FORAGE SOURCE ALTERS NUTRIENT SUPPLY TO THE INTESTINE WITHOUT INFLUENCING MILK-YIELD

Eight Holstein cows in early lactation and fitted with ruminal and duo denal cannulas were used in a 4 x 4 Latin square design experiment to determine the influence of forage source on microbial digestion in the rumen and nutrient supply to the intestine and to determine relations hips between DMI, ruminal fill, and NDF content of silage. Cows were f ed a TMR formulated to contain a 50:50 concentrate forage ratio. A sig nificant negative correlation was found between dietary NDF concentrat ion (range 32.2 to 37.9%) and DMI (16.7 to 19.6 kg/d). In addition to forage NDF concentration, the lower DMI of cows fed oat or triticale s ilage (16.7 and 17.2 kg/d, respectively) relative to that of cows fed barley or alfalfa silage (18.6 and 19.6 kg/d, respectively) might refl ect a lower true rate of NDF digestion (range 2.39 to 4.09%/h), higher ruminal turnover time (12.9 to 17.1 h), and lower rate of NDF intake (3.31 to 3.96%/h). However, differences in ruminal bacterial yield, ru minal metabolites, and nutrient supply to the intestine associated wit h different silages had no major effect on dairy cow performance. We c oncluded that the dairy cow can maintain similar milk yield despite ma rked differences in the type of end products arising from carbohydrate and protein digestion.