Improvement of quality of oocytes collected in the autumn by enhanced removal of impaired follicles from previously heat-stressed cows

Abstract

The fertility of dairy cows decreases during the summer and remains low during the cooler autumn although the animals are no longer under heat stress. The aim of this study was to characterize a delayed effect of summer heat stress on oocyte quality in the autumn and to improve oocyte quality by enhanced removal of follicles damaged during the previous summer. Lactating cows (n = 16) were subjected to heat stress during the summer. In autumn, ovarian follicles (3-7 mm in diameter) were aspirated by an ultrasound-guided procedure during four consecutive oestrous cycles. Follicles were aspirated from control cows on day 4 and from treated cows on days 4, 7, 11 and 15 of each oestrous cycle. All cows received PGF(2alpha) and GnRH injections on days 19 and 21, respectively, and maintained cyclicity, as indicated by plasma progesterone concentrations. On day 4 of each cycle, the oocytes recovered were examined morphologically, matured and activated in vitro, and cultured for 8 days. In cycle 1 (early October) both groups showed low percentages of grade 1 oocytes, cleavage, four- and eight-cell embryos, morulae and parthenogenetic blastocysts. Subsequently, the number of grade 1 oocytes increased earlier (cycle 2) in treated than in control cows (cycle 3; P < 0.05). The cleavage rate in the control group remained relatively low throughout (32-58%), whereas in the treated group it increased from 40% (cycle 1) to 75% (cycles 3 and 4; P < 0.05). The number at each stage of embryo development increased slightly but remained low throughout in the control group, whereas in the treated group significant (P < 0.05) increases of all stages were observed in cycles 3 and 4. The results show a delayed effect of summer heat stress on oocyte quality and embryo development in the autumn. Enhanced removal of the impaired cohort of follicles led to earlier emergence of healthy follicles and high quality oocytes in the autumn.

Effect of prepartum somatotropin injection in late-pregnant Holstein heifers on metabolism, milk production and postpartum resumption of ovulation

“…Although this hypothesis was never tested with regard to the NEB challenge, it was found to be true for cows undergoing a short period of heat stress (Roth et al, 2001a and2001b) and can explain the effects of prepartum IGF-I on postpartum follicle development observed in this study.…”

Influence of Common Saturated and Unsaturated Fatty Acids on Development of Ovine Oocytes in vitro

“…High NEFA concentrations arised from up-regulated lipolysis had been occupied as a key factor in the association between metabolic imbalances, cellular dysfunction and related pathologies (Van Hoeck et al, 2011). The high circulating NEFA levels, associated with NEB were reflected in the follicular fluid of dominant follicles in ruminants early postpartum (Roth et al, 2001;Asian J. Anim. Sci., 9 (6): 420-426, 2015Leroy et al, 2008a.…”

“…The saturated long chain fatty acids in particular (such as: palmitic and stearic acid) aggravated an inhibition of maturation rate, leading to comparatively low fertilization, cleavage and blastocyst formation rates. In addition, it had been shown that palmitic acid induces apoptotic changes in the cumulus cells (Roth et al, 2001;Leroy et al, 2008b), which in turn sway oocyte maturation and perhaps embryo development in a negative way.…”

Environmental Stress Effect on Animal Reproduction

“…Roth et al, [11] indicated that the lipid composition of membranes of oocytes are more deteriorated in summer than in winter. An important aspect to counteract the effect of heat stress on the quality of the oocyte and embryo development is the potential use of antioxidants to increase the strength of both the oocyte and embryo.…”