Artificial rearing strategies to optimise new-born lamb growth and development : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science at Massey University, Palmerston North, New Zealand

Figures 2.1, 2.2 & 2.3 are re-used with permission.A series of artificial lamb rearing experiments was conducted to investigate the effects of milk replacer protein to energy ratio (CP:ME), pellet fibre level and age at weaning on lamb growth and body composition, rumen development and rumen bacterial population. A mechanistic, dynamic, pre-weaned lamb growth and body composition simulation model was also validated using data generated from these experiments. The feeding of milk replacers with a high CP:ME ratio (15.89 g/MJ compared to a traditional industry value of 10.96 g/MJ) and adjustment of replacer CP:ME ratio (16.46 g/MJ to 10.96 g/MJ) to meet the lamb’s changing nutritional requirement as it aged resulted in higher pre-weaning lamb growth rates. Feeding a high CP:ME milk replacer also reduced carcass fat levels. When fed pellets ad libitum, an incrementally adjusted CP:ME milk replacer resulted in similar pre-and post-weaning growth rates as when fed milk replacer with a consistently high CP:ME ratio (12.28 g/MJ). Early milk weaning of lambs at 42 days of age did not impair growth rate to 57 days age but, reduced carcass fat, regardless of pellet fibre level. Early weaning of lambs also improved rumen n-butyric content and feeding low fibre pellets (NDF 116.76 g/kg) increased rumen n-valeric content. Early weaned lambs had increased rumen dorsal wall thickness. Nutrient intake from solid feed positively influenced rumen volatile fatty acid content, while both nutrient intake and rumen volatile fatty acid content positively impacted rumen physical development. The relative abundance of rumen bacteria phyla and genera were altered by weaning age and pellet fibre level, with Firmicutes being more abundant in milk-fed lambs at 57 days of age, while Bacteroidetes were the prominent phylum in early-weaned lambs. Prevotella was the prominent bacteria genus in early-weaned lambs. The most abundant bacteria genus in milk-fed lambs at 57 days of age was Succinovibrio. The existing pre-weaned lamb growth model was found to predict overall lamb growth accurately when utilising data collected in the present studies. However, it was not as accurate for predicting body composition components. In summary, results from thesis will contribute to improving new-born lamb growth and development in artificial rearing systems