Inability to predict sexual and aggressive behaviors by plasma concentrations of testosterone and luteinizing hormone in Hereford bulls

The relationships between sexual and aggressive behaviors and levels of plasma testosterone and luteinizing hormone (LH) were examined in Hereford bulls at 18 and 24 mo of age. Concentrations of hormones in bulls during periods of sexual rest (13 blood samples collected from each animal during a 24-h period) were compared with individual differences in sexual and aggressive behaviors when exposed to restrained females, either individually or in groups. Nearly all correlation coefficients were low and nonsignificant. It was concluded that individual differences in sexual performance and aggressive behavior cannot be predicted based on circulating levels of testosterone and LH in bulls during periods of sexual rest.     

Development of sexual and aggressive behaviors in Hereford bulls

The purpose of this study was to describe maturation-related changes in the sexual and aggressive behaviors of Hereford bulls. Two groups of 13 and 14 bulls, respectively, were tested for sexual and aggressive behaviors every 3 mo from 3 to 24 mo of age. At 3 and 6 mo of age, the bulls were exposed, as groups, to two estrous females, whereas at 9, 12, 15, 18, 21, and 24 mo these bulls were tested under each of the following several treatment conditions: 1) individual tests (single males were exposed to single females), 2) small-group tests (three or four bulls:three females), 3) large-group tests (13 or 14 bulls:3 females), and 4) male-only tests (13 or 14 bulls were placed in the test arena in the absence of females). Most bulls consistently mounted females by 9 mo of age. Twenty-one of the 27 bulls (78%) attained their first ejaculation at either 12 or 15 mo of age. The frequency of mounting without ejaculation was greatest in large-group tests at 12 mo of age, and ejaculation frequency peaked at 18 mo. The incidence of male-male mounting in large-group tests (with females) did not appreciably change from 3 to 24 mo, whereas male-male mounting in male-only tests was greatest at 9 and 24 mo. We conclude that sexual performance data obtained in serving capacity tests administered to yearling bulls before 18 mo of age may underestimate the mating potential of certain individuals.(ABSTRACT TRUNCATED AT 250 WORDS)     

Sexual and aggressive behaviors of Hereford bulls: interrelationship of variables and problems with the use of composite scores to describe overall sexual performance

The purpose of this investigation was to determine the interrelationships of the various sexual and aggressive behaviors exhibited by Hereford bulls in sexual performance (serving capacity) tests and to determine the extent to which these interrelationships change with age (maturity). Correlation matrices were constructed for the frequencies of sexual and aggressive behaviors exhibited by two groups of 13 and 14 bulls, respectively, during 120-min tests with females when the bulls were 12, 18, and 24 mo of age. The frequencies of selected sexual behaviors recorded during individual tests at 18, 21, and 24 mo were factor-analyzed using a principle components analysis. Also, a comparison was made of the length of the refractory periods following various sexual behaviors at 12 and 24 mo of age. Bulls varied greatly in the way they responded to sexual stimuli. Few sexual behaviors were intercorrelated and the factor analysis of selected sexual behaviors was inconclusive. Frequencies of aggressive behaviors were more highly correlated. Age (maturation) did not affect the interrelationship of the sexual behaviors recorded. Aggressive behavior variables were more highly correlated at 12 mo than at 18 or 24 mo of age. The average length of the refractory period following ejaculation was longer (112 s; P less than .05) than the refractory period following mounts without ejaculation (50 s), and the latter had a longer (P less than .05) refractory period than mount attempts, mount intentions and head throws (26 to 38 s).(ABSTRACT TRUNCATED AT 250 WORDS)     

