Aspects of the sexual development of Brahman versus Angus bulls in Florida

Postweaning growth and reproductive traits were studied in 10 Brahman and 12 Angus bulls from 8 through 20 months of age. Brahman bulls reached puberty at 15.9 +/- .4 months of age, weighed 432 +/- 16 kg, had a scrotal circumference (SC) of 33.4 +/- 1.2 cm, and plasma testosterone of 3.96 +/- 1.03 ng/ml. Breed differences in SC averaged over the entire study were not significant. However, the breed x day interaction (BxD) (P<.01) showed that, initially, the Brahman SC was smaller than the Angus SC; however, by the end of the study, the Brahman SC was larger than the Angus. When SC was adjusted for body weight, breed differences (P<.01) and BxD (P <.01) for SC/body weight (BW) reflected the later age and heavier weight at which the Brahman bull reached puberty. Plasma testosterone differed between breeds (Angus > Brahman, P< .01) and increased at a linear (P< .01) rate with age. There was no BxD in plasma testosterone. No breed differences in sperm concentration were observed. However, other semen traits were different (P< .01), i.e., rate of forward movement, sperm motility, total abnormalities and semen volume. A BxD (P< .01) was also evident for breed differences in these semen traits. Sexual development of the Brahman bull occurred at a later chronological age and in a nonparallel pattern to that of the Angus. Between animal variation in SC within the Brahmans and differences between this study and other reports suggest that differences in SC exist for various populations of Brahman bulls and should provide opportunities for progress in selection for this trait.     

Effect of dietary energy on growth and reproductive characteristics of Angus and Senepol bulls during summer in Florida

Pubertal Angus bulls (n=10, 503 days of age and weighing 366 kg) and Senepol bulls (n=10, 457 days of age and weighing 381 kg) were stratified by age and weight into 2 dietary treatments formulated to provide equal amounts of crude protein and 75% (below) or 150% (above) of the maintenance requirements for metabolizable energy. Measurements to assess body growth and libido were collected at 28-day intervals for 112 days (June through September). Twice during each 28-day interval, the bulls were subjected to breeding soundness examinations. At the end of the experiment, gonadotropin releasing hormone (GnRH) - induced secretion of luteinizing hormone (LH) and testosterone (T) in the serum were determined. At the end of the experiment, bulls fed the above maintenance diet (P<0.0001) were 91 kg heavier, had 1.7 mm more backfat thickness and 12.6 cm(2) larger ribeye area than bulls on a below maintenance diet. Diet affected (P<0.003) the average daily change in scrotal circumference, but not the libido score (P>0.1) or semen quality. In general, Angus bulls had superior initial semen quality (P<0.06); however, during summer, semen quality tended to decrease in Angus but not in Senepol bulls. The final rectal temperature was 0.5 degrees C lower (P<0.003) in Senepol than in Angus bulls. Basal T concentrations and area under the GnRH-induced T curve were greater (P<0.07) for bulls fed the above rather than the below maintenance diet. Angus bulls had a higher (P<0.03) maximal LH response to GnRH and larger area under the GnRH-induced LH curve than Senepol bulls.     

Breed-type effects on fertility traits of young bulls

Measures of fertility in young beef bulls (N=76) representative of divergent breeds and F₁ crosses were evaluated. Breed-types were straightbred Hereford and Red Poll, Hereford × Red Poll reciprocal crosses, Angus × Hereford, Angus × Charolais, Brahman × Hereford and Brahman × Angus.There was evidence of significant breed-type variation in scrotal circumference and total testicle weight, although differences were less pronounced when animal weight was taken into account. Scrotal circumference in Brahman × Hereford bulls was less (P<.05) than straightbred Hereford, Red Poll × Hereford and Angus × Hereford crosses at 8 months of age. However, at 13 months there was no difference in scrotal circumference measurements of Brahman × Hereford, Red Poll × Hereford and Angus × Hereford crosses, and all three crosses exceeded (P<.05) straightbred Herefords. Breed-type differences in semen score and presence of normal, mature sperm in the seminiferous tubules at 13 months of age approached significance at the .10 probability level. Heterosis effects on bull fertility characteristics were insignificant when body weight was included as a covariate in the analyses.     

