Knowledge of the capabilities and limitations of the reproductive capacity of bulls is vital in maximizing reproductive efficiencies. Bull semen collection guidelines established by researchers and industry personnel to maximize the sperm harvest from bulls have been evolving for more than 60 years. Today, a mature artificial insemination industry employs those strategies to meet demands. These efficient management schemes exploit the reproductive potential of each sire while minimizing the associated risk of injury to bulls and reduce associated production costs. Personnel employed by a semen producing facility must be authorized to make effective and rational decisions based on principles of bull sexual behavior and reproductive physiology. Furthermore, collection facilities must be well planned to allow for the safe presentation of novel sexual situations while affording maximum safety for employees and proper footing for bulls. Normal bulls produce and ejaculate tremendous numbers of sperm. Most bulls have a sufficient libido for routine sexual activity, but become satiated to predictable stimulus situations. Frequent changes to the novelty should allow weekly harvest of four to six ejaculates per week for most bulls. Utilizing the physiological characteristics associated with each ejaculate to establish the collection frequency of each bull, and empowering an integrated collection and laboratory staff to monitor and make adjustments to the ejaculation frequency are necessary in maximizing the sperm harvest. Young bulls can ejaculate 10 to 20 billion sperm per week, and mature bulls should ejaculate 40 to 60 billion sperm per week. Semen collection management procedures should be reviewed when bulls do not meet production goals.

l-Arginine is a nutritionally essential amino acid for spermatogenesis and plays versatile roles in animal health and can be utilized as a potential agent to improve reproductive performance of boars under high ambient temperature. The present study aimed to determine whether dietary l-arginine could alleviate heat stress-induced infertility in boars. In all, 20 boars (PIC 1040; 248.59±3.84 kg BW and 407.65±6.40 days of age) were selected and randomly assigned to four groups (group 0.0%, basal diet; group 0.6%, 0.8% or 1.0%, basal diet added with 0.6%, 0.8% or 1.0% l-arginine (wt:wt), respectively.) The four diets were made isonitrogenous by addition of appropriate amounts of l-alanine. Boars were pre-fed the corresponding experimental diet for 42 days. Then, the semen characteristics and libido were accessed for 6 weeks during the hot summer period (25.5° to 33.0°C). Results show that dietary l-arginine remarkably improved sperm motility, normality, total sperm number and effective total sperm number. Also, dietary l-arginine improved semen antioxidant capacity, such as decrease of malondialdehyde and 8-Hydroxy-2'-deoxyguanosine content in sperm (P<0.05), increase of the ratio of glutathione and oxidized glutathione, total antioxidant capacity, glutathione peroxidase and catalase activities in seminal plasma (P<0.05). Most of mitochondria contained intact ultrastructure in l-arginine-supplemented group which also accompany with higher ATP content than the 0.0% group. The boars fed 0.8% l-arginine show increased levels of estradiol-17β and testosterone and exhibit improved libido performance than boars in the 0.0% group. Adding dietary l-arginine linearly increased (P=0.002) nitric oxide content (as l-arginine increased). The scrotal surface temperature in the 0.6%, 0.8% and 1.0% group were decreased by 0.9°C, 0.9°C and 0.4°C, respectively, compared with the 0.0% group. l-Arginine levels caused linear effect on semen quality and antioxidant capacity, also caused quadratic effect on libido performance. During the hot summer months, the predicted optimal l-arginine levels for best semen quality and antioxidant capacity was 0.8% to 1.0% and for best libido performance was 0.8%. It can be concluded that l-arginine can be used as an effective agent to alleviate heat stress-induced infertility of boar, and that 0.8% to 1.0% can be considered as the optimum dosage.

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.

