Circadian variations of plasma LH and testosterone in adult swamp buffalo bulls

Three swamp buffalo bulls aged 1.5, 1.10 and 2 years were submitted to frequent blood sampling every 15 m during a period of 25 h using an indwelling infusion set. Plasma LH and testosterone were quantified by radioimmunoassay technique. The levels of the two hormones in each individual exhibited episodic and nonrhythmic patterns. The number of LH peaks varied according to individval, ranging from no peak in one bull to 2 in the other two bulls. The mean LH concentrations during the period of study for each bull were 0.74, 0.33 and 1.17 ng/ml. Whereas the number of testosterone peaks varied between 1-10 and the average testosterone concentrations were 0.1, 0.33 and 0.55 ng/ml for the younger to the older bulls respectively. The testosterone peaks related to the LH peaks in each individual bull.     

Effect of repeated sampling on concentrations of testosterone,LH and prolactin in blood of yearling angus bulls

Blood was collected at intervals of 29 to 31 min for 5 hr from six Angus bulls (15 mo of age) unaccustomed to capture, restraint and jugular venipuncture (stress) to evaluate temporal changes in certain hormones. Concentrations of testosterone and luteinizing hormone (LH) but not prolactin were decreased significantly after the first hour. Testosterone in plasma decreased (P < .01) about 11-fold between 0 hr and 5 hr (9.9 ± 1.7 to .85 ± .16 ng/ml) as described by equation log_e testosterone = log_e 2.4649 ? .5266 hr (r = .83; P < .01). Concentrations of LH in plasma remained low after the first hour and those of prolactin were high at all times and varied significantly only among bulls (27 ± 6 to 84 ± 14 ng/ml). Testosterone but not LH was measured with equal repeatability among duplicate measurements either in whole blood or plasma but its average concentration in whole blood was 66% that of plasma. This study demonstrated that sequential collection of blood from bulls unaccustomed to capture and restraint cannot be used to evaluate normal temporal variations in concentrations of testosterone.     

Ontogeny of growth hormone, prolactin, luteinizing hormone, and testosterone secretory patterns in the ram

The ontogenetic changes that occur in secretory patterns of growth hormone (GH), prolactin (Prl), luteinizing hormone (LH), and testosterone (T) in rams maintained in constant photoperiod were examined. Nine ram lambs were moved to individual pens in a controlled environment (12L: 12D cycle; 18-24 degrees C temperature) at 66 days of age. Blood samples were collected via indwelling cannulae at 15-min intervals for an 8-h period at 80, 136, 192, 248, and 304 days of age. Plasma concentrations of GH, Prl, LH, and T were quantitated and parameters of the secretory patterns determined. Mean concentration of GH tended to decline with age, probably because the amplitude of secretory peaks was significantly reduced with age. There were no age-associated changes in basal concentration of GH or incidence of GH peaks. There was an increase in Prl secretion (as estimated by mean concentration) at 136 and after 248 days of age. Significant age-associated changes occurred in all parameters of LH and T secretion. At the younger ages, testosterone concentrations were low and LH concentrations were elevated. At the older ages the relationship was reversed, with LH low and testosterone high. There were no significant correlations between frequency and magnitude of LH and T peaks. The significant correlations present among parameters of LH and T secretion were between basal concentration of LH and overall mean concentration and basal concentration of T. These results suggest that LH may not be the sole tropic stimulator of acute T secretion.     

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.     

Comparative response of rams and bulls to long-term treatment with gonadotropin-releasing hormone analogs

The objective was to compare the relative response between rams and bulls in characteristics of LH, FSH and testosterone (T) secretion, during and after long-term treatment with GnRH analogs. Animals were treated with GnRH agonist, GnRH antagonist, or vehicle (Control) for 28 days. Serial blood samples were collected on day 21 of treatment, and at several intervals after treatment. Injections of natural sequence GnRH were used to evaluate the capacity of the pituitary to release gonadotropins during and after treatment. Treatment with GnRH agonist increased basal LH and T concentrations in both rams and bulls, with a greater relative increase in bulls. Endogenous LH pulses and LH release after administration of GnRH were suppressed during treatment with GnRH agonist. Treatment with GnRH antagonist decreased mean hormone concentrations, LH and T pulse frequency, and the release of LH and T after exogenous GnRH, with greater relative effects in bulls. Rams previously treated with antagonist had a greater release of LH after administration of GnRH compared with control rams, while rams previously treated with agonist showed a reduced LH response. Bulls previously treated with agonist had reduced FSH concentrations and LH pulse amplitudes compared with control bulls while bulls previously treated with antagonist had greater T concentrations and pulse frequency. The present study was the first direct comparison between domestic species of the response in males to treatment with GnRH analogs. The findings demonstrated that differences do occur between rams and bulls in LH, FSH and testosterone secretion during and after treatment. Also, the consequences of treatment with either GnRH analog can persist for a considerable time after discontinuation of treatment.     

