Heritability of testicular size and consistency in Holstein bulls

Considerations for Using Natural Service with Estrous Synchronization Programs

Estrous synchronization, coupled with natural service, provides the benefit of female cows conceiving early, but there are an increased number of females expressing estrus in a short period of time. Thus, considerations need to be made for the bull. Select a protocol that will distribute estrus over a longer period of time and ensure bulls pass a breeding soundness examination. Mature bulls (3 years old or older) have increased efficiency in getting cows pregnant compared with younger bulls; therefore, a ratio of 1 mature bull to 25 cows is a good recommendation within an estrous synchronized herd.

Environmental Factors Affecting the Reproductive Efficiency of Italian Simmental Young Bulls

The objectives of the study aimed to evaluate the effect of weather conditions and scrotal circumference (SC) on standard semen characteristics of Italian Simmental young bulls (n = 577), all raised in the same performance station and sampled by the artificial vagina (AV) method. Considering the increasing SC, the results showed a significant increase in quantitative semen parameters (p < 0.05 and p < 0.0001, for sperm concentration and total number of spermatozoa, respectively); for every extra centimeter of SC, 17.5 × 106 spermatozoa/mL and 0.102 × 109 of total spermatozoa were produced. The age of the animal at semen collection (395 and 465 days) had similar positive effects. The effect of the average temperature humidity index (THI limits ≤ 40 and ≥70) in the previous 60, 30, and 10 days before the semen collection was also considered. Sixty days before the semen collection, the increasing THI increased both primary (p < 0.0001) and secondary (p < 0.0001) abnormalities while the percentage of morphologically normal spermatozoa decreased (p < 0.0001). Thirty and ten days before collection, the same effect on morphological traits was maintained, but total and progressive motility was also influenced (p < 0.01) with an unexpected increasing pattern. Thus, environmental conditions can influence semen quality during the entire spermatogenesis and results can guide future research on this breed.

Genome-wide association for testis weight in the diversity outbred mouse population

Testis weight is a genetically mediated trait associated with reproductive efficiency across numerous species. We sought to evaluate the genetically diverse, highly recombinant Diversity Outbred (DO) mouse population as a tool to identify and map quantitative trait loci (QTLs) associated with testis weight. Testis weights were recorded for 502 male DO mice and the mice were genotyped on the GIGAMuga array at ~ 143,000 SNPs. We performed a genome-wide association analysis and identified one significant and two suggestive QTLs associated with testis weight. Using bioinformatic approaches, we developed a list of candidate genes and identified those with known roles in testicular size and development. Candidates of particular interest include the RNA demethylase gene Alkbh5, the cyclin-dependent kinase inhibitor gene Cdkn2c, the dynein axonemal heavy chain gene Dnah11, the phospholipase D gene Pld6, the trans-acting transcription factor gene Sp4, and the spermatogenesis-associated gene Spata6, each of which has a human ortholog. Our results demonstrate the utility of DO mice in high-resolution genetic mapping of complex traits, enabling us to identify developmentally important genes in adult mice. Understanding how genetic variation in these genes influence testis weight could aid in the understanding of mechanisms of mammalian reproductive function.

Genetic parameters and relationships between growth traits and scrotal circumference measured at different ages in Nellore cattle

Records from 106,212 Nellore animals, born between 1998 and 2006, were used to estimate (co)variance components and genetic parameters for birth weight (BW), average weight gains from birth to weaning (GBW), average weight gains from weaning to after yearling (GWAY), weaning hip height (WHH), postweaning hip height (PHH) and scrotal circumferences at 9 (SC9), 12 (SC12) and 15 (SC15) months of age. (Co)variance components were estimated by an animal model using multi-trait analysis. Heritability estimates for BW, GBW, GWAY, WHH, PHH, SC9, SC12 and SC15 were 0.31 ± 0.01; 0.25 ± 0.02; 0.30 ± 0.04; 0.51 ± 0.04; 0.54 ± 0.04; 0.39 ± 0.01; 0.41 ± 0.01 and 0.44 ± 0.02, respectively. Genetic correlations between growth traits ranged from 0.09 ± 0.01 to 0.88 ± 0.01, thereby implying that, at any age, selection to increase average weight gains will also increase stature. Genetic correlations between BW and average weight gains with scrotal circumferences were all positive and moderate (0.15 ± 0.03 to 0.38 ± 0.01). On the other hand, positive and low genetic associations were estimated between hip height and scrotal circumference at different ages (0.09 ± 0.01 to 0.17 ± 0.02). The results of this study pointed out that selection to larger scrotal circumferences in males will promote changes in average weight gains. In order to obtain Nellore cattle with the stature and size suitable for the production system, both weight gain and hip height should be included in a selection index.

