Indicus Bulls Research Articles

Testicular thermoregulation in Bos indicus, crossbred and Bos taurus bulls: relationship with scrotal, testicular vascular cone and testicular morphology, and effects on semen quality and sperm production

Mechanisms of testicular thermoregulation, the relationship of scrotal, testicular vascular cone (TVC), and testicular morphology with thermoregulatory capability, and their effects on semen quality and sperm production were studied in 20 Bos indicus, 28 crossbred, and 26 Bos taurus bulls. The ratio of testicular artery length and volume to testicular volume were larger ( P<0.05) in B. indicus and crossbred bulls than in B. taurus bulls (1.03 and 0.94 cm/cm 3 versus 0.48 cm/cm 3; 0.034 and 0.047 ml/cm 3 versus 0.017 ml/cm 3, respectively). Testicular artery wall thickness (average 192.5, 229.0, and 290.0 μm, respectively) and arterial–venous blood distance in the TVC (average 330.5, 373.7, and 609.4 μm, respectively) were smallest in B. indicus, intermediary in crossbred, and greatest in B. taurus bulls ( P<0.05); the proximity between arterial and venous blood was consistent with the estimated decrease in arterial blood temperature after passage through the TVC (5.9, 5.0, and 2.9 °C, in B. indicus, crossbred, and B. taurus bulls, respectively). In crossbred and B. taurus bulls, there was a positive top-to-bottom scrotal temperature gradient and a negative testicular subtunic temperature gradient. However, in B. indicus bulls, both scrotal and testicular subtunic temperatures gradients were positive. Differences in the vascular arrangement, characteristics of the artery (e.g. wall thickness) or thickness of the tunica albuginea may have affected the testicular arterial blood and subtunic temperatures in B. indicus bulls. Better testicular thermoregulatory capability was associated with increased scrotal shape (pendulosity), testicular artery length and volume, and top-to-bottom gradient of the distance between the artery wall and the veins in the TVC. Increased semen quality was associated with increased testicular volume and scrotal subcutaneous (SQT) temperature gradient, and with decreased scrotal surface and testicular temperatures. Increased sperm production was associated with increased testicular artery volume, testicular volume, and SQT temperature gradient, and with decreased testicular artery wall thickness, scrotal circumference (SC), and scrotal surface, testicular subtunic, and epididymal temperatures. In conclusion, morphology of the TVC may contribute to the greater resistance of B. indicus bulls to high ambient temperatures by conferring a better testicular blood supply and by facilitating heat transfer between the testicular artery and veins. Testicular thermoregulation was associated with opposing scrotal and testicular subtunic temperatures gradients only in crossbred and B. taurus bulls. Scrotal, TVC, and testicular morphology influence testicular thermoregulatory capability and were associated with differences in semen quality and sperm production.

Effects of scrotal insulation on sperm production, semen quality, and testicular echotexture in Bos indicus and Bos indicus × Bos taurus bulls

