Effect of alternating bulls as a management tool to improve the reproductive performance of suckled Zebu cows in the humid tropics of Costa Rica.

A study was undertaken to evaluate the effect of alternating bulls between a single and a multiple sire mating (MSM) program on the reproductive performance of suckled Zebu cows raised under range conditions in the humid tropics of Costa Rica. Multiparous Zebu cows (n=94) suckling calves were distributed between two experimental trials (A and B) consisting of 47 animals each. A single sire mating (SSM) system was alternated weekly with a MSM system with three bulls. This period lasted for 8 weeks. To facilitate estrous expression, four cows were strategically synchronized (estrus-stimulated) in alternate weeks. Courtship predominated over mounting under non-stimulated estrus, for each mounting performed an average of 6.0 and 6.3 courtship activities were recorded in the SSM and MSM, respectively. Under the influence of strategic synchronization corresponding values were 3.9 and 4.2 in the SSM and MSM, respectively (P>0.05). Blood samples for progesterone evaluation were taken twice weekly. All cows in trial A were in anestrus at the start of the study. By second week, 5 out of the 47 cows had initiated estrous cycles and by the third week six were pregnant. In contrast in trial B, 9 out of 47 had initiated estrous cycles before interacting with the bulls and on week 3, only two females had become pregnant and three had initiated estrous cycles. Significant differences were found in the cumulative percentage of cows pregnant between trials A and B (P<0.05). Even though these results occurred, the rotation of the bulls (one or three), or the type of cows (estrus-stimulated or not) did not influence the results in this study.     

Influence of single-sire and multiple-sire natural mating on pregnancy rate of beef heifers

Twelve mature Angus bulls possessing similar semen quality were used to study the effects of single and multiple services and single-sire and multiple-sire mating on pregnancy rate of beef heifers. Heifers were observed for natural estrus twice daily and mated within 6 hr of onset of estrus. Pregnancy rate was determined by rectal palpation at 60 days post-mating. Pregnancy rate of heifers receiving one service per estrus averaged 62.1% (n=124) and pregnancy rate of heifers receiving multiple services (single-sire) per estrus averaged 62.9% (n=105). Pregnancy rate per estrus of heifers mated to three sires (multiple-sire, one service per sire; 74.0%, n=123) was significantly higher than that of heifers mated to a single sire (62.9%). The range in pregnancy rate per bull for single-sire matings was large (0 to 95%), but this range was reduced among the same bulls used for multiple-sire matings (68 to 84%). These results indicate that pregnancy rate to one service did not differ (P>.10) from pregnancy rate to multiple services among single-sire matings, but multiple-sire matings increased (P<.05) pregnancy rate per estrus by 11% over that obtained with single-sire matings.     

Beef bulls mated to estrus synchronized heifers: Single- vs multi-sire breeding groups

Beef bulls of approximately 15 months of age were placed with heifers at bull to female ratios (BFR) of 1:20 (n = 3) and 2:40 (n = 3) to compare the breeding efficiency of bulls used in either a single- or a multi-sire group. Prior to the breeding period, each bull was given a breeding soundness exam and two exposures to a libido/serving capacity test. For the purpose of synchronizing estrus, heifers received a nine-day Syncro-Mate-B((R)) (G. D. Searle & Co.) treatment. Twenty-seven hr after removal of the implants, bulls were placed with heifers and sexual activity was observed continuously for the succeeding 30 hr. With the exception of number of services per heifer, the mating performance of bulls and pregnancy rates at both BFR's were not different (P>.05). Heifers in single-sire groups were serviced more times (P<.05) than those in multi-sire groups (4.1 +/- 0.6 vs 2.6 +/- 0.2, respectively). Approximately 50% of heifers in multi-sire groups were serviced by both bulls. Due to the overlap in servicing heifers and the non-significant difference in pregnancy rates between the two BFR's, it was concluded that a single-sire mating program was more efficient.     

