Growth and pubertal development in Brahman-, Boran-, Tuli-, Belgian Blue-, Hereford- and Angus-sired F1 bulls

Growth and testicular development between 7 and 15 mo of age were evaluated in bulls produced by mating sires of six breeds (Hereford, Angus, Belgian Blue, Brahman, Boran, and Tuli) to Angus, Hereford, and MARC III (four-breed composite) cows. At 12 mo of age, Angus- and Hereford-sired bulls had the heaviest body weight (P < 0.08 to 0.001), whereas Brahman- and Belgian Blue-sired bulls were intermediate, and Boran- and Tuli-sired bulls weighed the least. Bulls sired by European breeds grew more rapidly after weaning (P < 0.01) than did Brahman-, Boran-, and Tuli-sired bulls, and these differences in growth rate were maintained through 15 mo of age, indicating that offspring of heat-adapted sire breeds (Brahman, Boran, and Tuli) have lower postweaning rates of gain, particularly during winter months, than do offspring of nonheat adapted sire breeds. Testis size was smaller initially (P < 0.01) and remained smaller in offspring of heat-adapted sire breeds through yearling age. By 15 mo of age, testis size was largest (P < 0.06 to 0.001) in Angus-sired bulls and had become similar among Hereford-, Brahman-, Boran- and Belgian Blue-sired bulls but remained smaller (P < 0.02 to 0.001) in Tuli-sired bulls. Thus, offspring of heat-adapted sire breeds had delayed testicular development compared with that of nonheat adapted sire breeds, particularly through yearling age. At puberty, Angus-sired bulls were 23 to 82 d younger (P < 0.05 to 0.001) than all other sire breeds except Hereford, and Brahman-sired bulls were older at puberty (P < 0.05 to 0.001) than were bulls of all other sire breeds except Boran. Testis size at puberty was quite similar among breeds of bulls (scrotal circumference = 27.9 +/- 0.1 cm) despite large breed differences in age, body weight, and hip height. Thus, measurement of yearling testis size was a reliable indicator of age at puberty among widely divergent breeds of bulls. In addition, the lower postweaning rates of gain and the smaller and slower testicular development in offspring of heat-adapted sire breeds should be noted by cattle producers considering use of such breeds in crossbreeding and breed improvement programs.     

Changes in mean scrotal circumference in performance tested Swedish beef bulls over time

Background

There is a growing interest in beef cattle breeding in Sweden. The majority of the females are bred naturally, which is why it is important to choose healthy fertile bulls to obtain good reproduction and profitability. The breeding soundness evaluation includes measurement of scrotal circumference (SC). Our aim was to analyze if the SC of performance tested beef bulls has changed over the years. In total, 1332 bulls (Angus, Charolais, Hereford and Simmental) from 13 batches (1997-2010) were included in the study. Case book entries from final evaluation of the bulls, 11-13 months old, were compiled and analyzed.

Results

An overall mean SC of 34.7 cm independent of breed and age was found which is above the set minimum level. Only eleven bulls did not reach the minimum level. An increase in SC of 0.06-0.07 cm/year was shown for all breeds. In all (1997-2010), the increase of the average SC (independent of breed and age) was approximately 1 cm. The positive trend was apparent for all breeds but only statistically significant for the Charolais breed.

Conclusions

In conclusion, our results indicated an increase in the SC over time, which improves the possibilities to obtain performance tested beef sires in Sweden with the potential for achieving better fertility results.     

Normal Values for the Scrotal Circumference in Rams of Gotlandic Breed

Selection of fertile sires is crucial for profitable lamb production. Males with larger testes tend to sire daughters that reach puberty at an earlier age and ovulate more ova during each oestrus period. Measurement of the scrotal circumference (SC) is thus an essential part of the breeding soundness evaluation. Testicular size varies with breed, age and time of the year. No SC values or recommendations for minimal values have been established in any of the Scandinavian domestic sheep breeds. Data were recorded of the SC, age and weight in 245 ram lambs and 27 mature rams of the Gotlandic breed, which is the breed that constitutes about 50% of the Swedish sheep population. For the ram lambs, the overall mean SC was 28.9 (+/-1.9) cm at an average age of 170 (+/-9) days and mean weight of 53.5 (+/-7.0) kg, and the mean SC varied between 27.1 and 29.6 cm depending on age and weight. For mature rams (17-54 month old), the mean SC was 32.4(+/-2) cm. To provide a practical tool for exclusion of rams with sub-optimal reproductive capacity (abnormal testes or those with small testes because of delayed puberty) a threshold value was established based on the average SC minus 2 SD. The calculated minimal SC is 26 cm for ram lambs >5.5 months of age with a body weight of >50 kg. For mature rams, minimum SC is 28 cm regardless of weight and age.     

