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Y. Tsukahara, T. A. Gipson, S. P. Hart, L. J. Dawson, Z. Wang, R. Puchala, A. L. Goetsch, 691 Effects of selecting growing male hair sheep of different flocks for internal parasite resistance on performance, Journal of Animal Science, Volume 95, Issue suppl_4, August 2017, Page 337, https://doi.org/10.2527/asasann.2017.691
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Abstract
Katahdin, Dorper, and St. Croix male lambs from farms (2 Katahdin, farms A and B; 1 Dorper; and 1 St. Croix) in the south-central United States were categorized as resistant (RS), moderately resistant (MR), and susceptible (SS) to Haemonchus contortus based on artificial larvae challenge in a central performance test at Langston University over 3 consecutive years. Animal groups consisted of 17, 15, and 15 Katahdin-A (initial age 3.9 mo and 38.8 kg); 18, 7, and 8 Katahdin-B (3.7 mo and 18.9 kg); 20, 15, and 16 Dorper (5.5 mo and 34.2 kg); and 13, 14, and 19 St. Croix (4.2 mo and 19.2 kg) in yr 1, 2, and 3, respectively. Males were randomly selected in yr 1, whereas progeny of RS and MR sires were evaluated in yr 2 and 3. The test entailed 2 wk of adjustment and 8 wk of data collection, with free access to a 15% CP and 50% concentrate diet in automated feeders. During adaptation, anthelmintic treatment resulted in low fecal egg count (FEC; <600 eggs/g), after which 10,000 infective larvae were orally administered. Body weight and packed cell volume (PCV) were measured weekly, and FEC was determined 4 to 5 times in wk 6 to 8. The cubic clustering criterion of SAS was used for resistance categorization, which resulted in 49, 35, and 37 RS; 38, 33, and 39 MR; and 28, 17, and 36 SS in yr 1, 2, and 3, respectively. The statistical model included animal group, resistance classification, year, interactions, and covariates; GENMOD of SAS was used for mean FEC. There were interactions (P < 0.05) in mean FEC between animal group and resistance classification (473, 928, 1,089, and 297 eggs/g for RS; 1,793, 3,058, 2,199, and 1,084 eggs/g for MR; and 4,198, 5,073, 3,164, and 2,176 eggs/g for SS [SEM 144.7]) and between animal group and year (1,573, 2,261, 3,196, and 1,388 eggs/g in yr 1; 2,417, 4,793, 1,932, and 1,006 eggs/g in yr 2; and 2,475, 2,005, 1,325, and 1,163 eggs/g in yr 3 for Katahdin-A, Katahdin-B, Dorper, and St. Croix, respectively [SEM 146.0]). The PCV ranked (P < 0.01) RS > MR > SS (29.9, 28.0, and 26.9% [SEM 0.25]). Intake of DM, ADG, and the ADG:DMI ratio were similar among resistance classifications (P > 0.05) and were not correlated with FEC or PCV (P > 0.05). In conclusion, hair sheep can be selected for resistance to internal parasites without adversely affecting growth performance, and selection progress appeared greatest for the Dorper flock, although FEC were relatively low for the St. Croix farm.
