Testicular development and its relationship to semen production in Murrah buffalo bulls

The objectives of this study were to determine the relationship of age and body weight to testicular development and to establish norms for breeding soundness evaluations of Murrah buffalo bulls. Testicular measurements of 133 Murrah buffalo bulls of various ages were recorded with a caliper and a tape. Semen was collected twice a week for 5 weeks from groups of bulls which were 25-36 (n=17), 37-48 (n=16), 49-60 (n=14), of >60 (n=10) months of age. After examining volume, sperm concentration, and progressive motility semen was diluted in Tris-citric acid-egg yolk-fructose extender and frozen in 0.5 ml French straws. Testicular measurements of buffalo bulls were lower than those recorded for European breeds of cattle bulls. Nevertheless, like cattle bulls, scrotal circumference was highly correlated with other testicular measurements. Also, it had a significant positive relationship with semen volume and sperm concentration per ejaculate. Average sperm output per week in order of increasing age group was 15.3, 18.2, 19.8 and 23.6 x 10(9). Corresponding values for sperm output per week per gram of testis were 59.1, 45.8, 41.1, 36.2 x 10(6) indicating a reduction in spermatogenesis per unit of testis with advancing age. Compared to European breeds, daily sperm output in Murrah bulls was nearly 45% lower, presumably due to their nearly 40% lower scrotal circumference than Holstein bulls of the same age. These results indicate that in buffalo, as in cattle, scrotal circumference is a useful indicator of potential sperm output and may serve as an important criterion for selecting young bulls as AI sires.     

Active immunization of prepubertal bulls against testosterone: Seminal and testicular characteristics after puberty

Twenty-four Holstein bull calves were immunized at 1.0 month of age against either testosterone-17-hemisuccinate-human serum albumin (treated bulls) or against human serum albumin alone (control bulls). Booster injections were given monthly through five months of age. Bulls were reimmunized at six months of age with testosterone-17-hemisuccinate-equine serum albumin (treated bulls) or equine serum albumin alone (control bulls). At 12 months of age, eight treated and eight control bulls were electroejaculated twice daily for two days and then castrated. The remaining four bulls in each group were electroejaculated and castrated at 18 months of age. Active immunization against testosterone significantly elevated the binding of (3)H-testosterone in plasma within four weeks. Body weights of bulls were not affected by treatment. Concentrations of luteinizing hormone (LH) and follicle stimulating hormone (FSH) in plasma were generally not altered by treatment. At castration at 12 months of age, testosterone-immunized bulls tended to have greater (P < 0.15) parenchymal weights and had 30% greater (P < 0.07) daily sperm production (DSP) rates than control bulls; seminal characteristics (motility and intact acrosomes) were not affected. At 18 months of age, testosterone-immunized bulls had 21% greater (P < 0.07) parenchymal weights and 35% greater (P < 0.04) DSP rates than control bulls; again, seminal characteristics were not affected. It appears that prepubertal active immunization against testosterone is a potential means of increasing testicular size and sperm production rates in postpubertal bulls.     

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.     

Testicular and epididymal function during the peripuberal period in Brahman bulls receiving various amounts of protein degradable in the rumen

Thirty-nine Brahman bulls with an initial age and weight of 301.7 +/- 4.1 d and 202.7 +/- 4.7 kg, respectively, were randomly allocated to 1 of 2 dietary treatment groups within age, weight and sire in order to study the influence of source of protein and stage of peripuberal period on testicular and epididymal function. In the soybean meal treatment the amount of protein undegradable in the rumen averaged 47%, while it was 72% in the fish meal treatment. The supplements were isocaloric and isonitrogenous. Bulls were electroejaculated, and castrations were performed randomly in a predetermined order when the first ejaculate with the first motile sperm cells (Stage 1), 10 to 25 million (Stage 2), and 50 million or more sperm cells (Stage 3 - puberty) was obtained. Testicular and epididymal traits were analyzed for a single testicle and epididymis. Daily sperm production, daily sperm production per gram of testicular parenchyma, testicular weight and testicular parenchyma weight were not affected by treatment. Bulls receiving fish meal had heavier (P < 0.01) epididymis than soybean meal-fed bulls (6.6 +/- 1.0 vs 3.9 +/- 0.6 g) but similar (P > 0.05) epididymal sperm reserves. Daily sperm production (1 testicle) was 115.2 +/- 0.1, 447.4 +/- 0.1, 792.7 +/- 0.1 million sperm cells, and daily sperm production per gram of testicular parenchyma was 1.5 +/- 0.5, 3.2 +/- 0.6 and 6.4 +/- 0.6 million sperm cells for bulls at Stage 1, 2 and 3, respectively. Sire and amount of undegradable intake protein had significant (P < 0.05) affects on the distribution of epididymal sperm reserves, with soybean meal-fed bulls having the higher proportions of epididymal sperm reserves in the cauda epididymis.     

