PSIII-6 Comparative performance of Florida native sheep and other breeds.

Abstract Gastrointestinal nematodes (GIN) infestations cause significant challenges to sheep production systems worldwide, due to increased costs and impaired productivity. Identifying sheep breeds more resistant to GIN and selecting more resistant individuals within breeds offers a promising long-term control strategy. Florida Native sheep, adapted to survive with low maintenance requirements, is known for its superior disease and parasite resistance. However, the mechanisms underlying this resistance and their productive performance warrant further investigation. Our objective was to evaluate the resistance of Florida Native sheep to GIN infestation, their ability to mount humoral and cellular immune responses to foreign antigen, and their production performance, compared to other breeds. A cohort of 44 Florida Native (FLN), 8 purebred Katahdin (KPB), 8 crossbred Katahdin (KXB) and 7 crossbred (XB) lambs, aged 4-5 months, were monitored over 5 consecutive weeks. Body weight (BW), FAMACHA score (FAM), body condition score (BCS) and fecal egg count (FEC) were evaluated weekly. The lambs were challenged with a keyhole limpet hemocyanin (KLH) antigen via intramuscular injections on days 0 and 14 to evaluate their capacity to develop humoral immune response (HIR). Additionally, a delayed-type hypersensitivity test was performed on day 28 as a proxy for cellular immune response (CIR) by administering intradermal KLH vaccines; skin-fold thickness was measured before and 24 hours post-injection. Blood samples were collected on days 0, 14 and 28 to determine the anti-KLH IgG concentrations, and on days 0 and 28 to determine packed cell volume (PCV) and total serum protein (TSP). FEC and anti-KLH IgG concentration were normalized using box-cox transformation. Statistical analyses were performed using a linear mixed model for repeated measures, with collection day, breed and their interaction fitted as fixed effects and animal and residual as random effects. BCS was significantly lower for FLN lambs compared to KXB on days 0 (2.70±0.03 vs. 3.06±0.08) and 28 (2.69±0.03 vs. 2.97±0.08) and to XB on day 14 (2.74±0.03 vs. 3.14±0.08). FLN had consistently lower BW (64.0±1.55) compared to KXB (82.20±3.63) and XB (84.60±3.88) across all weeks. Notably, FLN had higher PCV values (32.0±0.45) compared to KXB (28.90±1.04) throughout the study period. Additionally, TSP was higher for FLN (9.07±0.08) compared to KPB on day 0 (8.26±0.17) and to KXB on day 28 (8.80±0.17). FEC was significantly lower for FLN (14.60±1.30) compared to KPB (25.50±3.04) and XB (26.40±3.25) over the weeks. FLN showed higher HIR than KPB (2.26±0.04 vs. 2.01±0.09), indicating a stronger antibody response. CIR, FAM, ADG did not differ significantly between breeds (P-value>0.05). Although exhibiting lower productive performance, FLN demonstrated improved resistance and resilience to gastrointestinal nematode (GIN) infestations. Notably, FLN sheep displayed lower FEC and less adverse effects on blood parameters than other breeds at similar infestation levels.