The development of puberty and sexual maturity in the Australian Swamp buffalo bull

Testes from 47 juvenile Swamp buffalo bulls were examined for puberty and sexual maturity histologically and daily sperm production per gram of testis parenchyma was determined by enumeration of elongated spermatids in homogenates of testis parenchyma. Puberty was defined as the attainment of a daily sperm production per gram of testis parenchyma >0.5 x 10(6). In most bulls, puberty is attained by 24 mo of age, when scrotal circumference (SC) is approximately 16 cm, and liveweight exceeds 135 kg. Sexual maturity was defined as the attainment of adult levels of daily sperm production per gram of testis parenchyma (14 x 10(6)). In most bulls, this occurs at 30 to 33 mo of age, when SC is in the 17-to 20-cm range, and liveweight generally exceeds 250 kg. There was marked individual variation in age, liveweight and SC at both puberty and sexual maturity.     

Effect of implanting bull calves with testosterone propionate, dihydrotestosterone propionate or oestradiol-17 beta prepubertally on the pituitary-testicular axis and on postpubertal social and sexual behaviour.

Twelve non-implanted crossbred bull calves served as controls and 30 crossbred bull calves (10/treatment) were implanted for 82 days, beginning at 34 days of age, to determine the influence of testosterone propionate (TP), dihydrotestosterone propionate (DHTP) and oestradiol-17 beta (E2) on prepubertal and pubertal pituitary-testicular function and on postpubertal social and sexual behaviour. Compared with control bulls, concentrations of serum luteinizing hormone (LH), follicle-stimulating hormone (FSH) and inhibin concentrations were suppressed (P less than 0.01) in all implanted bulls. Testosterone (T) concentration increased (P less than 0.001) in TP-implanted, but decreased (P less than 0.01) in DHTP and E2 bulls during the implant period. LH response to gonadotrophin-releasing hormone (GnRH) challenge during the implant period (2.5 months of age) was less (P less than 0.01) in TP, E2 and DHTP bulls than in controls. A small but significant T response to GnRH occurred in control bulls at 2.5 months of age. LH and T responses to GnRH challenge at 7 months of age (100 days after implant removal) was similar (P greater than 0.20) in control and implanted bulls. Steroid implants administered prepubertally had no effect (P greater than 0.10) on postpubertal social and sexual behaviours, including number of flehmen responses, abortive mounts, services and competitive order score. Body weight did not differ (P greater than 0.10) between treatment groups, but testis size was reduced (P less than 0.01) during the implant period and up to 10 months of age in treated bulls compared with controls. Testes remained smaller in E2-treated bulls up to the end of the study (23 months of age), but daily sperm production and epididymal weight did not differ (P greater than 0.10) between treatment groups at slaughter. Control bulls reached puberty earlier (P less than 0.01; 270 +/- 11 days of age) than did TP (302 +/- 11 days), DHTP (309 +/- 11 days) or E2 (327 +/- 11 days) bulls. Although puberty was delayed in all implant groups, there was no difference in scrotal circumference at puberty (average 28.4 +/- 0.4 cm) between treatment groups. Our findings indicate that TP, DHTP and E2 implants administered prepubertally result in acute suppression of serum LH, FSH and inhibin during the implant period and in post-implant suppression of testis size and delayed puberty in bulls. The lack of treatment effect on behaviour suggests that steroidal programming of sexual behaviour occurs before 1 month of age in bulls.     

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.     

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.     

Influence of unilateral castration and increased plane of nutrition on sexual development of Holstein bulls. II. Histologic development of the testes

Sixty-five Holstein bull calves were assigned in an experiment to determine the effects of unilateral castration (UC) at 1 week of age and of two levels of nutrition after 6 months on reproductive development to 16 months. Five animals were killed at 1 wk and half the remainder UC at that age. Groups of 5 in all factorial groups were killed at 2, 4, 8 and 16 months. Tubular diameter increased with age (P<.01) and at 8 and 16 months with UC (P<.01). Epithelial area at 8 and 16 months increased with age and UC (P<.01). The percents of tubular and intertubular tissue varied with age (P<.01) with the tubular tissue having its highest value at 8 months. Indexes of both total tubular and intertubular tissue were increased with age and UC (P<.01). The number of type A spermatogonia per cross section of stage 1 tubules of 16-month bulls was increased by UC (P<.05).     

