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.     

Reproductive performance and productive traits of beef bulls selected for different levels of testosterone response to GnRH

In two separate studies, one with four Hereford-Shorthorn and one with three Zebu x British crossbred bulls, the efficacy of using the testosterone response to gonadotrophin-releasing hormone (GnRH; Lutal, Hoechst) to predict differences in reproductive performance was assessed. Young bulls (17 or 29 months of age) selected for low to high (3.1 to 10.3 ng/ml) peak plasma testosterone 2 to 2.5 hours after the intramuscular injection of GnRH (62.5 to 2000 ng/kg LWT) were each later individually joined with groups of 19 to 30 cows in which estrus had been synchronized. In both studies, the rankings of bulls for overall fertility (capable cows pregnant), for libido (estrous cows mounted), and for fertilizing ability (mounted cows pregnant) were in close agreement with rankings for testosterone responses to GnRH. In the Bos indicus bulls rankings for both reproductive performance and testosterone response to GnRH were repeatable when measured at two and four years of age. Other reproductive measurements (semen quality, scrotal circumference, pen-type serving capacity tests) were less reliable predictors of reproductive performance. Measurements of liveweight gains and parasite resistance indicated that bulls superior for these characteristics do not always have satisfactory reproductive performance. These studies suggest that the testosterone response to GnRH could be a useful test to ensure that bulls selected for productive traits have adequate reproductive potential.     

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.     

Serving capacity — A measure of the serving efficiency of bulls during pasture mating

The aim of the study was to determine whether the serving capacity of a bull, the number of services it achieved during a pasture mating period, was related to the proportion of oestrous cows in its herd it served. Twelve groups of 3 to 10 bulls were mated with spayed, oestrous heifers at a bull: cow ratio of 1 to 5 for a 7.5 hour period. The serving capacity of a group of bulls was highly correlated with the proportion of oestrous heifers the group of bulls served (r = 0.94), and the proportion of oestrous heifers the bulls served 2⁺ times (r = 0.98). The high correlations occurred because each bull, whatever its serving capacity (range 0 to 15 services), rarely served the same heifer twice. The correlation coefficient between the number of services a bull achieved and the number of heifers it served was 0.96 (n = 54). It was concluded that the serving capacity of a bull is an accurate measure of serving efficiency during pasture mating.     

Differences in biochemical profiles among spawners of eight common carp breeds

Eight breeds of common carp (Cyprinus carpio L.) spawners reared under identical conditions and sampled in spring after over‐wintering were examined in order to compare their basic biochemical blood profiles. The breeds compared were: Amur wild carp (AS), Ropsha scaly carp (ROP), Ukraine scaly carp (US), Northern mirror carp (M72), South Bohemian mirror carp (BV), Israeli mirror carp (Dor 70), Hungarian mirror carp (M2) and Tata scaly carp (TAT). Significant differences were found among breeds in glucose concentration (GLU), total protein concentration (TP), triacylglycerols concentration (TAG), and calcium (Ca) and phosphorus (P_i) concentration. No differences were observed in aspartate transaminase activity (AST) or alanine aminotransferase activity (ALT). The highest glucose, total protein, and calcium (Ca) concentrations were found in AS (GLU 8.3 ± 1.2 mmol L^?1, TP 32 ± 3 g L^?1, Ca 2.42 ± 0.22 mmol L^?1). High values of triacylglycerol concentration (TAG) were found in ROP (1.94 ± 0.52 mmol L^?1). Phosphorus (P_i) concentration was highest in M2 (3.82 ± 1.34 mmol L^?1). Amur wild carp and breeds originating therefrom (ROP, US, and M72) had significantly higher values of TP (P < 0.05), TAG (P < 0.05), and Ca (P < 0.01) and significantly lower values of P_i (P < 0.05) than did the other breeds. Scaly breeds had higher values of glucose (P < 0.01), TP (P < 0.01), ALT (P < 0.01), and Ca (P < 0.01) and significantly lower values of P_i (P < 0.01) than did mirror carp. Significant (P < 0.01) sex‐related differences were found in GLU, TAG and Ca concentrations.     