Breeding soundness evaluations of Senepol bulls in the US Virgin Islands

The breeding soundness evaluation (BSE) was used to evaluate Senepol (Bos taurus) bulls (n = 495) on St. Croix over a 7-year period. Young, unproven bulls (10-26 months of age) and breeding bulls (16 months to 8.5 years) were tested prior to sale or use in breeding. Inbreeding coefficients were determined for a subset of bulls (n = 290). The percentage of bulls passing the BSE increased (P < 0.0001) with age. Bulls that passed had a higher percentage (P < 0.0001) of normal and motile sperm as well as a larger (P < 0.0001) scrotal circumference than bulls that failed. No bulls failed the BSE for physical soundness traits or other health reasons. The incidence of testicular hypoplasia was 2.5 and 3.3% and the incidence of cryptorchidism was 1.4 and 0.9% in 12- and 16-month-old bulls, respectively, with no occurrence in bulls >20 months. The proportion of all bulls that failed the BSE and received an Unsatisfactory rating for scrotal circumference or sperm motility decreased (P < 0.0001) from >90 to <25% with age. The proportion of all bulls that failed the BSE and received an Unsatisfactory rating for sperm morphology decreased (P < 0.0001) from 99 to 83.3% with age. The inbreeding coefficient was higher (P < 0.03) in bulls that failed the BSE than in those that passed (2.24 +/- 0.19% versus 1.40 +/- 0.32%, respectively). There was a tendency for bulls with testicular hypoplasia or cryptorchidism to have a higher (P = 0.09) inbreeding coefficient than bulls with normal testes (2.90 +/- 0.46% versus 2.13 +/- 0.11%, respectively). In conclusion, Senepol bulls raised under tropical conditions had a low probability of passing the BSE at young ages, but the passing rate increased with age. Older Senepol bulls were more likely to fail the BSE due to abnormal sperm morphology than due to inadequate testicular size or sperm motility. To prevent unnecessary culling, a BSE should not be performed on Senepol bulls <16 months old.     

Determination of onset of puberty in Zebu bulls under tropical conditions of northern Nigeria

Age at puberty and related phenomena were investigated in White Fulani (Bunaji - WF), Sokoto Gudali (SG) and Friesian X Bunaji (FRXWF) Zebu bulls from 28 weeks to 72 weeks of age. Pubertal traits studied included body weight, heart girth, scrotal circumference and sperm production. Puberty was defined as the age at which an ejaculated semen contained at least 50 x 10(6) spermatozoa with a minimum of 10% motility. Age at puberty was 66.89 +/- 1.0, 73.4 +/- 2.2 and 62.4 +/- 10.7 weeks for WF, SG and FRXWF bulls respectively. The Bunaji bulls were significantly younger than the Sokoto Gudali bulls at production of first motile sperm cell and also at puberty (P<0.01). The SG bulls were significantly heavier (P<0.01) and had larger heart girth (P<0.05) than the FRxWF at production of first motile sperm cells. Body weight and heart girth for all the breeds were not different at puberty (P>0.1). Scrotal circumference of the bulls between the breeds at production of first motile sperm cells and at puberty, did not differ (P 0.>1), despite the variations in age, weight and heart girth at production of first motile sperm cell and at puberty. It is concluded from the data obtained that the indigenous breeds of bulls (Bos indicus ) seem to attain puberty later than exotic breeds (Bos taurus ). The inter-play of genetic, nutritional and environmental factors as a contribution to this delay in attainment of puberty could not be ruled out.     

