The Effect of Sperm Morphology and Sire Fertility on Calving Rate of Finnish Ayrshire AI Bulls

Good‐quality semen is a prerequisite for successful and profitable artificial insemination (AI) of modern dairy cattle. Fertility of the bulls is evaluated with andrological examinations and semen analyses, such as morphology. However, little attention has been paid to the inheritance of bull fertility. In this study, we correlated sperm morphology, birth year and station of 695 AI bulls with calving rate (CR). Sperm morphology was clearly associated with CR underlining the usefulness of morphological examination in the assessment of fertility. The correlation between the proportion of normal spermatozoa and CR was significant (p < 0.001). No significant differences were detected between stations or birth years. We also compared the CR of 695 AI bulls with the CR of their 27 sires to study the inheritance of fertility. Sire's CR did not correlate with the CR of the sons (p = 0.218). This result indicates that at least when sires of acceptable CR are used to produce sons for use in AI the inheritance of CR is not significantly correlated.     

Functional insulin‐like factor 3 (INSL3) hormone‐receptor system in the testes and spermatozoa of domestic ruminants and its potential as a predictor of sire fertility

Insulin‐like factor 3 (INSL3) is essential for fetal testis descent, and has been implicated in the testicular and sperm functions in adult males; however, similar functions in domestic ruminants remain largely unknown. This study investigated the functional INSL3 hormone‐receptor system in adult ruminant testes and spermatozoa, and explored its potential to diagnose the fertility of sires. Testes and spermatozoa were obtained from fertile bulls, rams and he‐goats, whereas subfertile testes and spermatozoa were obtained only from bulls. As expected, INSL3 was visualized in Leydig cells, while we clearly demonstrated that the functional receptor, relaxin family peptide receptor 2 (RXFP2), enabling INSL3 to bind was identified in testicular germ cells and in the sperm equatorial segment of bulls, rams and he‐goats. In comparison to fertile bulls, the percentage of INSL3‐ and RXFP2‐expressing cells and their expression levels per cell were significantly reduced in the testes of subfertile bulls. In addition, the population of INSL3‐binding spermatozoa was also significantly reduced in the semen of subfertile bulls. These results provide evidence for a functional INSL3 hormone‐receptor system operating in ruminant testes and spermatozoa, and its potential to predict subfertility in sires.     

Post mortem studies on infertile buffalo bulls: testicular histology

Testicular tissues of 22 buffalo bulls (Bubalus bubalis) which suffered from three types of infertility were examined histologically. Nine bulls with no sexual libido showed underdeveloped seminiferous tubules; five of them also had various forms of germinal tissue hypoplasia (bilaterally complete, partial or incomplete) and in the other four the seminiferous tubules showed developed layers of germinal epithelium but no complete spermiogenesis. Among 11 bulls which had always produced poor quality semen one suffered from incomplete bilateral testicular hypoplasia and two had simple testicular degeneration; five showed marked testicular degeneration associated with fibrosis of intertubular spaces, and in three there was intertubular fibrosis and tubular stasis. In two bulls in which the quality of semen had deteriorated one showed bilateral partial testicular hypoplasia and the other had bilateral testicular degeneration with unilateral intertubular fibrosis and tubular stasis.     

Clinical and anatomical studies on the scrotal and pelvic genitalia of Sokoto Gudali bulls in Northern Nigeria.

The scrotal and pelvic genitalia from 2400 Sokoto Gudali bulls aged three to five years were studied clinically (by ante mortem palpation and measurement) and anatomically (by direct examination and measurement of the post mortem material). In general the difference between the mean clinical and anatomical measurements was not significant (at the 5 per cent level). Gross abnormalities observed included: testicular degeneration, 60 bulls (2.5 per cent); orchitis, 48 bulls (2.0 per cent); testicular hypoplasia, 35 bulls (1.45 per cent); epididymitis, 37 bulls (1.54 per cent); spermatic granuloma, two bulls (0.08 per cent); seminovesiculitis, 43 bulls (1.79 per cent); scrotal stryptortrichosis, 126 bulls (5.25 per cent). Lesions had no seasonal pattern and occurred randomly throughout the year.     

