Selection based on the Breeding Soundness Evaluation is associated with the improvement of the reproductive quality of young Nellore bulls

Breeding soundness evaluation (BSE) is the best methodology to estimate the fertility potential of future bulls and performing indirect selection for their fertility. However, the outcome of the BSE is influenced by several factors, including genetics, environment, and BSE guidelines. Herein, in this retrospective study, our first aim was to characterize the reasons for failure in 46,566 BSE from 2-year-old beef Bos indicus bulls (Nellore) born from 1997 to 2018. Our second aim was to determine whether or not BSE was associated with reproductive potential improvement of the bulls over the years. Due to changes in the BSE criteria, we used the same dataset, but only bulls born from 2002 to 2018 were included resulting in 35,856 BSE. For the second aim, the effect of the year and farm were included in the model of the multivariate logistic regression. We also determined if the main reasons for BSE failure decreased over time. Bulls were classified as approved (satisfactory potential breeders and qualified for natural breeding service) and not approved (deferred and unsatisfactory potential breeders). The reasons for BSE failure in Nellore bulls were poor semen quality (53.1 %) and physical defects (46.9 %), with the main physical defect being testis abnormalities (19.7 %). The overall percentage of bulls approved each year was 87.1 %, with no improvement over the years of study. However, the percentage of approved bulls at the first BSE increased over the years (P < 0.05). This increase was evident by a reduction in the difference between the overall percentage of the bulls approved vs the percentage of bulls approved at the first BSE. Furthermore, there was an increase in the percentage of bulls classified as satisfactory potential breeders in the BSE and an evident decrease in the percentage of bulls qualified only for natural breeding service (P < 0.05). In addition, an increase of the scrotal circumference (SC) of the herd was found (P < 0.05). These results indicate the overall quality of the bulls improved over the years. To associate and identify the main sperm abnormalities, 3461 not approved bulls were clustered. The most frequent defects were strongly coiled tail spermatozoa, proximal droplets, and acrosomal defects. Overall, there was no change in the frequency of bulls not approved by the sperm morphology nor the frequency of the main sperm abnormalities over the years. Nevertheless, the frequency of the defects remained very low, implying they were controlled. Additionally, abnormalities in the testis decreased over the years and was associated with the increase in the SC of the herd and a decrease of culled bulls due to low SC. In conclusion, this study demonstrates that there is an association between implementation and use of BSE with improvements in the reproductive quality of future generation bulls.

Genetic Parameters of Semen Traits and Their Correlations with Conformation Traits in Chinese Holstein Bulls

The elite bull plays an extremely important role in the genetic progression of the dairy cow population. The previous results indicated the potential positive relationship of large scrotal circumference (SC) with improved semen volume, concentration, and motility. In order to improve bull's semen quantity and quality by selection, it is necessary to estimate the genetic parameters of semen traits and their correlations with other conformation traits such as SC that could be used for an indirect selection. In this study, the genetic parameters of seven semen traits (n = 66,260) and nine conformation traits (n = 3,642) of Holstein bulls (n = 453) were estimated by using the bivariate repeatability animal model with the average information-restricted maximum likelihood (AI-REML) approach. The results showed that the estimated heritabilities of semen traits ranged from 0.06 (total number of motile sperm, TNMS) to 0.37 (percentage of abnormal sperm, PAS) and conformation traits ranged from 0.23 (pin width, PW) to 0.69 (hip height, HH). The highest genetic correlations were found between semen volume per ejaculation (SVPE), semen concentration per ejaculation (SCPE), total number of sperm (TNS), and TNMS traits that were 0.97, 0.98, 1.00, and 0.99, respectively. Phenotypic correlations between SC and SVPE, SCPE, TNS, and TNMS were 0.35, 0.35, 0.48, and 0.42, respectively. In summary, the moderate or high heritability of semen traits indicates that genetic improvement of semen quality by selection is feasible, where SC could be a useful trait for indirect selection or as correlated information to improve semen quantity and production in the practical bull breeding programs.

