Response to Teladorsagia circumcincta infection in Scottish Blackface lambs with divergent phenotypes for nematode resistance

Abstract

The objective of this study was to identify Scottish Blackface lambs that were at the extremes of the spectrum of resistance to gastrointestinal nematodes and characterise their response to an experimental nematode challenge. Lambs (n = 90) were monitored for faecal egg count (FEC) (2 samples from each of 2 independent natural infections). The most resistant (n = 10) and susceptible (n = 10) individuals were selected and challenged with 30,000 Teladorsagia circumcincta larvae (L3) at 9 months of age. Response to infection was monitored by measuring FEC, plasma pepsinogen, serum antibodies against nematode larval antigens and haematology profile, until necropsy at 71 days post infection. Worm burden, worm fecundity and the level of anti-nematode antibodies in abomasal mucosa were determined at necropsy.FEC was consistently higher in susceptible animals (P < 0.05), validating the selection method. Worm fecundity was significantly reduced in resistant animals (P = 0.03). There was also a significant correlation (r = 0.88; P < 0.001) between the number of adult worms and FEC at slaughter. There was no effect of phenotype (resistance/susceptibility) on plasma pepsinogen or on haematology profile.Phenotype had a significant effect on the level of anti-nematode IgA antibodies in serum (P < 0.01), reflecting a higher peak in resistant animals at day 7 post infection.It is concluded that significant variation in the response to gastrointestinal nematode challenge exists within the Scottish Blackface population with resistant animals displaying significantly lower FEC, lower worm fecundity and higher concentration of anti-nematode IgA antibodies in serum.-4 -

Transcriptional profiling of the ovine abomasal lymph node reveals a role for timing of the immune response in gastrointestinal nematode resistance

“…This was expected, as resistance in this flock primarily manifests as reduced worm fecundity in resistant individuals, although worm burden may also be a contributing factor (McRae et al, 2014). In total, 75% of worms recovered from the abomasum of HighFEC lambs had developed to the L5 stage by 14 dpi with the remainder at L4.…”

“…2A). This selection method has previously been demonstrated to reliably identify resistant and susceptible individuals (McRae et al, 2014) and the difference in selection differential between High and LowFEC lambs was 3.18 standard deviation units.…”

“…Worm burden, female worm length, haematology variables and anti-nematode antibody level in both serum and abomasal mucosa were determined from samples taken at slaughter, as previously described (McRae et al, 2014). As all worms recovered at 7 dpi were immature and could not be sexed, worm length was measured at 14 dpi only.…”

“…However, the genes and pathways involved in regulating worm fecundity may differ from those involved in controlling worm burden. We previously described a method to reliably identify repeatable within-breed variation in the ability of Scottish Blackface lambs to resist GIN infection (McRae et al, 2014). Resistant lambs were found to display lower FEC, lower worm fecundity and a higher level of anti-nematode IgA in both serum and mucosa.…”

“…In this breed, repeatable differences among individuals in FEC, were positively associated with both increased worm burden and increased worm fecundity (McRae et al, 2014;Stear et al, 1995). Differentially expressed (DE) genes were considered candidate genes for mediating resistance and markers in these genes were tested for association with FEC in a larger Scottish Blackface cohort.…”