INFLUENCE OF LEVEL OF CONCENTRATE ALLOCATION AND FERMENTABILITY OF FORAGE FIBER ON CHEWING BEHAVIOR AND PRODUCTION OF DAIRY-COWS

Nine midlactation dairy cows were offered one of three mixed silage ra tions with neutral detergent fiber (NDF) that was similar in concentra tion but different in fermentability. Differences in fermentability we re achieved by substituting a high quality alfalfa silage for a low qu ality alfalfa silage and substituting a combination of ryegrass and ti mothy silages for a barley silage. In addition, concentrate was alloca ted at 0.30, 0.82, or 1.37 kg of dry matter/kg of dry matter intake (D MI) from the mixed silage ration. As expected, the NDF content of the mixed silage ration did not differ, although fermentability of NDF inc reased numerically as forage quality increased. Intake of NDF increase d linearly, and DMI tended to increase linearly, as fiber fermentabili ty of the mixed silage ration increased. In addition, cows produced mo re milk, milk fat, and milk protein and generated more total and milk energy. The calculated concentration of net energy for lactation of th e total diet also increased. Results support the concept that NDF qual ity influences and can be used to predict voluntary feed intake, at le ast in relatively high producing dairy cows. The DMI increased, and in take of NDF and crude protein declined, as the allocation of concentra te increased. In addition, as concentrate allocation increased, cows s pent less time eating and ruminating and more time resting and produce d more milk, milk protein, and milk lactose. Cows also generated more total energy and milk energy, although, despite a sharp decrease in th e forage proportion of the diet, the calculated energy density of the diet did not differ among concentrate levels. The lack of significant interactions between concentrate level and fiber fermentability for an y parameter measured supports the contention that high quality forage is critical to a successful dairy ration, regardless of the proportion of forage in the diet.