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Breeding Performance of Bulls Assigned either to 40 Cows per Bull or 80 Cows per Two Bulls during the Breeding Period^1,2,

University of Georgia³ Tifton 31793-0748

Abstract

The reproductive performance of Angus (A), Polled Hereford (PH) and Santa Gertrudis (SG) bulls was compared when exposed to 40 cows/bull vs 80 cows/two bulls during a 90- to 95-d breeding period on pasture. Cows were A, PH and SG straightbreds and crossbreds of these breeds. Each year, cows were allotted at random within breed composition and age of dam to breeding groups. A replicate consisted of two 40-cow single-sire units with bulls of two breeds and an 80-cow two-sire unit with two bulls of the same breeds and all four bulls of the same age. There were eight replicates of PH and SG bulls and five replicates of PH and A bulls. At breedint time, 20, 16, 12 and 4 bulls were 2-, 3-, 4- and 5-yr-olds, respectively. Reproductive performance of bulls was evaluated in terms of calving rate (CR) of cows exposed to them and number of days (NOD) from the beginning of the breeding period until calf birth. The 80-cow groups calved 3.7 d earlier (P<.05) in the calving period and had a simlar CR compared with the 40-cow groups. The PH-A replicates calved 3.5 d earlier (P<.05) and had 7.3 percentage units higher (P<.01) CR than PH-SG replicates. Results of this study indicated that 80-cow two-sire breeding groups had an advantage over the 40-cow single-sire groups in terms of calves born earlier in the calving period, with no reduction in CR.

¹ The authors appreciate the cooperation of personnel at the Rogers Correctional Institution, Reidsville (a part of the Georgia Dept. of Corrections), who permitted this research. Also, the authors gratefully acknowledge the assistance of Mr. B. G. Millinix, Jr. for conducting the statistical analyses.

² Supported by State, Hatch and Regional S-10 funds.

³ Dept. of Anim. Sci., Coastal Plain Sta.