Evaluation of fertility and infertility in natural service bulls

The potential fertility of bulls can be evaluated in the field by assessment of mating ability and physical examination. Both methods are useful for screening out low fertility bulls, although neither allows precise determination of the pregnancy rates that bulls actually achieve. Observations of coitus, libido testing and service capacity testing are the main methods of assessing mating ability in the field and, although not reliable for virgin bulls, are widely used for older bulls. Of the traits that are assessed during physical examination, those most closely correlated with fertility are scrotal circumference and the semen quality parameters of motility and morphology. Whilst these methods allow reasonable accuracy in determining the fertility potential of an individual bull, they do not take into account other managemental constraint to bulls' fertility. Although these are reasonable well understood for beef herds, the managemental factors that affect the performance of natural service sires in dairy herds are poorly understood.     

CONGENITAL AND DEVELOPMENTAL ANOMALIES OF THE GENITALIA OF SLAUGHTERED BULLS

The genital tracts of 968 slaughtered bulls (46% of which were young post-puberal animals) were examined for defects of a congenital or developmental nature. The overall occurrence of such lesions was 7%. These comprised persistent penile frenulum (0.5%), hypospadias (0.3%), detached urethral process (0.4%), testicular hypoplasia (0.2%), cryptorchidism (0.6%), mesonephric duct abnormalities (1.1%) and bulbourethral cysts, fusion and aplasia (3.6%). Segmental aplasia of the mesonephric duct, not previously recorded in the study area, was found in 4 Shorthorn bulls (0.4%); 2 affected animals were from one herd. In 3 cases of hypospadias (2 from one herd), the urethra communicated with the ventral surface of the penis at the junction of the body and glans through a slit-like orifice. The occurrence of defects observed was generally comparable to that found in bull populations elsewhere but elevated occurrence of several defects in particular herds emphasized the need for further study.     

DNA-based paternity analysis and genetic evaluation in a large, commercial cattle ranch setting

Deoxyribonucleic acid-based tests were used to assign paternity to 625 calves from a multiple-sire breeding pasture. There was a large variability in calf output and a large proportion of young bulls that did not sire any offspring. Five of 27 herd sires produced over 50% of the calves, whereas 10 sires produced no progeny and 9 of these were yearling bulls. A comparison was made between the paternity results obtained when using a DNA marker panel with a high (0.999), cumulative parentage exclusion probability (P(E)) and those obtained when using a marker panel with a lower P(E) (0.956). A large percentage (67%) of the calves had multiple qualifying sires when using the lower resolution panel. Assignment of the most probable sire using a likelihood-based method based on genotypic information resolved this problem in approximately 80% of the cases, resulting in 75% agreement between the 2 marker panels. The correlation between weaning weight, on-farm EPD based on pedigrees inferred from the 2 marker panels was 0.94 for the 24 bulls that sired progeny. Partial progeny assignments inferred from the lower resolution panel resulted in the generation of EPD for bulls that actually sired no progeny according to the high-P(E) panel, although the Beef Improvement Federation accuracies of EPD for these bulls were never greater than 0.14. Simulations were performed to model the effect of loci number, minor allele frequency, and the number of offspring per bull on the accuracy of genetic evaluations based on parentage determinations derived from SNP marker panels. The SNP marker panels of 36 and 40 loci produced EPD with accuracies nearly identical to those EPD resulting from use of the true pedigree. However, in field situations where factors including variable calf output per sire, large sire cohorts, relatedness among sires, low minor allele frequencies, and missing data can occur concurrently, the use of marker panels with a larger number of SNP loci will be required to obtain accurate on-farm EPD.     

