A comparison of Bonus and Quota mating systems for utilising the sex-determining region Y gene in terminal sire beef cattle breeding

The use of the sex-determining region Y gene in terminal sire beef cattle breeding was investigated, assuming that fertile transgenic bulls carrying this gene on an autosome can be created. The benefit of these transgenic bulls arises from having an increased proportion of calves with a male phenotype. Two mating strategies utilising the transgenic bulls were devised and compared; the Quota scheme whereby a quota of normal bulls is used alongside the transgenic bulls in a breeding nucleus, and the Bonus scheme in which a phenotypic bonus is assigned to transgenic bulls indicating the added value of their offspring. Bonus and Quota breeding schemes were comparable, in terms of the value of offspring of the bulls, for the first 6 years of selection, after which time the Quota breeding scheme was superior. For time horizons less than 10 years, and large assumed phenotypic superiorities of male calves, breeding schemes with transgenic bulls were superior to traditional breeding schemes without transgenic bulls. If the time horizon was longer, or if the assumed superiority of male calves was small, then traditional breeding schemes were generally superior to those utilising transgenic bulls. Scenarios were observed, however, where transgenic bulls were always superior to normal bulls, in terms of their value as sires. Equations were derived to predict genetic gain and the equilibrium genetic lag between normal and transgenic bulls in Quota breeding schemes.     

Bull selection and use in northern Australia. 4. Calf output and predictors of fertility of bulls in multiple-sire herds

On 10 northern Australian properties, the number of calves sired (calf output) by individual bulls in multiple-sire matings was measured by DNA typing for paternity. There were 235 bulls (92 Santa Gertrudis, 25 5/8 Brahman and 119 Brahman) from 37 multiple-sire mating groups. Number of bulls in groups ranged from 2 to 25 and ages of bulls ranged from 2 to 5 years. Mating periods were for 3-12 months and bull mating percentages were 2.5-6%. In all, there were 4251 calves tested and the resolution of paternity ranged from 92.5 to 100% and averaged 97.7% across all sites. This included 9.9% of calves with no potential sires in any of the mating groups. Of the 235 bulls mated, 58% sired 10% or less calves in each of their respective mating groups with 6% not siring any calves. In contrast, 14% sired over 30% of the calves in each of the respective mating groups. When bulls were mated in groups of 8-24, the maximum percent of calves sired by individual bulls was 26+/-7% (mean+/-S.D.) with a range 11-36%. However, when bulls were mated in groups of 2-7, the maximum percent of calves sired by individual bulls was 59+/-19% with a range 24-94%. Calf output of bulls was moderately repeatable across years at four of five sites. Multiple regression models relating pre-mating measures of physical, seminal and behavioural traits to calf output were developed for the three breed groups. In all, only 138 of the 235 bulls were included in the models (40 Santa Gertrudis, 24 5/8 Brahman and 74 Brahman). Sheath and testicular traits, such as scrotal circumference and testicular tone, were generally not related to calf output, the exceptions being sheath depth in Brahman bulls which was negatively related (P<0.05) and scrotal circumference in 5/8 Brahmans which was positively related (P=0.08) to calf output. Dominance was only included in the 5/8 Brahman model but there was no significant relationship between dominance hierarchy and calf output. Semen motility was only related (P<0.05) to calf output in 5/8 Brahmans. However, measures of semen quality based on spermatozoa morphology were important contributors to calf output in the Santa Gertrudis and Brahman models where percent normal spermatozoa was positively related (P<0.01) to calf output. In Santa Gertrudis and Brahman bulls, measures of sexual behaviour in the serving capacity test were related to calf output. In Santa Gertrudis, these were for the number of displays of sexual interest (P<0.05), and mounts (P<0.01), but not number of serves, whilst in Brahman bulls, libido score was positively related to calf output (P<0.05). The models only explained 35-57% of the variation in calf output.     

Paternity Tests in Multisired Beef Herds by Blood Grouping

The number of offspring sired by individual bulls in multisired beef herds was determined by blood grouping. Six series of tests, each having from 3 to 18 bulls as possible sires,, yielded from 35 to 114 dam-offspring pairs. The paternity was established for 45 to 90 % of the calves tested in each series. The rest were cases with either more than 1 bull not being excluded as the possible sire, or all bulls excluded from being the sire. The causes for the non-established paternities are discussed. Highly significant differences were found in the number of offspring sired by each bull. In each series, bulls ranking in the top third of the siring order sired 65–100 % of the calves with established paternities. Since a minority of the bulls sired the majority of the calf-crop, the generally recomended number of bulls for herds on the range can perhaps be reduced.     

