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The genetics of reproduction is poorly understood because the heritabilities of traits currently recorded are low. To elucidate the genetics underlying reproduction in beef cattle, we performed a genome-wide association study using the bovine SNP50 chip in 2 tropically adapted beef cattle breeds, Brahman and Tropical Composite. Here we present the results for 3 female reproduction traits: 1) age at puberty, defined as age in days at first observed corpus luteum (CL) after frequent ovarian ultrasound scans (AGECL); 2) the postpartum anestrous interval, measured as the number of days from calving to first ovulation postpartum (first rebreeding interval, PPAI); and 3) the occurrence of the first postpartum ovulation before weaning in the first rebreeding period (PW), defined from PPAI. In addition, correlated traits such as BW, height, serum IGF1 concentration, condition score, and fatness were also examined. In the Brahman and Tropical Composite cattle, 169 [false positive rate (FPR) = 0.262] and 84 (FPR = 0.581) SNP, respectively, were significant (P < 0.001) for AGECL. In Brahman, 41% of these significant markers mapped to a single chromosomal region on BTA14. In Tropical Composites, 16% of these significant markers were located on BTA5. For PPAI, 66 (FPR = 0.67) and 113 (FPR = 0.432) SNP were significant (P < 0.001) in Brahman and Tropical Composite, respectively, whereas for PW, 68 (FPR = 0.64) and 113 (FPR = 0.432) SNP were significant (P < 0.01). In Tropical Composites, the largest concentration of PPAI markers were located on BTA5 [19% (PPAI) and 23% (PW)], and BTA16 [17% (PPAI) and 18% (PW)]. In Brahman cattle, the largest concentration of markers for postpartum anestrus was located on BTA3 (14% for PPAI and PW) and BTA14 (17% PPAI). Very few of the significant markers for female reproduction traits for the Brahman and Tropical Composite breeds were located in the same chromosomal regions. However, fatness and BW traits as well as serum IGF1 concentration were found to be associated with similar genome regions within and between breeds. Clusters of SNP associated with multiple traits were located on BTA14 in Brahman and BTA5 in Tropical Composites.

A review of factors that may impact on the capacity of beef cattle females, grazing semi-extensive to extensive pastures in northern Australia, to conceive, maintain a pregnancy and wean a calf was conducted. Pregnancy and weaning rates have generally been used to measure the reproductive performance of herds. However, this review recognises that reproductive efficiency and the general measures associated with it more effectively describe the economic performance of beef cattle enterprises. More specifically, reproductive efficiency is influenced by (1) pregnancy rate which is influenced by (i) age at puberty; (ii) duration of post-partum anoestrus; (iii) fertilisation failure and (iv) embryo survival; while (2) weight by number of calves per breeding female retained for mating is influenced by (i) cow survival; (ii) foetal survival; and (iii) calf survival; and (3) overall lifetime calf weight weaned per mating. These measures of reproductive efficiency are discussed in depth. Further, a range of infectious and non-infectious factors, namely, environmental, physiological, breed and genetic factors and their impact on these stages of the reproductive cycle are investigated and implications for the northern Australian beef industry are discussed. Finally, conclusions and recommendations to minimise reproductive inefficiencies based on current knowledge are presented.

This experiment assessed the effects of different quality and quantity of handling and quality of the holding yard environment on the productivity and physiological parameters indicative of stress in beef cattle. One-hundred-and-forty-four steers were given one of three human handling and yarding experiences on six occasions during a 12-month grazing period post-weaning (backgrounding): Good handling/yarding, Poor handling/yarding and Minimal handling/yarding. At the end of this phase the cattle were lot-fed for 78 days, with no handling/yarding treatments imposed, before being transported for commercial slaughter. Temperament was assessed by flight speed (FS) and a fear of humans (FOH) test, which measured the proximity to a stimulus person (ZA), the closest approach to the person (CA) and the amount the cattle moved around the test arena (TT). Mid-way through backgrounding, the Minimal treatment group was heavier than the Good, which was heavier than the Poor (mean weights 207, 201 and 194 kg, respectively; P = 0.05; LSD = 5.4), but by the end of backgrounding there was no difference between treatments and treatment did not affect liveweight during lot-feeding. At the end of backgrounding, plasma cortisol levels were significantly lower (P < 0.001) in the Good treatment group compared to the Poor and Minimal groups but at the end of lot-feeding there was no significant difference between the groups. Treatment affected plasma non-esterified fatty acid levels in backgrounding (P = 0.060) and lot-feeding (P = 0.046) with levels being higher in the Minimal than the Good and Poor groups (backgrounding: 0.52, 0.44 and 0.47 nmol/L, respectively; SE 0.02; lot-feeding: 0.46, 0.41 and 0.41 mmol/L, respectively; LSD = 0.05). Significant weak to moderate (r-value