Genetic parameters for yearling male reproduction traits in tropical composite cattle population

Fertility is economically important but is hard to quantify and measure in breeding programs which has led extensive breeding programs to ignore fertility in their selection criteria. While female fertility traits have been extensively researched, male fertility traits have been largely ignored. It is estimated that 20% to 40% of bulls have sub-fertility, reducing the number of calves born and profits, highlighting the importance of investigating bull fertility. The most practical measure of male fertility is a bull breeding soundness evaluation (BBSE) which assesses structure as well as semen quality and quantity. Generally, traits recorded in a BBSE are neither genetically evaluated nor used for selection in breeding programs. All traits recorded during a BBSE were analyzed through a series of univariate and bivariate linear mixed models using a genomic relationship matrix to estimate genetic parameters. All genotype and phenotype data were obtained from a tropical composite commercial cattle population and imputed to 27,638 single-nucleotide polymorphisms (SNPs) with a total of 2,613 genotyped animals with BBSE records ranging from 616 to 826 animals depending on the trait. The heritabilities of the 27 traits recorded during a BBSE ranged from 0.02 to 0.49. Seven of the male fertility traits were recommended to be included in a breeding program based on their heritability and their phenotypic and genetic correlations. These traits are scrotal circumference, percent normal sperm, proximal droplets, distal midpiece reflex, knobbed acrosomes, vacuoles/teratoids, and sheath score. Using these seven traits in a breeding program would result in higher calving rates, increasing production and profitability.

Development of a RAPD marker-based classification criterion for quality semen production in Holstein crossbred bulls

In cattle production systems, an intense selection pressure for production traits has resulted in the decline of fertility traits. To optimize an efficient reproduction system, the inclusion of both male and female fertility traits in the selection process is very much essential. RAPD (Random Amplified Polymorphic DNA) was developed as a molecular biology tool and has been extensively used, to study intra- and interspecific genetic diversity. The present study was undertaken to utilize RAPD primers to investigate the association between DNA markers and semen quality traits viz. Sperm concentration, total sperm count ejaculate and initial sperm motility and thereby to identify good/poor semen producers. DNA isolated from the blood samples of healthy bulls was subjected to RAPD-PCR. The multiple regression analysis followed by independent t test was carried out to identify suitable markers. Based on the results, only 12 bands were identified as marker suitable for any of the quality trait. This includes, OPA2 ~ 760, OPA2 ~ 700, OPA6 ~ 1,200, OPA9 ~ 400, OPA9 ~ 380, OPA12 ~ 970, OPA14 ~ 715, OPA14 ~ 605, OPA16 ~ 485, OPA17 ~ 860 and OPA18 ~ 480. Multiple regression analysis selected, OPA2 ~ 760 and OPA2 ~ 1,750 for sperm concentration and OPA2 ~ 760, OPA2 ~ 700, OPA9 ~ 620, OPA4 ~ 670 and OPA18 ~ 1,015 for total sperm count/ejaculate. But the t test revealed a significant association between OPA2 ~ 760 and total sperm count. Further, discriminant function analysis also identified this marker in the first step itself. The results of the present study can be exploited as a low-cost alternative strategy for identification of good /poor semen producers in crossbred bulls at an early age.

Genetic parameter estimation for beef bull semen attributes

Improvements in bull reproductive performance are necessary to optimize the efficiency of cattle production. Female fertility has been enhanced through assisted reproductive technologies as well as genetic selection; however, improving beef bull fertility has been largely ignored. Phenotypes routinely collected at bull semen collection facilities are believed to affect fertility and provide the phenotypes necessary for a genetic evaluation. The first objective of this study was to determine the significant fixed effects for modeling beef bull fertility using data from bull semen collection facilities. The second objective was to estimate variance components, heritabilities, repeatabilities, and correlations between beef bull semen attributes. Beef bull fertility phenotypes including volume (VOL), concentration (CONC), number of spermatozoa (NSP), initial motility (IMot), post-thaw motility (PTMot), 3-h post-thaw motility (3HRPTMot), percentage of normal spermatozoa (%NORM), primary abnormalities (PRIM), and secondary abnormalities (SEC) were obtained from two bull semen collection facilities. A total of 1,819 Angus bulls with 50,624 collection records were analyzed. Of the fixed class and covariate effects tested, the significant class effects were collection location and collection day within year and the significant covariate effects included age at collection, days since previous collection, and cumulative comprehensive climate index (CCI). For this study, the CCI was calculated for a 75-d period including the 61-d spermatogenesis cycle and 14-d epididymal transit time. The 75 d prior to collection accounted for the environmental stress a bull may have experienced over the course of development of the spermatozoa, which was more significant than the CCI calculated for collection day or spermatogenesis start date. Pre-thaw beef bull semen traits had low heritability estimates of 0.11 ± 0.02 (VOL), 0.09 ± 0.02 (CONC), 0.08 ± 0.02 (NSP), and 0.12 ± 0.03 (IMot). Heritabilities of post-thaw beef bull semen attributes were more variable at 0.10 ± 0.02 (PTMot), 0.05 ± 0.04 (3HRPTMot), 0.10 ± 0.04 (%NORM), 0.03 ± 0.03 (PRIM), and 0.18 ± 0.04 (SEC). Correlations of breeding values for these traits with scrotal circumference (SC) expected progeny difference (EPD) are low. The low to moderate heritability estimates indicate that genetic improvement can be made in beef bull semen quality traits if new tools are developed to augment the scrotal circumference EPD that are currently available within the industry.

