Effects of the anabolic steroid, boldenone undecylenate, on certain reproductive parameters in bulls

A total of 17 bulls was used to study the effects of boldenone undecylenate on growth and semen characteristics in beef bulls. In trial 1 nine mature mixed-breed beef bulls with satisfactory semen quality were divided into two groups. Group I (n = 5) received boldenone undecylenate (1.1 mg/kg) at 21 d intervals for a total of seven treatments (147 d). Group II (n = 4) served as untreated controls. Semen was collected from each group by electroejaculation on each treatment day and evaluated according to the standards of the Society for Theriogenology. Although neither the percentage of spermatozoa with primary or secondary morphological abnormalities was different, the ejaculates of Group I bulls contained a higher percentage of abnormal spermatozoa than those in Group II. In trial 2, eight mixed-breed bull calves, average weight 140.4 kg, were maintained under drylot conditions in a single paddock. The bulls were divided into two equal groups. Group I (n = 4) received boldenone undecylenate as in Trial 1. Group II (n = 4) served as untreated controls. The bulls were weighed and the scrotal circumference (SC) was measured every 21 d until it reached 30 cm, at which time semen was collected and evaluated as in Trial 1. Group I bulls had a higher percentage of spermatozoa with primary morphological abnormalities than bulls in Group II. Group I bulls had a higher average daily gain (ADG) than Group II bulls and required 21 d longer for the SC to reach 30 cm. Semen quality for all bulls was satisfactory at each sampling day.     

The relationship between scrotal circumference and quantitative testicular traits in yearling beef bulls

A study was designed to investigate relationships between testicle size and histological, sperm production and endocrinological traits in yearling beef bulls at the end of performance test. Twenty-five beef bulls, (Hereford, n=16; Angus, n=4; and Charolais, n=5), with scrotal circumference (SC) measurements ranging from 28.5 to 36.0 cm, were used. Just prior to slaughter at 15 mo of age, SC measurements were taken, semen was collected, and a GnRH response test was conducted. Testicles were processed for daily sperm production (DSP), epididymal sperm reserves (ESR), seminiferous epithelial area (SEA), and degree of germinal epithelial loss (DGEL). There were significant positive correlations between SC and testicular weight (P<0.05), DSP/g (P<0.02), and DSP/bull (P<0.01) and ESR (P<0.01); however, the correlation between SC and SEA was not significant (P=0.4). Scrotal circumference was negatively correlated with DGEL (P<0.05). Degree of germinal epithelial loss was also negatively correlated with DSP/g, DSP/bull and ESR (P<0.01). Morphological characteristics of spermatozoa were diversely related to sperm production traits, and the percentage of normal spermatozoa was positively related to SC (P<0.02) and negatively related to DGEL (P<0.001). Gonadotropin releasing hormone stimulation did not reveal evidence of gonadotropin deficiency in any of the bulls. However, peak testosterone levels were lower in bulls with SC below 31 cm (P<0.05) than those with SC measurements above 31 cm.     

Relationship of scrotal circumference and testicular volume to age and body weight in the swamp buffalo (Bubalus bubalis)

Scrotal circumference (SC) and testicular volume (TV) were measured in 65 swamp buffalo bulls ranging in age from 7 to 60 months and weighing 130 kg to 560 kg. Ages and body weight (BW) were recorded for each male at the time of measurement to find out if they correlated with SC and TV. SC and TV increased linearly and correlated significantly with age and BW (SC vs age: r = 0.74, p<0.01; SC vs BW: r = 0.88, p<0.01; TV vs BW: r = 0.82, p<0.01). SC measurements ranged from 15.1 +/- 1.1 cm to 24.0 +/- 0.4 cm for ages ranging from 10.0 +/- 0.6 to 48.5 +/- 6.3 months, revealing that testicular size in swamp buffaloes was very much smaller than domestic cattle. The SC norms distributed with age would be useful in the evaluation of swamp buffalo males for breeding soundness.     