Effect of energy intake after weaning on the sexual development of beef bulls. II. Age at first mating, age at puberty, testosterone and scrotal circumference

Simmental and Hereford bulls were individually fed varying levels of the same diet to determine the effect of energy intake after weaning on rate of sexual development. For 200 d, 29 Simmentals were fed an average of 14.6, 19.2 or 23.8 Mcal and 27 Herefords were fed 13.4, 17.5 or 22.2 Mcal metabolizable energy per bull daily. Higher energy did not hasten sexual development, as measured by serum testosterone, age at first mating or age at puberty. As energy level increased, weight at puberty increased (P less than .05) for both breeds, and scrotal circumference at puberty increased (P less than .05) for Simmentals. When adjusted for breed and energy level, bulls that were heavier at 1 yr of age had larger scrotal circumference (P less than .05) and were younger at puberty (P less than .01). Bulls that had higher serum testosterone at 1 yr of age reached puberty earlier (P less than .01). At a constant age there was no relationship between testosterone and scrotal circumference. Although higher levels of energy increased scrotal circumference of Simmentals, it did not hasten sexual development for either breed.     

Genetic relationships between scrotal circumference and female reproductive traits

Records for yearling scrotal circumference (SC; n = 7,580), age at puberty in heifers (AP; n = 5,292), age at first calving (AFC; n = 4,835), and pregnancy, calving, or weaning status following the first breeding season (PR1, CR1, or WR1, respectively; n = 7,003) from 12 Bos taurus breeds collected at the Meat Animal Research Center (USDA) between 1978 and 1991 were used to estimate genetic parameters. Age at puberty (AP) was defined as age in days at first detected ovulatory estrus. Pregnancy (calving or weaning) status was scored as one for females conceiving (calving or weaning) given exposure during the breeding season and as zero otherwise. The final model for SC included fixed effects of age of dam at breeding (AD), year of breeding (Y), and breed (B) and age in days at measurement as a covariate. Fixed effects in models for AP and AFC were AD, Y, B, and month of birth. Fixed effects in models for PR1, CR1, and WR1 included AD, Y, and B. For all traits, random effects in the model were direct genetic, maternal genetic, maternal permanent environmental, and residual. Analyses for a three-trait animal model were carried out with SC, AP, and a third trait (the third trait was AFC, PR1, CR1, or WR1). A derivative-free restricted maximum likelihood algorithm was used to estimate the (co)variance components. Direct and maternal heritability estimates were 0.41 and 0.05 for SC; 0.16 and 0.03 for AP; 0.08 and 0.00 for AFC; 0.14 and 0.02 for PR1; 0.14 and 0.03 for CR1; and 0.12 and 0.01 for WR1. Genetic correlations between direct and maternal genetic effects within trait were -0.26, -0.63, -0.91, -0.79, -0.66, and -0.85 for SC, AP, AFC, PR1, CR1, and WR1, respectively. Direct genetic correlations between SC and AP and between those traits and AFC, PR1, CR1, and WR1 ranged from -0.15 (between SC and AP) to 0.23 (between AP and WR1). Estimates of heritability indicate that yearling SC should respond to direct selection better than AP, AFC, PR1, CR1, and WR1. Variation due to maternal genetic effects was small for all traits. No strong genetic correlations were detected between SC and female reproductive traits or between AP and the other female traits. These results suggest that genetic response in female reproductive traits through sire selection on yearling SC is not expected to be effective.     

