Chicken production has increased over the past decade, resulting in a concomitant rise in the demand for more humane options for poultry products including cage-free, free-range, and organic meat and eggs. These husbandry changes, however, have come hand-in-hand with increased prevalence of Ascaridia galli infection, which can cause clinical disease in chickens as well as the occasional appearance of worms in eggs. Additionally, development of anthelmintic resistance in closely related helminths of turkeys highlights the need for closely monitored anthelmintic treatment programs. Manual faecal egg counts (FECs) can be time-consuming and require specialist training. As such, this study sought to validate an automated FEC system for use in detection and quantification of A. galli eggs in chicken faeces. Automated counts using the Parasight System (PS) were compared to traditional manual McMaster counting for both precision and correlation between methods. Overall, ten repeated counts were performed on twenty individual samples for a total of 200 counts performed for each method. A strong, statistically significant correlation was found between methods (R2 = 0.7879, P < 0.0001), and PS counted more eggs and performed with statistically significant higher precision (P = 0.0391) than manual McMaster counting. This study suggests that PS is a good alternative method for performing A. galli FECs and provides a new tool for use in helminth treatment and control programs in chicken operations.

The inadequacy of current diagnostics for the detection of low worm burdens in humans means that schistosomiasis mansoni is more widespread than previously acknowledged. With the inception of mass drug treatment programmes aimed at disease elimination and the advent of human vaccine trials, the need for more sensitive diagnostics is evident. In this review, we evaluate the merits and limitations of the principal diagnostic methods, namely detection of eggs in faeces; anti-schistosome antibodies in serum; parasite-derived proteins and glycans in serum or urine; parasite DNA in blood, faeces or urine. Only in the baboon model, where actual worm burden is determined by portal perfusion, have faecal smear and circulating antigen methods been calibrated, and shown to have thresholds of detection of 10–19 worm pairs. There is scope for improvement in all the four methods of detection, e.g. the identification of single targets for host antibodies to improve the specificity of enzyme linked immunosorbent assay. Despite recent advances in the definition of the schistosome secretome, there have been no comprehensive biomarker investigations of parasite products in the urine of infected patients. Certainly, the admirable goal of eliminating schistosomiasis will not be achieved unless individuals with low worm burdens can be diagnosed.

An experiment was conducted to determine: (1) the effect of excess maternal I supplementation on the thyroid hormone status of the ewe and her progeny; (2) potential mechanisms underpinning the failure of passive transfer associated with excess I and (3) the growing lambs’ response to natural gastrointestinal infection. Twin-bearing ewes received one of two treatments (n 32/treatment group): basal diet (C) or C plus 26·6 mg of iodine/ewe per d (I), supplied as calcium iodate. Ewes were individually fed from day 119 of gestation to parturition. Progeny of I ewes had lower (P<0·01) serum IgG concentrations from 24 h to 28 d postpartum but higher serum IgG concentrations at day 70 postpartum (P<0·05). I supplementation increased the relative expression of Fc receptor, IgA, IgM high affinity and polymeric Ig receptor in the ileum of the lamb at 24 h postpartum; however, thyroid hormone receptor-β (THRB) and β-2-microglobulin (B2M) expression declined (P<0·05). Progeny of I ewes had higher growth rates to weaning (P<0·05) and lower faecal egg count (FEC) for Nematodirus battus (P<0·05) between weeks 6 and 10 postpartum. In conclusion, excess maternal I supplementation negatively affected the thyroid hormone status, serum IgG concentration, ileal morphology and the gene expression of THRB and B2M in the ileum and ras-related protein (RAB) RAB25 and the mucin gene (MUC) MUC1 in the duodenum of the lamb postpartum. These effects were followed by an enhancement of average daily gain and lower N. battus FEC in the pre-weaning period of I-supplemented lambs.

Acquired immunity influences the severity of parasitic disease, but modelling the effects of acquired immunity in helminth infections has proved challenging. This may be due to a lack of suitable immunological data, or to the perceived complexity of modelling the immune response. We have developed a model of T. circumcincta infection in domestic sheep that incorporates the effects of acquired immunity on parasite establishment and fecundity. A large data set from commercially managed populations of Scottish Blackface sheep was used, which included relationships between IgA activity and worm length, and between worm length and fecundity. Use was also made of a recently published meta-analysis of parasite establishment rates. This realistic but simple model of nematode infection emulates observed patterns of faecal egg counts. The end-of-season faecal egg counts are remarkably robust to perturbations in the majority of the parameters, possibly because of priming of the immune system early in the season, reducing parasite establishment and growth and, therefore, faecal egg counts. Lowering the amount of early infection leads to higher end-of-season egg counts. The periparturient rise in egg counts in ewes appears to have an important role in supplying infection for the priming of the immune response. This feedback in the immune priming suggests that nematode infections may be difficult to eliminate.

