Factors in the resumption of ovarian activity and uterine involution in postpartum dairy cows

As a step toward clarifying intricate relationships among the factors responsible for delay of postpartum ovarian cyclicity and uterine involution in high-producing dairy cows, we analyzed the clinical, production, and environmental findings derived from 72 Holstein—Friesian dams in one dairy herd for 13 consecutive months. The interval from calving to resumption of ovarian activity ranged from 13 to 64 days, the average being 25 ± 13 days SD. Variation in the number of days between calving and first ovulation was largely accounted for by the factors included in the investigative model (r2=0.75, P<0.001), as shown by covariance analysis. The greatest effect on resumed ovulation was, by far, that of the daily level of total digestible nutrients (TDN) at resumption of the postpartum ovarian activity (P<0.001), although the puerperal condition was also shown to play a significant role (P<0.05) on the resumption of ovulation. Dams without puerperal complications ovulated markedly earlier (at 22 days) than those encountering puerperal complications (≥ 31 days). The greatest influences on the uterine involution were puerperal condition (P<0.001) and parity (P<0.01), followed by season of calving (P<0.05). Age at calving, daily 4% fat corrected milk yield, daily TDN and crude protein levels had no significant bearing on involution. The puerperal condition had the most noticeably widespread influence in governing both ovarian activity and uterine involution in postpartum cows, while a level of TDN intake played an important role in the resumption of ovarian activity.