Development In Bulls Research Articles

РОСТ И РАЗВИТИЕ БЫКОВ-ПРОИЗВОДИТЕЛЕЙ В УСЛОВИЯХ ПЛЕМЕННОГО ПРЕДПРИЯТИЯ АО «КРАСНОЯРСКАГРОПЛЕМ»

The purpose of research is to study the growth and development of bulls in the conditions of JSC Krasnoyarskagroplem in the Krasnoyarsk Region. Objectives: to study changes in live weight, linear measurements and body composition indices during ontogenesis. The object of the study is bulls of the Holstein (red-motley) (n = 11) and red-motley (n = 4) breeds aged from one to five years. Study period: 2014–2019. Calculation of absolute growth, taking body measurements, and calculation of indices were carried out according to generally accepted methods. Holstein bulls at all age periods exceeded red-motley bulls in height at the withers and oblique length of the body. Bulls of the red-motley breed in chest width at one year of age exceeded Holstein sires by 3.25 %; at 1.6 years – by 13.8 (P > 0.95); in the 2-year period – by 14.1 (P > 0.999); in a 3-year-old – by 7.59; in a 4-year-old – by 6.1; in a 5-year-old – by 9.7 % and metacarpal girth: by 3.1; 2.4; 1.3; 4.5 % (P > 0.95), by 2.4 and 1.2 %, respectively. The variabi-lity of traits in bulls of the Holstein and red-motley breeds was characterized by a low degree at all age periods, which indicates the homogeneity of the population and high stability of exterior qualities. Calculation of indices characterizes red-motley bulls as compact with a low-set body, having a long body and a deeper chest. Holstein bulls have higher legs. Red-mottled breed and Holstein bulls have a pronounced milk type.

Review: Role of early life nutrition in regulating sexual development in bulls.

The availability of high-quality semen from genetically elite bulls is essential to support continued genetic gain and the sustainability of cattle production worldwide. While reducing the age at which usable semen is available also reduces the generation interval, it is dependent on timely onset of puberty in young bulls. There is now good evidence that hastened sexual development in bulls is achieved through enhancing nutrition in early life. This review will cover the physiological and molecular-based response to prevailing diet in key organs that orchestrate the ontogeny of sexual development in the bull calf. Given the central importance of the interaction between metabolic status and neuronal function to the progression of sexual development, we will discuss how communication between metabolic organs, reproductive organs and the brain are mediated via molecular and physiological processes. The availability of high-throughput nucleic acid and protein sequencing technologies and innovative data analytics have allowed us to improve our understanding of molecular regulation of puberty and sexual development. Analysing data from a number of organs, simultaneously, allows for a better understanding of the underlying biology and biochemical interactions that are influencing sexual development. Specifically, we can determine how early life nutritional interventions augment changes in potential key molecules regulating sexual development. Ultimately, a greater understanding of the inherent regulation of postnatal sexual development in the bull calf and how strategically targeted nutritional management can advance the ontogeny of this process, will facilitate the timely availability of high-quality semen from genetically elite animals, thus supporting more economically and environmentally sustainable beef and dairy production systems.

Study of the influence of the feeding type of calves during the milk fattening period on the subsequent growth and development of bulls up to 12 months of age

Research has been carried out on the intensive production of beef when raising dairy bulls up to 12 months of age drinking mainly dairy feed in the first 5 months of life (in group 1) and with the inclusion of a starter compound feed in the diet (in group 2). Different types of bull calves rearing in the first 5 months of life led to significant differences in the growth and development of the whole organism and all its individual organs and tissues, mainly in favour of bull calves raised with replacing part of the milk with vegetable feed, and subsequently had a decisive influence in the period from 6 up to 12 months of their life with the same type of feeding and maintenance. It has been established that the rearing system with a decrease in the drinking of whole milk and abstinence of the supply of roughage for the first 2 months of life, promotes the the growth of animals for a twelve-month period of life, leads to an increase in the yield of veal and beef meat, a decrease in feed consumption per unit of weight gain, and increasing the profitability of production by 8-9%, therefore it is recommended for production.

