Food intake and ruminal osmolality in sheep: differentiation of the effect of osmolality from that of the products of maize silage fermentation

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Abstract
Five rumen-cannulated Cheviot lambs were used in 2 successive experiments to differentiate the effect of osmolality from the specific effects of the soluble compounds in maize silage on voluntary intake and ruminal motility. In Expt [experiment] 1, extracts from fresh (FCE) and ensiled (CSE) maize were adjusted to pH 6.5 and tonicities of 200, 400, 800 and 1600 mosmol/kg with NaCl, then infused into the rumen according to a 5 .times. 5 repeated latin-square design. Water was infused as the control. In Expt 2 solutions of NaCl, with tonicities similar to those in Expt 1, were also infused into the rumen. The lambs were fed ad lib diet of pelleted lucerne but on the morning of infusion they were deprived of food for 4 h and infused continuously for 4 h commencing after 1 h of food deprivation. The infusion of FCE and CSE resulted in no significant difference in cumulative dry matter (D.M.) intake. Increasing the tonicities of the infusates caused a linear increase (P < 0.05) in ruminal osmolality and a corresponding linear reduction in food intake during the first 30 min of feeding. Infusion of NaCl alone produced a similar effect on intake. The linear regression coefficients of food uptake (Y) (g D.M./kg W0.75) against rumen osmolality (X) (mosmol/kg) were -0.077 .+-. 0.0085 (r2 = 0.78), -0.082 .+-. 0,0095 (r2 = 0.76) and -0.073 .+-. 0.0065 (r2 = 0.84) for FCE, CSE and NaCl, respectively, with no significant differences among the infusates. The frequencies of ruminal contractions during the infusion of FCE and CSE were similar (P > 0.05) and were unaffected (P > 0.05) by ruminal osmolality up to 550 mosmol.