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.     

Logistic regression analysis of pregnancy rate following transfer of Bos indicus embryos into Bos indicus x Bos taurus heifers

Factors affecting pregnancy rate of 5627 Zebu embryos in crossbred females with unknown proportions of Holstein and Zebu breeding were examined. After evaluation for developmental stage, quality, and viability, embryos were immediately transferred to recipients. Pregnancy diagnosis was conducted approximately 53 d after transfer; pregnancy rate was coded as a binomial event and analyzed using logistic regression models. Maximum likelihood methodology and the likelihood ratio statistic were used to estimate regression coefficients and test hypotheses. Explanatory variables were year of transfer (1992-1999), season of transfer (summer, autumn, winter and spring), breed of the embryo (Guzerat, Gyr or Nellore), stage of the embryo (morula, early blastocyst, blastocyst, expanded blastocyst, and hatching blastocyst), quality of the embryo (excellent, good or regular), and donor-recipient synchrony (estrus in the recipient occurred 2-3 d before, 1 d before, the day of, 1 d after, or 2-3 d after estrus in the donor). Average pregnancy rate was 63.7%. Pregnancy rates were not significantly affected by breed of embryo. The best multiple-logistic model to explain the pregnancy result included the effects of year and season of transfer, embryo stage and quality, and estrous synchrony between donor and recipient (P相似文献   

Internal artificial vagina (IAV) to assess breeding behavior of young Bos taurus and Bos indicus bulls

Bull breeding soundness evaluation (BBSE) usually neglects the libido and mating ability evaluation. The internal artificial vagina (IAV) permits semen sampling, as well as mating ability evaluation. Few studies have been performed using IAV with young bulls and there are none with Bos indicus bulls. The present study evaluated sexual behavior, mating ability and semen quality in young Bos taurus (Devon) and B. indicus (Nellore) bulls using the IAV device. In the first experiment, 52 Devon bulls, 18-25 months old were observed, and the behavior and mating ability recorded over a 10-min period within a restrained mount-cow with an IAV inserted. In the second experiment, 20 Nellore bulls, 20-30 months old were evaluated over a 20 min period. Of the 52 Devon bulls, 45 (86.5%) had semen recovered with the IAV, 31 (69.0%) were considered satisfactory. Nellore bulls exhibited a different sexual behavior, with 10 bulls not showing any interest in the females. Four bulls demonstrated sexual interest only once, e.g., sniffing, two showed interest on more than one occasion, and four had more than two mounts or mounting attempts. None out of the Nellore bulls was collected with IAV. The IAV was an effective and welfare-promoting animal technology for the evaluation of semen quality and mating ability of B. taurus bulls. However, the IAV was not adequate for young Nellore bulls, probably due to their quiescent sexual behavior and delayed sexual maturity. Further studies are needed to evaluate the performance of the IAV for older Nellore bulls.     

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.     

Spermiogram and sperm reserves in hybrid Bos indicus X Bos taurus bulls after scrotal insulation

Scrotal insulation for 48 h raised subcutaneous scrotal temperature by 4 degrees C in hybrid Bos indicus X Bos taurus bulls. The incidence of decapitated spermatozoa in the ejaculate increased significantly between 6 and 14 days and that of protoplasmic droplets and tail abnormalities between 20 and 23 days after insulation, respectively. Simultaneously, the percentages of spermatozoa with lost and damaged acrosomes increased significantly 12-17 days after insulation. At slaughter 23 days after scrotal insulation sperm production rates and gonadal reserves had not been affected by insulation, but epididymal reserves were markedly reduced, particularly in the cauda. Elevated testicular temperature therefore had an effect on immature spermatozoa in the caput epididymidis and on spermatids, but it is suggested that selective sperm resorption in the rete testis and excurrent ducts may prevent some of these changes being expressed in the ejaculate.     

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.     

Fertility of Bos indicus and Bos indicus x Bos taurus crossbreed cattle after estrus synchronization

Ninety-five cows (79 Boran and 16 Boran-Brahman crossbreeds) and 107 heifers (55 Boran and 52 Boran x Friesian F1 crossbreeds) were used to determine estrus response, estrus response interval and pregnancy rate following synchronization with prostaglandin (PGF(2)alpha), a progesterone-releasing intravaginal device (PRID) and Synchro-mate B (SMB). The proportion of cattle responding to synchronization treatment was 62.5, 43.5 and 57.7% for cows and 85.7, 68.0 and 81.5% for heifers using PGF(2)alpha, PRID and SMB, respectively. The overall mean response was 59 and 81.8% for cows and heifers, respectively. The estrus response of the control animals over a 45-d breeding period was 72.7 and 90% for cows and heifers, respectively. The estrus response interval for cows was 31.8, 22.1 and 18.0 h and it was 51.1, 38.0 and 21.6 h for heifers with PGF(2)alpha, PRID and SMB treatment, respectively. Mean pregnancy rate for cows was 50.0, 34.8, 46.2 and 68.8% and for heifers it was 60.7, 40.0, 55.6 and 77.8% in the PGF(2)alpha, PRID, SMB and control groups, respectively. Based on these findings, it was concluded that both PGF(2)alpha and SMB produce a satisfactory estrus response and pregnancy rate in the cattle studied.     

