Efficienza di utilizzo dell'azoto in bovine da latte alimentate con diete a base di fieno

Abstract

The objective of the present study was to evaluate the milk and casein nitrogen (N) use efficiency in farms in which cows were fed hay-based total-mixed ration (TMR). Nineteen Italian Holstein dairy farms were randomly selected within the ParmigianoReggiano cheese production area. Dry matter intake (DMI) was calculated based on the amount of TMR offered and orts weighed over a two days sampling period. The TMR was analysed to estimate dry matter (DM), neutral detergent fibre (NDF), starch, crude protein (CP) and N content, then N intake was calculated. For each farm, data on milk yield and composition were recorded; milk N efficiency (MNE) and casein N efficiency (CNE) were calculated as a ratio between milk or casein N yield and N intake. The farms were then divided in two categories based on milk yield: group 0 (≤ 33 Kg/day) and group 1 (> 33 Kg/day). The data were normally distributed, and they were analysed through the mixed model as a function of farm categories, with farm as random effect. Group 0 (average diet: 15.2% CP, 38.7% NDF and 21.5% starch) presented an average milk yield of 30.86 Kg/cow/day, while group 1 (average diet: 15.3% CP, 37.9% NDF; 22.0% starch) presented an average milk yield of 35.86 Kg/cow/day. No differences were highlighted between diet chemical composition, nutrient intake and milk composition. A trend for a higher CP intake but lower milk fat and protein percentage was observed in group 1, even if not statistically. No differences were observed concerning MNE and CNE between the two groups. Both MNE and CNE are linearly related to feed efficiency, thus representing promising parameters that need further attention in future studies.