Breed and other effects on reproductive traits and breeding soundness categorization in young beef bulls in Florida

Yearling, grass-fed, beef bulls at the USDA Subtropical Agricultural Research Station, Brooksville, Florida, were assessed for physical and semen traits in January, April, July and October of 1991 (Trial 1) and 1992 (Trial 2). Bulls were given a breeding soundness evaluation (BSE) using revised semen and scrotal circumference (SC) criteria. In Trial 1, the bulls consisted of Angus (n = 15), Brahman (n = 14), Hereford (n = 15) and Senepol (n = 14). In Trial 2, the breeds were Angus (n = 15), Brahman (n = 16), Romosinuano (n = 13) and Nellore x Brahman (n = 9). Trial bulls generally showed delayed growth compared with grain-fed bulls in temperate environments. Breed influenced semen traits (percentage sperm motility, normal spermatozoa and those with primary abnormalities) in both trials. Temperate Bos taurus breeds (Angus, Hereford) were generally superior to Bos indicus breeds (Brahman, Nellore x Brahman). Tropically-adapted Bos taurus breeds (Senepol, Romosinuano) were intermediate for those traits tested. In general, tropically-adapted Bos taurus breeds were more similar in reproductive development to temperate Bos taurus than to Bos indicus breeds. Breed by test period interactions occurred and were mainly influenced by delayed sexual maturity of Bos indicus bulls. Qualitative semen traits increased with bull age, particularly from 12 to 18 mo. Scrotal circumference development was slower in the Bos indicus breeds. Bulls of satisfactory BSE status at 18.1 to 22 mo of age were 73.9% in Trial 1 and 58.5% in Trial 2. Brahman bulls had the least satisfactory BSE scores in both years (Trial 1, 44.4%; Trial 2, 22.2%). Most bulls failed to achieve satisfactory BSE status due to a small SC relative to age (Trial 1, 66%; Trial 2, 72%). The most efficacious use of the BSE was > or = 15 mo in Bos taurus bulls and > 18 mo for Bos indicus bulls. Although the BSE has proven to be useful for the assessment of young, pasture-raised bulls in semi-tropical environments, use of SC thresholds linked more with growth traits than with calendar age would improve comparisons of relative reproductive development in such bulls, particularly those of Bos indicus derivation.     

Growth and reproductive development from weaning through 20 months of age among breeds of bulls in subtropical Florida

To determine the effect of breed on growth and reproductive development, weaned bulls in each of 2 yr were managed as a single group for approximately a year. In Year 1, the study group consisted of 24 Angus, 24 Brahman, 20 Hereford and 14 Senepol bulls, while in Year 2, it contained 25 Angus, 17 Brahman. 13 Romosinuano and 9 Nellore x Brahman bulls. Body and testicular growth measurements were recorded at 6-wk intervals. At approximately 1 yr of age and quarterly thereafter (4 periods), bulls were evaluated for libido, pubertal status, and GnRH-induced LH and testosterone secretion. Significant breed-by-age interactions occurred for most growth measurements. Brahman bulls (Bos indicus ) were (P < 0.05) older and heavier at puberty than Angus, Hereford, Senepol and Romosinuano bulls (Bos taurus ). Libido scores were lowest for Brahman and Nell ore x Brahman bulls (Bos indicus ). highest for Angus and Hereford bulls (temperate Bos taurus breeds) and intermediate for Senepol and Romosinuano bulls (tropical Bos taurus breeds; P < 0.05). Differences were not consistent among breeds or between years for GnRH-induced LH secretion. In both years, basal testosterone concentrations and areas under the GnRH-induced testosterone curve were higher (P < 0.05) for Angus and Hereford bulls (temperate breeds) than for Brahman, Senepol, Romosinuano and Nellore x Brahman bulls (tropical breeds). In conclusion, reproductive development of Senepol and Romosinuano bulls (tropical Bos taurus breeds) was more similar to Angus and Hereford bulls (temperate Bos taurus breeds) than to Brahman and Nellore x Brahman bulls (Bos indicus ).     

