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.     

A comparison of natural service fertility of yearling and two-year-old bulls on pasture

The natural service fertility of yearling bulls on pasture was compared with that of 2-year-old bulls in a study (2 experiments) which involved a total of 748 composite breed cows over 3 breeding seasons. Other factors such as age of the cows, breed, year effects, and the sequence in which bulls of a particular age were assigned to cows were also evaluated. Pregnancy and calving rates and calving date were used as criteria for assessing fertility. The age of the bull, breed, year, or bull sequence did not significantly affect any of the traits studied. The age of cow was important in all the traits studied, with mature cows (5 years and older at breeding) calving earlier (P < 0.05) than the youngest group (2 years old at breeding) of cows, in both experiments. The pregnancy rate was also lower in the younger cows than in the mature cows in the first experiment. The results suggest that the age range of the cow herd is more important in determining herd fertility than the age of the bull or any of the parameters studied.     

Effect of sire and sexual experience on serving capacity of yearling beef bulls

Two experiments were conducted in successive years on a Kansas ranch to determine 1) if serving capacity could be evaluated in virgin yearling beef bulls under field conditions, 2) the influence of sire on serving capacity, and 3) the effect of sexual experience on subsequent serving capacity for low serving capacity bulls. In Experiments 1 and 2, 70 and 78 Angus bulls 13 to 15 mo old representing four and six different sires, respectively, were used. In both experiments, a pretest session that measured reaction time to service preceded two successive serving capacity tests. Following the first serving capacity test, in Experiment 2, all low serving capacity bulls (n = 23) underwent sexual experience school, which consisted of exposure to nonrestrained estrus-induced females over a 4-d period. Five days after sexual experience school (9 d after the first serving capacity test), all Experiment 2 bulls were retested. In both experiments, sire influenced mean serving capacity scores of sons (P < 0.01, Experiment 1; P < 0.05, Experiment 2). Characteristics measured, including age, weight, scrotal circumference, and reaction time, were all unrelated to bulls serving capacity in both experiments, as well as to breeding soudness examination scores for bulls in Experiment 1. There was a dramatic impact of sexual experience school on subsequent serving capacity, since 85% of sexual experience school bulls moved into the medium or high serving capacity category at the second serving capacity test. It is concluded that serving capacity can successfully be evaluated in yearling beef bulls under field conditions, that sire has a profound impact on bulls serving capacity, and that providing sexual experience to low serving capacity bulls can improve their serving capacity.     

Relationship of seminal vesicle size and measures of libido in yearling beef bulls

Ninety-five yearling beef bulls were given routine Breeding Soundness Examinations, two libido tests and palpated rectally for internal genital disease and measurement of seminal vesicle size. Finger tips were premeasured, and then used as "glandometers". The bulls were examined at the end of a 140-day performance test. Sixteen lines of breeding were examined including 13 Hereford, 2 Angus and 1 Red Angus. Average age was 384 days and average weight was 961 lbs. Line and breed differences (P<.05) were observed for scrotal circumference, scrotal circumference score and second libido test. Similar differences were observed for SV length (P<.01), depth and volume both (P<.05). There were no significant correlations between seminal vesicle (SV) size and libido scores. There were, however, significant correlations between SV size and scrotal circumference (P<.05), BSE score (P<.01), body weight (P<.01), and semen morphology score (P<.05). Proximal droplets and midpiece abnormalities, respectively, were the most common spermatozoal abnormalities observed in semen from this group of bulls.     

Embryo development and survival in beef cattle administered ergotamine tartrate to simulate fescue toxicosis

Two experiments were performed to determine whether administration of ergotamine tartrate altered embryo development (Exp. 1) and uterine competency to establish pregnancy (Exp. 2) in beef cattle. Animals were fed daily either 0 (CON) or 40 mug/kg body weight of ergotamine tartrate (ERGOT). Following a 30-d period on respective diets, animals in Exp. 1 were artificial inseminated at estrus (d = 0) and single embryo recoveries performed on day 7; whereas, animals in Exp. 2 received two frozen-thawed embryos on day 7. As an indicator of ergotamine effects, prolactin was decreased throughout both experiments in ERGOT compared to CON animals (p<0.05). Furthermore, rectal temperature (RT) tended to increase during both experiments in ERGOT compared to CON (p= 0.06). In Exp. 1, embryo recovery (p=0.08) and the percentage of transferable embryos (p=0.09) tended to be greater for CON than for ERGOT. Percentage of embryos that developed to compacted morula or greater was increased for CON compared to ERGOT heifers (p<0.05). In Exp. 2, pregnancy rates of transferred embryos did not differ between treatment groups. Thus, administration of ERGOT to simulate fescue toxicosis altered developmental potential of embryos, but does not appear to affect uterine competency to establish pregnancy.     