A possible dominant white gene in Jersey cattle

A white heifer ("Snow") was born in 1991 from coloured registered Jersey parents. She produced six calves sired by coloured Jersey bulls: three white bull calves, two white heifer calves, and one coloured bull calf. One of the white bull calves was mated with 40 Hereford × Friesian yearling heifers (white face, predominantly black body with some white patches). The 38 resulting calves included 16 white and 22 coloured calves. Twelve of the 16 white calves were heifers and four were bulls. Red or black spotting was recorded on some white calves. The results are consistent with an autosomal dominant mutant causing the white phenotype. The mutation appears to have arisen spontaneously in Snow, then passing to her white progeny and white grand-progeny. The white individuals varied from entirely white in a few cases, to most having some residual small areas of red or black pigmentation in patterns not typical of other reported white spotting patterns of cattle.     

Effects of treatment with GnRH from 4 to 8 weeks of age on the attainment of sexual maturity in bull calves

In bull calves an early transient increase in circulating concentrations of LH occurs between 6 and 20 weeks of age. This has been shown to influence reproductive development and performance later in life. In an attempt to hasten the onset of sexual maturity, bull calves (Hereford x Charolais) were treated (im) with 120 ng/kg of GnRH (n=6) twice every day from 4 to 8 weeks of age; control calves received saline (n=6). Injection of GnRH resulted in an LH pulse in all animals. GnRH treated bulls displayed more rapid testicular growth rates between 22 and 44 weeks of age. Sexual maturity (SC>or=28 cm) was achieved earlier in GnRH treated bulls compared to saline treated bulls (41.7+/-2.22 and 47.0+/-0.45 weeks of age, respectively) and this was confirmed by age of sexual maturity based on ejaculate characteristics (>50 million spermatozoa, >10% motility; 45.0+/-0.86 and 49.0+/-1.13 weeks of age for GnRH and control treated bull calves, respectively; P<0.05). We concluded that treatment with GnRH, twice daily, from 4 to 8 weeks of age, prior to the endogenous early increase in plasma LH concentrations, could increase in plasma LH concentrations, advance testicular development and reduce age at puberty in beef bull calves. This may provide the basis for a simple regimen to hasten sexual development in the bull calf.     

Vitamin E Status of Healthy Swedish Cattle*

Using high pressure liquid chromatography the serum concentration of vitamin E was measured in dairy cows fed either hay or silage as their main roughage, in calves fed milk-replacer, and in young intensively fed bulls. The concentrates fed to the cows, calves and bulls were supplemented with 5–10, 25 and 5–10 mg DL-α-tocopheryl acetate per kg, respectively, and the milk-replacer for the calves was supplemented with 50 mg DL-α-tooopheryl acetate per kg powder. Cows fed silage as their main roughage had higher serum vitamin E concentrations ( $${\rm{\bar x}}$$ : 3.8–5.2 mg/l) than cows fed only hay ( $${\rm{\bar x}}$$ : 2.5–4.1 mg/1). Lactating cows had higher vitamin E concentrations than dry cows ( $${\rm{\bar x}}$$ : 4.1–5.2 and 2.5–3.8 mg/l, respectively) and calves and bulls had much lower vitamin E concentrations ( $${\rm{\bar x}}$$ : 1.4 and 1.2 mg/l, respectively) than cows. Thirty per cent of the calves and 41 % of the bulls had serum vitamin E concentrations less than 1.0 mg/l, suggesting that in these animals the conventional level of supplementation of feeds with DL-α-tocopheryl acetate in Sweden is probably inadequate for the prevention of nutritional muscular degeneration and other negative effects.     

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.     

Growth and fertility of bulls cloned from the somatic cells of an aged and infertile bull

In the present study, somatic cell cloning technology was used to produce eight newborn calves from an aged, infertile bull. Average birth weight of these calves was significantly higher than that of calves produced using AI. Four of the cloned calves died during the peripartum period; the remaining four (Clones A-D) survived and were used in this study. Two of the surviving calves (Clones C and D) were castrated; growth rates of the intact and castrated clones were similar to those of intact and castrated bulls, respectively, that had been derived by AI. Both uncastrated bulls (Clones A and B) began to produce normal semen at approximately 12 months of age. Semen produced by these clones, and their nuclear donor, was subsequently used for IVF; the proportion of IVM-IVF oocytes developing to the blastocyst stage was 23.4% (50/214), 28.4% (52/183) and 30.9% (63/204), respectively. Conception rates for AI were 54.5% (12/22) and 62.7% (64/102) for semen derived from Clone A and from the nuclear donor, respectively. The length of pregnancy and birth weight of the calves derived from semen collected from clones were similar to those of calves obtained by conventional AI using semen from their nuclear donor. Therefore, sires cloned from the somatic cells of an aged and infertile bull had normal fertility.     