Effects of scrotal insulation on sperm production,semen quality,and testicular echotexture in Bos indicus and Bos indicus x Bos taurus bulls

The objectives of the present study were to evaluate the effects of scrotal insulation on sperm production, semen quality, and testicular echotexture in Bos indicus and Bos indicus x Bos taurus crossbred bulls. In one experiment, B. indicus bulls (n=12) were allocated to control and whole-scrotum insulation groups, while in a second experiment, crossbred bulls (n=21) were allocated into control, whole-scrotum, and scrotal-neck insulation groups. Insulation was applied for 4 days (start of insulation = Day 0) and semen collection and testicular ultrasonographic examinations were performed twice weekly until Day 35. Sperm concentration and total sperm output during the post-insulation period were greater in control groups, but significant differences were observed only in B. indicus bulls. Overall, sperm motility in scrotal-insulated B. indicus bulls was lower (P<0.05) than in the control group. After whole-scrotum insulation in crossbred bulls, sperm motility was lower (P<0.05) than pre-insulation levels between Days 21 and 31, and lower than control levels on Day 24. The proportion of normal sperm after whole-scrotum insulation was lower than pre-insulation and control values from Day 11 to the end of the experiment in B. indicus bulls (P<0.05 from Days 14 to 21 and on Day 27), and from Days 14 to 25 in crossbred bulls (P<0.05 on Days 14 and 18). Insulation of the scrotal neck in crossbred bulls did not significantly affect semen quality. Loose sperm heads (Day 11), midpiece defects (Days 11 and 14), and acrosome defects (Days 27 and 31) increased (P<0.05) in insulated B. indicus bulls, while proximal cytoplasmic droplets (Days 14, 18 and 27 in B. indicus; Days 24 and 27 in crossbred bulls) and sperm vacuoles (Days 18 and 21 in B. indicus; Day 18 in crossbred bulls) increased (P<0.05) in whole-scrotum insulation groups in both experiments. There was considerable variation among bulls in the incidence of specific sperm defects. The timing of appearance of sperm defects after insulation provided insights into the pathogenesis of specific abnormalities. Neither whole-scrotum nor scrotal-neck insulation affected testicular echotexture in either experiment. In conclusion, whole-scrotum insulation resulted in decreased sperm production and semen quality in B. indicus and B. indicus x B. taurus bulls, but those changes were not associated with changes in testicular echotexture.     

Testicular thermoregulation in Bos indicus, crossbred and Bos taurus bulls: relationship with scrotal, testicular vascular cone and testicular morphology, and effects on semen quality and sperm production

Mechanisms of testicular thermoregulation, the relationship of scrotal, testicular vascular cone (TVC), and testicular morphology with thermoregulatory capability, and their effects on semen quality and sperm production were studied in 20 Bos indicus, 28 crossbred, and 26 Bos taurus bulls. The ratio of testicular artery length and volume to testicular volume were larger (P<0.05) in B. indicus and crossbred bulls than in B. taurus bulls (1.03 and 0.94 cm/cm3 versus 0.48 cm/cm3; 0.034 and 0.047 ml/cm3 versus 0.017 ml/cm3, respectively). Testicular artery wall thickness (average 192.5, 229.0, and 290.0 microm, respectively) and arterial-venous blood distance in the TVC (average 330.5, 373.7, and 609.4 microm, respectively) were smallest in B. indicus, intermediary in crossbred, and greatest in B. taurus bulls (P<0.05); the proximity between arterial and venous blood was consistent with the estimated decrease in arterial blood temperature after passage through the TVC (5.9, 5.0, and 2.9 degrees C, in B. indicus, crossbred, and B. taurus bulls, respectively). In crossbred and B. taurus bulls, there was a positive top-to-bottom scrotal temperature gradient and a negative testicular subtunic temperature gradient. However, in B. indicus bulls, both scrotal and testicular subtunic temperatures gradients were positive. Differences in the vascular arrangement, characteristics of the artery (e.g. wall thickness) or thickness of the tunica albuginea may have affected the testicular arterial blood and subtunic temperatures in B. indicus bulls. Better testicular thermoregulatory capability was associated with increased scrotal shape (pendulosity), testicular artery length and volume, and top-to-bottom gradient of the distance between the artery wall and the veins in the TVC. Increased semen quality was associated with increased testicular volume and scrotal subcutaneous (SQT) temperature gradient, and with decreased scrotal surface and testicular temperatures. Increased sperm production was associated with increased testicular artery volume, testicular volume, and SQT temperature gradient, and with decreased testicular artery wall thickness, scrotal circumference (SC), and scrotal surface, testicular subtunic, and epididymal temperatures. In conclusion, morphology of the TVC may contribute to the greater resistance of B. indicus bulls to high ambient temperatures by conferring a better testicular blood supply and by facilitating heat transfer between the testicular artery and veins. Testicular thermoregulation was associated with opposing scrotal and testicular subtunic temperatures gradients only in crossbred and B. taurus bulls. Scrotal, TVC, and testicular morphology influence testicular thermoregulatory capability and were associated with differences in semen quality and sperm production.     