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.     

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.     

Comparison of electroejaculation and transrectal massage for semen collection in range and yearling feedlot beef bulls

Two experiments were conducted to compare electroejaculation (EE) and transrectal massage (RM) of the ampullary region for semen collection from beef bulls, and to determine the effect of semen collection method on semen traits. In experiment 1, semen was collected either by EE or RM randomly assigned on an alternate basis in 137 range beef bulls unaccustomed to being handled. The maximum time allowed for RM was 4 min and if no semen was obtained, EE was used. In experiment 2, semen was collected from 39 yearling feedlot beef bulls that were accustomed to being handled, by RM followed immediately by EE. The maximum time allowed for semen collection by both methods was 4 min. In both experiments, sperm concentration, percent of progressively motile sperm, percent of sperm staining alive, and sperm morphology were determined. In experiment 1, RM resulted in fewer (P<0.001) successful semen collections and fewer bulls with penile protrusion than EE (80.9% versus 100% and 54.4% versus 91.5%, respectively). The success of RM was not influenced by bull age or breed, or by the veterinarian performing the massage. Transrectal massage required more time (30s, P<0.001) for obtaining a semen sample and resulted in samples with lower sperm concentration (P<0.001), percent motile sperm (P<0.05) and percent live sperm (P<0.001) when compared to EE. In experiment 2, EE and RM were equally effective for obtaining a semen sample (97.4 and 94.9%, respectively), but the proportion of bulls exhibiting penile protrusion during semen collection was lower (P<0.0001) with RM compared to EE. Percent of sperm staining alive was also lower (P<0.01) in samples collected by RM. Sperm morphology (normal sperm, head defects, midpiece defects, proximal cytoplasmic droplets, and detached sperm heads) did not differ between samples collected by EE and RM. In conclusion, semen could be collected by transrectal massage from approximately 80% of range beef bulls and from 95% of yearling beef bulls accustomed to handling. Sperm morphology was not affected by the method of semen collection, but percent of motile sperm and live sperm were lower in samples collected by RM. A reduced ability to stimulate penile protrusion with RM precluded examination of the penis in a large proportion of 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.     

Effects of label-dose permethrin administration in yearling beef cattle: I. Bull reproductive function and testicular histopathology

Pyrethroid administration to a wide variety of laboratory animals has been shown to cause detrimental effects on male fertility, including sperm quality, by means of endocrine disruption. The objective of this experiment was to study the effects of a commercial, permethrin-containing pour-on product on reproductive variables and testicular histopathology of yearling beef bulls. Black Angus bulls (n = 60; aged 369 ± 17 days; 511 ± 33 kg; 6.2 ± 0.5 body condition scores) were assigned to either (1) saline control (CON) or (2) permethrin pour-on administered at label dose (PYR). Blood samples were collected, and industry standard breeding soundness examinations (BSE), via electroejaculation, were performed on all bulls at 5 days before and 14 days after treatment. Progressive sperm motility and eosin-nigrosin–stained sperm were analyzed using high-power phase-contrast microscopy. Plasma testosterone concentrations were analyzed via radioimmunoassay. Bulls were slaughtered at 34 days, and one testicle per bull was randomly collected for histologic examination. Change in sperm motility between BSEs was not different because of treatment; sperm morphology however improved across treatments, but PYR bulls had less improvement in percent of head (P < 0.001) sperm abnormalities compared to CON, resulting in less improvement of primary abnormalities (P = 0.04). Nonetheless, morphological differences did not change the overall outcome for satisfactory breeder status. Change in testosterone concentration did not differ because of treatment. Histopathologic examination identified that testicular degeneration and tubule diameter did not differ as a result of treatment. It should be noted, however, that degeneration score (higher score having more degeneration) was positively correlated with primary abnormalities (P < 0.01; r = 0.35) and negatively correlated with normal sperm cells (P < 0.001; r = −0.43). In summary, these data indicate that a single use of permethrin at label dose in yearling Angus bulls results in minimal detrimental effects on sperm morphology but not to a degree that impacts the ability of bulls to pass a standard BSE.     