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.     

Plasma LH and testosterone in Zebu crossbred bulls after exposure to an estrous cow and injection of synthetic GnRH

Plasma hormone levels were examined in 4 mature Zebu bulls of normal libido (HL) and 4 which were sexually inactive (LL). When used in an artificial insemination programme the 8 bulls had similar fertility. Basal levels of LH and testosterone (T) estimated from 8 sequential blood samples at 30 minute intervals were not different in HL and LL bulls. Exposure of the animals to an estrous cow did not stimulate LH release. Following sexual stimulation plasma T levels actually decreased by an average (±S.E) of 2.9 (±1.9) ng/ml in the HL group and increased by 3.9 (±1.6) ng/ml in the LL group. An injection of 1 mg GnRH (Hoechst) caused LH release of similar magnitude in HL and LL bulls. The elevation of plasma T which followed GnRH injection was significantly larger in HL bulls.Low libido was not associated with a deficiency of basal LH or T, nor with the ability of the pituitary to respond to GnRH.     

Effect of repeated sampling on concentrations of testosterone,LH and prolactin in blood of yearling angus bulls

Blood was collected at intervals of 29 to 31 min for 5 hr from six Angus bulls (15 mo of age) unaccustomed to capture, restraint and jugular venipuncture (stress) to evaluate temporal changes in certain hormones. Concentrations of testosterone and luteinizing hormone (LH) but not prolactin were decreased significantly after the first hour. Testosterone in plasma decreased (P < .01) about 11-fold between 0 hr and 5 hr (9.9 ± 1.7 to .85 ± .16 ng/ml) as described by equation log_e testosterone = log_e 2.4649 ? .5266 hr (r = .83; P < .01). Concentrations of LH in plasma remained low after the first hour and those of prolactin were high at all times and varied significantly only among bulls (27 ± 6 to 84 ± 14 ng/ml). Testosterone but not LH was measured with equal repeatability among duplicate measurements either in whole blood or plasma but its average concentration in whole blood was 66% that of plasma. This study demonstrated that sequential collection of blood from bulls unaccustomed to capture and restraint cannot be used to evaluate normal temporal variations in concentrations of testosterone.     

Plasma insulin-like peptide 3 concentrations are acutely regulated by luteinizing hormone in pubertal Japanese Black beef bulls

Insulin-like peptide 3 (INSL3) is a major secretory product of testicular Leydig cells. The mechanism of acute regulation of INSL3 secretion is still unknown. The present study was undertaken in pubertal beef bulls to (1) determine the temporal relationship of pulsatile secretion among LH, INSL3, and testosterone and (2) monitor acute regulation of INSL3 secretion by LH using GnRH analogue and hCG. Blood samples were collected from Japanese Black beef bulls (N = 6) at 15-minute intervals for 8 hours. Moreover, blood samples were collected at −0.5, 0, 1, 2, 3, 4, 5, and 6 hours after GnRH treatment and −0.5, 0, 2, 4, and 8 hours on the day of treatment (Day 0), and Days 1, 2, 4, 8, and 12 after hCG treatment. Concentrations of LH, INSL3, and testosterone determined by EIAs indicated that secretion in the general circulation was pulsatile. The frequency of LH, INSL3, and testosterone pulses was 4.7 ± 0.9, 3.8 ± 0.2, and 1.0 ± 0.0, respectively, during the 8-hour period. Seventy percent of these INSL3 pulses peaked within 1 hour after a peak of an LH pulse had occurred. The mean increase (peak per basal concentration) of testosterone pulses was higher (P < 0.001) than that of INSL3 pulses. After GnRH treatment, LH concentrations increased (P < 0.01) dramatically 1 hour after treatment and remained high (P < 0.05) until the end of sampling, whereas an elevated (P < 0.05) INSL3 concentration occurred at 1, 2, 5, and 6 hours after treatment. Testosterone concentrations increased (P < 0.01) 1 hour after the treatment and remained high until the end of sampling. After hCG treatment, an increase of INSL3 concentration occurred at 2 and 4 hours, and Days 2, 4, and 8 after treatment (P < 0.05), whereas in case of testosterone, concentrations remained high (P < 0.01) until Day 8 after treatment. The increase (maximum per pretreatment concentration) of INSL3 concentrations after injecting GnRH or hCG was much lower (P < 0.001) than that of testosterone. In conclusion, secretion of INSL3 in blood of bulls occurred in a pulsatile manner. We inferred an acute regulation of INSL3 by LH in bulls because INSL3 concentrations increased immediately after endogenous and exogenous LH stimulation. The increase of INSL3 concentrations by LH was much lower than that of testosterone in bulls.     