Seasonal variation in semen quality in Bos indicus and Bos taurus bulls raised under tropical conditions

In the present study, we tested the hypothesis that Bos taurus taurus bulls have greater reactive oxygen species (ROS) and lower activity of antioxidant enzymes in their semen than Bos taurus indicus bulls. Sixteen Simmental bulls (B. t. taurus) and 11 Nelore bulls (B. t. indicus) were managed extensively in a tropical environment. Semen was collected twice annually (summer and winter) for 2 consecutive years. Simmental bulls had significantly higher percentages of major sperm defects during the summer than the winter (20.3+/-3.1% versus 12.2+/-2.4%, respectively; mean+/-S.E.M.). There was an interaction of breed and season for minor sperm defects (P=0.037; highest in Nelore bulls in the summer) and an effect of season on total defects (P=0.066; higher in summer). To evaluate oxidative damage, malondialdehyde (lipid-peroxidation metabolite) concentrations were indirectly measured by semen concentrations of thiobarbituric acid reactive substances (TBARS); these were higher in summer than in winter (728.1+/-79.3ng/mL versus 423.8+/-72.6ng/mL, respectively; P=0.01). Glutathione peroxidase/redutase (GPx) activity in semen was higher in Simmental versus Nelore bulls (741.6+/-62.1 versus 510.2+/-62.8; P<0.01). However, superoxide dismutase (SOD), another antioxidant enzyme, was not significantly affected by breed or season. There were correlations between TBARS and sperm primary defects during the summer for both Simmental and Nelore bulls (r=0.59, P=0.021 and r=0.40, P=0.034, respectively), and between SOD and primary defects during summer for Simmental bulls only (r=-0.51, P=0.041). In conclusion, there was a higher level of lipid peroxidation (ROS) in semen of Simmental versus Nelore bulls; apparently the higher GPx activity in Simmental bulls was insufficient to avoid damage that occurred concurrent with increased ROS production during the summer.     

A comparison of morphometric characteristics of sperm from fertile Bos taurus and Bos indicus bulls in Brazil

The current work has as main objective the systematic investigation of sperm morphometric characteristics of fertile Bos taurus and Bos indicus bulls living in Brazil by using several traditional as well as more modern and advanced computer vision concepts and methodologies. Ten smears of B. taurus semen and ten smears of B. indicus semen have been evaluated. Sperm morphology was quantified in terms of the following morphological features: head area, perimeter, width, length, width:length ratio, ellipticity, shape factor, width of sperm basis, the three first Fourier values, symmetry and hydrodynamics. Morphometric differences have been observed between the sperm cell of B. taurus and B. indicus bulls. The sperm cells of Zebu bulls tend to be smaller and less elliptic, however without modifying hydrodynamic, side symmetry and width of sperm head base. These differences clearly indicate that the geometrical characterization of bull sperm cells should take into account morphological peculiarities that are specific to each subspecies. Another important contribution is the identification that morphological differences implied by bulls of different fertility, as characterized by other authors, were found to be less as compared with those obtained in the current study where highly fertile animals from the two subspecies were studied.     

