Regulation of Feed Intake in Dairy Cows. I. Change in Importance of Physical and Physiological Factors with Increasing Digestibility

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Abstract
Voluntary dry feed intake and dry matter digestibility were determined in 114 trials with lactating dairy cows. The rations ranged between 52 and 80% in digestibility and cow weights ranged between 625 and 1,457 lb. In a multiple regression analysis digestibility (D), fecal dry matter per 1,000 lb body weight per day (F) and body weight (W) accounted for the variation in feed intake between 52 and 66% digestibility, provided the rations were mostly roughage. R =0.997 (P < 0.01). The terms W0.99, D1.53, and F1.01 expressing these relationships were essentially those predicted empirically if capacity limited feed intake. Between 67 and 80% dry matter digestibility, intake decreased with increasing digestibility and was related to W0.73.