The meat goat industry in Australia: geographical, seasonal and nutritional influences on reproduction in female goats

Australia is the largest exporter of goat meat worldwide. However, little data is available regarding goat production systems, goat enterprises and productivity of Australian commercial goat operations. The general aims of this thesis were to provide an overview of meat goat producing enterprises in Queensland and New South Wales, to understand the seasonality of the reproductive cycle in Boer and rangeland goats in the tropics and to gain further knowledge on the effect of nutrition on the development of ovarian follicles during the breeding and non-breeding seasons. This thesis is divided in six research chapters that are mentioned as scientific studies. Studies 1 and 2 present a survey of the meat goat industry conducted on properties located in Queensland and New South Wales that derived a significant proportion of their income from goats. This survey covered 31 landholders with a total land area of 567,177 ha and a reported number of 160,010 goats. Study 1 showed that 55% of producers were involved in 'opportunistic harvesting of rangeland goats' and 45% were specialized Boer goats producers. Stocking rate varied considerably (0.3 to 9.3 goats/ha) within and across surveyed properties and was found to be negatively associated with property size and positively associated with rainfall. The results have confirmed the importance of the international market as a source of income and the utilisation of goats to control weeds on many properties. The reasons for use of fencing appeared to be an important issue for goat farmers and this could potentially add to capital costs associated with better goat management and production. The strategies for pasture management, setting and adjusting the stocking rates, nutrition to meet market specifications and regional location of processing plants within 600 km of major areas of production could improve the utilisation and production of rangeland goats in New South Wales and Queensland. Study 2 showed that producers who engage in opportunistic goat harvesting maintain few records related to herd production, animal health and reproduction. On the other hand, commercial and seedstock producers generally keep more records and they are trying to improve the productivity of their goatherds. In general, properties in the pastoral regions showed low pregnancy and kidding rates, early age at first mating, high mortality rates, poor performance of Boer bucks and lower weights and weight gain compared to properties in the high rainfall regions. Few registered veterinary chemicals are available to control parasites of goats, and goat producers are using chemicals that are registered for use in sheep. The meat goat survey has highlighted areas that required further studies to validate the observations of producers. For instance, identifying management strategies that could improve the reproductive performance of Boer and rangeland goats, identify the timing of commencement of the breeding season in Boer and rangeland goats raised in the Queensland tropics and to gain further knowledge on the effect of nutrition on the development of ovarian follicles during the breeding and non-breeding seasons. The aim of Study 3 was to determine the timing of the onset of the breeding season in Boer and rangeland goats raised in a tropical region of northern Queensland. In this study, the ovarian activity in Boer does was more precocious than rangeland goats, which indicates that there are likely genetically driven differences in sensitivity to photoperiod between these breeds. Boer goats started to ovulate in December (8.3%) and had all ovulated by March, while most rangeland does started ovulating in March (84%) and had all ovulated by the end of April. Understanding the normal physiological patterns in follicular dynamics in female goats during the non-breeding and breeding seasons would help to illuminate physiological causes of differences in fertility and prolificacy when goats are bred at different times of the year. Therefore, Study 4 described the ovarian follicular dynamics in Boer goats during the non-breeding season and the following breeding season in the tropics of Queensland. The results of this study identified that 90% of Boer does were in anoestrus during the summer period (September to October) at latitude of 19°19'30" South. The pattern of follicular dynamics evaluated by ultrasonography over 21-day period was characterized by four follicular waves in the breeding season and five waves in the non-breeding season, but the number of codominant follicles was greater in the breeding season. In addition, follicular dynamics in the breeding season compared to the non-breeding season was characterised by the development of larger follicles and greater follicular growth rates. These results demonstrated some similarities and differences between follicular dynamics within does between the breeding and non-breeding seasons. The most common strategies to improve productivity in goats during the non-breeding season in the tropics are the use of hormonal synchronisation of oestrus and nutritional supplementation. Therefore, Study 5 evaluated the reproductive response of seasonally anoestrus goats that were either hormonally treated and/or supplemented with maize to determine which treatment combination was the most effective to stimulate follicular dynamic, and whether these responses were associated with increases in circulating concentrations of glucose, insulin, leptin and LH in anoestrus goats. The findings of this study showed that hormonal synchronisation of oestrus was a highly effective method of inducing oestrus and ovulation in seasonally anoestrus goats. A short-term nutritional supplementation with maize increased the concentrations of insulin, leptin and IGF-1 and appeared to have some influence on follicular development, but these changes were not mediated by an increase of the mean concentrations of LH and frequency of LH pulses. Nutritional supplementation with maize in combination with hormonal treatment increased the ovulation rate by 43%, although differences were not found to be statistically significant. Numerical differences in ovulation rates suggested that supplementation with maize in combination with the synchronisation of oestrus as a mechanism of potentially increasing ovulation rate did require further investigation in goats with larger groups of animals. Finally, Study 6 evaluated the ovarian follicular dynamics in goats, which were undergoing oestrus cycles supplemented with diets that differed in the composition of maize and the metabolisable energy content. In this study, it was used double the number of animals per group than in Study 5 to increase the statistical power. In Study 6, it was possible to demonstrate that the addition of maize in a diet to provide nutritional requirements for maintenance during nine days can be used as a management strategy to increase the ovulation rate in female goats undergoing oestrus cycles in the tropics. Similar results between groups 1.0 and 1.5 maintenance with maize showed that there is no necessity to increase the level of energy of a diet above maintenance when maize is a part of the diet, because this might increase the cost of the diet. This study has established that short-term nutritional supplementation with maize can be used as a management strategy to increase ovulation rate and potentially improve prolificacy in female goats in the tropics