Sexual development in early- and late-maturing Bos indicus and Bos indicus x Bos taurus crossbred bulls in Brazil

Two experiments were conducted to evaluate sexual development in early- and late-maturing Nelore (Bos indicus) and Canchim (3/8 Bos indicus x 5/8 Bos taurus crossbred) bulls and to determine predictors of sexual precocity, and pubertal and maturity status. In Experiment 1, 12 Nelore bulls where examined from 300 to 900 days of age. Puberty was characterized by an ejaculate containing > or =50 million sperm with > or =10% motile sperm, and maturity by an ejaculate containing > or =70% morphologically normal sperm. In Experiment 2, 28 Canchim bulls where examined from 295 to 488 days of age and puberty was characterized by an ejaculate containing > or =30% motile sperm. In both experiments, bulls were classified as early- or late-maturing based on age at puberty. Early-maturing bulls were younger (P < 0.05) than late-maturing bulls at puberty (527 days versus 673 days in Experiment 1 and 360 days versus 461 days in Experiment 2) and at maturity (660 days versus 768 days in Experiment 1). In general, early-maturing bulls were heavier and had greater scrotal circumference (SC), testes, and testicular vascular cone diameter than late-maturing bulls during the experimental period. Scrotal circumference adjusted for 365 days of age was a good predictor of sexual precocity; minimum yearling SC of 19 and 24 cm for Nelore and Canchim bulls, respectively, had the best predictive values. Early-maturing bulls were lighter and had smaller SC at puberty than late-maturing bulls; therefore, sexual precocity was not related to the attainment of a threshold body weight or testicular size earlier, but to lower thresholds in early-maturing bulls. When predictors of pubertal status were evaluated, SC had the best sensitivity/specificity relationship in Nelore bulls, and high sensitivity and specificity in Canchim bulls. When predictors of sexual maturity were evaluated in Nelore bulls, age, weight, and SC had similar sensitivity, specificity, and predictive values. At puberty, approximately 60% of the sperm present in the ejaculate were morphologically defective. Changes in semen quality after puberty in Nelore bulls were characterized by increased motility and proportion of morphologically normal sperm, with a decrease in the proportion of major sperm defects. In conclusion, early-maturing bulls were more developed in the pre-pubertal period and attained puberty at earlier stages of body and testicular development than late-maturing bulls. Yearling SC could be used to select bulls for sexual precocity and SC was the best predictor of pubertal status. Age, weight, and SC were equally good predictors of sexual maturity in B. indicus bulls.     

Comparative gene frequencies of nucleoside phosphorylase from cattle of Bos taurus and Bos indicus derivation in Brazil

1. Two nucleoside phosphorylase (NP) phenotypes were detected in 844 animals from four distinct genetic groups of Bos taurus and Bos indicus derivation. 2. Bos indicus breeds like Guzerat (Kankrej), Gir, Nellore (Ongole) and Indubrazil presented an NP-H frequency of 1.00, 0.928, 0.776 and 0.754 respectively, while the Canchim breed, a Bos taurus-Bos indicus crossbred cattle (5/8 Charolais-3/8 Zebu) presented a frequency of 0.372. 3. The high frequency detected from the NP-H allele in the Bos indicus breeds strongly suggests that this enzyme is a genetic marker for cattle and that it probably has a very high frequency in all Indian breeds.     

Influence of the breed of bull (Bos taurus indicus vs. Bos taurus taurus) and the breed of cow (Bos taurus indicus, Bos taurus taurus and crossbred) on the resistance of bovine embryos to heat