Selection for bull fertility: a review

Fertility is a critically important factor in cattle production because it directly relates to the ability to produce the offspring necessary to offset costs in production systems. Female fertility has received much attention and has been enhanced through assisted reproductive technologies, as well as genetic selection; however, improving bull fertility has been largely ignored. Improvements in bull reproductive performance are necessary to optimize the efficiency of cattle production. Selection and management to improve bull fertility not only have the potential to increase conception rates but also have the capacity to improve other economically relevant production traits. Bull fertility has reportedly been genetically correlated with traits such as average daily gain, heifer pregnancy, and calving interval. Published studies show that bull fertility traits are low to moderately heritable, indicating that improvements in bull fertility can be realized through selection. Although female fertility has continued to progress according to increasing conception rates, the reported correlation between male and female fertility is low, indicating that male fertility cannot be improved by selection for female fertility. Correlations between several bull fertility traits, such as concentration, number of spermatozoa, motility, and number of spermatozoa abnormalities, vary among studies. Using male fertility traits in selection indices would provide producers with more advanced selection tools. The objective of this review was to discuss current beef bull fertility measurements and to discuss the future of genetic evaluation of beef bull fertility and potential genetic improvement strategies.

Genetics of bull semen characteristics in a multi-breed cattle population

Little is known of the genetic variability in semen quality traits in cattle and their inter-relationships. The objective of the present study was to estimate genetic parameters for a range of semen quality measures. The data consisted of 35,573 ejaculates from 787 artificial insemination bulls of 16 breeds. Genetic parameters were estimated using a repeatability animal linear mixed model. Large breed differences were detected with Belgian Blue bulls, on average, producing lesser semen volume than all other breeds while the Charolais bulls, on average, produced semen with fewer live sperm and reduced motility. The within-breed coefficient of genetic variation for sperm concentration, semen volume and total number of sperm per ejaculate was 0.17, 0.15 and 0.19, respectively. The genetic standard deviation for percentage live sperm pre-cryopreservation was 5.6% units while the genetic standard deviation for progressive motility pre-cryopreservation (scale 0 to 5) was 0.25 units. The heritability of all traits was between 0.13 and 0.34. The repeatability of the semen quality traits varied from 0.22 to 0.45. Sperm concentration and volume were negatively genetically correlated (-0.40) although the phenotypic correlation was near zero (-0.01). The genetic correlations between percentage live sperm and sperm motility varied from 0.68 to 0.94 irrespective of whether the traits were measured pre- or post-cryopreservation or even the change in both traits during cryopreservation. A very strong genetic correlation existed between percentage live sperm pre- and post-cryopreservation (0.96) or sperm motility pre- or post-cryopreservation (0.92). Results highlight the large genetic variability in a range of semen quality traits, many of which are actually highly heritable, and therefore useful predictors of actual phenotypic measures.

Genetic parameters, predictions, and rankings for semen production traits in a Thailand multi-breed dairy population using genomic-polygenic and polygenic models

