Effect of supplemental protein feeding frequency on ruminal characteristics and microbial N production in sheep fed treated rice straw

Four rumen cannulated Suffolk ewes, fed a basal diet of rice straw treated with ammonia or urea-calcium hydroxide were used in a feeding trial to study the effects of supplemental protein, offered in either one meal per day at 08:00 h or two meals per day at 17:00 and 01:00 h, on feed intake, digestibility, N retention and microbial N yield. The study was a 4 × 4 Latin square design with 2 × 2 factorial arrangements. Intake of DM was not influenced by feeding frequency of protein supplement. However, digestibility of OM, NDF, and cellulose was higher (P < 0.05) for sheep offered supplemental protein twice than once. Urinary N excretion was lower (P < 0.05) and N retention was higher (P < 0.01) in sheep offered supplemental protein twice a day. Average rumen ammonia N and VFA were higher (P < 0.05) when sheep received the supplemental protein twice. Purine derivatives and estimated microbial N yield tended to be higher (P < 0.05) when supplemented protein was offered twice rather than once per day. This study indicated that the digestibility, rumen fermentation end products and microbial N yield of ammoniated straw would be improved by offering supplemental protein twice a day than once a day.