Breeding soundness evaluations of 3,648 yearling beef bulls using the 1993 Society for Theriogenology guidelines

Our objective was to perform a retrospective analysis of breeding soundness evaluations (BSEs) as classified by the 1993 Society for Theriogenology (SFT) guidelines [Chenoweth et al., Guidelines for using the bull breeding soundness evaluation form, in: Theriogenology Handbook, 1993, pp. B-10]. Data included BSE information obtained from five performance-testing stations in South Carolina (SC1, SC2, SC3) and Tennessee (TN1, TN2) from 1986 through 1999 on 3648 Angus, Brangus, Charolais, Chianina, Gelbvieh, Limousin, Polled Hereford, Santa Gertrudis, Simbrah, and Simmental bulls. Analyses were simplified by classifying all bulls as either satisfactory or unsatisfactory potential breeders. Of the 3648 bulls evaluated, 76.2% were classified as satisfactory potential breeders. Of all bulls evaluated, 4.0% were unsatisfactory due to inadequate spermatozoal motility, 7.0% due to inadequate spermatozoal morphology and 2.6% due to a combination of inadequate motility and morphology. Unsatisfactory classifications due to non-spermatozoal parameters out of all bulls were 10.2%, with 7.1% for inadequate scrotal circumference and 3.1% for physical abnormalities. For satisfactory and unsatisfactory bulls, respectively, means and standard deviations were 35.8 +/- 2.7 and 33.0 +/- 4.1 cm (P < 0.001) for scrotal circumference, 63 +/- 18 and 35 +/- 24% (P < 0.001) for percent motility, and 86 +/- 7 and 63 +/- 21% (P < 0.001) for percent normal morphology.     

Scrotal circumference of two-year-old bulls of several beef breeds

Scrotal circumference (SC) was measured on 7,918 2-yr-old Angus, Charolais, horned and polled Herefords, Limousin, Shorthorn, and Simmental bulls presented to culling committees at six show/sales between 1977 and 1983. Only SC data from bulls within the age range of 24 +/- 4 mo were used. Scrotal circumference data were corrected across breeds for the effects of location-year and sire and were adjusted to a common bull age of 730 d. The adjusted mean SC (+/- SE) for 2-yr-old beef bulls was Simmental, 38.8 +/- 0.10 cm (n = 540); Aberdeen Angus, 37.2 +/- 0.09 cm (n = 629); Charolais, 36.3 +/- 0.09 cm (n = 499); horned Hereford, 36.1 +/- 0.03 cm (n = 3,769); polled Hereford, 35.6 +/- 0.04 cm (n = 2,170); Shorthorn, 34.9 +/- 0.11 cm (n = 231); and Limousin, 32.2 +/- 0.18 cm (n = 80). The authors' recommendations of minimum acceptable SC for 2-yr-old beef bulls are Simmental, 36.0 cm; Angus and Charolais, 35.0 cm; horned and polled Herefords and Shorthorn, 34.0 cm; and Limousin, 33.0 cm.     

Breeding soundness examination of Chianina, Marchigiana, and Romagnola yearling bulls in performance tests over a 10-year period

The objectives of the present study were (i) to establish the mean value of scrotal circumference (SC), sperm motility, concentration and morphology at 13+/-1 months of age for Chianina, Marchigiana, and Romagnola breeds and (ii) to assign Italian beef bulls at the end of a growth performance test to a potential breeder category by applying the guidelines of the Society for Theriogenology in 1993 (SFT93). Of 1,315 bulls, 869 were not given the breeding soundness examination for the following reasons: not passing the growth performance test (n=445), no training for semen collection (n=404), and presence of genital abnormalities (n=20). Testicular length and diameter and SC exhibited a logarithmic trend over time, with an R(2) value of 0.963, 0.979, and 0.978 (P<0.001), respectively. The SC of Romagnola (33.82+/-2.47 cm) was higher than those of Chianina (33.28+/-2.65 cm, P<0.001) and Marchigiana (33.05+/-2.20 cm, P<0.001). Sperm concentration in Romagnola (875.89+/-416.13x10(6)cells/mL) was higher than those in Chianina (751.63+/-444.45 x 10(6)cells/mL, P<0.05) and Marchigiana (862.57+/-421.87 x 10(6) cells/mL). Progressive sperm motility was 61.30+/-11.24%, 62.18+/-11.17%, and 58.48+/-14.40% in Romagnola, Marchigiana, and Chianina, respectively. Total spermatozoal abnormalities were higher in Chianina (23.35+/-15.41%). Sperm concentration was positively related to testicular length (P<0.01), diameter (P<0.001), and SC (P<0.001). Satisfactory breeders presented high sperm motility compared with deferred and unsatisfactory ones, whereas unsatisfactory breeders had a higher number of abnormal spermatozoa. By applying the SFT93 guidelines, we showed that 74.72%, 78.01%, and 80.16% of Chianina, Marchigiana, and Romagnola bulls, respectively, have been classified as satisfactory potential breeders.     