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 ≥4-year-old Belmont Red bulls, respectively, completed 1 or more serves. This compared with 50, 50 and 66% of 2-, 3- and ≥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

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

A systematic breeding soundness examination, including assessment of serving capacity was conducted on 5/8 Brahman, Brahman and Belmont Red bulls, most aged 2–4 years, at 12 different cattle properties across northern Australia. A subset of bulls (n=235) were subsequently mated in various groups, as multiple-sires, to cows and heifers at bull:female ratios of 2.5–6%. The number of calves sired by individual bulls (calf output) was determined by DNA typing for paternity. Overall, the incidence of physical abnormalities that were judged likely to result in reduced reproductive performance was low (5.6–12% of bulls). Measures of key physical traits scrotal circumference, sheath depth (vertical distance from ventral abdominal wall to preputial orifice), and sheath score were moderately to highly repeatable. Except in Belmont Red bulls, liveweight was positively correlated with scrotal circumference (r=0.36–0.78; P

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 22 km2 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 84 km2 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 60 km2 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 250–750 ha 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 500 ha 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 500 ha 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.

Genetic correlations of young bull and heifer puberty traits with measures of early and lifetime female reproductive performance were estimated in two tropical beef cattle genotypes. Heifer age at puberty was highly (r(g) = -0.71 +/- 0.11) and moderately (r(g) = -0.40 +/- 0.20) genetically correlated with pregnancy rate at first annual mating (mating 1) and lifetime annual calving rate, respectively in Brahman (BRAH). In Tropical Composite (TCOMP), heifer age at puberty was highly correlated with reproductive outcomes from the first re-breed (mating 2), mainly due to its association with lactation anoestrous interval (r(g) = 0.72 +/- 0.17). Scrotal circumference were correlated with heifer age at puberty (r(g) = -0.41 +/- 0.11 at 12 months in BRAH; -0.30 +/- 0.13 at 6 months in TCOMP) but correlations were lower with later female reproduction traits. Bull insulin-like growth factor-I was correlated with heifer age at puberty (r(g) = -0.56 +/- 0.11 in BRAH; -0.43 +/- 0.11 in TCOMP) and blood luteinising hormone concentration was moderately correlated with lactation anoestrous interval (r(g) = 0.59 +/- 0.23) in TCOMP. Semen quality traits, including mass activity, motility and percent normal sperm were genetically correlated with lactation anoestrus and female lifetime female reproductive traits in both genotypes, but the magnitudes of the relationships differed with bull age at measurement. Preputial eversion and sheath scores were genetically associated with lifetime calving and weaning rates in both genotypes. Several of the early-in-life male and female measures examined were moderately to highly genetically correlated with early and lifetime female reproduction traits and may be useful as indirect selection criteria for improving female reproduction in tropical breeds in northern Australia.

Early-in-life female and male measures with potential to be practical genetic indicators were chosen from earlier analyses and examined together with genomic measures for multi-trait use to improve female reproduction of Brahman cattle. Combinations of measures were evaluated on the genetic gains expected from selection of sires and dams for each of age at puberty (AGECL, i.e. first observation of a corpus luteum), lactation anoestrous interval in 3-year-old cows (LAI), and lifetime annual weaning rate (LAWR, i.e. the weaning rate of cows based on the number of annual matings they experienced over six possible matings). Selection was on an index of comparable records for each combination. Selection intensities were less than theoretically possible but assumed a concerted selection effort was able to be made across the Brahman breed. The results suggested that substantial genetic gains could be possible but need to be confirmed in other data. The estimated increase in LAWR in 10 years, for combinations without or with genomic measures, ranged from 8 to 12 calves weaned per 100 cows from selection of sires, and from 12 to 15 calves weaned per 100 cows from selection of sires and dams. Corresponding reductions in LAI were 60–103 days or 94–136 days, and those for AGECL were 95–125 or 141–176 days, respectively. Coat score (a measure of the sleekness or wooliness of the coat) and hip height in females, and preputial eversion and liveweight in males, were measures that may warrant wider recording for Brahman female reproduction genetic evaluation. Pregnancy-test outcomes from Matings 1 and 2 also should be recorded. Percentage normal sperm may be important to record for reducing LAI and scrotal size and serum insulin-like growth factor-I concentration in heifers at 18 months for reducing AGECL. Use of a genomic estimated breeding value (EBV) in combination with other measures added to genetic gains, especially at genomic EBV accuracies of 40%. Accuracies of genomic EBVs needed to approach 60% for the genomic EBV to be the most important contributor to gains in the combinations of measures studied.

