Inability to predict sexual and aggressive behaviors by plasma concentrations of testosterone and luteinizing hormone in Hereford bulls

Tyrosine hydroxylase in the ventral tegmental area of rams with high or low libido-A role for dopamine

Dopamine synthesis in the ventral tegmental area (VTA) is necessary for the reinforcement of sexual behavior. The objective of this study determined if sexual stimuli initiates reward, and whether reward is attenuated in sexually inactive rams. Sexually active rams were exposed to urine from estrous (n=4) or ovariectomized (n=3) ewes with inactive rams (n=3) exposed to urine from estrous ewes. Following exposure, rams were exsanguinated and brains perfused. Alternating sections of the VTA were stained for Fos related antigens (FRA), tyrosine hydroxylase, and dopamine beta-hydroxylase activity. Forebrain tissue, mid-sagittal ventral to the anterior corpus callosum, was stained for dopamine D2 receptors. Concentrations of cortisol was determined prior to and following exposure. Exposure to ovariectomized-ewe urine in sexually active rams did not influence (P=0.6) FRA expression, but fewer (P<0.05) neurons were positive for tyrosine hydroxylase in the VTA. Sexually inactive rams had fewer (P<0.05) FRA and tyrosine hydroxylase positive neurons in the VTA than sexually active rams following exposure to estrous ewe urine. VTA neurons staining positive for dopamine beta-hydroxylase did not differ by sexual activity (P=0.44) or urine exposure (P=0.07). Exposure to stimulus did not influence (P=0.46) numbers of forebrain neurons staining positive for dopamine D2 receptors in sexually active rams, but fewer (P=0.04) neurons stain positive in inactive rams. Serum concentrations of cortisol did not differ (P≥0.52) among rams prior to or following stimulus. In conclusion sexual inactivity is unlikely due to stress, but may be partially a result of decreased tyrosine hydroxylase and/or the response to dopamine.

Sexual behavior of domesticated ruminants

Domesticated ruminants have lived in close association with humans for thousands of years and knowledge of the behavior of these organisms has contributed to their successful domestication, as well as to the management of animals in captivity, both extensive and intensive. Here we describe the reproductive behavioral endocrinology of cattle, goats and sheep. These relatively large and tame animals provide opportunities to conduct a wide range of behavioral studies from short-term to longitudinal or developmental in nature. Highlighted is some of the work from our laboratory describing the social, environmental and endocrine factors that influence the expression of sexual behavior in male and female goats.

Growth and reproductive development from weaning through 20 months of age among breeds of bulls in subtropical Florida

To determine the effect of breed on growth and reproductive development, weaned bulls in each of 2 yr were managed as a single group for approximately a year. In Year 1, the study group consisted of 24 Angus, 24 Brahman, 20 Hereford and 14 Senepol bulls, while in Year 2, it contained 25 Angus, 17 Brahman. 13 Romosinuano and 9 Nellore x Brahman bulls. Body and testicular growth measurements were recorded at 6-wk intervals. At approximately 1 yr of age and quarterly thereafter (4 periods), bulls were evaluated for libido, pubertal status, and GnRH-induced LH and testosterone secretion. Significant breed-by-age interactions occurred for most growth measurements. Brahman bulls (Bos indicus ) were (P < 0.05) older and heavier at puberty than Angus, Hereford, Senepol and Romosinuano bulls (Bos taurus ). Libido scores were lowest for Brahman and Nell ore x Brahman bulls (Bos indicus ). highest for Angus and Hereford bulls (temperate Bos taurus breeds) and intermediate for Senepol and Romosinuano bulls (tropical Bos taurus breeds; P < 0.05). Differences were not consistent among breeds or between years for GnRH-induced LH secretion. In both years, basal testosterone concentrations and areas under the GnRH-induced testosterone curve were higher (P < 0.05) for Angus and Hereford bulls (temperate breeds) than for Brahman, Senepol, Romosinuano and Nellore x Brahman bulls (tropical breeds). In conclusion, reproductive development of Senepol and Romosinuano bulls (tropical Bos taurus breeds) was more similar to Angus and Hereford bulls (temperate Bos taurus breeds) than to Brahman and Nellore x Brahman bulls (Bos indicus ).

Semen quality and behavior of Holstein bulls exposed to estradiol-treated bulls for mounts

The objectives were to test the effects of estradiol treatment of teaser bull mounts on sexual behavior and on quality and quantity of sperm obtained from sires managed as in large commercial AI breeding organizations. In a change-over design, the same teaser bulls were either untreated or treated with estradiol. Five semen-producing bulls were ejaculated twice per day on Tuesdays and Fridays after epididymal reserves were partially depleted. A 15-min period of continuous sexual preparation with three false mounts allowed was standard before each semen collection. All bulls were attracted to and licked the preputial area of the teaser bulls followed by the Flehmen response during the period of sexual preparation. Bulls usually completed the false mounts in < or = 15 min, and all thrusted vigorously with both hind feet moving forward synchronously at this time on 100% of the 80 semen collections. Major differences among bulls and between first and second ejaculates occurred in semen volume, semen concentration, and total sperm collected. An increase of 10% in total sperm output when bulls were exposed to treated teaser bulls could be of commercial benefit. The correlation between total time to first mount for the two ejaculates per bull each day and total sperm collected per bull per day was -.44. Thus, the shorter time to first mount may be useful as a low level predictor of higher sperm out-put per bull.

Effects of pretreatment with adrenocorticotropin on endocrine and behavioral responses of bulls to sexual activity

Peripheral concentrations of cortisol, growth hormone and testosterone were determined in two experiments which examined the endocrine and behavioral responses of sexually mature Angus bulls to an estrous female (Experiment 1) and to female exposure 5 hours following an adrenocorticotropin (ACTH) injection (Experiment 2). Sexual activity of bulls in Experiment 1 significantly increased levels of cortisol when compared with concentrations before exposure to a female. Administration of ACTH in Experiment 2 consistently elevated levels of cortisol by 30-fold (P<0.01) when compared with pre-ACTH concentrations. This heightened level of cortisol persisted throughout the period of exposure to an estrous cow, although a gradual decline in cortisol concentrations occurred over time (P<0.05). In Experiment 1, growth hormone profiles tended to increase in response to sexual activity (P<0.10), whereas in Experiment 2, growth hormone increased in response to ACTH administration (P<0.01) and to female exposure (P<0.01). Concentrations of testosterone were unaffected (P>0.10) by mating activity in Experiment 1. In Experiment 2, acute suppression (P<0.01) in testosterone concentrations 5 hours after ACTH administration coincided with the exposure period to the estrous female. Frequencies of mounting behavious (penis extension, mounting, intromission and ejaculation) exhibited by ACTH-treated bulls were significantly lower compared with the frequencies two days earlier. Exogenous ACTH administration suppressed reproductive behaviors of bulls and altered secretion of cortisol, growth hormone and testosterone. Furthermore, these data provide evidence that specific mating behaviors of the bull can be influenced by circulating steroids.

Aggressive behavior

This article considers the major fighting-related activities of the most common food animals. Instead of being seen as a largely pathologic phenomenon born solely of frustration and pain, aggressive behavior is now regarded as a natural part of an animal's behavioral equipment for survival and reproduction. There is a need, spurred by consideration for both productivity and animal well-being, to understand the fundamentals of the aggressive behavior of domestic species so that one can accommodate for this behavior in systems of livestock management.

Male sexual behavior

This article considers causes of variability in male sexual performance and identifies management techniques that can be used to improve the reproductive success and efficacy of our captive animal populations.