The objectives were to compare estimates of variance components, genetic parameters, prediction accuracies, and rankings of bulls for semen volume (VOL), number of sperm (NS), and motility (MOT) using genomic-polygenic (GPRM) and polygenic repeatability models (PRM). The dataset comprised 13,535 VOL, 12,773 NS, and 12,660 MOT from 131 bulls collected from 2001 to 2017 in the Semen Production and Dairy Genetic Evaluation Center of the Dairy Farming Promotion Organization of Thailand. Genotypic data encompassed 76,519 actual and imputed SNP from 72 animals. The three-trait GPRM and PRM included the fixed effects of contemporary group, ejaculate order, age of bull, ambient temperature, and heterosis. Random effects were animal additive genetic, permanent environmental, and residual. Variance components and genetic parameters were estimated using AIREMLF90. GPRM heritabilities were slightly greater than PRM for MOT (0.27 compared with 0.24), and slightly less for VOL (0.11 compared with 0.12), and NS (0.17 compared with 0.19). Repeatabilities were slightly less for GPRM than PRM (0.44 compared with 0.45 for MOT, 0.26 compared with 0.28 for NS, and 0.20 compared with 0.21 for VOL). Additive genetic correlations were high between NS and MOT (GPRM: 0.76, PRM: 0.78), moderate between VOL and NS (GPRM: 0.43, PRM: 0.55), and near zero between VOL and MOT (GPRM: -0.13, PRM: 0.04). Rank correlations between GPRM and PRM estimated breeding values (EBV) were high for all traits. The similarity between GPRM and PRM results suggested that SNP data from the small number of genotyped animals had a minimal impact on genetic predictions in this population.

Genetic analyses on bodyweight, reproductive, and carcass traits in composite beef cattle

In beef cattle, growth, reproductive, and carcass traits have been studied for improving productivity and quality of meat products. The aim of this study was to estimate genetic parameters for birth (BW), weaning (WW) and yearling (YW) weights, scrotal circumferences at weaning (SCW) and yearling (SCY), age at first calving (AFC), ribeye area (REA) and back fat thickness (BFT) in order to provide support for the evaluation program of the composite Canchim breed. Data on 12 967 (BW), 7481 (WW), 5131 (YW), 1447 (SCW), 1224 (SCY), 1400 (AFC), and 2082 (REA and BFT) animals were analysed using the Average Information Restricted Maximum Likelihood method under an animal model (single and multi-trait analyses). A substantial proportion of the variation in the bodyweights, scrotal circumferences and carcass traits was associated with the additive genetic term indicating that these traits may respond to the selection process. For AFC, a low heritability estimate was observed. Genetic correlations among bodyweights varied from 0.41 to 0.93. The genetic correlation among scrotal circumferences was 0.91. Important genetic correlations among YW, SCW, and SCY with AFC were observed (–0.48, –0.61, and –0.71, respectively), indicating that indirect responses to selection for these traits would be expected in the age of which the heifers calve. Furthermore, BFT presented an interesting result with calving performance due to the genetic correlation (–0.69) with AFC. Post-weaning weights showed moderate genetic correlations with REA. Many of the traits considered in the genetic evaluation of this breed are genetically correlated in a favourable manner. Genetic improvement through selection is expected for production, reproduction, and carcass traits in Canchim beef cattle.

Parameter estimates for reproductive and carcass traits in Nelore beef cattle

The aim of this study was to estimate genetic parameters for scrotal circumference at 365 (SC365) and 450 (SC450) days of age, age at first calving (AFC), ribeye area (REA), backfat (BF) thickness, and rump fat (RF) thickness, in order to provide information on potential traits for Nelore cattle breeding program. Genetic parameters were estimated using the Average Information Restricted Maximum Likelihood method in single- and multitrait analyses. Four different animal models were tested for SC365, SC450, REA, BF, and RF in single-trait analyses. For SC365 and SC450, the maternal genetic effect was statistically significant (P < 0.01) and was included for multitrait analyses. The direct heritability estimates for SC365, SC450, AFC, REA, BF, and RF were equal to 0.31, 0.38, 0.24, 0.32, 0.16, and 0.19, respectively. Maternal heritability for SC365 and SC450 was equal to 0.06 and 0.08, respectively. The highest genetic correlations were found among the scrotal circumferences. Testing for the inclusion of maternal effects in genetic parameters estimation for scrotal circumference should be evaluated in the Nelore breeding program, mostly for correctly ranking the animal's estimated breeding values. Similar heritability estimates were observed for scrotal circumference, as well as favorable genetic correlations of this trait with AFC and carcass traits. Thus, scrotal circumference measured at 365 days of age could be a target trait for consideration in the Nelore selection index in order to improve most of the traits herein analyzed.