The objectives of the present study were to evaluate the effects of scrotal insulation on sperm production, semen quality, and testicular echotexture in Bos indicus and Bos indicus × Bos taurus crossbred bulls. In one experiment, B. indicus bulls ( n=12) were allocated to control and whole-scrotum insulation groups, while in a second experiment, crossbred bulls ( n=21) were allocated into control, whole-scrotum, and scrotal-neck insulation groups. Insulation was applied for 4 days (start of insulation = Day 0) and semen collection and testicular ultrasonographic examinations were performed twice weekly until Day 35. Sperm concentration and total sperm output during the post-insulation period were greater in control groups, but significant differences were observed only in B. indicus bulls. Overall, sperm motility in scrotal-insulated B. indicus bulls was lower ( P<0.05) than in the control group. After whole-scrotum insulation in crossbred bulls, sperm motility was lower ( P<0.05) than pre-insulation levels between Days 21 and 31, and lower than control levels on Day 24. The proportion of normal sperm after whole-scrotum insulation was lower than pre-insulation and control values from Day 11 to the end of the experiment in B. indicus bulls ( P<0.05 from Days 14 to 21 and on Day 27), and from Days 14 to 25 in crossbred bulls ( P<0.05 on Days 14 and 18). Insulation of the scrotal neck in crossbred bulls did not significantly affect semen quality. Loose sperm heads (Day 11), midpiece defects (Days 11 and 14), and acrosome defects (Days 27 and 31) increased ( P<0.05) in insulated B. indicus bulls, while proximal cytoplasmic droplets (Days 14, 18 and 27 in B. indicus; Days 24 and 27 in crossbred bulls) and sperm vacuoles (Days 18 and 21 in B. indicus; Day 18 in crossbred bulls) increased ( P<0.05) in whole-scrotum insulation groups in both experiments. There was considerable variation among bulls in the incidence of specific sperm defects. The timing of appearance of sperm defects after insulation provided insights into the pathogenesis of specific abnormalities. Neither whole-scrotum nor scrotal-neck insulation affected testicular echotexture in either experiment. In conclusion, whole-scrotum insulation resulted in decreased sperm production and semen quality in B. indicus and B. indicus × B. taurus bulls, but those changes were not associated with changes in testicular echotexture.

Efficiency of Compensatory Growth of Borana Bulls (Bos indicus) Following Different Levels of Feed Restriction

Tolla, N., Mirkena, T. and Yimegnuhal, A. 2002. Efficiency of compensatory growth of Borana (Bos indicus) bulls following different levels of feed restriction. J. Appl. Anim. Res., 22: 129–136. To study the efficiency of compensatory growth following different levels of feed restriction, 25 Borana bulls were blocked by weight and randomly allocated to five dietary treatments of ad libitum feeding for the entire period (control), maintenance feeding for 91 days (maintenance), 15per cent weight loss in 91 days (-15%), 20per cent weight loss in 91 days (-20%) and 25per cent weight loss in 91 days (-25%) followed by 105 days of ad libitum (compensatory) feeding. The feed restriction imposed for treatments—15per cent, −20per cent and −25per cent during the initial period resulted in weight losses of -15 per cent, −19 per cent and −23 per cent, respectively. There was no significant (P>0.05) difference among treatments on feed intake during compensatory feeding period. Daily gain (ADG) for the restricted animals was directly proportional to the level of feed restriction. There was also significant (P<0.05) treatment effect on dressing percentage and proportion of fat in carcass. Animals subjected to weight losses of −15 per cent, −20 per cent and −25 per cent had lower yield of these carcass characteristics than the control and maintenance treatments. This study revealed that Borana bulls may not achieve complete compensation in 105 days of compensatory feeding, after 91 days of feed restriction below their daily maintenance requirement.

Effect of age and genetic group on characteristics of the scrotum, testes and testicular vascular cones, and on sperm production and semen quality in AI bulls in Brazil

The objectives were to determine the effects of age and genetic group on characteristics of the scrotum, testes and testicular vascular cones (TVC), and on sperm production and semen quality in 107 Bos indicus, B. taurus and cross-bred bulls at three artificial insemination (AI) centers in Brazil. In addition, predictors of sperm production and semen quality were identified. In general, scrotal circumference (SC), scrotal shape score, scrotal neck perimeter, and testicular size (length, width and volume) increased ( P<0.05) with age. Although there were no significant differences among genetic groups for SC or testicular size, B. indicus bulls had the least pendulous scrotal shape, the shortest scrotal neck length, and the greatest scrotal neck perimeter ( P<0.05). Fat covering the TVC was thinner ( P<0.05) in bulls ≤36 months of age and in B. taurus bulls than in older bulls and B. indicus bulls, respectively. Age and genetic group did not affect testicular ultrasonic echotexture. B. indicus bulls tended ( P<0.1) to have the lowest average scrotal surface temperature (SST). In general, ejaculate volume, total number of spermatozoa and number of viable spermatozoa increased ( P<0.05) with age. However, there was no significant effect of age on sperm concentration, motility, major and total defects. The proportion of spermatozoa with minor defects was highest ( P<0.05) in bulls 37–60 months of age. B. indicus bulls had higher ( P<0.01) sperm concentration, total number of spermatozoa and number of viable spermatozoa than B. taurus bulls, with intermediate values for cross-bred bulls. Increased sperm production was associated with increased testicular volume, SC, TVC fat cover, and SST top-to-bottom gradient. Decreased semen quality was associated with increased SC and bottom SST, and decreased scrotal shape, scrotal neck perimeter and vascular cone diameter. In summary, age and genetic group affected the characteristics of the scrotum, testes, and TVC, sperm production and semen quality. In addition, characteristics of the scrotum, testes and TVC were associated with sperm production and semen quality in bulls and could be assessed for breeding soundness evaluation.

