The effect of supplements of rumen-degradable protein and formaldehyde-treated casein on the intake of low-nitrogen roughages by Bos taurus and Bos indicus steers at different stages of maturity

Abstract

The response in voluntary feed intake, firstly to supplements of rumen-degradable protein and then to additional supplements of formaldehyde-treated casein (FTC) was studied in Aberdeen Angus (Bos taurus) and Brahman (Bos indicus) steers fed long-chopped spear grass (Heteropogon contortus) and pangola grass (Digitaria decumbens). The intake responses were measured at four stages of maturity of the steers ranging from soon after weaning to near maturity. On diets deficient in nitrogen the magnitude of the intake response to rumen-degradable protein was greater in Angus than in Brahmans. With the exception of the Angus steers fed spear grass soon after weaning, there was no significant response to FTC with either diet beyond that achieved with rumen-degradable protein. From published values of the digestible protein supplied by the diets and the protein requirements of cattle for maintenance, it was calculated that pangola grass, prior to supplementation with FTC, supplied sufficient digestible protein for maintenance. On the other hand, that supplied by spear grass, prior to supplementation with FTC, was substantially below that required for maintenance. These experimental and calculated data are discussed in terms of factors limiting feed intake, and conclusions drawn about protein requirements for the expression of maximum feed intake of roughage diets.