Sexual behavior of medium-ranked rams toward non-estrual ewes is stimulated by the presence of low-ranked rams

Determinants of ram sexual behavior and its impact on sheep breeding

In sheep, anatomical characteristics of the cervix and animal value limit application of reproductive technologies; therefore, most breeding is natural service. Rams are selected based on desired physical traits and semen capacity, but their contribution to flock genetics is constrained by expression of sexual behavior. In 1964, it was first reported that approximately one-third of rams expressed limited sexual interest toward ewes in estrus. Therefore, if rams were evaluated for expression of sexual behavior, it is estimated that as many rams would be culled for the lack of behavior as are currently culled for semen quality or physical deficiencies. Sexual behavior is complex, requiring sensory recognition and processing, integration of ram cohorts and social dominance, female mate choice, and a physical response. This review of the literature aims to provide insights into factors influencing expression of ram sexual behavior.

An automated method for the evaluation of ram libido in real mating conditions

We investigated if sexual behaviour of rams can be assessed with an electronic Alpha-Detector (AD) which automatically records mounts of mating rams. To evaluate the rams' libido (i.e. all sexual activities), we used six intact and six vasectomised rams in pen tests in three different seasons (late spring, autumn and early spring). The pen tests consisted of 30-min visual observations of each ram placed in a group of six Merino ewes (three ewes in oestrus and three ewes not in oestrus). In the pen tests, sexual behaviour was recorded and divided into two categories: pre-copulatory and copulatory. For validation purposes, during the pen tests the 12 rams were equipped with the AD and the number of times the 18 oestrous ewes were mounted were counted over a period of 3 days. Of the 1191 mounts visually identified in the six 30-min sessions, 1026 were recorded automatically by the AD (i.e. 94%). The paddock test is an automated method consisting of the same rams wearing an AD and placed in a flock of ~250 Merino ewes on two occasions (late spring (spring 1) and early spring of the following year (spring 2)), their copulatory activities were automatically recorded over a 5-day period. The results of the pen tests in the three seasons revealed no difference between the two types of rams (breeding v. detecting rams). Based on live observations high correlations (r=+0.81, P<0.003 for breeding and r=+0.76, P<0.02 for detecting rams) were found between pre-copulatory and copulatory behaviours. The libido of the two types of rams measured in pen tests showed high repeatability across the three seasons (83 and 75%, P<0.05 for copulatory and pre-copulatory behaviours, respectively). When measured automatically in paddock tests over two consecutive springs, even higher repeatability was observed in both breeding (94%; P<0.01) and detecting rams (97%; P<0.004) in the number of mounts. In addition, high correlations (+0.89<r<+0.94) between copulatory behaviours, as measured by live observations, and those measured by the AD were obtained. The automatic measurement of ram libido in paddock tests appears to be more reliable than pen tests and far less time consuming. We therefore recommend this automated method to estimate the libido of rams. In addition, this method can be used at any season of the year provided that ewes in oestrus are present in the flock.

Homosexual behavior in male goats is more frequent during breeding season and in bucks isolated from females

Male homosexual behavior is observed in many ruminant species; seasonality and isolation from females may affect the display of male-male sexual behavior. Our objectives were to determine whether: 1) homosexual behavior has a seasonal pattern in male goats (Capra hircus); 2) isolation from female goats influences the frequency of the display of homosexual behavior; and 3) the frequency of homosexual behaviors is related to testosterone concentration. Bucks were housed in a pen adjacent to another pen with 3 estrous goats (FC group) or in complete isolation from females (IF group). Homosexual behaviors and testosterone concentrations were recorded in October, December, February and May. Frequencies of penile display and flehmen increased in May and were observed more frequently in the IF than in the FC group. Ano-genital sniffing was more frequent in February and May and was more frequent in IF than in FC bucks. Lateral approaches were more frequent in May, in which period this was more frequently observed in IF bucks. Mount attempts and mounts were only observed in IF bucks. Testosterone concentrations increased from December to February and decreased in May, although they were still greater than in October and December. In May IF bucks had greater testosterone concentrations than FC bucks. Testosterone concentrations were only related to the number of lateral approaches in IF bucks in December. In conclusion, homosexual behavior was more frequent during the late breeding season than during the early and the non-breeding seasons, and in males isolated from females than in males housed near estrous females. Testosterone concentrations appear to be unrelated to homosexual behavior.