Effects of environmental factors, age and genotype on sperm production and semen quality in Bos indicus and Bos taurus AI bulls in Brazil

The effects of ambient temperature and humidity, month, age and genotype on sperm production and semen quality in AI bulls in Brazil were evaluated. Data from two consecutive years were analyzed separately. Seven Bos indicus and 11 Bos taurus bulls from one artificial insemination (AI) center were evaluated in Year 1 and 24 B. indicus and 16 B. taurus bulls from three AI centers were evaluated in Year 2. Ambient temperature and humidity did not significantly affect sperm production and semen quality, probably because there was little variation in these variables. Month accounted for less than 2% of the variation in sperm production and semen quality. Increased bull age was associated with decreased sperm motility ( P<0.10) and increased minor sperm defects ( P<0.001) in Year 1. B. indicus bulls had greater ( P<0.005) sperm concentration than B. taurus bulls in both years (1.7×10 9/ml versus 1.2×10 9/ml in Year 1 and 1.6×10 9/ml versus 1.2×10 9/ml in Year 2, respectively). Ejaculate volume was not significantly affected by genotype in Year 1 (6.6 ml versus 6.9 ml in B. indicus and B. taurus bulls, respectively), but B. indicus bulls had greater ( P<0.05) total (11.4×10 9 versus 8.2×10 9) and viable (6.7×10 9 versus 4.9×10 9) numbers of spermatozoa in the ejaculate than B. taurus bulls. In Year 2, B. taurus bulls had greater ( P<0.05) ejaculate volume than B. indicus bulls (8.2 ml versus 6.7 ml, respectively) and total and viable number of spermatozoa in the ejaculate were not significantly different between genotypes (10.3×10 9 versus 9.1×10 9 and 6.1×10 9 versus 5.4×10 9 in B. indicus and B. taurus bulls, respectively). Sperm motility was not significantly affected by genotype (mean, 59%). In Year 1, B. indicus bulls tended ( P<0.10) to have more major sperm defects and had more ( P<0.05) total sperm defects than B. taurus bulls (11.8% versus 8.7% and 13.6% versus 10.0%, respectively). In Year 2, B. indicus bulls tended ( P<0.10) to have more total sperm defects than B. taurus bulls (16.2% versus 13.3%, respectively). In conclusion, neither ambient temperature and humidity nor month (season) significantly affected sperm production and semen quality. B. indicus bulls had significantly greater sperm concentration and B. taurus bulls had significantly fewer morphologically defective spermatozoa.