Bull selection and use in northern Australia. 4. Calf output and predictors of fertility of bulls in multiple-sire herds

On 10 northern Australian properties, the number of calves sired (calf output) by individual bulls in multiple-sire matings was measured by DNA typing for paternity. There were 235 bulls (92 Santa Gertrudis, 25 5/8 Brahman and 119 Brahman) from 37 multiple-sire mating groups. Number of bulls in groups ranged from 2 to 25 and ages of bulls ranged from 2 to 5 years. Mating periods were for 3-12 months and bull mating percentages were 2.5-6%. In all, there were 4251 calves tested and the resolution of paternity ranged from 92.5 to 100% and averaged 97.7% across all sites. This included 9.9% of calves with no potential sires in any of the mating groups. Of the 235 bulls mated, 58% sired 10% or less calves in each of their respective mating groups with 6% not siring any calves. In contrast, 14% sired over 30% of the calves in each of the respective mating groups. When bulls were mated in groups of 8-24, the maximum percent of calves sired by individual bulls was 26+/-7% (mean+/-S.D.) with a range 11-36%. However, when bulls were mated in groups of 2-7, the maximum percent of calves sired by individual bulls was 59+/-19% with a range 24-94%. Calf output of bulls was moderately repeatable across years at four of five sites. Multiple regression models relating pre-mating measures of physical, seminal and behavioural traits to calf output were developed for the three breed groups. In all, only 138 of the 235 bulls were included in the models (40 Santa Gertrudis, 24 5/8 Brahman and 74 Brahman). Sheath and testicular traits, such as scrotal circumference and testicular tone, were generally not related to calf output, the exceptions being sheath depth in Brahman bulls which was negatively related (P<0.05) and scrotal circumference in 5/8 Brahmans which was positively related (P=0.08) to calf output. Dominance was only included in the 5/8 Brahman model but there was no significant relationship between dominance hierarchy and calf output. Semen motility was only related (P<0.05) to calf output in 5/8 Brahmans. However, measures of semen quality based on spermatozoa morphology were important contributors to calf output in the Santa Gertrudis and Brahman models where percent normal spermatozoa was positively related (P<0.01) to calf output. In Santa Gertrudis and Brahman bulls, measures of sexual behaviour in the serving capacity test were related to calf output. In Santa Gertrudis, these were for the number of displays of sexual interest (P<0.05), and mounts (P<0.01), but not number of serves, whilst in Brahman bulls, libido score was positively related to calf output (P<0.05). The models only explained 35-57% of the variation in calf output.     

Estimations of the efficacy and reliability of paternity assignments from DNA microsatellite analysis of multiple-sire matings

It is important for bovine DNA testing laboratories to provide the cattle industry with accurate estimates of the efficacy and reliability of DNA tests offered so that end users of this technology can adequately assess the cost-benefits of testing. To address these issues for bovine paternity testing, paternity exclusion probability estimates were obtained from breed panel data and were predictive of the efficacy of the DNA tests used in 39 multiple-sire mating groups, involving 5960 calves and 505 bulls. Paternity testing of these mating groups has demonstrated that the majority involve a variable proportion of unknown sires and this impacts on the reliability of sire allocation. Mathematical models based on binomial or beta-binomial probability distributions were used to estimate the reliability of single-sire allocations from multiple-sire matings involving unknown sires. Reliability of 98-99% is achieved when the exclusion probability is 0.99 or greater, after allowing for up to 20% unknown sires. When the exclusion probability drops below 0.90 and there are 20% unknown sires, the reliability is poor, bringing into question the benefits of testing. This highlights the need for DNA testing laboratories to offer paternity tests with an exclusion power of at least 99%.     