407 Nutrition and sexual development in bulls

Abstract Bull management for reproduction begins at birth. The objectives of this invited review are to provide a brief summary of the impact of nutrition on sexual development and reproductive function in beef bulls, followed by a discussion of management before, during and after the breeding season. Increased calfhood nutrition results in greater testicular development at maturity. Conversely, poor calfhood nutrition results in delayed puberty and reduced testicular development at maturity. Unfortunately, it is not possible to compensate for the effects of poor calfhood nutrition by subsequently providing supplemental feed. Previous research investigating sexual development and reproductive function in bulls 6 to 16 months of age focused on associations of average daily gain (ADG) and body weight with age at puberty, scrotal circumference, sperm production and morphology. Researchers reported no significant correlations between cumulative ADG and any of the factors investigated, and concluded ADG of 1.0 to 1.6 kg per day did not result in excessive scrotal fat accumulation, increased scrotal temperature, or reduction in semen quality. A common recommendation is for yearling bulls to have a body condition score of 5.5 to 6.5 (on a 9-point scale) at the start of the breeding season. Spermatogenesis occurs over a 60-day period; therefore, nutritional effects of inappropriate nutrition (over- or under-feeding) on sperm will have a carryover effect. During the breeding season bulls are usually limited to the same nutritional plane as the cow herd; however, bulls losing an excessive amount of weight should be replaced. Nutritional management of bulls after the breeding season is influenced by age (potential for further growth) and weight loss during the breeding season. Managing nutrition of bulls through early life phases and the first breeding season provides the opportunity for desired sexual development and reproductive function.

ВЗАИМОСВЯЗЬ ЭКСТЕРЬЕРНЫХ ПРИЗНАКОВ БЫКОВ АЙРШИРСКОЙ ПОРОДЫ И ИХ ДОЧЕРЕЙ

It is necessary to determine through the correlation variability the direction of changes in the relationship between the signs of the exterior and milk yield in the process of age development of bulls and their daughters. Type traits of four age groups of 45 bulls taken at different periods of their life (12, 16, 18, 24, 36, 48 months), their daughters in the first lactation (8366 heads) were analyzed and founded relationship between the measurements of father - daughter and economically useful traits. Young bulls at the age of 7.2 years from the group (5 to 9 years) are the best in all measurements in all evaluation age periods the estimates exterior compared to other groups. High and reliable relationships were found for stature, body depth, girth of pastern and selectively for other measurements of bulls taken at different measurement times, which gives the right to predict the body type of animals during ontogenesis. Calculated 92 correlation coefficient of measurements of bulls and the same of daughters, as well as their milk yield, taking into account the age of the manufacturer and the date of measurement. Reliable correlation coefficients were obtained from the stature and body depth in bulls of different ages. The relationship measurements of a body of bulls with milk yield of their daughters in most cases low, but reliable (as a large number of daughters). Milk yield of daughters for 305 days of lactation significantly correlates with their body depth and girth of pastern 0,428*** and 0,307***. The relationship between mother and daughter on a number of exterior features is established. The largest - milk yield with stature 0,153 **, body depth 0,173 **, girth behind the shoulder blades 0,154 **, slanting body length 0,157 **. For daughters, milk yield for 305 days of lactation reliably correlates with their body depth and girth behind the shoulder blades 0.428 *** and 0.307 ***. The measurement of the body depth has been established: the body depth bull - daughters 0.156 **; body depth mother - daughter 0,707 **; body depth daughters with a yield 0.428 **; the body depth of bull with daughters milk yield 0.173 **.

Enhanced sperm production in bulls following transient induction of hypothyroidism during pre-pubertal development.

Male reproductive capacity is a critical component of cattle production and the majority of genetic gain is made via selective utilization of gametes from desirable sires. Thus, strategies that enhance sperm production increase the availability of elite genetics for use in improving production characteristics of populations on a worldwide scale. In all mammals, the amount of sperm produced is strongly correlated to the number of Sertoli cells in testes. Studies with rodents showed that the size of the Sertoli cell population is set during pre-pubertal development via signaling from thyroid hormones. Here, we devised a strategy to increase Sertoli cell number in bulls via induction of a transient hypothyroidic state just prior to and extending beyond the period of Sertoli cell proliferation that we found to normally cease between 4.5 and 5 months of age. In adulthood, these bulls produced a significantly greater number of sperm compared to age matched controls and their testes contained nearly two times more Sertoli cells. Importantly, sperm motility, morphology, fertilizing ability, and viability after cryopreservation were found to be no different for treated bulls compared to untreated control bulls. This strategy of transient induction of hypothyroidism during a defined period of pre-pubertal development in bulls could prove to be an efficacious approach for enhancing daily sperm production in genetically desirable sires that will, in turn, provide an avenue for improving the efficiency of commercial cattle production.