Trucking stress at breeding does not lower conception rate of beef heifers

The goal of this study was to determine whether 1 h of trucking stress before or after artificial insemination (AI) altered the conception rate of beef heifers. Estrus was synchronized in heifers with prostaglandin F(2alpha).The 3 treatment groups consisted of 1) AI (control heifers, n = 93); 2) Truck + AI (trucked for 1 h immediately before AI, n = 81); and 3) AI + Truck (trucked for 1 h immediately after AI, n = 82). All heifers were artificially inseminated by a single technician with semen from a single ejaculate. Blood samples were collected for cortisol measurement 1 h before AI, immediately before and after AI, and 1 h after AI in the AI (n = 6), Truck + AI (n = 9), and AI + Truck (n = 8) groups Pregnancy in heifers was confirmed either at slaughter or by palpation per rectum. Trucking before AI elevated (P < 0.01) serum cortisol concentrations. Artificial insemination alone increased (P < 0.01) serum cortisol concentrations in AI heifers. The increase in serum cortisol concentrations caused by trucking after AI was not significant (P > 0.05). Areas under the cortisol curves in Truck + AI heifers are greater (P < 0.05) than in AI heifers. The conception rates of AI heifers (50.5%), Truck + AI heifers (51.9%) and AI + Truck heifers (58.5%) are not different (P > 0.05). This study demonstrates that 1 h of trucking stress either before or after AI did not lower the conception rate of heifers.     

Adjusted 200-day scrotal size as a predictor of 365-day scrotal circumference

Data collected from 264 bulls of 13 beef breeds at the Michigan Bull Test Station was evaluated to determine if scrotal circumference (SC) adjusted to 200 d of age could be used to predict scrotal circumference at 1 yr of age. Scrotal circumference of each bull was recorded on arrival at the test station and at the time of breeding soundness examination (BSE) and was adjusted to 200 and 365 d of age, respectively. Bulls with adjusted SC>34.0 cm by 365 d of age averaged a larger SC at 200 d (P < 0.0001) and faster scrotal growth (P < 0.0001) than bulls with a 365 d adjusted SC /= 23.0 cm had a 95% probability of achieving SC > 34.0 cm by one year of age. Calves measuring < 23 cm at 200 d had a 54% probability of achieving > 34.0 cm scrotal size by one year. This information can contribute to the selection of breeding bulls that will achieve desirable scrotal size by one year of age.     

Scrotal circumference measurements in 764 beef bulls.

A total of 764 breeding soundness examinations was conducted on beef bulls utilizing the method of examination and criteria for classifying bulls of the Society for Theriogenology. In addition to this examination each bull was subjected to scrotal circumference measurement and to weighing. Classification of the bulls according to breeding soundness potentials was as follows: 88% of the bulls were satisfactory potential breeders, 8% of the bulls were questionable potential breeders and 4% of the bulls were unsatisfactory potential breeders. The proportions of bulls in each classification; satisfactory, questionable, or unsatisfactory; were not different among the four breeds evaluated. The majority of bulls evaluated in this study were between 14 and 36 months of age and weighed between 900 and 1500 pounds. For the ages and weights evaluated, scrotal circumference measurement variances were not closely related to age and weight differences. There was a tendency shown for “Questionable” and “Unsatisfactory Potential Breeders” to have smaller scrotal circumference measurements. The study indicates that Angus, Charolais, Horned Hereford and Polled Hereford bulls of breeding ages and weights should have scrotal circumference measurements of at least 32 centimeters in order to be classified as “Satisfactory Potential Breeders”.     