Mapping of Calf Death in Japanese Black Cattle

Weak calf syndrome (WCS) is a major cause of calf death in Japanese Black cattle. Among IARS disorders, the isoleucyl-tRNA synthetase c.235G>C mutation has been identified as one of the causes of WCS. However, calf deaths differing from those attributed to IARS disorder has been occurring. To identify other genes potentially responsible for these calf deaths, we constructed three populations of three bulls (Bull-1, -2 and -3) that did not carry the IARS mutation, and dead calves (18, 28, and 31 calves) and healthy cattle (18, 15, and 10 cattle) sired by these bulls. The populations were genotyped using the BovineSNP50 BeadChip, but homozygosity mapping did not detect any associated genomic regions with calf death. Linkage analysis performed using each population as a paternal half-sib family of Bull-1, Bull-2, and Bull-3 revealed that, in the Bull-1 population, calf death was mapped to the 8.94?Mb–14.53?Mb and 29.82?Mb–33.77?Mb regions of BTA29. The findings suggested that the incidence of calf death in calves sired by Bull-1 was a hereditary disease exhibiting a dominant, not recessive, inheritance pattern.     

Bull selection and use in northern Australia. Part 2. Semen traits

Detailed semen evaluations were carried out on approximately 363 Santa Gertrudis, 5/8 Brahman and Brahman bulls on 12 different properties across northern Australia, as part of systematic breeding soundness examinations. A subset of bulls (n=245) were subsequently mated in groups, to cows and heifers at bull:female ratios of 2.5-6.0%, with the paternity of resulting calves being determined by microsatellite DNA testing. Motility traits of semen and spermatozoa were moderately repeatable and correlated with each other, but were unrelated to calf output. The percentage of morphologically normal spermatozoa in ejaculates was moderately to highly repeatable (e.g. r=0.10-0.64). The most common morphological abnormalities seen were mid-piece abnormalities, in particular, distal mid-piece reflex associated with a cytoplasmic droplet. Semen quality, particularly percent normal spermatozoa, was consistently related to calf output. In general, bulls with <50% normal spermatozoa sired few calves while bulls with the highest calf outputs had >70% normal spermatozoa. The presence or absence of heparin binding proteins in semen did not influence calf output. Semen from 93% of tested bulls was positive for heparin binding proteins. These results confirm that examination of semen, in particular, evaluation of percent morphologically normal spermatozoa, should be included in the breeding soundness examination of bulls.     

Changes in profiles of serum sex steroids of male buffaloes from birth to maturity

Age-related changes in testosterone, progesterone and estradiol 17-beta were determined by radioimmunoassay (RIA) in the serum of 155 male buffalo calves of varying ages. The calves were classified into 17 age groups. The mean weight of calves increased from 33.6 +/- 9.6 kg at one week of age to 531 +/- 41.4 kg at 42 months. The testosterone levels were less than 100 pg/ml from birth until 15 months of age, followed by peak concentrations of 422 +/- 79 pg/ml at 24 to 30 months and 793 +/- 193 pg/ml at 42 to 48 months (corresponding to puberty and maturity, respectively). The progesterone levels were higher in newly born calves and mature bulls. Otherwise, the levels continued to be low throughout the period of growth and development. Estradiol 17-beta was significantly higher in postnatal calves up to two months of age. The testosterone revealed a positive correlation with weight and age while E2 17-beta showed a negative correlation with age. These results do not support a direct role of peripheral progesterone and estradiol 17-beta in the onset of puberty and sexual maturity of buffalo bulls.     

