Effect of total mixed ration composition and daily grazing pattern on milk production, composition and fatty acids profile of dairy cows

The possibilities of using high quality pastures in conjunction with total mixed ration (TMR) during the grazing season have been examined. An experiment with sixteen Holstein cows blocked and randomly assigned to four treatments in a factorial arrangement was conducted in order to evaluate the influence of grazing time of day (day or night) and type of silage (maize or Italian ryegrass) included in the TMR of dairy cows grazing 12 h daily on milk yield, composition and fatty acid profile. The silage type had no effect on the dry matter intake, milk yield and fat and protein proportions. However, cows grazing during the night ate more grass than cows grazing during the day (8.53 vs. 5.65 kg DM/d; P<0.05). No differences were seen between grazing-time with respect to milk production, fat and protein contents. However, the proportion of polyunsaturated fatty acid was higher in milk of dairy cows grazing at night-time than grazing at day-time, especially 18:2n-6 (2.37 vs. 2.12 g/100 g FA respectively, P<0.05) and 18:2cis9trans11 (2.08 vs. 1.74 g/100 g FA respectively, P<0.05).