Milk progesterone profiles during anoestrus through to pregnancy in Greek dairy goats (Capra prisca): the effect of melatonin treatment and male introduction

Abstract

AbstractTwo groups of 10 lactating does were housed separately, in isolation from bucks. Does in one group (T) were implanted with melatonin; the second group (U) were not implanted. After 30 days, five implanted and five non-implanted bucks were introduced, singly, into both groups of females each day. Subsamples of milk were taken from the daily output of each doe on 3 days each week for progesterone analysis.Mean milk progesterone concentration during anoestrus varied significantly amongst individuals (P < 0·001), but the difference between T and U groups was not significant (1·51 and 1·93 (s.e.d. 0·52) μg/l, respectively). Elevated progesterone levels, indicative of a short oestrous cycle and commencing days 2 to 5 after male exposure, were observed in most does. Mean progesterone concentrations were 9·9 and 9·6 (s.e.d. 1·32) μg/l in T and U does respectively. Most does showed a second short cycle starting at 12 to 18 days, (mean concentration 8·4 and 10·6 (s.e.d. 1·64) ng/l, respectively). Untreated does then returned to anoestrus until mated at 63·1 (s.e. 0·94) days after male introduction. In contrast, T does either became pregnant or had a normal oestrous cycle, followed by a repeat cycle or pregnancy (mean onset 21·7 (s.e. 2·22) days after male introduction). The mean time of effective mating for group T does was 37·3 (s.e. 5·91) days, 26 days earlier than for U does (P < 0·001). Mean progesterone concentration in early pregnancy was 65·7 (s.e. 5·78) and 67·6 (s.e. 5·41) μg/l in T and U does, respectively. Males did not become sexually active until after the onset of luteal activity in the females, although treated males were earlier than untreated. There were no significant differences in lactation pattern associated with the progesterone profiles in the two groups.The introduction of males during late anoestrus initiates short luteal cycles. Only those does closest to onset of the breeding season, in this case induced by melatonin, continue to cycle normally and mating success may require early stimulation of sexual activity in males.