Effect of Graded Levels of Cottonseed Cake Supplementation on Intake, Nutrient Digestibility, Microbial N Yield of Growing Native (Bos Indicus) Bulls Fed Rice Straw

Effect of Graded Levels of Cottonseed Cake Supplementation on Intake, Nutrient Digestibility, Microbial N Yield of Growing Native (Bos Indicus) Bulls Fed Rice Straw

Sexual behaviour of Zebu bulls in the humid tropics of Costa Rica: single versus multiple-sire groups

This study compares the courtship and mounting behaviour of Bos indicus bulls in single- and multiple-sire groups in Costa Rica (latitude 10°25′N, longitude 84°32′W, annual precipitation of 3096 mm, temperature of 24°C and humidity of 85.3%). Four, 3–4 year-old Brahman bulls with previous sexual experience were used to sire a group of 120 multiparous cows (average of 128 days post-partum and a body condition score of 2.5) allocated to two groups of 60 each: (1) single-sire mating group (SSM) and (2) multiple-sire mating group of three bulls (MSM). Bulls were rotated among groups every 7 days for 28 days. The frequency, type and duration of sexual activities (mounting and mounting attempts) and courtship activities (smelling and licking genital area, butting, supporting the head over a female and the sign of Flehmen) were calculated for each mating group. Descriptive and non-parametric statistics (Wilcoxon, Mann-Withney tests) were used to calculate differences between mating programmes. Sexual activities tended to be more frequent in the SSM group than the MSM group (267 versus 124, P>0.05). Differences in the ratios of sexual to courtship activities between both groups were significant (1:3 in SSM and 1:6 in MSM, P>0.05). Pregnancy rate averages were 28 and 37%, respectively, ( P>0.05). It is concluded that under these conditions multiple-sire mating and single-sire mating achieved similar pregnancy rates.

Sexual behavior and pregnancy rate of Bos indicus bulls

To study sexual behavior and pregnancy rate of Zebu bulls, 9 Brahman and 6 Nelore bulls were first examined for libido and serving capacity, semen characteristics and scrotal circumference, a week before being placed, individually, into a group of 16 estrus-syncronized heifers to observe mating activity. Scores for libido (0 to 10) and for serving capacity (based on the number of services per period) were assigned for each bull over a 15-min period. Estrus was synchronized with Norgestomet (3 mg, sc impfant and 3 mg, im) and estradiol valerate (5 mg, im). The implants remained in place for 10 d, then 40 h after their removal a bull was placed with the heifers. Four Brahman and 6 Nelore bulls were monitored for 2 h while the remaining 5 Brahman bulls were observed for 30 h. Number of services and mounts per bull, the hour at which each event took place, and the identification of the heifers serviced were recorded. Pregnancy was diagnosed by transrectal palpation 50 to 60 d after mating. Mean libido score (± SEM) of the 15 bulls was 6.4 ± 0.5, and mean serving capacity was 0.53 ± 0.19; both of these measures were correlated with age (r = 0.78, P < 0.01, and r = 0.56, P < 0.05, respectively). In the 2-h trials, the number of mounts was correlated with the libido score (r = 0.73, P < 0.05), and the number of services was correlated with age (r = 0.76, P < 0.05) and with libido and serving capacity score (r = 0.91 and 0.92, P < 0.01). In the 30-h trials, the mean (± SEM) number of mounts and of services per bull was 74.4 ± 21.1 and 14.6 ± 0.5, respectively. The mount-to-service ratio and percentage of serving efficiency were 5.1 ± 1.4, and 19.8 ± 4%, respectively. Libido score was correlated with the mount-to-service ratio (r = −0.86, P < 0.10) and with serving efficiency (r = 0.84, P < 0.10). The percentage of heifers serviced, of those serviced 2 or more times and of those pregnant was 55 ± 5.3; 47.1 ± 6.4, and 59.2 ± 5.8, respectively. Pregnancy rate was not correlated with any trait (P > 0.10). It was concluded that libido and the serving capacity test seem to indicate the mating potential of Zebu bulls over a relatively short period of time (e.g. 30 hours), in which resultant pregnancy rates are comparable to those of European bulls.