Relationships among fertility, scrotal circumference, seminal quality, and libido in Santa Gertrudis bulls

Forty Santa Gertrudis bulls were used to examine relationships among scrotal circumference, seminal quality, libido, and fertility [assessed as the percent pregnant of estrous females (PE rate) and the percent pregnant of females mated (PM rate)]. These bulls were selected from 220 two year old bulls to represent variations in scrotal circumference and seminal quality. Each of the 40 bulls were exposed to 100 cyclic Santa Gertrudis heifers for a 4-day (96 hr) breeding period. The number of estrous females available to each bull varied from 12 to 27. A breeding soundness examination (BSE) was conducted on each bull approximately 45 days prior to the 4-day breeding period and immediately after the 4-day breeding period. The three components of the BSE scroe (scrotal circumference, spermatozoal abnormalities and spermatozoal motility) were not significantly correlated with PE rate or PM rate at either evaluation. There was no significant correlation between PM rate and scrotal circumference; however, each of the 4 bulls having a scrotal circumference less than 30 cm had a PM rate below 31%. Relationships between seminal quality and PM rate were unclear and differed between the two evaluations. There was a trend for bulls having poor seminal quality at the first evaluation to improve by the second evaluation. Consequently, fluctuations in seminal quality between evaluations is one possible explanation for low correlations between seminal parameters and PM rate. Libido (number mated/number in estrus x 100) was positively correlated (r = 0.44) with PE rate. Using a stepwise regression procedure, the independent variables accounting for the most variation in PE rate (dependent variable) included libido, secondary spermatozoal abnormalities, and BSE score (r(2) = 0.44). Results of this study indicate that current methods of fertility evaluation did not accurately predict the fertility of individual Santa Gertrudis bulls as measured by PE rate and PM rate during a 4 day breeding period.     

Genetic parameters of libido in Brazilian Nellore bulls

Genetic, environmental and phenotypic correlations between libido, testicular measurements, body weight and semen traits were estimated by multiple-trait-restricted maximum likelihood (MTDFREML) under animal models. Reproductive records, collected from 1992 to 1997, of 288 Nellore bulls were used. Estimates of heritability for libido unadjusted, adjusted for scrotal circumference and adjusted for body weight, were 0.34 +/- 0.10, 0.31 +/- 0.10, and 0.19 +/- 0.11, respectively. Genetic correlations between libido and body weight, scrotal circumference, testis length, testis width, testis volume and testis consistency were, respectively, 0.69, -0.43, -0.31, -0.16, 0.10, 0.87, and between libido and semen volume, sperm motility, vigor, gross motility, major, minor and total defects were, respectively, 0.71, 0.51, 0.12, 0.16, 0.31, 0.26 and 0.43. Results suggested that selection for libido would be effective and that it would lead to desirable correlated response for scrotal circumference, physical and morphological semen traits and undesirable correlated response in body weight.     

Phenotypic relationships of scrotal circumference to frame size and body weight in performance-tested bulls

The objective of this study was to determine if frame size (height) is related to scrotal circumference. A total of 695 bulls (425 Angus, 65 Hereford, 70 Charolais, 135 Simmentals) were tested for postweaning gain in five stations over a period of 1 to 3 years. Variables examined included hip height, weight and scrotal circumference at beginning and completion of a 140-d feeding period. Correlations among these traits, adjusted for age (7 to 10 months at entry), year, station and management were estimated for each breed. Both height and weight were correlated positively with scrotal circumference at the start and the end of the test period in all four breeds. When height and scrotal circumference were adjusted for weight, correlations were negligible, with the exception of end-of-test values for Charolais bulls (-0.26). Negative correlations were obtained between the scrotal circumference at the start of the test and the change in height during the test after adjustment for weight in Angus bulls (-0.18) and in Charolais bulls (-0.15). These small negative phenotypic relationships indicate that a bull's fertility is not seriously reduced by large frame size at the completion of a feedlot performance test. For maximum fertility in bulls, scrotal circumference needs to be evaluated independently of frame size.     

