Relationships among Feed Intake, Blood Metabolites, Follicle Size and Progesterone Concentration in Ewes Exhibiting or Not Exhibiting Estrus after Estrous Synchronization in the Tropics

AbstractThe aim of this study was to determine the relationships among feed intake, blood metabolites, follicle size, and progesterone (P4) concentration in ewes that did or did not exhibit estrus after estrous synchronization. Sixteen cycling, Merino ewes were synchronized for 12 days with a controlled internal drug release (CIDR) devices (300mg P4). Ewes were classified by estrous behavior as exhibited estrus (n=12) or did not exhibit estrus (n=4). Blood samples were collected at 0, 24, 48, and 72h after CIDR removal to measure glucose, blood urea nitrogen (BUN), and P4 concentrations. Follicular size was examined by transrectal ultrasonography on the day of CIDR removal. Ewes exhibiting estrus had greater concentrations of glucose at 24 and 48h after CIDR withdrawal than ewes that did not exhibit estrus. Ewes exhibiting estrus had decreased concentrations of P4 at 24 and 48h after CIDR withdrawal compared with ewes that did not exhibit estrus. At the time of CIDR withdrawal, the diameter of largest follicle was observed greater in ewes exhibiting estrus than that in ewes not exhibiting estrus. By 48h after CIDR removal, 91.7% of ewes that displayed estrous behavior had exhibited estrus. In all ewes, a significant positive relationship was observed between feed intake and glucose concentration. Follicle diameter was positively correlated with glucose and P4 concentrations but was negatively correlated with time to onset of estrus in ewes exhibiting estrus. No relationship was detected between BUN and other parameters in all ewes. In conclusion, increased estrous activity in ewes synchronized to estrus may result from increased size of follicle, low P4 levels, and sufficient production of glucose during the follicular development. Thus, these data highlight the importance of follicle diameter, glucose concentration, and time to onset of estrus in ewes exhibiting estrus under tropical conditions