Effects of and interactions between the extent of silage fermentation and protein supplementation in lactating dairy cows

Twelve Ayrshire cows were used to study the effects of and interactions bet ween extent of silage fermentation and level of protein supplementation on silage intake and milk production. Experimental design was a cyclic change- over with six dietary treatments, with two replicate blocks of six cows and four 3-week periods. Dietary treatments in a 2 x 3 factorial arrangement c onsisted of two wilted silages treated with either a formic acid-based (FA) 5 l/t or a bacterial inoculant additive (I) and three levels of protein su pplementation obtained by fish meal (FM) inclusion (0, 60 and 120 g/kg conc entrate). Grass silage was given ad libitum and concentrates were offered a t a rate of 10 kg/d. Both silages were well-preserved but I-silage was more extensively fermented than FA-silage. Feeding FA-silage decreased diet org anic matter digestibility, particularly that of neutral detergent fibre, co mpared with I-silage. Inclusion of FM increased the digestibility of all di etary constituents. Dry matter (DM) intake of I-silage was lower than that of FA-silage but milk yield was not significantly affected. Restricting sil age fermentation increased milk fat content, fat yield and energy corrected milk yield. FM inclusion increased silage DM intake, milk yield, milk prot ein content and yield. FM120 inclusion increased milk fat yield more with F A-silage than with I-silage, whereas the response in milk protein yield was greater with I-silage. plasma glucose, plasma urea and milk urea concentra tions were lower and blood beta-hydroxybutyrate higher in cows given FA-die ts than those given I-diets.