ИСПОЛЬЗОВАНИЕ ОТЕЧЕСТВЕННЫХ БИОПРЕПАРАТОВ ДЛЯ ПОВЫШЕНИЯ МЯСНЫХ КАЧЕСТВ БЫЧКОВ

Scientifically substantiated and experimentally proved the feasibility of the zootechnical application of the developed biological products Prevention-N and Prevention N E in technology of beef production for the realization of bio-resource potential meat quality of calves of black-motley breed. Against the background of the use of biopreparations, activation of growth and development of bulls during cultivation, rearing and fattening was established, which led to higher slaughter and meat qualities of carcasses and, as a result, the yield of valuable cuts: spinogrudnogo – by 6.1 and 4.0 kg (P<0.01-0.001), lumbar – by 2.6 and 1.7 kg (P<0.05-0.01) and hip – by 8.6 and 7.1 kg (P<0.001). The quality of meat carcasses was proved by organoleptic, biochemical and spectrometric parameters and, consequently, the safety of the tested preparations. It was found that the implementation of the biological potential of the body of bulls due to the activation of hematopoiesis, cellular and humoral factors nonspecific resistance of biopreparations. The novelty of the obtained data is confirmed by the patents of the Russian Federation for invention № 2602687 and № 2622765 registered in the State register of inventions of the Russian Federation on 26.10.2016 and 19.06.2017, respectively.

Peri-conception and first trimester diet modifies reproductive development in bulls.

Nutritional perturbation during gestation alters male reproductive development in rodents and sheep. In cattle both the developmental trajectory of the feto-placental unit and its response to dietary perturbations is dissimilar to that of these species. This study examined the effects of dietary protein perturbation during the peri-conception and first trimester periods upon reproductive development in bulls. Nulliparous heifers (n=360) were individually fed a high- or low-protein diet (HPeri and LPeri) from 60 days before conception. From 24 until 98 days post conception, half of each treatment group changed to the alternative post-conception high- or low-protein diet (HPost and LPost) yielding four treatment groups in a 2×2 factorial design. A subset of male fetuses (n=25) was excised at 98 days post conception and fetal testis development was assessed. Reproductive development of singleton male progeny (n=40) was assessed until slaughter at 598 days of age, when adult testicular cytology was evaluated. Low peri-conception diet delayed reproductive development: sperm quality was lowered during pubertal development with a concomitant delay in reaching puberty. These effects were subsequent to lower FSH concentrations at 330 and 438 days of age. In the fetus, the low peri-conception diet increased the proportion of seminiferous tubules and decreased blood vessel area in the testis, whereas low first trimester diet increased blood vessel number in the adult testis. We conclude that maternal dietary protein perturbation during conception and early gestation may alter male testis development and delay puberty in bulls.

Testicular ultrasonogram pixel intensity during sexual development and its relationship with semen quality, sperm production, and quantitative testicular histology in beef bulls

This study was conducted to evaluate testicular ultrasonogram pixel intensity during sexual development in bulls and to determine its relationship with semen quality, sperm production, and quantitative testicular histology. Beef bulls (N = 152) were examined from 14 - 26 to 70 - 74 wk of age in four different years. Testicular echogenicity increased during sexual development, but the pattern of change differed among years. Echogenicity increased between 26 and 42 to 46 wk of age in 2 yr, but increased considerably earlier in the other 2 yr, reaching maximum values at 34 wk of age. Because increased echogenicity was likely associated with testicular changes leading to initiation of spermatogenesis, these differences were difficult to explain considering that age at puberty did not differ significantly among years. When data were evaluated according to age normalized to puberty, echogenicity started to increase 16 to 12 wk before puberty and reached maximum values 4 wk before or at puberty. These results indicate that a certain developmental stage of the testicular parenchyma must be reached before puberty and that the composition of the parenchyma remained consistent after puberty. Testicular echogenicity was associated with sperm production, seminiferous tubule and epithelium area, and sperm morphology, but the associations were not consistent. Testicular echogenicity was a good indicator of pubertal and mature status, but was not superior to scrotal circumference. In conclusion, although testicular ultrasonogram pixel intensity analysis might be useful for research purposes, clinical application of this technology in the present form for bull breeding soundness evaluation is not justifiable.

