Extended day length in late winter/early spring, with a return to natural day length of shorter duration, increased plasma testosterone and sexual performance in rams with or without melatonin implants

Abstract

Sixteen rams were used to quantify the effects of long days, imposed during late winter/early spring, with or without exogenous melatonin, on plasma testosterone concentrations and ram serving capacity. Rams were assigned to two groups: photoperiod-treated rams (Artificial Photoperiod, AP; n = 8), exposed to 2 months of long days (16 hr of light/day) between 22 December and 22 February, and control rams (Natural Photoperiod, NP; n = 8). At the end of the long-day period, AP rams were returned to the natural photoperiod, and each ram in the two groups either did (+M) or did not (-M) receive three subcutaneous melatonin implants. Four groups were created as follows: AP+M (n = 4), AP-M (n = 4), NP+M (n = 4) and NP-M (n = 4). Thirty days after of the onset of photoperiodic treatment, AP rams (13.5 ± 2.8 ng/ml) had significantly (p < .05) lower testosterone levels than NP rams (36.7 ± 1.0), and similar differences were not apparent at the end of the photoperiod treatment. A month later, AP rams (24.3 ± 7.9) had higher (p < .10) testosterone levels than NP rams (13.1 ± 5.0), with no effect of melatonin treatment. Fifty days after melatonin implantations, rams were exposed for 20 min to three oestrous ewes. AP rams (2.50 ± 0.42) exhibited significantly (p < .05) more serves than did NP rams (1.11 ± 0.39), and melatonin treatment had no significant effect; however, the interaction between treatments was significant. Time to first serve was significantly (p < .05) shorter in AP (2.30 ± 1.20 min) than it was in NP rams (5.58 ± 0.68 min). In conclusion, exposure to 2 months of long days in late winter/early spring, with a return to natural day length of shorter duration, increased plasma testosterone concentrations and sexual performance in rams with or without exogenous melatonin. This particular management is an option if a non-hormonal reproductive strategy is scheduled; yet, if the use of exogenous hormones is feasible, melatonin implants increase the mating efficiency of rams.

Melatonin Treatment in Rams and Their Replacement with Novel Treated Rams Advance First Lambing and Increase Fertility in Sarda Ewe Lambs

“…These findings support past research as melatonin treatment and photoperiodic effects were also associated with improvements in ram reproductive performance in Rasa Aragonesa rams, and earlier onset of puberty in Rasa Aragonesa ewe lambs [ 12 , 21 ]. The reduction in the age at which first lambing occurred, as observed in this study, is also comparable to that found in previous experiments with melatonin-treated Sarda ewe lambs [ 22 , 23 ].…”

Testicular Degeneration and Infertility following Arbovirus Infection

“…6G ). Under normal conditions, the levels of blood testosterone in rams varies considerably ( 34 – 36 ). Hence, we measured the levels of testosterone in each BTV-1-infected ram at day 5, and late at days 8 to 11 or day 15, relative to the levels found in the same rams at day 0 before infection (taken as 100).…”

Light-induced sexually active rams provoke LH preovulatory surges and enhances LH concentrations in ewes after progestagen treatment

“…Although sexual-performance tests were not performed in this experiment to avoid the effect of previous contact with females on sexual activity, especially in the control rams, our previous studies have confirmed that light-treated rams exhibit higher sexual behavioral expression [14] than do rams kept under the natural seasonal photoperiod, and have high plasma testosterone concentrations in spring [6,7,14]. It has been found [15] that the proportion of ewes that ovulated was highest in groups that had been exposed to rams that exhibited intense, rather than moderate, sexual behavior, and concluded that, in addition to a pheromone signal, the sexual intensity of the ram is important in initiating ovarian cycles.…”