Effects of abomasal infusions of sodium caseinate, soya‐protein isolate and a water extract of fish meal on the utilisation of nitrogen by dairy cows

Abstract

AbstractA nitrogen‐balance study was conducted with four lactating cows in mid‐to‐late lactation given the following treatments in a 4 × 4 latin square design with 14‐day periods: (1) basal diet of grass silage and barley, (2) basal diet plus sodium caseinate into the abomasum, (3) basal diet plus soya‐protein isolate (SPI) into the abomasum, and (4) basal diet plus a water‐extract of fish meal (FE) into the abomasum. All infusions supplied 184 g day−1 of total amino acids but differed in amino acid composition. All infusions increased (P < 0.01) the output of nitrogen in milk relative to basal, the values being 72.6, 90.4, 84.5 and 84.9 (SED 2.6) g day−1 for basal, caseinate, SPI and FE respectively; caseinate yielded more milk‐nitrogen (P < 0.05) than the other infusions. Urinary nitrogen was increased by all infusions relative to basal (P < 0.05) but differences between infusions were not significant (P > 0.05); values were 136.1, 155.8, 159.5 and 167.2 (SED 6.2) g day−1 for basal, caseinate, SPI and FE respectively. Nitrogen retention was not significantly affected by treatment. Despite their differences in amino acid composition, SPI and FE produced similar responses in the pattern of utilisation of nitrogen.