Vascular endothelial growth factor regulates germ cell survival during establishment of spermatogenesis in the bovine testis

Vascular endothelial growth factor-A (VEGFA) is a hypoxia-inducible peptide essential for angiogenesis and targets nonvascular cells in a variety of tissues and cell types. The objective of the current study was to determine the function of VEGF during testis development in bulls. We used an explant tissue culture and treatment approach to test the hypothesis that VEGFA-164 could regulate the biological activity of bovine germ cells. We demonstrate that VEGFA, KDR, and FLT1 proteins are expressed in germ and somatic cells in the bovine testis. Treatment of bovine testis tissue with VEGFA in vitro resulted in significantly more germ cells following 5 days of culture when compared with controls. Quantitative real-time RT-PCR analysis determined that VEGF treatment stimulated an intracellular response that prevents germ cell death in bovine testis tissue explants, as indicated by increased expression of BCL2 relative to BAX and decreased expression of BNIP3 at 3, 6, and 24 h during culture. Blocking VEGF activity in vitro using antisera against KDR and VEGF significantly reduced the number of germ cells in VEGF-treated testis tissue to control levels at 120 h. Testis grafting provided in vivo evidence that bovine testis tissue treated with VEGFA for 5 days in culture contained significantly more differentiating germ cells compared with controls. These findings support the conclusion that VEGF supports germ cell survival and sperm production in bulls.

199 EFFECT OF HEPARIN CONCENTRATION ON BOVINE PREIMPLANTATIONAL DEVELOPMENT IN VITRO USING SEX-SORTED SPERM

The objective of this study was to examine the effect of heparin on bovine IVF and to improve the efficiency of IVF production by using sex-sorted sperm. The fertility performance of sex-sorted and unsorted semen from 4 bulls was compared to determine the optimal heparin concentration during preimplantational embryo development. A total of 7615 matured bovine oocytes were randomly allocated among different heparin concentrations (0, 2.5, 5, 10, 20, 40, 60, 80, and 100 μg mL–1) in Brackett-Oliphant medium and coincubated with either sex-sorted or unsorted sperm for 6 h. Presumptive zygotes were cultured in CR1aa+ 6 mg mL–1 of BSA in 5% O2 , 5% CO2 and 90% N2 at 39°C until Day 8 (Day 0, culture post-IVF). Cleavage rates at Day 2 and embryo development to blastocyst (BL) at Day 8 were recorded. Data (4 replicates) were analyzed by a general linear model (SPSS 11.0, SPSS Inc., Chicago, IL). The optimal heparin concentration for each treatment was determined as the lowest value from those groups that resulted in the highest BL rates. The results (Table 1) demonstrated that a differential requirement of heparin concentration was important for the highest preimplantational BL development between sexed sperm and unsorted control within each bull. By optimizing heparin concentration, in 3 out of 4 (75%) bulls, the in vitro BL development with sex-sorted sperm could be increased to a level that was comparable to the highest BL rate from unsorted sperm (bulls A, B, and C, P > 0.05). A higher heparin concentration was required for optimal BL development in bulls A and C; however, a lower concentration was desirable for bulls B and D, indicating that a partial capacitation to the sperm may have taken place in bulls B and D during the sorting process, as reported by Lu and Seidel (2004 Theriogenology 62, 819–830). The fertility of sorted sperm from bull D (1 out of 4, 25%) was adversely affected, even after heparin optimization for BL development (P < 0.05). This result suggests that sperm sorting could affect the IVF fertility of sorted sperm in a bull-specific manner, but it was not significant for all bulls. Table 1. Blastocyst (BL) development in bovine IVF after heparin optimization using sorted and unsorted sperm This project was supported by the SBIR program under a USDA Cooperative State Research, Education, and Extension Service (CSREES) grant to F. Du (USDA #2006-03069).