Production objectives and breeding goals of Sahiwal cattle keepers in Kenya and implications for a breeding programme

The Sahiwal breed has been used for upgrading the East African Zebu (EAZ) for improved milk production and growth performance in the southern rangelands of Kenya. Main users of this breed are Maasai pastoralists. Until now, there has been no deliberate effort to understand why these pastoralists specifically prefer to keep Sahiwal genetic resources as well as which traits are considered important by them and what is the underlying reason for this. However, this information is regarded vital for further development of the breed. A survey was conducted between May and October 2009 among Maasai pastoralists in Kajiado and Narok counties in the Southern part of Kenya, and private ranches and government farms to identify production objectives and breeding goals of Sahiwal cattle producers. Sahiwal genetic resources were mainly kept for domestic milk production and for revenue generation through milk sales and live animals. To a limited extent, they were kept for breeding and also for multiple objectives that included insurance against risks and social functions. Production aims were influenced to varying extents by various household and farmer characteristics. Sahiwal cattle and their crosses were generally perceived to be better with respect to productive traits and fertility traits when compared to the EAZ. However, the EAZ was rated higher with respect to adaptation traits. The breeding objective traits of primary importance were high milk yield and big body size, good reproductive efficiency and relatively good adaptation to local production conditions. Performance and functional traits are important breeding goals that play a major role in fulfilling the multiple production objectives. This forms the basis for the optimisation of a breeding programme for sustainable utilisation to meet the needs of Sahiwal cattle producers.     

Genome-wide association study for age at puberty in young Nelore bulls

Selection for bulls that would reach puberty early reduces the generation interval and increases fertility and herd productivity. Despite its economic importance, there are few QTL associated with age at puberty described in the literature. In this study, a weighted single-step genome-wide association study was performed to detect genomic regions and putative candidate genes related to age at puberty in young Nelore bulls. Several protein-coding genes related to spermatogenesis functions were identified within the genomic regions that explain more than 0.5% of the additive genetic variance for age at puberty in Nelore bulls, such as ADAM11, BRCA1, CSNK2A, CREBBP, MEIOC, NDRG2, NECTIN3, PARP2, PARP9, PRSS21, RAD51C, RNASE4, SLX4, SPA17, TEX14, TIMP2 and TRIP13 gene. Enrichment analysis by DAVID also revealed several GO terms related to spermatogenesis such as DNA replication (GO:0006260), male meiosis I (GO:0007141), double-strand break repair (GO:0006302), base excision repair (GO:0006284), apoptotic process (GO:0006915), cell–cell adhesion (GO: 0098609) and focal adhesion (GO:0005925). The heritability for age at puberty shows that this trait can be improved based on traditional EBV selection. Adding genomic information to the system helps to elucidate genes and molecular mechanisms controlling the sexual precocity and could help to predict sexual precocity in Nelore bulls with greater accuracy at younger age, which would speed up the breeding programme for this breed.     

Genetic Improvement of Dairy Cow Reproductive Performance

The welfare of cow along with profitability in production are important issues in sustainable animal breeding programmes. Along with an intense/intensive selection for increased milk yield, reproductive performance has declined in many countries, in part due to an unfavourable genetic relationship. The largely unchanged genetic trend in female fertility and calving traits for Scandinavian Red breeds shows that it is possible to avoid deterioration in these traits if they are properly considered in the breeding programme. Today's breeding is international with a global selection and extensive use of the best bulls. The Nordic countries have traditionally recorded and performed genetic evaluation for a broad range of functional traits including reproduction. In recent years many other countries have also implemented genetic evaluation for these traits. Thus, the relative emphasis of dairy cattle breeding objectives has gradually shifted from production to functional traits such as reproduction. Improved ways of recording traits, e.g. physiological measures, early indicator traits, assisted reproductive techniques and increased knowledge of genes and their regulation may improve the genetic selection strategies and have large impact on present and future genetic evaluation programmes. Extensive data bases with phenotypic recordings of traits for individuals and their pedigree are a prerequisite. Quantitative trait loci have been associated to the reproductive complex. Most important traits, including reproduction traits are regulated by a multitude of genes and environmental factors in a complex relationship, however. Genomic selection might therefore be important in future breeding programmes. Information on single nucleotide polymorphism has already been introduced in the selection programmes of some countries.     

Crossbred bull selection for bigger scrotum and shorter age at puberty with potentials for better quality semen.

