Submitted to: American Society of Animal Science Southern Section Meeting
Publication Type: Abstract Only
Publication Acceptance Date: November 16, 2001
Publication Date: February 1, 2002
Citation: BURKE, J.M. 2002. ARE DORPER CROSSBRED WEANED LAMBS AS TOLERANT TO INTESTINAL PARASITES AS ST. CROIX OR KATAHDIN LAMBS IN THE SOUTHEASTERN UNITED STATES? AMERICAN SOCIETY OF ANIMAL SCIENCE SOUTHERN SECTION MEETING. 80(Suppl. 2):32. Technical Abstract: A study was conducted to evaluate tolerance to natural parasite infection over a 60 d period in Dorper crossbred (DO; Dorper x Romanov x St. Croix or 3/4 Dorper x 1/4 Romanov; n = 17) or St. Croix (SC; n = 17) lambs born in October 2000. Ewe and wether lambs were weaned at 60 days of age and treated with anthelmintic at that time. Fecal egg counts (FEC) were determined at weaning, 28 and 56 d later and packed cell volume (PCV) was determined at weaning and every 14 d until day 56. In a second study, natural parasite infection was evaluated among DO (7/8 or 3/4 Dorper; n = 24), Katahdin (KA; n = 26), SC (n = 8), and Suffolk (SU; n = 10; wethers only) ewe and wether lambs born in February and March 2001 from weaning (60 d of age; April) to approximately 190 days of age (August). Lambs were treated with anthelmintic if PCV declined below 20 or breed average FEC rose above 1000 eggs/g. Treatment for all breeds occurred in early and late June (first anthelmintic was ineffective). In both studies, lambs grazed bermudagrass overseeded with ryegrass, which previously had been exposed to infected sheep, and were supplemented with 225 to 500 g corn/soybean meal supplement. In the first study, FEC and PCV were similar between DO and SC lambs. In the second study, on the other hand, FEC were greatest and PCV least in DO lambs when most challenged (after \ineffective anthelmintic treatment) compared with other breeds (breed x time, P < 0.001). After anthelmintic treatment, PCV was lowest in SU lambs (breed x time, P < 0.001). With a moderate biological challenge, parasite tolerance was similar among the three hair breeds examined and greater in hair than wool breed lambs. When the challenge escalated, the Dorper crossbred lambs were less tolerant than the other breeds.