Methods of estimating the digestibility and voluntary intake of range forage consumed by grazing cattle
Dissertation Abstracts B, The Sciences and Engineering 27: 1680-1681
ISSN/ISBN: 0420-073X Accession: 014560460
In conventional digestion studies with cattle in which chromic oxide paper, Lucite particles or Delrin particles were used to estimate the total output of faeces, chromic oxide paper and Delrin particles were recovered quantitatively but were found to be unreliable. In grazing studies with cattle carrying oesophageal fistulae chromic oxide paper gave low recovery of faeces because of incomplete collection of faeces. Sampling of faeces from the ground was impractical. Reliable estimates of output of faeces were made with chromic oxide paper and rectal faeces samples.When samples of both intake and output were obtained from the cattle with oesophageal fistulae and digestibility estimated from lignin ratio the coefficient of variation in digestible dry matter among animals within trials was +or- 64% in one year and +or-15.8% in the next. The coefficient of variation for voluntary intake per unit metabolic weight among animals within trials was +or-12.2% with chromic oxide and lignin ratio. With collection bags for faeces the variation was 15.7%. Prediction of digestible energy of the forage grazed was made from the lignin content of the diet with a predicted mean variation of about +or-10%. Estimation of digestibility of N was impractical but the coefficient of variation of N content of the diet among animals within trials was +or- 61% in one year and 48% in the next. N content of the diet was higher with greater rainfall but digestible energy was higher with lower rainfall. Voluntary intake was closely correlated with dry matter content of the forage. It is considered that excretion: digestibility ratio could be used to estimate digestibility and voluntary intake of range forage eaten by grazing cattle if the correct techniques were followed.