A total of 4063 young bulls of two tropical genotypes (1639 Brahman and 2424 Tropical Composite) raised in northern Australia were evaluated for a comprehensive range of production and reproduction traits up to 24 months of age. Prior to weaning, peripheral blood concentrations of luteinising hormone (LH) and inhibin were measured at 4 months of age. At weaning (6 months) blood insulin-like growth factor-1 (IGF-I) and flight time were recorded. Body composition traits of fat depth and eye-muscle area were determined by ultrasonography at 15 months of age when additional measurements of liveweight, hip height and body condition score were recorded. Bull breeding soundness was evaluated at ~12, 18 and 24 months of age when measurements of scrotal circumference, sheath score, semen mass activity, progressive motility of individual sperm and percent morphologically normal sperm were recorded. Magnitude of heritability and genetic correlations changed across time for some traits. Heritability of LH, inhibin, IGF-I and of 18-month scrotal circumference, mass activity, progressive motility and percent normal sperm was 0.31, 0.74, 0.44, 0.75, 0.24, 0.15 and 0.25, respectively, for Brahmans and 0.48, 0.72, 0.36, 0.43, 0.13, 0.15 and 0.20, respectively, for Tropical Composites. Inhibin and IGF-I had moderate genetic association with percent normal sperm at 24 months in Brahmans but low to negligible associations in Tropical Composites. Body condition score in Brahmans and sperm motility (mass and individual) traits in both genotypes had moderate to strong genetic correlation with percent normal sperm and may prove useful candidates for indirect selection. There is scope to increase scrotal circumference by selection and this will be associated with favourable correlated responses of improved semen quality in both genotypes. The lack of genetic antagonism among bull traits indicates that selection for improved semen quality will not adversely affect other production traits.

Hip height, body condition, subcutaneous fat, eye muscle area, percentage Bos taurus, fetal age and diet digestibility data were collected at 17 372 assessments on 2181 Brahman and tropical composite (average 28% Brahman) female cattle aged between 0.5 and 7.5 years of age at five sites across Queensland. The study validated the subtraction of previously published estimates of gravid uterine weight to correct liveweight to the non-pregnant status. Hip height and liveweight were linearly related (Brahman: P < 0.001, R2 = 58%; tropical composite P < 0.001, R2 = 67%). Liveweight varied by 12–14% per body condition score (5-point scale) as cows differed from moderate condition (P < 0.01). Parallel effects were also found due to subcutaneous rump fat depth and eye muscle area, which were highly correlated with each other and body condition score (r = 0.7–0.8). Liveweight differed from average by 1.65–1.66% per mm of rump fat depth and 0.71–0.76% per cm2 of eye muscle area (P < 0.01). Estimated dry matter digestibility of pasture consumed had no consistent effect in predicting liveweight and was therefore excluded from final models. A method developed to estimate full liveweight of post-weaning age female beef cattle from the other measures taken predicted liveweight to within 10 and 23% of that recorded for 65 and 95% of cases, respectively. For a 95% chance of predicted group average liveweight (body condition score used) being within 5, 4, 3, 2 and 1% of actual group average liveweight required 23, 36, 62, 137 and 521 females, respectively, if precision and accuracy of measurements matches that used in the research. Non-pregnant Bos taurus female cattle were calculated to be 10–40% heavier than Brahmans at the same hip height and body condition, indicating a substantial conformational difference. The liveweight prediction method was applied to a validation population of 83 unrelated groups of cattle weighed in extensive commercial situations on 119 days over 18 months (20 917 assessments). Liveweight prediction in the validation population exceeded average recorded liveweight for weigh groups by an average of 19 kg (~6%) demonstrating the difficulty of achieving accurate and precise animal measurements under extensive commercial grazing conditions.

Research into the genetics of whole herd profitability has been a focus of the Beef Cooperative Research Centre for Beef Genetic Technologies over the past decade and it has been identified that measures of male reproduction may offer a potential indirect means of selecting for improved female reproduction. This paper describes the experimental design and provides a descriptive analysis of an array of male traits in Brahman and Tropical Composite genotypes managed under the medium to high stress, semi-extensive to extensive production systems of northern Australia. A total of 1639 Brahman and 2424 Tropical Composite bulls with known pedigrees, bred and raised in northern Australia, were evaluated for a comprehensive range of productive and reproductive traits. These included blood hormonal traits (luteinising hormone, inhibin and insulin-like growth factor-I); growth and carcass traits (liveweight, body condition score, ultrasound scanned 12–13th rib fat, rump P8 fat, eye muscle area and hip height); adaptation traits (flight time and rectal temperature); and a bull breeding soundness evaluation (leg and hoof conformation, sheath score, length of everted prepuce, penile anatomy, scrotal circumference, semen mass activity, sperm motility and sperm morphology). Large phenotypic variation was evident for most traits, with complete overlap between genotypes, indicating that there is likely to be a significant opportunity to improve bull fertility traits through management and bull selection.

