Abstract
Twelve Finnish Ayrshire cows were used in a cyclic change-over design to examine the effects of replacing barley (7 kg/d) gradually with wheat bran at three levels (barley 7 kg (B), barley 3.5 kg + wheat bran 3.5 kg (BW) and wheat bran 7 kg (W)) given with 1.5 kg/d of untreated (R-) or treated rapeseed meal (R+). Grass silage was given ad libitum. The experiment consisted of four 4-week periods with feed intake and performance measurements made during the last two weeks and digestibility measurements during the last week of each period. Feeding wheat bran had no significant effect on silage or total dry matter (DM) intake. Replacing of barley with wheat bran led to a significant decrease in milk yield and in the yield of milk constituents. The yields for treatments B, BW and W were: milk (kg/d) 25.2, 24.9 and 23.7 (SEM 0.38), fat (g/d) 1076, 1086 and 1001 (SEM 17.9) and protein (g/d) 809, 801 and 751 (SEM 8.6). The treatment of rapeseed meal had no significant effect on feed intake, milk yield or milk composition. With increasing level of wheat bran in the diet the digestibility of organic matter and cell wall constituents determined by using acid insoluble ash as an internal marker was reduced. Feeding wheat bran decreased (p<0.01) milk energy yield but because the amount of ME available for milk production was reduced at the same time from 143 to 125 MJ/d, estimated efficiency of the utilization of ME improved with the level of wheat bran. Calculation of feed protein utilization according to Nordic system indicated that no response in milk protein yield was obtained when AAT supply exceeded 40 g/kg FCM.