Effects of forage particle size and long hay for cows fed total mixed rations based on alfalfa and corn.

A 2 x 2 factorial arrangement of treatments, in which particle length of alfalfa silage in the TMR and supplementary long alfalfa-grass hay were the factors, was used to determine whether hay benefits lactating cows and whether its effects depend on fibrosity of the main forage source. Without supplementary hay, TMR contained 45% forage, including corn silage, and 26 to 27.5% NDF. When hay was fed, the amount of alfalfa silage in the corresponding TMR was reduced. In the production trial, 40 cows (20 multiparous) were fed the diets for 8 wk in early lactation. No interactions of silage length and hay occurred on any production variables except lactose concentration in the milk of multiparous cows. Addition of hay to the diet enhanced DMI, without effect on production, so efficiency of milk production was reduced. Shorter alfalfa silage enhanced DMI by multiparous cows, reduced SCM and FCM in primiparous cows, and depressed fat test in both groups. Milk composition and component production generally were unaffected. Five rumen-fistulated cows in early to midlactation each were given the four treatments during four 3-wk periods. Hay enhanced rumination when short alfalfa silage was fed but tended to reduce it on long alfalfa silage. Hay also depressed rumen pH and enhanced VFA concentrations. Alfalfa silage length had minimal effects on rumination and no effect on fermentation, and neither hay nor silage length affected digestion of silage DM or NDF in the rumen. Addition of hay to the diet may not be beneficial for cows fed TMR, but longer term feeding studies are needed.