Acquisition and expression of resistance by Bos indicus and Bos indicus X Bos taurus calves to Amblyomma americanum infestation

Purebred and crossbred Bos indicus calves were infested 1, 2, or 3 times with 10 female and 5 male Amblyomma americanum. Resistance was acquired by both the purebred and the crossbred calves after 1 infestation and resulted in statistically significant decreases in the percentages of females that engorged, the mean weights of engorged females, and the mean weights of egg masses. Comparisons between breeds of the percent of female ticks that engorged during the first and second infestations indicate that purebred B. indicus expressed a stronger acquired resistance to A. americanum more readily than did crossbred animals. However, calves of both genetic compositions displayed similar levels of resistance during a third exposure. All tick-exposed and control animals were skin tested with salivary gland extracts of A. americanum, A. cajennense and Dermacentor andersoni. Control, uninfested calves, did not display significant cutaneous reactivity to these extracts. All calves that had been infested had immediate, 30-min, 5-hr and delayed, 24-hr, skin reactions to Amblyomma species antigens. Reactions to D. andersoni salivary antigens in tests of both purebred and crossbred calves with acquired resistance to A. americanum suggest that Amblyomma species salivary gland antigens might have cross reactive moieties with a salivary extract prepared from D. andersoni. Peripheral blood lymphocyte in vitro responsiveness to Amblyomma species antigens was detected in purebred calves after a first, second, and third infestation, indicating the presence of cells of the immune system capable of recognizing and undergoing blast transformation in response to tick salivary components.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of early luteolysis in progesterone-based timed AI protocols in Bos indicus, Bos indicus x Bos taurus, and Bos taurus heifers

The objective of this study was to evaluate the effects of treatment with an intravaginal progesterone-releasing device (CIDR) and estradiol benzoate (EB) on follicular dynamics in Bos indicus (n=23), Bos taurus (n=25), and cross-bred (n=23) heifers. To assess the influence of reduced serum progesterone concentrations during 8 days of treatment with a progesterone-releasing device on follicular dynamics, half of the heifers received PGF at CIDR insertion (Day 0; 3 x 2 factorial design). Mean (+/-S.E.M.) serum progesterone concentrations during CIDR treatment varied (P<0.05) among genetic groups: B. indicus (5.4+/-0.1 ng/mL), B. taurus (3.3+/-0.0 ng/mL), and cross-bred (4.3+/-0.1 ng/mL). Maximum diameter of the dominant follicle (DF) was smaller (P<0.01) in B. indicus heifers (9.5+/-0.5 mm) than in cross-bred (12.3+/-0.4 mm) or B. taurus heifers (11.6+/-0.5 mm). B. indicus experienced lower (P<0.01) ovulation rate (39.1%) than did B. taurus (72.7%) and cross-bred (84.0%). Heifers treated with PGF on Day 0 had lower (P<0.05) serum progesterone concentrations during progesterone treatment. The PGF treatment on Day 0 increased (P<0.01) the diameter of the DF (11.9+/-0.4 mm vs. 10.5+/-0.4 mm). Moreover, greater (P=0.02) ovulation rates (78.8 vs. 54.0%) occurred in heifers treated with PGF on Day 0. In summary, B. indicus heifers had greater serum progesterone concentrations, smaller DF diameter, and a lower ovulation rate compared to B. taurus heifers. Prostaglandin treatment on the day of CIDR insertion reduced serum progesterone during treatment, and resulted in increased maximum DF diameter and ovulation rate.     

Heritable testicular hypoplasia in Nguni (Bos indicus) bulls: vascular characteristics and testosterone production.

The biased unilateral occurrence of heritable gonadal hypoplasia was investigated by examining the gross- and microanatomy of the testicular artery and vein, testicular blood flow and testicular testosterone secretion in normal Nguni bulls and in Nguni bulls showing unilateral left, unilateral right and bilateral hypoplasia of the testis. A high incidence of branching of the testicular artery was found ipsilateral to hypoplastic testes. The branching occurs a short distance from the dorsal aorta: one branch proceeds to the testis, the other to the ipsilateral kidney. The association between arterial branching to the kidney and ipsilateral hypoplasia of the testis held for both unilaterally left and unilaterally right hypoplastic bulls. Variations in the anatomy of the testicular vein occurred in both normal and hypoplastic bulls but there was no specific association between the variations and ipsilateral hypoplasia. The lumen diameter of the testicular artery or branch correlated with testis mass. Wall thickness of the artery ipsilateral to hypoplastic testes was not different from that in normal bulls, discounting hyperplasia of the endothelium. Total blood flow to the testis correlated with testis mass. The secretion rate of testosterone from hypoplastic testes was lower than that of normal testes but there was no difference when compared on a unit mass basis.     