Changes in profiles of serum sex steroids of male buffaloes from birth to maturity

Age-related changes in testosterone, progesterone and estradiol 17-beta were determined by radioimmunoassay (RIA) in the serum of 155 male buffalo calves of varying ages. The calves were classified into 17 age groups. The mean weight of calves increased from 33.6 +/- 9.6 kg at one week of age to 531 +/- 41.4 kg at 42 months. The testosterone levels were less than 100 pg/ml from birth until 15 months of age, followed by peak concentrations of 422 +/- 79 pg/ml at 24 to 30 months and 793 +/- 193 pg/ml at 42 to 48 months (corresponding to puberty and maturity, respectively). The progesterone levels were higher in newly born calves and mature bulls. Otherwise, the levels continued to be low throughout the period of growth and development. Estradiol 17-beta was significantly higher in postnatal calves up to two months of age. The testosterone revealed a positive correlation with weight and age while E2 17-beta showed a negative correlation with age. These results do not support a direct role of peripheral progesterone and estradiol 17-beta in the onset of puberty and sexual maturity of buffalo bulls.     

Testosterone secretion in young and adult buffalo bulls

Studies were conducted to determine the 24-hour fluctuations in blood serum testosterone concentration in adult buffalo bulls, and to measure testosterone secretion before and after GnRH administration in male buffaloes of different age groups. Testosterone levels in three sexually mature bulls ranged from 0.2 to 2.7 ng/ml with a mean of 0.6 +/- 0.2 ng/ml. Samples collected in November had significantly higher (P<0.05) testosterone than those drawn in February (dry season) as did samples collected during the day as opposed to the night. Sera testosterone concentrations were lower in younger bulls with a range of 0.2 to 0.6 ng/ml. GnRH induced an increase in testosterone in 6, 12, 24 and 36-month old bulls with the greatest response being observed at 36 months. GnRH did not elicit a response in one-month old bulls. It may be concluded that baseline sera testosterone concentrations in buffalo bulls, as well as responsiveness to GnRH injection, increase with sexual maturity and are subject toseasonal and diurnal variations.     

Relationship of scrotal circumference and testicular volume to age and body weight in the swamp buffalo (Bubalus bubalis)

Scrotal circumference (SC) and testicular volume (TV) were measured in 65 swamp buffalo bulls ranging in age from 7 to 60 months and weighing 130 kg to 560 kg. Ages and body weight (BW) were recorded for each male at the time of measurement to find out if they correlated with SC and TV. SC and TV increased linearly and correlated significantly with age and BW (SC vs age: r = 0.74, p<0.01; SC vs BW: r = 0.88, p<0.01; TV vs BW: r = 0.82, p<0.01). SC measurements ranged from 15.1 +/- 1.1 cm to 24.0 +/- 0.4 cm for ages ranging from 10.0 +/- 0.6 to 48.5 +/- 6.3 months, revealing that testicular size in swamp buffaloes was very much smaller than domestic cattle. The SC norms distributed with age would be useful in the evaluation of swamp buffalo males for breeding soundness.     

Effect of hemicastration on the level of testicular steroids and growth in bulls and boars

Ten, bull calves of the Norwegian Red breed were hemicastrated at the age of 1 1 2 -3 months . Ten, normal bull calves of similar age served as controls. No significant differences were found in plasma testosterone levels or in weight between the two groups during the ensuing seven-month test period. Eight, male pigs were hemicastrated at 1-2 months of age. Eight, normal male pigs served as controls. Plasma testosterone, androstenone, and body weight were measured fortnightly in all pigs until the age of 6-7 months. Androstenone in adipose tissue was measured from 4-5 months of age. No significant differences were found between normal and hemicastrated animals in any monthly interval. However, when combining the measurement at 5-6 and 6-7 months of age for plasma testosterone and 5alpha-androstenone and 5alpha-androstenone in fat, the normal pigs had significantly higher values than the hemicastrates (p<0.05). The weight of the single testis from the hemicastrated pigs at slaughter nearly equalled the combined weight of both testes from the controls. Thus, hemicastration did not appear to have any significant effect on the level of testicular steroids in plasma in bulls or growth rate in bulls and boars, but did have a slight effect on testicular steroids in plasma in pigs at 5-7 months of age.     