A description of the findings from bull breeding soundness evaluations and their association with pregnancy outcomes in a study of western Canadian beef herds

The primary objectives were to describe beef bulls considered for use and those reported as used in 205 beef herds in western Canada, and to determine whether factors typically assessed during breeding soundness evaluations were associated with reproductive success. More than 100 veterinary clinics reported 2990 breeding soundness evaluations for bulls considered for natural service in client's herds. Differences among clinics explained 5.2% of the variation in scrotal circumference (SC) and 6.9% of the variation in percentage of morphologically normal sperm of all bulls considered for use (after accounting for age, breed, body condition, significant physical abnormalities, month, and year). The percentage of morphologically normal sperm was lower in bulls with an SC ≤34 versus >34 cm (P < 0.006). This study included data from 1384 and 1370 bulls used for breeding in 2001 and 2002, respectively. Most (80%) of the bulls used were Simmental, Black Angus, Charolais, Red Angus, or Hereford, and 80% were ≤4 y of age. Before the breeding season, a veterinarian evaluated 89.5% of all bulls used in these herds. Of the bulls subjected to a breeding soundness evaluation and subsequently used, 93.1% were satisfactory. In 2001 and 2002, injuries were reported in 2.5 and 2.1% of bulls and in 16.6 and 11.4% of herds, and necrobacillosis of the foot was reported in 2.5 and 1.2% of bulls and 11.2 and 6.5% of the herds. The average number of cows exposed to each bull was 26 (both years). Cows exposed to bulls with a smaller SC were less likely to be diagnosed pregnant (P < 0.047) and had a longer median interval from first bull exposure to calving (P < 0.016) than bulls with a larger SC. In conclusion, our findings emphasized the value of breeding soundness evaluations, including measurements of SC, in fertility management of beef cattle.     

Nutritional influences on growth and onset of puberty in Boran and Boran x Friesian bulls in Ethiopia

Twenty-seven Boran and 37 Boran x Friesian crossbred bulls were weaned at 6 months of age and randomly assigned to either a dry season supplementary feed containing 16% crude protein or control groups. Data were collected on body weight, wither height and scrotal circumference (SC) at monthly intervals. Bulls were also challenged with 100 mug of gonadotropin releasing hormone (GnRH) at 2-month intervals and plasma testosterone responses were determined. Semen was collected at monthly intervals by electroejaculation. Post weaning average daily weight gain was significantly (P<0.001) higher in supplemented than in control groups (302 vs 208 g/day). Scrotal circumference growth rates were also significantly (P<0.001) higher in supplemented than in control bulls (0.38 vs 0.31 mm/day). Bulls fed supplemented diets were younger (430 vs 473 days; P<0.001) and heavier (217 vs 203 kg; P<0.05) and had better semen quality at puberty than the control bulls. There was a trend for larger SC at puberty in supplemented than in control bulls (P=0.06). There were no significant differences in wither height or in testosterone response to GnRH at puberty between supplemented and control bulls. Body and SC growth rates to puberty for Boran and Boran x Friesian bulls were 189 and 321 g/day (P<0.001) and 0.27 and 0.42 mm/day (P<0.01), respectively. Boran bulls were older (513 vs 406 days; P<0.01) and lighter (201 vs 215 kg; P<0.05), and had smaller SC (23.9 vs 26 cm; P<0.01) at puberty than Boran x Friesian bulls. Testosterone responses to GnRH increased (P<0.001) with age and were significantly higher (P<0.05) in supplemented and in Boran x Friesian bulls than in control and Boran bulls. Wither height, testosterone response to GnRH and semen quality at puberty did not differ between breeds. Dry season supplementation improved growth rate and enhanced sexual development and maturity in both Boran and Boran x Friesian bulls, and would be a useful management strategy for enhancing fertility in bulls in the tropics.     

Associations of scrotal circumference with semen traits in young beef bulls

Associations of percent live sperm, sperm number, sperm concentration, sperm motility, and potential breeding efficiency score with scrotal circumference were studied using data from the records of 465 Polled Hereford and 264 Simmental bulls. Data were subdivided by breed and within breed into three groups according to scrotal circumference (SC) size. Group I bulls had SC measurements <32 cm. Group II included bulls with SC measurements between 32 cm and the mean measurement of the breed (i.e., 35 cm for Polled Hereford and 38 cm for Simmentals). Group III was comprised of bulls with SC values above their respective breed averages. Age and body weight differences were also evaluated in the three groups. Average age differences among bulls in the three groups differed by not more than nine days in the two breeds. Average body weight differences among the three groups were statistically significant (P<0.05) with the maximum difference between any two groups within breed being 80 pounds. Average differences in percent live sperm and sperm number were greater (P<0.05) in Groups II and III than in Group I. For sperm concentration ratings, sperm motility ratings and potential breeding efficiency score, and for both breeds, Group I had a significantly lower (P<0.05) number of bulls classified satisfactory and a significantly greater (P<0.05) number of bulls classified unsatisfactory than did groups II and III.     