Effects of pretreatment with adrenocorticotropin on endocrine and behavioral responses of bulls to sexual activity

Peripheral concentrations of cortisol, growth hormone and testosterone were determined in two experiments which examined the endocrine and behavioral responses of sexually mature Angus bulls to an estrous female (Experiment 1) and to female exposure 5 hours following an adrenocorticotropin (ACTH) injection (Experiment 2). Sexual activity of bulls in Experiment 1 significantly increased levels of cortisol when compared with concentrations before exposure to a female. Administration of ACTH in Experiment 2 consistently elevated levels of cortisol by 30-fold (P<0.01) when compared with pre-ACTH concentrations. This heightened level of cortisol persisted throughout the period of exposure to an estrous cow, although a gradual decline in cortisol concentrations occurred over time (P<0.05). In Experiment 1, growth hormone profiles tended to increase in response to sexual activity (P<0.10), whereas in Experiment 2, growth hormone increased in response to ACTH administration (P<0.01) and to female exposure (P<0.01). Concentrations of testosterone were unaffected (P>0.10) by mating activity in Experiment 1. In Experiment 2, acute suppression (P<0.01) in testosterone concentrations 5 hours after ACTH administration coincided with the exposure period to the estrous female. Frequencies of mounting behavious (penis extension, mounting, intromission and ejaculation) exhibited by ACTH-treated bulls were significantly lower compared with the frequencies two days earlier. Exogenous ACTH administration suppressed reproductive behaviors of bulls and altered secretion of cortisol, growth hormone and testosterone. Furthermore, these data provide evidence that specific mating behaviors of the bull can be influenced by circulating steroids.     

Behaviour and mating performance of paddock-mated beef bulls

Paddock-mating performance was studied in seven beef bulls which were each joined to 28 or 29 females of mixed dairy and beef breeds for 8 weeks in single-sire joining groups in paddocks ranging from 4.0 to 28 ha. Seven unmated bulls were used as control animals. The estimated weight of testicular tissue per cow joined ranged from 12 to 32 g. Liveweight and testicular size and tone were recorded prior to, during and after joining. There was no apparent effect of mating on testicular characteristics of bulls, and pre-joining testicular size of the bulls was not significantly related to the calving results of the cows.Mating activity of the bulls was detected with a chin-ball harness and by behavioural observations covering eight intervals during the joining period. During the first 21 days (cycle I) of the joining period, 81% of the cows were mated and this increased to 89% by the end of the joining period. The overall return rate was 21%, the overall calving rate was 85% and no significant differences between the seven bulls were recorded in these two parameters. The relatively high level of sexual activity during cycle I apparently had no adverse effect on the fertility of the bulls since there was an even distribution over time of the return to first service of cows mated during cycle I. Mating activity of the bulls during cycle I had no significant effect on the mean percentage of time spent grazing or lying, but time spent standing was lower (P < 0.001) during cycle I than the remainder of the joining period.General activity, expressed as km travelled per day, was measured at regular intervals during the joining period for one working bull and one heifer in each of four mating groups. Mean activity of the bulls was significantly higher (11.3 km/day) during cycle I than the remainder of joining (2.45 km/day) and was significantly correlated (r = 0.8) to the mean number of cows mated per bull per day.     

Effects of sexual stimulation on the sexual performance of rams

The sexual performance of bulls and male goats is improved if they are allowed to view the hetero-sexual behavior of other males as a prelude to mating. The purpose of the following study was to determine whether sexual stimulation enhances the sexual performance of rams. In Experiment 1, 11 sexually experienced ram lambs ( 9 months of age) and 18 sexually experienced yearling and 2-year-old rams were individually exposed to 4 unrestrained, hormone-induced estrous ewes for 60 min after viewing the courtship and mounting behaviors of a male conspecific for 20 min (two tests) and in the absence of stimulator animals (two tests). In contrast to the results with bulls and bucks, the rams were hardly influenced by the sexual stimulation treatment. Latencies for first mount and first ejaculation were shorter for sexually stimulated ram lambs; otherwise, treatment differences were negligible.

A similar follow-up experiment was administered to 12 mature rams using restrained females in the sexual performance tests. Again, treatment differences were minor.

It was concluded that sexual stimulation does not functionally enhance the sexual performance of rams. Species differences in response to sexual stimulation are discussed in terms of female sexual behaviors that may result in a selective (competitive) advantage to males that are stimulated to locate and mate with females early in the estrous period.     

