Estrous Behavior, Progesterone in Peripheral Plasma and Milk in Dairy Goats at Onset of Breeding Season

Two large flocks of 60 and 120 French Alpine dairy does were studied beginning in late June. Estrous behavior was checked daily in the presence of bucks, and numerous blood and milk samples were collected. The end of the anestrus was characterized by consistent low progesterone around .1 ng/ml in plasma and 2 to 4 ng/ml in milk. Cyclic activity was detected in early July in one flock and in early August in the other. Individual patterns of plasma and milk progesterone in cyclic females were correlated greater than .5. Estrus was short (4 to 5 days) in 3 to 10 goats sampled daily following first estrus, and a small and transient rise of concentrations of progesterone was concomitant. Mean plasma and milk progesterone increased from about .1 to .5 and 2 to 4 ng/ml at the time of estrus to 6 to 8 in plasma and 6 to 10 ng/ml in milk 10 days later (midluteal phase). Twenty-one days after mating, concentrations in plasma and milk of pregnant animals were of the same magnitude as during the midluteal phase and higher than those in nonpregnant does (.1 to .7 and 2 to 3 ng/ml in plasma and milk).