Testicular size at weaning in tropically-adapted beef bulls as influenced by breed of sire and dam

This study was conducted to evaluate testicular size at weaning for bulls representing diverse tropically-adapted genotypes. Calves from 2 locations were weighed and castrated at weaning. In one herd, calves were born to Brahman dams and Angus, Tuli, and Brahman sires. Body weights and paired testes weights were heavier (P < 0.01) for Angus x Brahman (AB) genotype than for Tuli x Brahman (TB) and purebred Brahman (BB) genotype calves. The testes:body weight ratio was greater (P < 0.01) for AB than for TB and BB calves. In a second herd, calves were born to Angus cows and Brahman, Tuli, and Senepol sires. Means were similar between Brahman- (BA), Tuli-(TA), and Senepol-sired (SA) calves for body weight and testes:body weight ratio. Paired testes weight was heavier (P < 0.05) for SA than BA calves. Across locations, paired testes weights were heavier (P < 0.01) for TA than TB calves but their body weights were similar. Within-herd deviations were greater (P < 0.01) for AB than BA calves for paired testes weight and testes:body weight ratio. The correlation between the proportion of Bos indicus genetic contribution and testes:body weight ratio was significantly negative. Tropically-adapted calves differed in testicular size at weaning due to breed of sire and dam effects.     

Breeding soundness and sex drive by breed and age in beef bulls used for natural mating

A total of 92 range beef bulls (Hereford = 60; Angus = 32) were given a breeding soundness examination (BSE) and two assessments for sex drive prior to their use in 23 breeding trials employing estrous synchronized females. Bulls were in three age groups: yearlings (n=29), two year olds (n=36), and three year olds and older (n=27). All yearling bulls were virgins, but the majority of the older bulls had previous mating experience. Angus bulls were superior (P<0.01) to Herefords in spermatozoal morphology and BSE score. Scrotal circumference increased with age beyond two years in Angus bulls but not in Herefords. Spermatozoal abnormalities generally decreased with age. BSE scores did not differ significantly among age groups. Apart from number of mounts, measures of sex drive did not differ with age or breed of bulls. This represents qualified justification for the current practice of using the same sex-drive assessment procedures for Bos taurus bulls of various ages and breeds.     

Analysis of genetic correlations between beef traits in young bulls and primiparous cows belonging to the dual-purpose Rendena breed

Selection for beef traits in Italian dual-purpose breeds is often carried out using growth and in vivo conformation recorded on young, performance tested bulls and muscularity traits scored during routinely linear type evaluation on primiparous cows. In this context, the knowledge of the genetic structure of traits obtained in different sexes and at different times is necessary for a proper selection plan. This study aimed to estimate, in the local dual-purpose Rendena breed, the genetic relationships between muscularity linear type traits from primiparous cows, the same traits scored on candidate young bulls, and the performance test traits recorded in candidate young bulls. Type traits included: front (chest and shoulder), back (loins and rump); thigh, buttocks side and rear views (two traits). Performance test traits were: average daily gain; EUROP fleshiness evaluation; and dressing percentage. Muscularity linear type traits were recorded on 11 992 first parity cows, and the muscularity type traits were scored on 957 candidate young bulls. Heritability estimates obtained for muscularity traits were moderate in young bulls (on average 0.326), about 16% higher than in primiparous cows. The average heritability for performance test traits in young bulls resulted 0.342. Moderate to strong genetic correlations were found between performance test and muscularity type traits collected in young bulls (from 0.500 between front (chest and shoulder) and average daily gain to 0.955 between thigh, buttocks side view and in vivo dressing percentage). The genetic relationships obtained between muscularity linear type traits of primiparous cows and performance traits of young bulls were variable (from a null correlation between front (chest and shoulder) and average daily gain to 0.822 between thigh, buttocks rear view and dressing percentage), with an average genetic correlation of 0.532. Generally, the traits measured during performance testing in young bulls were favourably correlated with muscularity traits evaluated on primiparous cows, indicating a common selection pathway.     

