Breeding season of Criollo and Granadina goats under constant nutritional level in the Mexican highlands

The objective of this work was to characterize the anoestrous season of Criollo and Granadina goats kept on a constant nutritional level to determine the time of year when ovarian activity ceases, the duration and depth of anoestrus, and the time at which these animals start cycling again. A sample of 19 Criollo and 11 Granadina goats were fed oat hay, concentrate and mineral salts to cover 100% of their nutritional requirements. All animals were adult, non-pregnant and non-lactating and were kept isolated from the males for the duration of the study. Blood samples, taken from all animals twice a week from November 1986 to July 1987 into heparinized tubes, were kept refrigerated until centrifugation for harvest of plasma and then frozen until assayed. Ovarian activity was monitored from the circulating levels of progesterone determined by the FAO/IAEA solid phase radioimmunoassay kit. Concentrations above 1 ng/mL were considered indicative of the presence of a functional corpus luteum and reproductive activity. The majority of the Criollo goats were cycling during November and December, ovarian activity decreasing gradually during February; from March to May most of the goats ceased to ovulate but ovarian activity resumed again in June or July; thus anoestrus was only evident during the spring. In contrast, Granadina goats had a longer and deeper anoestrus; 54% of these animals never showed significant increases in progesterone above basal levels during the period under study (November to July). The short anoestrous season of the Criollo goats and the weak inhibition of ovarian activity during this period suggest that these animals have a greater reproductive potential than the Granadina goats. (author). 21 refs, 7 figs