Effects of Silage Fermentation and Post‐ruminal Casein Supplementation in Lactating Dairy Cows: 1—Diet Digestion and Milk Production

Abstract

Two silages were prepared from the first-cut sward of timothy-meadow fescue and wilted to a dry matter (DM) content of 300 g kg-1. One was ensiled with the addition of a formic-acid-based additive (4 litres formic acid (FA) per tonne) and the other with the addition of a bacterial inoculant (LAB) at a rate of 5×106 colony forming units g-1. Both silages were well preserved, but the extent of fermentation was greater in LAB-silage than in FA-silage as indicated by a lower concentration of water soluble carbohydrates (68 vs 177 g kg-1 DM) and a higher concentration of lactic acid (147 vs 32 g kg-1 DM). Four Ayrshire cows were used in a 4×4 Latin square experiment with 21-day periods to study the effects of silage fermentation and postruminal casein supplementation on silage intake, nutrient supply and milk production. The four treatments were FA-silage without casein (FA-0), LAB-silage without casein (LAB-0), FA-silage with casein (FA-C) and LAB-silage with casein (LAB-C). Both silages were given ad libitum with 8 kg day-1 of barley without or with 400 g day-1 of casein infused into the duodenum. Organic matter digestibility was lower (0·723 vs 0·753; P<0·01) for FA-silage than for LAB-silage. Cows offered FA-silage had a higher molar proportion of acetate and a lower proportion of propionate in ruminal fluid than cows offered LAB-silage. Microbial protein synthesis estimated from the output of purine derivatives in urine was greater (288 vs 260 g N day-1; P<0·05) for cows given FA-silage compared with LAB-silage. Feeding LAB-treated silage tended (P<0·10) to decrease silage DM intake compared with FA-treated silage (10·61 vs 11·77 kg DM day-1). Silage composition did not affect significantly milk yield or milk composition. Casein infusion increased milk yield (25·1 vs 27·1 kg day-1; P<0·05), milk protein content (32·4 vs 33·8 g kg-1; P<0·05) and protein yield (808 vs 905 g day-1; P<0·01). The responses were similar for both silages. © 1997 SCI.