A total of 2115 heifers from two tropical genotypes (1007 Brahman and 1108 Tropical Composite) raised in four locations in northern Australia were ovarian-scanned every 4–6 weeks to determine the age at the first-observed corpus luteum (CL) and this was used to define the age at puberty for each heifer. Other traits recorded at each time of ovarian scanning were liveweight, fat depths and body condition score. Reproductive tract size was measured close to the start of the first joining period. Results showed significant effects of location and birth month on the age at first CL and associated puberty traits. Genotypes did not differ significantly for the age or weight at first CL; however, Brahman were fatter at first CL and had a small reproductive tract size compared with that of Tropical Composite. Genetic analyses estimated the age at first CL to be moderately to highly heritable for Brahman (0.57) and Tropical Composite (0.52). The associated traits were also moderately heritable, except for reproductive tract size in Brahmans (0.03) and for Tropical Composite, the presence of an observed CL on the scanning day closest to the start of joining (0.07). Genetic correlations among puberty traits were mostly moderate to high and generally larger in magnitude for Brahman than for Tropical Composite. Genetic correlations between the age at CL and heifer- and steer-production traits showed important genotype differences. For Tropical Composite, the age at CL was negatively correlated with the heifer growth rate in their first postweaning wet season (–0.40) and carcass marbling score (–0.49), but was positively correlated with carcass P8 fat depth (0.43). For Brahman, the age at CL was moderately negatively genetically correlated with heifer measures of bodyweight, fatness, body condition score and IGF-I, in both their first postweaning wet and second dry seasons, but was positively correlated with the dry-season growth rate. For Brahman, genetic correlations between the age at CL and steer traits showed possible antagonisms with feedlot residual feed intake (–0.60) and meat colour (0.73). Selection can be used to change the heifer age at puberty in both genotypes, with few major antagonisms with steer- and heifer-production traits.

The genetics of heifer performance in tropical ‘wet’ and ‘dry’ seasons, and relationships with steer performance, were studied in Brahman (BRAH) and Tropical Composite (TCOMP) (50% Bos indicus, African Sanga or other tropically adapted Bos taurus; 50% non-tropically adapted Bos taurus) cattle of northern Australia. Data were from 2159 heifers (1027 BRAH, 1132 TCOMP), representing 54 BRAH and 51 TCOMP sires. Heifers were assessed after post-weaning ‘wet’ (ENDWET) and ‘dry’ (ENDDRY) seasons. Steers were assessed post-weaning, at feedlot entry, over a 70-day feed test, and after ∼120-day finishing. Measures studied in both heifers and steers were liveweight (LWT), scanned rump fat, rib fat and M. longissimus area (SEMA), body condition score (CS), hip height (HH), serum insulin-like growth factor-I concentration (IGF-I), and average daily gains (ADG). Additional steer measures were scanned intra-muscular fat %, flight time, and daily (DFI) and residual feed intake (RFI). Uni- and bivariate analyses were conducted for combined genotypes and for individual genotypes. Genotype means were predicted for a subset of data involving 34 BRAH and 26 TCOMP sires. A meta-analysis of genetic correlation estimates examined how these were related to the difference between measurement environments for specific traits. There were genotype differences at the level of means, variances and genetic correlations. BRAH heifers were significantly (P < 0.05) faster-growing in the ‘wet’ season, slower-growing in the ‘dry’ season, lighter at ENDDRY, and taller and fatter with greater CS and IGF-I at both ENDWET and ENDDRY. Heritabilities were generally in the 20 to 60% range for both genotypes. Phenotypic and genetic variances, and genetic correlations, were commonly lower for BRAH. Differences were often explained by the long period of tropical adaptation of B. indicus. Genetic correlations were high between corresponding measures at ENDWET and ENDDRY, positive between fat and muscle measures in TCOMP but negative in BRAH (mean of 13 estimates 0.50 and –0.19, respectively), and approximately zero between steer feedlot ADG and heifer ADG in BRAH. Numerous genetic correlations between heifers and steers differed substantially from unity, especially in BRAH, suggesting there may be scope to select differently in the sexes where that would aid the differing roles of heifers and steers in production. Genetic correlations declined as measurement environments became more different, the rates of decline (environment sensitivity) sometimes differing with genotype. Similar measures (LWT, HH and ADG; IGF-I at ENDWET in TCOMP) were genetically correlated with steer DFI in heifers as in steers. Heifer SEMA was genetically correlated with steer feedlot RFI in BRAH (0.75 ± 0.27 at ENDWET, 0.66 ± 0.24 at ENDDRY). Selection to reduce steer RFI would reduce SEMA in BRAH heifers but otherwise have only small effects on heifers before their first joining.