Efficiency of single-sire mating programs with beef bulls mated to estrus synchronized females

Efficiency in reference to pregnancy rates of breeding beef bulls with estrus synchronized cows and heifers was tested. Most bulls (104 of 112) were given a breeding soundness examination and two 10-min libido/serving capacity tests. Females received either Syncro-Mate-B (SMB) or two injections of Prostaglandin F(2)alpha (PGF) to synchronize estrus. They were assigned to single-sire breeding groups with bull-to-female ratios ranging from 1:7 to 1:51. Control groups consisted of untreated females maintained in single-sire breeding pastures with ratios from 1:24 to 1:37. Continuous observations of sexual activity were made for 30 h (SMB) and 48 h (PGF). After the 120-h posttreatment breeding period, females were placed in breeding pastures. During the synchronized breeding period the percentage of pregnant cattle of total treated was 43.5 +/- 1.7% compared (P < 0.01) with 58.9 +/- 3.3% for the control group after 23 d of breeding. At end of 28-d (treated) and 46-d (control) period, the percentage of pregnant females was 75.0 +/- 2.4 and 79.6 +/- 4.7, respectively (P > 0.05). In SMB trials, the percentages of females exhibiting estrus, those serviced at estrus and those pregnant following service during the synchronized breeding period were 90.8 +/- 1.5, 73.3 +/- 4.5 and 56.4 +/- 5.6%, respectively. In PGF trials, the means for these same factors were 78.3 +/- 2.4, 70.4 +/- 5.9 and 56.1 +/- 6.5%, respectively.     

Bull selection and use in northern Australia. 3. Serving capacity tests

Serving capacity studies were conducted on Santa Gertrudis, 5/8 Brahman, Brahman and Belmont Red bulls at 10 sites. Modifications, such as providing prior sexual experience, using females in oestrus and comparing restrained with unrestrained females, were made to the standard Bos taurus serving capacity test in a series of experiments with Santa Gertrudis bulls. Providing sexual experience to virgin bulls prior to testing improved the number of serves and libido scores in a serving capacity test. In serving capacity tests that used restrained females, expressions of sexual behaviour of bulls were not improved by having females in oestrus compared with non-oestrus females. There were more sexual behaviours, particularly mounts, in serving capacity tests involving restrained rather than unrestrained females. Summary statistics were collated from over 1100 serving capacity tests, in the 2 months prior to mating, across the 10 sites. In serving capacity tests using restrained females, in bulls of the same age, there were more expressions of sexual behaviours (except interest) in Belmont Red than in Brahman or 5/8 Brahman bulls with Santa Gertrudis bulls intermediate. The percentage of bulls displaying serves tended to increase with age; 82, 83 and 86% of 2-, 3- and > or =4-year-old Belmont Red bulls, respectively, completed 1 or more serves. This compared with 50, 50 and 66% of 2-, 3- and > or =4-year-old Santa Gertrudis bulls and 31% of 2-year-old Brahman bulls. Between 2 and 9% of bulls did not display any sexual behaviour in serving capacity tests with restrained females. Across genotypes, there were few and inconsistent relationships between either mounts or serves and liveweight, condition score, scrotal circumference, testicular tone and sheath measurements. The exceptions were in 2-year-old Brahmans where mounts were negatively correlated (r=-0.61; P<0.05) with umbilicus thickness and in 3-year-old Santa Gertrudis bulls, where serves (r=-0.53; P<0.01) and mounts+serves (r=-0.49; P<0.01) were negatively correlated with navel score. Measures of sexual behaviour were unable to consistently predict calf output of bulls in multiple-sire mating groups in extensive pastoral conditions. The main value of the serving capacity test in these genotypes is to identify whether a bull is capable of natural service.     

