Abstract
Australian sheep production occurs across a wide agroclimatic zone with a variety of sheep breeds to produce wool and sheepmeat. Mating time varies from farm to farm and can be influenced by multiple considerations. For example, if producers take advantage of the ewe’s natural seasonal cycle, it may not be possible to align available feed resources with the ewe’s nutritional requirements. Further, producers may also consider other factors, such as grass seed burden and extreme weather events (impacting conception and lamb survivability) and market access. Management guidelines to assist producers have been developed, providing liveweight and body condition score targets across gestation to optimise enterprise profitability. These guidelines, however, are limited by rigid mating seasons and regions and their suitability across breeds is unknown. The overall objective of the research reported within this thesis was to explore the impact of both breed and mating season on the predicted profitability and risk of different ewe production systems across southern Australia, while allowing for different breed management practices. A combination of methodologies were employed including a producer management practice survey, analysis of reproductive data collected from ewes across south-eastern Australia, computer simulation modelling of various sheep enterprises and a digestibility study to validate production differences.
A variety of management practices were reported in the producer survey that generally aligned with current guidelines. These practices were similar within breeds but mating season generally had no influence. This survey also revealed most producers are often seeking new information and made changes to their management within the last five years. A small proportion of producers, however, did not align with current guidelines, were not seeking new information and had not recently made management changes. Further investigation of the barriers for the latter producers is required. Producers responding to the survey were also involved in a field survey collecting mature ewe liveweight and BCS data at mating and subsequent reproductive information (pregnancy outcome and fetal number) from over 30,000 ewes to determine the most influential variable. A Bayesian Network was developed and found that the variables (breed, mating season, liveweight, BCS, seasonal conditions and region) and pregnancy outcome and fetal number were lowly associated. This analysis did reveal curvilinear relationships between mating liveweight, BCS and ram percentage with pregnancy outcome and fetal number. The curvilinearity of mating liveweight and BCS is in line with previous research findings, however the relationship with ram percentage requires further investigation. Practically, reproductive potential is best managed on a breed basis with consideration of all variables explored.
Outputs from these two studies were used to inform AusFarm simulation models to investigate production, profit and risk across locations (n = 8), breeds (n = 3) and mating seasons (n = 8). A limitation of the AusFarm software was the inability to model shedding sheep or production systems in the rangeland zone. Supplementary feeding can be costly and so the impact of increasing the amount of supplementary feed supplied to ewes in alignment with current industry feed budgeting was investigated. Increased supplementary feed consumption generally led to greater productivity and profitability but this also incurred greater risk. Increasing the supplementary feed allowance did not influence production, profitability or risk when calculated in units of per ewe mated. The impact of increasing and decreasing reproductive rate (n = 3) and grain price (n = 3) was then explored using the higher supplementary feed allowance. Generally, increasing the reproductive rate increased productivity and profit and reduced risk, observed across the different grain prices investigated, but profit and risk were not always linked. Risk was associated with mating season and the cost efficiency of purchasing replacement ewes but not with supplement consumption when comparing breeds. For the parameters modelled, it may be more cost effective to increase supplementary feeding as the improved production achieved through greater supplement consumption outweighs the cost. This highlights the importance of understanding the drivers of production, profitability and risk.
A key difference between the breeds investigated in this thesis is the production of hair versus wool, with shedding breeds increasing in popularity in Australia. An animal nutrition experiment attempted to explore that research gap in computerised animal models. Composite, Dorper and Merino ewes were supplied a pelleted total mixed ration at varied levels of feeding over a period of seven weeks. The ewes commenced in a shared pen (n = 3) and then moved to individual pens and metabolism crates. No difference in BCS change and apparent nutrient digestibility was observed between breeds. Further investigation of ruminal microbial populations, retention times and grazing behaviour is required. Variations in the components of digestion or grazing behaviour may explain the anecdotal production differences reported by produces between wool- and hair-based sheep. The research presented in this thesis contributes to our understanding of current sheep management practices, pregnancy scanning outcomes across breeds and mating seasons and the potential profit and risk across a range of south-eastern Australian scenarios. It also provides further evidence that diet digestibility may not differ between wool and hair breeds. Producers may be able to establish their own reproductive management guidelines through the monitoring of their flock’s performance and understanding the response to different stimuli (breed, season, available feed). Nutritional management guidelines for different breeds are still required as a sound understanding of potential breed differences is lacking. This would allow producers to be more specific in their feed budgeting, according to the unique set of circumstances of their enterprise.