In vitro studies have shown that Bos taurus indicus (B. t. indicus) embryos submitted to heat shock at early stages of development are better able to survive as compared to Bos taurus taurus embryos. Embryo genotype influences resistance to heat shock thus leading to the question as to whether embryos sired by thermo-tolerant breeds exhibit the same resistance to heat shock. In the present study the influence of both oocyte and semen, on the resistance to heat shock (HS) at early stages of in vitro development, was assessed in B. t. indicus [Nelore (N) breed], B. t. taurus [Holstein (H) and Angus (A) breeds] and crossbreds. In Experiment 1, Nelore and crossbred oocytes were collected from slaughterhouse ovaries and fertilized with spermatozoa from Nelore and Angus bulls. Presumptive embryos were collected and randomly assigned to control (39 degrees C) or HS at 12, 48 or 96 h post insemination (hpi; 41 degrees C for 12h) treatments. The cleavage rates and proportion of embryos developing to the blastocyst and hatched blastocyst stages were recorded on Days 2, 8 and 10, respectively. Heat shock treatment decreased development of both Nelore and crossbred embryos. There was a significant interaction between time (12, 48 or 96 hpi) and temperature for blastocyst rates, i.e., the embryos became more thermotolerant as development proceeded. In Experiment 2, oocytes from Nelore and Holstein cows were fertilized with semen from bulls of either Nelore or Angus breeds, and subjected to 12 h HS at 96 hpi. Heat shock at 96 hpi, decreased embryo development. Additionally, cowxtreatment and bullxtreatment interactions were significant for blastocyst rates, i.e., both breed of cow and breed of bull affected the decline in blastocyst rate caused by heat shock treatment. In conclusion, the present results indicate that Nelore embryos (indicus) are more resistant to heat shock than Holstein (taurus) at early stages of in vitro development, and that embryos become more thermo-tolerant as development proceeds. Additionally, the resistance to heat shock was a result of the genetic contribution from both oocyte and spermatozoa.     

Use of internal artificial vaginas for breeding soundness evaluation in range bulls: an alternative for electroejaculation allowing observation of sex drive and mating ability

The objective of this study was to test the efficacy of an inexpensive, reusable internal artificial vagina (IAV) developed for breeding soundness evaluation of range beef bulls. In addition, sexual behavior during semen collection by IAV was compared to behavior during pasture breeding. Breeding soundness exams (BSEs) were conducted on 165 bulls in two consecutive years (96 in Year 1 and 69 in Year 2). In Year 1, BSEs were done twice in all bulls, once by a conventional protocol using electroejaculation (EEJ), followed by the IAV method, one week later. In Year 2, all BSEs were done on one day; 69 bulls by the IAV method followed by EEJ in 21 bulls that failed to serve the IAV. For semen collection using an IAV, mount cows were restrained in breeding crates and an IAV was inserted into the vagina just beyond the depth of the vestibular sphincter. After each copulation, the IAV was replaced for the next bull to be tested. Semen collection by IAV was successful for all bulls that mounted and penetrated cows during the testing period (54.3 and 69.6% of the bulls served the cows with IAVs in Year 1 and 2, respectively). Semen was collected successfully by EEJ from all bulls in both years. Differences were observed between semen collection methods in semen volume and percentage of sperm staining alive; however, the differences were opposite in Year 1 and 2 and, therefore, were probably due to natural variations in time and within bull rather than the method of semen collection. Semen collection by IAV allowed the detection of problems that prevented copulation in 8 bulls (4.8%) that were determined to be satisfactory potential breeders when semen was collected by EEJ. In Year 1, breeding observations were made at pasture for 15 bulls that served, and 15 bulls that did not serve cows with an IAV. Bulls that did not serve the IAV during the test period had fewer mounts, attempts to mount, and completed services at pasture than bulls that had served the IAV, indicating that such bulls are likely to be less efficient breeders. In conclusion, IAVs might be used as an alternative to EEJ for breeding soundness evaluation in about 50-70% of range bulls. Semen collection by IAV also allows observation of sex drive and mating ability thus improves the ability to select sound breeding bulls.     

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.     