Effect of feed restriction during calfhood on serum concentrations of metabolic hormones, gonadotropins, testosterone, and on sexual development in bulls

The objective of the present study was to evaluate the effects offeed restriction during calfhood on serum concentrations of metabolic hormones, gonadotropins, and testosterone, and on sexual development in bulls. Eight beef bull calves received a control diet from 10 to 70 weeks of age. An additional 16 calves had restricted feed (75% of control) from 10 to 26 weeks of age (calfhood), followed by either control or high nutrition (n=8/group) during the peripubertal period until 70 weeks of age. Restricted feed during calfhood inhibited the hypothalamic GnRH pulse generator, reduced the pituitary response to GnRH, impaired testicular steroidogenesis, delayed puberty, and reduced testicular weight at 70 weeks of age, regardless of the nutrition during the peripubertal period. Restricted feed reduced serum IGF-I concentrations, but concentrations of leptin, insulin, and GH were not affected. In conclusion, restricted feed during calfhood impaired sexual development in bulls due to adverse effects on every level of the hypothalamus-pituitary-gonad axis and these effects were not overcome by supplemental feeding during the peripubertal period. Furthermore, based on temporal associations, the effects of restricted feed on the hypothalamus-pituitary-gonad axis might be mediated by serum IGF-I concentrations. These results supported the hypotheses that the pattern of LH secretion during the early gonadotropin rise during calfhood is the main determinant of age of puberty in bulls and that gonadotropin-independent mechanisms involved in testicular growth during the peripubertal period are affected by previous LH exposure.

Circulating Metabolic Hormones During the Peripubertal Period and Their Association with Testicular Development in Bulls

The objective of the present study was to characterize changes in serum metabolic hormones concentrations from 20 weeks before to 20 weeks post-puberty in bulls and to investigate the associations of metabolic hormones concentrations with testicular development. Leptin concentrations increased from 16 weeks before puberty to 8 weeks post-puberty and insulin concentrations increased from puberty to 8 weeks post-puberty. Growth hormone concentrations decreased after 4 weeks post-puberty, whereas IGF-I concentrations increased from 8 weeks before puberty to 8 weeks post-puberty. During this period, testicular growth was accelerated and testosterone secretion increased substantially, without any significant changes in gonadotropin secretion. Monthly circulating concentrations of leptin, IGF-I and insulin accounted for 63% of the variation in scrotal circumference and 59% of the variation in paired testes volume. In conclusion, the secretion of metabolic hormones was not associated with changes in gonadotropins concentrations. Furthermore, the associations of leptin, IGF-I and insulin concentrations with testes size indicated that these hormones might be involved in a gonadotropin-independent mechanism regulating the testicular development in peripubertal bulls.

Effect of improved nutrition during calfhood on serum metabolic hormones, gonadotropins, and testosterone concentrations, and on testicular development in bulls

The objective of the present study was to evaluate the effects of improved nutrition during calfhood on serum metabolic hormones, gonadotropins and testosterone concentrations, and on sexual development in bulls. Bulls received high ( n = 17) or control nutrition ( n = 16) diets from 10 to 30 week of age and the same control nutrition diet from 31 to 74 week of age. Improved nutrition during calfhood resulted in a more sustained period of elevated LH secretion (pulse frequency and total secretion in 10 h) during the early gonadotropin rise. GnRH-stimulated LH secretion was not affected by diet, indicating that pituitary responsiveness was not altered; therefore, improved nutrition had direct effects on GnRH secretion by the hypothalamus. Insulin and insulin-like growth factor-I (IGF-I) concentrations were greater during calfhood in bulls receiving high nutrition, indicating that these metabolic hormones might be involved in regulating GnRH and LH secretion. Improved nutrition also resulted in increased testosterone secretion that was associated with greater circulating IGF-I concentrations, suggesting a role for this metabolic hormone in regulating Leydig cell number and function. Furthermore, improved nutrition during calfhood resulted in greater testicular weight and sperm production in mature bulls, indicating that increased LH secretion during calfhood, and increased IGF-I and testosterone concentrations during calfhood and peripubertal period were associated with greater testicular cell proliferation and enhanced function.

