The influence of dietary energy concentration and feed intake level on feedlot steers: 1. Digestibility of diets and rumen parameters
Slabbert, N.; Campher, J.P.; Shelby, T.; Kuhn, G.P.; Meissner, H.H.
Suid-Afrikaanse Tydskrif vir Veekunde 22(4): 101-106
Three ruminally cannulated mature steers were fed, in a crossover design, diets with concentrate to roughage (C:R) ratios of 80:20, 55:45 and 30:70, twice a day (09:00 and 15:30) in a predetermined feed intake sequence of ad libitum, 80% ad libitum and 90% ad libitum. Following the faeces collection period of 12 days, ruminal contents were removed a 2 h post feeding and were weighed, mixed, sampled and returned. DM intake decreased and then increased (non-linear; P ltoreq 0.01) as C:R ratio increased. DM digestibilities of the three intake levels were respectively 72.9, 73.8 and 76.1% for the 80:20 diet, 64.9, 65.0 and 65.1% for the 55:45 diet and 55.3, 56.3 and 57.1% for the 30:70 diet. DM digestibility was not influenced (P = 0.28) by feeding level, but was linearly reduced (P ltoreq 0.05) as C:R ratio decreased, which indicated that no significant associative effect had occurred. Both a decrease in feeding level and in C:R ratio increased rumen OM retention linearly (P ltoreq 0.01). Volatile fatty acid concentration (VFA) 2h postfeeding was not influenced (P ltoreq 0.05) by feeding level, but was reduced linearly (P ltoreq 0.01) by a decrease in C:R ratio. A decrease in C:R ratio increased the molar percentage acetic acid and decreased propionic acid linearly, while feeding level had no significant influence. The lowest rumen pH (6.1) 2 h post feeding occurred at 80% of ad libitum on the 80:20 diet, which indicates that the ruminal environment was relatively stable on all treatments.