Shortening age at puberty of crossbred breeding bull is an important issue in the tropics. This study aimed at selecting crossbred bulls at earliest possible age with bigger scrotum and potential for donating quality semen. One hundred and 31 pre-joining crossbred bulls of Central Artificial Insemination Laboratory, Saver, Dhaka were examined. The bulls being trained by seeing semen collection from mature bulls were allowed ejaculation into the artificial vagina at homosexual mount during a 20 min time at three occasions, every three months. Eighty one of 131 bulls produced at least one ejaculate during the study and their mean +/- SD age and scrotal circumference (SC) were 20.3 +/- 4.7 months and 28.2 +/-2.7 cm, respectively. Bulls' body weight, body condition score (BCS) and SC influenced the attainment of their puberty (p < 0.05). Bull's body weight had positive effects on scrotal circumference and ejaculate volume (p < 0.05). Scrotal circumference positively influenced the percentages of normal spermatozoa (p < 0.05). Scrotal skin-fold thickness negatively influenced the proportion of spermatozoa with normal head (p < 0.05). Based on age at first ejaculate and SC, 29.6% bulls (n = 24) were selected by cluster analysis. Selected bulls had mean +/- SD age 17.9 +/- 2.2 months, body weight 287.3 +/-48.6 kg, SC 30.5 +/- 1.5 cm, ejaculate volume 3.4 +/- 1.3 ml, sperm motility 50.8 +/- 17.2%, total spermatozoa per ejaculate 2541.9 +/- 1699.2 million and normal spermatozoa 81.5 +/-14.5%. The selected pubertal bull group was different from the unselected pubertal bulls at MANOVA (p < 0.0001). About 30% of pubertal crossbred bulls can be selected with shorter age and larger scrotum at puberty under conditions prevailed in Bangladesh.     

牛的肉用指数及影响因素

牛的肉用指数(活重kg/体高cm,BP I)是一区分役用型牛与肉用型牛的易测指标,将役牛转化为肉用型牛,其成年公牛BP I应达5.6以上,成年母牛平均达到4以上,这即是“由役转肉”转化成功的“转折点”。黄牛品种内存在BP I类型的多样性,这为选优转化提供了依据。影响牛的BP I因素包括品种(类型)、饲养条件、年龄和性别等。根据实际情况本文提出了公母牛(黄牛)BP I的年龄校正系数,按BP I选牛,可以提早到1~2岁。     

Developmental Changes of Bull (Bos taurus) Genitalia as Evaluated by Caliper and Ultrasonography

The objective of the present study is to follow the growth of the testes and the pelvic genitalia in cattle bulls, using ultrasonographic examination and measurements of external genitalia by caliper. Six Friesian bulls were examined periodically from 3 to 24 months of age with 3-month interval. Scrotum circumference (SC) and length were measured by tape. Testicular length, width and depth were measured by caliper. Scrotal contents including testes and epididymis, and the pelvic genitalia including bulbourethral gland (BUG), prostate and seminal glands (SG) were examined using transrectal ultrasonography. Scrotal circumference, length and the three dimensions of the testes showed significant increase with the advancement of age. Significant correlation was present between SC and testes breadth. At the same time, testis breadth as estimated by sonar showed positive correlation with that estimated by caliper. A positive correlation was also found between testicular breadth with each of the BUG and SG. Finally, it was concluded that ultrasonography gave appreciable benefits in studying the developmental changes of the testes and accessory glands of growing bulls. The obtained data could provide a useful tool for predicting bull puberty and fertility.     

Crossbreeding among British and continental European dual-purpose breeds in the coastal Pacific Northwest