Bull selection and use in northern Australia. 3. Serving capacity tests

Serving capacity studies were conducted on Santa Gertrudis, 5/8 Brahman, Brahman and Belmont Red bulls at 10 sites. Modifications, such as providing prior sexual experience, using females in oestrus and comparing restrained with unrestrained females, were made to the standard Bos taurus serving capacity test in a series of experiments with Santa Gertrudis bulls. Providing sexual experience to virgin bulls prior to testing improved the number of serves and libido scores in a serving capacity test. In serving capacity tests that used restrained females, expressions of sexual behaviour of bulls were not improved by having females in oestrus compared with non-oestrus females. There were more sexual behaviours, particularly mounts, in serving capacity tests involving restrained rather than unrestrained females. Summary statistics were collated from over 1100 serving capacity tests, in the 2 months prior to mating, across the 10 sites. In serving capacity tests using restrained females, in bulls of the same age, there were more expressions of sexual behaviours (except interest) in Belmont Red than in Brahman or 5/8 Brahman bulls with Santa Gertrudis bulls intermediate. The percentage of bulls displaying serves tended to increase with age; 82, 83 and 86% of 2-, 3- and > or =4-year-old Belmont Red bulls, respectively, completed 1 or more serves. This compared with 50, 50 and 66% of 2-, 3- and > or =4-year-old Santa Gertrudis bulls and 31% of 2-year-old Brahman bulls. Between 2 and 9% of bulls did not display any sexual behaviour in serving capacity tests with restrained females. Across genotypes, there were few and inconsistent relationships between either mounts or serves and liveweight, condition score, scrotal circumference, testicular tone and sheath measurements. The exceptions were in 2-year-old Brahmans where mounts were negatively correlated (r=-0.61; P<0.05) with umbilicus thickness and in 3-year-old Santa Gertrudis bulls, where serves (r=-0.53; P<0.01) and mounts+serves (r=-0.49; P<0.01) were negatively correlated with navel score. Measures of sexual behaviour were unable to consistently predict calf output of bulls in multiple-sire mating groups in extensive pastoral conditions. The main value of the serving capacity test in these genotypes is to identify whether a bull is capable of natural service.     

Postpartum fertility in beef cattle producing twins

Postpartum fertility was measured in 42 plur iparous Hereford cows and first calf Hereford heifers that calved after embryo transfer to induce twins. Dams were exposed to a Hereford bull from 4: 00 P.M. to 8:00 A.M. each day from 60 days postpartum until pregnancy was confirmed or calves were weaned at 180 days of age. Days open ($\text{X}\text{± SE}$) for dams that produced single and twin calves were 84.1 ± 4.6 (n = 12) and 94.9 ± 6.2 (n = 30), respectively. Corresponding values for dams that nursed one calf, including six females that lost one calf of a twin set at birth, and dams that nursed twins were 89.3 ± 6.4 (n = 18) and 93.4 ± 8.5 (n = 24). No significant differences were observed due to calving or suckling twin calves. Heifers that calved twins had a shorter mean interval to conception than cows that calved twins. These results are interpreted to mean that with proper management during the prepartum and postpartum periods, reduced fertility in beef cattle that produce twins need not occur.     

