Effects of Forage Particle Size and Grain Fermentability in Midlactation Cows. II. Ruminal pH and Chewing Activity

Abstract

Ourstudyinvestigatedtheeffectsof,andinteractions between, level of dietary ruminally fermentable carbo- hydrate (RFC) and forage particle size on rumen pH and chewing activity for dairy cows fed one level of dietaryNDF.Also,correlationsbetweenintake,produc- tion, chewing, and ruminal pH parameters were inves- tigated. Eight cows (61 days in milk) were assigned to four treatments in a double 4 × 4 Latin square. Treat- ments were arranged in a 2 × 2 factorial design; finely choppedalfalfasilage(FS)andcoarsealfalfasilage(CS) were combined with concentrates based on either dry, cracked-shelled corn (DC; low RFC) or ground, high- moisture corn (HMC; high RFC). Diets were fed ad libitum as a total mixed rations with a concentrate:for- age ratio of 60:40. Diets averaged 18.7% crude protein, 24.0% neutral detergent fiber, 18.3% , acid detergent fiber and 27.4% starch on a DM basis. Mean particle size of the four diets were 6.3, 2.8, 6.0, and 3.0 mm for DCCS, DCFS, HMCCS, and HMCFS, respectively.