Influence of unilateral castration and increased plane of nutrition on sexual development of Holstein bulls. III. Endocrine responses

Pituitary gonadotropic hormones were assayed in 65 Holstein bulls from 7 days to 16 months. Pituitary LH concentration and content at 2, 4, 8 and 16 months increased (P<.01) with age, while FSH content increased with age (P<.01) but was lower in UC bulls at 2, 4 and 8 months and higher at 16 months (A x UC, P<.01) as compared to intact bulls. In five samples of plasma collected at 90-minute intervals, one day each month from 1 to 15 months in 10 of the bulls killed at 16 months, LH concentration and variance changed (P<.01) with age reaching maxima at 4 and 3 months respectively. Plasma testosterone concentration and variance changed (P<.01) with age, reaching maxima at 10 and 9 months respectively. In the other 10 bulls killed at 16 months, assays of plasma collected before and after exposure to a teaser showed that stimulation increased LH by 20 minutes after exposure but LH declined by 60 minutes while testosterone was increased 20 (P<.05) and 60 (P<.01) minutes after exposure.     

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.     

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.     

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.     

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.     

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.     

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.     

Patterns of puberal development in Sahiwal and Brahman cross bulls in tropical Australia II. LH and testosterone concentrations before and after GnRH

Plasma LH and testosterone (T) concentrations were measured before (basal) and two hours after (peak) GnRH stimulation in 52 Bos indicus strain bulls between one and two years of age. The animals comprised 13 1 2 Brahman, 20 3 4 Brahman, 8 1 2 Sahiwal and 11 3 4 Sahiwal cross bulls and samples were collected at approximately seven week intervals. Basal- and peak-T concentrations increased between one and two years of age, and basal LH concentrations decreased; no changes in peak LH were noted over time. Peak-T concentrations were significantly correlated with scrotal circumference (SC), sperm per ejaculate and seminal fructose. Significant genotype differences were noted, Sahiwal cross bulls had higher peak-T concentrations at puberty than Brahman cross bulls.     

Influence of season of birth on growth and reproductive development of Brahman bulls

Seasonal effects on reproduction are more dramatic in Bos indicus than Bos taurus cattle. This experiment evaluated reproductive development of fall- (n=7) versus spring- (n = 10) born Brahman bulls to determine if season of birth affects reproductive development. Measurements of growth and reproductive development began after weaning and continued at bi-weekly intervals until each bull reached sexual maturity. Different stages of sexual development were classified according to characteristics of the ejaculate and included first sperm in the ejaculate, puberty (> 50 x 10(6) sperm/ejaculate), and sexual maturity (two ejaculates with > 500 = 10(6) sperm/ejaculate). Average daily increases in all measured traits were similar in fall- and spring-born bulls and there were no differences in age, body weight, scrotal circumference, or paired testis volume between groups at first sperm or puberty. However, fall-born bulls were older (P < 0.05) than spring-born bulls at sexual maturity (553 days versus 481 days, respectively) as the interval between puberty and sexual maturity was longer (P < 0.05) in fall- than in spring-born bulls (82 days versus 54 days, respectively). The prolonged interval between puberty and sexual maturity in fall-born calves coincided with a short photoperiod (winter) whereas the short interval between puberty and sexual maturity in spring-born calves coincided with a long photoperiod (summer). In conclusion, season of birth affected sexual development; photoperiod might be involved in regulating testicular function immediately after puberty in Brahman bulls.     

Patterns of puberal development in Sahiwal and Brahman cross bulls in tropical Australia. I. Growth and semen characteristics

Reproductive development was monitored in 13 1 2 Brahman (BX), 20 3 4 BX, 8 1 2 Sahiwal (SX) and 11 3 4 SX crossbred bulls between one and two years of age. Liveweight increased during wet season (0.7 kg/day) and decreased during dry season conditions (-0.25 kg/day). Scrotal circumference (SC) increased from 18.6 to 25.0 cm, but decreased slightly during the later stages of the dry season. First ejaculates containing 50 x 10(6) spermatozoa were obtained from 25% of the bulls at 15.3 months of age and from 84% by two years of age. Sperm motility and morphology showed no consistent pattern, but number of sperm per ejaculate increased and seminal fructose concentrations decreased with advancing age. Significant genotype differences were noted for SC and seminal characteristics. Estimated age and liveweight at puberty were 570, 563, 578 and 542 days, and 251, 265, 247 and 256 kg for 1 2 BX, 3 4 BX, 1 2 SX and 3 4 SX bulls, respectively.     