Relationships between breeding soundness and sex drive classifications in beef bulls

Prior to use in single-sire mating trials, ninety-two beef bulls were evaluated to determine the relationships between. Breeding Soundness Examination (BSE) and sex drive assessment categories. A BSE score was given to each bull based on scrotal circumference, spermatozoal motility and morphology. Eighty bulls were classified as satisfactory potential breeders, while 12 were classified as questionable potential breeders. Each bull was exposed to two, 10 min modified libido/serving capacity tests. Sixty-nine bulls were classified as high libido and 23 were classified as medium libido. Differences in scrotal circumference and spermatozoal motility did not influence (P > 0.05) the BSE classifications. However, differences in primary, secondary and total spermatozoal abnormalities were the major factors affecting the BSE classification. Bulls classified as high libido serviced three times more (P < 0.01) during the two test periods than bulls classified as medium libido. High libido bulls were superior in all sex drive traits. However, bulls in the two libido categories did not differ (P > 0.05) in semen quality or scrotal circumference. There was no relationship (P > 0.05) between BSE and sex drive traits (r = -0.16 to 0.24).     

Seminal selenium concentrations and spermatozoal abnormalities in beef bulls

The relationship between seminal selenium (Se) concentration and spermatozoal abnormalities in 24 Angus and 12 Simmental bulls maintained on a Se adequate diet was studied. Two semen samples were collected by electroejaculation 50 days apart from each bull. Measurements of primary and secondary spermatozoal abnormalities, seminal Se concentration, and blood plasma Se concentration were determined at each semen collection. The mean (chi +/- SD ) Se concentration of semen (0.535 +/- 0.267) was approximately 8 fold greater than the Se concentration of blood plasma (0.069 +/- 0.066) and the values were similar for both collections. Spermatozoa concentration was correlated (r = 0.50; P<.01) with seminal Se concentration; however, seminal Se concentration was not highly correlated (P<.01) with primary spermatozoal abnormalities (r = -0.29) and secondary spermatozoal abnormalities (r = 0.16). This study indicates that the Se concentration of semen is high relative to blood plasma in bulls maintained on a Se adequate diet; however, the seminal Se concentration is not highly correlated with spermatozoal abnormalities.     

Correlation of in vivo testicle and seminal vesicle size with post mortem dimensions in bulls

This study was conducted to quantify the relationships between in vivo measurements of testicular and seminal vesicle size and post mortem size of these organs in 30 Santa Gertrudis bulls. The in vivo measurements of testicles were obtained by transrectal ultrasonography and palpation per rectum, while scrotal circumference was measured by scrotal tape. Linear post mortem dimensions were obtained by direct measurements of the excised organs. Volume was assessed by water displacement while the testicles were weighed. Seminal vesicle length, determined by palpation, had the highest correlation with post mortem measurements (r = 0.70; P = 0.0001). Accurate estimation of the thickness of the vesicles (1.47 vs 1.55 cm for in vivo and post mortem, respectively) was performed by ultrasonograph. Of all seminal vesicle linear measurements, width had the highest correlations with volume measured by water displacement (r = 0.67; P = 0.0001 and r = 0.38; P = 0.04 for post mortem and in vivo, respectively). Testicular diameter was accurately measured by ultrasonography (5.54 vs 4.58 cm in vivo and post mortem, respectively) and was highly correlated (range r = 0.84 to 0.89; P = 0.0001) with post mortem measurements of testicular volume, weight and circumference. The correlation between scrotal circumference and diameter of the testicle was 0.75 (P = 0.0001). The correlations of testicular diameter measured by ultrasound with the post mortem measurements of testicular weight and circumference were similar to the correlations between scrotal circumference and those 2 post mortem measurements. We conclude that palpation of vesicle length is highly correlated with volume of the seminal vesicle in situ. Individual linear measurements do not seem to be an accurate predictor of the relativ size of the seminal vesicle. Furthermore, ultrasonography does not seem to be a more accurate measure of testicular size than scrotal circumference for evaluation of breeding soundness.     

