Effects of dry matter concentration and ammonia treatment of alfalfa silage on digestion and metabolism by heifers.

Alfalfa was harvested as second-cutting regrowth herbage, ensiled either at low DM (direct-cut) or high DM (wilted), untreated or treated with .82 or .66% anhydrous NH3 (percentage of DM), respectively, and offered to four Holstein heifers. Silages low in DM had more gross energy and more NDF in DM than silages high in DM. Ammonia treatment increased total, soluble, rumen-insoluble, and NH3 N fractions in treated silages compared with those fractions in untreated silages. Ammonia treatment of low DM silage reduced digestible energy intake but increased intake of high DM silage. Digestibility of DM was lower by heifers fed low than high DM silages, but hemicellulose digestibility was higher. Tissue N retention was lower by heifers fed low than high DM silage. Dry matter and cell solubles digestibilities decreased for NH3-treated silages compared with digestibilities for untreated silages. Digested DM contained more digested NDF and cellulose for NH3-treated silages compared with untreated silages. Retained N was higher for heifers fed NH3-treated alfalfa than untreated alfalfa, particularly for the low DM silages. Wilting alfalfa was more effective in improving nutrient use by heifers than treatment with NH3, which improved preservation of plant protein through ensiling.