The relative importance of the total cell wall and quantity of digested cell wall in the regulation of the voluntary intake of grass hays by sheep

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Abstract
SUMMARY: In 18 digestibility experiments with sheep, 9 diets consisting of single-grass hays and 9 diets each consisting of equal quantities of a good and poor quality hay were fed. Correlations between the voluntary intake of organic matter, digested organic matter, total cell wall and digested cell wall in all possible combinations were investigated. There were no significant differences among the simple correlation coefficients for hays fed singly or as mixtures, even though they were eaten in very different amounts. The simple pooled correlationswere significant (P < 0·01) among voluntary intake, digested organic matter and cell wall. The cell wall was significantly correlated with digested cell wall, but there was no simple correlation between voluntary intake and digested cell wall. However, when considered together in a multiple linear model they explained 58% of the variation in voluntary intake compared with 43% explained by the total cell wall alone. The additional variation accounted for by the digested cell wall was significant (P < 0·05).The relative importance of the total cell wall and digested cell wall is discussed in relation to selection in grass breeding.