Neville W E, Richardson K L, Williams D J, Utley P R
J Anim Sci. 1987 Aug;65(2):345-50. doi: 10.2527/jas1987.652345x.
A 2-yr study was conducted to compare the subsequent cow breeding and calf performance of cows that were nonpregnant with cows that were pregnant at the time calves were weaned. Cows were Angus (A), Polled Hereford (PH), Santa Gertrudis (SG) straightbreds and crossbreds of these breeds. Nonpregnant cows (G1) were 4- to 9-yr-olds that had a calf the previous year and appeared to be physically sound with no detection (by rectal palpation) of an abnormal reproductive tract due to disease, abnormal growth or calving difficulties. Pregnant cows (G2) were of similar age and breed composition to G1 cows. The 93 G1 and the 193 G2 cows were assigned within age and breed composition to sire breeding groups on pasture in an approximate 1:2 ratio, respectively, per sire. There were six A, three PH and one SG sires. The year prior to G1 cows being nonpregnant, G1 cows calved 11 d later (P less than .01) than G2 cows. Subsequent to their being nonpregnant, G1 cows gained 27 kg more (P less than .001) weight during the breeding period, had 5.4 percentage units more (P less than .29) calves born, had calves 17 d earlier (P less than .001) in the calving period, had calves that gained at a similar rate to weaning and had calves that were 14 kg heavier (P less than .01) at weaning (due to their being 17 d older) compared with G2 cows and calves.
进行了一项为期两年的研究，以比较犊牛断奶时未怀孕的母牛与怀孕的母牛后续的繁殖情况及犊牛的生长性能。母牛品种包括安格斯牛（A）、无角海福特牛（PH）、圣格特鲁迪斯牛（SG）以及这些品种的杂交牛。未怀孕的母牛（G1组）年龄在4至9岁之间，上一年产过犊，身体状况良好，经直肠触诊未发现因疾病、生长异常或产犊困难导致的生殖系统异常。怀孕的母牛（G2组）与G1组母牛年龄和品种组成相似。93头G1组母牛和193头G2组母牛按照年龄和品种组成，以大约1:2的比例分别分配到各公牛的配种牧场组中。有6头A品种公牛、3头PH品种公牛和1头SG品种公牛。在G1组母牛未怀孕的前一年，G1组母牛产犊时间比G2组母牛晚11天（P<0.01）。在未怀孕之后，G1组母牛在配种期体重增加了27千克（P<0.001），所产犊牛数量多5.4个百分点（P<0.29），产犊期比G2组母牛早17天（P<0.001），所产犊牛到断奶时生长速度相似，但断奶时犊牛体重比G2组母牛和犊牛重14千克（P<0.01）（因为G1组犊牛大17天）。
