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Context Annual liveweight production of a cow is the sum of the weight of its calf at weaning and its own annual liveweight change. Along with value per kg, annual liveweight production constitutes the business income contributed by the animal; however, it is not well described for north Australian beef herds. Aims This study aimed to quantify cow liveweight production and to measure impacts of reproduction and other risk factors. Methods Liveweight production data from 2122 Brahman and tropically adapted composite cows aged 2.5–8.5 years and grazing the four primary country types in northern Australia were analysed as a function of current and previous mating outcomes, mating age, breed, hip height, and body condition or liveweight. Key results Cow liveweight production was highly variable (coefficient of variation 40%) among and within years. Liveweight production of cows averaged 154 kg/year from their first mating, 168 kg/year from their second, and 190 kg/year from subsequent matings; however, production efficiency remained constant, with a liveweight production ratio of 0.31–0.32 kg produced annually per kg of grazing animal. Within environment, average weaner production (kg/cow) approximated the estimated average annual weight gain of yearling cattle. Weight of calves weaned contributed ~87% of annual liveweight production. Liveweight production averaged 103–143 kg higher for cows that weaned a calf than those that lost a calf, with the effect greater in older cows (P < 0.001). Liveweight production averaged 39–43 kg higher for non-pregnant cows than those that lost a calf (P < 0.001). These effects were attenuated by ~20% over a lifetime. Cows weaning a calf from a previous mating had liveweight production 57–85 kg higher (P < 0.001) than those not weaning a calf, having begun the year in poorer condition because of lactation. Calf weaning weight was 25 kg higher in mature cows than in first- and second-lactation cows. Liveweight production advantages of tropical composites over Brahmans appeared primarily associated with consistently higher calf weaning weights, and higher cow growth during their first reproductive year. Conclusions This research successfully demonstrated the concept of liveweight production in breeding beef cows, showing it to be primarily governed by available nutrition and mating outcome. Implications These findings provide a previously unavailable reference point for beef-systems management in northern Australia; for example, liveweight production could be used to determine the potential achievable increases in cow performance for a specific nutritional environment.

A population-based epidemiological study was conducted between 2007 and 2011 and involved 78 northern Australian commercial beef-breeding herds and in excess of 56 000 cattle concurrently monitored. Cow reproductive performance was described from the biannual assessment of fetal age and lactation status. Both novel and well established measures of performance were used within four broad country types and included the following: percentage of lactating cows pregnant within 4 months of calving; percentage of cows pregnant within an approximate 12-month reproductive cycle (annual pregnancy); fetal and calf loss between confirmed pregnancy and weaning; percentage of cows contributing a calf at weaning and percentage of non-pregnant females retained for re-mating. The results from the present study described the variation in reproductive performance of commercial beef herds across northern Australia and defined typical and achievable levels of performance. The results from the study suggest that a weaning rate of 66% is a more realistic target level of performance for the Northern Forest, while weaning rates of at least 75–80% are realistic for other country types. Female-cattle performance was much lower in the Northern Forest than in the other country types. In absolute terms, there were 15–20% fewer surviving mated cows contributing a calf at weaning in an annual production year and ~4% more missing pregnant cows, which was associated with the ~20% higher retention of non-pregnant cows for re-mating. The reproductive performance of herds varied substantially among and within country types, with a 20–30% variation in reproduction rates and 5–15% variation in fetal and calf loss for half of the herds in all regions. Further analyses were performed and identified the major causes of this variation and are reported in subsequent papers within this series. The results from the present study appear to suggest that substantial opportunities to increase the reproductive performance of northern beef herds exist, providing that the causes of this variation are able to be identified and alleviated.

Approximately 60% of Australia’s beef cattle are located in the vast rangelands of northern Australia. Despite the often low stocking densities and extensive management practices of the observed herd, animal prevalence of BVDV infection and typical rates of transmission are similar to those observed in intensively managed herds in southern Australia and elsewhere in the world. A recent large three- to four-year study of factors affecting the reproductive performance of breeding herds in this region found that where there was evidence of widespread and/or recent BVDV infection, the percentage of lactating cows that became pregnant within four months of calving was reduced by 23%, and calf wastage was increased by 9%. BVDV is now considered the second most important endemic disease affecting beef cattle in northern Australia, costing the industry an estimated AUD 50.9 million annually. Although an effective killed vaccine was released in Australia in 2003, the adoption of routine whole herd vaccination by commercial beef farmers has been slow. However, routine testing to identify persistently infected replacement breeding bulls and heifers has been more widely adopted.