Cycle of the seminiferous epithelium and its duration in the zebu, Bos indicus

The cycle of the seminiferous epithelium was studied in Nelore zebu bulls 4–6 years old. The stages of the cycle were determined according to the shape and position of spermatid nuclei and the presence of meiotic divisions in cross-sections of seminiferous tubules. The relative frequencies of stages 1 to 8 were, respectively: 31.3 ± 0.5, 12.2 ± 0.7, 21.2 ± 0.5, 8.8 ± 0.6, 4.2 ± 0.4, 5.7 ± 0.6, 6.3 ± 0.5 and 10.3 ± 0.5. The duration of the cycle was estimated by autoradiography using tritiated thymidine injected directly into the testes. The mean duration of one cycle was estimated to be 14.0 ± 0.4 days.     

Health,behaviour and growth performance of Charolais and Limousin bulls fattened on different types of flooring

Intensive fattening of late-maturing breeds on concrete or rubberized slatted floors is the prevalent beef production system in mainland Europe. The rationale behind this study is that specific beef breeds with different slaughter weights might have a diverse response to different flooring systems. The study aimed at assessing whether growth performance, health, behaviour and claw condition of two beef breeds, Charolais (CH) and Limousine (LIM), would be affected by their housing on concrete (CS) or rubber-covered (RCS) fully slatted floor. A total of 228 CH (116 on CS; 112 on RCS) and 115 LIM (57 on CS; 58 on RCS) were housed in four and two commercial farms, respectively, in groups of 9.0 ± 2.1 animals/pen with an average space allowance of 3.1 ± 0.2 m². Draining gaps of CS and RCS pens were 16.9 ± 1.7% and 11.6 ± 1.2% of the total surface, respectively. Bulls of both breeds had similar initial body weight (429.4 ± 31.5 kg for CH; 369.6 ± 31.7 kg for LIM), and they were slaughtered when they reached suitable finishing. Charolais had a higher final body weight (BW) than LIM (750.8 ± 8.6 v. 613.7 ± 10.9 kg; P < 0.01), and bulls of both breeds on RCS had higher average daily gain than on CS (1.47 ± 0.02 v. 1.39 ± 0.02 kg/day; P < 0.05). The percentage of bulls early culled or treated for locomotor disorders were reduced by RCS only for LIM, while RCS tended to prevent the occurrence of bursitis for both breeds. During two 8-h behavioural observations, bulls on RCS performed more head butt/displacements and chases than on CS, and they reduced the frequency of abnormal lying down events. The use of RCS increased mounts’ frequency only in LIM, while its reduced drainage capacity impaired only the cleanliness of CH. Postmortem hoof inspection showed longer claw dorsal wall and diagonal lengths, and sharper toe angles for CH on RCS than LIM on both floors. Results of this study point out that fully slatted floors, regardless of being rubberized or not, are not suitable for bulls finished at a final BW above 700 kg due to their detrimental effects on health and welfare. The use of RCS could be recommended as an alternative to CS only if bulls are slaughtered at a lower final BW (around 600 kg), like in the case of LIM breed.     

The effect of using the Breeding Soundness Evaluation as a selection criterion for Santa Gertrudis bulls on bulls in subsequent generations

Results of Breeding Soundness Evaluations (BSE) used to select Santa Gertrudis bulls over a 10-yr period were analyzed in retrospect to determine the effect on bulls in subsequent generations. Bulls were tested at three ages: 16 mo (n = 1,936), 20 mo (n = 3,111) and at maturity (≥ 24 mo, n = 3,814). Scrotal circumference (SC) and sperm motility and morphology were evaluated. Sixteen-mo-old bulls were required to have an SC ≥ 30 cm to be tested. During 1977 to 1980, 20-mo-old bulls with an SC < 30 cm were culled, and the minimum SC was increased to 32 cm during 1981 to 1986. Mature bulls during this period were required to have an SC ≥ 35 cm to be tested. A BSE < 60 was considered a failing score, and bulls were culled at this level. There was a positive correlation between SC and sperm motility and SC and sperm morphology in 16-mo-old and 20-mo-old but not in mature bulls (P < 0.0001). The percentage of bulls passing the BSE was positively correlated with SC at all ages (P < 0.0001), and the passing rate increased over the years (P < 0.0001). Scrotal circumference increased over the years in bulls that passed the BSE (P < 0.0001). This increase with years was not as apparent in the semen quality traits measured. By using the BSE and a minimum SC to select prospective herd sires, the proportion of bulls passing the BSE is expected to increase in subsequent generations. Santa Gertrudis bulls can be reliably selected for use as herd sires at 16 mo of age.     

