Postpartum Estrus and Involution of the Uterus in an Experimental Herd of Holstein-Friesian Cows

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Abstract
A study of the intervals from parturition to involution of the uterus and from parturition to first heat was made respectively on 252 and 322 normal calvings in a Holstein-Friesian herd. Average interval to involution was 47 days, and to first heat was 33 days. The difference in the involution interval between primiparous (42 days) and pluriparous (50 days) cows was highly significant, and significant differences were observed among seasons, being shortest in the summer and autumn. Cows calving during summer tended to come in heat earlier than those calving in the other seasons, whereas those calving during winter had the longest intervals from parturition to first heat. Examination was made of the data on cows that had come into heat by end of different intervals of time postpartum to determine the proportions of such cows whose uteri were involuted. Of all cows in heat after an interval of 30 days, 6% had their uteri involuted, 44% had them involuted at 45 days, 75% at 60 days, 87% at 75 days, 96% at 90 days, 99% at 105 days, and approximately 100% at 120 days. A slight association within the parity season groups (r = 0.147; P = 0.05) was found between intervals to first heat and to involution of the uterus. A study of 71 abnormal calvings indicated a little longer interval (5 days) to involution than for cows calving normally. The primiparous cows in this group also involuted earlier than pluriparous cows.