Use of naloxone challenge to predict sexual performance of young rams

The possibility of developing a hormone-based test to predict libido was evaluated using the response of LH and testosterone to naloxone. This test has been used to identify sexually active and inactive mature rams during the breeding season. The objective of this study was to determine whether the blood test could be used to detect differences in sexual activity of early postpubertal (29 +/- 0.1 wk) rams during the breeding season in November and again at 70 +/- 0.1 wk of age in August before the next breeding season. Rams were classed as sexually active or inactive using serving capacity tests (8 30-min observation periods to record sexual behaviors [mounts and ejaculations] of each ram individually exposed to three ewes in estrus) after the naloxone challenges. Naloxone (0.75 mg/kg of BW) was injected i.v. into 38 white-faced crossbred, 16 Polypay, and 49 Targhee rams. Blood samples were collected at 15-min intervals for 1 h before and 2 h after naloxone to measure LH and testosterone. Separate mixed-model analyses for repeated measures were used to analyze data for the same rams at 29 and 70 wk of age. Logistic regression procedures were used to model probabilities that rams were correctly predicted to be sexually active. A breed-type x sexual activity x time interaction for LH was observed (P < 0.05) after naloxone injection in 29-wk-old rams. At 70 wk of age, a breed-type x time interaction was detected (P < 0.001) for LH response to naloxone, but LH did not differ by sexual activity. At 29 wk of age, a breed-type x time interaction for testosterone response after naloxone was detected (P < 0.001), and at 70 wk of age, a sexual activity x time interaction was detected (P < 0.05) for testosterone after naloxone. Sexually active and inactive rams were not predicted accurately at 29 wk of age and were predicted 69 and 29% of the time for sexually active and inactive rams, respectively, at 70 wk of age. In conclusion, breed type at 29 and 70 wk of age can influence the naloxone challenge test, but the test cannot be used to discriminate between sexually active and inactive rams at 29 wk of age during the breeding season or at 70 wk of age immediately before the breeding season.     

Using ultrasound measurements to predict body composition of yearling bulls

Carcass traits have been successfully used to determine body composition of steers. Body composition, in turn, has been used to predict energy content of ADG to compute feed requirements of individual animals fed in groups. This information is used in the Cornell value discovery system (CVDS) to predict DM required (DMR) for the observed animal performance. In this experiment, the prediction of individual DMR for the observed performance of group-fed yearling bulls was evaluated using energy content of gain, which was based on ultrasound measurements to estimate carcass traits and energy content of ADG. One hundred eighteen spring-born purebred and crossbred bulls (BW = 288 +/- 4.3 kg) were sorted visually into 3 marketing groups based on estimated days to reach USDA low Choice quality grade. The bulls were fed a common high-concentrate diet in 12 slatted-floor pens (9 to 10 head/pen). Ultrasound measurements including back-fat (uBF), rump fat, LM area (uLMA), and intramuscular fat were taken at approximately 1 yr of age. Carcass measurements including HCW, backfat over the 12th to 13th rib (BF), marbling score (MRB), and LM area (LMA) were collected for comparison with ultrasound data for predicting carcass composition. The 9th to 11th-rib section was removed and dissected into soft tissue and bone for determination of chemical composition, which was used to predict carcass fat and empty body fat (EBF). The predicted EBF averaged 23.7 +/- 4.0%. Multiple regression analysis indicated that carcass traits explained 72% of the variation in predicted EBF (EBF = 16.0583 + 5.6352 x BF + 0.01781 x HCW + 1.0486 x MRB - 0.1239 x LMA). Because carcass traits are not available on bulls intended for use as herd sires, another equation using predicted HCW (pHCW) and ultrasound measurements was developed (EBF = 39.9535 x uBF - 0.1384 x uLMA + 0.0867 x pHCW - 0.0897 x uBF x pHCW - 1.3690). This equation accounted for 62% of the variation in EBF. The use of an equation to predict EBF developed with steer composition data overpredicted the EBF predicted in these experiments (28.7 vs. 23.7%, respectively). In a validation study with 37 individually fed bulls, the use of the ultrasound-based equation in the CVDS to predict energy content of gain accounted for 60% of the variation in the observed efficiency of gain, with 1.5% bias, and identified 3 of the 4 most efficient bulls.     

