Effects of variation in herbage sodium levels and salt supplementation on the nutritive value of perennial ryegrass for sheep

Abstract

AbstractSix groups of five 18‐month‐old wether sheep received a diet of dried grass ad libitum with a pelleted ground barley/oat supplement containing various levels of salt for 30 d. The first group received grass of high Na concentration (7·3 g per kg DM) with no added salt in the supplement, a second group received low sodium grass (4·2 g per kg DM) with no salt additions, and the other four groups received the low sodium grass with varying levels of salt added to the supplement to provide a final dietary Na concentration ranging from 7·0 to 18·0 g per kg DM.Dry matter (DM) and organic matter (OM) intakes were significantly reduced for groups receiving salt supplementation. The digestibilities of DM and OM were reduced for all groups on the low sodium grass diets compared with the high sodium grass diet, but were not affected by salt supplementation.No consistent changes were observed in the molar proportions of volatile fatty acids in rumen fluid, but N availability and retention were higher for the animals on the high sodium grass diet.The high sodium grass diet gave a better apparent availability and retention of minerals than the low sodium grass diets and, while addition of salt tended to improve the availability of minerals, the urinary loss of minerals increased with salt addition to the diet.There were no changes in plasma Na levels, and plasma K changes were inconsistent. However, plasma Ca concentration was reduced significantly for salt‐supplemented diets with a Na concentration above 7·0 g per kg DM, and plasma Mg was significantly depressed at dietary Na concentrations above 15·0 g per kg DM.