Samoa J.R. Wallach

The role of the striated penile muscles of the male rat in seminal plug dislodgement and deposition

Seminal plugs, which must be tightly adhered to the vaginal walls for optimal fertilization, are disturbed or loosened by copulatory intromissions. In multi-male mating encounters, a male may reduce the sperm delivered by a previous male by dislodging the former males plug and depositing his own sperm and plug. Recent work has documented that the striated penile muscles are involved in the production of penile erectile cups and flips. This study focused on the effects of penile muscle excision on the ability of male rats to dislodge and deposit tight plugs. Using a radiopaque contrast medium to visualize if a seminal plug was tightly adhered to the vaginal wall, displaced caudally or dislodged, Experiment 1 examined the manner in which plugs were removed during a series of intromissions. The dislodgement process was envisioned as a gradual one beginning with caudal displacement which occurs during the first or second intromission. Following excision of either the bulbocavernosus (BCX) or ischiocavernosus (ICX) muscles in Experiment 2, plug disturbance ability was impaired in 54 percent and 40 percent of BCX and ICX subjects respectively. Ability to deposit tight plugs was impaired in 45 and 20 percent of BCX and ICX subjects respectively.

Differences in responsiveness to testosterone of penile reflexes and copulatory behavior of male rats.

The display of penile reflexes and copulatory behavior appears to reflect the activity of two different underlying neuronal system, both of which are modulated by systemic testosterone (T) concentration. To indirectly compare the two systems, the responsiveness to T of penile reflexes and copulatory behavior was examined. In the first experiment castrated spinal male rats were given penile reflex tests while receiving replacement T through Silastic capsule implants filled with T (50 mm T). After capsule removal the number of penile erections and flips declined within 24 hr and gradually decreased for 12 days. Subjects were then reimplanted with new 50-mm T capsules. The number of penile flips and erections increased within 6 and 12 hr. respectively. This is a much more rapid response rate to T than has been established for copulatory behavior. In the second experiment castrated spinal male rats were tested for penile reflexes with a 50-mm T capsule, which was then replaced with a 10-, 5-, or 2-mm T or an empty capsule. The number of penile reflexes declined in a dose-response fashion. In the third experiment, castrated sexually experienced male rats were tested for copulatory behavior with two 25-mm T capsules which were then replaced with a 10 or 2-mm T or an empty capsule. Only males with empty capsules had decrements in copulatory behavior, revealing that a low level of T can maintain virtually normal sexual behavior despite a marked decline in penile reflex activity. The neuronal system underlying penile reflexes (spinal neurons) is apparently much more responsive to changes in T concentrations than the neuronal system underlying motivational and appetitive aspects of copulatory behavior (brain neurons).

The relationship of male-male mounting to the sexual preferences of young rams

Abstract The purpose of this study was to determine the relationship between the frequency of male-male mounting of young rams in all-male groups and their subsequent preferences for female vs. male sexual partners. Mount interactions were monitored in the home pen of 29 rams reared in 1984 and 25 rams reared in 1985. At ∼ 8–10 months of age, and prior to copulatory experience, individual rams were simultaneously exposed to two unfamiliar estrous ewes and two unfamiliar rams. The four stimulus animals were restrained and cloth covers were placed over their perinea to prevent copulations. The Binomial Test was used to verify sexual preferences. Of the 44 rams that were sexually active in the sexual performance tests, 30 (68.2%) met the criterion for female preference, 4 (9.1%) preferred males and 10 (22.7%) exhibited no preference (i.e., were bisexual in orientation). There was little relationship between the frequency of male-male mounting by rams in all-male rearing groups and their subsequent sexual preferences. The majority of young rams prefer to mount ewes, even prior to copulatory experience, but in the absence of females will often mount other males.

Effects of sexual stimulation on the sexual performance of rams

Abstract The sexual performance of bulls and male goats is improved if they are allowed to view the hetero-sexual behavior of other males as a prelude to mating. The purpose of the following study was to determine whether sexual stimulation enhances the sexual performance of rams. In Experiment 1, 11 sexually experienced ram lambs (∼ 9 months of age) and 18 sexually experienced yearling and 2-year-old rams were individually exposed to 4 unrestrained, hormone-induced estrous ewes for 60 min after viewing the courtship and mounting behaviors of a male conspecific for 20 min (two tests) and in the absence of stimulator animals (two tests). In contrast to the results with bulls and bucks, the rams were hardly influenced by the sexual stimulation treatment. Latencies for first mount and first ejaculation were shorter for sexually stimulated ram lambs; otherwise, treatment differences were negligible. A similar follow-up experiment was administered to 12 mature rams using restrained females in the sexual performance tests. Again, treatment differences were minor. It was concluded that sexual stimulation does not functionally enhance the sexual performance of rams. Species differences in response to sexual stimulation are discussed in terms of female sexual behaviors that may result in a selective (competitive) advantage to males that are stimulated to locate and mate with females early in the estrous period.