From 1979 through 1987, British breed and crossbred cows were mated to Simmental, Pinzgauer or Tarentaise bulls or to Hereford-Angus crossbred bulls. Beginning in 1982, continental European crossbred females also entered the herd, to be mated for first calving to Hereford-Angus or Angus bulls and as cows to continental European or Hereford-Angus bulls. In progeny of British breed and crossbred cows, dam breed effects on birth and weaning weight were not important, but continental European crossbred calves were heavier than British crossbred contemporaries at birth and weaning. Pinzgauer- and Simmental-sired calves were heavier at birth than Tarentaise crosses, but calves sired by each of the continental breeds had similar weaning weights. Maternal heterosis was greater than direct heterosis effects on weaning weight (8% vs 5%), but only direct heterosis (13%) influenced birth weight. Within progeny of continental European crossbred cows, calves with a Tarentaise maternal grandsire were lighter at birth, with no significant difference among other maternal grandsire breeds. Maternal breed effects on weaning weight were not significant. Nevertheless, in contemporary years, continental European crossbred cows reared calves that were 10% heavier than calves reared by British crossbred cows. Pacific Northwestern cattle producers could achieve substantial increases in weaning weight from introducing inheritance from continental European dual-purpose breeds into cow herds and calf crops of British ancestry.     

Breed performance in organic dairy farming in Northern Spain

Organic farm management combines best environmental practices, a high level of biodiversity, preservation of natural resources and high animal welfare standards. To meet these criteria, farmers must have livestock well adapted to local organic conditions and information about how different breeds and crosses perform under different conditions. The objective of this study was to compare the performance of different pure breeds and cross-breeds of cattle in organic dairy systems in Northern Spain. The data analysed were obtained from monthly records kept between 2010 and 2016 on organic farms registered in the regional milk recording system. Analysis of various traits indicated that the Holstein-Friesian breed suits the organic production system in the study region. Although the reproductive performance of Holstein-Friesian cows was poorer (in terms of number of services per conception) than that of cross-breed and Brown Swiss cows, the Holstein-Friesian produced more milk and lived longer. In addition, there was no difference in calving type or calving ease between the different breed groups. The better milk fat and protein yields produced by the crosses may be useful traits for farmers interested in milk transformation. The advantage of continuing to use Holstein-Friesian cattle is that the breed is predominant worldwide, and the genealogy is well documented. If Holstein-Friesian cattle continue to be used, the main priority will be to search for well-adapted bulls (particularly for pasture-based conditions) and to elaborate a genetic merit index for organic and pasture-based systems with the aim of predicting and minimizing genotype × environment interactions.     

基因芯片技术在晋南牛种公牛选育中的应用

为了更好的保护开发利用晋南牛,确保晋南牛的遗传多样性,本研究应用基因芯片技术,对晋南牛进行群体遗传特性的检测及后备种公牛的遗传评估,为晋南牛的分子辅助选育与保种提供理论与技术支持。采集18月龄健康、体重相近（（350±20）kg）的荷斯坦牛、和顺肉牛、西门塔尔牛、延边牛及利木赞牛血样各10份,及晋南牛后备公牛血样25份,根据不同牛品种分为6组,其中前5组每组10个重复,晋南牛后备公牛25个重复。应用Illumina SNP 50K高密度牛SNP芯片进行基因型检测,分析比较晋南牛的群体遗传特征,运用亲缘矩阵计算晋南牛后备公牛的亲缘系数,同时用BLUP进行遗传评估。结果表明,晋南牛在遗传结构上与荷斯坦牛、和顺肉牛、西门塔尔牛及利木赞牛关系较远,与延边牛较近,为中国地方品种群体;对晋南牛后备公牛进行遗传评估,得出了牛的基因组胴体重方差育种值排名,JN23的胴体重倍数性状标准差最大,从基因组水平可选作肉用种公牛;应用亲缘分析对晋南牛后备公牛家系进行分类,避免群体间的近交。本研究对晋南牛后备公牛进行了遗传评估、近交家系分析、传统表型选择及遗传疾病检测,最终选留的种公牛为JN07、JN23、JN05、JN08、JN02、JN13、JN19、JN14,通过多种选育方法结合提高了公牛的选择准确性,为晋南牛的群体选育提高奠定了基础。     

Conservation priorities for the different lines of Dutch Red and White Friesian cattle change when relationships with other breeds are taken into account