Effect of nutrition during calfhood and peripubertal period on serum metabolic hormones, gonadotropins and testosterone concentrations, and on sexual development in bulls

The objective of the present study was to characterize the effects of nutrition on circulating concentrations of metabolic hormones, gonadotropins, and testosterone during sexual development in bulls. Nutrition regulated the hypothalamus–pituitary–testes axis through effects on the GnRH pulse generator in the hypothalamus and through direct effects on the testes. Pituitary function (gonadotropin secretion after GnRH challenge) was not affected by nutrition. However, nutrition affected LH pulse frequency and basal LH concentration during the early gonadotropin rise (10–26 weeks of age). There were close temporal associations between changes in insulin-like growth factor-I (IGF-I) concentrations and changes in LH pulse frequency, suggesting a role for IGF-I in regulating the early gonadotropin rise in bulls. The peripubertal increase in testosterone concentration was delayed in bulls with lesser serum IGF-I concentrations (low nutrition), suggesting a role for IGF-I in regulating Leydig cell function. Serum IGF-I concentrations accounted for 72 and 67% of the variation in scrotal circumference and paired-testes volume, respectively (at any given age), indicating that IGF-I may regulate testicular growth. Bulls with a more sustained elevated LH pulse frequency during the early gonadotropin rise (high nutrition) had greater testicular mass at 70 weeks of age relative to the control group (medium nutrition), despite no differences in metabolic hormone concentrations after 26 weeks of age. Therefore, gonadotropin-independent mechanism regulating testicular growth might be dependent on previous gonadotropin milieu.

Changes in Circulating and Testicular Levels of Inhibin A and B During Postnatal Development in Bulls

We investigated testicular and circulating levels of dimeric inhibins in Holstein bulls from the infantile to postpubertal periods (5 to 50 weeks of age) and examined the relationship between the profiles of circulating dimeric inhibins and FSH. Concentrations of total inhibin and inhibin B in the testis were highest at 4 to 5 weeks of age but decreased gradually as the bulls aged. Testicular inhibin A levels showed a gradual decline to a nadir at 15 to 26 weeks of age, but by 39 weeks, they were high again. The contents of total inhibin, inhibin A, and inhibin B per testis generally increased with age. Fractionation of testicular homogenates obtained from 15-week-old bulls by a combination of immunoaffinity chromatography and SDS-PAGE confirmed the presence of two major molecular weight forms (32 and 45 kDa) of dimeric inhibins in the testes. Circulating levels of total inhibin and inhibin A showed a significant increase in bulls at around 10 to 14 weeks of age compared to the levels between 5 and 7 weeks of age but decreased thereafter. However, immunoreactivity for inhibin B was not detected in the peripheral circulation, probably because of low sensitivity of the inhibin B assays. The concentrations of plasma FSH were high at 5 weeks of age but declined to lower levels between 11 and 40 weeks, and then increased from 41 weeks onward. There was no significant correlation between the plasma levels of FSH and inhibin A or total inhibin. The results clearly indicate that the bull testis produces inhibin A and B and secretes at least inhibin A into the circulation during postnatal development. However, the profile of circulating FSH in bulls shows no reciprocal relationship with the inhibin A or total inhibin profile during the postnatal period.

The relationship between secretory patterns of gonadotrophic hormones and the attainment of puberty in bull and heifer calves born early or late during the spring calving season