Effects of hemicastration and unilateral vasectomy on the remaining gonad and on the FSH,LH and testosterone blood concentration in bulls

The effects of unilateral castration and vasectomy on the weight and microscopic appearance of the contralateral testis and on the blood levels of testosterone, LH and FSH, were studied in German Fleckvieh bulls. Testicular weights were higher in hemicastrated bulls (P < 0.01) and unilaterally vasectomized bulls (P < 0.05) when compared to controls, 377 ± 45g (x ± s, N = 4 and 281 ± 12g, N = 4 vs 226 ± 38g, N = 3, respectively.Testosterone concentrations were higher during the weeks 14 to 22 after surgery in both treated groups. LH levels were not different from controls, but FSH levels increased significantly (P < 0.01) two weeks after hemicastration and unilateral vasectomy.Different factors appear to regulate the LH and the FSH concentrations in bulls. The increase of FSH after hemicastration may indicate a reduced production of inhibin or an inhibin-like substance from the testes, and a similar increase after unilateral vasectomy suggests that this substance may be resorbed distal to the testes.     

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.     

Small-angle X-ray scattering studies of Escherichia colil-asparaginase

Small angle X-ray scattering studies on Escherichia colil-asparaginase solutions show that the enzyme has a radius of gyration of 34.0 Å ± 0.5 Å at pH 7. The radius of gyration of the dissociated monomer is 16.0 Å ± 1.0 Å; it has the general shape of a prolate ellipsoid with an axial ratio of 1.4. A tetramer of four such ellipsoids arranged with 222 symmetry gives good agreement between measured and calculated radii of gyration if the distance between subunit centers is 43 Å. The tetramer dissociates on dilution below 1% and at pH values below 3.0. Acid-induced denaturation at pH 2.0 is irreversible in contrast to the reversible guanidine-HCl-induced denaturation.     

Modulation of phospholipase A2 activity in human endometrium and amniotic membrane by steroid hormones

Phospholipase A2 (PLA2) activity was measured in endometrium and amnion by a double isotope ratio technique using 1-palmitoyl-2-oleoyl phosphatidylcholine as substrate in the presence and absence of a range of unconjugated steroids and steroid sulphates (0.2–6.4 × 10⁻⁴ M). In the presence of 0.1% Triton, PLA2 activity was inhibited by the majority of steroids tested, pregnenolone sulphate being the most effective (12.9 ± 3.0% control activity) while oestradiol sulphate, oestrone and testosterone had only a minimal or no effect (99.1 ± 19.0, 85.4 ± 4.4 and 104.2 ± 16.3% control respectively). In the absence of Triton, the inhibitory effect of the free steroids was reduced or absent but oestradiol sulphate and testosterone sulphate stimulated activity by 2–13 and 1.5–3 times respectively. The effect was dose related, linear with time and independent of the stage of the menstrual cycle. Inhibition by pregnenolone sulphate, dehydroepiandrosterone (DMA sulphate and oestrone sulphate was maintained in the absence of Triton (24.9 ± 3.8, 67.1 ± 10.1 and 87.2 ± 13.8% control respectively). In amnion all 5 steroid sulphates caused a marked stimulation of PLA2 activity in both the presence and absence of Triton. The effect was greatest without Triton and at 6.4 × 10⁻⁴ M, testosterone, pregnenolone, oestrone, DHA and oestradiol sulphates increased PLA2 activity 20, 15, 12, 10 and 6-fold respectively. These findings indicate a direct action of steroid sulphates on PLA2 activity in endometrium and amnion.     

