73 Deworming to improve growth in early-weaned spring born hair sheep lambs

Abstract In lambs, the stress of weaning and the lack of a fully developed immune system can increase susceptibility to gastrointestinal nematodes (GIN). Lack of an effective GIN control strategy around this time can have a significant impact on lamb growth, productivity and mortality. The objective of this study was to determine the influence of deworming at weaning on growth performance in hair sheep lambs. St. Croix (STX) and Barbados Blackbelly (BB) lambs used in the study were born on pasture, weaned at 60.2 ± 0.4 d of age, and transitioned in pens for 87 d post-weaning before turning out to pasture. After accounting for initial FAMACHA eyelid color score, breed, and birth type (single or multiple) at weaning, 54 STX (n = 32) and BB (n = 22) lambs weighing 11.7 ± 0.4 kg were dewormed (DEW) or not (CON) with a combination of levamisol (Prohibit; 8 mg/kg BW) moxidectin (Cydectin; 0.2 mg/kg BW) and albendazole (Valbazen; 7.5 mg/kg BW). To evaluate the effect of deworming treatment, BW and body condition scores (BCS; scale 1-5) were recorded at weaning and at end of transition to pasture. Blood and fecal samples were also collected for determination of packed cell volume (PCV) and fecal egg counts (FEC). Pooled treatment group feces (d 0 – 98) were collected and cultured to determine GIN genera at weaning. Data were analyzed using repeated measures in a mixed model, and FEC were log transformed prior to analysis. There was a mixed population of GIN at weaning averaging 65% and 35% for H. contortus and Tricostrongylus spp. At weaning, BCS, PCV, and FEC were similar between treatment groups and averaged 1.6 ± 0.07, 36.5 ± 0.6%, and 399 ± 54.4 epg, respectively. Combination deworming reduced FEC by 99%. At turnout, DEW lambs (2.3 ± 0.1) tended (P = 0.08) to have greater BCS than CON lambs (2.0 ± 0.1) and PCV was greater (P 0.001) in DEW versus CON lambs (37.2 ± 0.9 and 33.3 ± 0.8%, respectively). There was also a tendency (P = 0.09) for breed to influence BCS (2.3 ± 0.1 and 2.0 ± 0.1 for BB and STX, respectively). The FEC at turnout was not influenced by treatment or breed (496.7 ± 75.1 epg). Additionally, DEW lambs (131.8 ± 5.2) tended (P = 0.09) to grow faster than CON (119.9 ± 4.7 g/d) lambs, a difference more pronounced in STX DEW (g/d) than STX CON lambs (136 ± 6.1 vs 110 ± 6.5 g/d; P 0.05). Even though deworming tended to promote faster growth rates in lambs used in this study, alternative, more sustainable, parasite control strategies should be considered in the wake of increasing dewormer resistance.