Brahman bull fertility in a north Australian rangeland herd

Low and variable bull fertility was identified as a constraint on reproductive rates in beef cattle grazed in an extensive, multiple sire mating regimen on Mount Bundey station in the Darwin pastoral district of northwestern Australia. Erratic conception patterns were attributed to a high proportion of bulls with low breeding soundness evaluation scores (BSE), a high proportion of aged bulls (40%>8 yr), and to running bulls of mixed age groups. Liveweight, scrotal circumference (SC) and age were positively correlated. An experiment was subsequently designed to investigate the ability of a number of bull measurements to predict fertility in an extensively-managed, multiple-sire mating system. Blood typing was used to match calves to sires. It proved to be an accurate and useful technique which successfully identified the parentage of 94% of calves examined. Single measurements of serum testosterone after administration of gonadotrophin-releasing hormone (GnRH) were not correlated with fertility. However six of the seven most fertile bulls exhibited high peak serum testosterone levels in summer, and lower levels in the winter. In contrast, the less fertile bulls did not exhibit seasonal variation in GnRH-induced serum testosterone levels. Social dominance ratio was weakly ralted to fertility (r=0.51: P<0.05). BSE (r=0.51: P<0.05) and SC (r=0.49: P<0.05) prior to, but not subsequent to, mating were correlated with bull fertility. Under the conditions of this experiment, a bull to cow ratio of 1:20 was excessive for bulls with a satisfactory BSE score.     

Breeding soundness, libido and performance of beef bulls mated to estrus synchronized females

Ninety-three beef bulls and 2316 females were used to determine the relationships between breeding assessments of bulls and subsequent mating performance. Each bull was given a breeding soundness examination (BSE) and two 10-min libido/serving capacity (L/SC) tests. Breeding potential of each bull was classified as satisfactory (BSE score = 60 to 100) or questionable (BSE score = 30 to 59); libido was classified as either high (mean score = 9.0 to 10) or medium (mean score = 6.0 to 8.5). Bulls were then joined, single-sire, with groups of females which had received one of two treatments to synchronize estrus. Bull-to-female ratios ranged from 1:7 to 1:51. Continuous observations were conducted on the mating activity of each group. One bull was removed from the experiment due to a severe breeding problem. Bulls of satisfactory breeding potential (n = 80) did not differ (P > 0.10) from bulls of questionable breeding potential (n = 12) in measurements of mating activity. However, by the end of the synchronized breeding period, bulls classified as satisfactory breeders achieved approximately a 9% higher (P < 0.10) pregnancy rate than did bulls of questionable breeding status (45.6 +/- 2.1% vx 36.5 +/- 5.3%). Bulls with a high libido (n = 69) serviced more (P < 0.01) estrous females (81.3 +/- 3.1% vs 63.5 +/- 4.2%) than bulls with a medium libido (n = 23). However, pregnancy rates achieved by bulls of either libido classification did not differ significantly. Individual components of the BSE as well as mean libido score were poorly correlated with pregnancy rates (r = -0.22 to 0.18). It was concluded that classification of bulls by mean libido score can aid in identifying groups of bulls that service more estrus synchronized females, whereas classification by BSE score aids in identifying groups of bulls that impregnate more females.     

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

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

Selection of buffalo bulls: Sexual behavior and its relationship to semen production and fertility

Forty-four buffalo bulls, used for artificial insemination, were studied to develop libido, mating ability and sexual behavior indices for selection purposes. For each index, 5 categories (i.e., excellent, very good, good, fair and poor) were established. The sexual behavior index was found to be more reliable than the libido and mating ability indices. Buffalo bulls in good to excellent categories were considered acceptable sires.

Reaction time, sexual aggressiveness, and scores of libido, mating ability and sexual behavior differed significantly among the various categories of the 3 indices. Libido significantly correlated with mating ability (r=0.89; P<0.001). Sexual behavior expressed significant relationship with age (r=0.41; P<0.01) and body weight (r=0.48; P<0.01), but was nonsignificant with the scrotal circumference (r=0.28; P>0.05) of buffalo bulls. However, these relationships were absent (P>0.05) in the acceptable sires. Semen production was correlated with sexual behavior in only the fair and poor categories of buffalo bulls (r=0.84; P<0.005). Sexual behavior had no relationship with the fertility rate of buffalo bulls (r=0.44; P>0.05). It is concluded that the sexual behavior index can be used successfully for the selection of buffalo bulls. Excellent- to good bulls should be used in an artificial breeding program if they qualify in the other selection indices.     

