Ovulatory activity of female goats adapted to the subtropics is responsive to photoperiod

The objective of this study was to determine whether reproductive seasonality of local well-fed female goats from subtropical Mexico (26°N) can be controlled by photoperiod. The control group (n = 12) remained in an open pen under natural photoperiod variations. The two experimental groups (n = 8 each) were placed in light-proof rooms and exposed for 2 yr to alternations of 3 months of long days and 3 months of short days. One group was first exposed to long days, Group 1, and the other one to short days, Group 2. Blood samples were obtained twice a week to determine ovulation status by progesterone plasma concentrations. Goats from the control group displayed a seasonality of ovulations. The mean (±SEM) dates of the onset and end of the ovulations were September 10 ± 5 d and February 16 ± 4 d, respectively. In contrast, in both experimental groups, ovulations were modified (P < 0.05) by the photoperiodic treatments such that ovulations started and ended during short and long days, respectively. In Groups 1 and 2, ovulations started 67 ± 2 and 66 ± 2 d (P > 0.05), respectively, after the transfer from long to short days. In contrast, the timing of the cessation of ovulations after the transfer from short to long days differed (P < 0.05) between groups (19 ± 3 and 31 ± 3 d for Groups 1 and 2, respectively). Local female goats from subtropical Mexico are, therefore, sensitive to photoperiodic changes that they are exposed to at this latitude and this environmental cue may control the timing of the breeding season in natural conditions.