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

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 rumenfistulated 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 digest a in the reticulo-rumen, and a decreased apparent digestibility of the diet, compared to the HR diet. The net inflow of fluid to the reticulorumen 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.