Estimation of net ruminal protein synthesis from urinary allantoin excretion by bulls given tropical feeds

An experiment was carried out to determine net microbial protein supply to ruminants from 15 tropical feeds. The study was done at Lyamungo research institute, on the slopes of Mt. Kilimanjaro, Tanzania in 1993. Twenty Bos Taurus × Bos Indicus bulls were used in three periods in a completely randomised design. The initial 19 days of each period were for adaptation by the bulls to their new environment and diets, followed by 2, 7 and 7 days for total urine collection, spot urine sampling and digestibility, respectively. The feeds included urea treated and untreated maize stover (3 feeds), green maize stover (3 feeds), bean straw (2 varieties), cultivated forage (5) and banana plant residues (2). Both total and spot urine collections were made for estimation of allantoin. Daily excretion of allantoin ranged from 5.63 to 48.89 mmol/day for banana leaves and 5% urea treated maize stover, respectively. Excretion of allantoin increased with level of dry matter intake (DMI) for all the feeds. Microbial N supply (MNS) and efficiency of microbial N supply (EMNS) followed the same trend (4.1–35.5 g N/day and 5.5–17.4 g of N/kg DOMR (digestible organic matter in the rumen) for banana leaves and 5% urea treated maize stover, respectively. Correlation coefficients between allantoin excreted ( A e), DMI and BW 0.75were r = 0.79 and r = 0.54, respectively. That between MNS, DMI and BW 0.75were r = 0.80 and r = 0.52, respectively, while that between EMNS, DMI and BW 0.75were r = 0.78 and r = 0.54, respectively. It was concluded that all the tropical feeds tested were poor sources of MNS and EMNS

Effect of Graded Levels of Mustard Oil Cake Supplementation on Intake, Nutrient Digestibility, Microbial N Yield of Adult Cannulated Native (Bos Indicus) Bulls Fed Rice Straw

Effect of Graded Levels of Mustard Oil Cake Supplementation on Intake, Nutrient Digestibility, Microbial N Yield of Adult Cannulated Native (Bos Indicus) Bulls Fed Rice Straw

Heterologous and homologous fertilizing capacity of cryopreserved felid sperm: A model for endangered species

The aim of the present study was to compare the viability and fertility of bovine semen diluted in Botu-Bov (BB) commercial extender with and without the cryoprotectant glycerol then cooled at 5 °C for 24 hours in the Botu-Flex passive cooling system and of semen diluted in BB with glycerol then frozen. One ejaculate of 30 Nelore Bos taurus indicus bulls between 24 and 30 months of age was used for in vitro analysis. Sperm kinetics and cell viability were analyzed using computer-assisted sperm analysis and flow cytometry, respectively. Three Nelore bulls approximately 30 month old were used for in vivo test using fixed-time artificial insemination for the fertility analysis. The ejaculates were divided into three experimental groups: semen in BB extender with 7% glycerol cooled at 5 °C for 24 hours (cooled semen with cryoprotectant), semen in BB without glycerol cooled at 5 °C for 24 hours (cooled semen without cryoprotectant), and semen diluted in BB with 7% glycerol then subsequently frozen rather than cooled (frozen semen). For the fertility analysis, 762 Nelore cows (B taurus indicus) were randomly inseminated using fixed-time artificial insemination. For the groups corresponding to cooled semen with cryoprotectant, cooled semen without cryoprotectant, and frozen semen, 278, 268, and 216 cows were inseminated, respectively, and the resulting conception rates were 51%a, 44%ab and 41%b (P < 0.05), respectively. In conclusion, the fertility rates improved, when samples were cooled with glycerol at 5 °C for 24 hours compared with the frozen samples.

Breed and other effects on reproductive traits and breeding soundness categorization in young beef bulls in Florida