Breeding soundness examination of Chianina, Marchigiana, and Romagnola yearling bulls in performance tests over a 10-year period

The objectives of the present study were (i) to establish the mean value of scrotal circumference (SC), sperm motility, concentration and morphology at 13+/-1 months of age for Chianina, Marchigiana, and Romagnola breeds and (ii) to assign Italian beef bulls at the end of a growth performance test to a potential breeder category by applying the guidelines of the Society for Theriogenology in 1993 (SFT93). Of 1,315 bulls, 869 were not given the breeding soundness examination for the following reasons: not passing the growth performance test (n=445), no training for semen collection (n=404), and presence of genital abnormalities (n=20). Testicular length and diameter and SC exhibited a logarithmic trend over time, with an R(2) value of 0.963, 0.979, and 0.978 (P<0.001), respectively. The SC of Romagnola (33.82+/-2.47 cm) was higher than those of Chianina (33.28+/-2.65 cm, P<0.001) and Marchigiana (33.05+/-2.20 cm, P<0.001). Sperm concentration in Romagnola (875.89+/-416.13x10(6)cells/mL) was higher than those in Chianina (751.63+/-444.45 x 10(6)cells/mL, P<0.05) and Marchigiana (862.57+/-421.87 x 10(6) cells/mL). Progressive sperm motility was 61.30+/-11.24%, 62.18+/-11.17%, and 58.48+/-14.40% in Romagnola, Marchigiana, and Chianina, respectively. Total spermatozoal abnormalities were higher in Chianina (23.35+/-15.41%). Sperm concentration was positively related to testicular length (P<0.01), diameter (P<0.001), and SC (P<0.001). Satisfactory breeders presented high sperm motility compared with deferred and unsatisfactory ones, whereas unsatisfactory breeders had a higher number of abnormal spermatozoa. By applying the SFT93 guidelines, we showed that 74.72%, 78.01%, and 80.16% of Chianina, Marchigiana, and Romagnola bulls, respectively, have been classified as satisfactory potential breeders.

Fertility estimation: a review of past experience and future prospects

Fertility has many components and stages which require that males and females be functionally capable of carrying out all critical stages if each generational reproductive cycle is to be completed. To accomplish this, the male must produce and ejaculate normal fertile sperm. The female must produce, store and ovulate normal fertilizable oocytes. Furthermore, the female must provide a reproductive system compatible with sperm transport, capacitation, and fertilization of the oocytes, embryo and fetal development, and finally birth of healthy young. Reproductive success or failure at several of these points can be estimated quantitatively on a population basis, and in a few situations on an individual basis. It is important that fertility estimates be determined accurately and with precision to be most useful to researchers and managers of animal enterprises. Many studies have underestimated the biological relationship of fertility to other traits because the estimates lacked precision. Many in vitro manipulations of sperm in artificial insemination, of gametes in various assisted reproductive technologies, and of embryos in embryo transfer are utilized in animal breeding programs. Accurate estimation of reproductive efficiency of these in vitro procedures also is important. Conditions surrounding different sets of fertility estimates almost certainly will be different. These conditions should be described as precisely as possible, and appropriate controls included in all experiments. When possible, experiments should be replicated over time and place to determine the repeatability of the various criteria used to estimate fertility and reproductive efficiency. Advances in genomic information and molecular biology should facilitate characterizing more fully inherent potential fertility of animals at birth. In vitro tests will improve, and automated techniques will facilitate making multiple determinations possible on a large scale. Reliability of fertility estimates will increase, with the potential for enhanced animal reproductive performance through more accurate selection, genetic engineering, and enlightened animal care. Simultaneously, it is important to recognize that prediction of future fertility is more hazardous than estimating fertility, as a completely new set of circumstances may occur which are not predictable. Because fertility estimation may be applied under a myriad of conditions, principles and factors affecting fertility will be emphasized in this review as being more useful than a compilation of numerical examples.

