| Abstrakt: |
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] |