Approximately half of Australiars beef breeding herds are located in northern Australia with reproductive performance being identified as having a significant impact on the profitability of these businesses. Although many of the risk factors affecting the reproductive performance of beef cattle have been previously identified, the relative contribution of major risk factors to key measures of performance, after partitioning the effects of other confounding variables, is lacking, particularly for extensive tropical rangeland systems typical of northern Australia. The overall objective of the research described in this thesis was to, i) describe the reproductive performance of commercial beef breeding cattle in northern Australia and, ii) determine, and quantify the effect of the major risk factors associated with three key measures of reproductive performance (lactating cows becoming pregnant within 4 months of calving, cows failing to become pregnant within an approximate 12 month reproductive cycle, and foetal/calf loss between confirmed pregnancy and weaning). It was hypothesised that the major risk factors determining the probability of lactating cows becoming pregnant within four months of calving are similar to those determining the probability of foetal/calf loss between confirmed pregnancy and weaning. To address these objectives, a prospective population-based epidemiological study was conducted between 2007 and 2011 involving 78 commercial beef properties located across northern Australia. Attainable and typical levels of reproductive performance for cow-age cohorts were described using a dataset containing 114,154 annual production cycles of performance data that represented approximately 78,000 heifers and cows managed in 142 breeding groups. Properties were assigned to one of four broad country types following a subjective assessment of the production potential of the grazing land and cross-referencing with pasture and vegetation descriptions reported by the herd owners/managers. The typical overall reproductive performance of cows in the Northern Forest (57 live calves at muster per 100 surviving mature cows), was considerably lower than that for the other country types (71-83 live calves at muster per 100 surviving mature cows). This was due to typically much lower percentage of cows becoming pregnant within 4 months of calving, higher foetal and calf loss and higher estimated mortality of pregnant cows in the Northern Forest compared to the other genotypes. These findings are consistent with the generally poorer quantity and quality of pasture, harsher environment and higher disease risk of cattle managed in the Northern Forest compared to the other country types. Country type and predicted calving period were top-order determinants of pregnancy within 4 months of calving while lactating. The effect of cow-age class cohort was dependent on country type with the expected occurrence of lactating cows pregnant within 4 months of calving estimated to be 23.1-53.8, 38.1-61.6, 35.4-56.5 and 38.5-59.4 percentage points lower for first-lactation, second-lactation, mature and aged cows, respectively in the Northern Forest, compared to that in other country types. The expected occurrence of cows predicted to calve in July-September which became pregnant within 4 months of calving while lactating was 49 percentage points lower than those predicted to calve in December-January (15% vrs 64%, respectively). The outcome of the previous production cycle (including the current period of calving) and the average digestibility of dry season pasture in the current production cycle were ranked as the most important risk factors for non-pregnancy. Cows which grazed pasture during the dry season with an average dry matter digestibility of l55% were estimated to have 10.2 percentage points higher occurrence of non-pregnancy than those which grazed pasture with a dry matter digestibility of g55%. Cows predicted to calve between October and November were expected to have 15.6% fewer occurrences of non-pregnancy, compared to cows expected to calve between February and March. Hip height of cows, risk of phosphorus deficiency and heat stress were determined as high-ranking contributors of foetal/calf loss in the study population. Foetal/calf loss was estimated to be 3.7 percentage points higher in tall cows than short cows. The association between temperature-humidity index (THI) and foetal/calf loss was dependent on country type, with the largest effect expected in the Northern Downs with 6.7 higher expected occurrence of foetal/calf loss estimated when the THI exceed 79 for at least two weeks during the expected month of calving. The associated effect of the risk of phosphorus deficiency was moderated by body condition score measured at the pregnancy diagnosis muster and country type. An 8 percent point higher expected occurrence of foetal/calf loss was estimated where risk of phosphorus deficiency was categorised as high in heifers and cows in poor body condition (BCS l2.5). While there was evidence at a management group-level that infectious diseases had a significant impact on reproductive performance, the dominating effect of more universal risk factors such as nutritional, management and environmental factors were highlighted in this study. In groups which had evidence of widespread infection with bovine viral diarrhoea virus (BVDV) at the time of the pregnancy diagnosis muster (g80% seropositive with evidence of recent infection) there were 23 percentage points fewer expected occurrences of lactating cows pregnant within 4 months of calving, compared to that in groups with a low BVDV seroprevalence (l20%). In groups where there was widespread evidence of Campylobacter fetus venerealis (Cfv) infection at the time of the pregnancy diagnosis muster (g30% of vaginal mucus ELISA test results positive), the percentage foetal/calf loss was 7 percentage points higher than where estimated prevalence of infection was lower (l30%). The research presented in this thesis describes the first ever population based study of the performance of commercial beef cattle breeding herds in northern Australia and the factors affecting performance. Generally the major risk factors identified were different for each measure of reproductive performance, but overall all were non-infectious factors, primarily nutritional and herd management, and environmental factors. However, when outbreaks of infection with BVDV or Cfv did occur in breeding groups this did result in significantly lower reproductive performance. The findings from this research clearly identify what factors beef cattle producers and their advisors need to focus on when investigating poorer than expected reproductive performance, and provide the basis for future research to investigate the impact of specific management interventions to control these factors.

