Bulk milk quality differs across welfare levels in Italian dairy cattle farms with different housing systems

We investigated the effect of the welfare level measured with the Italian ClassyFarm protocol on bulk milk quality traits, differentiating between loose (LHS) and tied housing system (THS). The overall welfare ClassyFarm score combines the scores of management, biosecurity, structures, and animal-based measures. The scores of 89 THS farms and 105 LHS farms located in Northern Italy were merged with the milk analyses carried out in 2022 for milk payment systems (n = 6971). The fixed effects of welfare level (3 classes: <65%, insufficient; 65–84%, intermediate; and ≥85%, excellent), type of housing system, month, and interaction between type of housing system and welfare score were tested. Herd season was the random effect. On average, the THS farms' welfare score was 72.56%, while LHS farms had a score equal to 78.82%. For THS, 80 farms were intermediate, 4 excellent, and 5 insufficient, while for LHS, 79 were intermediate, 21 excellent, and 5 insufficient. A significant effect of welfare level was found for lactose, total bacterial count (TBC), and fat-to-protein ratio. The first-order interaction affected more traits, namely fat, protein, and casein content, somatic cell score and TBC. Farms classified as insufficient exhibited the worst/highest somatic cell score and TBC and the lowest lactose content. Results indicated that rearing conditions, here evaluated with the ClassyFarm protocol, affect bulk milk quality. At the same time, this system presents a multifaceted nature, owing to the intricate interactions among various factors. Additional research is warranted to provide clearer insights and a better understanding of cause-and-effect relationships.