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Context The performance of commercial beef-breeding herds in northern Australia is highly variable. Identifying and understanding the major factors that influence this is critical in determining which management interventions should be implemented to best manage these factors. Aims This study aimed to describe the occurrence and magnitude of the risk factors identified as being strongly associated with one or more measures of cow performance in northern Australia. Methods A prospective epidemiological study was conducted in a cross-section of commercial beef-breeding herds in northern Australia, to determine and quantify the major associations of up to 83 candidate herd management, nutritional and environmental risk factors with cow performance. Descriptive analyses of significant risk factors were conducted. Key results Unfavourable levels of risk factors were observed for all country types and across three cow-age groups. However, generally, adverse property-level nutritional, environmental and management risk factors had a higher incidence in the Northern Forest, which was associated with significantly lower performance of heifers and cows. This was reflected in generally lower body condition of heifers and cows in this country type. Although the performance of heifers and cows was generally higher in the Southern Forest, the irregular incidence of adverse risk factors contributed to the observed quite variable performance. Conclusions The factors significantly affecting the performance of cows in the major beef-breeding regions of northern Australia are described. These factors were additively more adverse in the Northern Forest. Implications In this study, the necessary understanding of the factors most likely to be affecting the performance beef cows in this environment has been described. This is required to make appropriate decisions about management interventions to control these factors.

Context Sound reproductive efficiency is a key determinant for the overall productivity and profitability of a beef breeding business. Failure of a cow to conceive results in either culling or the cost of carrying non-pregnant animals. Aims This study aimed to determine and quantify the major factors associated with non-pregnancy in commercial beef breeding herds of northern Australia. Methods A prospective population-based epidemiological study of the likelihood of non-pregnancy in cows after an annual mating in northern Australian beef breeding cows used data from 73 herds from four broad country types and 62 323 animal years; approximately 80 property-, management-group- and cow-level risk factors were considered. A multivariable model building process was employed to scrutinise the resulting dataset, so as to identify what herd management practices, nutritional, environmental, and individual cow factors were associated with non-pregnancy and estimate their magnitude of effect. Key results Non-pregnancy was disproportionately high in the Northern Forest (32.1%), compared with the Northern Downs, Central Forest and Southern Forest where it was 17.1%, 16.0% and 13.2% respectively. Time of expected calving had the largest impact on occurrence of non-pregnancy. Parity also had a significant influence, with first-lactation cows typically having 5–12% higher non-pregnancy than did mature cows. Non-pregnancy decreased with an increasing body condition score at the branding/weaning muster for lactating cows. The difference in non-pregnancy when comparing availability of wet-season pasture phosphorus content and digestibility of pasture during the dry season was 13.2 and 10.2 percentage points respectively. Conclusions This study demonstrated the substantial impact environment, herd management practices, nutrition and disease factors can have on the reproductive performance of females. Implications To optimise the efficiency of females (through reducing the occurrence of non-pregnancy) under commercial conditions in northern Australia, production systems should support beef herds calving early in the production year, being in at least moderate body condition and having access to more digestible pastures that address the nutritional requirements for both protein and phosphorus. This indicates focus for management, especially in the Northern Forest where the likelihood of non-pregnancy was highest.

