The influence of early postpartum uterine and ovarian recovery status on subsequent reproductive performance in Holstein dairy cows

Abstract

Examination of uterine involution and ovarian cycle resumption at approximately one month postpartum in dairy cows and treatment interventions based thereon are widely performed; however, it has not been clearly demonstrated whether doing so improves the profitability of farms. One reason for this is that current reproductive examinations by rectal palpation and ultrasonography depend heavily on veterinarian knowledge, skills, and experience. If there are simpler and objective diagnostic criteria for these examinations, it might be possible to increase the cost-effectiveness of early postpartum reproductive examinations. Therefore, we aimed to establish suitable diagnostic criteria based on relatively simple findings for the uteri and ovaries through these examinations. A total of 4,912 Holstein Friesian cattle subjected to reproductive examinations between 28 and 45 days postpartum were examined at 12 dairy farms conducting regular reproductive examinations. The uteri were divided into three groups based on the diameter of the gravid uterine horn: Small, <30 mm; Medium, ≧30 mm; and Large, ≧30 mm, with pus retention. Ovaries were classified into four groups: heat (HT); corpus luteum (CL); no structure (NS); and ovarian cyst (OC). The incidence in each group was examined. The number of days from calving to conception (days open) for cows was analyzed using Kaplan–Meier survival analysis. As a result, the incidence rates for all of the tested cattle were 48.1% in the Small group, 45.3% in the Medium group, and 6.6% in the Large group, with the median days open being 107 days, 118 days, and 205 days for each group, respectively, with significant differences observed between each group. Going by ovary classifications, the figures were 10.9% for the HT group, 51.3% for the CL group, 20.6% for the NS group, and 17.2% for the OC group, with the median days open being 98, 104, 126, and 149, respectively. The number of open days was significantly shorter in the HT group than in the other groups. Upon combining three groups of uterine and four groups of ovarian statuses and then dividing them into 12 groups, the days open was especially prolonged in the Large-CL, Large-NS, and Large-OC groups. The Large-CL group showed a significant increase in days open, even when compared with all the groups in the Medium and Small groups. The shortest days open was found in the Small-HT group, which was significantly shorter than all the other groups except the Medium-HT group. Based on the findings for the uteri and ovaries in the reproductive examinations performed 28–45 days postpartum, it was suggested that it would be possible to improve productivity by selecting cows who are likely to have extended days open and by appropriately applying treatment interventions.