Neville W E, Richardson K L, Utley P R
Dept. of Anim. Sci., University of Georgia, Tifton 31793-0748.
J Anim Sci. 1987 Oct;65(4):872-6. doi: 10.2527/jas1987.654872x.
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 breeding 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 less than .05) in the calving period and had a similar CR compared with the 40-cow groups. The PH-A replicates calved 3.5 d earlier (P less than .05) and had 7.3 percentage units higher (P less than .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.
在为期90至95天的牧场繁殖期内，将安格斯（A）、无角海福特（PH）和圣赫特鲁迪斯（SG）公牛分别与40头母牛/头公牛和80头母牛/两头公牛进行配种，比较其繁殖性能。母牛为A、PH和SG纯种以及这些品种的杂交种。每年，根据品种组成和母牛年龄将母牛随机分配到不同的繁殖组。一个重复单元包括两个40头母牛的单公牛组，每组配备两个品种的公牛，以及一个80头母牛的双公牛组，配备两个相同品种的公牛，且所有四头公牛年龄相同。PH和SG公牛有八个重复单元，PH和A公牛有五个重复单元。在配种时，2岁、3岁、4岁和5岁的公牛分别有20头、16头、12头和4头。公牛的繁殖性能根据与之配种的母牛的产犊率（CR）以及从繁殖期开始到犊牛出生的天数（NOD）进行评估。与40头母牛组相比，80头母牛组在产犊期提前3.7天产犊（P小于0.05），且产犊率相似。PH-A重复单元比PH-SG重复单元提前3.5天产犊（P小于0.05），产犊率高7.3个百分点（P小于0.01）。本研究结果表明，在产犊期更早产犊方面，80头母牛的双公牛繁殖组比40头母牛的单公牛组更具优势，且产犊率没有降低。
