Extruded urea levels in lamb supplementation in rainy tropical savanna conditions: the triad host-gastrointestinal nematodes-environment

The objective of this study was to evaluate the influence of increasing levels of extruded urea (EU, Amireia®) in the diet of lambs naturally infected by gastrointestinal nematodes on the interactions in the host-pasture-soil components in edaphoclimatic conditions of the tropical rainy savanna. A total of 60 Texel lambs with a mean initial weight of 20.7 ± 0.87 and mean age of 2.5 ± 0.70 months were distributed in a completely randomized design, in five treatments consisting of different levels of EU supplementation viz., 0, 6, 12, 18, and 24 g 100 kg^-1 live weight (LW). The performance of lambs, parasitological variables, gastrointestinal nematodes (NGIs), and larvae recovery in pasture and soil were evaluated. The highest animal performance was observed in animals that received 0 to 18 g kg^-1 LW (146.0 g day^-1) and the lowest in animals supplemented with 24 g kg^-1 LW (81.0 g day^-1) of EU. The body condition score (BCS) was similar in the animals (P > 0.05). Parasitic infection did not differ as a function of EU level (P > 0.05). Eggs of Haemonchus spp., Trichostrongylus spp., Cooperia spp., and Oesophagostomum spp. were found. The largest amount of larvae in the L1/L2 and L3 stages was recovered in the pastures occupied by the animals that received supplementation 0 g kg^-1 LW of EU (750 larvae), the smallest in those that the animals received 6 g 100 kg^-1 LW of EU (54 larvae). The presence of larvae in the L1/L2 stages changed significantly (P < 0.05) in the soil; in the other stages, it did not differ in the soil. Increasing levels of extruded urea do not influence the eggs per gram of feces (EPG) count. The 0 to 18 g 100 kg^-1 LW level maintains animal performance, BCS and FAMACHA^©. There is less dispersal of NGI larvae in pasture and soil when EU levels increase in the edaphoclimatic conditions of the rainy tropical savannah, which suggests that this supplement can be implemented in the diet of beef lambs, in addition to to be a lower cost nitrogen source.