Effect of growth rate from 6 to 16 months of age on sexual development and reproductive function in beef bulls

Sexual development and reproductive function were studied in 22 Angus × Charolais and 17 Angus bulls from 6 to 16 mo of age. Associations of average daily gain (ADG) and body weight with ages at puberty and at maturity (satisfactory semen quality), scrotal circumference, paired-testes volume and weight, testicular vascular cone diameter and fat thickness, scrotal temperature, sperm production and morphology, and testicular histology, were determined. There were no significant correlations between cumulative average daily gain and any of the end points investigated. Body weight at various ages was negatively correlated with ages at puberty and maturity in Angus × Charolais bulls, positively correlated with paired-testes weight in Angus × Charolais and Angus bulls, and positively correlated with seminiferous tubule volume in Angus bulls (P < 0.05). Semen quality improved gradually with age and the interval between puberty and maturity (mean ± SD; 309.4 ± 29.7 and 357 ± 42 days of age) was approximately 50 days. Age, weight, scrotal circumference, and paired-testes volume were all good predictors of pubertal and mature status, with moderate to high sensitivity and specificity (71.6% to 92.4%). In summary, growth rate between 6 and 16 mo of age did not affect sexual development and reproductive function in beef bulls. However, greater body weight at various ages was associated with reduced age at puberty and maturity, and with larger testes at 16 mo of age, indicating that improved nutrition might be beneficial, but only when offered before 6 mo of age. Average daily gains of approximately 1 to 1.6 kg/day did not result in excessive fat accumulation in the scrotum, increased scrotal temperature, or reduction in sperm production and semen quality, and could be considered “safe” targets for growing beef bulls.     

Relationships among production traits and estimates of sex drive and dominance value in yearling beef bulls

Average daily gain (ADG) and final test weight (FTW) were compared with libido score (L), serving capacity score (SC), reaction time to first mount (RTM), reaction time to first service (RTS) and dominance value (DV) in 90 purebred yearling beef bulls which had just completed an 140-day performance test. The bulls represented 15 breeding lines (12 Hereford, 2 Black Angus and 1 Red Angus) and nine sires within lines. Libido and serving capacity assessments were applied to randomly selected groups of two bulls which were tested for 10-minutes with nonestrous heifers restrained in service crates. RTM and RTS were recorded for both tests. Social dominance was assessed during randomized observations of social interactions between bulls within their pen groups (comprising 9 to 10 bulls) over four days. Two methods of determining social dominance (DV1 and DV2) were employed initially. Differences occurred among both lines and sire/lines in mean and best libido scores (P < .05). Sire/lines differed in L1, while both lines and sire/lines differed in L2 (P < .05). These differences were not reflected in either reaction times or serving capacity scores. Sires and sire/lines both differed in FTW (P < .05 and P < .01 respectively), while DV1 differed with sire/lines (P < .01). DV1 and DV2 were highly correlated (r = .84). Those sex-drive estimates which correlated with DV1 were the mean and best libido scores, mean serving capacity score, L2 and RTS 1 (P < .05). All correlations were negative, indicating that dominance and sex-drive may be unfavourably related in yearling beef bulls. ADG and FTW showed negative correlations with the mean and best serving capacity scores and with SC2 (P < .05). The only positive correlations between the two production traits and a sex-drive estimate was with RTM 2 (P < .05). This indicates that ADG and FTW may be unfavourably related to sex-drive in yearling beef bulls.     

