This summary has been extracted from the application. A copy of the student’s Abstract/Thesis has not been received.
This project is part of a larger AWI funded project (Genetic Evaluation: Productivity, Efficiency and profitability (GEPEP) that uses wethers from the Merino Lifetime Productivity (MLP) examining the lifetime production and reproduction of Merino sheep from a range of industry sires.
The profitability of Merino sheep enterprises is largely determined by stocking rate and the amount of wool and surplus sheep produced per hectare, rather than the productivity of individual animals such as clean fleece weight and growth rate or liveweight (Blackshaw and Ough 2016). Despite this, there is a strong emphasis on increasing fleece weight and liveweight in most Merino sheep breeding objectives including several standard industry indexes in Australia (Brown and Swan 2016). This results in a disconnect between increasing per head production and profitability of Merino based enterprises per hectare. The “Selection in a Resource Limiting Environment” project (RLE) shows that optimum stocking rate and level of grain feeding has a tight relationship with change in whole body energy stores and feed intake. The profit equations developed by RLE quantify these differences in optimum stocking rate and level of grain feeding based on feed intake and differences in body energy stores. Therefore, having measurements of body composition (lean and fat) could greatly improve the estimation of a sheep’s potential profit per hectare.
The selection of sheep on a per head production basis has inadvertently led to increased inter genotype variation in the size and shape of progeny, and may explain some of the potential intake and fatness differences that are observed between genotypes. Currently, measurement of body composition requires the use of DEXA scanning which is not commercially applicable and the use of condition scoring can only predict the ~55-60% of body composition. Therefore, the aim of the current project is to develop the use of frame size measurements in sheep for use in combination with condition scoring to enhance the accuracy of on-farm prediction of body composition.
Adult Merino wethers (n=320; 2017 drop), the progeny of 15 industry sires, from the existing MLP project at Ridgefield, Pingelly, WA will be allocated to one of 10 blocks, balanced for sire, feeding group, condition score and liveweight and allocated to individual pens at Katanning Research Facility. Following a 10-day acclimation period, wethers will be fed at 100% of maintenance during the first 35-day period followed by either ad libitum or 60% of maintenance for 35 days. On day 0, 35 and 70 wethers will be weighed, and condition scored, before being scanned using dual X-ray absorptiometry (DEXA) for assessment of body composition. Whole body energy was derived by valuing tissue components as follows: whole body energy (MJ) = (Kg fat x 35.9 MJ) + (Kg lean x 5.31MJ). Frame size will also be calculated at these timepoints by measuring the following body dimensions: shoulder height, chest circumference, length of back and pelvic width, both manually and by collecting a photographic image as they walk through a crate. These measurements will provide data that can create a wether body size profile (similar to BMI in humans) which, in combination with condition score, will be used to develop on- farm predictions of body composition.