Effects of intraruminal infusions of sodium acetate and sodium chloride on silage intake by lactating cows.

Lactating dairy cows prepared with rumen fistulas were fed on grass silage and concentrates and used in two experiments to compare the effects of sodium acetate and sodium chloride infused over 3 h into the rumen on the voluntary intake of silage. Silage intake was depressed in an approximately linear manner by increasing amounts (6-15 mol) of sodium acetate (NaOAc) and 15 mol NaCl had an effect similar to that of 12 mol NaOAc. Sodium in rumen fluid was significantly correlated with intake as was osmolality. 5.5, 7.4 or 9.1 mol of NaOAc significantly depressed silage intake, while 7.4 and 9.1 mol NaCl had significant effects. There were significant negative relationships between intake and the level of NaOAc or NaCl. It is concluded that the major effect of either salt was via the elevation of osmolality of rumen fluid and the relevance to normal control of feeding is discussed.