Context Sound reproductive efficiency is a key determinant for the overall productivity of a beef breeding business. For beef breeding herds to obtain high levels of reproductive productivity, breeding females need to efficiently become pregnant while lactating. Aims This study aimed to determine and quantify the major factors associated with lactating cows becoming pregnant within 4 months of calving (P4M) in commercial beef breeding herds of northern Australia. Methods A prospective epidemiological study was conducted using 78 commercial northern Australian beef breeding herds and involved 78 000 cattle that were monitored for 3–4 years. A multivariable model-building process was employed to scrutinise the resulting dataset to identify what herd-management practices, and nutritional, environmental and individual cow factors were major determinants of lactating cows becoming pregnant within 4 months of calving (P4M) and to estimate their magnitudes of effect. Key results Overall, 41.6% of cows per production year were successful for P4M. Country type was strongly associated with 65.4%, 57.5%, 61.8% and 16.4% P4M for the Southern Forest, Central Forest, Northern Downs, and Northern Forest respectively. Between-year variability ranged between 3.3 and 11.7 percentage points. Cows calving in December–January (61%) had a substantially higher occurrence of P4M than did cows calving between July and September (15%). The difference in P4M when comparing availability of wet-season pasture protein and phosphorus was 12.7 and 20.3 percentage points respectively. Modelling of the impact of group seroprevalence and management group prevalence of recent infection with several infectious diseases was estimated, with a large negative association between group bovine viral diarrhoea seroprevalence and P4M suggested. Conclusions This study further demonstrated the substantial impact that environment, herd management practices, nutrition and disease factors can have on the reproductive performance of females. Implications To optimise the performance of females (through increasing the occurrence of cows contributing calves in consecutive years) under commercial conditions in northern Australia, herd managers should focus on maximising the proportion of cows within a herd calving at the desired time of the year, ensuring that any nutritional deficiencies and herd health issues are managed, and that cows are managed such that they are of good body condition score at the time of calving.

Context There are multiple reports of high annual cow mortality rates in northern Australia, but no reports clearly indicating the overall rates and the impact of primary risk factors. Aims The research aimed to determine which measured region-, property-, management group- and animal-level risk factors are associated with missing pregnant females. Methods Risk factors for the annual rate of pregnant-cow mortality were investigated in an epidemiological study using outcomes for 21 554 cows from 52 beef herds in 2009 and 2010 in four primary country types within the mostly-dry tropical north Australian environment. Modelling of 2001–2011 Australian beef-herd statistics was used to corroborate and further quantify findings. Key results In the epidemiological study, the overall predicted annual mean incidence of missing pregnant cows, a surrogate for mortality, was 10.9%, including lost tags and unrecorded cow movement that were estimated to constitute up to 9% missing cows. Risk factors associated with higher pregnant-cow mortality were as follows: not having follow-up rainfall more than 30 days after the first wet-season storms (4 percentage point increase)

Context Poor nutrition of late-pregnant cows is highly prevalent in the dry tropics and associated with high levels of calf mortality. Aims It was hypothesised that supplementation with protein to prepartum cows would restore the normal decline in progesterone prepartum and increase the transfer of passive immunity to calves, with this being further enhanced by inclusion of yeast fermentation products. Methods In total, 84 heifers and 45 cows were selected for a completely randomised block design, with the following three dietary treatments: unsupplemented, receiving ad libitum low-protein hay only; hay supplemented with 1 kg/day of protein; and supplementation with both protein and 14 g/day of a Saccharomyces cerevisiae fermentation product. Supplementation occurred for an average of 14 days before calving. Cow plasma samples in the week before parturition, and the first plasma sample after parturition, were analysed for progesterone and metabolites. Newborn calves were weighed and blood-sampled three times per week during the first 2 weeks after birth. The first two calf plasma samples were analysed for total protein, albumin, and globulin concentrations. Data were analysed using a mixed-effects model and the decline of progesterone concentration over time was modelled using a non-linear segmented model. Key results Prepartum supplementation reduced cow liveweight loss, increased glucose, reduced fat mobilisation metabolites and tended to increase average daily weight gain of calves. Including yeast fermentation products in the supplement tended to increase the transfer of passive immunity to calves. Supplementation decreased plasma progesterone before parturition and including yeast fermentation products further advanced the initiation of progesterone decline. Conclusion Protein supplementation of protein-deficient beef cows during late pregnancy helps restore the normal decrease in progesterone before parturition. Implications This study identified a plausible hormonal mechanism explaining how poor nutrition around birth can increase calf loss, opening new possibilities for short-term diet management strategies to reduce calf mortality and improve calf health.

