Effect on milk cheese-making features of dietary fermentable energy and crude protein in dairy cows.

The milk cheese-making aptitude depends on physico-chemical, bacteriological and fermentability traits, including the natural aptitude of milk to be fermented by lactic acid bacteria (i.e. acidification rate; AR). This trial aimed to evaluate the effect of dietary carbohydrates composition and crude protein (CP) on milk traits, in particular on AR. The trial involved 6 Italian Friesian mid-lactating dairy cows reared in an experimental barn. A crossover (21 d per period) was used to compare B with L diet, characterized by different forage:concentrate ratio (respectively 52:48 vs. 62:38 DM basis), carbohydrate composition (23.9 vs. 20.3% starch; 34.8 vs. 37.5% NDF on DM) and CP content (15.5 vs. 15.1% on DM). Individual dry matter intake (DMI) and milk yield (MY) were measured daily. Milk samples were collected twice a week and analyzed for: fat, protein, casein, lactose, somatic cell count, urea, titratable acidity (SH), renneting properties and AR. Fecal samples were also collected at the end of each period and analyzed for pH and DM. Lower MY (27.9 vs. 30.6 kg/d; P<0.001) and lower DMI (21.2 vs. 23.2 kg/d) was observed in L compared with B. The fecal pH values indicate that digestive processes were not altered by the diets. High values of milk fat and protein content were observed, with lower protein (P<0.05) in L (3.59%) than B (3.66%), with effect on SH (3.61 in L vs. 3.70 °SH/50 mL in B; P<0.05) and curd firming rate (7.5 in L vs. 5.7 min in B; P<0.05). The diet did not modify milk AR, which was lower than the optimal value. Our results confirm that high fermentable diets, if well balanced, do not alter digestive functions and animal health. The reduction of dietary fermentable carbohydrate and CP slightly reduced protein content and SH, but did not modify milk AR.