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

Abstract

Six 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 70 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 signifi-

Effect of varying sodium and potassium intakes on sodium, potassium, and magnesium contents of the ruminoreticulum and apparent absorption of magnesium in non-lactating dairy cattle

“…In this study, increasing the Na intakes, particularly at the high K intake, decreased the apparent absorption of Mg whereas in sheep increased Na intakes increased the apparent Mg absorption (Moseley & Jones 1974;Moseley 1980). However, as the urinary Mg excretion increased with Na intake, the overall apparent Mg retention was decreased (Moseley 1980).…”

“…In this study, increasing the Na intakes, particularly at the high K intake, decreased the apparent absorption of Mg whereas in sheep increased Na intakes increased the apparent Mg absorption (Moseley & Jones 1974;Moseley 1980). However, as the urinary Mg excretion increased with Na intake, the overall apparent Mg retention was decreased (Moseley 1980). A decrease in the plasma Mg levels has been observed in both cows and sheep (Moseley 1980) fed indoors as well as in grazing beef cattle on high K pasture recently topdressed with 100-200 kg NaCI/ha (Smith et al 1983).…”

“…The influences of K on the absorption ofMg and plasma Mg levels in ruminants has been well documented (Fontenot et al 1960;Suttle & Field 1967;Thomas and Potter 1976) whereas those ofNa have not (Moseley 1980). The K did not alter the concentration of the absorbable Mg associated with a low molecular weight fraction (Fig.…”

“…However, as the urinary Mg excretion increased with Na intake, the overall apparent Mg retention was decreased (Moseley 1980). A decrease in the plasma Mg levels has been observed in both cows and sheep (Moseley 1980) fed indoors as well as in grazing beef cattle on high K pasture recently topdressed with 100-200 kg NaCI/ha (Smith et al 1983). The extent of the effect of the increased Na intake, like the Kintake, on plasma Mg concentrations will depend upon the Mg status of the animals (Suttle & Field 1967, 1969.…”

“…In other studies, with sheep, it has been reported that increased Na intakes led to increased urinary excretion of Mg and decreased its apparent retention and concentration in plasma (Moseley 1980). Likewise, decreases in the blood Mg levels have been observed in grazing beef cattle when the pasture eaten was topdressed with NaCI (Smith et al' 1983).…”