Subtropical goats ovulate in response to the male effect after a prolonged treatment of artificial long days to stimulate their milk yield.

The objectives of this study were to determine (i) if in subtropical goats that gave birth during mid-December, the exposition to an artificial long-day photoperiod consisting in only 14 hr of light per day can increase the milk yield and (ii) to test whether these females can respond to the male effect at the end of the prolonged photoperiodic treatment. In experiment 1, 17 lactating goats were maintained under natural short days (control group), while another 22 goats were maintained under artificial long days (treated group) consisting in 14 hr light and 10 hr darkness starting at day 10 of lactation. The continuous exposition to an artificial long-day photoperiod produced an increase in the milk yield level during the first 110 days of lactation (time × treatment interaction; p = .01), while none of the milk components were modified due to the photoperiodic treatment (p > .05). In experiment 2, all control and treated anovulatory goats were submitted to the male effect using photostimulated males. All females showed oestrous behaviour within the first 10 days that were in contact with males (100% in both groups; p > .05). Thus, the latency to onset of oestrus did not differ between females from control (58.2 ± 3.0 hr) and treated (62 ± 4.6 hr) groups. Male exposition provoked ovulation independently if females were previously under long days or natural photoperiod (96 vs 100%, respectively; p = .79). It was concluded that exposure to 14 hr of light per day in subtropical goats that gave birth in late autumn stimulates milk yield without preventing the ovulation in response to the male effect at the end of the prolonged photoperiodic treatment.

Continuous light after a long-day treatment is equivalent to melatonin implants to stimulate testosterone secretion in Alpine male goats.

In rams, artificial long days followed by continuous light stimulate testosterone secretion during the non-breeding season. The objective of this study was to determine whether artificial long days followed by continuous light could stimulate testosterone secretion in Alpine bucks as well as in those exposed to long days followed by a melatonin treatment. All bucks were kept in shaded open pens. Control males were exposed to natural photoperiod conditions (n=5). Males of the two experimental groups were exposed to 2.5 months of long days from 1 December (n=5 each). On 16 February, one group of males was exposed to 24 h of light per day until 30 June; the other group was exposed to natural variations of photoperiod and received two s.c. melatonin implants. Testicular weight was determined every 2 weeks, and the plasma testosterone concentrations once a week. In the control and the two photoperiodic-treated groups, a treatment×time interaction was detected for testicular weight and plasma testosterone concentrations (P<0.001). In control bucks, testicular weight increased from January and peaked in June, whereas in both photoperiodic-treated groups, this variable increased from January, but peaked in April, when the values were higher than in controls (P<0.05). In the control group, plasma testosterone concentrations remained low from January to June, whereas in both photoperiodic-treated groups, this variable remained low from January to March; thereafter, these levels increased in both photoperiodic-treated groups, and were higher than controls in April and May (P<0.05). We conclude that continuous light after a long-day treatment stimulate testosterone secretion in Alpine male goats during the non-breeding season as well as the long days followed by a melatonin treatment. Therefore, continuous light could replace the implants of melatonin.

Stimulation of reproductive activity in anovulatory Alpine goats exposed to bucks treated only with artificially long days.

Two experiments were conducted in a subtropical latitude to determine the response of Alpine male goats to a treatment with artificially long days (experiment 1), and the response of anovulatory lactating Alpine does exposed to males treated only with artificially long days (experiment 2). In experiment 1, one group of males was kept under natural photoperiod (n = 4) while another was exposed to 2.5 months of artificially long days (16 h of light/day) from 1 December (n = 4). Plasma testosterone concentrations were determined weekly. Intensity of odor of males was determined every 2 weeks. Sexual behavior of bucks was observed during 3 days about 90 days after the end of the long day treatment. A treatment-by-time interaction was detected for testosterone secretion (P < 0.001). In control males, low plasma concentrations of testosterone were observed from March to June. In contrast, in long-day treated males, high levels of testosterone were observed from March to June (P < 0.05). A treatment-by-time interaction was detected for the intensity of male odor (P < 0.01). The male odor was stronger in long-day treated bucks than in untreated ones from March to June (P < 0.05). The number of ano-genital sniffing, nudging and flehmen was greater in long-day treated males than in untreated ones when exposed to anestrous does (P < 0.05). In experiment 2, one group of males was left under natural photoperiod variations (n = 5) and the other (n = 5) was submitted to the same photoperiodic treatment described in experiment 1. On 3 May, three untreated and three long-day treated males were put in contact with anestrous Alpine does left under natural photoperiod. Fertility was higher in does exposed to light-treated males (36/45, 80%) than those in contact with untreated ones (3/45, 7%; P < 0.05). Prolificacy was similar (P > 0.05) in does exposed to treated (1.8 ± 0.1) and untreated males (1.7 ± 0.3). These results indicate that the sexual activity of Alpine male goats raised in subtropical latitudes can be induced using only artificially long days and that such males are effective in stimulating reproductive activity in anovulatory females in late spring.