The flow of endogenous protein to the omasm and abomasum of cattle.

Abstract

Animal Production in Australia THE FLOW OF ENDOGENOUS PROTEIN TO THE OMASUM AND ABOMASUM OF CATTLE F.J. HART*, JANE LEIBHOLZ* and J.P. HOGAN** There are very few published estimates of flows of endogenous protein in the digestive tract of cattle. This information is required for the correction of nitrogen (N) flow measured over a range of dietary intakes. In this experiment endogenous protein flowing to the omasum and abomasum of cattle was measured. Alkali-soaked oat straw was washed free of digestible crude protein with NaOH and then sprayed with a mineral mixture plus urea at a rate of 13 g N/kg. The diets were also sprayed with indigestible markers (52Cr EDTA and lD1Ru(phen)3 Cl,) (McGarrity and Siebert 1977). The flow of endogenous protein N (EPN) to the omasum and abomasum was measured by difference between the total protein N and the sum of the non-protein nitrogen (NPN), microbial protein N (MPN) and undegraded dietary protein N fractions. The NPN fraction was estimated by tungstic acid precipitation and the MPN fraction by 'N. Between 1.70 and 4.08 kg/day of the diet was fed to three steers (300 kg live weight) fitted with rumen and abomasal cannulae. Omasal samples were obtained by suction through a tube passed into the omasum via the rumen. TABLE 1 Flow of total nitrogen (TN), protein nitrogen (NPN), and omasum and abomasum, and the fed alkali-washed oat straw microbial protein nitrogen (MPN), nonendogenous protein nitrogen (EPN) to the gain in EPN in the abomasum of calves at different dry matter intakes (DMI) The mean flow of EPN to the omasum was 5.6 g/day or 2 g/kg DM1 and to the abomasum 23 g/day or 8 g/kg DMI. These EPN values do not estimate the total secretions of EPN but the difference between their secretion into the forestomachs and their absorption to the omasum and abomasum. Also, the above estimates of EPN have a large standard error due to their method of calculation by difference. Kennedy and Milligan (1980), using similar methods of calculation but from 15N studies, found that EPN flow to the abomasum in sheep fed brome grass was about 5 g N/kg DM1 of which about 1 g N/kg DM1 was from saliva, 1 g N/kg DMI from gastric secretions and the remainder of about 3 g N/kg DMI were due to the sloughing of rumen epithelium. In the present experiment, gastric secretions represented 5.9 g/kg DM1 of the flow to the abomasum while saliva and other sources added only 2.2 g EPN/kg DM1 to the flow of N at the abomasum. KENNEDY, P.M., and MILLIGAN, L.P. McGARRITY, R-G., and SIEBERT, B.D. (1980). Can. J. Anim. Sci. 60: 1029. (1977). Analyst, Land. >102795. * Department of Animal Husbandry, University of Sydney, Camden, N.S.W. 2570. ** Division of Animal Production, CSIRO, P-0. Box 239, Blacktown, N.S.W. 2148. 602