The objective was to determine the effects of immunization against gonadotropin-releasing hormone on reproductive characteristics in boars. A total of 72 boars were used in a randomized design with three treatments: single immunization (SI) (10 weeks of age) or double immunization (DI) (10 and 15 weeks of age) with Improvest® and intact controls (no Improvest®; CNT) (n=24/group). At 10, 15, 20, 25 and 40 weeks of age, blood was collected and serum harvested to evaluate testosterone concentrations. Testosterone concentrations were less for DI boars compared with CNT boars and SI boars at 20 and 25 weeks (P<0.001), but not at 40 weeks of age. At week 25, 18 pigs (n=6/group) were sacrificed and testes were removed, weighed and measured, and seminiferous tubules were examined and scored using histological slides of testes parenchyma. A sample of neck fat was assessed for boar taint aroma. All testicular measurements and weights and seminiferous tubule scores were less for DI boars compared with SI and CNT boars (P<0.001). More (P<0.05) SI and CNT boars had detectable boar taint aroma than DI boars. Libido was assessed at 32, 36, 47, 60 and 63 weeks of age and semen collected at 60 weeks of age was analyzed for indicators of quality. There were no effects of treatment (P=0.41) or treatment by week (P=0.71) on libido. Semen volume, gel weight and total number of sperm cells, determined in a subset of boars (n=3/treatment), were not different among treatments. Sperm concentration was greater for DI than SI (P=0.01), and tended to be greater for DI compared with CNT (P=0.10). Sperm motility tended to be greater for DI boars compared with CNT boars (P=0.066). In conclusion, our results show that there are no long-term effects of immunocastration on reproductive characteristics in boars.

The objective of this study was to determine any differences in the competitive ability of rams differing in levels of sexual performance. Twenty sexually experienced Targhee-type rams were preselected from a population of 95 males for exhibiting relatively high and low ejaculation rates when individually exposed to oestrous ewes for 30 min. Each of 10 high performers (HP) were paired with each of 10 low performers (LP) on three occasions when competing for food (after food deprivation) and twice when competing for an oestrous female. Tests were 5 min in duration. Food-deprived HP and LP rams were equally aggressive when competing for a source offood that could only be accessed by one ram at a time. Time offeeding by HP and LP rams did not differ. HP rams spent more time with the oestrous ewe and attained more mounts in a greater number of pairings than LP rams even though HP and LP rams did not differ in number of successful agonistic interactions (active displacements and successful defences) when competing for the ewe. It was concluded that HP and LP rams, taken as groups, do not differ in their basic competitive ability and that the greater mating success of HP rams can be explained by their higher levels of libido.

The effects of months and seasons of the year on the testis size, libido and plasma testosterone (T) concentrations were studied in 10 young sexually mature male goats over a 12-month period. Testis size was expressed in terms of scrotal circumference, testis diameter and paired testes width while the libido was measured as stimulation and reaction times,number of mounts and services, and libido index. These measurements were recorded fortnightly.

The body weight increased from 33·5 (s.e. 0·95) kg in October, to a maximum of 62·8 (s.e. 1·55) kg in July. All parameters of testis size decreased from October through January with a sharp increase noted in July and August. These parameters were significantly higher in the summer and autumn than in the winter and spring (P < 0·01). The libido in the goats increased from October to a maximum in December, declined gradually to reach the minimum in July, and then improved again in August. Thus, libido was lowest during the summer and highest in winter, the difference being significant (P < 0·01). Plasma T concentrations were high during October, with the lowest values noted in June. An increase in the T concentrations was observed in August, reaching the maximum value in September, the difference being significant (P < 0·01). The T concentrations were significantly higher during autumn than in all other seasons (P < 0·01).

In the Mediterranean environment and subtropical microclimate of the south-east Iberian Peninsula (37° 59' N), testicle size and sexual behaviour of male goats were studied and the influence of season (day length, air temperature and relative humidity) on these factors examined.

Nine, 13-month-old Murciano-Granadina male goats weighing 47 to 53 kg were used. The experiment began during the month of January and extended for a complete year. Every 2 weeks, anterior-posterior maximum testis diameter was measured. They were tested twice a week for levels of sexual behaviour using ovariectomized goats and libido was evaluated as reaction time to mating.

The annual mean testis diameter was 5·06 (s.e. 0·02) cm, varying significantly with season of the year. The lowest values were measured during winter 4·89 (s.e. 0·03) cm. These increased (P <0·01) in spring (5·16 (s.e. 0·01) cm) and summer (5·19 (s.e. 0·02) cm), but decreased again (P <0·01) in the autumn (5·04 (s.e. 0·02) cm). The annual mean reaction time was 197 (s.e. 12) s, but was longest (P <0·01) in spring (318 (s.e. 30) s), and shortest during summer (144 (s.e. 16) s) and autumn (132 (s.e. 17) s). The testicle diameter measurement was correlated with day length (r = 0·41; P <0·01) and air temperature (r = 0·45; P<0·01), while the reaction time showed no relationship with climatic measurements.

It was concluded that day length is not the only factor responsible for seasonal variation in testis size of Murciano-Granadina male goats and that, in their natural habitat, libido is unlikely to be a limiting factor in the breeding programme.