Effect of a sustained-release intra-ruminal sulfamethazine bolus on Eimeria spp. oocyst output and weight gain of naturally infected lambs in the Mexican tropics

This trial determined the effect of a sustained-release intra-ruminal sodic sulfamethazine (SMZ) bolus on the Eimeria spp. oocyst output and the cumulative live-weight gain (CLWG) of naturally infected lambs in two different production systems (penned and penned-grazing). Forty male Pelibuey lambs (2–2.5 months old), naturally infected with Eimeria spp., were randomly included in four groups of 10 animals at weaning: (a) penned with SMZ bolus treatment (P-B), (b) penned untreated (P-U), (c) penned-grazing with bolus treatment (PG-B), and (d) penned-grazing untreated (PG-U). Treated lambs (P-B and PG-B) were dosed orally on day 0 with a single SMZ bolus (28.5% of SMZ). Lambs in the PG-U and PG-B groups were allowed to graze 10 h/day. Faecal samples and live-weights were obtained from each lamb on days 0, 8 and every 7 days until day 57 post-treatment (PT). Oocyst per gram of faeces (OPG) were determined for each animal on the same dates. Mean CLWG and log transformed OPG values were compared within production systems using the Student's t-test. Partial budget analysis was used to evaluate the economic impact of bolus treatment. Untreated animals (P-U and PG-U) showed higher OPG excretion than animals treated with bolus (P-B and PG-B). OPG were reduced in the treated groups of both production systems (P < 0.001), especially in the first 29 days post-treatment. PG-B lambs showed higher CLWG than PG-U lambs (P < 0.05). CLWG of P-U and P-B lambs were similar. Bolus treatment was economically feasible in both systems (PG-B: $1.78 USD/animal and P-B: $0.11 USD/animal). Intra-ruminal SMZ boluses reduced excretion of Eimeria OPG in P-B and PG-B groups; however, CLWG was only improved in PG-B lambs.