Testosterone, luteinizing hormone, follicle stimulating hormone, and prolactin response to unilateral castration in prepubertal Holstein bulls

Hemicastration of Holstein bulls at 3 months of age resulted in increased (P<0.005) testicular weitht and testis sperm cell content at 330 days after treatment, but did not alter sperm cell concentration in the remaining hypertrophied testis. Radioimmuroassay of blood hormones at 1, 6, 12, and 24 weeks after treatment revealed that unilateral castration did not alter (P>0.1) basal levels or GnRH response profiles of either LH or testosterone compared to intact bulls. Hemicastration caused FSH to be elevated (P<0.01) compared to intact bulls at all sampling periods in both unstimulated and GnRH stimulated bulls. Prolactin varied with season and was greater (P<0.001) in hemicastrated bulls than in intact bulls at 1 and 6 weeks after treatment. Results indicate that unilateral castration at 3 months of age caused testicular hypertrophy of both steroidogenic and gametogenic function and this phenomena may be triggered by increased FSH or prolactin secretion, or both. Further, results indicate different testicular regulation mechanisms exist for pituitary LH and FSH release in bulls.     

Immunoneutralization of inhibin modifies hormone secretion and sperm production in bulls.

The objective of this study was to examine the role of endogenous inhibin in the regulation of FSH, LH, and testosterone secretion and sperm production in bulls. Bulls were actively immunized against bovine inhibin alpha 1-26 gly-tyr (bINH) conjugated to human alpha globulin (HAG) or HAG alone (controls) and emulsified in Freund's complete adjuvant. Primary immunization was at 14 wk of age, followed by booster immunizations in Freund's incomplete adjuvant at 28, 30, and 34 wk of age. Ten days after each booster immunization, scrotal circumferences and body weights were measured, and blood was sampled for determination of bINH antibody titer. Ten days after the third booster, blood was sampled at 1-h intervals for 8 h to quantify serum concentrations of FSH, LH, and testosterone. After this blood sampling period, bulls were castrated and testicular sperm production was determined. Serum diluted 1:4,000 from bINH-immunized bulls bound 36%, 52%, and 53% of radioiodinated bINH after the first, second, and third boosters, respectively. Serum from controls bound less than 1% radioiodinated bINH. After the third booster, serum concentrations of FSH and testosterone were increased (p less than 0.05) and LH concentrations were decreased (p less than 0.001) in bINH-immunized bulls compared with controls. After the third booster, daily sperm production per gram of testicular parenchyma was increased (p less than 0.05) in bINH-immunized bulls compared with controls. Scrotal circumferences and body weights were similar between treatment groups throughout the experiment. We concluded that inhibin has a role in regulation of secretion of gonadotrophins and testosterone and testicular sperm production, but not testicular growth, in bulls.(ABSTRACT TRUNCATED AT 250 WORDS)     

Androgen binding protein, sperm production, semen output and LH and testosterone profiles in young postpubertal bulls

An androgen binding protein (ABP), which binds 5alpha-dihydrotestosterone with high affinity (Ka = 0.3 x 10(9) M(-1)), has been demonstrated in testicular and epididymal cytosols of 5 young post pubertal bulls (15-17 months old) of the Montbeliarde dairy breed. Simultaneously, daily sperm production (DSP), semen output and plasma LH and testosterone concentrations (from frequent samplings) were determined. ABP levels were 21 fmoles/mg protein in testis and 59, 22 and 43 fmoles/mg, respectively, in caput, corpus and cauda epididymis. Mean DSP, per gram of testis, was 16.6 x 10(6) spermatozoa, and the mean sperm output was approximately 1.5 x 10(9) spermatozoa per ejaculate. Mean LH and testosterone levels were 1.5 ng/ml and 2.1 ng/ml, respectively. One bull (882) was clearly distinguishable from the others, in showing higher ABP and testosterone levels together with a lower daily sperm production. Results of this study may (1) suggest a physiological role of ABP in sperm epididymal maturation and (2) give a new parameter in the evaluation of individual bulls testicular function.     

