Sensitivity of the breeding values for growth rate and worm egg count to environmental worm burden in Australian Merino sheep

The objective of this study was to explore the sensitivity of breeding values for growth rate and worm egg count (WEC, cube root transformed) to environmental worm burden, measured as the average WEC for each contemporary group (CGWEC). Growth rate and WEC were measured on 7,818 naturally infected Merino lambs in eight flocks across Australia, linked through common use of AI sires. Through bivariate analysis, genetic correlations of 0.55 ± 0.23 and 0.30 ± 0.16 were found for growth rate and WEC between low and high CGWEC, respectively. In a second analysis, breeding values for growth rate and WEC were regressed on CGWEC with a random regression model. The heritability for growth rate varied from 0.23 to 0.16 from low to high CGWEC, and the heritability for WEC varied from 0.25 to 0.36. Results suggest that breeding values for both growth rate and WEC are sensitive to environmental worm burden. Animals expressed less genetic variation for growth rate and more genetic variation for WEC in high CGWEC than in low CGWEC. This form of genotype‐by‐environment interaction should therefore be considered in genetic evaluation of both growth rate and WEC, to increase the efficiency of selection for animals that are more parasite resistant and more resilient to environmental worm challenge.     

Comparison of in vitro methods and faecal egg count reduction test for the detection of benzimidazole resistance in small strongyles of horses

The objective of the study was to compare the in vitro egg hatch test (EHT), larval development test (LDT) and in vivo faecal egg count reduction test (FECR test) for the detection of benzimidazole resistance in equine strongyles. The presence of resistant or susceptible strongyle populations was determined in 25 stud farms using the in vivo FECR test and in vitro EHT. On the basis of the FECR values, resistance to fenbendazole was detected on 15 of the 25 farms (60%). The ED₅₀ value (anthelmintic concentration producing 50% inhibition of hatching) for suspected resistant populations varied from 0.110 to 0.222 g/ml thiabendazole (TBZ). Final LD₅₀ values (anthelmintic concentration inhibiting development of 50% of eggs into L₃ infective larvae) above 0.029 g/ml TBZ in the in vitro larval development test on samples from 11 stud farms revealed the presence of populations of small strongyles suspected of being benzimidazole-resistant.     

A quantitative trait locus for faecal worm egg and blood eosinophil counts on chromosome 23 in Australian goats

Three microsatellite markers on goat chromosome 23 adjacent to the MHC were used to test for quantitative trait loci (QTL) affecting faecal worm egg count (WEC) and leukocyte traits in ten Australian Angora and twelve Australian Cashmere half‐sib families (n = 16–57 per family). Data were collected from 280 Angora and 347 Cashmere kids over a 3‐ and 4‐year period. A putative QTL affecting trichostrongyle WEC was found in two small families at the 5% chromosome‐wise threshold level. The biggest QTL effect for WEC of 1.65 standard deviations (σ_p) was found within the region of OarCP73‐BM1258. A significant QTL affecting blood eosinophil counts at the 1% chromosome–wise threshold level was detected at marker BM1258 (at 26 cM) in two Angora and Cashmere families. The magnitude of the putative QTL was 0.69 and 0.85 σ_p in Angora and Cashmere families, respectively. Due to the comparatively low power of the study these findings should be viewed as indicative rather than definitive.     

Courses for horses: Rethinking the use of proton pump inhibitors in the treatment of equine gastric ulcer syndrome

Oral omeprazole has been the cornerstone of equine gastric ulcer syndrome (EGUS) treatment for nearly 20 years. However, approximately 15–30% of equine squamous gastric disease (ESGD) cases and 75% of equine glandular gastric disease (EGGD) cases fail to heal within current treatment guidelines. Recently, a number of factors that may affect the efficacy of oral omeprazole have been highlighted and the pharmacodynamics of a number of novel proton pump inhibitors (PPIs) have been described in the horse. The purpose of this article is to review the factors that affect oral omeprazole efficacy, with the goal of maximising therapeutic response, and the novel PPIs recently described.