Study on the relationships between the main milk cheese-making features and dairy cows rearing conditions.

The cheese-making aptitude of milk depends on chemical composition, renneting properties, bacteriological and fermentability traits. The aim of our research was to study the relationships between dairy cows rearing conditions and milk cheese-making features, with particular attention to the natural aptitude of milk to be fermented by lactic acid bacteria (i.e. acidification rate; AR). This study was carried out on 12 dairy herds identified through a preliminary investigation on 56 herds: six characterized by slow (L) and six by fast (R) AR of bulk milk. Besides AR measurement on bulk milk of each farm, the following determinations were performed: fat, protein, casein, lactose, urea, somatic cell count, titratable acidity and rennet clotting properties. Furthermore, checks on feeds and diets as well as on DM and pH of the feces, collected from six cows per farm (3 in early and 3 in advanced lactation), were carried out. In L farms the rations had a greater content of concentrates, fermentable carbohydrates and crude protein and lower content of NDF. The pH of feces was lower (P<0.001) in L (6.06) compared with R (6.35). Greater milk protein content (3.40 vs. 3.23%; P=0.07) and casein (2.65 vs. 2.48%; P<0.05) were observed in L compared with R; conversely, worse rennet clotting features were observed in the former (clotting time: 22.1 vs. 17.8 min, P=0.06; curd firmness: 17.4 vs. 24.6 mm; P=0.08). Milk urea was greater (P=0.07) in L (34.6 mg/dl) compared with R (24.4 mg/dl). In conclusions the diets characterized by greater fermentable carbohydrates with low pH of the feces (i.e. effect of fermentation in the digestive tract), despite a probable positive contribution on milk protein content, seem negatively associated with the acidification rate and the rennet clotting features.