Parasite Resistance in Straightbred and Crossbred Barbados Blackbelly Sheep

Publisher Website
Google Scholar
Abstract
Resistance to gastrointestinal parasites was studied in a total of 193 sheep with widely different points of origin and genetic backgrounds. Breed groups compared were Dorset (D), Barbados Blackbelly (B) and Dorset × Blackbelly (D × B), Dorset × Landrace (D × L) and Rambouillet × Landrace (R × L) crosses. In Exp. I, the sheep were carrying mixed infections of parasites, and D × B sheep had lower (P<.05) total fecal egg counts (EPG, eggs/g feces) than the D, D × L and R × L groups. Breed differences were not related to ewe hemoglobin type, but were primarily the result of significantly lower egg production by CTO parasites {Cooperia spp, Trichostrongylus spp, Ostertagia spp) in D × B animals. Fecal egg counts for HO parasites (H. contortus, Oesophagostomum spp) did not vary significantly among breed groups. Differences in Nematodirus spp EPG levels were not consistent among trials. In Exp. II, D × B and D ewe and ram lambs with zero EPG levels were administered standard doses of a mixed infection of larvae and maintained on concrete, and showed that breed differences in eggs per gram of feces were the result of less fecund parasites in the digestive tract of D × B animals. While numbers of parasites recovered from the digestive tract did not vary significantly, egg production per CTO parasite recovered was lower (P<.05) in D × B rams and ewes. Eggs per HO parasite were lower (P<.05) in D × B ewes, but not in D × B rams. Based on significantly lower EPG levels and higher hemoglobin (Hb) and mean corpuscular hemoglobin concentration (MCHC) levels obtained in Exp. Ill, B and D × B ewes were shown to be more resistant to a mixed infection of parasites than D ewes. However, this was not the case when the same ewes were reinfected with a relatively pure culture of H. contortus larvae. While EPG, Hb and usually MCHC levels consistently favored B and D × B sheep, breed differences were not significant. There was no evidence that levels of circulating antibodies were involved in breed resistance. Copyright © 1979. American Society of Animal Science . Copyright 1979 by American Society of Animal Science.

This publication has 1 reference indexed in Scilit: