Increasing of rumen undegradable protein in dairy cows. 1. Effects on milk production, milk composition and nutrients utilization

Abstract

One of the most limiting and expensive nutrients for high producing dairy cows is crude protein (CP) and particularly RUP. Winter diets for dairy cattle in Southern Chile are based mainly on silages. The aim of the study was to analize the effects of the level of RUP in diets which include high levels of pasture silage and alfalfa haylage. High silage diets were fed to twelve multiparous Holstein cows in two trials to establish the effects of RUP supplementation on milk production, composition and efficiency of production. A complete Latin square design was used. Diets identified as A1 and B1 included (on a DM basis) 45% grass silage (GS) and 20% alfalfa haylage (AH) while diets A2 and B2 had 38% GS and 27% AH. The B diets were adjusted considering RUP (NRC, 1989) with fishmeal in the concentrate while the A diets considered only CP requirements, accepting up to a 20% RUP deficiency, and included soybean meal. DM, NEL and CP intakes were similar between treatments Daily milk and protein yield and concentration were higher with fish meal supplemented diets (P<0.05) but fat concentration was lower (P<0.05). MUN was similar between treatments and all values were lower than 19 mg dl-1. Apparent efficiency of utilisation of DM and NEL for milk production, FCM and milk protein were higher (P<0.05) with fish meal diets. There was no interaction between alfalfa haylage and RUP level, except for milk protein level. Therefore providing RUP with fishmeal resulted in a higher milk and protein production and improved the efficiency of nutrient utilization, and this effect was not related to alfalfa haylage level.