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.     

Serum profiles of androstenedione, testosterone and LH from birth through puberty in buffalo bull calves

Blood samples were taken once per week for 4-7 weeks from 59 buffalo calves in 14 age groups, 1-2 months apart. Hormones were quantified by validated radioimmunoassays. Values of androstenedione and testosterone were low at birth (141.3 +/- 33.5 pg/ml and 18.0 +/- 2.9 pg/ml, respectively; mean +/- s.d.). Serum androstenedione concentrations gradually increased from birth until 8 months of age and declined (P less than 0.05) thereafter, whereas mean testosterone values were low up to 8 months and then significantly (P less than 0.05) increased as age advanced. LH concentrations averaged 2.12 +/- 0.47 ng/ml at birth. Thereafter, a decline in LH values was followed by an increase between 6 and 15 months of age. We conclude that, in buffalo bull calves, the pubertal period occurs from about 8 to 15 months of age. For pubertal buffalo bulls 15-17 months of age, serum concentrations of androstenedione, testosterone and LH were 156.9 +/- 54.6 pg/ml, 208.4 +/- 93.8 pg/ml and 2.10 +/- 0.70 ng/ml, respectively.     

Effect of long-term immunization against inhibin on sperm output in bulls.

To determine the effect of neutralization of inhibin on sperm output, 12 Holstein bulls were paired by birth date and weight on Day 1 of age. Each bull was actively immunized against bovine inhibin alpha1-26 gly-tyr (bINH) conjugated to human alpha globulin (HAG, n = 6 bulls) or HAG alone (controls, n = 6) at 60 days of age; booster immunizations were administered at 90, 104, 124, 270, and 395 days of age. Body weights and scrotal circumferences were measured at the time of primary immunization and at 10 days after each booster. In addition, jugular blood was obtained at 60, 70, 100, 114, 134, 280, and 405 days of age, during the 3-wk sperm collection period, and during a 6-h blood-sampling period after sperm collection to determine bINH antibody titer and concentrations of FSH, LH, testosterone, and estradiol. Beginning at 405 days of age, sperm output was measured 3 days/wk for 3 wk with two successive ejaculates collected each day for a total of 18 ejaculates per bull. During Days 60-405 of age, the increase in titer of bINH antibodies, scrotal circumference, and serum concentration of FSH was greater (p < 0.01) for the bINH-immunized compared with control bulls. There were significant (p < 0.01) pair x treatment interactions for sperm output and serum FSH and LH concentrations. Specifically, bINH-immunized bulls for four of the six pairs had nearly 50% greater serum FSH concentrations and sperm output. For the remaining two pairs, sperm output was lower and FSH was either lower or only marginally higher in the bINH-immunized bulls compared with controls. Also, the control bulls for the two remaining pairs produced more sperm than all but one bINH-immunized bull, and had markedly higher serum LH concentrations than all other bulls. To summarize, enhancement of sperm output after immunization against inhibin depends on the subsequent increment in FSH concentrations. We conclude that inhibin suppresses spermatogenesis. Thus, methods to immunoneutralize inhibin may have merit as a therapeutic route to enhance sperm production in reproductively maturing bulls.     

