Photoperiod-melatonin-induced, sexually-activated rams increase pregnancy rate and number of lambs per ewe in a ram effect

International audienceIntroduction - The use of sexually-activated rams to induce a ram effect in ewes is a practical tool to induce out-of-season sexual activity in ewes. Aim - To determine whether the introduction of sexually activated rams to a flock of anestrous ewes, to induce a ram effect, would improve the ovulatory response and reproductive performance of Rasa Aragonesa ewes. Materials and methods - Rams exposed to two months of either long days (16 h of light/d) between 1 Feb and 31 Mar (Treated group, n=4), or the natural photoperiod (Control group, n=4). At the end of the long-day period, rams were returned to the natural photoperiod and received three melatonin implants. Fifty-eight anestrous ewes were assigned to one of three groups: i) mated with Treated rams (TR group, n=17), ii) mated with Control rams (CR group, n=18), or iii) kept isolated from rams during the experiment (Isolated group, n=23). Mating occurred between 11 May and 20 Jun. Results and discussion - Treated rams performed 81% of nudging, 75% of anogenital sniffing, and 90% of self-urination (P<0.001). Those rams had higher plasma testosterone concentrations than the rams in the Control group at 15 and 30 d (P<0.05) after exposure to the natural photoperiod. All ewes ovulated and presented estrus within the mating period, and 39% of the Isolated ewes began ovulatory activity (P<0.001). TR ewes had a higher proportion of ewes that lambed (100%) and higher fecundity (1.44 +/- 0.51 lambs/ewe) than CR ewes (78% and 1.00 +/- 0.69 lambs/ewe) (P