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.     

Effects of treatment with GnRH from 4 to 8 weeks of age on the attainment of sexual maturity in bull calves

In bull calves an early transient increase in circulating concentrations of LH occurs between 6 and 20 weeks of age. This has been shown to influence reproductive development and performance later in life. In an attempt to hasten the onset of sexual maturity, bull calves (Hereford x Charolais) were treated (im) with 120 ng/kg of GnRH (n=6) twice every day from 4 to 8 weeks of age; control calves received saline (n=6). Injection of GnRH resulted in an LH pulse in all animals. GnRH treated bulls displayed more rapid testicular growth rates between 22 and 44 weeks of age. Sexual maturity (SC>or=28 cm) was achieved earlier in GnRH treated bulls compared to saline treated bulls (41.7+/-2.22 and 47.0+/-0.45 weeks of age, respectively) and this was confirmed by age of sexual maturity based on ejaculate characteristics (>50 million spermatozoa, >10% motility; 45.0+/-0.86 and 49.0+/-1.13 weeks of age for GnRH and control treated bull calves, respectively; P<0.05). We concluded that treatment with GnRH, twice daily, from 4 to 8 weeks of age, prior to the endogenous early increase in plasma LH concentrations, could increase in plasma LH concentrations, advance testicular development and reduce age at puberty in beef bull calves. This may provide the basis for a simple regimen to hasten sexual development in the bull calf.     

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 >or=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.     

Plasma Testosterone in Bulls

Levels of peripheral plasma testosterone and LH were studied in 4 bulls hourly during a 12 hr. sampling period at 5 times of the year. The average plasma testosterone levels were significantly lower in October (1.8 ng/ml, Ρ < 0.001) and December (2.5 ng/ml, Ρ < 0.05) than in February, June and August (3.5, 3.7 and 3.7 ng/ml respectively). LH showed a slight fluctuation during the day, with values ranging between 0.8 and 3.8 ng/ml, but underwent no significant seasonal variation. A significant increase in average plasma testosterone was observed 1 hr. after the LH peaks (P < 0.001).     

The relationship between 13,14-dihydro-15-keto PGF2 alpha and LH secretion in bulls

Half-life (t1/2), volume of distribution (Vd) and total body clearance (TBC) of 13,14-dihydro-15-keto PGF2 alpha (PGFM) were measured in order to determine optimal sampling frequency for accurate measurement of PGFM. Three yearling Holstein bulls (349.2 +/- 6.7 kg) and 3 yearling Holstein steers (346.7 +/- 7.0 kg) were utilized in a 3 X 3 Latin square design. Animals were given 0, 25 or 50 micrograms PGF2 alpha I.V.; blood samples collected every 2 min and plasma PGFM determined. The t1/2, Vd and TBC of PGFM were 2.3 +/- .2 min, 43.3 +/- 3.3 liters and 13.7 +/- 1.9 liters/min, respectively and were similar for 25 and 50 micrograms doses. To determine the relationship between endogenous PGFM and LH secretion in bulls, blood samples were collected every 2 min for 12 h in 4 yearling Angus bulls (489.1 +/- 11.6 kg). All animals elicited at least one LH surge and PGFM concentrations were measured in samples coincident with the LH surge. Mean plasma PGFM concentrations were greater prior to the LH surge than during the LH surge. In addition, mean plasma PGFM concentration and frequency of PGFM peaks appeared to increase prior to the LH surge suggesting an association between PGFM and pulsatile LH secretion in the bull.     

Increased blood LH and testosterone after administration of prostaglandin F2α in bulls

