Quantity and composition of digesta in the reticulo-rumen of cows offered two diets differing in K:Na ratio

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Abstract
Pasture diets of high potassium (K): sodium (Na) ratio (HR) or low K: Na ratio (LR) were offered for 2 h each day to eight rumen-fistulated cows that were neither lactating nor pregnant. Dry matter (DM) intake averaged 4.47 kg per cow per day. Na and K intakes were, respectively, 9 g and 176 g on the HR diet and 21 g and 142 g on the LR diet. Offering the LR diet was associated with an increased Na concentration and decreased K concentration in rumen fluid both before and after feeding, an increased quantity of digesta in the reticulo-rumen, and a decreased apparent digestibility of the diet, compared to the HR diet. The net inflow of fluid to the reticulo-rumen and outflow to the omasum were higher on the LR diet than on the HR diet during 7 h after feeding. The K concentration in saliva was lower and the packed cell volume of blood higher in cows when offered the LR diet. The mechanism by which diets of low K: Na ratio may affect bloat is discussed.