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This study investigated the effect of five post-weaning supplementation strategies and two weaning weight groups on long-term growth, puberty and pregnancy percentage of Brahman crossbred heifers. Early-weaned (118 ± 6 kg liveweight) and normally-weaned (183 ± 6 kg liveweight) heifers were allocated to group pens (n = 4 and n = 5/pen for early- and normally-weaned respectively) and offered one of five levels of post-weaning protein supplementation: 0, 1, 2.5, 5 and 10 g of supplement/kg liveweight.day with ad libitum access to a low quality sabi grass (Urochloa mosambicensis) hay during the first dry season (169 days) after weaning. After the post-weaning supplementation period, all heifers grazed the same pastures as a single mob until the end of the experiment and were exposed to fertile bulls from January to May 2016. During the first dry season, supplement intake had a positive linear effect on liveweight gain and hip width gain with no difference in the response between weaning groups. Overall, heifers with higher supplement intakes (i.e. 5 and 10 g/kg) had higher hip height gain (P < 0.005), hip width gain (P < 0.001), body condition score (P < 0.001), and concentration of insulin-like growth factor-1 (P = 0.001), triiodothyronine (P = 0.04) and insulin (P = 0.05) in plasma compared to unsupplemented heifers. These changes resulted in thicker proliferative and hypertrophic zones (both P = 0.03) of the tuber coxae growth plate, larger diameter of terminal hypertrophic chondrocytes (both P = 0.004) at the end of the post-weaning supplementation period when comparing the highest level of supplementation with unsupplemented group. Unsupplemented heifers from both weaning weight groups demonstrated compensatory liveweight gain over the first wet season while evidence of catch-up growth in skeletal dimensions was observed in the second wet season. The main determining factor for pregnancy status of two-year-old Brahman crossbred heifers was pre-mating liveweight (P < 0.001), the pre-mating liveweight was in turn affected by post-weaning supplementation (P = 0.02) or weaning weight group (P < 0.001). This study further demonstrated the positive relationship between premating weight and the occurrence of pregnancy, with an approximate 300 kg pre-mating liveweight required to achieve approximately 80% (67.1-90.3% for a 95% confidence interval) probability of pregnancy in two-year-old Brahman crossbred heifers mated for 4 months., Competing Interests: The authors have declared that no competing interests exist.

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. Annual liveweight production of cows in north Australian beef-breeding businesses, which along with value per kg constitutes business income, has not been well defined. Liveweight production over the life of 2122 tropically adapted cows grazing four primary country types was highly variable, being limited by available nutrition, and increased to maturity, whereas efficiency remained constant. Relative to cows weaning calves, the loss of a conceptus or weaner had a larger negative impact on liveweight production than failure to conceive. [ABSTRACT FROM AUTHOR]