The effect of cattle breed, season and type of diet on nitrogen fractions and amino acid profile of raw milk
The aim of the study was to describe the differences in nitrogen fractions and deepen the knowledge in the amino acid profile of raw milk affected by the breed of cattle, season and type of feeding. The study was conducted from June 2005 to February 2007 on 64 bulk milk samples collected from eight herds consisting of Czech Fleckvieh (four herds) and Holstein (four herds) breed. One half of the herds of each breed was grazed while the other half was not. Samples were collected twice in winter and twice in summer. The effect of the breed resulted in differences in milk yield that was lower in Czech Fleckvieh (5 385.50 kg) than in Holstein (7 015.15 kg, P<0.05). The content of nitrogen fractions was higher in Czech Fleckvieh than in Holstein ( P<0.05). No effect of the breed on the amino acid profile of milk was observed except on the concentration of Glu ( P<0.05). The effect of the season was demonstrated in the decrease of the concentrations of nitrogen fractions and Met during summer in comparison to winter ( P<0.05). The effect of the type of feeding resulted in lower milk yield (5 197.50 and 7 203.75 kg) and lower concentrations of nitrogen fractions in grazed herds compared to non-grazed herds ( P<0.05), respectively. Furthermore, the amino acid profile of milk differed significantly between grazed and non-grazed herds ( P<0.05).