Testosterone dehydrogenase activity in koala liver: characterisation of cofactor and steroid substrate differences

We have studied the hepatic microsomal 17β-hydroxysteroid dehydrogenase (17β-HSD) capacity of koala (Phascolarctos cinereus) and tammar wallaby (Macropus eugenii). A detailed comparison of the activity in hepatic fractions from koala and rat was made. Hepatic microsomal NADP-supported 17β-HSD activity was significantly higher in koala (11.64±3.35 nmoles/mg protein/min), (mean±S.D.) than in tammar wallaby liver (1.52±0.79 nmoles/mg protein/min). However, when NAD was utilised as cofactor the activity was similar in both marsupial species (2.83±2.03 nmoles/mg protein/min, koala; 0.70±0.71 nmoles/mg protein/min, tammar wallaby). Data for rat indicated a cofactor preference for NAD rather than NADP (17.94±6.40 nmoles/mg protein/min, NAD; 2.18±1.04 nmoles/mg protein/min, NADP). Michaelis–Menten parameters for the kinetics of 17β-HSD testosterone oxidation by NADP and NAD were determined in the koala. The Km for testosterone was of the order of 10.0–24.0 μM (n=6) irrespective of the cofactor used, whilst the Km for NADP was 0.28–0.43 μM (n=2) and for NAD was 13.9–18.5 μM (n=2). 17β-estradiol was found to be an inhibitor of both NAD- and NADP- supported 17β-HSD activity. These findings indicate that NADP-mediated, but not NAD-mediated testosterone dehydrogenation is a major pathway of steroid biotransformation in koala liver; the reaction is less extensive in fractions from wallaby, human and rat. Such species-related differences in cofactor preference may contribute along with species differences in gene expression to observed rates of 17β-HSD activity in mammals.     

Sexual behavior and pregnancy rate of Bos indicus bulls

To study sexual behavior and pregnancy rate of Zebu bulls, 9 Brahman and 6 Nelore bulls were first examined for libido and serving capacity, semen characteristics and scrotal circumference, a week before being placed, individually, into a group of 16 estrus-syncronized heifers to observe mating activity. Scores for libido (0 to 10) and for serving capacity (based on the number of services per period) were assigned for each bull over a 15-min period. Estrus was synchronized with Norgestomet (3 mg, s.c. implant and 3 mg, i.m.) and estradiol valerate (5 mg, i.m.). The implants remained in place for 10 d, then 40 h after their removal a bull was placed with the heifers. Four Brahman and 6 Nelore bulls were monitored for 2 h while the remaining 5 Brahman bulls were observed for 30 h. Number of services and mounts per bull, the hour at which each event took place, and the identification of the heifers serviced were recorded. Pregnancy was diagnosed by transrectal palpation 50 to 60 d after mating. Mean libido score (+/- SEM) of the 15 bulls was 6.4 +/- 0.5, and mean serving capacity was 0.53 +/- 0.19; both of these measures were correlated with age (r = 0.78, P < 0.01, and r = 0.56, P < 0.05, respectively). In the 2-h trials, the number of mounts was correlated with the libido score (r = 0.73, P < 0.05), and the number of services was correlated with age (r = 0.76, P < 0.05) and with libido and serving capacity score (r = 0.91 and 0.92, P < 0.01). In the 30-h trials, the mean (+/- SEM) number of mounts and of services per bull was 74.4 +/- 21.1 and 14.6 +/- 0.5, respectively. The mount-to-service ratio and percentage of serving efficiency were 5.1 +/- 1.4, and 19.8 +/- 4%, respectively. Libido score was correlated with the mount-to-service ratio (r = -0.86, P < 0.10) and with serving efficiency (r = 0.84, P < 0.10). The percentage of heifers serviced, of those serviced 2 or more times and of those pregnant was 55 +/- 5.3; 47.1 +/- 6.4, and 59.2 +/- 5.8, respectively. Pregnancy rate was not correlated with any trait (P > 0.10). It was concluded that libido and the serving capacity test seem to indicate the mating potential of Zebu bulls over a relatively short period of time (e.g. 30 hours), in which resultant pregnancy rates are comparable to those of European bulls.     