This experiment tested the hypothesis that relocating cattle is detrimental to their growth. The study examined the effect of having relocated cattle mixed with, or segregated from, the local acclimatised cattle at the destination property. Bos indicus cross steers (120) were allocated to three groups and were relocated, in two separate cohorts, 980 km from northern Queensland to improved pastures in central Queensland. At the start of Phase 1, the control group (C) was moved 3 months before the other two groups. The remaining two groups grazed native pastures; one group was supplemented (SR) to increase growth rate similar to that expected from improved pasture in central Queensland and the other was not supplemented (R). At the end of Phase 1, C was significantly (P < 0.05) heavier than SR, which was significantly (P < 0.05) heavier than R. At the start of Phase 2, the SR and R groups were relocated and after transportation the R and SR groups lost 12 kg or 4.4% of liveweight and 18 kg or 5.7% of liveweight, respectively; this weight loss was recovered after 5 days. All steers were reallocated to segregated (SEG) or mixed (MIX) treatment groups forming six treatments (SEG.C, SEG.R and SEG.SR and MIX.C, MIX.R and MIX.SR). There were no significant differences in liveweights within the SEG treatments by 57 days or within the MIX treatments by 106 days after relocation. There were few if any significant differences in the plasma constituents and differential leucocyte counts of the steers and most results were within physiologically normal ranges. We conclude on the basis of these results and of other experiments that the anecdotal poor performance of cattle after relocation appears to be unfounded.

Fifty Bos indicus steers, 2–3 years old, were exposed to aspects of a feedlot environment on their home property for 9 days (pre-exposed). A further 50 steers were placed in a holding paddock for the 9 days (naïve). Twenty steers in each group became 'focal animals' for periodic blood sampling and behaviour observations. The cattle were transported for 15 h (950 km) to an experimental feedlot where they were lot-fed for 100 days, with productivity (liveweight, body condition and feed intakes) and flight speeds recorded at intervals. A subjective fear of humans test was conducted on the pre-exposed group during the 9 days in the yards on the home property and carcass traits were measured on all cattle.Both groups lost substantial weight on the property and during transportation. On the property, the pre-exposed steers lost about 12% of their original liveweight and the naïve about 9%. Transit losses were a further 5 and 4% of pre-transport liveweights, respectively. The steers did not reach their initial liveweights until day 41 of feedlotting. The pre-exposure treatment did not affect final liveweight, but feed intakes were lower for the pre-exposed animals than the naïve ones during the first 16 days of feedlotting, and the pre-exposed steers had superior average daily gains and feed conversion efficiencies. These effects were probably due to a combination of compensation and improved feed digestibility, as a result of the pre-exposed animals being under-fed on the property, but receiving concentrated grain supplement. There was no effect of focal status on productivity.Flight speed and the subjective fear of humans test were significantly correlated. Neither treatment nor focal status affected flight speeds, but flight speeds decreased in the latter part of feedlotting, were highly correlated between days and negatively correlated with average daily gain and intakes.

One hundred and twenty Bos indicus cross steers were allocated to 3 treatments (good, mixed and poor) on the basis of flight speed, as a measure of cattle temperament. The cattle were lot-fed for 100 days and data collected at intervals on their temperament (flight speeds) and productivity (liveweight changes, body condition, pen feed intakes) during this time. After slaughter, data were collected on carcass traits and meat quality. Eating-quality attributes were measured in meat samples from 22 carcasses from each treatment. Flight speeds were highly correlated across animals and within treatments, showed little change in variability over time and were highly repeatable. Flight speed indicated a slight deterioration in temperament with time in the feedlot until day 70, suggesting an increasing fearfulness in the steers. Differences in flight speeds between treatments were maintained throughout the feedlotting period; poor-temperament animals retained poor temperaments and good retained good. Flight speed was correlated with measures of production, and flight speed measured at feedlot induction was a predictor of performance. Correlations and treatment effects showed that cattle with poor temperaments had poorer average daily gains, feed conversion efficiencies, body conditions and dressing percentages compared with those with good temperaments. Reduced performance in the poor-temperament animals may have resulted from their fearfulness and state of high arousal. Treatment (temperament grouping) did not influence carcass traits, but there was evidence of lower initial pH levels and indicators of 'heat-shortening' in the meat of steers with poor temperament compared with those with good temperament. These findings suggest that the poor temperament steers were more susceptible to pre-slaughter stressors than the good temperament animals. However, the meat quality differences were not detected in eating-quality measurements.

