Characteristics of dairy farms in the North-Eastern part of Italy: rations, milk yield and nutrients excretion

This survey was aimed to evaluate the characteristics of dairy farms in the North-Eastern part of Po valley in terms of ration composition, milk yield and N and P excretions. Eighty-nine farms, with Italian Holstein Friesian cows, were selected in order to cover different situations in term of farm size and milk yield (MY). MY and quality were obtained from the national database of functional controls. Each farm was visited in order to collect information about ingredients and chemical composition of rations used. Farms were classified in four groups differing for dietary crude protein density (L(CP)<15.3% DM; H(CP)>15.3% DM) and for MY (L(MY)<30 kg/d; H(MY)>30 kg/d). N and P excretions were quantified by following a mass balance approach. Dietary crude protein content (CP) was not correlated to milk yield (MY) and quality. The estimated amounts of N excreted, discounted for 28% of N losses in atmosphere, were 78.5, 78.2, 87.2 and 89.1 kg/cow/year, and P excreted were 20.2, 18.6, 18.7 and 19.8 kg/cow/year for the L(CP)L(MY), L(CP)H(MY), H(CP)L(MY), H(CP)H(MY) groups, respectively. On corn silage and cereals based rations, a dietary CP of 14.3% DM can support 31 kg MY/cow/day.