Effect on scrotal circumference of trucking beef bulls medium and long distances

Scrotal circumference (SC) was measured both before and after 2- to 3-yr-old beef bulls were trucked either medium (138 km) or long (565 km) distances. Two SC measurement techniques were used, one recommended by the Society for Theriogenology and the “slip-off” technique. No differences (P > 0.05) were observed between pre-and post- trucking SC measurements using the Theriogenology technique when bulls were trucked either medium (n = 12; 35.9 ± 0.8 vs 35.8 ± 0.7 cm) or long (n = 16; 36.5 ± 0.5 vs 36.6 ± 0.4 cm) distances. However, when the SC of the same bulls was measured using the “slip-off” technique, there was a small, but significant (P < 0.05), reduction in SC for bulls trucked medium (38.0 ± 0.7 vs 37.5 ± 0.7 cm) and long (38.9 ± 0.4 vs 38.6 ± 0.4 cm) distances. Bulls having SC at or below the recommended minimum standard reacted no differently to the stress of trucking than did bulls having a SC well above the standard. Errors in measurement technique, severe weather conditions and testicular degeneration over an extended interval are discussed in terms of their potential contribution to the reduction in SC observed by some cattlemen. These data support the use of the SC measurement technique recommended by the Society for Theriogenology because its accuracy is not affected by trucking of bulls. The suggested implementation of an adjustment period between the trucking of beef bulls and measurement of their SC using the Theriogenology technique is not supported.     

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.     

Treatment with recombinant bovine somatotrophin enhances ovarian follicle development and increases the secretion of insulin-like growth factor-I by ovarian follicles in ewes

To investigate the effect of recombinant bovine somatotrophin (rGH) on ovarian folliculogenesis in sheep, 18 mature Scottish Blackface ewes were assigned randomly to two treatment groups. Starting from day 5 of the synchronised oestrous cycle, animals were injected daily with either vehicle (control group) or 12.5 mg rGH (rGH-treated group) for 7 days. Blood samples were collected once daily during the experimental period for the measurement of growth hormone (GH), insulin-like growth factor-I (IGF-I), insulin, follicle-stimulating hormone (FSH), luteinising hormone (LH) and progesterone. At the end of treatment animals were killed and ovaries collected. All follicles at least 1.0 mm in diameter were dissected out and diameters measured to assess follicular populations for individual animals. Five small follicles (1.0–3.4 mm in diameter) and all the large follicles (at least 3.5 mm) from each animal were incubated in 1 ml of Medium 199 for 1 h. Medium was then changed and incubation continued for a further hour. All medium samples were assayed for IGF-I, oestradiol, testosterone and progesterone.Treatment of ewes with rGH had no effect on the total number of follicles at least 1.0 mm in diameter (control, 34.4 ± 2.6; rGH-treated, 31.3 ± 1.4; P > 0.2). However, when follicles were further classified into different size categories (1.0–2.0, 2.1–3.0, 3.1–4.0, 4.1–5.0, 5.1–6.0 and over 6.0 mm in diameter), the population of follicles 2.1–3.0 mm in diameter was significantly increased by rGH treatment (control, 9.2 ± 0.7; rGH-treated, 13.8 ± 1.1; P = 0.02). The number of follicles of 3.1–4.0 mm diameter in the rGH-treated group tended to be increased (P = 0.09), whilst the population of follicles 1.0–2.0 mm in diameter was reduced (P = 0.07). Treatment of ewes with rGH significantly increased peripheral concentrations of GH (P < 0.01), IGF-I (P < 0.01), insulin (P < 0.01) and progesterone (P < 0.05). There was no effect of rGH treatment on circulating concentrations of FSH and LH. Both large and small follicles from rGH-treated ewes secreted significantly (P < 0.001) more IGF-I (37.8 ± 2.2 ng ml h⁻¹, n = 50) than follicles from the control group (26.7 ± 1.6 ng ml⁻¹ h⁻¹, n = 73). However, there was no significant effect of rGH treatment on the secretion of oestradiol, testosterone and progesterone by either large or small follicles.It is concluded that treatment of mature ewes with rGH can enhance the development of ovarian follicles to the gonadotrophin-dependent stages. Furthermore, rGH appears to act through increased secretion of ovarian IGF-I, as well as increased peripheral concentrations of IGF-I and insulin.