Regulation of egg production, worm burden, worm length and worm fecundity by host responses in sheep infected with Ostertagia circumcincta

Abstract

Following infection with Ostertagia circumcincta there was considerable variation in worm burdens, worm size and number of inhibited larvae even among sheep matched for age, sex, breed, farm of origin and history of parasite exposure. There was also substantial variation among sheep in the concentration of mast cells, globule leucocytes, eosinophils, IgA-positive plasma cells and parasite-specific IgA in the abomasal mucosa. With the exception of faecal egg counts over time, the parasitological and immunological traits were all continually distributed among animals and sheep did not fall into discrete high and low-responder categories. The responses were correlated. Sheep with more mast cells also had more globule leucocytes, more eosinophils, more IgA plasma cells and greater amounts of parasite-specific IgA in the abomasal mucosa. Female worm length was strongly and positively correlated with the number of eggs in utero. Faecal egg counts were associated with variation in worm number and with variation in the number of eggs in utero. The worm burden was negatively correlated with the number of globule leucocytes in the abomasal mucosa, suggesting that worm numbers are regulated by immediate hypersensitivity reactions. Decreased female worm length was associated with an increased local IgA response to fourth stage larvae. The number of inhibited larvae was positively associated with the size of the local IgA response and positively associated with the size of the worm burden. The results suggest that variation among mature sheep in faecal egg counts is due, at least in part, to variation in local IgA responses which regulate worm fecundity and to variation in local immediate hypersensitivity reactions which regulate worm burdens.

Markers/parameters for the evaluation of natural resistance status of small ruminants against gastrointestinal nematodes

“…Among phenotypic parameters, FEC is the most reliable, practical and frequently used indicator to assess the host resistance/tolerance potential against GINs in natural infection (Gray, 1991;Woolaston, 1992;Kemper et al, 2009). In lambs, it is well documented that FEC is highly correlated with worm counts (McKenna, 1981;Eady, 1995;Stear et al, 1995;Douch et al, 1996;Woolaston and Baker, 1996;Good et al, 2006), particularly when infections are of Haemonchus (H.) contortus and Trichostrongylus (T.) colubriformis. Selection based on low FEC has satisfactory upshots as GINs will not adapt quickly to sheep bred for nematode resistance (Kemper et al, 2009).…”

“…Lambs have a capability to control worm length but not worm number. Resistance to H. contortus has been linked to the lengthening of prepatent periods, lower FEC, lower parasite establishment rate, lower adult worm burden and increase in larval inhibition in the abomasal mucosa (Altaif and Dargie, 1978;Stear et al, 1995). found a curvilinear relation between worm length and fecundity in Tel.…”

“…Resistance is the ability to suppress the establishment or the growth of worm infection while resilience is the capability of an animal to maintain acceptable health/performance under worm challenge mainly blood-sucking parasites like H. contortus (Albers et al, 1987). It has been found in many studies that FEC is highly correlated with the worm burden (McKenna, 1981;Eady, 1995;Stear et al, 1995). If the differences between breeds or individuals in FEC are ambiguous then worm count could be a powerful aid to assess host genetic resistance to H. contortus.…”

“…Sheep with increased numbers of mucosal mast cells had more globule leucocytes, eosinophils and IgA plasma cells against Teladorsagia (Tel.) circumcincta larval antigens (Stear et al, 1995). Live weight and worm burden are other imperative parameters for evaluating the resilience and resistance status, respectively (Woolaston and Baker, 1996;Burke and Miller, 2004), but live weight may vary depending on the breed.…”

Protein supply influences the nutritional penalty associated with the development of immunity in lambs infected with Trichostrongylus colubriformis

“…The worm burdens at slaughter and pattern of total daily egg excretion (Figure 2), however, confirmed that the ability to limit worm population and its fecundity was indeed compromised by corticosteroid treatment. In view of the putative role of IgA in the regulation and expulsion of nematodes (Stear et al, 1995) and the negative relationship between rise in serum IgA and VFI observed by Greer et al (2005b), the serum IgA responses of these sheep were Table 3 Mean and standard deviation (s.d.) of the absorbance (optical density (OD)) of IgA specific to L3 T. colubriformis antigen in serum collected from lambs during day 49 to day 77 of infection with 2000 L3 T. colubriformis larvae/day and mean worm burden for animals offered high protein (H) and low protein (L) diets according to initial immuno-suppressed (ISIF) or non-suppressed (IF) treatments and re-classified groups termed L3 IgA responders (R) and non-responders (N) (changes in liveweight gain, carcass composition estimated by computed tomography and the effect on gross efficiency of metabolizable energy (ME) utilization for net energy (NE) deposition for the reclassified groups are also given -) Protein influences ME utilization in parasitized lambs carefully examined.…”