A comparison of three methods of assessing sex-drive in yearling beef bulls and relationships with testosterone and LH levels

Three methods of assessing sex-drive were compared in 113 yearling beef bulls. These were the serving capacity score (SC), the libido score (L) and reaction time to first service (R). Ovariectomized heifers restrained in service crates were the stimulus for all tests. Bulls were assessed twice by each method. For the first libido and serving capacity tests (L1 and SC1), the heifers were induced to show estrus. For the second tests (L2 and SC2), the heifers were not induced to show estrus. On a non test day, single blood samples were taken from all bulls and assayed for LH and testosterone. Reaction times to first service (R1 and R2) in the two serving capacity tests were not significantly correlated. Although the numbers of services (SC1 and SC2) in both serving capacity tests, were significantly correlated (r = .67), 57% of the bulls did not achieve a service in both the tests with heifers in heat and with heifers not in heat. Libido scores between the test with heifers in heat and heifers not in heat were significantly correlated (r = .67). The libido score method had the advantage that more bulls received a positive score and the test duration was shorter than in the serving capacity test. Of the three scoring procedures compared, libido score appeared to have most advantage in assessing sex-drive in yearling beef bulls. The total number of services achieved in the first serving capacity tests (using 'estrus' heifers) did not differ from that achieved in the second tests (using non-estrus heifers). The total services achieved in 10-min compartments of the 30-min serving capacity tests showed no difference either within or between tests. It is concluded that a 10-min test provides as much comparative information on the sex-drive of yearling beef bulls as longer tests. Further, the use of females in estrus appears unnecessary to satisfactorily assess bull sex-drive, provided proper restraint and presentation of stimulus females is employed. LH and testosterone values were not significantly correlated or were poorly correlated with sex-drive measurements.     

The relationship between breeding soundness evaluation and fertility of beef bulls under group mating at pasture

The relationships between natural service fertility of beef bulls and the components of breeding soundness evaluation, age, preweaning average daily gain, yearling weight and scores of two libido tests were studied in two seedstock herds. In one of the herds (YBH), 15 yearling bulls were rotated during six-week breeding season so that each group of five bulls served the cows for a period of one week and rested for two weeks before the next exposure. Five older bulls (one 3-year old and four 2-year old) were assigned to the other herd (MBH) during the entire breeding season (six weeks). The progeny of each bull were identified by blood typing.Calf crop was 6.4% higher (P=0.14) in the MBH compared with that in the YBH. There were large differences in fertility between the bulls in the MBH. The 3-year old bull sired 40.9% of the calves, presumably due to his high social dominance order. The third group of yearling bulls, which served the herd during the third and sixth weeks of breeding, sired the highest number of calves (49.4%) compared with the other two groups (28.4% and 22.2%). In each of the groups one and two of the yearling bulls, one bull did not produce any progeny, while another one sired 44% of the calves. The correlation coefficients between fertility of the bulls and the traits used to predict their fertilizing capacity were generally small and inconsistent in different groups, when the effect of age in the mixed age group was removed. The correlation coefficients of bull fertility with scrotal circumference and reproductive system score were higher and more consistent in different groups as compared with the other traits studied.     

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.     

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.     

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.     

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.     

Effect of route of dexamethasone administration on parturition,fertility and calf performance in beef cattle

Three trials (A, B and C) were conducted using 162 beef cows and heifers from a fall calving herd to determine the effect of route of administration of dexamethasone on induced parturition and retained placenta. Each trial contained a control group, a treated group receiving dexamethasone intramuscularly and a treated group receiving all or part of the dexamethasone intravenously. Dexamethasone treatment ranged between 20 and 50 mg and resulted in 81 to 100% induced parturition and in an increased incidence (P<.01 and P<.05 in trials A and C, respectively) of retained placenta compared to nontreated controls. Incidence of retained placenta in dexamethasone treated groups ranged between 23 and 78%, and in control groups between 0 and 6%. Route of dexamethasone injection did not affect either the incidence of cows responding with parturition or the incidence of retained placenta. Neither subsequent reproduction of cows nor growth performance of calves was significantly affected by induced parturition or route of dexamethasone injection.