Artificial long days in addition to exogenous melatonin and daily contact with bucks stimulate the ovarian and oestrous activity in Mediterranean goat females

Abstract

One experiment was conducted to determine whether the treatment with artificial long days and exogenous melatonin can induce reproductive activity during spring (seasonal anoestrus) in Mediterranean goats that are in daily contact with bucks and whether this treatment causes a variation in the reactivation of the reproductive activity in the normal breeding season. The experiment started on 4 November 2005 and finished on 27 October 2006. Thirty-four adult and barren does were used, distributed into two groups balanced according to their live weight (LW) and body condition score (BCS). Seventeen females were exposed to long days (16 h of light/day) from 14 November 2005 to 20 February 2006. On 20 February, they received one s.c. melatonin implant (LD-M group) and were exposed to natural photoperiodic changes in an open shed. The other females during the experiment were placed in an open shed under natural photoperiod and remained as the control group (C group). The C and LD-M groups were keeping in contact with males during the whole experiment. During the experiment, the LW, BCS and plasma progesterone concentrations were measured weekly, oestrous activity was tested daily using entire aproned bucks, and ovulation rate was evaluated by laparoscopy 7 days after positive identification of the oestrus. A clear treatment–time interaction was observed for plasma progesterone concentrations ( P,0.001), with a period of high progesterone concentrations during the natural seasonal anoestrus in the LD-M group. Although 94.1% of females in the LD-M group presented ovarian activity during this period, no female in group C did. Resumption of ovarian activity in the subsequent natural breeding season was 2 weeks later in the LD-M group in comparison with group C ( P,0.05). We can conclude that in Mediterranean goat breeding systems, when females are in daily contact with bucks, the treatment with 3 months of long days and melatonin implant at the end of the light photoperiodic treatment can induce ovarian and oestrous activity during the seasonal anoestrus. Finally, this treatment causes a short delay in the subsequent reactivation of ovarian activity in the natural breeding season.