From a genetic point of view, the selection of breeds and animals within breeds for conservation in a national gene pool can be based on a maximum diversity strategy. This implies that priority is given to conservation of breeds and animals that diverge most and overlap of conserved diversity is minimized. This study investigated the genetic diversity in the Dutch Red and White Friesian (DFR) cattle breed and its contribution to the total genetic diversity in the pool of the Dutch dairy breeds. All Dutch cattle breeds are clearly distinct, except for Dutch Friesian breed (DF) and DFR and have their own specific genetic identity. DFR has a small but unique contribution to the total genetic diversity of Dutch cattle breeds and is closely related to the Dutch Friesian breed. Seven different lines are distinguished within the DFR breed and all contribute to the diversity of the DFR breed. Two lines show the largest contributions to the genetic diversity in DFR. One of these lines comprises unique diversity both within the breed and across all cattle breeds. The other line comprises unique diversity for the DFR but overlaps with the Holstein Friesian breed. There seems to be no necessity to conserve the other five lines separately, because their level of differentiation is very low. This study illustrates that, when taking conservation decisions for a breed, it is worthwhile to take into account the population structure of the breed itself and the relationships with other breeds.     

Relationships of metabolic hormones and serum glucose to growth and reproductive development in performance-tested Angus, Brangus, and Brahman bulls

Understanding mechanisms that regulate growth and reproduction are important for improving selection strategies in cattle. In this study, Angus, Brangus, and Brahman bulls (n = 7 per breed) of similar age were selected from a group of 65 weanlings. Bulls were evaluated after weaning (i.e., approximately 6 mo of age) for 112 d for serum concentrations of metabolic hormones and glucose, growth, and reproductive traits. Performance data and blood sera were collected on d 0, 28, 56, 84, and 112. Sera were also collected in periods from d 50 to 59 (56D) and 103 to 112 (112D). Angus bulls were heavier (P < 0.05) throughout the study than Brahman bulls and were heavier than Brangus bulls on d 56, 84, and 112. Initial and final BW for Angus, Brangus, and Brahman bulls were 292.7, 260.6, and 230.4 and 468.3, 435.6, and 350.7 +/- 12 kg, respectively. Conversely, Brahman bulls had greater hip height (P < 0.05) than Brangus, and Brangus were taller (P < 0.05) than Angus. Angus bulls had the greatest (P < 0.05) scrotal circumference (SC) and Brahman bulls the least. Mean SC across days was 31.5, 29.7, and 25.0 +/- 0.6 cm for the three respective breeds. Serum testosterone was greater (P < 0.01) in Angus and Brangus bulls (10.0 and 8.9 +/- 1.4 ng/mL) than in Brahman bulls (4.0 +/- 1.4 ng/mL) throughout the study. After d 112, 100, 86, and 57% of the Angus, Brangus, and Brahman bulls passed a breeding soundness exam (P = 0.51). Serum concentrations of IGF-I and leptin were greater (P < or = 0.06) in Angus bulls on d 56, 84, and 112 than in Brangus and Brahman bulls. Serum concentrations of GH (P < 0.08) and glucose (P < 0.03) were greater in Brangus bulls than in Angus or Brahman bulls throughout the study. Prediction analyses suggested that serum concentrations of leptin could be used to predict (P < or = 0.08) BW and SC (R2 > 0.82) in the 56D and 112D periods among these breeds. Leptin was also useful in predicting (P < or = 0.09) serum concentrations of GH and testosterone in the 112D period (R2 > 0.32). Residual correlation analyses with the effect of breed removed suggested that leptin was correlated (r > or => 0.53, P < 0.05) with both SC and serum testosterone. Angus and Brahman cattle differ in phenotype, level of adiposity, and rate of sexual development. Data herein suggest that these characteristics could be due to varying mechanisms by which metabolic hormones such as leptin, GH, and(or) IGF-I are regulated.     

Breed effects and heterosis in advanced generations of composite populations for puberty and scrotal traits of beef cattle

