Investigation on meteorological variables affecting sheep bulk milk quality in Sardinian farming systems

Milk yield, quality and composition are influenced by several factors. Various studies investigated how heat stress acts on milk production, with special focus on dairy cattle. In Sardinia’s economy, sheep farming plays a crucial role but harsh climatic conditions may affect negatively milk quantity and quality. In this study, this effect was assessed on dairy sheep by statistical analysis of bulk milk characteristics at farm level in Sardinia. The main relationships among relevant variables of about 5000 farms were analysed to detect how farm facilities, geographical and meteorological variables affect milk traits. Furthermore, we quantified losses in milk quantity and quality due to heat stress by means of temperature humidity index (THI). A mixed model was used to predict milk characteristics and the effect of heat stress in a low-cost determination. Multivariate statistics on meteorological variables, referred to the whole island in the late spring and summer, produced an alternative index describing the heat stress condition. We do not observed a close relationships between farm structural variables and milk composition traits in Sardinian farms. When THI < 68, lactose content was higher whereas fat, proteins and caseins percentages are lower. Compared to the average milk production assumed as 100% a drop of 5% of milk every 10 THI point was estimated. Mixed model analyses highlighted a relevant quota of trait variance explained by random flock effect (from 32 to 64%).