Milk production response to increased fatty acid level in the feed.

Milk production response to increased dietary fatty acid (FA) level was investigated using 16 Danish Holstein cows at two production levels (8 cows 32.2 kg energy corrected milk (ECM)/d, LM; 8 cows 40.0 kg ECM/d, HM) in a Latin square design. LM and HM groups were in average 158 and 74 DIM at experimental onset, respectively. Treatments were four levels of FA in ration dry matter (DM), unsupplemented (17 g FA/kg DM) and three increasing substitutions of barley with Palm Fatty Acid Distillate (PFAD) fat, resulting in 29, 40 and 52 g FA/kg DM, respectively. PFAD fat is free FA, mainly C16 and C18:1. Rations were fed as total mixed rations, 63% of ration DM was grass/clover silage. Milk production and composition were recorded the last 3 days in each of the four 3 week periods. DM intake decreased with increased FA level, resulting in a constant net energy intake. The general linear responses to increased FA level when FA level was increased with 10 g/kg DM (1% of ration DM) were 1.1 kg ECM (P<0.0001), 0.061 kg milk fat (P<0.0001), 0.012 kg milk protein (P=0.09) and 0.052 kg lactose (P=0.0002) per day, and linear responses in milk composition were 0.39 g fat (P=0.07), -0.71 g protein (P<0.0001) and 0.05 g lactose (P=0.3) per kg milk, and in milk fat average globule diameter 0.092 μm (P<0.0001). It was expected that the response in milk production to increased dietary FA would be almost proportional to cows' actual milk yield, however, the opposite was the case. When responses were analysed separately for the two groups of cows, response in kg ECM from lowest to highest FA level was slightly larger for the medium than for the high yielding group. Statistical analysis with likelihood ratio tests, using random regression in PROC MIXED across all cows, confirmed that the ECM response (regression coefficient) was significantly negatively correlated to the production level of the cows (intercept). A negative correlation was also found for the other milk production and concentration parameters except for milk fat concentration. However, the correlations were only significantly different from zero for kg milk, kg ECM, kg protein, kg lactose and fat concentration. [ABSTRACT FROM AUTHOR]