Testicular development, body weight changes, puberty and semen traits of growing guzerat and Nellore bulls

One hundred fifty-nine purebred Guzerat (8 to 110 months of age) and sixty Nellore bulls (8-30 months of age) were used in two trials to examine testicular development and consistency, body weight changes, puberty and semen traits. Scrotal circumference measurements and semen collections by electroejaculation were made every 28 d. At both trial locations, bulls were maintained under grazing conditions and fed commercial protein supplements (2 kg/head/day) during the dry season. Age and body weight affected (P<0.01) scrotal circumference in both breeds. Scrotal circumference increased (P<0.01) linearly with age and body weight. However, scrotal circumference tended to reach mature size more rapidly than did body weight in both Guzerat and Nellore bulls. Correlation coefficients between scrotal circumference and semen traits were positive (P<0.01) ranging from 0.49 to 0.73 in the two breeds, but were not significant for testicular consistency in either breed. Scrotal circumference and age at puberty of Guzerat and Nellore bulls averaged 25.6 +/- 2.2 cm at 18.0 +/- 2.0 mo and 23.6 +/- 0.2 cm at 18.5 +/- 2.7 mo, respectively. Nellore bulls were 42 kg lighter than Guzerat at puberty. Testicular consistency was not affected by either age of body weight (P>0.10) in these young bulls. The percentages of abnormal spermatozoa were higher (P<0.01) at 13 to 15 mo of age in Guzerat (11.1%) and Nellore (14.4%) bulls than at 22 to 24 mo (6.7 and 8.0%, respectively). These data indicate that scrotal circumference measurements can be a useful tool for selecting and improving semen traits of young Guzerat and Nellore bulls under tropical grazing conditions.     

Relationships among seminal culture, seminal white blood cells, and the percentage of primary sperm abnormalities in bulls evaluated prior to the breeding season

Semen samples from 100 beef breed bulls were evaluated for sperm morphology (phased contrast microscopy), seminal white blood cells, and the presence of potential reproductive pathogens. Eligibility required visualization of the glans penis throughout semen collection. Based on clinical spermiograms, bulls were grouped into normal, marginal, or unsatisfactory morphology classifications. The 3 experimental groups were similar in age and scrotal circumference and differed significantly in the percentage of primary sperm abnormalities. Most semen samples (94%) contained one or more potential reproductive pathogens (Hemophilus somnus. Mycoplasma bovigenitalium, Arcanobacterium pyogenes and Ureaplasma diversum). No significant relationship could be demonstrated between primary abnormalities and the assigned culture score. Our experimental results suggest that clinicians should interpret clinical semen culture results with great care. No significant relationship could be demonstrated between primary abnormalities and assigned white blood cell (WBC) score, although, only 1% of the samples was scored >5 WBC per high power field. The use of seminal WBC score may be valid adjunct to routine semen evaluation when that threshold is the basis for clinical decisions.     

Relationship of breeding soundness evaluation score and its components with reproductive performance of beef bulls

Angus, Polled Hereford and Santa Gertrudis bulls were subjected to a breeding soundness evaluation (BSE) just prior to being exposed to cows for 90 to 95 days in single-sire units under natural breeding conditions on pasture. Forty-eight of 55 bulls subjected to scrotal and semen evaluations passed the BSE and were considered acceptable for breeding. Of the bulls that passed BSE, 18 (six bulls from each breed) were used for breeding for each yr of the 2-yr study. Of the bulls used for breeding, breed of sire differences were significant for scrotal circumference and calving rate, while differences among sires within breed of sire were significant for secondary morphology, motility score and calving rate. The difference between means for bulls used vs bulls that failed BSE was significant for all eight traits. Correlations among various scrotal and semen evaluations were compared for bulls used vs bulls that failed BSE. Of the eight traits, only the motility score was significantly correlated with the calving rate. After the exclusion of bulls that failed to pass BSE, there remained differences (P<0.01) among bulls within breed of sire for calving rate. Thus, there is a need for an additional easy-to-use procedure that would more accurately predict the breeding performance of bulls.     

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.     