Evaluation of equations to predict body composition in Nellore bulls

The equations developed by Hankins and Howe (1946, HH), Marcondes et al. (2010, M10), Marcondes et al. (in press, M11) and Valadares Filho et al. (2006, V6) were evaluated to predict the body composition from the 9–10–11th rib cut in Nellore bulls. The evaluated equations estimated the physical and the carcass chemical composition, the empty body chemical composition and the noncarcass chemical composition. Thirty-seven Nellore bulls (14±1 months old initially) with shrunk body weight of 259±24.9 kg were used in this experiment. The bulls were randomly divided into three groups: five bulls to the reference group, four bulls were fed at maintenance level and twenty-eight bulls were fed ad libitum. The bulls fed ad libitum were separated into four groups, one of which was slaughtered every 42 days. The diet was composed of corn silage and concentrate (55:45). After slaughter, the 9–10–11th rib cut was dissected into muscle, fat and bone fractions. The remaining carcass was similarly dissected. The others parameters that were evaluated as partial predictors included the empty body weight, the dressing percentage, the visceral fat percentage, the organ and viscera percentage and the composition of the noncarcass components. The values estimated with prediction equations were compared to the observed values. The equations obtained by M11 predicted correctly the carcass physical composition. However, the muscle and fat tissues were under- and overestimated, respectively, by HH. Some constituents of the noncarcass components can be predicted from equations developed by M10. The equations obtained by M10 predicted correctly the carcass and empty body chemical composition. The carcass water was underestimated by HH. The equations by V6 did not predict the carcass or empty body chemical composition. The carcass physical and chemical composition and empty body chemical composition can be predicted from the composition of 9–10–11th rib cut by equations obtained by Marcondes et al., 2010 and MarcondesPlease complete and update the reference given here (preferably with a DOI if the publication data are not known): Marcondes et al. (in press). For references to articles that are to be included in the same (special) issue, please add the words ‘this issue’ wherever this occurs in the list and, if appropriate, in the text. et al., while the composition of these components cannot be predicted by Hankins and Howe (1946) and Valadares Filho et al. (2006) in Nellore bulls.     

Testosterone and luteinizing hormone responses to naloxone help predict sexual performance in rams

The first objective of this study was to determine whether LH and testosterone respond differently to a naloxone injection in relation to varying sexual performance in rams. If differences occurred, the second objective was to determine whether differences would predict variation in sexual performance. From a group of 1.5- to 3-yr-old rams, 20 sexually active and 39 sexually inactive rams were selected based on previously observed sexual behavior with estrual ewes. Each ram was exposed to three estrual ewes for 18 30-min sexual performance tests, and those found to be inactive were given two 30-min sexual partner preference tests. The final distribution was 28 sexually active, 22 inactive, and nine male-oriented rams. Rams were treated with 1.5 mg of naloxone/kg BW in December of Year 1 and again with either 0.75 or 1.5 mg of naloxone/kg BW in November of Year 2. Plasma concentrations of LH and testosterone were evaluated with mixed model analyses for repeated measures separately for each year to coincide with logistic procedures for modeling the probability that rams were sexually active. For Year 1, a sexual activity x age x time interaction for LH after naloxone was observed (P < 0.03). For testosterone, there was a sexual activity x time interaction (P < 0.03), with a similar, early increase for sexually active female-and male-oriented rams compared with a delayed, minimal increase for inactive rams. For Year 2, when all rams were over 2.5 yr of age, a sexual activity x time interaction for both LH and testosterone (P < 0.02) seemed more related to an earlier increase of both hormones for sexually active rams than the increase observed for inactive rams. In addition, sexually active rams had a greater increase in testosterone than inactive rams. No significant difference was observed between 0.75 and 1.50 mg of naloxone/kg BW. Testosterone and LH were used as explanatory variables and sexual activity was used as the response variable in logistic procedures. In Year 1, greatest prediction accuracy was 73.5% using testosterone at 60 min after naloxone injection. In Year 2, the greatest prediction accuracy was 85% using LH at 15 min multiplied by testosterone at 60 min after naloxone. Test repeatability for both years on the same rams was 76%. In conclusion, pattern and magnitude of naloxone-induced changes in endocrine function may facilitate identification of sexually active and inactive rams during the breeding season. Prediction accuracy of the naloxone-based test was 69 to 85%.     

Effect of zeranol on sexual development of crossbred bulls

Three groups of 1/2 Simmental X 1/4 Brahman X 1/4 Hereford bull calves were used during two different years to study effects of zeranol on sexual development. At 154 d of age, half the calves were implanted with 36 mg zeranol and half, not implanted, served as controls. Implanted calves were reimplanted at 90-d intervals throughout the trial (9 mo) each year. Trial 1 was conducted with 24 calves and Trial 2 was conducted the following year with 10 bulls. Twenty-four days after weaning (200 d of age) and at 28-d intervals thereafter, bulls in drylot in Trial 1 were weighted, scrotal circumference (SC) was measured and an ejaculate of semen was collected by electroejaculation to determine puberty. At these times, bulls were given 200 micrograms of GnRH i.m. and blood was collected at 0, 1, 2, 3, 4 and 5 h after GnRH. Serum concentrations of LH and testosterone (TEST) were determined. At slaughter, testis weight, length and circumference and pubertal status were recorded. Bulls implanted with zeranol had smaller SC than control bulls during the entire 9-mo period (P less than .0001). More control bulls reached puberty than did implanted bulls (82.4 vs 23.5%, respectively; P less than .001). Control bulls had larger testis measurements at slaughter (P less than .0001). Implants did not alter total weight gain or ADG (P greater than .10).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of group size and the male-to-female ratio on the sexual performance and aggressive behavior of bulls in serving capacity tests

