The effect of nutrition and metabolic hormones on follicular development in cattle

• Main Author: Gutierrez-Aguilar, Carlos Guillermo
• Published: University of Edinburgh 1997
• Subjects: 636.089
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.651905

Nutrition has profound effects on reproductive performance in cattle. Although these effects have been documented, the underlying mechanisms are not yet fully understood. The aim of this project was to investigate the role of metabolic hormones, in mediating these nutritional effects, by studying bovine folliculogenesis. The interaction of metabolic hormones and gonadotrophins on granulosa cell function <I>in vitro</I> was also investigated. To determine the effect of nutrition on ovarian follicular development, twenty-eight heifers were allocated to different dietary treatments. Small follicle number (< 4 mm) was increased by 37% on days 1 and 2 of the oestrous cycle in heifers consuming twice maintenance requirements (2M). Insulin concentrations were higher in 2M than in control or feed-deprived heifers. The increased small follicle number was independent of changes in peripheral FSH and insulin-like growth factor-I (IGF-I), negatively associated with growth hormone (GH) but positively associated with circulating insulin. Number of medium-sized (4 to 8 mm) and large (> 8mm) follicles and FSH concentrations were not different among treatments. The relationship between follicular development postpartum and endocrine and metabolic changes in lines selected for high or low predicted breeding value for milk yield (PVB) was investigated. PVB was strongly correlated with milk production during a 305 day-lactation. This was associated with higher peripheral GH and β-hydroxybutyrate and lower insulin and glucose concentrations in high genetic merit cows. Although no differences were seen in follicular development between selection lines, changes in body weight influenced follicle number, and day to first ovulation postparum was delayed in cows selected for high milk production. To gain an insight into the mechanisms underlying the nutritional effect of folliculogenesis, a serum-free (SF) bovine granulose cell culture system was developed. In the presence of FSH, granulosa cells from small follicles differentiated <I>in vitro</I> and oestradiol (E<SUB>2</SUB>) secretion increased with time. Cells from medium-sized large follicles secreted E<SUB>2</SUB> throughout the culture period. Insulin and FSH promoted proliferation and E<SUB>2</SUB> production in a dose-responsive manner. The inclusion of IGF-I enhanced proliferation and E<SUB>2</SUB> production, even in the absence of FSH. Furthermore, cultured granulosa cells formed clumps of spherical cells with ultrastructural characteristics that resembled those of granulosa cells <I>in vivo</I>. In contrast, granulosa cells growing either in the base of the clump, or as monolayers on serum-coated wells, possessed morphological characteristics suggestive of early luteinisation.