Rumen microbial populations were measured in Brahman-cross steers that were relocated from spear grass (Heteropogon contortus) dominant pastures in northern Queensland to buffel grass (Cenchrus ciliasis) dominant pastures in central Queensland, to assess whether aspects of rumen function may contribute to the sometimes reported depressed growth rates following relocation. Nine genera of ciliate protozoa (Isotricha, Dasytricha, Entodinia, Epidinium, Diplodinium, Ostracodinium, Metadinium, Elytroplastron, and Eudiplodinium) were recorded in the rumen fluid of the steers. In most steers all genera were present at any time and the generic mix persisted throughout the 10 months over which the study was conducted. Protozoal population composition fluctuated only slightly over the sampling period. Entodinia were predominant, occupying 50-70% of the population. Population density varied according to season, with the highest density (4-8×105 /mL rumen fluid) occurring in the wet season. Bacterial and protozoal populations were remarkably stable and little affected by relocation. Again, the major impact on population density was the season, with all carbohydrate (soluble sugar, starch, xylan, and cellulose) utilising bacterial subpopulations reaching the greatest density with the onset of the wet season.

Strategies for culling on reproductive outcome were evaluated for 2 herds at Swan's Lagoon in the northern speargrass region and 1 herd at Kidman Springs in the semi-arid tropics by editing the records from actual culling to simulate more stringent culling policies. The greatest impact was for young cows, with 13.6 and 27.5% of 2-year-old cows in the 2 herds at Swan's Lagoon failing to rear a calf, and 39.8% at Kidman Springs failing to rear a calf. The corresponding failure rates as 3-year-old cows were 48.1, 54.9, and 80.2%, respectively. Culling for 2 consecutive reproductive failures at Kidman Springs resulted in cumulative wastage of cows >60% by 4 years of age. Other strategies based on 1 or 2 failures had cumulative wastage >SO% by 5 years of age and were too severe to be sustained in the harsh environment at Kidman Springs, with low productivity. At Swan's Lagoon, heifer replacement rates were 17.5-22.2% for strategies based on 2 failures and averaged 37.3% for a single reproductive failure but were 28.7% when failure as a 3-year-old was not penalised. At Kidman Springs, heifer replacement rates were 29.3% for 2 consecutive reproductive failures and reduced to 21.3% when 2-year-olds were retained but were very high (33.7-56.7%) for stricter culling strategies. With current branding rates, only culling on 2 reproductive failures in the speargrass region and extremely limited culling on 3 failures in the semi-arid tropics can be recommended as practical options. The lifetime number of calves reared from cows up to 10 years of age at Swan's Lagoon averaged 3.1 when culling was based on 2 failures and 2.2 for culling on a single failure; this increased to 2.8 calves reared when the strategy was relaxed for 3-year-olds. At Kidman Springs the number of calves reared was 2.3 with culling on 2 consecutive reproductive failures but was closer to the actual level at 2.9 when 2-year-old cows were not culled for reproductive failure.

Mortality and wastage rates and lifetime productivity for seasonally mated, Bos indicus cows were studied over 8000 cow year records from 1972 to 1992 at Swan's Lagoon in the subcoastal speargrass region of North Queensland. The proportional hazards model was used to estimate age-specific mortality and wastage rates, adjusted for cohort and genotype effects. The 1970-72 cohorts had an average mortality of 1.7% (range 0-4.2%), with this low overall rate tending to increase with age. The average mortality rate for the 1973-87 cohorts was 1.2% (range 0.5-2.6%), with no pattern with age. For 1970-72 cohorts, the average wastage rate was 8.9% and ranged from 2.1 to 18.3% with no clear age pattern. However, there was a clear age pattern for the 1973-87 cohorts, with an average wastage rate of 9.2% comprising very high rates (27.5%) for 2-year-olds and low rates (2.8-8.9%) for 3-7-year-olds, increasing to 11.9% for 8-year-olds and 14.2% for 9-year-olds. The heifer replacement rates to maintain a stable herd size were 17.5 and 19.2% for the 2 herds. Lifetime productivity was very low, with 1970-72 cohorts rearing 3.3 calves over 4.7 years at a rate of 57.5% calves per year, and 1973-87 cohorts rearing 3.1 calves over 4.9 years at a rate of 45.0% calves per year. Total weaner weights reared up to 10 years of age were 578 kg for 1970-72 cohorts and 315 kg for 1973-87 cohorts. However, variability between individual cows was high, indicating scope for selection based on productivity, provided that better performing cows can be identified from predictors early in life.

