Prediction of fleece insulation after shearing and its impact on maintenance energy requirements of Romney sheep

Calculation of the maintenance metabolisable energy (ME) requirements should include the additional ME required to counteract heat loss in cold conditions if ambient temperatures occur below the lower critical temperature (LCT) of sheep. This correction requires an estimate of the fleece length of sheep during the year. Equations are presented to estimate the monthly fleece length of Romneys assuming different patterns of seasonality of wool growth, month of shearing and total fleece length. These lengths are discussed in the context of predicted levels of fleece insulation, which in turn influence sheep energy requirements under New Zealand climatic conditions. Predicted fleece insulation varied from 1 to 8 °C m2 d/MJ in different months. The additional maintenance ME requirements of ewes are predicted for each month following shearing for different months of shearing. An example calculation resulted in an estimated additional 30% of ME being required when the average daily ambient temperature in the month of shearing was 5 °C below the LCT.