Effects of lucerne supplementation and defaunation on feed intake, digestibility, N retention and productivity of sheep fed straw based diets

Abstract

The effects of a lucerne supplement and defaunation on feed intake, digestibility and N retention were studied in cannulated wethers given either an ammoniated wheat straw or an untreated wheat straw diet. Supplementation of the wheat straw diets with lucerne chaff (150 g day −1) significantly increased total dry matter (DM) intake from 520 to 715 g day −1 (untreated wheat straw) and from 615 to 815 g day −1 (ammoniated wheat straw). Intake of wheat straw was not significantly altered by the lucerne supplement. Defaunation of the wethers had no significant effect on feed intake. The rumen digestibility of untreated straw and ammoniated straw were measured using the nylon bag technique. Lucerne supplementation significantly increased the digestibility (% DM disappearance after 24 h incubation) of untreated wheat straw from 26 to 31% and ammoniated wheat straw from 39 to 43%. When defaunation was combined with lucerne supplementation the digestibility of untreated wheat straw increased from 26 to 33% and ammoniated wheat straw increased from 39 to 50%, indicating that the effects of these two treatments were additive. Lucerne supplementation significantly increased N retention in wethers fed either the untreated wheat straw diet or the ammoniated wheat straw diet and defaunation significantly increased N retention in the animals fed the wheat straw diet. In a second study, 64 crossbred lambs (32 faunated and 32 defaunated) were offered one of four dietary treatments. The dietary treatments were either wheat straw or ammoniated wheat straw supplemented with two levels of lucerne (0 and 150 g day −1). Daily feed intake, liveweight gain and wool production were measured over a 70 day period. Daily liveweight gain was significantly increased by lucerne supplementation ( P<0.01) and ammoniation of straw ( P<0.01) while the effects of defaunation were not statistically significant. Wool production was significantly increased by defaunation ( P<0.01), lucerne supplementation ( P<0.01) and ammoniation of straw ( P<0.01). A combination of these three treatments increased wool production by 2.51 g clean wool day −1.