THE BEHAVIORAL COMPONENT OF THE RAM EFFECT - THE INFLUENCE OF RAM SEXUAL-BEHAVIOR ON THE INDUCTION OF ESTRUS IN ANOVULATORY EWES

The objective of this study was to test whether the sexual behavior of the ram affects the ram effect. Rams exhibiting either high (HP) or l ow (LP) levels of sexual performance (on the basis of serving capacity tests) were exposed to 89 anestrous ewes for 28 d. Thirty-two anestro us ewes were not exposed to rams. The objective of this study was to c ompare the efficacy of estrus induction by HP (n = 4) vs LP (n = 4) ra ms. Plasma progesterone concentration was used as an index of ovarian activity. Groups of ewes were exposed to either an HP or an LP ram in a .32-ha pasture. Courtship behaviors of rams were recorded for 6 h on the initial day of exposure and for 30-min periods on alternate days thereafter. A greater percentage of ewes exposed to HP rams ovulated ( 95%) compared with ewes exposed to LP rams (78%) (P < .02). On the 1st d of exposure, the HP rams exhibited more courtship behavior and spen t more time near the ewes (P < .04). The HP rams spent more time withi n 1 m of ewes during the 28-d exposure. There were no differences in t he amount of contact with rams (LP or HP) between ewes that did and di d not ovulate (P > .05). The first rise in progesterone indicative of ovulation tended to occur earlier (P = .06) in ewes penned with HP ram s. A seater percentage of ewes exposed to LP rams (P = .03) bad early elevations of progesterone with no concurrent sexual behavior. These d ata imply that in addition to a pheromone the sexual behavior of the r am may be important in initiating ovarian cycle activity.