Composition and properties of bovine milk: A study from dairy farms in northern Sweden; Part Ⅰ. Effect of dairy farming system

摘要

This study was part of a larger project that aimed tounderstand the causes for increasing variation in cheeseripening in a cheese-producing region in northern Sweden.The influence of different on-farm factors on rawmilk composition and properties was investigated andis described in this paper, whereas the monthly variationin the milk quality traits during 1 yr is describedin our companion paper. The dairy farming systems ona total of 42 dairy farms were characterized througha questionnaire and farm visits. Milk from farm tankswas sampled monthly over 1 yr and analyzed for qualityattributes important for cheese making. On applyingprincipal component analyses to evaluate the variationin on-farm factors, different types of farms were distinguished.Farms with loose housing and automaticmilking system (AMS) or milking parlor had a highernumber of lactating cows, and predominantly SwedishHolstein (SH) breed. Farms associated with tiestallshad a lower number of lactating cows and breeds otherthan SH. Applying principal component analyses tostudy the variation in composition and properties oftank milk samples from farms revealed a tendency forthe formation of 2 clusters: milk from farms with AMSor a milking parlor, and milk from farms with tiestallmilking. The interaction between the milking system,housing system, and breed probably contributed to thisgrouping. Other factors that were used in the characterizationof the farming systems only showed a minorinfluence on raw milk quality. Despite the interaction,milk from tiestall farms with various cow breeds hadhigher concentrations (g/100 g of milk) of fat (4.74)and protein (3.63), and lower lactose concentrations(4.67) than milk from farms with predominantly SHcows and AMS (4.32, 3.47, and 4.74 g/100 g of milk,respectively) or a milking parlor (4.47, 3.54, and 4.79g/100 g of milk, respectively). Higher somatic cell count(195 × 10~3/mL) and lower free fatty acid concentration(0.75 mmol/100 g of fat) were observed in milk fromfarms with AMS than in milk from tiestall systems (150× 10~3/mL and 0.83 mmol/100 g of fat, respectively).Type of farm influenced milk gel strength, with milkfrom farms with predominantly SH cows showing thelowest gel strength (65.0 Pa), but not a longer rennetcoagulation time. Effects of dairy farming system(e.g., dominant breed, milking system, housing, andherd size) on milk quality attributes indicate a needfor further studies to evaluate the in-depth effects offarm-related factors on milk quality attributes.