It was suggested that an early increase in gonadotrophin secretion in calves aged between 6 and 24 weeks might be critical for initiating developmental changes culminating in puberty. An early rise in luteinizing hormone (LH) release appears to be caused by an increase in LH pulse frequency in bull calves and by an increase in LH pulse amplitude in heifer calves. Previously we have found differences in the characteristics of the LH rise between prepubertal beef calves born in spring or fall; however, age at puberty was not affected by season of birth. Here we report the LH/FSH secretory patterns in prepubertal bull and heifer calves (Hereford x Charolais), born in March or April, respectively (i.e., early or late during the spring calving season; six animals of each sex born at each time). The bull calves of both groups reached puberty (defined as an attainment of scrotal circumference of ≥ 28 cm) at 43.2 ± 1.3 weeks of age ( P > 0.05). Age at puberty for March- and April-born heifer calves (defined as the age at which serum progesterone concentrations first exceeded 0.4 ng/ml) averaged 56.0 ± 1.4 weeks ( P > 0.05). Based on blood samples taken weekly from birth to 26 weeks of age, and then every other week until puberty, bull calves born in March exceeded April-born bull calves in mean serum LH concentrations at 6, 10 and 12 weeks of age ( P < 0.05). Mean FSH concentrations were greater ( P < 0.05) in March-born compared to April-born bull calves from 34 to 32 weeks before puberty. Mean serum LH (at 40, 42 and 56 weeks) and FSH concentrations (at 2, 10, 20, 22–26, 30 and 56 weeks of age) were greater ( P < 0.05) in heifer calves born in April than March. On the basis of frequent blood sampling (every 12 min for 10 h), heifer calves born in April exceeded March-born animals in mean LH and FSH concentrations, at 5 and 25 weeks, and LH pulse frequency, at 5, 10 and 25 weeks of age ( P < 0.05). None of the parameters of LH secretion (i.e., mean concentrations of LH, LH pulse frequency and amplitude based on frequent blood collection) differed between March- and April-born bull calves in this study ( P > 0.05). In summary, March-born bull calves had greater mean serum LH and FSH concentrations prior to 24 weeks of age than April-born calves. April-born heifer calves had greater mean serum concentrations of LH and FSH but this difference was not confined to the early postnatal period. Although there were significant differences in absolute amounts of LH secreted, there were no differences in the frequency of LH secretory pulses amongst March- and April-born bull calves and no differences in LH pulse amplitude in heifer calves born in March or April. As these particular parameters of LH secretion, as well as age at puberty, are not affected by the time or season of birth, they may be primary hormonal cues governing sexual development in bulls and heifers, respectively.

Pasture management effects on diet composition and cattle performance on continuously stocked rhizoma peanut-mixed grass swards.

In Florida, rhizoma peanut (RP; Arachis glabrata Benth.), a tropical legume, combines the attributes of excellent nutritive value, competitive ability with tropical grasses, and high animal performance. The objective of this study was to determine the effects of spring N fertilization (0 vs 35 kg/ha) and summer stocking rate (1.5 and 2.5 bulls/ha) on herbage mass, nutritive value, herbage allowance, and diet botanical composition of grazed RP-grass swards and their interaction with growth and development of bulls (Senepol, and Brahman or Angus). The study was conducted in 1995 and 1996 at the USDA, ARS, Subtropical Agriculture Research Station in Brooksville, FL. Nitrogen was applied in April of each year, and all pastures were stocked with 1.5 bulls/ha until approximately July of each year, when stocking rate was increased on half the pastures to 2.5 bulls/ha. Herbage mass (HM, kg/ha), herbage allowance (HA, kg/kg BW), nutritive value (CP and in vitro organic matter digestibility [IVOMD]), and diet botanical composition (fecal microhistological) readings were determined. Animal measurements included total and seasonal (spring vs summer), ADG, hip height (cm), scrotal circumference (SC, cm), and plasma urea nitrogen (PUN, mg/dL). Herbage mass (3.0 +/- 0.12 Mg/ha and 3.4 +/- 0.13 Mg/ha in 1995 and 1996, respectively) was not affected by nitrogen fertilization or stocking rate but was affected by season (P < 0.05) due to increased plant growth rate associated with summer rainfall. Stocking rate did affect herbage availability, but it never fell below 3 kg/kg BW, indicating herbage availability was never limiting. Crude protein (200 to 140 g/kg) and IVOMD (650 to 540 g/kg) were not affected by treatment, but declined (P < 0.001) from spring until fall. Treatments also had no effect on diet botanical composition. Summer ADG averaged about 0.2 kg/d lower than spring ADG, due, in part, to seasonal declines in nutritive value. Because herbage allowance was never limiting, full-season ADG was not affected by stocking rate or N fertilization and averaged 0.61 +/- 0.03 and 0.60 +/- 0.02 kg/d in 1995 and 1996, respectively. There were season x breed interactions (P < 0.05) for ADG due to greater declines during the summer for Angus than for Senepol or Brahman. There were no differences in final BW, SC, BCS, hip height, or PUN due to treatments, but breed differences were noted (P < 0.05) for all measures except BCS.