Two types of experiments were conducted to determine the relationship of changes in blood luteinizing hormone (LH) and testosterone in bulls given prostaglandin F_2α (PGF_2α). Episodic surges of LH and testosterone occurred in tandem, apparently at random intervals, on the average once during the 8-hr period after bulls were given saline. In contrast, after sc injection of 20 mg PGF_2α, blood serum testosterone increased synchronously to a peak within 90 minutes four-fold greater than pre-injection values, and the testosterone surges were prolonged about three-fold compared to those in controls. Each of the PGF_2α-induced surges of testosterone was preceded by a surge of blood serum LH which persisted for about 45 minutes and peaked at about 3 ng/ml. In a second experiment, PGF_2α was infused (iv, 0.2 mg/min) for 20 hr; blood plasma testosterone increased from 7.0 ± 0.6 to 16.0±1.5 ng/ml within 2.5 hr and remained near this peak for 10 hr. Then testosterone gradually declined to about 9 ng/ml at the conclusion of the 20-hr infusion. These changes in testosterone were paralleled by similar changes in blood plasma LH, although LH declined 3 hr earlier than testosterone. Random episodic peaks of blood plasma LH and testosterone typical of untreated bulls resumed within 8 hr after conclusion of PGF_2α infusion. In both experiments, the surge of testosterone after PGF_2α was preceded by increased blood LH. We conclude that increased LH after administration of PGF_2α probably caused the increased testosterone. However the mechanisms of these actions of PGF_2α remain to be determined.     

Circadian and pulsatile variations in plasma levels of inhibin, FSH, LH and testosterone in adult Murrah buffalo bulls

The present study investigated pulsatile and circadian variations in the circulatory levels of inhibin, gonadotrophins and testosterone. Six adult buffalo bulls (6 to 7 yr of age) were fitted with indwelling jugular vein catheters, and blood samples were collected at 2-h intervals for a period of 24 h and then at 15-min interval for 5 h. Plasma concentrations of inhibin, FSH, LH and testosterone were determined by specific radioimmunoassays. Plasma inhibin levels in Murrah buffalo bulls ranged between 0.201 to 0.429 ng/mL, with a mean of 0.278 +/- 0.023 ng/mL. No inhibin pulses could be detected during the 15-min sampling interval. Plasma FSH levels ranged between 0.95 to 3.61 ng/mL, the mean concentration of FSH over 24 h was 1.66 +/- 0.25 ng/mL. A single FSH pulse was detected in 2 of 6 bulls. The LH levels in peripheral circulation ranged between 0.92 to 9.91 ng/mL, with a mean concentration of 3.33 +/- 1.02 ng/mL. Pulsatility was detected in LH secretion with an average of 0.6 pulses/h. Plasma testosterone levels in 4 buffalo bulls ranged from 0.19 to 2.99 ng/mL, the mean level over 24 h were 1.34 +/- 0.52 ng/mL. Testosterone levels in peripheral circulation followed the LH secretory pattern, with an average of 0.32 pulses/h. The results indicate parallelism in inhibin, FSH and LH, and testosterone secretory pattern. Divergence in LH and FSH secretory patterns in adult buffalo bulls might be due to the presence of appreciable amounts of peripheral inhibin.     

Pattern of gonadotropin secretion and ultrasonographic evaluation of developmental changes in the testis of early and late maturing bull calves

This was a study that retrospectively analyzed serum gonadotropin secretion and the ultrasonographic appearance of the testis during development in prepubertal bull calves to determine whether there were differences between early and late maturing bulls. Blood samples were taken every other week from 2 wk of age until puberty. Samples were also taken at 12 minute intervals for 12 hours at 4, 10, 20, 25, 30, 35, 40 and 45 wk of age. The GnRH treatment was administered 10 hours after the start of each period of frequent blood sampling. Bull calves fell into two distinctive groups, with one group maturing between 36.6 and 44.2 wk (n = 12) and the other between 46.4 and 48.9 wk of age (n = 8). In samples taken every other week mean serum LH concentrations were greater in early maturing bulls than in late maturing bulls at 12, 14 and 16 wk of age (P<0.05). In blood samples taken every 12 minutes for 10 hours early maturing bull calves had higher mean serum LH concentrations at 4 and 10 wk of age (P<0.05) and higher LH pulse frequency at 10 and 20 wk of age (P<0.05). Mean serum LH concentrations at 4, 10 and 40 wk of age and LH pulse frequency at 10 and 20 wk of age were negatively correlated with age at puberty in bull calves. Mean pixel units of the right and left testis were higher from 34 to 40 wk of age in early maturing than in late maturing animals (P<0.05). It seems possible that hormone measurements and ultrasonographic characteristics of the testes could be developed into powerful tools for studies on the regulation of reproductive development and may aid in the prediction of reproductive potential.     

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.     