Heterosis effects were evaluated in F1, F2, and F3 generations of females and in the F1, F2, and combined F3 and F4 generations of males in three composite populations of beef cattle. Traits included weight, height, and condition scores at different ages, percentage of females reaching puberty at 368, 410, and 452 d, adjusted age, and adjusted weight of females at puberty and scrotal circumference and paired testicular volume of males. Breed effects were evaluated for the nine parental breeds (Red Poll [R], Hereford [H], Angus [A], Limousin [L], Braunvieh [B], Pinzgauer [P], Gelbvieh [G], Simmental [S], and Charolais [C]) that contributed to the three composite populations (MARC I = 1/4 C, 1/4 B, 1/4 L, 1/8 H, 1/8 A; MARC II = 1/4 G, 1/4 S, 1/4 H, 1/4 A; and MARC III = 1/4 R, 1/4 P, 1/4 H, 1/4 A). Breed effects were significant for all traits evaluated. Heterosis was significant for weight, height, and condition score at all ages and for most measures of puberty in each generation of each composite and for the mean of the three composite populations. Heterosis for age at puberty was largely independent of heterosis effects on 368-d weight. Heterosis was significant for scrotal circumference and paired testicular volume in each generation of each composite and for the mean of the three composite populations. Heterosis effects on scrotal measurements are mediated both through heterosis effects on growth rate and through factors that are independent of growth rate. Correlation coefficients among breed group means and correlations of breed rank for scrotal measurements with puberty traits of females were greater than or equal to .88 (P less than .01) for all puberty traits except weight at puberty, which was not associated with scrotal measurements. There was close agreement in heterosis observed for most traits and expectation based on retained heterozygosity. These results support the hypothesis that heterosis in cattle for size, puberty, and scrotal measurement traits is due to dominance effects of genes.     

Biological type effects on gestation length, calving traits and calf growth rate

Gestation length, birth weight calving difficulty, calf mortality rate at birth, calf mortality rate from birth to weaning, preweaning calf growth rate and calf 200-d weight were evaluated in a biological type study in which four sire breeds were bred by AI to Hereford dams. Angus and Red Poll sires represented breeds of medium size, and Pinzgauer and Simmental sires represented large breeds. Angus and Pinzgauer represented breeds with medium milk production, and Red Poll and Simmental represented breeds with high milk production. Dams mated to large sire breeds had longer (P less than .01) gestation lengths (.95 d) and higher calving difficulty scores than dams mated to medium-sized sire breeds. Calves from large sire breeds had heavier birth weight (P less than .01) and 200-d wt (6.1 kg; P less than .01) than calves from medium-sized sire breeds. Calf death loss and ADG to weaning were similar (P greater than .10) for all breeds of sire. Calves from the higher milk level sire breeds exceeded the medium-milk breeds in birth weight (1.3 kg; P less than .01) but did not (P greater than .10) in other traits. Calves from the higher milk level sire breeds exceeded the medium-milk breeds in birth weight (1.3 kg; P less than .01) but not (P greater than .10) in other traits. Interaction between size and milk production of sire breed existed for gestation length, birth weight, ADG from birth to weaning and 200-d calf weight (P less than .01). In general, mature size of sire breed was a good indication of expected performance traits not easily influenced by environment. Not all differences, however, could be explained by size and milk production of the size breed.     

Characterization and validation of bovine gonadotripin releasing hormone receptor (GNRHR) polymorphisms

Gonadotropin releasing hormone and its receptor (GNRHR) play a critical role in sexual differentiation and reproduction. Available evidence shows a strong genetic component in the timing of puberty. In bovines, there are significant differences within and among beef breeds in the time when bulls reach puberty. Despite its economic importance, there are not many SNPs or genetic markers associated with this characteristic. The aims of the study were to identify DNA polymorphism in the bovine GNRHR by re-sequencing analysis, determine haplotype phases, and perform a population study in a selected tag SNP in six breeds. Eight SNPs were detected, including: one in the Upstream Regulatory Region (URR), five in the coding regions, and two in non-coding regions. This polymorphism level corresponds to one variant every 249.4 bp and a global nucleotide diversity of 0.385. Two haplogroups comprising nine haplotypes and two linkage blocks were detected. Despite 5 tag SNPs were required to capture all variability, just one SNP allowed to define both haplogroups, and only two SNPs were needed to differentiate the most common haplotypes. An additional taq SNP was necessary to identify both URR variants. Allele-frequency analysis of a selected taq SNP among breeds showed a geographical cline. European Bos taurus breeds had lower frequencies of the C allele than B. indicus type cattle, while Creole cattle and Wagyu breeds had intermediate frequency. There was a significant correlation between frequency profile and timing of puberty among the studied breeds, which seems to suggest that genetic variation within bovine GNRHR gene could explain at least part of the reported variability.