Seminal quality and sperm production in beef bulls with chronic dietary vitamin A deficiency and subsequent re-alimentation

Sixteen Hereford bulls (16 mo of age, 462 kg average body weight) were used in each of 2 yr to evaluate the effects of hypovitaminosis A on seminal quality and sperm production. Bulls were fed a high-concentrate diet with (+VIT) or without (-VIT) supplemental Vitamin A until the apparent onset of hypovitaminosis A (28 and 32 wk in Year 1 and 2, respectively). Half of the bulls on each treatment were then slaughtered and those remaining were re-alimented with Vitamin A. Plasma retinol concentration in -VIT bulls reached a nadir at approximately 25 wk. In Year 1, the proportion of progressively motile spermatozoa was lower in -VIT bulls after 17 wk but returned to that of the +VIT group after re-alimentation. The proportion of spermatozoa with primary morphological defects appeared to be greater in -VIT bulls compared to +VIT bulls by 26 and 24 wk in Year 1 and 2, respectively. The incidence of these defects declined in -VIT bulls upon re-alimentation, and approached the incidence observed in +VIT bulls by 8 to 12 wk of re-alimentation. Hypovitaminosis A decreased paired testes weight, daily sperm production, and epididymal sperm reserves but did not affect daily gain. Prolonged dietary Vitamin A deficiency impaired semen quality and sperm production in the absence of other clinical symptoms. However, under practical feeding conditions, diets that result in long-term, marginal Vitamin A deficiency or a relatively short-term absence of Vitamin A intake probably would have minimal effects on spermatogenesis.     

Scrotal circumference of Australian beef bulls

Normal range for scrotal circumference in Australian beef bulls was established using more than 300,000 measurements of breed, management group, age, liveweight, and scrotal circumference. The data used were derived from Australian bull breeders and two large research projects in northern Australia. Most bulls were within 250 to 750 kg liveweight and 300 to 750 days of age. The differences between breeds and variances within breeds were higher when scrotal circumference was predicted from age rather than liveweight, because of variance in growth rates. The average standard deviation for predicted scrotal circumference from liveweight and age was 25 and 30 mm, respectively. Scrotal circumference by liveweight relationships have a similar pattern across all breeds, except in Waygu, with a 50 to 70 mm range in average scrotal circumference at liveweights between 250 and 750 kg. Temperate breed bulls tended to have higher scrotal circumference at the same liveweight than tropically adapted breeds. Five groupings of common beef breeds in Australian were identified, within which there were similar predictions of scrotal circumference from liveweight. It was concluded that liveweight and breed are required to identify whether scrotal circumference is within normal range for Australian beef bulls that experience a wide range of nutritional conditions.     

The development of beef breeding bulls

Management of the bull battery will have a dramatic impact on profitability of the cow/calf enterprise. It is critical that young bulls be selected and developed to maximize longevity and productivity for the eventual buyer. Bulls must be structurally sound, healthy, and have adequate libido in order to service the required number of females. Once bulls complete their first breeding season, special care must be taken in order to ensure that they recover and regain needed body condition and pass a bull breeding soundness examination (BBSE). Mature bulls that have reached their genetic potential for growth require less intensive management, but the health program and annual BBSE cannot be overlooked. Mature bulls are also more likely to carry venereal disease and should be screened according to local disease incidence and state regulations. All bulls, regardless of age, should be observed early during the breeding season to ensure that they are physically capable of mounting and servicing females. The establishment of a complete management program, especially for young bulls, is essential to ensure that ranch resources are used efficiently, including maintenance of a high level of reproductive performance of the cow herd.     

Comparison of the BullMate sperm quality analyzer with conventional means of assessing the semen quality and breeding soundness of beef bulls