The periparturient relaxation of immunity (PPRI) to parasites in mammals is sensitive to both metabolisable protein (MP) supply and animal genotype (different reproductive outputs). We tested the hypothesis that the sensitivity of PPRI to MP scarcity would not differ between different levels of reproductive output when nutrient intake is adjusted for associated differences in MP demand; this hypothesis assumes that PPRI has a nutritional basis only. Scottish Blackface (BF) and the more productive Mule (MU) ewes were infected with the abomasal parasite Teladorsagia circumcincta, and from day− 21 to day32 (day0 is parturition), they were fed restrictedly at either 0·8 (low protein (LP)) or 1·3 (high protein (HP)) times their breed-specific estimated MP requirement (n 18 for each breed–feeding treatment combination). During late pregnancy, LP feeding reduced ewe body weight gain in both breeds, tended to increase faecal egg count (FEC), but it did not affect plasma pepsinogen. During lactation, LP feeding reduced litter growth rate and ewe plasma urea and plasma albumin concentrations compared with HP feeding in both breeds. However, breed and feeding treatment interacted for ewe FEC, worm egg excretion and plasma pepsinogen, which were higher for the LP-MU ewes compared with the HP-MU and BF ewes. The lower degree of PPRI of the BF ewes during lactation compared with the MU ewes at a similar degree of MP scarcity suggests that the effect of reproductive output on nutritional sensitivity of PPRI cannot be explained by associated differences in nutrient demand only.

Understanding the frequency distribution of parasites and parasite stages among hosts is essential for efficient experimental design and statistical analysis, and is also required for the development of sustainable methods of controlling infection. Nematodirus battus is one of the most important organisms that infect sheep but the distribution of parasites among hosts is unknown. An initial analysis indicated a high frequency of animals without N. battus and with zero egg counts, suggesting the possibility of a zero-inflated distribution. We developed a Bayesian analysis using Markov chain Monte Carlo methods to estimate the parameters of the zero-inflated negative binomial distribution. The analysis of 3000 simulated data sets indicated that this method out-performed the maximum likelihood procedure. Application of this technique to faecal egg counts from lambs in a commercial upland flock indicated that N. battus counts were indeed zero-inflated. Estimating the extent of zero-inflation is important for effective statistical analysis and for the accurate identification of genetically resistant animals.

A potential control strategy for nematode infection in sheep is the implementation of a breeding programme to select for genes associated with resistance. The Texel breed is more resistant to gastrointestinal nematode infection than the Suffolk breed, based on faecal egg count, and this difference should enable the identification of some of the genes responsible for resistance. The objective of this study was to determine if variation at the ovine MHC-DRB1 locus was associated with variation in faecal egg count in Suffolk and Texel sheep. Ovar-DRB1 alleles and faecal egg count were determined for Texel (n=105) and Suffolk (n=71) lambs. Eight Ovar-DRB1 alleles, including 1 previously unknown allele, were identified in the Texel breed by sequence-base-typing. Seven Ovar-DRB1 alleles were identified in the Suffolk breed. Two Ovar-DRB1 alleles were common to both breeds, but were among the least frequent in the Suffolk population. In the Suffolk breed 1 Ovar-DRB1 allele was associated with a decrease in faecal egg count and 2 alleles with an increase in faecal egg count. This locus accounted for 14% of the natural variation in faecal egg count in Suffolks. There was no evidence for an association between Ovar-DRB1 alleles and faecal egg count in the Texel breed and the Ovar-DRB1 locus accounted for only 3% of the phenotypic variation in faecal egg count. These results suggest that the Ovar-DRB1 gene plays an important role in resistance to nematode infection in the Suffolk breed. The difference in faecal egg counts between these breeds may be attributable in part to the different allele profile at the Ovar-DRB1 locus.

