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RECENT RESEARCH by a group of scientists, Dr Paul (Long) Cheng, Chris Logan, Professor Grant Edwards and Dr Huitong Zhou, from the Faculty of Agriculture and Life Sciences at Lincoln University, is helping to unravel a long-standing puzzle in the farming world.
"Traditional wisdom among farmers is that sheep with the genetic potential to grow faster will be more efficient at converting their feed into weight gain (known as higher feed conversion efficiency) than sheep without this genetic potential," said Dr Cheng, the lead researcher.
"Work in this field has, however, been restricted by the inability to make accurate measurements of the intake of individual animals."
Dr Cheng discovered to his surprise, after analysing the results of measurements taken during the trial, that the expectation that sheep with the potential to grow faster would be more efficient was only true when the sheep were well feed (170% of maintenance metabolisable energy requirement, in this case).
For this trial, two groups of 14 Coopworth sheep from Ashley Dene, a Lincoln University dry land farm were selected. Dr Cheng chose the groups based on Sheep Improvement LTD (SIL) data taken from farm records – one group from a non-improved strain from the 1990s with low genetic growth potential (with an average of 124 in the SIL Dual Purpose Overall Index for growth), and the
other from an improved strain with high genetic growth potential (with an average of 1711 in the SIL Dual Purpose Overall Index for growth).
Dr Cheng further divided each group into two feed allowance groups (170% and 110% of maintenance metabolisable energy requirements) balanced for live weight and age for the five-week trial.
All sheep were fed on commercially purchased lucerne pellets. Regular measurements were taken throughout the trial, including individual sheep live weight and daily intake.
Dr Cheng found that at the low feed allowance level (110% of maintenance metabolisable energy requirement), the sheep with low genetic growth potential actually performed better compared with the high genetic growth potential sheep, with 49% and 71% higher average daily gain (ADG) and feed conversion efficiency, respectively.
"This may be due to the higher maintenance requirement of high genetic growth potential sheep with larger organs, as previously found in high producing dairy cows," said Dr Cheng.
In addition, Dr Cheng used this dataset to validate his newly developed stable nitrogen isotope technique to indicate feed conversion efficiency. He took weekly blood samples from each sheep and also sampled the mid-side wool of each sheep at the end of the trial. It came out with a very promising relationship, that both stable nitrogen isotope concentration in blood and wool provided a good indication of the feed conversion efficiency of the individual sheep.
Dr Cheng believes this may be developed in the future as a cost-effective way of assessing larger numbers of sheep. "It has been very satisfying to be able to expand on the research I did for my PhD studies and apply it to another common farming system," said Dr Cheng
Dr Cheng will continue to use this newly developed isotope technique to further his postdoctoral research in the use of plantain and chicory for heifer production, which is funded by AGMARDT, New Zealand.
By Janette Busch, Lincoln University
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