The purpose of the following study was to determine the effects of group size and the male-to-female ratio on the sexual and aggressive behaviors of bulls in the context of serving capacity tests. Tests were administered to two groups of 13 and 14 polled Hereford bulls, respectively, under four test conditions in which the number of bulls and the ratio of males to females was varied. The test conditions were as follows: 1) individual tests (single males were exposed to single females), 2) small-group tests (three or four bulls:three females), 3) large-group tests (13 or 14 bulls:3 females), and 4) male-only test (13 or 14 bulls were placed in the test area in the absence of females). In addition, the sexual performance of 44 Hereford and 12 Angus bulls was compared when competing (small-group tests) vs not competing (individual tests) for females. Ejaculation rate (serving capacity) was similar in individual and small-group tests in which a male-to-female ratio of approximately 1:1 was maintained. Increasing the male-to-female ratio to approximately 4.5:1 enhanced levels of aggression and reduced overall sexual performance. Angus bulls were more aggressive than their Hereford counterparts when competing for females and exhibited lower (P less than .05) ejaculation rates in small-group tests than when evaluated individually. We concluded that the sexual performance of polled Hereford bulls can be reliably evaluated when tested in small groups as long as a 1:1 male-to-female ratio is approximated.(ABSTRACT TRUNCATED AT 250 WORDS)     

Breeding performance of bulls assigned either to 40 cows per bull or 80 cows per two bulls during the breeding period

The reproductive performance of Angus (A), Polled Hereford (PH) and Santa Gertrudis (SG) bulls was compared when exposed to 40 cows/bull vs 80 cows/two bulls during a 90- to 95-d breeding period on pasture. Cows were A, PH and SG straightbreds and crossbreds of these breeds. Each year, cows were allotted at random within breed composition and age of dam to breeding groups. A replicate consisted of two 40-cow single-sire units with bulls of two breeds and an 80-cow two-sire unit with two bulls of the same breeds and all four bulls of the same age. There were eight replicates of PH and SG bulls and five replicates of PH and A bulls. At breeding time, 20, 16, 12 and 4 bulls were 2-, 3-, 4- and 5-yr-olds, respectively. Reproductive performance of bulls was evaluated in terms of calving rate (CR) of cows exposed to them and number of days (NOD) from the beginning of the breeding period until calf birth. The 80-cow groups calved 3.7 d earlier (P less than .05) in the calving period and had a similar CR compared with the 40-cow groups. The PH-A replicates calved 3.5 d earlier (P less than .05) and had 7.3 percentage units higher (P less than .01) CR than PH-SG replicates. Results of this study indicated that 80-cow two-sire breeding groups had an advantage over the 40-cow single-sire groups in terms of calves born earlier in the calving period, with no reduction in CR.     

Breeding performance of beef bulls assigned to two-sire cow groups on pasture

Angus, Polled Hereford and Santa Gertrudis bulls from ages 1 through 5 and 7 yr were assigned to 26 two-sire breeding groups. Each year, straightbred and crossbred cows of these breeds were allotted at random within breed composition, age of dam and calving date to breeding groups on pasture. Sires within each breeding group or pair were the same age at breeding and were two of the three breeds of sires. Neither calving rate nor the proportion of calves born by one vs the other sire in the two-sire breeding groups was affected by sire age among breeding groups. For a given breed, there was no uniformity among the sires in the proportion of calves they sired in their two-sire breeding groups. The proportion of calves born for the 26 sire pairs averaged .64 vs .36 (SE = 0.4 for either high or low value) for one vs the other sire in a sire pair with no indication that calving rate was affected by unequal proportions of calves by sires within sire pairs. Cows calved significantly earlier in the calving period (b = -.775 +/- .127) as calving rate increased among sire pairs. The number of days from the start of the breeding period to calf birth was affected by differences between sires in sire pairs for 8 of the 26 pairs, but there were no significant differences due to sire pair or breed of sire because of interaction between these two variables.     