Relationships between breeding soundness and sex drive classifications in beef bulls

Prior to use in single-sire mating trials, ninety-two beef bulls were evaluated to determine the relationships between. Breeding Soundness Examination (BSE) and sex drive assessment categories. A BSE score was given to each bull based on scrotal circumference, spermatozoal motility and morphology. Eighty bulls were classified as satisfactory potential breeders, while 12 were classified as questionable potential breeders. Each bull was exposed to two, 10 min modified libido/serving capacity tests. Sixty-nine bulls were classified as high libido and 23 were classified as medium libido. Differences in scrotal circumference and spermatozoal motility did not influence (P > 0.05) the BSE classifications. However, differences in primary, secondary and total spermatozoal abnormalities were the major factors affecting the BSE classification. Bulls classified as high libido serviced three times more (P < 0.01) during the two test periods than bulls classified as medium libido. High libido bulls were superior in all sex drive traits. However, bulls in the two libido categories did not differ (P > 0.05) in semen quality or scrotal circumference. There was no relationship (P > 0.05) between BSE and sex drive traits (r = -0.16 to 0.24).     

The time required for the presence of bulls to alter the interval from parturition to resumption of ovarian activity and reproductive performance in first-calf suckled beef cows

This experiment was designed to determine 1) if exposure of firstcalf suckled beef cows to mature bulls in the first 30 days, after 30 days, or continuously post partum reduces the postpartum anestrous period and 2) if exposure to bulls alters the first service pregnancy rate. Postpartum first-calf suckled crossbred (Angus x Hereford; Hereford x Angus) cows were randomly assigned to be 1) exposed continuously to mature, epididectomized bulls (BE; n = 18); 2) exposed to bulls for the first 30 days post partum (BE/NE; n = 17); 3) exposed to bulls after the first 30 days post partum (NE/BE; n = 16); or not exposed to bulls (NE; n = 18). Blood samples were collected weekly to be assayed for progesterone to determine resumption of ovarian cyclic activity. All the cows were bred for 21 days by AI while under their respective treatment regimens and were then exposed to fertile bulls for an additional 35 days. The postpartum interval to resumption of ovarian cyclic activity did not differ (P>0.10) among the 3 (BE, BE/NE, and NE/BE) treatment groups, but it was 15.4 d shorter (P<0.05) than for cows in the NE group. The overall pregnancy rates did not differ (P>0.10) among the treatment groups. The AI pregnancy rates for the BE/NE and NE/BE treatment groups were higher (P<0.05) than for the NE group. The AI pregnancy rates for the BE and NE treatment groups did not differ (P>0.10). The results showed that all three treatments (BE, BE/NE and NE/BE) similarly decrease the postpartum interval and that exposure to bulls may improve the reproductive performance of first-calf suckled beef cows.     

