Dietary Energy and Protein Effects on Rumen Volatile Acids and Ration Digestibility by Beef Heifers1

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Abstract
Effects of energy and protein intakes on digestibility and ruminal VFA were studied using 54 Angus heifers in a 3×3 factorial arrangement of treatments. The heifers were full-fed (high energy), 66% full-fed (medium energy) or fed for maintenance (low energy). Across each energy level high, medium and low protein lots received 0.22, 0.12 and 0.03 kg. of digestible protein per 100 kg. of body weight per day, respectively. Apparent digestibility of organic matter, energy and nitrogen-free extract were highest at the medium level of energy intake, and the digestibility of crude protein, crude fiber and ether extract were lowest when animals were fed at high-energy levels. Organic matter, energy, crude fiber and ether extract were less digested at the low level of protein intake. Crude protein digestibility decreased with decreasing protein intake. Concentrations of acetic, propionic, butyric plus higher and total acids, and the percent of butyric plus higher acids were greatest and the percent of acetic acid was lowest at the high level of energy intake. The concentration of acetic, propionic, butyric plus higher and total acids was greatest at the medium level of protein intake. There was an interaction between percent of propionic acid and the energy and protein levels of intake. Copyright © 1966. American Society of Animal Science . Copyright 1966 by American Society of Animal Science