Abstract
Research has shown that variation in ovine immunoglobulin A (IgA) levels are associated with reduced faecal egg counts (FECs) in sheep hosting gastro-intestinal (GI) parasites. Variation in the constant region of the ovine IgA heavy alpha chain gene (
IGHA) may result in structurally and functionally different IgA molecules and may consequently lead to variation in the IgA response to parasitisation. This study involved three sheep breeds (Merino, Polwarth and Corriedale) and a total of 2098 lambs from eight New Zealand farms that underwent a mixed field-challenge of nematode parasites. Faecal samples were taken at approximately 4 and 9 months of age and FECs for
Nematodirus and Strongyle species determined along with total eggs per gram (EPG). Analysis of all eight farms collectively revealed no significant differences in FECs associated with the presence or absence of a particular
IGHA allele. However, when the data was split into predominant challenge type groups, associations were detected. In 4-month-old lambs predominantly challenged by
Nematodirus sp., the presence of the
IGHA allele *01 was associated (
P
<
0.05) with higher Strongyle FECs. In 9-month-old lambs predominantly challenged by
Trichostrogylus sp., the presence of
IGHA allele *02 was associated (
P
<
0.006) with a higher mean total EPG at 9 months of age. These results suggest that
IGHA gene variation will not be an effective gene-marker for reducing overall FEC but may be useful in defined or specific species challenges.