Comparative performance of straightbred and crossbred (F1) sires

The first phase of this study was the production of contemporary straightbred (SB) and reciprocal crossbred (F1) bulls by mating Angus (A) bulls to A and Santa Gertrudis (SG) cows and SG bulls to SG and A cows. Of the bulls produced during the 4-yr period, those used for breeding included 15 A, 15 SG, 8 A X SG and 8 SG X A. For 205-d weight and weight/day of age (W/DA) postweaning, A X SG had higher (P less than .05) performance than SG X A bulls and SG had higher (P less than .05) performance than A bulls. There was no difference (P greater than .05) between SG and A X SG for 205-d weight, postweaning average daily gain (ADG) or postweaning W/DA. Heterosis estimates were 5.2 (P less than .10), 9.9 (P less than .01) and 5.8% (P less than .01) for 205-d weight, postweaning ADG and W/DA, respectively. The second phase of this study was the comparison of SB and F1 bulls for reproductive and progeny performance by exposing them as yearlings to 25 Polled Hereford cows each. There were no differences (P greater than .05) among the four sire groups for proportion of cows exposed that had a calf, had a live calf or weaned a calf. Reproductive performance of sires also was evaluated in terms of number of days (NOD) from the beginning of the breeding period until calves were born. The NOD for calves by SG was greater (P less than .05) than for calves by A or F1 sires. Compared with calves from SB sires, the NOD for calves from A X SG and SG X A sires were 5.0 and 10.6 d (P less than .05) lower. Differences among sires within year and breeding of sire were significant for all preweaning traits and for W/DA postweaning of their progeny. The SG-sired calves were heavier (P less than .05) for birth and 205-d weight and had higher (P less than .05) postweaning ADG than A-sired calves. Mean performance of calves by reciprocal F1 sires did not deviate (P greater than .05) from the mean performance of those by SB sires. Calves by A X SG sires had higher (P less than .05) 205-d weight, postweaning ADG and W/DA than calves by SG X A sires. Results indicated that the primary genetic effects responsible for differences in performance of calves sired by F1 vs SB bulls were mean transmitted and mean heterotic effects.(ABSTRACT TRUNCATED AT 400 WORDS)     

Relationship between testicular measurements, body weight and semen quality in young dairy bulls.

Dairy bulls, 322 Ayrshires (Ay) and 85 Friesians (Fr), were studied at the age of 11 months. Of the bulls, 286 Ay-bulls and 80 Fr-bulls produced semen of acceptable quality for use in A.I. Scrotal circumference, tonometer measure, scrotal fold thickness, 1-year body weight and testicular palpation were used to predict unsuitable bulls for A.I. Non-return rate was used as a measure of fertility. Scrotal fold thickness and 1-year weight had no significant correlation with fertility or semen quality. Scrotal circumference had a significant positive correlation with fertility. Tonometer ratio had a significant negative correlation with fertility. Testicular palpation was the best basis for predicting bulls with poor semen quality in this study. Twelve bulls were recorded as having testicles of different sizes, 1 testicle being more than 20% bigger than the other. Only 2 of these 12 bulls produced semen of acceptable quality. One of these 2 bulls was, after slaughter, diagnosed as having a hereditary testicle disease. Friesians were shown to have significantly higher fertility than Ayshires.     

Efficacy of methods used to test fertility of beef bulls used for multiple-sire breeding under range conditions

A study was conducted during the 1982, 1983 and 1984 breeding seasons with 277 crossbred bulls, 1 to 3 yr of age, that were evaluated for physical soundness, testicular development, seminal quality, and both sexual and social behavior immediately before exposure to crossbred cow herds ranging in size from 89 to 329 cows. Crossbred cow herds were exposed to 4 to 24 bulls per breeding group (mean of 14) at a mean female: male ratio of 21.2 +/- .6:1 under extensive range conditions for 31 to 62 d (mean 46.6 d). All resulting calves were blood-typed to determine the number of calves sired by each bull as an estimate of his fertility. The mean number of calves sired by 1- (n = 116), 2- (n = 126) and 3-yr-old (n = 35) bulls was 4.7 +/- .1, 8.2 +/- .1 and 10.5 +/- .1, respectively. A regression model for predicting bull fertility under multiple-sire, range breeding conditions was selected that accounted for 29% of the total variance in fertility. Similar models accounted for a greater proportion of variance in fertility of 1-yr-old (37%) than of 2-yr-old bulls (22%). Due to the large amount of unexplained variation, the model could not predict individual bull fertility precisely. However, this study demonstrated that selection of herd sires with large scrotal circumference, low backfat thickness, low levels of primary sperm defects, and a low number of mounts in combination with a moderate number of services during libido testing would be expected to improve fertility of beef bulls used under extensive range conditions.     

