Influence of forage quality on ruminal degradation kinetics of feedlot diets for lambs formulated according to neutral detergent fiber

Abstract

This study evaluated fattening diets for lambs formulated with forages of different quality at similar neutral detergent fiber from the forage. Ruminal kinetics of dry and organic matter was determined using three non-castrated crossbred hair lambs (20.6±1.8 kg) fitted with permanent rumen cannulae assigned in a 3 x 3 Latin Square experiment. Treatment diets contained 6.5% NDF from forage (eNDF), which was supplied by low quality forage (sorghum stover, SS); a mix of low quality plus high quality forage (sorghum stover and alfalfa hay, SS-ALF); and high quality forage (alfalfa hay, ALF). Diets were incubated at 0, 4, 8, 12, 24, 48, and 72 hours; pH in ruminal liquid was measured 4 h after feeding. Rapidly soluble fraction (a), rate constant (c) and effective degradability modeled at 5%/h ruminal turnover were similar among all diets (p >0.05). Degradable (b) and potentially degradable (a+b) fractions were more degraded (p <0.05) in the rumen in ALF than SS; diet SS-ALF was similar (p >0.05) to SS and ALF. There was no effect of treatment on in situ organic matter at any ruminal incubation time (p >0.05). Ruminal pH was not influenced by dietary treatments (p >0.05). In conclusion, the good quality forage may have minimal advantage over the low quality forage on ruminal degradation kinetics when they are included at similar NDF from forage in fattening diets for lambs.