Effects of environmental factors, age and genotype on sperm production and semen quality in Bos indicus and Bos taurus AI bulls in Brazil

The effects of ambient temperature and humidity, month, age and genotype on sperm production and semen quality in AI bulls in Brazil were evaluated. Data from two consecutive years were analyzed separately. Seven Bos indicus and 11 Bos taurus bulls from one artificial insemination (AI) center were evaluated in Year 1 and 24 B. indicus and 16 B. taurus bulls from three AI centers were evaluated in Year 2. Ambient temperature and humidity did not significantly affect sperm production and semen quality, probably because there was little variation in these variables. Month accounted for less than 2% of the variation in sperm production and semen quality. Increased bull age was associated with decreased sperm motility (P<0.10) and increased minor sperm defects (P<0.001) in Year 1. B. indicus bulls had greater (P<0.005) sperm concentration than B. taurus bulls in both years (1.7×10⁹/ml versus 1.2×10⁹/ml in Year 1 and 1.6×10⁹/ml versus 1.2×10⁹/ml in Year 2, respectively). Ejaculate volume was not significantly affected by genotype in Year 1 (6.6 ml versus 6.9 ml in B. indicus and B. taurus bulls, respectively), but B. indicus bulls had greater (P<0.05) total (11.4×10⁹ versus 8.2×10⁹) and viable (6.7×10⁹ versus 4.9×10⁹) numbers of spermatozoa in the ejaculate than B. taurus bulls. In Year 2, B. taurus bulls had greater (P<0.05) ejaculate volume than B. indicus bulls (8.2 ml versus 6.7 ml, respectively) and total and viable number of spermatozoa in the ejaculate were not significantly different between genotypes (10.3×10⁹ versus 9.1×10⁹ and 6.1×10⁹ versus 5.4×10⁹ in B. indicus and B. taurus bulls, respectively). Sperm motility was not significantly affected by genotype (mean, 59%). In Year 1, B. indicus bulls tended (P<0.10) to have more major sperm defects and had more (P<0.05) total sperm defects than B. taurus bulls (11.8% versus 8.7% and 13.6% versus 10.0%, respectively). In Year 2, B. indicus bulls tended (P<0.10) to have more total sperm defects than B. taurus bulls (16.2% versus 13.3%, respectively). In conclusion, neither ambient temperature and humidity nor month (season) significantly affected sperm production and semen quality. B. indicus bulls had significantly greater sperm concentration and B. taurus bulls had significantly fewer morphologically defective spermatozoa.     

Plasma progesterone concentration in Bos taurus and Bos indicus heifers

Progesterone concentrations were determined by radioimmunoassay in the plasma of heifers of German Brown Swiss, Holstein-Friesian and White Fulani cattle during two consecutive estrous cycles in the dry and wet seasons in a tropical climate. Seasonal differences in the levels were not significant but peak levels were significantly higher in the $\text{Bos}$$\text{taurus}$ than in the $\text{Bos}$$\text{indicus}$ heifers. The low levels at estrus and the gradual rise five days after estrus were similar among the heifers. The levels on the 1st and 2nd days preceding estrus were significantly higher in the $\text{Bos}$$\text{taurus}$ than in the $\text{Bos}$$\text{indicus}$ heifers, and suggest a possible tendency for the former to be more susceptible to infertility arising from high progesterone levels 1 and 2 days preceding estrus and insemination. The genital tract and ovaries at the mature luteal phase were generally smaller in the $\text{Bos}$$\text{indicus}$ than in the $\text{Bos}$$\text{taurus}$ heifers.     

Genome sequence and assembly of Bos indicus

Cattle are divided into 2 groups referred to as taurine and indicine, both of which have been under strong artificial selection due to their importance for human nutrition. A side effect of this domestication includes a loss of genetic diversity within each specialized breed. Recently, the first taurine genome was sequenced and assembled, allowing for a better understanding of this ruminant species. However, genetic information from indicine breeds has been limited. Here, we present the first genome sequence of an indicine breed (Nellore) generated with 52X coverage by SOLiD sequencing platform. As expected, both genomes share high similarity at the nucleotide level for all autosomes and the X chromosome. Regarding the Y chromosome, the homology was considerably lower, most likely due to uncompleted assembly of the taurine Y chromosome. We were also able to cover 97% of the annotated taurine protein-coding genes.     

Peripheral plasma progesterone concentration in zebu (Bos indicus) cows during pregnancy

Plasma progesterone concentrations were determined weekly during gestation averaging 283 +/- 2 d in Ethiopian zebu (Bos indicus) cows. Mean progesterone levels increased from 0.2 +/- 0.1 ng/ml at oestrus (service) to 3.1 +/- 1.6 ng/ml on d 7 and 8.1 +/- 2.1 ng/ml on d 21. Progesterone levels remained elevated throughout pregnancy. Hormone concentration differed significantly between cows (P less than 0.001) and with the wk of pregnancy (P less than 0.05); it tended to be higher during the last trimester of pregnancy. Mean levels dropped sharply to below 1 ng/ml during the last wk of pregnancy with considerable variation (C.V. = 39 to 63%) among cows. These data indicate that pregnancy in Ethiopian zebu cows can be reliably diagnosed by determining circulatory plasma progesterone levels.     

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.