The birth weights and weaning weights of Bos indicus cross calves from 4 inter se mated herd groups in a dry tropical environment were studied. The calving season commenced in late October, about 2 weeks before the start of the pasture-growing season. Second and subsequent generations of 1/2 Brahman and 1/2 Sahiwal crosses and first backcross, and later generations of 3/4 Brahman and 3/4 Sahiwal crosses, were represented. The Bos taurus component of the crosses was primarily Beef Shorthorn. In general, Brahman crosses were heavier at birth and grew faster to weaning than Sahiwal crosses (P

Postweaning growth to slaughter at 42 months of age in males and to initial mating at 27 months of age in females was studied in 4 inter se mated Bos indicus crosses in a dry tropical environment. Six-monthly growth periods from weaning (at about 6 months of age) generally coincided with wet and dry seasons. The cattle represented were second and subsequent generations of 112 Brahman and 112 Sahiwal crosses and first backcross and later generations of 314 Brahman and 314 Sahiwal crosses, The Bos taurus component of the crosses was primarily Beef Shorthorn. Annual growth averaged 300 g/day, with annual gain ranging from 60 to 180 kg. Average growth rates were about 50 g/day in the dry season (-352 to +374 g/day) and 500 g/day in the wet season (221-830 g/day). Postweaning growth of Brahman crosses was about 4% higher than Sahiwal crosses, with most of this advantage expressed in wet seasons. Sahiwal crosses were earlier maturing than Brahman crosses. Wet season growth was higher in 314 crosses than in 1/2 crosses, which probably reflected significant environmental stress in this period. Higher growth of 3/4 crosses tended to be maintained during dry seasons. Calves born late in a wet season grew more rapidly in dry seasons than early-born calves, so that liveweight differences which were apparent at weaning were reduced by one-third at 24 months of age. The difference between liveweights of weaners with young dams and those with mature dams was also reduced from 12-18 kg to 5-6 kg by 24 months. Dressing percentages of 3/4 cross steers at slaughter were 0.6 units higher than in half crosses, with no difference between Brahman and Sahiwal crosses. Sarcomere lengths, Warner-Bratzler shear force values, and Instron compression values together showed that M. longissimus dorsi muscle samples from 1/2 Brahman steers were the most tender of the breed crosses studied. Samples from Sahiwal cross and 3/4 Brahman steers appeared most affected by connective tissue toughness. Those from 3/4 Sahiwals appeared most affected by meat processing factors, causing them to be the least tender.

Factors influencing the conception rates of 1332 Bos indicus cross maiden heifers in the dry tropics of North Queensland were studied between 1973 and 1986. The heifers, which were 112 and 314 Bos indicus (Brahman or Sahiwal) crosses with Bos taurus, were mated at 24-27 months of age over a 3-month period commencing in mid to late January. The effects of liveweights and growth rates on conception rate were initially assessed in separate models which always included cohort (year of branding group) as an additional factor. Cohort and liveweight at weaning, 18 months of age or the start of mating significantly (P

Three drafts of Brahman cross calves (phenotypically half to three-quarters Bos indicus) were either early weaned (EW) in April (mean age 5 months) or late weaned (LW) in July (mean age of 8 months). Their postweaning performance on native pastures in the dry tropics of North Queensland was monitored through to 2.5 years of age for females and 3.5 years for males. At late weaning, LW calves of both sexes were significantly (P

The female reproductive rates and liveweight performance of F2 et seq. generations of 1/2 Brahman (1/2 B), 1/2 Sahiwal (1/2 Sah), 3/4 Brahman (3/4 B) and 3/4 Sahiwal (3/4 Sah) were evaluated in the dry tropics of northern Queensland from 1978 to 1986. The balance of the breed composition was predominantly Shorthorn. A preliminary comparative analysis of F2 and F3 data showed no differences between the filial generations and data were subsequently pooled. Crossbreed differences between groups had a small effect on pregnancy rate and were not a major determinant of fertility compared with age and year effects. Any crossbreed differences were counteracted by inconsistent cross x year effects. For mature cows, 3/4 Sah had significantly (P

SUMMARY The roles of helminths and coccidia in post-weaning diarrhoea in beef calves in the dry tropics were investigated. Diarrhoea occurred approximately one month after weaning in both anthelmintic treated and untreated calves. The highest numbers of coccidial oocysts were seen 29 days after weaning and 3 necropsies confirmed Eimeria zuernii coccidiosis. In the absence of wet overcrowded conditions, disease may have been precipitated by environmental interactions leading to suppression of host immunity. Other Eimeria identified were E. bukidnonensis, E. wyomingensis, E. bovis, E. auburnensis, E. cylindrica, E. ellipsoidalis and E. subspherica. The last 5 species are believed not to have been previously documented in Australia. The presence of E. canadensis was strongly suspected.