Effect of age and genetic group on characteristics of the scrotum,testes and testicular vascular cones,and on sperm production and semen quality in AI bulls in Brazil

The objectives were to determine the effects of age and genetic group on characteristics of the scrotum, testes and testicular vascular cones (TVC), and on sperm production and semen quality in 107 Bos indicus, B. taurus and cross-bred bulls at three artificial insemination (AI) centers in Brazil. In addition, predictors of sperm production and semen quality were identified. In general, scrotal circumference (SC), scrotal shape score, scrotal neck perimeter, and testicular size (length, width and volume) increased (P < 0.05) with age. Although there were no significant differences among genetic groups for SC or testicular size, B. indicus bulls had the least pendulous scrotal shape, the shortest scrotal neck length, and the greatest scrotal neck perimeter (P < 0.05). Fat covering the TVC was thinner (P < 0.05) in bulls < or = 36 months of age and in B. taurus bulls than in older bulls and B. indicus bulls, respectively. Age and genetic group did not affect testicular ultrasonic echotexture. B. indicus bulls tended (P < 0.1) to have the lowest average scrotal surface temperature (SST). In general, ejaculate volume, total number of spermatozoa and number of viable spermatozoa increased (P < 0.05) with age. However, there was no significant effect of age on sperm concentration, motility, major and total defects. The proportion of spermatozoa with minor defects was highest (P < 0.05) in bulls 37-60 months of age. B. indicus bulls had higher (P < 0.01) sperm concentration, total number of spermatozoa and number of viable spermatozoa than B. taurus bulls, with intermediate values for cross-bred bulls. Increased sperm production was associated with increased testicular volume, SC, TVC fat cover, and SST top-to-bottom gradient. Decreased semen quality was associated with increased SC and bottom SST, and decreased scrotal shape, scrotal neck perimeter and vascular cone diameter. In summary, age and genetic group affected the characteristics of the scrotum, testes, and TVC, sperm production and semen quality. In addition, characteristics of the scrotum, testes and TVC were associated with sperm production and semen quality in bulls and could be assessed for breeding soundness evaluation.     

Influence of sire and sire breed (Gyr versus Holstein) on establishment of pregnancy and embryonic loss in lactating Holstein cows during summer heat stress

Heat stress has negative effects on pregnancy rates of lactating dairy cattle. There are genetic differences in tolerance to heat stress; Bos taurus indicus (B. t. indicus) cattle and embryos are more thermotolerant than Bos taurus taurus (B. t. taurus). In the present study, the effects of sire and sire breed on conception and embryonic/fetal loss rates of lactating Holstein cows during the Brazilian summer were determined. In Experiment 1, cows (n=302) were AI after estrus detection or at a fixed-time with semen from one Gyr (B. t. indicus) or one Holstein sire (B. t. taurus). Pregnancy was diagnosed 80 days after AI. In Experiment 2, cows (n=811) were AI with semen from three Gyr and two Holstein sires. Pregnancy was diagnosed at 30-40 and at 60-80 days after AI. Cows diagnosed pregnant at the first examination but non-pregnant at the second were considered as having lost their embryo or fetus. Data were analyzed by logistic regression. The model considered the effect of sire within breed, sire breed, days postpartum, period of lactation, and AI type (AI after estrus versus fixed-time). There was no effect of the AI type, days postpartum or milk production on conception or embryonic loss rates. The use of Gyr bulls increased pregnancy rate when compared to Holstein bulls [9.1% (60/657) versus 5.0% (23/456), respectively, P=0.008; data from Experiments 1 and 2 combined]. Additionally, in Experiment 2, cows inseminated using semen from sire #4 (Gyr) had lower embryonic loss (10%) when compared with other B. t. indicus (35.3% and 40%) or B. t. taurus sires (18.2% and 38.5%, P=0.03). In conclusion, the use of B. t. indicus sires may result in higher conception rates in lactating Holstein cows during summer heat stress. Moreover, sire can affect embryonic loss and selection of bulls according to this criterion may result in higher parturition rates in lactating Holstein cows.     

Reproductive behaviour in bulls raised under tropical and subtropical conditions

The present review describes the behavioral characteristics of bulls raised under tropical and subtropical conditions and emphasizes the difficulties associated with adequately monitoring their performance in the field to predict reproductive potential. Most of the information generated for improving our understanding of bull behavior under range conditions has been generated in Bos taurus bulls. The limited information available in Bos indicus indicates that males searching for cows in estrus display different sexual patterns when compared to B. taurus bulls and a poor selection of a sire utilized in range conditions can have an important impact in cattle production. Screening and selecting [cg1] bulls for desirable reproductive traits and high libido is known to improve the reproductive performance of the herd. The reproductive and genetic potential of a bull is influenced by factors such as management, age, nutrition and problems related to the female such as embryonic death and anestrus. However, behavioral characteristics of bulls when detecting and serving cows in estrus is poorly understood.     