An instrument called the Optibreed, BullMate sperm quality analyzer (SQA) contains a densitometer for determining sperm cell concentration and an optical sensor to evaluate light deflections caused by sperm movement. Analysis of light deflections enables the generation of a value called the sperm quality index (SQI). The SQI represents the quality of a semen sample defined by sperm motility, concentration, viability and morphology. The SQA was compared to conventional, microscopic techniques for determining percent motile sperm and sperm concentration in bull semen samples and evaluated for its ability to classify bulls as satisfactory or unsatisfactory potential breeders. Semen samples were collected from 105 mature beef bulls by electroejaculation (day 1) and from 51 of the same bulls by internal artificial vagina (IAV) on day 2. SQI values were arranged into 20 categories in increments of 50units from 0 to 1000units. Percent motile sperm and sperm concentration values from both methods were significantly positively correlated (P<0.000) with respective r values of 0.82 and 0.80. A calculation of kappa to evaluate the differences in percent motile sperm generated by each system yielded a value of 0.20 and 0.54 for unweighted and weighted determinations, respectively. The intraclass correlation coefficient used to evaluate the reliability of sperm cell concentration determinations was 0.62 (P<0.05). SQI values generated on days 1 and 2 ranged from 0-994 to 0-906, respectively. Bulls were categorized as satisfactory or unsatisfactory potential breeders in all categories. The most appropriate SQI for determining whether a bull was a satisfactory or unsatisfactory potential breeder was 500 with respective sensitivity, specificity, positive predictive values (PPV) and negative predictive values (NPV) of 81, 65, 90.79 and 44.83%. In this experiment the BullMate SQA was not a reliable substitute for conventional semen analysis and was not useful for determining bull breeding soundness.     

Behaviour and mating performance of paddock-mated beef bulls

Paddock-mating performance was studied in seven beef bulls which were each joined to 28 or 29 females of mixed dairy and beef breeds for 8 weeks in single-sire joining groups in paddocks ranging from 4.0 to 28 ha. Seven unmated bulls were used as control animals. The estimated weight of testicular tissue per cow joined ranged from 12 to 32 g. Liveweight and testicular size and tone were recorded prior to, during and after joining. There was no apparent effect of mating on testicular characteristics of bulls, and pre-joining testicular size of the bulls was not significantly related to the calving results of the cows.Mating activity of the bulls was detected with a chin-ball harness and by behavioural observations covering eight intervals during the joining period. During the first 21 days (cycle I) of the joining period, 81% of the cows were mated and this increased to 89% by the end of the joining period. The overall return rate was 21%, the overall calving rate was 85% and no significant differences between the seven bulls were recorded in these two parameters. The relatively high level of sexual activity during cycle I apparently had no adverse effect on the fertility of the bulls since there was an even distribution over time of the return to first service of cows mated during cycle I. Mating activity of the bulls during cycle I had no significant effect on the mean percentage of time spent grazing or lying, but time spent standing was lower (P < 0.001) during cycle I than the remainder of the joining period.General activity, expressed as km travelled per day, was measured at regular intervals during the joining period for one working bull and one heifer in each of four mating groups. Mean activity of the bulls was significantly higher (11.3 km/day) during cycle I than the remainder of joining (2.45 km/day) and was significantly correlated (r = 0.8) to the mean number of cows mated per bull per day.     

Fertility of yearling beef bulls during mating

Crossbred (Bos taurus) yearling beef bulls were assessed for breeding soundness and physical traits prior to multi-sire natural mating at pasture. Bulls (n = 60) were assigned to six groups of nine or 10 bulls and two bull-groups were rotated on 14-day intervals during a 63-day mating season in each breeding herd (n = 3) of 191-196 cows. The remaining bulls (n = 14) were maintained under similar environmental conditions without mating exposure. Bulls were observed during mating and assessed for breeding soundness and changes following mating. Bulls used for breeding (UFB) lost 77 kg of body weight and declined from body condition scores of 6 to 4.5, whereas bulls not used for breeding (NUB) maintained body condition scores of 6 and gained 27 kg. The UFB bulls incurred a 75% total injury rate with 63% incidence of lameness and 12% incidence of reproductive injuries, resulting in a 22% attrition rate. Only 45% were physically sound at the end of mating. Scrotal circumference declined in UFB bulls (-4.58%) and increased in NUB bulls (2.49%). From the 98% BSE-satisfactory rate (UFB) prior to breeding, only 61% were BSE-satisfactory post-breeding. The NUB bulls declined from 57 to 36% satisfactory. The BSE classification was influenced by significant increases in abnormal spermatozoa (primary and secondary), which was significantly associated with injuries incurred during mating. Group and breed differences in injury rates and BSE-status following mating were evident. Environmental conditions and mating activity influenced bull seminal quality and physical condition. Pregnancy rates in all three breeding herds (91-96%) were similar, with insignificant differences between bull-groups; the effects of physical and reproductive changes on individual bull fertility were immeasurable.     

