INFLUENCE OF SUPPLEMENTARY FISH-OIL AND RUMEN-PROTECTED METHIONINE ONMILK-YIELD AND COMPOSITION IN DAIRY-COWS

The effects of a daily supplement of 300 mi fish oil and 20 g rumen-pr otected methionine, alone or in combination, were investigated in mid- lactation cows receiving a maize silage-based diet ad lib. Fish oil si gnificantly decreased feed intake, increased milk yield, decreased pro tein and casein concentrations: and especially fat concentration (by 1 3.1 g/kg) and output. Fat concentration decreased more in primiparous than in multiparous cows. Methionine supplementation increased protein and casein concentrations and outputs. No significant interaction bet ween oil and methionine supplementation was found on milk composition. Treatments did not modify live weight or body condition changes, or l actose and non-casein nitrogenous compounds in milk. Oil plus methioni ne supplementation made it possible to decrease milk fat content witho ut changing protein content.