Karyotype analysis of mithun (Bos frontalis) and mithun bull x Brahman cow hybrids

We examined the cytogenetics of mithun (Bos frontalis), a domesticated version of the Asian gaur, and hybrids (F(1) generation) produced by artificial insemination of Brahman cows (Bos indicus) with mithun semen. Reproductive potential was also examined in the F(1) generation and a backcrossed heifer for utilization of heterosis. Metaphase chromosome spreads were examined by conventional staining and fluorescence in situ hybridization hybridized with the entire chromosome 1 of mithun as a specific probe. Chromosome 1 of mithun was found to be equivalent to Bos taurus chromosomes 2 and 28. The karyotype of the female mithun (N = 4) comprised 58 chromosomes, including 54 acrocentric and four large submetacentric chromosomes, without the four acrocentric chromosomes found in the domesticated species B. indicus. However, one of the four female mithuns with a normal mithun phenotype had an abnormal karyotype (2n = 59), indicating introgression from B. taurus or B. indicus. The F(1) karyotypes (N = 6, 3♂3♀) of the mithun bull × Brahman cow cross had 2n = 59, intermediate between their parents; they were consistent heterozygous carriers with a centric fusion involving rob(2;28), as expected. Two pronounced red signals were seen in the mithun karyotypes, three red signals in the mithun × Brahman hybrids, and four red signals in the Brahman cattle, in good agreement with centric fusion of bovine rob(2;28). The female backcross hybrid (N = 1) with 2n = 59 had a similar chromosome configuration to the F(1) karyotypes and had rob(2;28). Such female backcross hybrids normally reproduce; however, the F(1) bulls (N = 3) had not yet generated normal sperm at 24 months.     

Assessing sex-drive in young Bos taurus bulls

Objectives in this study were to determine the accuracy of different methods of evaluating libido score (L), service rate (SR) and reaction time to service (RTS) in yearling Bos taurus bulls. Using restrained, non-estrus females, 26 yearling Bos taurus bulls were evaluated a total of eight times (four sessions, two tests per session) over 2 consecutive months for L, SR, and RTS. Individual bull variation influenced both L (P<0.0001) and SR (P<0.003). Repeatability was moderate for L (R=0.64) and low for both SR (R=0.12) and RTS (R=0.04). Under the conditions of this study and characteristics of these tests, variance was reduced to 69-73% for L and 26-23% for SR with four to eight repetitions, respectively. Bulls that scored highly in the first session, however, tended to score highly throughout. Although, three bulls did not serve in any test, RTS was independent of effects. However, the tendency of RTS to decrease, and for L and SR to both increase with consecutive tests, suggests influences other than genetic, such as learning and/or environmental factors. These tendencies were most evident in bulls which obtained low L scores at the first session. It was concluded that, despite the important degree of individual variability observed in L and SR, accurate quantitative evaluation of the sex-drive in young Bos taurus beef bulls would benefit from use of test procedures of greater repeatability.     

Synaptonemal complex analysis of hybrid cattle. II. Bos indicus x Bos taurus F1 and backcross hybrids

The levels of meiotic chromosome pairing abnormalities observed in six Australian F1 Bos indicus x Bos taurus cattle crosses (mean = 23%) were significantly higher than those of the full-blood breeds (9%). The abnormal configurations in the F1 hybrids included partial pairing failure, multivalents, interlocks, and inversion pairing. Abnormal configurations were also present, but at lower frequency, in backcross hybrid bulls. The main types of abnormal configurations and the levels of XY-autosomal associations and autosomal asynapsis observed were unlikely to cause significant fertility problems in the hybrids.     

