Interpretive Summary: Genetic parameters for fecal egg counts and their relationship with body weights in Katahdin lambs.
By: Dr. Caitlin Vonderohe
Gastrointestinal parasites are among the most significant health and production challenges facing the global sheep industry. This problem is amplified by an increasing number of parasites that are resistant to anthelmintics, or “de-wormers”. One of the solutions to this problem is to genetically select for sheep that are resistant to gastrointestinal parasites. Ngere et al. explored how Katahdin sheep genetics and body weights correlate with gastrointestinal parasite infection in an article published in the May, 2018 issue of the Journal of Animal Science.
When one genetic trait is selected upon, there is a possibility that other, economically significant traits will be selected against. In this case, if genetically resistant sheep failed to grow as quickly as the genetically susceptible sheep, it would be unlikely that producers would elect to incorporate those genetics into their flocks. Therefore, the authors elected to correlate degree of parasite resistance with birth, weaning and post-weaning body weights in Katahdin lambs.
The authors collected data on 12,869 lambs, from 13 flocks in the eastern United States. All of these flocks were located in areas where animals were likely to encounter the most economically significant gastrointestinal parasite, Haemonchus contortus (the barber pole worm). The degree of parasitic infection was estimated using fecal egg counts. Fecal egg counts were measured using feces collected directly from the rectum at 60 and 120 days of age. Dam age, type of birth and rearing, management group (including flock, age, birth year and season), maternal genetics, sire genetics, body weights and fecal egg counts were included in the statistical analyses.
The heritability estimates derived from the generated statistical models indicate that it is possible to improve Katahdin lamb resistance to gastrointestinal parasites with genetic selection. The authors noted that the estimated heritability of parasite resistance was lower in this study than in previous studies, particularly studies that focused on other sheep breeds. This could be due to a number of differences between studies (this study is much larger and more inclusive than previous studies, which may have affected the statistical models), differences in management among the flocks included in the model, and the ages that the fecal egg counts were measured.
Interestingly, the authors found a high genetic correlation between pre-weaning and weaning fecal egg counts, indicating that the genetic resistance is not affected by increased parasite exposure that is expected when sheep start grazing. The statistical correlations between parasite resistance and body weights showed that these traits are not antagonistic, meaning that selection for parasite resistance should not affect genetic selection for body weight.
The authors conclude that producers can breed for parasite resistance (based on weaning or post weaning fecal egg counts) in Katahdin sheep without adversely affecting body weight of those sheep.
To view the full article " Genetic parameters for fecal egg counts and their relationship with body with body weights in Katahdin lambs," visit the Journal of Animal Science.