Latest research sheds new light on the cause of production losses in lambs infected with parasites but leaves farmers with another choice to make when selecting animals.
Andrew Greer, from the Agricultural and Life Sciences Division at Lincoln University, has been studying the metabolic and productive costs of immunity to gastro-intestinal parasites in sheep.
"While it is clear that young animals are adversely affected by parasitic infections it is still unclear exactly why or how this happens," said Mr Greer.
Mr Greer used a group of Coopworth ewe lambs and hoggets to investigate the costs and benefits of the immune response in sheep harbouring gastro-intestinal parasites. There were four treatment groups, with and without both infection and immuno suppression.
After measuring the parasitic load, feed intakes, wool production, bone, muscle and fat and immune response levels, he found that the immuno-suppressed animals suffered no ill-effects from a parasite infection, despite harbouring a much larger parasite burden than their immunologically normal controls.
"This means that the typical reduction of feed intake and subsequent production losses (reduced live weight gains and reduced efficiency of nutrient utilisation) suffered by lambs appear to be caused by the lambs own developing immune response rather than, as conventionally assumed, the physical damage caused by the parasite," said Mr Greer.
"This information provides direct evidence that the immune response is the primary cause of production losses associated with infection in young lambs, and so it raises questions about the benefit of selecting animals that are genetically predisposed to mount a stronger immune reaction".
"This is because selecting a sheep with a strong immune response may also mean that they are more likely to have a larger negative response to a parasitic infection, consequently, diverting nutrients away from productive functions".
"Farmers should, therefore exercise caution when considering the weightings to be placed on disease traits relative to production traits, as a strong emphasis on disease may mask lower producing individuals".
Mr Greer is a Teaching Fellow at Lincoln University and is studying for a PhD in animal nutrition.
When he presented his results recently at the New Zealand Society of Animal Production Conference held at Lincoln University the calibre of his presentation resulted in him winning the Young Presenter's Award.
All experimental work was carried out with approval from the Animal Ethics Committee.
FOR FURTHER INFORMATION CONTACT
Janette Busch, Technical Writer
Lincoln University, Canterbury
Tel: 64 3 325 3838 ext 8114
Email: Janette Busch