Evolution of ejaculates: patterns of phenotypic and genotypic variation and condition dependence in sperm competition traits

Sperm competition is widely recognized as a potent force in evolution, influencing male behavior, morphology, and physiology. Recent game theory analyses have examined how sperm competition can influence the evolution of ejaculate expenditure by males and the morphology of sperm contained within ejaculates. Theoretical analyses rest on the assumption that there is sufficient genetic variance in traits important in sperm competition to allow evolving populations to move to the evolutionarily stable equilibrium. Moreover, patterns of genotypic variation can provide valuable insight into the nature of selection currently acting on traits. However, our knowledge of genetic variance underlying traits important in sperm competition is limited. Here we examine patterns of phenotypic and genotypic variation in four sperm competition traits in the dung beetle Onthophagus taurus. Testis weight, ejaculate volume, and copula duration were found to have high coefficients of additive genetic variation (CV(A)S), which is characteristic of fitness traits and traits subject to sexual selection. Heritabilities were high, and there was some evidence for Y-linked inheritance in testis weight. In contrast, sperm length had a low CV(A), which is characteristic of traits subject to stabilizing selection. Nevertheless, there was little residual variance so that the heritability of sperm length exceeded 1.0. Such a pattern is consistent with Y-linked inheritance in sperm length. Interestingly, we found that testis weight and sperm length were genetically correlated with heritable male condition. This finding holds important implications for potential indirect benefits associated with the evolution of polyandry.

Reproductive characteristics of Ethiopian highland sheep. II. Genetic parameters of semen characteristics and their relationships with testicular measurements in ram lambs

A study was conducted to investigate the effect of season on, and to estimate heritabilities of, and genetic correlations among, semen and spermatozoa characteristics and the relationship of these characteristics with measures of testicular or scrotal size in 6-, 9- and 12-month old ram lambs of Menz and Horro sheep breeds indigenous to Ethiopian highlands. A total of 278 ram lambs with substantial pedigree information were involved in the study. There was improvement in all semen and spermatozoa traits with age, the means at 12 months being consistently superior to values at 6 and 9 months of age. There were no significant breed differences in any of the traits studied, except semen volume at 9 months (0.67, S.E. 0.07 for Horro versus 0.39, S.E. 0.05ml for Menz) and proportion of dead spermatozoa at 12 months (0.18, S.E. 0.03 versus 0.23, S.E. 0.02, respectively). Season was significant (p<0.05) for most of the traits studied, and differences were attributed primarily to nutrition. Semen collected in the wet season had higher spermatozoa concentration while samples collected in the dry season had higher proportion of abnormalities. After correcting for differences in total spermatozoa abnormalities, the wet season (of collection) had the highest spermatozoa output (volumexconcentration) in 12-month old ram lambs. Heritability estimates varied substantially in magnitude, ranging from zero to over 0.4. Traits with non-trivial heritability estimates were mass motility at 9 months (0.32, S.E. 0.11), individual motility at 9 months (0.32, S.E. 0.12) and at 12 months (0.16, S.E. 0.12) and proportion of abnormal spermatozoa at 9 months (0.35, S.E. 0.13). Genetic correlations among semen and spermatozoa characteristics, as well as correlations with testicular measurements, were medium to high and generally favourable, but were associated with large standard errors. The genetic correlations of scrotal circumference with semen volume (0.55, S.E. 0.11), mass motility (0.62, S.E. 0.20), individual motility (0.54, S.E. 0.12), concentration (0.25, S.E. 0.04) and proportion of abnormal spermatozoa (-0.75, S.E. 0.24) in 12-month old rams indicated that selection based on this trait, which is highly heritable and easy to measure and can be measured early in life, should have appreciable favourable correlated response in semen quality and spermatozoa production.