The crossbred sire: experimental results for sheep

Crossbreeding of sheep is practiced to exploit simultaneously the use of additive and nonadditive genetic effects. The goal is to achieve optimal levels of performance appropriate for defined systems of sheep production and marketing. Although the beneficial effects of individual and maternal heterosis on sheep production have been well documented and widely implemented, considerably less is known about the effects of paternal heterosis. Limited evidence suggests that crossbred rams are more sexually aggressive and exhibit greater testicular growth than do purebred rams. Average estimates of paternal heterosis effects were 1.4, -.7 and 2.3% for seasonal fertility, prolificacy and preweaning survival, respectively. The average effect of paternal heterosis on fertility during spring breeding was 29.5%. Progeny of crossbred and purebred sires were similar in birth weight, weaning weight and postweaning growth rate and in phenotypic variation for these growth traits. However, favorable paternal heterosis effects need not exist to warrant the use of crossbred sires. Composite or F1 sires can be used as an effective method to manage the composition of additive breed effects. For example, varying proportions of germ plasm from highly prolific breeds such as the Finnsheep and Romanov can be realized through the use of crossbred sires to set reproductive rates at desired levels. Crossbred sires may be used to a greater extent to optimize additive breed effects than to exploit effects of paternal heterosis. The role of composite breeds in managing both additive and nonadditive effects is discussed.     

Testicular traits as selection criteria for young Nellore bulls

The objective of this study was to evaluate the possible use of biometric testicular traits as selection criteria for young Nellore bulls using Bayesian inference to estimate heritability coefficients and genetic correlations. Multitrait analysis was performed including 17,211 records of scrotal circumference obtained during andrological assessment (SCAND) and 15,313 records of testicular volume and shape. In addition, 50,809 records of scrotal circumference at 18 mo (SC18), used as an anchor trait, were analyzed. The (co)variance components and breeding values were estimated by Gibbs sampling using the Gibbs2F90 program under an animal model that included contemporary groups as fixed effects, age of the animal as a linear covariate, and direct additive genetic effects as random effects. Heritabilities of 0.42, 0.43, 0.31, 0.20, 0.04, 0.16, 0.15, and 0.10 were obtained for SC18, SCAND, testicular volume, testicular shape, minor defects, major defects, total defects, and satisfactory andrological evaluation, respectively. The genetic correlations between SC18 and the other traits were 0.84 (SCAND), 0.75 (testicular shape), 0.44 (testicular volume), -0.23 (minor defects), -0.16 (major defects), -0.24 (total defects), and 0.56 (satisfactory andrological evaluation). Genetic correlations of 0.94 and 0.52 were obtained between SCAND and testicular volume and shape, respectively, and of 0.52 between testicular volume and testicular shape. In addition to favorable genetic parameter estimates, SC18 was found to be the most advantageous testicular trait due to its easy measurement before andrological assessment of the animals, even though the utilization of biometric testicular traits as selection criteria was also found to be possible. In conclusion, SC18 and biometric testicular traits can be adopted as a selection criterion to improve the fertility of young Nellore bulls.     