Luteinizing hormone release by gonadotropin releasing hormone before and after castration in bulls

The magnitude of gonadotropin releasing hormone (GnRH) induced lutei nizing hormone (LH) release prior to castration, following castration, a nd during testosterone replacement in males, was compared, using 6 9-mon th-old Holstein bulls. Also, the effects of castration and testosterone replacement on patterns of episodic changes in serum LH were studied. Blood samples were collected at hourly intervals for 24 hours prior to castration, at 21 days after castration, and at 23 days postcastration a fter testosterone, 20 mg thrice daily, has been given for 24 hours. Each animal was given GnRH, 40 mcg iv, at 24 hours before castration, at 7 and 14 days after castration, and at 28 days postcastration following 6 days of testosterone treatment. GnRH caused LH release before and after castration. The LH increase was 2.5-fold at 14 days postcastratio n. Testosterone replacement did not reduce the magnitude of LH response to GnRH to precastration levels. The number of episodic increases in serum LH prior to castration averaged 3.7 daily and increased to 6.5 daily at 21 days after castration (p less than .05). The magnitude of increase in LH concentration in these epidsodic events was not affected by castration. Testosterone replacement failed to restore either the average number or change the magniture of LH increase above precastratio n levels. It was shown that LH is normally released episodically in bulls. The peaks of LH release were followed by increased testosterone in serum. Results suggest that LH release in bulls is controlled by gonadic factors other than testosterone.     

Pulsatility of systemic FSH and LH concentrations during follicular-wave development in cattle

Changes in systemic FSH and LH pulsatility in temporal association with follicular-wave emergence and follicle deviation were studied in cattle. Wave emergence was defined as occurring when the future dominant follicle first reached 4 mm, as established retrospectively. Follicle deviation was defined as the beginning of a change in growth rates between the 2 largest follicles and occurred 60.4 +/- 4.2 h after wave emergence. Follicles were tracked by transrectal ultrasound scanning every 8 h, and blood samples for pulse characterization were collected every 20 min from before emergence until after deviation. Pulses were characterized by the Pulsar program applied to each 8-h increment, centered on the hour of follicle scanning in each heifer (n = 6). Pulsatility of FSH was not detected for any of the 8-h increments. The mean FSH concentrations for the 24 samples per 8 h increased (P < 0.05) between 8 h before and 8 h after wave emergence, followed by a decrease 40 to 16 h before deviation. The low mean values continued for 24 h after deviation. Pulses of LH were detected for all 8-h increments. The LH mean of all concentrations per 8 h and pulse frequency increased (P < 0.05) between the hour of wave emergence and 32 h after emergence and then pulse frequency plateaued at a mean interpeak interval of 1.3 h. Increased LH means for all concentrations per 8 h and basal concentration were reached 32 h before deviation. The results indicated that elevated concentrations of LH and reduced concentrations of FSH were present 32 to 16 h before to at least 24 h after the beginning of follicle deviation. However, an abrupt, short-term change in FSH concentrations or in LH pulsatility in close temporal association with follicle deviation that could act as an acute stimulus to initiate deviation was not found.     

Differences in early patterns of gonadotrophin secretion between early and late maturing bulls, and changes in semen characteristics at puberty

In prepubertal bull calves there is an early transient rise in gonadotrophin secretion between 10 and 20 wk of age, and it has been suggested that this plays a role in the attainment of sexual maturation. To test this, we looked for differences in the gonadotrophin secretory pattern from birth to puberty between early and late maturing bulls. We also characterized the changes in semen morphology that occur about the time of puberty. Blood samples were collected (n=28) every wk from 2 to 20 wk of age and then every 2 wk until 50 wk of age. Semen was collected by electroejaculation at approximately 4-wk intervals from 36 to 49 wk of age. Puberty was defined as the first age at which an ejaculate contained 50 million spermatozoa with a minimum of 10 % motility Bulls were divided into early (n = 14) and late (n = 14) maturing groups based on the age at puberty (41.9 +/- 0.3 and 48.3 +/- 0.7 wk of age, respectively). There was a transient increase in serum concentrations of LH and FSH between 2 and 24 wk of age; LH concentrations were greater in early maturing bulls than in late maturing bulls at 12, 13, 15, 17 and 48 wk of age (P < 0.05). Serum concentrations of testosterone and FSH did not differ between groups (P > 0.05). As the bulls matured there was an increase in the percentage of normal and live sperm cells, cell motility and the number of cells per ejaculate (P < 0.05), and a decrease in the percentage of proximal droplets and knobbed acrosomes (P < 0.05). We concluded that, during the early rise in LH secretion, early maturing bulls had higher circulating LH concentrations than late maturing bulls. During the weeks preceding and following puberty there was an increase in the quality of semen collected by electroejaculation.     

