Effect of level and source of nutrients in late gestation on subsequent milk yield and composition and fertility of dairy cows

The effect of level and source of nutrients in late gestation on food intake, milk yield, milk composition and fertility in the subsequent lactation were evaluated in a randomized block design experiment involving 76 cows. Four experimental diets, based on grass silage, were offered to provide two levels of metabolizable energy (ME) intake (80 and 125 MJ/cow/day) either from 100:0 or 40:60 forage:concentrate (F:C) ratios for the last 28 days of gestation. Post-calving all cows were offered the same grass silage supplemented with 7 kg/day concentrates. For treatments 80 ME, 125 ME and 100:0 F:C, 40:60 F:C total dry matter (DM) intakes were 6.8, 10.5, 9.0 and 8.4 kg DM/day and ME intakes were 80, 126, 102 and 104 MJ/day, respectively, during the last 4 weeks of gestation. For weeks 1-16 of the subsequent lactation, treatment 125 ME increased milk fat content and yield but had no effect on food intake, milk protein content or onset of cyclicity. Treatment 125 ME increased condition score and live weight at calving. Altering the F:C ratio of the diets in late gestation had no effect on food intake, milk yield, milk composition or on the onset of cyclicity in the subsequent lactation. Cow parity and level of nutrient intake in late gestation provided the best fit relationships for the yields of fat and fat plus protein (R² relationships=0.49 and 0.52, respectively) during weeks 1-16 of lactation. It is concluded that increasing nutrient intake in late gestation increased milk fat content and yield but had no effect on milk protein concentration. The improved milk fat content and yield observed in a previous study was due to increased nutrient intake rather than altering the F:C ratio. Furthermore there was no measurable benefit in food intake or animal performance in the subsequent lactation through feeding concentrates in late gestation.