Yearling, grass-fed, beef bulls at the USDA Subtropical Agricultural Research Station, Brooksville, Florida, were assessed for physical and semen traits in January, April, July and October of 1991 (Trial 1) and 1992 (Trial 2). Bulls were given a breeding soundness evaluation (BSE) using revised semen and scrotal circumference (SC) criteria. In Trial 1, the bulls consisted of Angus (n = 15), Brahman (n = 14), Hereford (n = 15) and Senepol (n = 14). In Trial 2, the breeds were Angus (n = 15), Brahman (n = 16), Romosinuano (n = 13) and Nellore x Brahman (n = 9). Trial bulls generally showed delayed growth compared with grain-fed bulls in temperate environments. Breed influenced semen traits (percentage sperm motility, normal spermatozoa and those with primary abnormalities) in both trials. Temperate Bos taurus breeds (Angus, Hereford) were generally superior to Bos indicus breeds (Brahman, Nellore x Brahman). Tropically-adapted Bos taurus breeds (Senepol, Romosinuano) were intermediate for those traits tested. In general, tropically-adapted Bos taurus breeds were more similar in reproductive development to temperate Bos taurus than to Bos indicus breeds. Breed by test period interactions occurred and were mainly influenced by delayed sexual maturity of Bos indicus bulls. Qualitative semen traits increased with bull age, particularly from 12 to 18 mo. Scrotal circumference development was slower in the Bos indicus breeds. Bulls of satisfactory BSE status at 18.1 to 22 mo of age were 73.9% in Trial 1 and 58.5% in Trial 2. Brahman bulls had the least satisfactory BSE scores in both years (Trial 1, 44.4%; Trial 2, 22.2%). Most bulls failed to achieve satisfactory BSE status due to a small SC relative to age (Trial 1, 66%; Trial 2, 72%). The most efficacious use of the BSE was ≥ 15 mo in Bos taurus bulls and > 18 mo for Bos indicus bulls. Although the BSE has proven to be useful for the assessment of young, pasture-raised bulls in semi-tropical environments, use of SC thresholds linked more with growth traits than with calendar age would improve comparisons of relative reproductive development in such bulls, particularly those of Bos indicus derivation.

The assessment of sexual performance in young Bos taurus and Bos indicus beef bulls

Yearling beef bulls, representing different Bos indicus and Bos taurus breeds, were given two sexual performance assessments (libido score, number of services, time to first mount and time of sexual inactivity) at four test periods (January, April, July and October) in 1991 (Trial 1) and 1992 (Trial 2) at the Subtropical Agricultural Research Station, Brooksville, Florida. Breed and test period, as well as their interactions, influenced most results. Sexual performance assessments generally improved with age in Bos taurus breeds, but not in Bos indicus. The temperate Bos taurus breeds (Angus and Hereford) were most sexually active, the tropically adapted Bos taurus breeds (Senepol and Romosinuano) intermediate and the two Bos indicus breeds (Brahman and Nellore × Brahman) were least active. Service rates were generally low. Seasonal patterns in sexual performance were not apparent, with breed and year differences occurring. Although breeds showed consistent test results, the failure of Bos indicus bulls to service in any test, indicates either sexual immaturity, or inadequate procedures for assessment of sexual performance in this breed group.

Testicular ultrastructure of Zebu bulls in Costa Rica.

The testicular ultrastructure of sexually mature Zebu (Bos indicus) bulls from Costa Rica was studied in relation to their classification based on andrological examinations undertaken in the field. Based on the testicular consistency at palpation, each bull was assigned to one of three groups, ranging from normal (Group A) to markedly reduced testicular consistency (Group C). The ultrastructure of the clinically normal testicle (Group A) in the Zebu bull resembled that of Bos taurus. In testicles with a slight to moderate reduction of testicular consistency (Group B) degenerated primary spermatocytes and spermatids were common at all stages of the seminiferous cycle. Abnormalities in the condensation of the chromatin, acrosomal defects, and the presence of degenerated cells and cellular debris were the most common of disturbances found. In testicles from bulls with a marked reduction of testicular consistency (Group C) the seminiferous epithelium of most tubules showed degenerative changes, thereby making it impossible to classify the stage of the cycle. The changes were mainly restricted to spermatocytes and spermatids, whose relative numbers were reduced. The number of cells undergoing meiotic divisions was also greatly reduced. Changes in the spermatids were also found including the appearance of severe acrosomal defects, such as acrosomal pouches, the failure of nuclear elongation and clear defects in chromatin condensation. The present ultrastructural findings in Bos indicus do not differ from the picture of normal testicular structure and of testicular degeneration usually found in Bos taurus bulls.

