The effects of New Zealand sheep milk on mineral absorption and bone health

In recent times, there has been increasing interest in, and development of dairying involving other lactating species in New Zealand, as well as elsewhere in the World, as alternatives to cow milk (CM). In particular, the current emerging dairy industry in New Zealand is sheep dairying. Although there has been extensive investigation of the effects of CM consumption on human health and growth, it is well recognised that sheep milk (SM) has a unique composition in having higher mineral, vitamin, protein, and lipid concentrations compared to CM. It is therefore timely to conduct research directed to investigation of the health consequences of consuming SM, compared to CM. The present study aimed to develop an understanding of the effects of SM consumption on bone health compared to that of CM in vitro, using a human sarcoma osteogenic (SaOs-2) cell system, and then complement this study in vivo, by conducting feeding trials using an animal model. The effect of SM, compared to CM, on the formation of mineralised nodules by SaOs-2 cells was investigated, using SM and CM that had been subjected to simulated gastrointestinal digestion. It was found that the SM hydrolysate resulted in a higher level of mineralised nodule formation compared to that of CM (using either whole or skim milk) (p < 0.05), indicating that SM has enhanced potential to improve the formation of bone compared to CM. Supplementing a well-balanced diet with either SM or CM in a male weanling rat feeding trial showed that the consumption of SM did not affect weight when compared to CM (p > 0.05). Lower concentrations of iron were found in the livers of rats consuming a SM supplemented diet, compared to rats consuming CM (p 0.05). These results suggest that diet supplementation with SM, compared to supplementation with CM, may improve the development of bone trabecular microstructure. In a second animal feeding trial conducted in the present study, male weanling rats were fed a basal diet supplemented with either SM or CM that had a 50% reduction in calcium and phosphorus content (Low Ca/P-diet), and the results were compared to rats consuming a regular balanced diet. The consumption of either SM or CM in addition to the Low Ca/P-diet was found to increase the growth rate, femora dimensions, femora micro-structure, femora mechanical properties, zinc concentration in the liver, and copper concentration in the liver, compared with the Low Ca/P-diet alone (p < 0.05). However, it should be noted that this was achieved with a lower consumption of SM compared to that of CM by the rats in the diet trial (p < 0.05). A reduction was found in the cobalt and iron concentrations in the spleen and liver of the rats consuming either SM or CM milk in addition to a Low Ca/P-diet, when compared with rats that consumed the Low Ca/P-diet on its own (p < 0.05). Rubidium concentrations were higher in the soft organs and serum of the rats that consumed either SM or CM in addition to a Low Ca/P-diet, compared to the rats that consumed the Low Ca/P-diet on its own (p < 0.05). Caesium concentrations were higher in the soft organs and serum of the rats that consumed SM compared with the other diet groups (p < 0.05). These results show that both SM and CM were able to prevent the negative effects of a Low Ca/P-diet, but a lower amount of SM was required to achieve this compared to CM. The present study reported in this thesis demonstrates that the high nutritional density characteristics of SM differentiates it from CM as a food product, and that SM has a potential advantage in the diet, in that consumption of a smaller amount of SM compared to CM can achieve an equivalent positive effect on growth, development and health in the rat model studied