Effects of neo-adjuvant chemotherapy for oesophago-gastric cancer on neuro-muscular gastric function

Delayed gastric emptying symptoms are often reported after chemotherapy. This study aims to characterise the effects of chemotherapy on gastric neuro-muscular function. Patients undergoing elective surgery for oesophago-gastric cancer were recruited. Acetylcholinesterase, nNOS, ghrelin receptor and motilin expressions were studied in gastric sections from patients receiving no chemotherapy (n?=?3) or oesophageal (n?=?2) or gastric (n?=?2) chemotherapy. A scoring system quantified staining intensity (0–3; no staining to strong). Stomach sections were separately suspended in tissue baths for electrical field stimulation (EFS) and exposure to erythromycin or carbachol; three patients had no chemotherapy; four completed cisplatin-based chemotherapy within 6?weeks prior to surgery. AChE expression was markedly decreased after chemotherapy (scores 2.3?±?0.7, 0.5?±?0.2 and 0?±?0 in non-chemotherapy, oesophageal- and gastric-chemotherapy groups (p?<?0.03 each) respectively. Ghrelin receptor and motilin expression tended to increase (ghrelin: 0.7?±?0.4 vs 2.0?±?0.4 and 1.2?±?0.2 respectively; p?=?0.04 and p?=?0.2; motilin: 0.7?±?0.5 vs 2.2?±?0.5 and 2.0?±?0.7; p?=?0.06 and p?=?0.16). Maximal contraction to carbachol was 3.7?±?0.7?g and 1.9?±?0.8?g (longitudinal muscle) and 3.4?±?0.4?g and 1.6?±?0.6 (circular) in non-chemotherapy and chemotherapy tissues respectively (p?<?0.05 each). There were loss of AChE and reduction in contractility to carbachol. The tendency for ghrelin receptors to increase suggests an attempt to upregulate compensating systems. Our study offers a mechanism by which chemotherapy markedly alters neuro-muscular gastric function.     

Seasonal variation in the semen characteristics of Muturu (Bos brachyceros) bulls

Semen was collected by electroejaculation from seven mature Muturu bulls at weekly intervals for 9 weeks in each of three seasons (‘Dry’, ‘Rainy’, and ‘Late Rainy/Early Dry’) to study the effect of season on semen characteristics. The respective mean values for the ‘Dry’, ‘Rainy’ and ‘Late Rainy/Early Dry’ seasons were: volume 1.8 ± 0.1, 2.3 ± 0.1 and 2.0 ± 0.1 ml; percentage motility 36.2 ± 2.6, 37.7 ± 2.8 and 27.5±2.9; and percent morphologically normal sperm 70.0 ± 3.1, 79.1 ± 2.6 and 79.8 ± 2.3. No seasonal differences were found for sperm concentration/ml (overall mean 1.92 ± 0.16 × 10⁸) and for sperm output/ejaculate (overall mean 4.14 ± 0.39 × 10⁸). The chemical composition of seminal plasma (mg %) for the respective seasons was calcium: 4.8 ± 1.0, 7.9 ± 0.9 and 2.5 ± 0.7; magnesium: 4.8 ± 0.4, 4.3 ± 0.7 and 2.5 ± 0.7; and chloride: 330.7 ± 33.7, 136.0 ± 9.6 and 344.3 ± 31.8. No seasonal differences were found in sodium or potassium concentrations. Fructose was found in the semen of only one bull and only during the ‘Dry’ season.     

