Spineless Cactus plus Urea and Tifton-85 Hay: Maximizing the Digestible Organic Matter Intake, Ruminal Fermentation and Nitrogen Utilization of Wethers in Semi-Arid Regions

SIMPLE SUMMARY: In semi-arid regions, providing a roughage adapted to water deficient conditions, such as spineless cactus, associated with a source of physically effective fiber, could be a feed alternative for sheep. Five inclusion levels of spineless cactus plus urea and ammonium sulfate to replace Tifton-85 hay were tested in sheep diets with a roughage/concentrate ratio of 70:30. The dry matter and digestible organic matter intake, as well as ruminal fermentation, nitrogen balance, and microbial protein supply, were evaluated. The results suggested that spineless cactus inclusion affected quadratically the dry matter and digestible organic matter intake, as well as retained nitrogen and microbial protein supply. The spineless cactus plus urea and ammonium sulfate improved nitrogen utilization, reducing linearly urinary nitrogen excretion, serum urea, and ammonia plasma. On the other hand, spineless cactus inclusion increased the ruminal acetate and propionate concentrations, while ruminal pH and ruminal ammonia nitrogen were decreased. We recommend a roughage consisting of spineless cactus (plus urea and ammonium sulfate) and Tifton-85 hay in a 41:29 ratio, in order to maximize the digestible organic matter intake and N-utilization. This could lead to an improvement in the productive performance of animals in semi-arid regions. ABSTRACT: The aim of this study was to evaluate the effect of replacing Tifton-85 hay (Cynodon spp. cv. Tifton 85) with 0, 150, 300, 450 and 600 g/kg dry matter (DM) of spineless cactus (SC, Nopalea cochenilifera Salm-Dyck) plus urea and ammonium sulfate (UAS; 9:1) on DM, digestible organic matter (DOM) and indigestible neutral detergent fiber (iNDF) intakes, as well as ruminal fermentation, N-balance, and microbial protein supply (MPS). Five rumen-fistulated and cannulated crossbred wethers, weighing 43.8 ± 5.80 kg, were randomized in a 5 × 5 Latin square design. Isonitrogenous diets (14% crude protein) were supplied with a roughage/concentrate ratio of 70:30. The DOM intake, N-retained, and MPS showed quadratic responses (p < 0.05), with maximum values estimated at the levels of SC+UAS of 414, 438 and 418 g/kg DM, respectively. Rumen pH and ammonia nitrogen, iNDF intake, N-urinary excretion, and serum urea and plasma ammonia reduced linearly (p < 0.05) with increasing SC+UAS inclusion. Ruminal acetate and propionate concentrations increased linearly with increasing SC+UAS inclusion. In wethers fed diets with a roughage/concentrate ratio of 70:30, roughage constituted of a SC+UAS/hay (Tifton-85) ratio of 41:29 is recommended in order to maximize the DOM intake, N-retention, and MPS.