Growth, puberty, and carcass characteristics of Brahman-, Senepol-, and Tuli-sired F1 Angus bulls

Postweaning growth, sexual development, libido, and carcass data were collected from two consecutive calf crops using 31 Brahman x Angus (B x A), 41 Senepol x Angus (S x A), and 38 Tuli x Angus (T x A) F1 bulls. Following weaning (by mid-September) and preconditioning, at the start of the study (late September) bulls were fed concentrate (three times each week at a rate equivalent to 4.5 kg/d) on bahiagrass pasture for approximately 250 d. At the start of the study and at 28-d intervals, BW, hip height, and scrotal circumference (SC) were measured. Concurrently at 28-d intervals, when the SC of a bull was > or = 23 cm, semen collection was attempted using electroejaculation. Ejaculates were evaluated for presence of first spermatozoa (FS), 50 x 10(6) sperm with at least 10% motility (PU), and 500 x 10(6) sperm with at least 50% motility (PP). After all bulls reached PP they were subjected to two libido tests. Carcass data were collected on all bulls (n = 110) and Warner-Bratzler shear (WBS) force values were assessed on a subset (n = 80). For both years, B x A bulls were heavier (P < 0.05) and taller (P < 0.05) than S x A and T x A bulls at the start and end of the study. However, breed type did not influence (P > 0.10) gain in BW or hip height during the study. Scrotal circumference of T x A bulls was larger (P < 0.05) than that of B x A or S x A bulls at the start of the study, but there was no effect (P > 0.10) of breed type by the end of the study. At PU and PP, B x A bulls were older (P < 0.05), heavier (P < 0.05), and taller (P < 0.05) and had larger (P < 0.05) SC than S x A and T x A bulls. Tuli x Angus bulls were younger (P < 0.05) than S x A bulls at PU and PP but had similar SC. Libido scores tended (P < 0.10) to be lower for B x A than for S x A and T x A bulls. Breed type affected (P < 0.05) carcass traits; B x A bulls had the heaviest (P < 0.05) hot carcass weight, greatest (P < 0.05) dressing percentage, larger (P < 0.05) longissimus muscle area than S x A bulls, and higher (P < 0.05) USDA yield grade than T x A bulls but greatest (P < 0.05) WBS force values. Breed type did not affect (P > 0.10) USDA quality grade. In conclusion, tropically adapted F1 bulls produced from Senepol (Bos taurus) and Tuli (Sanga) sires bred to Angus cows in Florida had lighter BW, shorter hip heights, and smaller carcasses than those from Brahman sires but reached puberty earlier and had higher libido scores and lower WBS force values.     

Responses to Selection against Clinical Mastitis in the Norwegian Cattle Population

The genetic trend for clinical mastitis was estimated for Norwegian Cattle, a population in which mastitis resistance has been included in the breeding programme since 1978. More than 1.2 million first-lactation daughters, with clinical mastitis records registered from 1978 to 1995, bred by 2043 sires, were analysed with a linear sire model. For bulls born from 1974 to 1990 a flat genetic trend for clinical mastitis was found. However, bull sires born from 1983 onwards, selected on a breeding goal with increased weight on mastitis relative to milk production, showed consistently larger and favourable selection differentials for mastitis relative to bull sires born earlier, which had an average selection differential of approximately zero. This will influence genetic trend in the population through their sons, which were born from 1990 onwards.     

Responses to Selection against Clinical Mastitis in the Norwegian Cattle Population

The genetic trend for clinical mastitis was estimated for Norwegian Cattle, a population in which mastitis resistance has been included in the breeding programme since 1978. More than 1.2 million first-lactation daughters, with clinical mastitis records registered from 1978 to 1995, bred by 2043 sires, were analysed with a linear sire model. For bulls born from 1974 to 1990 a flat genetic trend for clinical mastitis was found. However, bull sires born from 1983 onwards, selected on a breeding goal with increased weight on mastitis relative to milk production, showed consistently larger and favourable selection differentials for mastitis relative to bull sires born earlier, which had an average selection differential of approximately zero. This will influence genetic trend in the population through their sons, which were born from 1990 onwards.     