Semen and reproductive profiles of genetically identical cloned bulls

In this comparative study, reproductive parameters and semen characteristics of cloned bulls (n = 3) derived from somatic cell nuclear transfer (SCNT) were compared to their original cell donor Holstein-Friesian (n = 2) bulls from the same enterprise to assess the differences in reproductive potential between a donor bull and its clones. The parameters evaluated included motility of fresh, frozen-thawed and Percoll-treated frozen-thawed spermatozoa, as well as in vitro fertilization (IVF) ability, embryo quality, birth and survival of calves following IVF and embryo transfer with frozen-thawed semen. With fresh semen, spermatozoa from one cloned bull had lower motility than its donor. Cloned bulls had higher velocity parameters in fresh semen, but those effects were not obvious in frozen-thawed or frozen-thawed semen selected with a Percoll gradient. Semen collected from cloned bulls had significantly higher IVF rates compared to donors; however, embryo development per cleaved embryo or quality of blastocysts did not differ between donors and cloned bulls. Pregnancy and live offspring rates from one donor and its cloned bull did not differ between fresh (40%, 16/40 versus 46%, 17/37) and vitrified/thawed (13%, 2/16 versus 25%, 4/16) embryo transfer following IVF. A total of 26 calves were obtained from genotypically identical donor and cloned bulls with no signs of phenotypical abnormalities. These preliminary results suggested that the physiology of surviving postpubertal cloned bulls and quality of collected semen had equivalent reproductive potential to their original cell donor, with no evidence of any deleterious effects in their progeny.     

Brahman bull fertility in a north Australian rangeland herd

Low and variable bull fertility was identified as a constraint on reproductive rates in beef cattle grazed in an extensive, multiple sire mating regimen on Mount Bundey station in the Darwin pastoral district of northwestern Australia. Erratic conception patterns were attributed to a high proportion of bulls with low breeding soundness evaluation scores (BSE), a high proportion of aged bulls (40%>8 yr), and to running bulls of mixed age groups. Liveweight, scrotal circumference (SC) and age were positively correlated. An experiment was subsequently designed to investigate the ability of a number of bull measurements to predict fertility in an extensively-managed, multiple-sire mating system. Blood typing was used to match calves to sires. It proved to be an accurate and useful technique which successfully identified the parentage of 94% of calves examined. Single measurements of serum testosterone after administration of gonadotrophin-releasing hormone (GnRH) were not correlated with fertility. However six of the seven most fertile bulls exhibited high peak serum testosterone levels in summer, and lower levels in the winter. In contrast, the less fertile bulls did not exhibit seasonal variation in GnRH-induced serum testosterone levels. Social dominance ratio was weakly ralted to fertility (r=0.51: P<0.05). BSE (r=0.51: P<0.05) and SC (r=0.49: P<0.05) prior to, but not subsequent to, mating were correlated with bull fertility. Under the conditions of this experiment, a bull to cow ratio of 1:20 was excessive for bulls with a satisfactory BSE score.     

Renal Corticopapillary Concentration Gradient in Calves

From 31 calves samples were taken from blood, urine and kidneys in a slaughterhouse. The calves were divided into three age groups: A. Newborn calves, B. Grazing calves, C. Bulls and heifers. The renal cortical and papillary potassium concentrations were higher in younger than in older calves. The corticopapillary urea and sodium concentration gradients during antidiuresis give good information about renal concentrating ability. The urea gradient was fully developed in the newborn calves. The sodium gradient, however, showed a small, but statistically significant difference between the age groups. Thus the papillary sodium content was lower in the newborn calves than in the older animals while the cortical sodium concentration was higher in the newborn and in the grazing calves than in bulls and heifers. Compared to the neonatal rat and rabbit the newborn calf has a high, but not fully developed corticopapillary concentration gradient.     

Influence of season of birth on growth and reproductive development of Brahman bulls

Seasonal effects on reproduction are more dramatic in Bos indicus than Bos taurus cattle. This experiment evaluated reproductive development of fall- (n=7) versus spring- (n = 10) born Brahman bulls to determine if season of birth affects reproductive development. Measurements of growth and reproductive development began after weaning and continued at bi-weekly intervals until each bull reached sexual maturity. Different stages of sexual development were classified according to characteristics of the ejaculate and included first sperm in the ejaculate, puberty (> 50 x 10(6) sperm/ejaculate), and sexual maturity (two ejaculates with > 500 = 10(6) sperm/ejaculate). Average daily increases in all measured traits were similar in fall- and spring-born bulls and there were no differences in age, body weight, scrotal circumference, or paired testis volume between groups at first sperm or puberty. However, fall-born bulls were older (P < 0.05) than spring-born bulls at sexual maturity (553 days versus 481 days, respectively) as the interval between puberty and sexual maturity was longer (P < 0.05) in fall- than in spring-born bulls (82 days versus 54 days, respectively). The prolonged interval between puberty and sexual maturity in fall-born calves coincided with a short photoperiod (winter) whereas the short interval between puberty and sexual maturity in spring-born calves coincided with a long photoperiod (summer). In conclusion, season of birth affected sexual development; photoperiod might be involved in regulating testicular function immediately after puberty in Brahman bulls.     