Reversibility of the reproductive toxicity of gossypol in peripubertal bulls

Gossypol has been shown to impair sperm production in male ruminants. The purpose of this study was to determine if the adverse effects of gossypol on spermatogenesis in peripubertal bulls were reversible. Twenty-eight crossbred Angus bulls were allocated into treated and control groups at 11 months of age. For 8 weeks, treated bulls were fed a ration containing 8 mg of free gossypol per kilogram of body weight per day while control bulls were fed a soybean meal ration free of gossypol. At 28-days intervals, scrotal circumference was measured and semen collected to assess sperm motility and morphology. Seven control and seven treated animals were castrated 56 days after the start of the experiment and the testes were examined histologically. The remaining bulls were fed a gossypol-free diet for 210 days prior to castration. There were significant increases in primary and secondary sperm abnormalities in treated bulls 28 and 56 days after gossypol feeding. The number of sperm with proximal droplets was significantly higher in gossypol-treated bulls, suggesting testicular degeneration. There was no significant effect on the sperm motility, scrotal circumference, or histopathological characteristics of the testes. Four weeks after the end of gossypol feeding, primary and secondary abnormalities were still increased in gossypol-treated bulls, however in subsequent collection periods the percentage of abnormalities were similar between groups. At 210 days, there was no treatment effect on scrotal circumference, and histological characteristics of the testes were not different between groups. The deleterious effects of gossypol on the morphological characteristics of spermatozoa were reversible. Gossypol (8 mg/kg per day for 56 days) increased sperm abnormalities but the effects were reversible.     

Heritability estimates and adjustment factors for the effects of bull age and age of dam on yearling testicular size in breeds of bulls

Scrotal circumference, testicular length and body weight were measured in 3,090 yearling bulls of 12 breed groups finishing growth performance tests during a 5 yr period. Breeds were Limousin, Hereford, Charolais, Angus, Red Poll, Simmental, Pinzgauer, Brown Swiss, Gelbvieh and three crossbred breed groups. All bulls were born during a 60-d calving season starting in late March of each year and were subjected to similar management and environmental influences during the study. The bulls were the progeny of 307 sires averaging approximately 26 sires per breed group and 10 sons per sire. Breed group, sire within breed group, year and age-of-dam effects were important (P<0.01) for all testicular traits at both a constant age (354 d) and constant body weight (418 kg). Paternal half-sib estimates of heritability were 0.41 +/- 0.06 for ageconstant scrotal circumference, 0.34 +/- 0.06 for testicular length and 0.37 +/- 0.06 for calculated paired testicular volume, respectively. Age-constant genetic correlations between yearling body weight and testicular traits were small, indicating that testicular growth and body growth rates are largely independent, regardless of breed. Testicular size of bulls from 2-yr-old dams was smaller than that of bulls from older dams. Most of these age-of-dam effects on testicular size were removed when testicular size was adjusted for the effects of body weight, suggesting that age-of-dam effects on testicular size are primarily the result of age-of-dam effects on body weight. Age adjustment factors for yearling scrotal circumference did not differ (P>0.20) among breed groups and averaged 0.032 cm per day of age. Adjustment factors for age of dam were +1.3, +0.8, +0.4, and +0.0 cm for sons of 2-, 3-, 4- and 5-yr-old dams, respectively.     

Bull influences on conception percentage and calving date in Angus Hereford, Brahman and Senepol single-sire herds

Bull breeding soundness parameters, semen characteristics and sexual behavior were evaluated for effects on reproductive performance in single-sire beef herds. A total of 155 cow herds (Angus, 50 herds; Hereford, 40 herds; Brahman, 46 herds; and Senepol, 19 herds) bred to bulls of the same breed were observed for 8 yr. All bulls produced adequate quality semen and had scrotal circumference (SC) >/= 30 cm. Reproductive performance was evaluated by the conception rate (CON), conception rate during the first 21 d of the breeding season (21dCON), mean calving date (MCD), and mean calving date of the first half of the herd to calve (HHCD). Correlations were determined between breeding soundness parameters and reproductive performance for all bulls combined, by breed, and by age. The Cp statistic was used to select models for the effects of parameters on CON, 21dCON, MCD and HHCD. Breeding season length and breed had significant effects. The percentages of normal cells, proximal droplets, detached heads and the semen score (motility plus percentage of normal cells) had a significant effect on CON when all bulls were considered. After the effect of season was deleted, the most significant parameter affecting CON in the Brahman was the percentage of detached sperm heads. In the Angus, motility was significantly correlated with all reproductive performance indices. In the Hereford, breeding soundness examination score (BSE) was positively correlated with 21dCON.     

