Harri Miettinen

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

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 x 10 6 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 x 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.

Effects of Silage Fermentation and Post-ruminal Casein Supplementation in Lactating Dairy Cows: 2—Energy Metabolites and Plasma Amino Acids

Four cows were used in a 4 x 4 Latin square design with a 2 x 2 factorial arrangement of treatments to examine the effects of the extent of silage fermentation and post-ruminal casein infusion on the arterial concentrations and mammary arterial-venous (A-V) difference of energy-yielding nutrients and plasma amino acids. Of the two silages one was preserved with formic acid (FA-silage) and the other with an inoculant of lactic acid bacteria (LAB-silage). Both silages were given ad libitum with 8 kg day -1 of barley, without or with duodenal casein infusing (400 g day -1 ). Blood was sampled from the coccygeal vessel and milk vein. FA-silage less fermented than LAB-silage as indicated by higher concentration (g kg -1 dry matter) of water soluble carbohydrates (178 vs 68) and lower concentration of lactic acid (32 vs 147). Plasma concentration of glucose was lower (P < 0.05) and concentrations of essential amino acids (P < 0.001) and blood β-hydroxybutyrate (BHB) (P < 0.01) were higher with FA-silage than with LAB-silage. There was a strong linear relationship between arterial concentration and mammary A-V difference of blood metabolites, except BHB, and amino acids. The relationship between arterial concentration and mammary A-V difference of glucose was different between the silages. Mammary extraction rates of glucose, BHB, histidine, leucine and lysine were affected by their arterial concentrations. The interaction between silage fermentation and casein infusion was significant (P < 0.05) in arterial concentration of branched-chain amino acids, the increase being greater with FA-silage than with LAB-silage. The results suggest that the supply of glucose may limit milk synthesis in cows given restrictively fermented grass silage and barley, whereas the supply of amino acids may be more limiting with extensively fermented silages. It is further suggested that the mammary gland has a capacity to adapt its efficiency of nutrient uptake according to the supply and mammary demand of nutrients.