Bull selection and use in northern Australia. 5. Social behaviour and management

Calf output of bulls was derived using DNA typing for paternity following multiple-sire mating at two sites in northern Australia. At Swan's Lagoon Beef Cattle Research Station, 12, mixed-age, Brahman cross bulls were continuously mated with an average of 325 females in a 22km2 open-savannah paddock. Water was available in two troughs. Behaviour of the bulls and location of cows were monitored. At Kamilaroi Station, 2- to 2.5-year-old Brahman bulls were introduced to the study. Twenty-four bulls (HIGH%) were mated in an 84km2 paddock for 3.5 months to 411 heifers in 1995/1995 and for 4.5 months to 350 heifers and 320 first-lactation cows in 1995/1996. A second group of 10 bulls (LOW%) selected on reproductive soundness was mated concurrently in a neighbouring 60km2 paddock to 411 heifers in 1995/1995 and to 350 heifers and 298 first-lactation cows in 1995/1996. In each paddock in both years, 300-350 females were expected to cycle during mating. Both paddocks were flat and semi-forested and water was available only at troughs. At both sites, detailed physical and reproductive examinations of all bulls were conducted prior to and post-mating.Calf output of individual bulls was highly variable but repeatable (r=0.6-0.7) between years. Up to 90% of the 270-380 calves resulting from each mating were sired by between 6 and 8 bulls. Reducing from 3.7 to 2.8% bulls:females at Swan's Lagoon did not delay conceptions. At Kamilaroi, reproductively sound bulls achieved an estimated 5-6 conceptions per week over the peak mating period when sufficient cycling females were available. Differences in pregnancy rates between paddocks appeared due to differences in nutrition and it appeared that conceptions were not delayed with LOW% vs. HIGH% bulls. Variance between bulls in calf output was substantially lower when fewer bulls were used. Bull attrition occurred each year in the HIGH% paddock but not in the LOW% paddock. Calf output was unrelated to body condition of bulls.Seven of the 12 bulls in one 2-year period at Swan's Lagoon appeared to restrict their movement range to 250-750ha for 90-100% of the time. These ranges expanded when the bull:female ratio was reduced. Only one of the nine bulls remained within a 500ha home range for at least 85% of the time during peak mating in 1998 at 2.8% bulls:females. In previous years with 3.7% bulls:females, up to eight of the 12 bulls had remained within a 500ha home range for 85% of the time. Bull behaviour related to high calf output included restricted movement range, grazing with females at a majority of observations, stable social behaviour, and social dominance.These observations demonstrate that multiple-sire mating of reproductively sound Brahman and Brahman-derived bulls at 2.5% of cycling females will not jeopardise herd fertility under extensive management in northern Australia.     

Exploring the influence of individual courtship behaviors on male mating success in a blow fly

Male courtship behavior and displays influence female mating decisions, and therefore affect mating success in a diverse range of organisms. While there is substantial evidence confirming that females prefer males who invest more in courtship, less attention has been paid to the relative importance of individual behaviors, and the discrete sequences of courtship that result in mating success. The small hairy maggot blow fly, Chrysomya varipes, performs stereotyped courtship behaviors, involving orienting, tapping, waving, arching, wing vibration and mounting. This study aimed to quantify male investment in specific courtship behaviors, and compare courtship investment and behavioral transitions between males who gained mating success (successful males) and those that did not (unsuccessful males). Our results show that mating success was influenced by the behaviors orienting, tapping, arching and mounting. Behavioral transitions revealed a distinct pattern of behaviors leading to a mating attempt, and some differences were observed between successful and unsuccessful males. Overall, our findings suggest that female mating decisions were based on differences in specific male courtship behaviors. This detailed observational study has quantified multiple courtship behaviors for the first time in C. varipes, and highlights the importance of considering multiple behavioral traits when exploring the influence of male courtship on mating success.     

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.     

The reproductive--endocrine response of adult rams to sexual encounters with estrual ewes is season dependent

An experiment was conducted with four adult, sexually inexperienced Finnish Landrace rams during the ovine nonbreeding (July) and breeding (October) seasons to determine the influence of components of the rams' mating behavior on the secretion of luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin (PRL), and testosterone. On four occasions in both seasons, blood was collected by jugular venipuncture at 20-min intervals during an 8-hr period while rams were (1) separated from, (2) observing with minimal direct physical contact, (3) mounting without intromission, or (4) mating estrous-induced ewes. In comparison with separation periods, mating activity in July was associated with increased mean LH (P less than 0.05) and testosterone levels and number of LH peaks, while in October, obvious increases were detected in only baseline LH levels (P less than 0.05). Circulating LH and testosterone levels either did not change (July) or were depressed (October) during the mounting and observation periods. FSH levels generally remained unaffected by engagement in the various sexual activities. Although a clear relationship between type of sexual activity and mean PRL levels was not observed in July, activities which appeared to involve the most physical exertion tended to be associated with much higher circulating PRL levels in October. These data suggest (1) the act of ejaculation is important in the induction of increases in LH and testosterone secretion that occur in rams in response to mating activity during the nonbreeding season and (2) excessively stressful sexual activities during the breeding season may alter the pattern of secretion of some reproductive hormones.