Motility, acrosome integrity, membrane integrity and oocyte cleavage rate of sperm separated by swim-up or Percoll gradient method from frozen-thawed buffalo semen

Frozen-thawed semen of five buffalo bulls was used to compare efficacy of swim-up and Percoll gradient methods for separating viable spermatozoa. Sperm separated by the two methods were also tested to differentiate buffalo bulls on the basis of in vitro fertilization (IVF) rates. Recovery of motile sperm (%), increase in membrane integrity (%) and acrosome integrity (%) were compared after two sperm separation methods in experiment I, and in vitro fertilization rate (cleavage rate and cleavage index) was compared in experiment II. Swim-up separated sperm showed a higher motility (P<0.05), while percent recovery of motile sperm was higher with Percoll separation (P<0.05). Membrane integrity (%) of sperm separated with swim-up was significantly higher (P<0.05) as compared to sperm separated with Percoll gradient. Swim-up separated sperm gave a higher cleavage rate and cleavage index (P<0.001). Sperm separated by swim-up showed significant difference among the bulls in cleavage rate and cleavage index (P<0.05), while the Percoll gradient method did not. It has been concluded that separation of sperm from frozen-thawed buffalo semen by swim-up method can be more expedient for IVF in buffalo.     

Effect of growth rate from 6 to 16 months of age on sexual development and reproductive function in beef bulls

Sexual development and reproductive function were studied in 22 Angus × Charolais and 17 Angus bulls from 6 to 16 mo of age. Associations of average daily gain (ADG) and body weight with ages at puberty and at maturity (satisfactory semen quality), scrotal circumference, paired-testes volume and weight, testicular vascular cone diameter and fat thickness, scrotal temperature, sperm production and morphology, and testicular histology, were determined. There were no significant correlations between cumulative average daily gain and any of the end points investigated. Body weight at various ages was negatively correlated with ages at puberty and maturity in Angus × Charolais bulls, positively correlated with paired-testes weight in Angus × Charolais and Angus bulls, and positively correlated with seminiferous tubule volume in Angus bulls (P < 0.05). Semen quality improved gradually with age and the interval between puberty and maturity (mean ± SD; 309.4 ± 29.7 and 357 ± 42 days of age) was approximately 50 days. Age, weight, scrotal circumference, and paired-testes volume were all good predictors of pubertal and mature status, with moderate to high sensitivity and specificity (71.6% to 92.4%). In summary, growth rate between 6 and 16 mo of age did not affect sexual development and reproductive function in beef bulls. However, greater body weight at various ages was associated with reduced age at puberty and maturity, and with larger testes at 16 mo of age, indicating that improved nutrition might be beneficial, but only when offered before 6 mo of age. Average daily gains of approximately 1 to 1.6 kg/day did not result in excessive fat accumulation in the scrotum, increased scrotal temperature, or reduction in sperm production and semen quality, and could be considered “safe” targets for growing beef bulls.     

Peripubertal traits of Brahman bulls in Yucatan

In order to investigate elements of puberty in Brahman (Bos indicus) bulls, 12 animals were studied from 10 mo of age until puberty, which was defined as the moment of production of the first ejaculate with at least 50 x 10(6) sperm with 10% progressive motility. Body weight and scrotal circumference were recorded every 2 weeks. From 14 mo of age onwards, the bulls were electroejaculated at the same intervals and ejaculates were evaluated. Blood samples were taken from 6 of the bulls every 30 min for 6 h at 12, 14, 17 and 20 mo of age to study serum concentrations of testosterone, which were determined by RIA. Mean age (+/- SEM) at puberty was 17 +/- 0.4 mo, body weight was 374.6 +/- 22.5 kg and scrotal circumference was 28.6 +/- 0.6 cm. Serum testosterone increased from 12 to 17 mo and then decreased slightly, mean (+/- SEM) concentration being 0.4 +/- 0.1, 1.4 +/- 0.4, 2.9 +/- 0.5 and 2.7 +/- 0.3 at 12, 14, 17 and 20 mo of age, respectively. It was concluded that Brahman bulls, under the conditions studied, attain puberty between 16 and 17 mo of age, with considerable variation, and that serum concentrations of testosterone prior to puberty seem to form a pattern similar to that shown by Bos taurus bulls, however the pattern occurs at a later age.