Testicular development in bulls treated with recombinant bovine somatotropin.

This study was conducted to test the hypothesis that administering recombinant bovine somatotropin (rbST) would affect testicular development in Holstein bulls. From 4 until 32 wk of age, bulls received a daily injection of either placebo (C) or rbST (.2 mg/kg BW.75, i.m.; n = 10/group). At 14-d intervals, blood was obtained and assayed for testosterone (T); BW, shoulder height (SH), and testis length (TL) were recorded. At 7, 12, and 24 wk of age, bulls were bled at 10-min intervals for 6 h to determine the secretory patterns of LH, growth hormone (GH), and IGF-I. All bulls were killed at 40 wk of age. One testis was used for determination of daily sperm production (DSP), and the number of spermatids per gram of parenchyma (SP/G); the remaining testis was perfused and fixed for histological analysis of numbers of Sertoli cell nuclei (SCN/ST) and spermatids per seminiferous tubule cross-section (SP/ST). Epididymal spermatozoa were collected to test effects of rbST on the integrity of spermatozoal chromatin structure. Administration of rbST increased (P < .0001) concentrations of GH (nanograms/milliliter) in plasma at all ages (C vs rbST; wk 7, 8.9 +/- 1.0 vs 51.9 +/- 6.8; wk 12, 12.8 +/- 1.4 vs 59.2 +/- 6.4; and wk 24, 5.2 +/- 1.5 vs 42.6 +/- 12.2). There was an age x treatment interaction (P < .0183) for concentrations of IGF-I (nanograms/milliliter) in plasma (C vs rbST; wk 7, 149.7 +/- 6.1 vs 148.6 +/- 8.6; wk 12, 184.1 +/- 12.8 vs 216.6 +/- 15.9; and wk 24, 392.8 +/- 24.8 vs 484.7 +/- 19.9).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of feeding endophyte-infected ( [formula omitted][formula omitted]) KY-31 fescue hay on the reproductive development of Holstein bulls

This study was designed to assess the effect of endophyte-infected ( Acremonium coenophialum ) tall fescue (KY-31) on reproductive development in bulls. Eighteen Holstein bull calves (2 mo old) were randomly allocated to one of two dietary treatments consisting of 1) noninfected KY-31 fescue hay (NON) supplemented with grain (n=9) and 2) infected (67% infected by Acremonium coenophialum ) KY-31 fescue hay (INF) supplemented with grain (n=9). Both dietary treatments consisted of equal amounts of hay and grain. Data were collected every 14 d. Body weight, hip height and scrotal circumference did not differ (P>0.05) in the two treatments. Mean rectal temperatures also were not different in bulls (P = 0.12); however the infected bulls experienced higher rectal temperatures in all but four collection periods. Animals were sacrificed at 13 mo of age. Testicular weight and dimensions, epididymal weight and length as well as seminal vesicle weight were not different (P>0.05). Maturity of spermatozoa taken from each cauda epididymides was assessed by the incidence of cytoplasmic droplets and was not different (P>0.05) between treatments. Daily sperm production potential was not different (P>0.05) between treatments; however, large variations were noted among the infected bulls. Blood testosterone levels were not different (P=0.29) between the two dietary treatments, but were different over time (P<0.001) with NON and INF bulls having 2.14 ± 0.21 and 2.41 ± 0.22 ng/ml, respectively. Prolactin levels were different (P<0.02) between the NOn and INF bulls, 29.35 ± 3.35 vs 18.31 ± 3.39 ng/ml, respectively; and over time (P<0.001). The data generated in this study showed some important biological trends. Overall, the results indicate that endophyte infected KY-31 fescue hay fed to growing bulls did not appear to have severe detrimental effects on body growth or reproductive development. However, additional studies will be necessary to further delineate the patterns established in this study.