Context Sound reproductive efficiency is a key determinant for the overall productivity of a beef breeding business. For beef breeding herds to obtain high levels of reproductive productivity, breeding females need to efficiently become pregnant while lactating. Aims This study aimed to determine and quantify the major factors associated with lactating cows becoming pregnant within 4months of calving (P4M) in commercial beef breeding herds of northern Australia. Methods A prospective epidemiological study was conducted using 78 commercial northern Australian beef breeding herds and involved 78 000 cattle that were monitored for 3–4years. A multivariable model-building process was employed to scrutinise the resulting dataset to identify what herd-management practices, and nutritional, environmental and individual cow factors were major determinants of lactating cows becoming pregnant within 4months of calving (P4M) and to estimate their magnitudes of effect. Key results Overall, 41.6% of cows per production year were successful for P4M. Country type was strongly associated with 65.4%, 57.5%, 61.8% and 16.4% P4M for the Southern Forest, Central Forest, Northern Downs, and Northern Forest respectively. Between-year variability ranged between 3.3 and 11.7 percentage points. Cows calving in December–January (61%) had a substantially higher occurrence of P4M than did cows calving between July and September (15%). The difference in P4M when comparing availability of wet-season pasture protein and phosphorus was 12.7 and 20.3 percentage points respectively. Modelling of the impact of group seroprevalence and management group prevalence of recent infection with several infectious diseases was estimated, with a large negative association between group bovine viral diarrhoea seroprevalence and P4M suggested. Conclusions This study further demonstrated the substantial impact that environment, herd management practices, nutrition and disease factors can have on the reproductive performance of females. Implications To optimise the performance of females (through increasing the occurrence of cows contributing calves in consecutive years) under commercial conditions in northern Australia, herd managers should focus on maximising the proportion of cows within a herd calving at the desired time of the year, ensuring that any nutritional deficiencies and herd health issues are managed, and that cows are managed such that they are of good body condition score at the time of calving.

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 ᾰ0.19, 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.

During mammalian spermiogenesis nucleosomal histone proteins bound to DNA are replaced by protamines. The integrity and stability of the protamine-DNA association in sperm can be measured using the sperm chromatin structure assay (SCSA). The recent emergence of compelling information from assisted reproduction in humans of a relationship between sperm chromatin stability and the establishment and maintenance of pregnancy has led to considerable interest in production and recreational animals.1 The aim in the present study was to determine the incidence of sperm chromatin instability amongst bulls in a subtropical region of northern Australia, as a first step in evaluating whether sperm chromatin instability is a contributing factor to reproductive wastage in cattle. Semen was obtained from 565 Bos indicus and Bos indicus x taurus bulls from northern and central Queensland aged between 20months and 10years. Samples were subjected to standard semen evaluation2 and aliquots stored in liquid nitrogen until chromatin integrity was determined using the SCSA.3 Samples exposed to the SCSA for 0.5min revealed 4.9% of bulls had a DFI >27% and this increased to 11.5% of bulls with DFI >27% when samples were exposed to the SCSA for 5 min. DFI was significantly correlated with sperm density, mass activity, motility and morphology. Location appeared to have a greater influence on DFI than genotype. Preliminary data from a small sample of bulls would suggest that a relatively high DFI can be repeatable for individual bulls. These findings indicate that sperm chromatin instability occurs in bulls in northern Australia although the prevalence might be considered to be relatively low. The relationship of sperm chromatin instability to the contribution of bulls to embryonic mortality requires further study and likewise the impact on reproductive wastage remains to be determined. (1)Boe-Hansen GB et al. (2005). Theriogenology 63, 1789.(2)Fitzpatrick LA et al. (2002). Anim. Reprod. Sci. 71, 39.(3)Evenson D and Jost L (2000). Methods Cell Sci. 22, 169.