Acute BRSV Infection in Young AI Bulls: Effect on Sperm Quality

Bovine respiratory syncytial virus (BRSV) infection is an important part of the calf pneumonia complex, occasionally affecting even adult cattle. However, the pathogenicity of BRSV in animals older than 6 months is often neglected. Finland is free of many contagious diseases in farm animals, and this gives a good opportunity to study the effects of specific pathogens on bovine reproduction. This report describes the deteriorating effects of BRSV epizootics on sperm morphology and fertility of young dairy bulls (n = 79) at a bull station. More than half of the young bulls had a clinical respiratory disease caused by BRSV during their quarantine when they were 6 months old. Four of seven subsequent quarantine groups were affected. Six months later, when these seropositive bulls (n = 54) came into semen production, they had poorer sperm morphology, and the proportion of normal spermatozoa was 74.1% in BRSV-seropositive animals compared with 81.2% in seronegative bulls (n = 25) (p = 0.035). Field fertility was also slightly affected, the 60-day non-return rates were 75.2% and 76.8% for BRSV seropositive and seronegative bulls respectively (p = 0.014). Potential reasons for lowered sperm quality are discussed here.     

Pathophysiology of small testes in beef bulls: relationship between scrotal circumference, histopathologic features of testes and epididymides, seminal characteristics, and endocrine profiles

Tissue sections from testes and epididymides obtained from 17 young beef bulls with scrotal circumference (SC) between 27 and 40.5 cm were studied to determine whether small testes were a manifestation of lesions or a result of less, but otherwise normal, seminiferous epithelium. The SC correlated negatively with the estimates of germinal epithelial loss and positively with seminiferous epithelial area. Four bulls with SC less than 30 cm had severe lesions in their testes. Hypoplastic tubules were characterized by Sertoli's cells only with no evidence of germinal cells. Loss of germinal cells, leaving vacuolated epithelium and atrophy, were observed in degenerated tubules. Hyperplasia of Leydig's cells was observed in the vicinity of Sertoli's cell-only tubules, resulting either from degeneration or hypoplasia, and atrophy of Leydig's cells was associated with tubules devoid of Sertoli's cells. These findings indicated that Sertoli's cells may produce a factor(s) required for maintenance and regulation of Leydig's cell function. Epididymal epithelium, especially in the head, had regressed in bulls with hypoplastic and degenerative changes in their testes. Decreased sperm concentration and motility and an increased frequency of morphologic defects were observed in the 4 bulls with testicular lesions and regressed epididymal epithelium. Blood plasma profiles of cortisol, follicle-stimulating hormone, luteinizing hormone, and testosterone were determined in the 4 bulls with SC less than 30 cm and 10 of the 13 bulls with SC greater than 30 cm. There were no statistically significant (P greater than 0.1) differences in the responses to exogenous gonadotropin-releasing hormone or base-line patterns of blood plasma follicle-stimulating hormone and luteinizing hormone between the 2 groups. However, in the bulls with SC less than 30 cm, the mean concentration of testosterone was lower, whether spontaneous (P less than 0.05) or exogenous gonadotropin-releasing hormone induced (P less than 0.1). The fact that these bulls were not deficient in gonadotropins indicated that Leydig's cell function was impaired by local factors, either the factors that caused the tubular damage or those consequent to the tubular damage.     

Comparative proteomic analysis of high‐ and low‐fertile buffalo bull spermatozoa for identification of fertility‐associated proteins

