Ovarian and hormonal responses to a progesterone-releasing controlled internal drug releasing treatment in dietary-restricted goats

An experiment was conducted to evaluate the effects of dietary restriction on ovarian, endocrine (ovarian steroids and luteinizing hormone (LH) pulse) and metabolic (glucose, insulin and non-esterified fatty acid (NEFA)) profiles in goats treated with a progesterone-releasing controlled internal drug releasing (CIDR-G) device. Cycling goats were offered either a maintenance or a restricted (30% of requirement; n=4 per treatment) level of feeding. The dietary restriction was started on the day following ovulation. At 30–32 days after the start of food restriction, the goats received a prostaglandin F2α (2 mg of dinoprost) injection followed by 10 days of CIDR-G treatment. Ovarian ultrasonographic images were monitored daily throughout the experiment and blood samples were collected daily just before the morning feeding for analysis of endocrine and metabolic profiles. Frequent blood samples (1 ml) were also collected at 10 min intervals for 8 h from −8 h to CIDR-G removal, and from 32 to 40 h after CIDR-G removal for analysis of LH pulses. Body weight was significantly (P<0.05) decreased in the food-restricted animals. Oestrous behaviour and ovulation followed by a rise of plasma progesterone concentration were observed after the CIDR-G removal in all control animals but not in any of the food-restricted animals within 12 days after CIDR-G removal. The LH pulse frequency from 32 to 40 h after the CIDR-G removal was significantly (P<0.05) lower in the food-restricted animals than in control animals (1.5±0.6 versus 3.8±0.5 pulses for 8 h). There was no significant difference in the glucose concentration in weekly plasma samples between control and food-restricted animals. Insulin concentrations from 2 weeks after the start of feed restriction were significantly (P<0.05) lower in restricted animals than in control animals. The NEFA concentration in restricted animals was significantly (P<0.05) increased after the start of feed restriction, and then decreased gradually to the basal level. The present results suggest that nutritionally induced anovulation after CIDR-G treatment is associated with a reduction in the frequency of LH pulses, and that insulin and NEFA, rather than the glucose concentration in the circulation, may be associated with the metabolic suppression of LH pulses.