Post-partum anoestrus is a primary contributor to low branding rates in Bos indicus cattle herds in the dry tropics of northern Australia [Entwistle, K. W. (1983). Australian Meat Research Committee Review No. 431. To increase branding rates, it was hypothesised that creep feeding for a short period in mid-late lactation during the latter half of the growing season may trigger an earlier onset of post-partum oestrus cycling, just as short-term, high-level, prepartum supplementation can achieve. Two experiments were conducted using Fn Brahman-cross cows (1/2, 5/8 and 3/4 crosses with Beef Shorthorn) which calved from late October to late Januarv. Cows were mated from mid-late Januarv to mid-April. Calves in one treatment in both experiments had ad libitum access to creep feed (calf pellets: 16% crude protein, 10 MJ ME/kg) for 4042 days from late February to early April. In experiment 2, the effects on cow growth and fertility due to supplementation with either cottonseed meal (1.5 kg/day) or molasses with 7.4% (w/w) urea for 49 days late in the dry season before calving ('spike' feeding) were also evaluated. Control cattle were unsupplemented. Creep feed was only consumed at 0.1 and 0.4 kg/day in experiments 1 and 2, respectively. Short-term creep feeding had no consistent effects on cow liveweights, condition, or fertility, or on calf growth and temperaments under extensive grazing conditions during the tropical wet season. Spike feeding reduced weight loss by 0.2-0.4 kg/day (P

A herd of 802 Brahman cross cows, managed under extensive conditions (7000 ha paddock with twice-yearly handling) in a dry tropical environment, was studied during the severe drought of 1982-83. Twenty-one per cent of the cows died. Cows more advanced in pregnancy and those in poorer condition in the early stages of the drought had lower (P

A breeding program was established at Swan's Lagoon Beef Cattle Research Station in the dry tropics of northern Queensland to evaluate the productivity of cattle which were genotypically at least one-half Bos indicus. Brahman or Sahiwal bulls were initially mated to B. taurus cows (predominantly Shorthorn) to produce the first filial generation (F1 1/2 Brahman and F1 1/2 Sahiwal). First backcross 314 Brahman and first backcross 314 Sahiwal were derived from crossing F1 1/2 Brahman or F1 1/2 Sahiwal cows to their respective sire breeds. This paper reports on the female reproductive rates and liveweight performance in 2 data sets: 1972-79, F1 1/2 Brahman v. F1 1/2 Sahiwal; 1975-83, first backcross 3/4 Brahman v. first backcross 3/4 Sahiwal. In both data sets, significant differences in fertility (pregnancy rate and calving date) between F1 or first backcross groups were infrequent, and where differences did occur, they were often inconsistent due to cross x year interactions. The difference between weaning rates and pregnancy rates (representing foetal and calf wastage) was 5 percentage units higher in Sahiwal crosses than Brahman crosses for lactating cows Year effects significantly (P

The temperaments of 170 bullocks and 240 cows from 2 commercial properties in northern Queensland were scored by rating their behaviours, especially movement, while they were handled in a crush and pound. High scores indicate poor temperaments. Brahman cross cattle had higher temperament scores than did Shorthorns (P< 0.05). The heaviest cattle tended to have the lowest scores, suggesting that selection for high growth rate may not result in poorer temperament. Horned cattle tended to have lower temperament scores than hornless cattle (P> 0.05), though it is suggested that any advantage to horned cattle may be outweighed by the production and husbandry advantages of the latter. There was no relationship between temperament scores and age, fatness and, in cows, pregnancy status.

The effects on carcass bruising and muscle properties of the temperament scores of 170 bullocks and 240 cows (Brahman cross and Shorthorn) from 2 properties in northern Queensland were studied. Temperaments were scored by rating their behaviours when the cattle were handled in a crush and pound. High scores indicate poor temperaments. The bullocks and cows were respectively transported 740 and 1155 km to abattoirs and slaughtered 5-7 days after mustering. In both experiments, the estimated bruise trim per carcass increased by approximately 0.3 kg per unit increase in movement score for both temperament tests. Cattle with high temperament scores had more bruising along the back and around the tuber coxae and tuber ischii. Muscle samples from cattle with higher temperament scores tended to have higher mean initial yield and peak force shear values, thus indicating that their meat may have been less tender. Neither ultimate pH nor sarcomere length was related to temperament score.