The welfare outcomes for Bos indicus cattle (100 heifers and 50 cows) spayed by either the dropped ovary technique (DOT) or ovariectomy via flank laparotomy (FL) were compared with cattle subjected to physical restraint (PR), restraint by electroimmobilization in conjunction with PR (EIM), and PR and mock AI (MAI). Welfare assessment used measures of morbidity, mortality, BW change, and behavior and physiology indicative of pain and stress. One FL heifer died at d 5 from peritonitis. In the 8-h period postprocedures, plasma bound cortisol concentrations of FL, DOT, and EIM cows were not different and were greater (P 0.05) between treatments in BW changes. For both heifers and cows, FL and DOT spaying caused similar levels of acute pain, but FL had longer-lasting adverse impacts on welfare. Electroimmobilization during FL contributed to the pain and stress of the procedure. We conclude that: i) FL and DOT spaying should not be conducted without measures to manage the associated pain and stress; ii) DOT spaying is preferable to FL spaying; iii) spaying heifers is preferable to spaying cows; and iv) electroimmobilization causes pain and stress and should not be routinely used as a method of restraint.

Objective To determine the value of peripheral blood concentrations of cortisol, creatine phosphokinase (CPK), aspartate aminotransferase (AST), non-esterified fatty acids (NEFAs) and haptoglobin as indicators of welfare in Brahman heifers spayed by either the Willis dropped ovary technique (WDOT) or the flank laparotomy method. Design A total of 24, 2-year-old Brahman heifers were allocated to: crush (head-bail) restraint alone (Control, n = 5); crush restraint and ear-punch (Ear-punch, n = 5); crush restraint, WDOT spay and ear-punch (WDOT, n = 9); or crush restraint, elecrtoimmobilisation, flank spay and ear-punch (Flank; n = 5). Cattle were blood sampled frequently to 8 h, and then daily to day 4 and were monitored to 42 days post-procedure. Peripheral blood concentrations of bound and unbound cortisol, CPK, AST, NEFAs and haptoglobin were determined. Results Concentrations of plasma bound cortisol peaked in the spayed heifers 3-4 h post-procedure; values in the Flank (1603 nmol/L) and WDOT (1290 nmol/L) groups were similar and significantly greater (P < 0.05) than in the Controls (519 nmol/L). Flank heifers had elevated plasma haptoglobin levels to day 4 postprocedure. Liveweights were significantly lower in the spayed compared with the Control heifers at 21 and 42 days post-procedure, with liveweight gains also significantly reduced at day 21. Conclusions Bound cortisol responses in spayed heifers were elevated to 6 h post-procedure and similar in WDOT- and flank-spayed animals, indicating comparable levels of pain and stress. An inflammatory response, indicated by haptoglobin concentrations, was sustained for longer in Flank than in WDOT spayed heifers, suggesting longer-lasting adverse effects on welfare from flank spaying than WDOT spaying. © 2011 The State of Queensland (Department of Employment, Economic Development and Innovation). Australian Veterinary Journal © 2011 Australian Veterinary Association.

To determine morbidity and mortality rates in yearling heifers spayed by two methods under commercial conditions in northern Australia. Design In study 1,600 Brahman heifers were allocated to one of three treatments: physical restraint and ear-tagging (Control); physical restraint, ovariectomy by the Willis dropped ovary technique, ear-tagging and ear-marking (WDOT); or electroimmobilisation, ovariectomy via flank incision, ear-tagging and ear-marking (Flank). Heifers were monitored post spaying. Mortalities occurred at unanticipated times, so study 2 investigated their timing and cause in similar WDOT-spayed heifers (n = 574). Results In study 1, morbidity on the day of spaying was 6.0% in the Flank and 2.7% in the WDOT group (not statistically different). Spayed heifers showed behaviours indicative of acute pain/discomfort in the 6 h post spaying. Body weights and gains were significantly lower in the spayed compared with control heifers at days 21 and 42, and 5% of flank wounds were not healed at day 42. Mortalities were 0%, 1.5% and 2.5%, respectively, for Control, WDOT (3 estimated to have occurred on day 11) and Flank (2 on the day after spaying and 1 on each of days 5, 11 and 22). In study 2, the mortality was 0.5%, all within 4 days of spaying. Conclusions In yearling heifers, WDOT spaying resulted in lower morbidity and short-term mortality compared with flank spaying. Both methods compromised the health and welfare of some animals for up to 4 days and body weight gains were reduced during the 6 weeks post spaying. © 2010 The Authors. Australian Veterinary Journal