Seminal quality and sperm production in beef bulls with chronic dietary vitamin A deficiency and subsequent re-alimentation

Sixteen Hereford bulls (16 mo of age, 462 kg average body weight) were used in each of 2 yr to evaluate the effects of hypovitaminosis A on seminal quality and sperm production. Bulls were fed a high-concentrate diet with (+VIT) or without (-VIT) supplemental Vitamin A until the apparent onset of hypovitaminosis A (28 and 32 wk in Year 1 and 2, respectively). Half of the bulls on each treatment were then slaughtered and those remaining were re-alimented with Vitamin A. Plasma retinol concentration in -VIT bulls reached a nadir at approximately 25 wk. In Year 1, the proportion of progressively motile spermatozoa was lower in -VIT bulls after 17 wk but returned to that of the +VIT group after re-alimentation. The proportion of spermatozoa with primary morphological defects appeared to be greater in -VIT bulls compared to +VIT bulls by 26 and 24 wk in Year 1 and 2, respectively. The incidence of these defects declined in -VIT bulls upon re-alimentation, and approached the incidence observed in +VIT bulls by 8 to 12 wk of re-alimentation. Hypovitaminosis A decreased paired testes weight, daily sperm production, and epididymal sperm reserves but did not affect daily gain. Prolonged dietary Vitamin A deficiency impaired semen quality and sperm production in the absence of other clinical symptoms. However, under practical feeding conditions, diets that result in long-term, marginal Vitamin A deficiency or a relatively short-term absence of Vitamin A intake probably would have minimal effects on spermatogenesis.     

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.     

Spermatogenesis, sperm output and seminal quality of Holstein bulls electroejaculated after administration of oxytocin

The 12- to 24-month-old Holstein bulls were electroejaculated twice on each of 3 days per week throughout the study. After a 2-week stabilization period and subsequent 2-week pre-treatment period, 7 bulls were given 50 i.u. oxytocin via the jugular vein 10 min before each first ejaculate for 10 weeks. The 7 control bulls were handled identically but did not receive oxytocin. All bulls were castrated at the end of the study. Oxytocin was without effect on spermatogenesis (P greater than 0.10). Oxytocin did not alter the total number of spermatozoa harvested per collection day (P greater than 0.10), but increased the number of spermatozoa in first ejaculates by an average of 34.2% (P less than 0.025). Oxytocin did not affect sperm quality (P greater than 0.10) as judged by the motility of spermatozoa in fresh semen or by the motility or percentage of spermatozoa with intact acrosomes in thawed semen. It is concluded that 50 i.u. oxytocin enhanced sperm output in first ejaculates of electroejaculated bulls without altering daily sperm production or seminal quality.     

Effects of dry season nutritional supplementation on growth, onset of puberty and subsequent fertility in Boran and Boran x Friesian heifers in Ethiopia

Shortly after weaning at 8 months of age, 43 Boran and 46 Boran x Friesian crossbred heifers were randomly divided to either receive a supplementary feed containing 16% crude protein during the dry season or to serve as controls. Heifers were examined monthly, and data on body weight, wither height and body condition score were recorded. Ovarian size and structures were determined per rectum and heifers were kept under continuous observation for standing estrus. Blood samples were collected at 10-day intervals every month for determination of plasma progesterone levels. All heifers were exposed to intact bulls for 4 months after they attained 18 months of age. Average daily weight gain to puberty was significantly (P<0.01) higher in heifers given supplementation than in the controls (360 vs 326 g/day). The average daily weight gain in Boran heifers (296 g/day) was significantly (P<0.01) lower than in crossbred (392 g/day) heifers. Mean age at puberty differed significantly (P<0.001) between heifers given supplementation (573 days) and the controls (627 days). Boran heifers attained puberty at a significantly later age (660 vs 540 days; P<0.001) than crossbred heifers. Body weight at puberty did not differ between supplemented and control heifers (226 vs 222 kg); while the difference between Boran and crossbred heifers was significant (216 vs 232 kg; P<0.01). Pelvic size and body condition score were not influenced by supplementation but differed significantly between genotypes. Pregnancy rate after 4 months of breeding was higher in supplemented (79%) than in control (64%) heifers. Boran heifers had a significantly (P<0.001) lower pregnancy rate than crossbred heifers (52 vs 91%). Mean age and body weight at conception were not affected by supplementation but differed significantly (P<0.05) between genotypes. The results indicate that prepubertal supplementary feeding during the dry season increased growth rate, reduced age at puberty and improved fertility in both Boran and Boran x Friesian heifers.