Reproductive characteristics of Ethiopian highland sheep. I. Genetic parameters of testicular measurements in ram lambs and relationship with age at puberty in ewe lambs

A study was conducted to estimate heritabilities of, and genetic correlations among, body weight (WT) and testicular measurements - scrotal circumference (SC), testicular diameter (TD), testicular length (TL) and epididymal diameter (ED) - in ram lambs between 6, 9 and 12 months old, and relationship of the testicular traits with age at puberty in ewe lambs (AP). Two fat-tailed sheep breeds, the Horro and Menz, indigenous to the Ethiopian highlands were studied. Experimental lambs were produced by mating 250 oestrus-synchronized ewes of each breed to 10 sires in a single-sire mating system over three mating periods which produced, for this study, a total of 361 ram lambs and 148 ewe lambs, with substantial pedigree information, in two dry seasons (October/November 1992 and 1993) and one wet season (June/July 1993). Mean AP was 322.7 days. Breed was not significant (P0.05) for all testicular measurements, except ED at 9 months for which the Horro had a higher (P<0.01) value (20.6, s.e. 0.38 versus 19.3 s.e. 0.30). Horro ewe lambs had their first oestrus 28 days earlier (P<0.05) than the Menz. Heritability estimates were obtained from a sire model (M1) and from an individual animal model with additive direct and maternal effects (M2). The maternal effect was not fitted in M2 for AP. Repeatability and heritability estimates were also obtained by analysing records at the three ages in a repeated measures model (M3). M1 and M2 heritability estimates were generally low to moderate but were associated with large standard errors. Heritability estimates for testicular measurements were generally similar to those for WT. Among the testicular measurements, SC had the highest heritability estimates at 6 (0.45, s.e. 0.24 for M1) and at 12 months (0.41, s.e. 0.21 and 0.41, s.e. 0.20 for M1 and M2, respectively). Model 3 heritability estimates were 0.29 (s.e. 0.14), 0.24 (s.e. 0.12), 0.09 (s.e. 0.07), 0.11 (s.e. 0.08) and 0.12 (s.e. 0.08) for WT, SC, TD, TL and ED, respectively. Only repeatability estimates for WT (0.34, s.e. 0.02) and SC (0.25, s.e. 0.03) were significant. Heritability of AP was estimated at 0.16 (s.e. 0.21) by M1 and 0.14 (s.e. 0.19) by M2. Genetic correlations of AP with testicular measurements, especially with SC (-0.57, s.e. 0.38 and -0.78, s.e. 0.33, at 9 and 12 months, respectively) and TD (-0.72, s.e. 0.33 and -0.83, s.e. 0.48), were desirable and generally high. Adjustment of testicular measurements for liveweight consistently resulted in a reduction in estimates of heritability and genetic correlations. SC was suggested as the most appropriate selection candidate for the genetic improvement of both male and female reproductive performance in these breeds.

Correlated response in reproductive and life history traits to selection on testis length in Drosophila hydei

Flies in the genus Drosophila have undergone striking evolutionary divergence in the size and number of sperm produced. Based on comparative studies of sperm length, testis length, and other reproductive and life history traits, including body size, age at first reproduction, and the number of sperm produced, macroevolutionary trade-offs resulting from the need to produce high-investment testes have been postulated. To understand better the microevolutionary processes underlying these interspecific patterns, we imposed replicated bidirectional selection for testis length for 11-12 generations on D. hydei, a species with 23.5 mm-long sperm and 30 mm-long testes. Testis length exhibited realized heritabilities ranging from 0.45 to 0.72. Following selection, traits were assayed for correlated responses. Thorax length, testis mass, sperm length, egg-to-adult development time, and posteclosion maturation time showed consistent positive correlated responses. Numbers of sperm produced and transferred to females, male longevity, female egg productivity, and seminal receptacle length did not show consistent correlated responses to selection on testis length. The pattern of correlated responses to testis length reveal the potential for the evolution of reproductive strategies to alter important life history attributes.

