Ruminant Nutrition: Dairy Cattle

A total of 45 lactating Holstein cows averaging 617 kg of BW were allotted at wk 20 of lactation to 9 groups of 5 cows blocked for similar DIM to determine the effects of feeding different concentrations of flax hulls (FH) on DMI, milk production, milk composition, and digestion. Cows within each block were assigned to one of the 5 isoenergetic TMR containing 0, 5, 10, 15 or 20% FH. The experiment was carried out from wk 20 to 24 of lactation and diets were fed for ad libitum intake. Milk samples were obtained from 2 consecutive milkings on wk 5 of the experiment and were analyzed separately to determine milk composition. Total tract digestibility was determined on wk 5. Data recorded during the digestibility trial were analyzed as a randomized block design and block and treatment were the main sources of variation. Data on production were analyzed as repeated measurements using PROC MIXED of SAS. Treatment sum of squares were partitioned to provide linear, quadratic, and cubic contrasts after a significant F-test (i.e., P < 0.05). There was no significant cubic effect of treatment on any parameter measured. Intake of DM averaged 20.9 kg/d and was similar among treatments. Concentration of FH in the diet had no effect on milk yield, proportions of protein and fat and yields of protein, fat and lactose. There was a linear increase in proportion of lactose in milk and a quadratic effect of feeding level of FH on somatic cell count. Total tract apparent digestibility of DM, ADF, and NDF was similar among diets. Ether extract digestibility increased with higher proportions of FH in the diet but the increase was more important from 0 to 50 g/kg. These data suggest that corn and barley can be partially substituted by flax hulls (up to 20% of the DM) as the energy source in the diet of mid-lactating dairy cows.