Spermatogenesis in Bali cattle (Bos sondaicus) and hybrids with Bos indicus and Bos taurus

Semen quality, testis size and efficiency of sperm production in Bali cattle (Bos sondaicus) and hybrids with Bos indicus and Bos taurus were determined. Mean (+/- SEM) daily sperm production per gram of testis parenchyma (DSPG) in six purebred Bali bulls was 12.2 +/- 0.7 x 10(6). F1 B sondaicus cross B taurus bulls and F1 B sondaicus cross B indicus bulls were sterile. Spermatogenesis was arrested at the late primary spermatocyte stage. In 11 B sondaicus cross B indicus crosses, mean DSPG was lower than in the purebred B sondaicus, although four (one 1/4 B sondaicus, one 3/4 B sondaicus, one 5/8 B sondaicus inter se and one 3/8 B sondaicus inter se) exhibited DSPG levels similar to the foundation stock. Semen from those crossbreeds which exhibited complete spermatogenesis was more variable in terms of spermatozoal concentration, percentage of spermatozoa exhibiting progressive motility and levels of spermatozoal abnormalities. In crossbreeds where sperm production was reduced or absent, there was seminiferous epithelial dysfunction, manifested as an increased frequency of degenerative late pachytene and diplotene primary spermatocytes and germinal cells occurring later in the cycle, or in extreme cases, as complete arrest of spermatogenesis at the late primary spermatocyte stage.

Factors influencing sexual behaviour of young Bos indicus bulls under pen and pasture mating conditions

Some of the factors which influence the pen and subsequent pasture mating activity of young (20 months of age) Afrikaner bulls were investigated. The bulls ( n=18) were subjected to 12 Blockey-type pen tests. Eight of these bulls, four high and four low serving capacity, were subsequently mated to small groups of oestrous-synchronised females under pasture conditions. During the serving capacity tests, bulls showed no preference for nocturnal sexual behaviour and were not hindered by the presence of personnel scoring their activity. Many of the bulls did not serve consistently from one test to another. However, their serving capacity improved with progression of the tests. The inconsistent serving behaviour of the bulls suggests that restrained females do not present the ideal mating stimulus. Furthermore, agonistic interactions had a depressive effect on sexual behaviour. There was, however, a significant relationship between pen and pasture mating behaviour; high-serving-capacity bulls achieved superior conception rates to low-serving-capacity bulls. Pasture mating performance was significantly influenced by the degree of cow receptiveness, the bull's previous activity and duration of his exposure to an oestrous female within a given observation period. The need to identify the specific oestral characteristics which attract and promote copulatory behaviour in Bos indicus bulls clearly exists.

Reproductive performance and productive traits of beef bulls selected for different levels of testosterone response to GnRH

In two separate studies, one with four Hereford-Shorthorn and one with three Zebu × British crossbred bulls, the efficacy of using the testosterone response to gonadotrophin-releasing hormone (GnRH; Lutal, Hoechst) to predict differences in reproductive performance was assessed. Young bulls (17 or 29 months of age) selected for low to high (3.1 to 10.3 ng/ml) peak plasma testosterone 2 to 2.5 hours after the intramuscular injection of GnRH (62.5 to 2000 ng/kg LWT) were each later individually joined with groups of 19 to 30 cows in which estrus had been synchronized. In both studies, the rankings of bulls for overall fertility (capable cows pregnant), for libido (estrous cows mounted), and for fertilizing ability (mounted cows pregnant) were in close agreement with rankings for testosterone responses to GnRH. In the Bos indicus bulls rankings for both reproductive performance and testosterone response to GnRH were repeatable when measured at two and four years of age. Other reproductive measurements (semen quality, scrotal circumference, pen-type serving capacity tests) were less reliable predictors of reproductive performance. Measurements of liveweight gains and parasite resistance indicated that bulls superior for these characteristics do not always have satisfactory reproductive performance. These studies suggest that the testosterone response to GnRH could be a useful test to ensure that bulls selected for productive traits have adequate reproductive potential.