Glutathione content in the semen of bulls of the lowland black-white breed

Glutathione concentration in the semen was determined in 113 ejaculates obtained from 30 bulls of the lowland black-white breed. The quantitative and morphological characteristics of the studied sperm samples indicated considerable individual differences but always within normal range. Glutathione content was determined in the plasma and in isolated spermatozoa by the method of Saville (Analyst, 1958, 83, 670). A high glutathione level in the spermatozoa (31 nmols in 10(9) cells) and in plasma (28.8 microM) was found. A positive correlation was demonstrated (p less than 0.05) between the level of the peptide in plasma and its level in spermatozoa. It was found that the glutathione level in spermatozoa was higher in the ejaculates with the cell count below the average level.     

Characterization of gossypol-induced sperm abnormalities in bulls

To characterize sperm abnormalities induced by gossypol in cattle, young Brahman bulls (n=8) received either cottonseed meal delivering 8.2 g free gossypol/bull/d (treatment, n=4) or isonitrogenous soybean meal (control, n=4) for 11 wk. At slaughter, semen was collected from the following extragonadal sites: mediastinum/rete testis (Site 1), caput (Site 2), corpus (Site 3) and cauda epididymis (Site 4), and ductus deferens (Site 5). At least 200 fixed spermatozoa per site were examined via differential-interference-phase contrast (DIC) microscopy, with electron microscopy (EM) being employed with select samples. Sperm midpiece abnormalities were categorized as aplastic, fragile or asymmetric, with detached sperm heads being tabulated separately. Of these, aplastic defects were considered most likely to occur during spermatogenesis. Bull sperm midpiece lesions induced by gossypol were ultrastructurally similar to those observed in other, nonruminant, species. Combined midpiece abnormalities generally increased with extragonadal passage (EGP) in the treated bulls, as did fragile and asymmetric but not aplastic midpieces, or detached sperm heads. This pattern of EGP changes in bull sperm morphology following gossypol spermatoxicity suggests that structural weakness induced during spermatogenesis leads to secondary spermatozoal changes during EGP, possibly due to the imposition of motility stressors upon prior weakened structures.     

The testicular vascular cone, scrotal thermoregulation, and their relationship to sperm production and seminal quality in beef bulls

The objectives of the present study were to determine changes with age and relationships among characteristics of the testicular artery, scrotal surface temperature, scrotal circumference, testicular consistency, seminal quality and sperm production. Beef bulls aged 6 mo (n=12), 1 yr (n=12), 2 yr (n=11), and 3 yr (n=12) were used in this study. The mean length of the testicular artery as well as the length, width, and surface area of a latex cast of the testicular artery all increased between 6 mo and 1 yr of age (P<0.01). Wall thickness of the testicular artery and testicular arterial-venous distance in the spermatic cord decreased with age and with proximity to the testicle (P<0.01). Distance from the testicular vascular cone to the inner surface of the skin at the top of the scrotal neck (primarily fat) increased between 1 and 3 yr of age (P<0.01), and was associated with an increased top scrotal surface temperature (P<0.09). Increased epididymal sperm reserves were associated with an increase in testicular consistency, scrotal circumference and scrotal surface temperature gradient, and with a decrease in testicular arterial wall thickness and testicular vascular cone to skin distance. A decrease in sperm defects was associated with an increase in testicular consistency and with a decrease in the average scrotal surface temperature. Increased sperm motility was associated with increased scrotal circumference and a decreased top testicular vascular cone to skin distance. These findings emphasize the importance of thermoregulation to sperm production and seminal quality.     

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.     

