Further studies on the effect of fat supplementation of concentrates fed to lactating dairy cows. 3. Effect on rumen fermentation and site of digestion of dietary components.

Abstract

Fat-supplemented concentrates were given to dairy cows with rumen and duodenal cannulae, and the effect on rumen fermentation and site of digestion of dietary components was studied. Treatments were feeding concentrates supplemented with 7% fat (treatment C7), supplemented with 12% fat (treatment C12) and supplemented with 12% fat adsorbed on a carrier (treatment C12C). Small but significant changes in rumen fermentation characteristics such as pH, total VFA (volatile fatty acids) and NGR (non-glucogenic/glucogenic ratio) were observed with treatments C12 and C12C as compared with treatment C7. Numbers of protozoa were severely reduced with treatments C12 and C12C, but not with treatment C7. Site of digestion of organic matter and energy was affected by treatments C12 and C12C but this could be attributed to increased postruminal fat digestion. Total digestion and site of digestion of carbohydrate fractions (crude fibre, neutral detergent fibre, starch, sugars) were not affected by fat supplementation. Recovery of hydrogen in CH₄ actually measured was close to 90% of that estimated from the rumen fermentation balance. Nitrogen flow to the small intestine was not affected by replacing part of the carbohydrates by fat, indicating an increased efficiency of microbial protein synthesis in the rumen when fat was increased. (Abstract retrieved from CAB Abstracts by CABI’s permission)