Genetic and environmental effects on a temperament score in beef cattle

Temperament scores were taken on 8-month-old calves from five calf drops (1976-80) and over three sections of a large crossbreeding trial on the North Coast of New South Wales. A 0-5 scale was used, with lower values for quieter cattle. The heritability �s.e. of temperament score of Bos taurus calves (sired by Hereford, Simmental and Friesian bulls) was 0.03�0.28, and for B. indicus-sired calves (Brahman, Braford and Africander bulls) 0.46�0.37, and for all data combined 0.44�0.25. There was a significant difference (P &lt; 0.01) between the mean score of Brahman-sired halfbred calves (1.96) and B. taurus-sired calves (1.05). The difference was halved to 0.45 points for quarterbred Brahman calves versus B. taurus calves, i.e. as expected for an additive trait. There were significant differences in temperament among calves sired by B. indicus bulls, but there were no significant differences amongst the B. taurus sire breeds. The repeatability (mean � s.e.) of operators' score of 701 weaner calves was 0.67�0.08. From temperament scores of 315 cows at weaning in 1981, an operator repeatability of 0.82�0.08 was obtained. Correlations of cow and calf score were not consistent, but averaged 0.18�0.04 from 547 records. The repeatability of scores taken at two separate times on 132 calves, was 0.43�0.09. The group given a medium level of nutrition had significantly higher temperament scores than those given high or low levels. Sex effects were not significant on scores at weaning. A log transformation of the data equalized the variance of scores of different breeds, but did not affect the conclusions.

C- and G-banding patterns and chromosomal morphology of some breeds of Australian cattle.

A cytogenetical study using metaphase chromosomes from cultured lymphocytes, was made of 2 Banteng (Bibos banteng) steers and 218 bulls representing 13 purebreeds (Bos taurus type, Bos indicus type and Sanga) and 7 cross-breeds. Studies were made of photographic karyotypes of Giemsa stained and C-banded chromosomes of bulls of each breed and of B-banded chromosomes from 3 breeds of Bos indicus and one cross-breed Australian Friesian Sahiwal) cattle. The relative lengths of chromosomes of Bos taurus and Bos indicus bulls were compared and significant difference in relative lengths of the X chromosomes were noted between these two species. There was a differences in morphology of the Y chromosomes; Sanga, Banteng and Bos taurus type breeds had a small submetacentric Y chromosome, except for the Jersey which had a metacentric Y chromosome. All Bos indicus type bulls had an acrocentric Y chromosome but the Droughtmaster breed had two forms of the Y chromosome (submetacentric and acrocentric). The C-banding patterns of the autosomes and X chromosomes were similar for all breeds while those of the Y chromosomes of Bos indicus type cattle allowed their accurate identification. G-banding patterns of Bos indicus resembled those of Bos taurus and enabled pairing of homologous chromosomes. Centromeres of the autosomes were unstained but those of the sex chromosomes were darkly stained.

Bos indicus and Bos taurus crossbred dairy cattle in Australia. IV.* Progeny testing and expected rate of genetic improvement

A dairy improvement program designed to develop a breed of cattle adapted to tropical environments is described. Each year young crossbred (Bos indicus x Bos taurus) bulls are screened for heat tolerance and tick resistance, and then progeny-tested in the herds of cooperating dairy farmers. Estimates of phenotypic and genetic means, variances and correlations are presented for production of milk and milk components, and the rate of genetic improvement is discussed. In particular the heritability of milk yield in the crossbred progeny is 0.27, and the theoretical rate of improvement is 2.6% per year. ____________________ *Part III, Aust. J. Agric. Res., 25: 1023 (1974).