A variety of management practices were reported in the producer survey that generally aligned with current guidelines. These practices were similar within breeds but mating season generally had no influence. This survey also revealed most producers are often seeking new information and made changes to their management within the last five years. A small proportion of producers, however, did not align with current guidelines, were not seeking new information and had not recently made management changes. Further investigation of the barriers for the latter producers is required. Producers responding to the survey were also involved in a field survey collecting mature ewe liveweight and BCS data at mating and subsequent reproductive information (pregnancy outcome and fetal number) from over 30,000 ewes to determine the most influential variable. A Bayesian Network was developed and found that the variables (breed, mating season, liveweight, BCS, seasonal conditions and region) and pregnancy outcome and fetal number were lowly associated. This analysis did reveal curvilinear relationships between mating liveweight, BCS and ram percentage with pregnancy outcome and fetal number. The curvilinearity of mating liveweight and BCS is in line with previous research findings, however the relationship with ram percentage requires further investigation. Practically, reproductive potential is best managed on a breed basis with consideration of all variables explored.
Outputs from these two studies were used to inform AusFarm simulation models to investigate production, profit and risk across locations (n = 8), breeds (n = 3) and mating seasons (n = 8). A limitation of the AusFarm software was the inability to model shedding sheep or production systems in the rangeland zone. Supplementary feeding can be costly and so the impact of increasing the amount of supplementary feed supplied to ewes in alignment with current industry feed budgeting was investigated. Increased supplementary feed consumption generally led to greater productivity and profitability but this also incurred greater risk. Increasing the supplementary feed allowance did not influence production, profitability or risk when calculated in units of per ewe mated. The impact of increasing and decreasing reproductive rate (n = 3) and grain price (n = 3) was then explored using the higher supplementary feed allowance. Generally, increasing the reproductive rate increased productivity and profit and reduced risk, observed across the different grain prices investigated, but profit and risk were not always linked. Risk was associated with mating season and the cost efficiency of purchasing replacement ewes but not with supplement consumption when comparing breeds. For the parameters modelled, it may be more cost effective to increase supplementary feeding as the improved production achieved through greater supplement consumption outweighs the cost. This highlights the importance of understanding the drivers of production, profitability and risk.
A key difference between the breeds investigated in this thesis is the production of hair versus wool, with shedding breeds increasing in popularity in Australia. An animal nutrition experiment attempted to explore that research gap in computerised animal models. Composite, Dorper and Merino ewes were supplied a pelleted total mixed ration at varied levels of feeding over a period of seven weeks. The ewes commenced in a shared pen (n = 3) and then moved to individual pens and metabolism crates. No difference in BCS change and apparent nutrient digestibility was observed between breeds. Further investigation of ruminal microbial populations, retention times and grazing behaviour is required. Variations in the components of digestion or grazing behaviour may explain the anecdotal production differences reported by produces between wool- and hair-based sheep. The research presented in this thesis contributes to our understanding of current sheep management practices, pregnancy scanning outcomes across breeds and mating seasons and the potential profit and risk across a range of south-eastern Australian scenarios. It also provides further evidence that diet digestibility may not differ between wool and hair breeds. Producers may be able to establish their own reproductive management guidelines through the monitoring of their flock’s performance and understanding the response to different stimuli (breed, season, available feed). Nutritional management guidelines for different breeds are still required as a sound understanding of potential breed differences is lacking. This would allow producers to be more specific in their feed budgeting, according to the unique set of circumstances of their enterprise.
Original language | English |
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Qualification | Doctor of Philosophy |
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Place of Publication | Australia |
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Publication status | Published - 2024 |