Reproductive cycles in Bos indicus cattle

Several studies using transrectal ovarian ultrasonic scanning in Bos taurus (B. taurus) cattle and more recently in Bos indicus (B. Indicus) females evaluated the reproductive cycles of heifers and cows under different conditions. In general, B. indicus cattle have more follicles and more follicular waves during the estrous cycle and ovulate from smaller follicles than B. taurus. Consequently B. indicus females have smaller corpora lutea and it is assumed circulating concentrations of estradiol and progesterone are also less. However, these findings may vary depending on the nutritional status and regimen in which the animals are managed. Moreover, there are significant differences between B. taurus and B. indicus regarding follicle size at the time of deviation of the dominant follicle. These differences in ovarian function between B. indicus and B. taurus, e.g. greater antral follicle population are, probably, the main reasons for the great success of in vitro embryo production programs in Zebu cattle, especially in Brazil.     

Complete mitochondrial genomes of Bos taurus and Bos indicus provide new insights into intra-species variation, taxonomy and domestication

The taurine and zebuine cattle breeds comprise the majority of the world cattle population but their taxonomic status is still controversial. The two forms of cattle are currently classified as Bos taurus and Bos indicus species and are differentiated primarily by the presence or absence of a hump. However, these two species hybridize readily, producing fully fertile offspring. We have determined and analyzed complete B. taurus and B. indicus mitochondrial genome sequences to investigate the extent of sequence divergences and to study their taxonomic status by molecular dating. The sequences encompassed 16,338 and 16,339 nucleotides, respectively, and differed at 237 positions. Estimated divergence times indicated that the two cattle lineages separated 1.7-2.0 million years ago. Combined phylogenetic analyses of 18 new and 130 previously reported extant B. taurus and B. indicus control region sequences with data from 32 archaeological specimens of the extinct wild aurochs (Bos primigenius) identified four major maternal lineages. B. primigenius haplotypes were present in all but the B. indicus lineage, and one B. taurus sequence clustered with B. primigenius P haplotypes that were not previously linked with domestic cattle. The B. indicus cluster and a recently reported new B. primigenius haplotype that represents a new lineage were approximately equidistant from the B. taurus cluster. These data suggest domestications from several differentiated populations of B. primigenius and a subspecies status for taurine (B. primigenius taurus) and zebuine (B. primigenius indicus) cattle.     

Effect of single nucleotide polymorphisms of CAPN1 and CAST genes on meat traits in Nellore beef cattle (Bos indicus) and in their crosses with Bos taurus

The objectives of this work were to study the segregation of single nucleotide polymorphisms of the calpain 1, large subunit ( CAPN1 ) and calpastatin ( CAST ) genes in Nellore ( Bos indicus ) and Nellore × Bos taurus beef cattle, as well as to evaluate their effects on meat traits. For this, 300 animals, including 114 Nellore, 67 Angus × Nellore, 44 Rubia Gallega × Nellore, 41 Canchim, 19 Brangus three-way crosses and 15 Braunvieh three-way crosses, were genotyped for the CAPN4751 [AF_248054.2:g.6545C>T (GenBank accession AF248054.2 )] and CAST/DdeI [AF_159246.1:g.2959A>G (GenBank accession AF159246.1 )] polymorphisms and phenotyped for Ribeye Area, Backfat Thickness, Intramuscular Fat, Shear Force (SF) and Myofibrillar Fragmentation Index (MFI). In relation to the CAPN4751 polymorphism, a frequency of 10.5% was observed for the C allele in the Nellore breed. In the total sample of studied animals, a significant association was found between genotypes and meat tenderness, assessed by SF ( P  = 0.005) and MFI ( P  = 0.008), with genotype CT being more favourable than TT. For the CAST/DdeI polymorphism, a frequency of 55.7% was found for the A allele in the Nellore breed. In the total sample, a significant association was observed between genotypes and meat tenderness – SF ( P  = 0.004) and MFI ( P  = 0.006), with genotype AA being more favourable than AG. The relationship between genotypes and aged meat tenderness in confluence with the distribution of favourable alleles shows great potential for application of the CAPN4751 and CAST/DdeI polymorphisms in the genetic improvement of the Nellore breed, whilst contributing to the validation, in this breed and in its crosses with B. taurus , of the association results previously described in the literature.