Responses of bulls to copper supplementation in a record of performance test station

A Hereford bull from a test station, routinely treated for footrot and not responding, was further examined at the Large Animal Clinic at the Western College of Veterinary Medicine. A slight arthropathy of the right shoulder was radiographically visible. The bull was found to have a marginally low plasma copper level of 0.52 ppm. All bulls in the test station were subsequently sampled for an initial plasma copper determination. At this time 76% of the bulls at the station had plasma copper levels below 0.50 ppm. A mineral mix containing 0.2% copper was added to provide 15 ppm copper in the final ration. All bulls were sampled 28 days later with less than 1% of the bulls showing plasma copper levels below 0.50 ppm.

Correlation coefficients between plasma copper levels and average daily gain were +0.067 for the presupplementation period, −0.255 for the supplementation period and −0.085 for the relationship between the change in plasma copper levels and the change in average daily gain. None of these correlations were significant (P > 0.05).

During the copper supplementation period plasma copper levels increased for all breeds of bulls studied. However, there was no concomitant improvement in rate of gain by the bulls.

     

无角夏南牛育肥公牛屠宰性能分析

[目的]通过屠宰测定分析,了解无角夏南牛的屠宰性能和肉质品质,为下一步无角夏南牛的选育提供资料。[方法]通过对20头24月龄无角夏南牛育肥公牛进行屠宰测定和肉质分析。[结果]20头无角夏南牛的屠宰率、净肉率、眼肌面积、肉骨比、高档优质肉块比率、高档肉块率分别为：62.62%、52.8%、111.17 cm2、5.82:1、49.69%和28.36%;肩肉、大黄瓜条、外脊3个部位的蛋白质含量分别为：23.602%±0.192%、20.852%±1.212%、21.522%±1.282%;脂肪含量分别为4.262%±1.612%、3.122%±1.052%、2.802%±2.492%;肌肉剪切力分别为：4.60kg±1.92kg、3.59kg±1.58kg、4.49kg±1.44kg。[结论]无角夏南牛的品种培育、改良效果显著,生产高档部位肉块的能力强、肉质好。     

Level of plasma testosterone in relation to age, gonad size and sexual libido in bulls

The level of plasma testosterone (PT) was determined by the direct RIA method with tritium-labelled testosterone. An average level of 2.25 +/- 1.46 nmol PT/l was found in 57 bullocks old 47 to 106 days. Until the age of 67 days, the level of PT was 1.11 +/- 0.69 nmol/l and from the 68th to the 110th day 2.74 +/- 1.32 nmol. In the period from the 7th to the 13th month of age, 108 bulls were found to have the PT level of 23.04 +/- 19.81 nmol/l, which was a statistically significant increase (P = 0.01) as compared with the prepubertal period. In 154 bulls old two years and older, the PT level was found to be 21.72 +/- 14.78 nmol/l. In comparison with bulls old 7 to 13 months, no statistically significant difference was recorded in PT levels. Neither was found any correlation between the gonad size and PT level and any relation between libido and PT level. In the bulls having no libido the PT level was insignificantly higher than in the bulls with pronounced libido sexualis. In all the studied groups of bulls, a comparatively high variation was found in PT values.     

Technical note: Use of near-infrared reflectance spectroscopy to predict intake and digestibility in bulls and steers

Multiple fecal samples were collected from growing Angus bulls (264 to 419 kg of BW, 3.0 to 11.4 kg/d of DMI) to predict DMI of a corn-silage-based diet. Contemporaneous digestion trials were conducted with the same diet in 12 steers in yr 1 to 3 and bulls in yr 4. Near-infrared spectra from fecal samples (n = 730 from 282 growing bulls, n = 240 from 36 steers and 12 bulls for digestion trials) were obtained from dried and ground fecal samples, and modified partial least squares regression was used to develop equations to predict DMI and DM digestibility (DMD). Although mean predicted DMI of the growing bulls (7.52 ± 0.04 kg/d or 22.4 ± 0.1 g/kg of BW) was within 2% of mean measured DMI (7.63 ± 0.06 kg/d or 22.7 ± 0.1 g/kg of BW), the mean of paired differences within samples (0.11 ± 0.04 kg/d or 0.3 ± 0.1 g/kg of BW) was greater (P < 0.01) than zero. Measured DMD (72.3 ± 0.5%) was identical (P < 0.97) to predicted DMD (72.3 ± 0.5%), and DMD for bulls in the digestion trial did not differ (P < 0.27) from DMD for steers. Prediction of intake requires incorporation of some measured values from the set of fecal samples to be predicted. Lack of similarity between spectra of fecal grab samples from the growing bulls and daily fecal collection of steers and bulls in the digestion trials in this study indicates the need for further verification before prediction of DMD with fecal grab samples.