SUMMARY Five experiments with Leptospira interrogans serovar hardjo vaccine were carried out over a 6-year period in pregnant Brahman-cross and Sahiwal-cross cows in the dry tropics of northern Queensland. The numbers ranged from 127 breeders aged 2 to 5 years in 1972 to 344 breeders aged 2 to 9 years in 1977. Half of the cows were vaccinated twice in midpregnancy except for 1977, when they were vaccinated once. In 1975–1977 inclusive, half of the heifers were given an additional dose of vaccine at commencement of mating. Vaccination caused a significant (P

Post-weaning Eimeria zuernii coccidiosis in beef calves was treated prophylactically with monensin from intra-ruminal continuous release devices. The evaluation of four treatments during three consecutive years also allowed observations on the epidemiology of this disease to be made. Monensin was an effective prophylactic and the intra-ruminal devices were a convenient method of continuous administration over a one to two month period. The three years of the trial included two characteristically very dry and one unusually wet weaning period. Coccidiosis was more severe in the dry years suggesting that oocyst challenge was less important than the immunodepressive effect of weaning and dietary stress in precipitating disease. Severe disease also occurred in calves subsequent to elimination of oocyst shedding by monensin during the initial treatment trial. The occurrence of disease in conditions inimical to oocyst survival and development and after treatment suggested a role for arrested endogenous stages.

The effect of spraying for buffalo fly (Haematobia irritans exigua) on infestations, growth rate and lesion development on Bos indicus x B. taurus steers (18 months old) and bullocks (30 months old) were studied in the dry tropics of North Queensland. There were four consecutive drafts commencing between July and September and terminating the following June-July. Half of the animals were sprayed with 200 g/l fenvalerate to control buffalo flies. Treated animals carried, at most, a few flies. The size of the fly populations on the untreated animals varied with the seasons, with the most flies being recorded during the wet season. Light coloured animals carried fewer flies than those with darker colours and bullocks carried more flies than steers. Except for steers in one dry season, repeatabilities of fly counts were significant (P < 0.01). In steers, treatment had no significant (P > 0.05) effect on growth over the four treatment periods, although there were significant effects of treatment on growth in some intermediate periods. Treatment significantly (P < 0.05) affected bullock growth in two of the four years. Significant (P < 0.05) positive correlations were found between fly counts and growth rate in two years. Few lesions were recorded on treated animals. Lesion prevalence and size on untreated animals were generally not associated with fly counts, coat colour or growth rate.

Epitheliogenesis imperfecta (EI) has been diagnosed in calves on a north Queensland beef cattle research station. There are five Bos indicus cross, inter se mated breed groups on the station: 1/2 Brahman, 3/4 Brahman, 1/2 Sahiwal, 3/4 Sahiwal and High Grade Sahiwal. The disease was confined to the three Sahiwal breed groups and caused calf losses over seven years from 1978 of 0.2%, 3.4% and 1.0% in the 1/2, 3/4 and High Grade groups respectively. The Sahiwal breed was identified as the origin of the gene responsible for the disease. The source of the gene within the Sahiwal breed was investigated, and several ancestors were identified as almost certainly being heterozygotes. Analyses of relationships of affected and non-affected calves to the 10 Sahiwals that were originally imported into Australia identified the one that was most likely the source of the El gene.

In a 3-year study in the dry tropics, 2 management practices of dry season supplementation of cows and early weaning of calves were concurrently examined as possible techniques for improving reproductive, liveweight and survival performance of Brahman cross cows (phenotypically 1/2 - 3/4 Bos indicus) grazing native pastures. Cows were either supplemented with a drylick mixture of salt, urea and sulfur (DL) commencing in July for 4-6 months; supplemented with a crisis mixture of salt, urea, grain, molasses, meatmeal and monoammonium phosphate (CM) in the latter part of the dry season; or were not supplemented (C). Mating commenced in January, and calves were either early weaned (EW) at the end of mating in April (mean age of 5 months) or late weaned (LW) in July (mean age of 8 months). Supplements and weaning treatments had little effect on cow liveweight, except between early weaning and late weaning when EW cows gained more or lost less weight (mean advantage of 30.8 kg) than LW cows and were heavier (mean advantage of 44.8 kg) than LW cows at late weaning time. Across all years, 1.4, 2.1 and 4.2% of cows in DL, CM and C groups respectively died from malnutrition or required survival feeding; whereas, in the second and third years, mortality rates due to malnutrition were 0.7 and 2.1% in EW and LW groups respectively. Neither supplement nor weaning treatments had any significant effect on lactating cow pregnancy rates, although data pooled across treatments showed that liveweights at various stages pre-mating were correlated with pregnancy rate. Supplementation or weaning treatments did not influence calving date or birth weight, but LW calves grew significantly faster (mean advantage of 0.52 kg/day) between early weaning and late weaning and were significantly heavier (mean advantage of 57.4 kg) at late weaning than EW calves.