Differences between reproductive traits in beef bulls used for multiple-sire breeding under range conditions

Brauner, C. C., Menezes, L. M., Lemes, J. S. and Pimentel, M. A. 2014. Differences between reproductive traits in beef bulls used for multiple-sire breeding under range conditions. Can. J. Anim. Sci. 94: 647–652. The aim of this study was to evaluate the reproductive traits (scrotal circumference and semen quality) of different breeds of beef bulls used for multiple-sire breeding under range conditions, as well as to verify the relation between four sperm concentration scores and the reproductive traits of beef bulls. Two hundred and one bulls of three different breeds (Angus, Nelore and Brangus) and three different age groups (18, 24 and 36 mo old) were evaluated. Angus showed better (P>0.05) reproductive traits than Brangus and Nelore bulls, in which scrotal circumference, mass motility spermatozoa, motility spermatozoa, as well as spermatic vigor were greater than those of other breeds. Two-year-old bulls demonstrated better reproductive traits as compared with the other age groups. The sperm concentration score had a linear effect (P<0.01) on all reproductive traits evaluated, and the same evidence was also detected for body weight. It was concluded that genetic groups should be considered differently for multiple-sire breeding under range conditions, especially because Bos taurus and Bos indicus have significant reproductive trait differences. Moreover, the sperm concentration score can be used as an auxiliary method of semen quality in beef bulls, having a positive relation with other breeding soundness evaluation traits.

Male traits and herd reproductive capability in tropical beef cattle. 2. Genetic parameters of bull traits

A total of 4063 young bulls of two tropical genotypes (1639 Brahman and 2424 Tropical Composite) raised in northern Australia were evaluated for a comprehensive range of production and reproduction traits up to 24 months of age. Prior to weaning, peripheral blood concentrations of luteinising hormone (LH) and inhibin were measured at 4 months of age. At weaning (6 months) blood insulin-like growth factor-1 (IGF-I) and flight time were recorded. Body composition traits of fat depth and eye-muscle area were determined by ultrasonography at 15 months of age when additional measurements of liveweight, hip height and body condition score were recorded. Bull breeding soundness was evaluated at ~12, 18 and 24 months of age when measurements of scrotal circumference, sheath score, semen mass activity, progressive motility of individual sperm and percent morphologically normal sperm were recorded. Magnitude of heritability and genetic correlations changed across time for some traits. Heritability of LH, inhibin, IGF-I and of 18-month scrotal circumference, mass activity, progressive motility and percent normal sperm was 0.31, 0.74, 0.44, 0.75, 0.24, 0.15 and 0.25, respectively, for Brahmans and 0.48, 0.72, 0.36, 0.43, 0.13, 0.15 and 0.20, respectively, for Tropical Composites. Inhibin and IGF-I had moderate genetic association with percent normal sperm at 24 months in Brahmans but low to negligible associations in Tropical Composites. Body condition score in Brahmans and sperm motility (mass and individual) traits in both genotypes had moderate to strong genetic correlation with percent normal sperm and may prove useful candidates for indirect selection. There is scope to increase scrotal circumference by selection and this will be associated with favourable correlated responses of improved semen quality in both genotypes. The lack of genetic antagonism among bull traits indicates that selection for improved semen quality will not adversely affect other production traits.

Polymorphisms of mitochondrial ATPase 8/6 genes and association with milk production traits in Holstein cows

The maternal effect has been widely proposed to affect the production traits in domestic animals. However, the sequence polymorphisms of mitochondrial DNA (mtDNA) and association with milk production traits in Holstein cows have remained unclear. In this study, we investigated the single nucleotide polymorphisms (SNPs) of mtDNA ATPase 8/6 genes and association with four milk production traits of interest in 303 Holstein cows. A total of 18 SNPs were detected among the 842 bp fragment of ATPase 8/6 genes, which determined six haplotypes of B. taurus (H1-H4) and B. indicus (H5-H6). The mixed model analysis revealed that there was significant association between haplotype and 305-day milk yield (MY). The highest MY was observed in haplotype H4. However, we did not detect statistically significant differences among haplotypes for the traits of milk fat (MF), milk protein (MP), and somatic cell count (SC). The overall haplotype diversity and nucleotide diversity of ATPase 8/6 genes were 0.563 ± 0.030 and 0.00609 ± 0.00043, respectively. The results suggested that mitochondrial ATPase 8/6 genes could be potentially used as molecular marker to genetically improve milk production in Holstein cows.