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Regulation of Feed Intake in Dairy Cows. I. Change in Importance of Physical and Physiological Factors with Increasing Digestibility¹

Department of Dairy Science, Ohio Agricultural Experiment Station, Wooster

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: W^0.99, D^1.53, and F^1.01 expressing these relationships were essentially those predicted empirically if capacity limited feed intake. With high-roughage rations between 67 and 80% dry matter digestibility, intake decreased with increasing digestibility after adjusting for body weight and productive energy. In this region, intake was directly related to the 0.73 power of the body weight at peak lactation.

It was concluded that physical and physiological factors regulating feed intake change in importance with increasing digestibility. At low digestibility they were: Body weight (reflecting roughage capacity), undigested residue per unit body weight per day (reflecting rate of passage), and dry matter digestibility. At higher digestibilities intake appeared to be dependent on metabolic size, production, and digestibility.

¹ Journal article No. 101-62, The Ohio Agricultural Experiment Station, Wooster.

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