Estudo preliminar da influência do perímetro escrotal sobre a libido em touros jovens da raça Nelore

O perímetro escrotal (PE) de 202 touros jovens da raça Nelore, sem experiência sexual prévia, classificados pela Associação Brasileira de Criadores de Zebu como superiores ou elite, foi medido aos 7, 12, 18 e 28 meses de idade, aproximadamente. Após a última medição, eles foram submetidos ao teste de libido e procedeu-se à colheita de sêmen por eletroejaculação, seguida de avaliação andrológica. As medidas do PE aos 7, 12, 18 e 28 meses foram de 18,30; 22,29; 27,54 e 33,26cm, respectivamente. Os coeficientes de correlação simples entre estas medidas variaram de 0,35 a 0,53. O coeficiente de correlação entre PE aos 28 meses e peso corporal na mesma idade foi de 0,43. A correlação entre a nota da libido e o perímetro escrotal medido aos l8 meses foi de 0,15 e entre aquela e o perímetro escrotal aos 28 meses foi de 0,13. Observou-se elevado crescimento do perímetro escrotal entre o 7º e 18º meses de idade. Utilizou-se o método de quadrados mínimos para analisar a libido, incluindo ano de nascimento como efeito fixo e como covariáveis os efeitos lineares da idade e peso no momento da avaliação e medidas de perímetro escrotal aos 7, l2, l8 e 28 meses. Cada covariável foi retida de forma seqüencial obtendo-se vários modelos de análises e as somas de quadrados foram decompostas de forma seqüencial e parcial. O ano de nascimento, a idade e o perímetro escrotal aos 18 meses de idade afetaram significativamente a libido. Os coeficientes de correlação entre a libido e concentração espermática, motilidade, peso e idade do animal no momento da avaliação foram de 0,34, 0,l6, 0,38 e 0,35, respectivamente.

Breeding soundness evaluation of extensively managed bulls in Costa Rica

This paper describes the results of single breeding soundness evaluations (BSE) in 898 Bos indicus, Bos taurus and B. indicus x B. taurus bulls, 1 to 12 yr old, extensively reared in different climatic regions of Costa Rica and representing approximately 2% of the total breeding bull population. Thirty-three percent (n = 296) of the bulls were classified as unsound for breeding owing to clinical problems (9.1%, n = 82), low scrotal circumference (SC) being the most common finding, followed by unsatisfactory sperm morphology (23.9%, n = 214). The prevalence of bulls unsound for breeding was lowest in Bos indicus (29%, P < 0.01), intermediate in B. taurus (41%), and highest in B. indicus x B. taurus (48%). The percentages of abnormal sperm heads, acrosomes and midpieces tended to be higher in the ejaculates of bulls with softer testicular consistency (P < 0.001), a long scrotum (P < 0.01) or a low SC (P < 0.05), and such bulls were more often classified as being unsound for breeding (P < 0.05). Frequencies of sperm abnormalities were higher in bulls < 2 yr of age than in older males (P < 0.01) and were highest in B. indicus x B. taurus bulls (P < 0.001). The results confirm differences between species in their adaptability to a tropical environment and support earlier evidence of an association between SC, testicular consistency and scrotal length clinical parameters, and testicular function in bulls.

Breeding soundness evaluation of yearling bulls

Breeding Soundness Evaluations (BSEs) are a useful tool to improve reproductive performance and profitability in beef herds. Veterinarians providing this service must be thorough in their evaluation, especially in yearling bulls. The 1993 Society for Theriogenology guidelines for BSE provide appropriate standards for classifying yearling bulls; veterinarians are advised to adhere to these standards as minimums for classification of the satisfactory potential breeder.

The relationship between scrotal circumference and quantitative testicular traits in yearling beef bulls

A study was designed to investigate relationships between testicle size and histological, sperm production and endocrinological traits in yearling beef bulls at the end of performance test. Twenty-five beef bulls, (Hereford, n=16; Angus, n=4; and Charolais, n=5), with scrotal circumference (SC) measurements ranging from 28.5 to 36.0 cm, were used. Just prior to slaughter at 15 mo of age, SC measurements were taken, semen was collected, and a GnRH response test was conducted. Testicles were processed for daily sperm production (DSP), epididymal sperm reserves (ESR), seminiferous epithelial area (SEA), and degree of germinal epithelial loss (DGEL). There were significant positive correlations between SC and testicular weight (P<0.05), DSP/g (P<0.02), and DSP/bull (P<0.01) and ESR (P<0.01); however, the correlation between SC and SEA was not significant (P=0.4). Scrotal circumference was negatively correlated with DGEL (P<0.05). Degree of germinal epithelial loss was also negatively correlated with DSP/g, DSP/bull and ESR (P<0.01). Morphological characteristics of spermatozoa were diversely related to sperm production traits, and the percentage of normal spermatozoa was positively related to SC (P<0.02) and negatively related to DGEL (P<0.001). Gonadotropin releasing hormone stimulation did not reveal evidence of gonadotropin deficiency in any of the bulls. However, peak testosterone levels were lower in bulls with SC below 31 cm (P<0.05) than those with SC measurements above 31 cm.