Breeding capacity, behavior and fertility of bulls with Brahman genetic influence during synchronized breeding of beef females

The objective of this experiment was to evaluate the feasibility of using bulls of Brahman-derived breeds for synchronized breeding of females treated with Syncro-Mate-B (SMB). Suckled, postpartum cows (n = 261) and virgin heifers (n = 227) were given the standard SMB treatment. Calves were removed from cows for 48 h beginning at implant removal, and individual bulls were placed in pens with 15 to 20 females (x = 1:15.7 ) for 48 h beginning at implant removal. Bulls (n = 31) were 18 to 36 mo of age and had scored satisfactorily on a breeding soundness evaluation (BSE). The mean +/- SEM percentage of females in estrus, percentage of estrous females serviced and percentage of total females serviced were 77.2 +/- 2.4, 72.9 +/- 2.9 and 55.7 +/- 3%, respectively. Total average services per bull was 23.6 +/- 1.6; however, average number of individuals serviced was only 8.6 +/- 0.42. Mean +/- SEM percentage of females conceiving of those serviced, percentage conceiving of those in estrus and percentage conceiving of total females available were 57.3 +/- 3.7, 40.6 +/- 2.6 and 32.6 +/- 2.5%, respectively. Mean BSE scores of eight Simbrah bulls tested immediately before and 5 d after synchronized breeding did not differ (P > 0.05). These data suggest that the conception rate of Brahman-influenced bulls servicing SMB-synchronized cows is within the normal range. However, the total number of individual females serviced and the total pregnancy rate under the protocol employed was low. This occurred because all estrous females were not inseminated, and some bulls exhibited unpredicted low fertility.     

Effects of castration and time-on-feed on Mertolenga breed beef quality

Physicochemical characteristics were determined in the longissimus lumborum muscle, after 8 days of ageing of steers (n=12) and bulls (n=12) from Mertolenga breed slaughtered directly from pasture (day 0) or after a finishing period of 50, 100 and 150 days in a feed-lot facility. Bulls and steers presented similar live weight (averaging 388 kg), carcass weight (CW; averaging 213 kg), dressing percentage (averaging 60%), carcass fatness (11.9% CW) and carcass fat thickness (averaging 3.03 mm). Live weight, CW, carcass fatness and fat thickness increased along time-on-feed. Gender only had a negligible effect on meat characteristics, with b* and h* being the only parameters of colour affected by gender, also presenting a significant interaction gender×time-on-feed. Nevertheless, both the genders presented a high-quality grade concerning tenderness (Warner–Bratzler shear force (WBSF)). L* increased until 50 days on feed and decreased afterwards, whereas a* and C* values increased along time-on-feed. Pigment content was also affected by time-on-feed and showed a gender×time-on-feed interaction. Beef colour became darker and redder along time-on-feed, but still in a colour range highly acceptable by Portuguese consumers. Despite the increase in intramuscular fat and myofibrillar fragmentation index, as well as the decrease in collagen content of steers and bulls along time-on-feed, it did not affect the tenderness/hardness, indicating a small effect of time-on-feed in meat characteristics. Despite only small differences in carcass characteristics and meat-quality parameters that have been noticed along time-on-feed, those differences were only significant after 100 days on feed. Principal component analysis (PCA) was performed. The first PC axis (39.6% of the total variance) included colour variables a*, b* and C*, and carcass fatness, fat thickness, CW and live weight, whereas the second one (12.7% of the total variance) included h*, cooking losses and dressing-out. The principal component (PC) analysis confirmed the lack of differences between bulls and steers and indicates a differentiation of the first two periods of feeding (0 and 50 days on feed) from the two latter (100 and 150 days on feed) periods of feeding.     

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.     

Further studies on the serving capacity test for beef bulls

In four experiments to investigate aspects of the conduct of the serving capacity (SC) test for beef bulls, it was found that (i) the 60-minute yard test could be shortened to 40 or even 30 minutes without sacrificing the test's accuracy (r = 0.98 between SC40 and SC60, r = 0.97 between SC30 and SC40), (ii) generally 2-year-old bulls displayed their inherent SC on their virgin test (r = 0.86 between SC on their virgin test and SC in a later test), and (iii) as long as bulls were tested within their own age group, their social ranking in their testing group did not significantly influence the SC they displayed in the test.     

Modification of a serving capacity test for beef bulls

Five sets of identical twin bulls were used to determine how the various components of the serving capacity (SC) test influenced the SC a bull showed in the test. It was found that females must be restrained in service crates rather than by a halter. Females restrained in this way need not be in oestrus and bulls must be sexually stimulated before the test (10 min of watching other bulls mounting females being adequate). Bulls tested in this way displayed little variation in SC from one test to another (SD of SC being 1.1 services).