13 THE RELATIONSHIP BETWEEN EARLIER POSTPARTUM CYCLICITY AND SUBSEQUENT REPRODUCTIVE PERFORMANCE IN DAIRY COWS: A FIELD TRIAL

Abstract

Earlier postpartum cyclicity based on hormonal analysis was related to the subsequent fertility, although it has not been clarified under field conditions. This field study examined the relationship between the detection of corpus luteum (CL) at the first post partum month and subsequent reproductive performance in dairy cows. Holstein dairy cows underwent ultrasonography (Sonoace 600 with 7.5 MHz linear-array transducer; Medison Co. Ltd., Korea) at 30 (±7) days postpartum to determine the existence of CL in ovaries and then divided into 2 groups based on the existence of CL; the CL group (n = 156) or the non-CL group (n = 281). At the same time of ultrasonography, all cows were scored for body condition. Cows received the normal herd reproductive management program including oestrous detection or synchronization, or synchronization of ovulation in the breeding period. Pregnancy was determined per rectum 60 days after artificial insemination by both ultrasonography and palpation. Reproductive performance data were collected for a minimum of 210 days postpartum. Reproduction data between the CL and non-CL groups were evaluated by t-test, chi-square test, or logistic regression using an SAS program (Version 9.1: SAS Institute, Inc., Cary, NC, USA). The proportion of cows with CL in ovaries at 30 (±7) days postpartum was 35.7% of all cows. The number of days to first insemination after calving was more delayed (P < 0.0001) in the non-CL group (100.1 ± 2.7 days) than in the CL group (80.9 ± 2.9 days), while the pregnancy rate to first insemination did not differ (P > 0.05) between the CL group (44.2%) and the non-CL group (45.9%). The CL group had higher pregnancy proportions (PP) within 60 (odds ratio, OR = 2.3; P = 0.0063), 90 (OR = 1.6; P = 0.04), and 120 days (OR = 1.5; P = 0.05) postpartum than the non-CL group; however, the PP within 150 or 210 days postpartum did not differ between the 2 groups (P > 0.05). Besides, logistic analysis revealed that cows with body condition score (BCS) ≥3.00 were more likely to have CL (OR = 1.8; P = 0.015) compared with cows with BCS ≤ 2.75, while primiparous cows were less likely to have CL (OR = 0.6; P = 0.0085) compared with multiparous cows. In addition, cows that underwent ultrasonography later than 30 days postpartum were more likely to have CL (OR = 1.6; P = 0.0192) compared with cows that underwent ultrasonography earlier. In conclusion, the earlier cyclicity based on the detection of CL using ultrasonography at the first postpartum month, which might be in part due to a higher BCS, predicts an enhanced reproductive performance in dairy cows, particularly during the early and early-mid lactations.