Increasing the digestible undegraded protein intake of lactating dairy cows by feeding fishmeal or a rumen protected vegetable protein blend

Abstract

An experiment was conducted to investigate the effect on milk yield and composition of increasing the digestible undegraded protein (DUP) supply to dairy cows in early-lactation either by inclusion of fishmeal (FM) or a blend of rumen protected vegetable protein in the diet. The vegetable protein blend was formulated to supply a balance of amino acids similar to that of FM. Thirty-two Holstein–Friesian dairy cows in early-lactation were assigned to one of the four dietary groups of eight cows. Cows were offered a basal diet consisting of grass silage, maize silage and brewers grains, together with a fixed daily allowance of 1 kg molassed sugar beet nuts and 7.5 kg per day concentrates. Each group was fed a different experimental concentrate: concentrate C was a cereal based control containing rapeseed meal and soyabean meal; FM contained 30 g kg −1 FM; VP-L and VP-H contained 60 and 120 g kg −1 rumen protected protein blend respectively. FM had no effect upon milk yield, but milk protein output was 60 g per day higher ( P<0.01) compared with control (C) cows. Concentrate VP-L did not increase milk yield, but milk protein output increased by 110 g per day ( P<0.01). Concentrate VP-H increased milk production by 2.0 kg per day ( P<0.05) and milk protein output by 110 g per day ( P<0.01). Retrospective calculations of protein and amino acid supplies to the intestinal absorptive site suggested that rumen degradable protein was slightly limiting with all diets and that leucine supply may have been limiting for diets C and FM. The vegetable protein blend replaced FM in diets for the dairy cows without any adverse effects on milk protein output.