Differentiation between organic and conventionally produced milk in pasture based farming systems : 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
Consumer perception of organic cow’s milk is associated with the assumption that organic milk differs from conventionally produced milk. The value associated with this difference, justifies the premium retail price. It includes the perception that organic dairy farming is kinder on the environment, animals and people; that organic milk products are produced without the use of antibiotics, added hormones, synthetic chemicals and genetic modification and may have potential benefits for human health. Controlled studies investigating the chemical differences between organic and conventionally produced milk have so far fallen short of a conclusion as to whether or not these exist. Reasons for this are many folds, caused principally by the complexity of the research problem. A main complication is that farming practices and their impacts differ depending on country, region, year and season between and within organic and conventional systems. Factors influencing milk composition (e.g. diet, breed, and stage of lactation) have been studied individually, while interactions between multiple factors have been largely ignored. Studies fail to consider that factors other than the farming system (organic versus conventional) could have caused or contributed to, the reported differences in milk composition. These omissions make it impossible to determine whether there is a system related difference between organic and conventional milk, or not. The present study investigated the chemical differences between organic and conventionally produced milk in a pasture based farming system. Milk samples have been collected on two farm sets each comprised of one organic and one conventional farm. All farms applied year-round pasture grazing. Milk samples were collected from individual animals on Farm Set 1 and throughout the milking season on both farm sets. Milk samples have been analysed for fatty acid, free oligosaccharides, major casein and whey proteins, and milk fat volatiles, as well for a limited set of milk metabolites using a non-targeted NMR method. Considering the known influence factors on milk composition and the differences observed between the farms on the farm sets in our study, we postulated that fatty acids were influenced by breed and fertilizer application. Oligosaccharides differed between farming systems, with causes presently unknown. The farm set was the dominant influence factor on protein composition, while none of the compounds identified using NMR show any trend. Thus, the major conclusions from this study were that the factors influencing milk composition are not exclusive to either farming system, and pasture feeding conventional cows will most probably remove differences previously reported in other organic and conventionally produced milk studies.