Individual variations in FSH release after a GnRH challenge and relationship with semen output in young bulls

Blood samples collected from 54 Montbéliarde young post-pubertal bulls were assayed for FSH. In the first trial, 0.25 mg GnRH was given to each of 25 bulls at 12 months of age. In a second group of 29 bulls, each received 20 mg dexamethasone followed by 0.25 mg GnRH 5 h later. Based on measurements of semen output, the bulls were classified into three categories: good, medium and poor semen producers. The total FSH response was significantly different among individuals (P less than 0.05) and repeatable (r = 0.45) only after the combined treatment. The mean total responses did not differ significantly between the 3 categories of semen producers, but individual FSH responses were significantly and negatively correlated to quantitative and qualitative semen production characteristics (r = 0.4-0.7). It was concluded that measurement of FSH after a combined dexamethasone-GnRH challenge permits the demonstration of a significant relationship between FSH release and semen production in individual bulls.     

Exposure of prepubertal beef bulls to cycling females does not enhance sexual development

The objective of this study was to determine whether continuous, long-term, fenceline exposure of prepubertal beef bulls to cycling beef females reduced age at puberty and influenced the percentage of bulls that passed an initial breeding soundness examination (BSE). Bulls (Angus, n = 37; Simmental, n = 22; Hereford, n = 10; Simmental × Angus, n = 8) at an average age of 202 ± 21.5 days were given either continuous fenceline and visual exposure to cycling females (exposed, n = 41) or no exposure (control, n = 36). Estrus was induced in cycling beef females so at least three females were in standing estrus each week during the 182 days of exposure to bulls. Scrotal circumference (SC), body weight, and blood samples were collected every 28 days. When bulls had SC of 26 cm or more, semen samples were obtained monthly via electroejaculation until puberty was achieved (≥50 × 10⁶ sperm/mL with at least 10% progressive motility). Behavioral observations were conducted twice monthly: once when females were in estrus and once during diestrus. Homosexual mounting, flehmen responses, and number of times near penned females were recorded for each observation period. Breeding soundness examinations were conducted when the average age of bulls was 364 ± 21.5 days. Normal sperm morphology of at least 70% and sperm motility of at least 30% were required to pass the BSE. Age, body weight, and SC at puberty did not differ between exposed and control bulls (320 ± 28 and 311 ± 29 days; 466.2 ± 12.2 and 437.7 ± 13.5 kg; and 34.4 ± 2.5 and 34.9 ± 2.5 cm, respectively). Percentage of bulls passing their initial BSE did not differ between treatments (exposed, 87.8%; control, 75.0%). Treatment, month, and female estrous stage interacted (P = 0.05) to affect the number of mount attempts and flehmen responses. Exposed bulls entered the cow area more times (P < 0.001) during estrus than diestrus in Months 1, 2, and 3. We concluded that bulls given continuous, long-term, fenceline exposure to cycling beef females do not have enhanced sexual development.     

Breeding soundness, libido and performance of beef bulls mated to estrus synchronized females

Ninety-three beef bulls and 2316 females were used to determine the relationships between breeding assessments of bulls and subsequent mating performance. Each bull was given a breeding soundness examination (BSE) and two 10-min libido/serving capacity (L/SC) tests. Breeding potential of each bull was classified as satisfactory (BSE score = 60 to 100) or questionable (BSE score = 30 to 59); libido was classified as either high (mean score = 9.0 to 10) or medium (mean score = 6.0 to 8.5). Bulls were then joined, single-sire, with groups of females which had received one of two treatments to synchronize estrus. Bull-to-female ratios ranged from 1:7 to 1:51. Continuous observations were conducted on the mating activity of each group. One bull was removed from the experiment due to a severe breeding problem. Bulls of satisfactory breeding potential (n = 80) did not differ (P > 0.10) from bulls of questionable breeding potential (n = 12) in measurements of mating activity. However, by the end of the synchronized breeding period, bulls classified as satisfactory breeders achieved approximately a 9% higher (P < 0.10) pregnancy rate than did bulls of questionable breeding status (45.6 +/- 2.1% vx 36.5 +/- 5.3%). Bulls with a high libido (n = 69) serviced more (P < 0.01) estrous females (81.3 +/- 3.1% vs 63.5 +/- 4.2%) than bulls with a medium libido (n = 23). However, pregnancy rates achieved by bulls of either libido classification did not differ significantly. Individual components of the BSE as well as mean libido score were poorly correlated with pregnancy rates (r = -0.22 to 0.18). It was concluded that classification of bulls by mean libido score can aid in identifying groups of bulls that service more estrus synchronized females, whereas classification by BSE score aids in identifying groups of bulls that impregnate more females.