Effects of slow-release urea and molasses on ruminal metabolism of lambs fed with low-quality tropical forage

The effects of two sources of slow-release urea (SRU) with a source of soluble carbohydrates on ruminal fermentation in lambs fed with a low-quality forage hay were evaluated. Optigen is a commercial source of slow-release urea, whereas Surelease is an ethyl cellulose-coated urea prepared in the Laboratorio de Farmacotecnia at the Metropolitan Autonomous University. Five Pelibuey lambs cannulated in the rumen and duodenum (24.8 ± 0.4 kg BW) were used in a Latin Square design. Lambs were fed a basal diet that consisted of Brachiaria brizantha hay and concentrate (ratio 67:33) with the following treatments: (1) feed-grade urea; (2) Surelease-coated urea (SRU-S); (3) SRU-S + molasses; (4) SRU Optigen (OPT); and (5) OPT + molasses. All sources of urea were dosed daily intra-ruminally (0.6 g/kg/BW), and molasses was fed at 1.2 g/kg BW. Compared to feed-grade urea, both sources of SRU decreased ruminal pH between 3 and 6 h after dosing (P < 0.05). At 3 and 9 h after dosing and at 15 and 21 h, both sources of slow-release urea reduced the rumen ammonia compared to urea (P < 0.05). The two sources of slow-release urea did not improve the total tract or rumen digestibility of dry matter (DM) and neutral detergent fiber (NDF) or the rate of microbial protein synthesis in growing lambs fed low quality forage.