156 EFFECT OF DURATION POSTPARTUM ON OOCYTE QUALITY IN LACTATING HOLSTEIN COWS FOLLOWING TRANSVAGINAL FOLLICLE ASPIRATION AND IN VITRO FERTILIZATION

Abstract

The objective of this study was to examine the effect of duration postpartum on oocyte quality in lactating dairy cows, as assessed by oocyte morphology and development after fertilization and culture in vitro. Holstein-Friesian spring-calving cows were used (n = 16; parity 3.0 ± 0.36, weight at calving 611 ± 16.2 kg, previous 305-day milk yield 6454.0 ± 276.4 kg). Body weight (BW) and body condition score (BCS) were recorded at approximately 2 weeks before the expected calving date, at calving and then weekly until the end of the experiment (approximately 80 days postpartum). Blood plasma samples were collected weekly, beginning 2 weeks before the expected calving date and continuing until the end of the experiment and were analysed for nonesterified fatty acids (NEFA), β-hydroxybutyrate (BHBA), insulin, insulin-like growth factor I (IGF-I) and glucose. There was a linear decline in BW from calving (Day 0) to Day 28, after which it remained stable. The BCS declined from 14 days precalving, reaching a nadir at approximately Day 35 to 42, after which it increased to the end of the period. Nonesterified fatty acids were significantly elevated from the week before calving until Day 42 postcalving, whereas BHBA was significantly elevated from calving to Day 49. The IGF-I declined dramatically from Day –14 to a nadir on Day 7. There was a significant increase in glucose from Day –7 to Day 0, followed by a precipitous decline to Day 7. Based on the assumption that uterine involution (UI) is complete by approximately Day 42 postpartum in most cows, data from Day 0 to 42 postpartum (pre-UI) were compared with corresponding data from Day 42 to 80 (post-UI). Apart from BCS, all the physiological parameters measured (milk yield, BW and blood metabolites) differed significantly between the 2 periods. In particular, IGF-I, insulin and glucose concentrations were higher after Day 42, whereas BHBA and NEFA were lower compared with before Day 42. The number of oocytes recovered per session and oocyte quality grade did not differ between periods. Positive associations of follicles aspirated and insulin, BHBA and NEFA were detected. Number of oocytes recovered was positively associated with milk yield, BW, glucose and NEFA. Number of cleaved oocytes was positively associated with BW and NEFA. In conclusion, the data do not provide evidence of an effect of lactation-induced metabolic stress on oocyte developmental competence in the postpartum dairy cow assessed in terms of morphological quality and ability to develop after IVF.

This work was supported by Science Foundation Ireland (07/SRC/B1156).