Relationships between seminal vesicle size and copulatory activity in bulls

Two experiments were designed to investigate the hypothesis that dimensions of the seminal vesicle are positively correlated with copulatory behavior in bulls. In Experiment 1, thirty Santa Gertrudis bulls (16.5 mo old) were used to study the relationship between copulatory activity and seminal vesicle length and width (palpation per rectum), seminal vesicle thickness (ultrasonography), and volume. The bulls showed a low level of copulatory activity (6.0+/-1.5, 0.8+/-0.3 and 0.3+/-0.1 for mean number of mounts, intromissions and ejaculations, respectively) in 2 tests. The mean number of mounts but not the mean number of intromissions or ejaculations differed (P<0.01) among bulls. No significant correlations were found between seminal vesicle size and any of the variables of sexual behavior. In Experiment 2, 16 beef bulls (18 mo old) were used to study the relationship between copulatory activity and seminal vesicle length (palpation) or dorso-ventral thickness (ultrasonography). Differences were detected (P<0.01) among bulls in mean number of mounts, intromissions and ejaculations achieved in 2 serving capacity tests. No significant correlations were found between copulatory activity and seminal vesicle length or thickness. These data do not support the hypothesis of a positive relationship between seminal vesicle length or thickness with copulatory activity, even for bulls with marked diffences in intensity of sexual behavior.     

Breed and other effects on reproductive traits and breeding soundness categorization in young beef bulls in Florida

Yearling, grass-fed, beef bulls at the USDA Subtropical Agricultural Research Station, Brooksville, Florida, were assessed for physical and semen traits in January, April, July and October of 1991 (Trial 1) and 1992 (Trial 2). Bulls were given a breeding soundness evaluation (BSE) using revised semen and scrotal circumference (SC) criteria. In Trial 1, the bulls consisted of Angus (n = 15), Brahman (n = 14), Hereford (n = 15) and Senepol (n = 14). In Trial 2, the breeds were Angus (n = 15), Brahman (n = 16), Romosinuano (n = 13) and Nellore x Brahman (n = 9). Trial bulls generally showed delayed growth compared with grain-fed bulls in temperate environments. Breed influenced semen traits (percentage sperm motility, normal spermatozoa and those with primary abnormalities) in both trials. Temperate Bos taurus breeds (Angus, Hereford) were generally superior to Bos indicus breeds (Brahman, Nellore x Brahman). Tropically-adapted Bos taurus breeds (Senepol, Romosinuano) were intermediate for those traits tested. In general, tropically-adapted Bos taurus breeds were more similar in reproductive development to temperate Bos taurus than to Bos indicus breeds. Breed by test period interactions occurred and were mainly influenced by delayed sexual maturity of Bos indicus bulls. Qualitative semen traits increased with bull age, particularly from 12 to 18 mo. Scrotal circumference development was slower in the Bos indicus breeds. Bulls of satisfactory BSE status at 18.1 to 22 mo of age were 73.9% in Trial 1 and 58.5% in Trial 2. Brahman bulls had the least satisfactory BSE scores in both years (Trial 1, 44.4%; Trial 2, 22.2%). Most bulls failed to achieve satisfactory BSE status due to a small SC relative to age (Trial 1, 66%; Trial 2, 72%). The most efficacious use of the BSE was > or = 15 mo in Bos taurus bulls and > 18 mo for Bos indicus bulls. Although the BSE has proven to be useful for the assessment of young, pasture-raised bulls in semi-tropical environments, use of SC thresholds linked more with growth traits than with calendar age would improve comparisons of relative reproductive development in such bulls, particularly those of Bos indicus derivation.