Studies on the nutritive value of the diet selected by grazing sheep IV. Variation in the diet selected by sheep differing in age, breed, sex, strain and previous history

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Abstract
SUMMARY The ability of two groups of six Merino wethers aged 6 and 66 months to digest a lucerne ration was examined in order to detect possible biases in the use of faecal nitrogen as a faecal index substance. Earlier work with this technique had indicated a difference in selectivity between young and older sheep. No difference in ability to digest the ration was observed and it was concluded that the earlier observation was not an artefact in the faecal nitrogen technique. Oesophageal fistulae were prepared in 120 sheep differing in breed, sex, age, strain and previous history. Determinations were made of the nitrogen content, and in one experiment of the in vitro digestibility of the diet selected by sheep grazing various pastures. Significant differences in the nitrogen content of the diet selected by sheep varying in breed, age and previous grazing history were recorded on some pastures on some occasions but not on others. No significant differences were observed between sheep varying in strain or sex. No reason could be suggested for the occasional differences between groups in the nitrogen content or digestibility of the diet selected, but it appeared unlikely that it would be a major source of variation in the productivity of the different groups at pasture.

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