In several countries the gastro-intestinal parasites of sheep show evidence of resistance to the commonly used anthelmintic treatments. The use of animals with genetic resistance to such parasites has been shown to be a viable alternative in a number of resource flocks. However, the genetics of host resistance to parasites in industry flocks and the effects on production traits of using resistant sheep is relatively unknown. This study addresses these questions using data from 55 commercial Merino flocks in Australia. The heritability and genetic correlations were estimated for faecal egg count (FEC), an indicator of host resistance, and eleven fleece and body production traits. The heritability of FEC (0·26 (s.e. 0·018)), using a sire model, was found to be similar to other estimates reported in the literature from resource flocks. The heritabilities of production traits were also consistent with published reports from resource flocks. The genetic correlations between FEC and the 11 production traits, calculated using a sire model, were mostly zero, except for staple strength (-0·17 (s.e. 0·096)), fat depth (-0·26 (s.e. 0·088)) and eye-muscle depth (-0·18 (s.e. 0·091)). Animal model estimates of heritability and the genetic correlations between the traits were largely similar to the sire model estimates. Correlated responses to selection for reduced FEC based on the sire model genetic parameters were calculated to be less than 0·15% of the trait mean per generation for all traits except staple strength, fat depth, muscle depth and live weight. These were expected to increase slightly under selection for reduced FEC. Thus industry-based selection programmes to increase host resistance to parasites should be effective and have no detrimental effect on production characteristics of Merino sheep in Australia. The full benefit of such industry-based schemes could be improved by a better level of recording in the flocks studied.

Genetic analyses were carried out on Nematodirus spp. egg counts (NEM) of lambs from a set of Romney breeding lines. The lines had been under selection for 22 seasons (1979 to 2000) for divergence in resistance to infection by strongyle nematodes other than NEM, using faecal egg count (FEC) as the selection criterion. Heritabilities and genetic correlations for NEM were estimated using residual maximum likelihood procedures. Correlated responses in NEM were also determined. Heritability estimates for loge(NEM + 100) in lambs at 4 months of age (NEM1) or 6 months of age (NEM2) were 0·15 (s.e. 0·03) and 0·26 (s.e. 0·04) respectively (c.f. 0·28 (s.e. 0·02) and 0·35 (s.e. 0·02) for loge(FEC + 100)). The genetic correlation between loge(NEM1 + 100) and loge(NEM2 + 100) was 0·85 (s.e. 0·08), while the genetic correlations between measurements of loge(NEM + 100) and loge(FEC + 100) on both sampling occasions had a weighted average of 0·43, with estimates ranging from 0·30 (s.e. 0·08) to 0·52 (s.e. 0·07). Divergence in loge(NEM + 100) between the high and low FEC lines, estimated over both sampling times combined, was 1·07 phenotypic standard deviations, compared with 3·6 phenotypic standard deviations for loge(FEC + 100). Expressed in terms of back-transformed eggs per g, the high and low FEC lines differed by factors of 7·6 and 32·2 for NEM and FEC, respectively. The results support earlier parasitological data indicating that the genetic mechanisms in sheep which are responsible for resistance to other strongyle nematodes probably also influence resistance to Nematodirus infection.

Faecal nematode egg counts (FECs) were examined in lactating ewes from divergent flocks of Romney sheep which had been selectively bred from 1979 to 1996 for or against FEC in 4 to 7 month old lambs. Faecal samples were obtained from the ewes while under normal grazing management, 1 to 2 months after lambing in spring for each of 6 years between 1987 and 1996 (no. = 785 records; 298 animals). Analyses were carried out on loge (FEC + 100)–transformed data using animal-model maximum likelihood procedures, accounting for repeated records on ewes, within and between lactations. An examination of non-genetic effects indicated that there was no significant effect of age class of ewe on FEC but ewes which gave birth to single lambs had significantly lower post-parturient FECs than those bearing twins (back-transformed means of 184 v. 276 egg per g, respectively; P < 0·001). In relation to genetic effects, post-parturient FECs were significantly lower in ewes from the flock bred for low lamb-FEC than in their counterparts from the flock bred for high lamb-FEC, with ewes from the most recent birth years (1991 to 1994) showing a nine-fold difference (back-transformed means of 33 and 305 eggs per g faeces respectively; P < 0·001). This was equivalent to 69% of the divergence observed between loge (FEC + 100) in their lambs in the same years. Heritability and repeatability estimates for loge (FEC + 100) in ewes were 0·37 (s.e. 0·06) and 0·46 (s.e. 0·03) respectively. Genetic correlation estimates between a ewe's post-parturient loge (FEC + 200) and her loge (FEC + 100) as a lamb, based on analysis of (co)variance or realized responses, were 0·70 or 0·58 respectively. The phenotypic correlation between a ewe's loge (FEC + 100) and that of her lamb(s) in the same lactation was 0·29 (s.e. 0·06) (P < 0·001). From the results it is clear that substantial genetic changes in post-parturient FECs of breeding ewes can be induced through a correlated response to selective breeding for or against reduced FEC in lambs. This may have important implications for the epidemiology of nematode parasite infections in spring-born lambs, a possibility which is currently being investigated.