The present study identified few potential proteins in the spermatozoa of buffalo bulls that can be used as an aid in fertility determination through comparative proteomics. The sperm proteome of high‐fertile buffalo bulls was compared with that of low‐fertile buffalo bulls using two‐dimensional difference gel electrophoresis (2D‐DIGE), and the differentially expressed proteins were identified through mass spectrometric method. The protein interaction network and the functional bioinformatics analysis of differentially expressed proteins were also carried out. In the spermatozoa of high‐fertile bulls, 10 proteins were found overexpressed and 15 proteins were underexpressed at the level of twofold or more (p ≤ 0.05). The proteins overexpressed in high‐fertile spermatozoa were PDZD8, GTF2F2, ZNF397, KIZ, LOH12CR1, ACRBP, PRSS37, CYP11B2, F13A1 and SPO11, whereas those overexpressed in low‐fertile spermatozoa were MT1A, ATP5F1, CS, TCRB, PRODH2, HARS, IDH3A, SRPK3, Uncharacterized protein C9orf9 homolog isoform X4, TUBB2B, GPR4, PMP2, CTSL1, TPPP2 and EGFL6. The differential expression ranged from 2.0‐ to 6.1‐fold between the two groups, where CYP11B2 was high abundant in high‐fertile spermatozoa and MT1A was highly abundant in low‐fertile spermatozoa. Most of the proteins overexpressed in low‐fertile spermatozoa were related to energy metabolism and capacitation factors, pointing out the possible role of pre‐mature capacitation and cryo‐damages in reducing the fertility of cryopreserved buffalo spermatozoa.     

A genetic analysis of the concentrations of blood metabolites and their relationships with age and liveweight gain in young British Friesian bulls

Blood samples were taken from 428 young British Friesian bulls, the sons of 72 sires, between 3 and 15 months of age. The concentrations of blood glucose and haemoglobin and serum cholesterol, urea, albumin, globulin, inorganic phosphate, Ca, Mg, Na, K and Cu were measured and correlated with age and growth rate.Most of the constituents showed highly significant but small changes in concentration with age. The largest changes occurred in the concentrations of urea, albumin and haemoglobin which increased as bulls reached maturity. The concentrations of urea, albumin and globulin were also lower and concentrations of glucose, inorganic phosphate, Ca and K higher than usually occur in older cattle.Highest estimates of heritability, based on the mean of 3 samples, were for K and globulin (> 0.6) and for haemoglobin, cholesterol, inorganic phosphate, Cu and glucose (0.4–0.6). Phenotypic correlations between 0.2 and 0.4 occurred with growth rate for albumin and glucose between 24 and 35 weeks and with body weight for albumin between 27 and 50 weeks of age; however, the phenotypic correlations with average growth rate up to 53 weeks were only 0.15 and 0.07 for albumin and glucose, respectively. Genetic correlations with growth rate were also determined, but standard errors were large.     

Genetic characterisation of the mithun (Bos frontalis) and studies of spermatogenesis, blood groups and haemoglobins of its hybrids with Bos indicus

The mithun (Bos frontalis) and its hybrids with Bos indicus were studied to provide further cytogenetic information which might throw light on the mechanisms of the male hybrid infertility and facilitate the establishment of a stable crossbreed. It was shown that compared with conventional cattle the mithun has a homozygous, species specific 2/27 centric fusion which reduced the diploid chromosome number from 60 to 58. This provided further proof that Robertson translocation-type rearrangements have been the major source of interspecies karyotype differences in the evolution of the Bovidae. In the mithun there was also significant polymorphism between centromeres of non-homologous chromosomes and there was heteromorphism between several homologous chromosomes which could possibly serve as useful genetic markers for breeding programmes. In F1 hybrids spermatogenesis progressed to a relatively advanced stage, without going so far as to produce spermatozoa. In back crosses to B indicus spermatogenesis progressed further so that spermatozoa could be seen, though not as numerous as in normal bulls. In most hybrids there were haemoglobin bands which corresponded either to Hb A or Hb B of cattle but were much wider. It was shown that these were a combination of Hb Mi derived from the mithun and Hb A or Hb B derived from B indicus. In a few hybrids there were only Hb Mi. In these cases Hb Mi had been present in both parents and proved that the dam was not a pure siri. The possible mechanism of hybrid male infertility is discussed including faults in the epistatic gene effect between chromosomes and changes in the degree of association of centromeric regions in interspecies hybrids. It is suggested that additional cytogenetic examination of blood lymphocytes and especially of testicles would help the understanding of the fertility barriers of hybrid males and would make a breeding programme for a stable crossbreed possible.