and MARC III (4 breed composite) cows. Progeny were placed in three treatment groups moderate nutrition, 80% of moderate nutrition, or fed as mixed groups. Average daily gain from 228 d of age through breeding was measured. Age and BW at puberty and pregnancy rates were determined. Heifers out of Hereford cows had higher rates of gain (.64 +/- .02) in the drylot than did heifers from Angus (.57 +/- .02) or MARC III (.55 +/- .02) cows. There was a sire breed by group interaction (P < .0001) for ADG in the drylot. During breeding, heifers that had been in the low group in the drylot had a higher ADG (.58 +/- .02 kg/d) than did heifers in the high group (.39 +/- .03 kg/d). Age at which heifers became pubescent did not differ (P = .06) between the low group (362 +/- 5 d) and the high group (357 +/- 5 d). Heifers from MARC III (358 +/- 5 d) and Angus (358 +/- 6 d) dams reached puberty at a younger age than did heifers with Hereford dams (380 +/- 9 d). Age at which puberty was expressed differed with sire breed (P < .001). The proportion of heifers that were pregnant at palpation (.90) did not differ between sire breeds, dam breeds, or group (P > .24). Breed differences in postweaning ADG and in the manner that the population expresses puberty allow for selection of breed types that will optimize cow herd performance.