Nutrition and the development of replacement heifers

Does the system work? After having been on a controlled heifer replacement program for 3 to 5 years, the entire herd will develop a short calving season resulting in more weaned calf weight per cow exposed to breeding. Wiltbank has reported on the advantage of feeding heifers for a selected target weight at breeding. Two groups of Brahman-cross heifers were fed to weigh 600 or 700 lbs at the beginning of the breeding season. They were pastured and fed similarly from breeding through weaning their first calves. The heifers that weighted 700 lb at breeding weaned 86 lb more calf per heifer exposed. They bred earlier and more became pregnant. The return above feed costs after 2 years breeding was $52 greater for the heavier heifers. Obviously, the benefits continue through subsequent calvings, emphasizing the importance of managing the replacement heifers for 3 years, through their second breeding and calving.

Environmental and genetic sources of variation for seminal quality in mature Holstein bulls

Various environmental and genetic factors that influence seminal quality were evaluated for 149 Holstein bulls used extensively in nine artificial insemination organizations (studs). These bulls were sons of 16 sires. Seminal quality was measured by percent progressive motility immediately postthaw and after incubation at 3 h, 37 degrees C, percent intact acrosomal membrane after incubation at 3 h 37 degrees C, and percent primary and secondary abnormalities. Semen was thawed at 37 and 24 degrees C. Spermatozoal concentration was counted with a hemocytometer. Bull age and season of collection were determined. Interaction of stud X thaw existed for both motility assessments and intact acrosomes, but 37 degrees C thaw resulted in higher motility and acrosomal integrity across all studs. Motility at zero hour was affected by season. Secondary abnormalities were influenced by season and stud X season. Interaction of thaw X season existed for incubated motility, which also was influenced by concentration and age. Age influenced secondary abnormalities. Heritabilities and repeatabilities (%) were .21, 44; .40, 34; .81, 74; and .31, 50 for 0-h motility, intact acrosomes, primary abnormalities, and secondary abnormalities. Genetic correlations were 0-h motility with acrosomal integrity and primary and secondary abnormalities, .88, -.70, -.93; acrosomal integrity with primary and secondary abnormalities, -.90, -.05; primary with secondary abnormalities, -.12. Selection for semen quality could improve fertility of bulls.

Considerations in multiple trait evaluation

Traits of dairy cattle known to contribute to genetic merit are discussed briefly. Focus is on alternative measures and research to reflect more closely genetic pathways of performance because knowledge is expanding about cellular, organ, and animal function. Improved measurement of physiological traits of economic characters portends increased genetic control of animal productivity by considering more alternative traits. Research should clarify multiple trait selection programs to maximize profit. The null hypothesis to test is that selection for milk is optimal index selection for milk income and costs of production.

Maximizing the impact of dairy and beef bulls through breeding technology

Both biological and monetary considerations influence adoption of new breeding technologies. Therefore, genetic, reproductive, and economic factors that determine productivity of dairy and beef operations are reviewed. Improved sire evaluation programs, more efficient artificial insemination, and effective natural service are discussed and related to the present and future impact of dairy and beef bulls. Potential benefits of heterosis, artificial control of reproduction, improved bull management, computers, and multidiscipline research also are suggested. The dramatic impact of artificial insemination on genetic improvement and profitability of most commercial dairy herds is outlined. The uncertain expansion of beef artificial insemination is examined. Comparisons of dairy and beef industries indicate that expectation of similar results from the same animal breeding technologies are unwarranted. Dairy artificial insemination is and should continue to be economically feasible for commercial operations. Commercial beef producers will use little artificial insemination and rely on natural service bulls until precise human control of conception in the bovine is cost effective.