Productivity of pure- and crossbred cattle in a subtropical environment

The influence of different breeds of sire and dam types on cow productivity in an arid, subtropical environment was studied. Cows with calves sired by Simmentaler, Hereford and Bonsmara bulls were more (P<0.05) productive than those with calves sired by Afrikaner bulls. Simmentaler sires were superior (P<0.05) to Bonsmara sires. Crossbred cows of predominant (>50%)Bos taurus breeding were generally superior to crossbreds of predominantB. indicus breeding and purebreds. Crossbreeding systems to utilize breed effects to optimise cow productivity within environmental constraints are discussed.     

Artificial insemination of Reindeer (Ragifer tarandus)

Semen collected from reindeer bulls in an artificial vagina was used for the artificial insemination of 16 reindeer cows: two with undiluted semen, five with diluted semen and nine with frozen semen. The two cows which received undiluted semen gave birth to normal calves 217 days later. The other cows returned to oestrus 23.5 days (mean) after insemination and subsequently calved, having been served by a fertile bull.     

The effect of continuous light on prolactin secretion in prepubertal Holstein bulls

Effects of 16 (16 light:8 dark) and 8 (8L:16D) h of daily light were compared with continuous light (24L:0D) exposure on prolactin (PRL) concentrations in serum of prepubertal bulls. Concentrations of PRL in serum were 2 to 3 fold greater in bulls exposed to 24L:0D or 16L:8D as compared with 8L:16D. However, PRL concentrations attained a maximum approximately 3 weeks later in calves exposed to 24L:0D than in calves given 16L:8D. Continuous low intensity (11 to 16 lux) lighting supplemented with 16 or 8 h of high intensity (449 to 618 lux) light per day increased PRL concentrations in serum of prepubertal bulls 1.5 to 2.5 fold relative to 8L:16D (470 lux). We found that relative to 8L:16D, 1) photoperiods of 16 or 24 h of light per day increased serum concentrations of PRL in prepubertal bulls; however, the time required to achieve maximum PRL concentrations was longer in animals exposed to 24L:0D, 2) continuous low intensity lighting supplemented with 16 or 8 h of high intensity daily light also increased concentrations of PRL in serum.     

Contraception of bison by GnRH vaccine: a possible means of decreasing transmission of brucellosis in bison

Preventing pregnancy in brucellosis-infected bison (Bison bison) provides a potential means of preventing transmission of disease. To determine whether a gonadotropin-releasing hormone (GnRH) vaccine was effective in reducing pregnancy in bison and to study the safety of injecting GnRH in pregnant bison, a study was conducted at the Idaho Fish and Game Wildlife Health Laboratory in Caldwell, Idaho (USA). Four pregnant and two nonpregnant female bison were given a single injection of GnRH vaccine, and five pregnant adult females were given a sham injection that contained only adjuvant. Three of the GnRH-vaccinated bison that were pregnant at the time of vaccination delivered healthy calves. One treated bison had dystocia that resulted in a dead calf. All control bison delivered healthy calves. After calving, females of both groups were exposed to two bulls. Treated bison were palpated 6 wk after exposure to the bulls, and blood was drawn for pregnancy-specific protein B analysis. The six treated bison were not pregnant. The sham-treated bison became pregnant and delivered viable calves. This study demonstrates that a single dose of GnRH vaccine is effective in preventing pregnancy in female bison for at least 1 yr.     

Repeatability of reproductive performance of beef bulls as yearlings and two-year-olds at pasture

Bull fertility, measured as pregnancy rate, percentages of calves born during the first 4 and 6 weeks of calving and means and medians of calving date distributions, was studied in 62 single-sire breeding herds of three breed groups over a 10-year period. Each bull was used as a yearling and then again as a 2-year-old. Average bull-to-cow ratio was approximately 1:20, and the breeding season started on 1 July and extended for approximately 60 days. The average pregnancy rate of cows mated to yearling bulls was similar to that for 2-year-old bulls (83.9% vs. 82.5%, respectively). There was a tendency towards earlier breeding among 2-year-old compared to yearling bulls as shown by 6.8% more (P = 0.09) calves born during the first 4 weeks of calving and 2.5 days advancement (P = 0.10) in the median of calving date distribution. Year and breed group of bull had no significant effect on the measures of bull fertility. The repeatability estimates of the measures of bull fertility were low, indicating that the reproductive performance of a 2-year-old bull cannot be accurately predicted from his performance as a yearling.