Effects of copulation on timing of the LH surge following synchronization of estrus in the bovine

Forty-four crossbred postpubertal bovine females were used to study how mating with a bull affected estradiol-17beta (E(2)) secretion and timing of the preovulatory LH surge. Estrous cycles were synchronized with two injections of prostaglandin-F(2alpha) (PGF(2alpha)) 11 d apart. Females were either isolated from males (NE) or exposed to epididectomized bulls (BE) after the second PGF(2alpha) injection. Females exposed to bulls were allowed to mate once and then were separated from the bull. Blood samples were collected at 2-h intervals from the second PGF(2alpha) injection until 12-h post injection to monitor progesterone (P(4)) and luteinizing hormone (LH) concentrations and at hourly intervals from 12 h to 60 h post-injection to monitor LH secretion and timing of the preovulatory LH surge. Samples were also collected at 4-h intervals until 60 h post-injection to monitor estrogen (E(2)) secretion. LH surges were detected in 16 and 14 of 22 females from the BE and NE groups, respectively, during the 60-h period after PGF(2alpha) injection Mean P(4) concentrations and time of P(4) decline to <1 ng/ml were not different between the two treatment groups (P>0.30). Mean E(2) concentration during the 60-h sampling period was different (P<0.003) between BE and NE groups, and a significant treatment effect (P<0.002) occurred 48 h, 52 h and 60 h after the second PGF(2alpha) injection. However, mean LH concentration before the LH surge, duration of the LH surge and peak LH concentration during the surge were not different between the BE and NE groups (P>0.40). Mean time for the second PGF(2alpha) injection to the beginning of the LH surge was 51.6 +/- 1.5 h (X +/- S E) for the females not exposed to bulls and 48.5 +/- 1.4 h for females exposed to bulls (P>0.14). In this study, the presence of and/or mating by a bull did not affect LH secretion or timing of the preovulatory LH surge after PGF(2alpha) administration.     

Testosterone and dihydrotestosterone concentrations in elephant serum and temporal gland secretions

Serum and temporal gland secretions (TGS) were obtained from mature wild African (Loxodonta africana) and captive Asian elephants (Elephas maximus). Samples were obtained from five cows and eight bulls culled for management purposes in Kruger National Park, South Africa, and from four females and two males residing at the Washington Park Zoo, Portland, Oregon. Our purpose was to describe the levels of the androgens, testosterone (T), and dihydrotestosterone (DHT), and to correlate these observations with sex, species and behavioral status. Male-female differences in serum T were pronounced in the Asian species, whereas male and female concentrations overlapped in the African elephant serum. Serum T concentrations in African females were greater than in Asian females. Serum DHT reflected T levels, except that the striking elevation of testosterone in Asian bulls during musth was not paralleled by equal increases in DHT levels. A species difference observed among males was higher serum T levels in nonmusth Asian bulls (1.84-5.35 ng/ml) compared to the levels in African bulls (0.38-0.68 ng/ml), except for one dominant African bull (6.64 ng/ml). This single African value was still considerably lower than the serum T values of the Asian males during musth. These musth values were the highest serum androgen concentrations: T was between 19 and 40 ng/ml (average 26.10 ng/ml). The TSG values of T and DHT were much higher than serum levels except in the Asian female. T/DHT ratios in TGS were more similar than in serum. One dominant African bull had a T TGS value of 78 ng/ml, which was much higher than the rest of the African males or females, but considerably lower than as Asian bull in musth (547 ng/ml). It seems apparent that a change in androgen status as reflected in serum and TGS levels of T and DHT precedes or is concomitant with overt alteration in behavior in the Asian male. The temporal gland appears to actively concentrate androgens in both African males and females, but in the Asian male the gland secretes only during musth when the greatest concentration of both T and DHT were observed. The apparent difference in the degree of temporal gland secretory activity between the two species suggests a more specific communicative function within the Asian male.     

Serving capacity — A measure of the serving efficiency of bulls during pasture mating

The aim of the study was to determine whether the serving capacity of a bull, the number of services it achieved during a pasture mating period, was related to the proportion of oestrous cows in its herd it served. Twelve groups of 3 to 10 bulls were mated with spayed, oestrous heifers at a bull: cow ratio of 1 to 5 for a 7.5 hour period. The serving capacity of a group of bulls was highly correlated with the proportion of oestrous heifers the group of bulls served (r = 0.94), and the proportion of oestrous heifers the bulls served 2⁺ times (r = 0.98). The high correlations occurred because each bull, whatever its serving capacity (range 0 to 15 services), rarely served the same heifer twice. The correlation coefficient between the number of services a bull achieved and the number of heifers it served was 0.96 (n = 54). It was concluded that the serving capacity of a bull is an accurate measure of serving efficiency during pasture mating.