Social preferences of domestic ewes for rams (Ovis aries)

Abstract A series of four experiments was performed to investigate the social preferences of 16 domestic ewes for potential mating partners. Ewe preferences were assessed by measuring the time spent in proximity to each of 2 restrained rams and/or 1 or 2 restrained ewes, in 5- or 20-min tests. In the first experiment, it was shown that oestrous ewes preferred to be in proximity to rams, while anoestrous ewes preferred other ewes. The second experiment showed that ewe preferences were strongly correlated with the rates of ram sexual solicitations and that ewes preferred older, larger rams over younger, smaller rams. The third experiment demonstrated that ewes preferred rams that had a history of higher sexual performance, independent of their rates of sexual solicitation. The fourth experiment demonstrated that the presence of other oestrous ewes interacting with rams can enhance the attractivity of some, but not all rams. Taken together, these results suggest that ewes can have strong preferences for potential mates and that these preferences may account, in part, for the findings that older, larger, more sexually active rams tend to be more reproductively successful. These findings suggest specific management practices which could improve breeding efficiency in domestic flocks.

Rearing bulls with females fails to enhance sexual performance.

Abstract The purpose of this study was to determine if continuous exposure of beef bulls to female conspecifics from weaning to 18 months of age enhanced their sexual performance relative to age mates reared in unisexual groups. Two groups of 12 Hereford bulls (BMF) were each reared with 6 ovariectomized female age mates from weaning (7 months) to 18 months of age while two additional groups of 12 males (BM) were reared in the absence of females. The stimulus females were induced to exhibit estrus via hormone administration every 4 weeks starting when the bulls averaged 12 months of age. Four biweekly sexual performance evaluations were administered to the bulls starting at 18.5 months. Each sexual performance evaluation consisted of an hour-long observation of 6 bulls with 5 unrestrained estrous females whose perinea had been covered to prevent intromissions, and an hour-long observation of 6 bulls with 5 different unrestrained estrous females whose perinea were not covered. Differences in sexual performance between BMF and BM bulls were relatively few in number and short lived. BM bulls were reluctant to mount estrous females in the first test of the first sexual performance evaluation, but thereafter rates of mounting and successful copulations were similar to those of BMF bulls. Treatment did not affect mount intention frequencies, but BM bulls attended females a greater percentage of the test time ( P It was concluded that rearing bulls in the absence of females does not significantly retard the development of sexual behavior.

The effects of long-term individual vs. group housing on the sexual behavior of beef bulls

Abstract The objective of this study was to determine the effects of long-term individual housing on the sexual performance of Hereford bulls. The bulls were hand reared from birth and maintained in individual (N = 7) or group pens (N = 9) through testing at 19 months of age. Four sexual performance tests were administered 2 to 3 days apart and consisted of exposing individual bulls to 3 restrained estrous females for 40 min. Individually reared (IR) bulls exhibited a greater proportion of disoriented (side) mounts than their group reared (GR) counterparts (12.8 vs. 2.9%, respectively; P

Fostering lambs by odor transfer: Two-lamb substitution

Abstract Odor specific to individual lambs enables ewes to discriminate between their own and alien offspring. Previous research has demonstrated that many post-partum ewes will adopt a single alien lamb in addition to their own natural lamb if the alien lamb is wearing a jacket impregnated with own-lamb odor (“add-on” odor transfer fostering technique). The following study investigates whether a higher percentage of ewes will adopt “extra” lambs if their own natural young is exchanged for 2 alien lambs (two-lamb substitution). Cloth stockinettes were placed on the natural lambs of 47 multiparous ewes shortly after parturition. Forty-eight to 72 h later, 27 ewes that had given birth to single lambs and 20 ewes that bore twins were given 2 alien lambs in exchange for their own offspring. Approximately half of the ewes in each group received alien lambs wearing jackets impregnated with own-lamb odor (experimental odor transfer group); the remaining ewes received aliens wearing their own jackets (control group). Standard acceptance tests were conducted daily for 5 days. Only 14.3% of the experimental (odor transfer) ewes that bore single young accepted both alien lambs in exchange for their own. However, 90% of the experimental ewes that bore twins accepted both aliens. Control ewes had lower adoption rates of alien lamb pairs. Ewes bearing single young tended to accept only 1 lamb. Experimental ewes that received siblings (twins) were more likely to accept both alien young than ewes that received non-siblings (57.1 vs. 30%, respectively). Ewes that bore single lambs were more likely to accept a single alien lamb if they were presented with non-sibs than sibling pairs (84.6 vs. 42.9%, respectively). It was concluded that two-lamb substitution via the odor transfer fostering technique is inferior to the add-on procedure for increasing the number of lambs reared by ewes. However, it is an effective method for replacing twin sets that have died.