Influence of concentrate level on dry matter intake, N balance, nutrient digestibility, ruminal outflow rate, and nutrient degradability in sheep

The objective of this study was to investigate the effects of concentrate level on ad libitum DMI, N balance, digestibility, ruminal degradability and feed efficiency (feed:gain, F:G) of sheep fed a diet based on corn stalk and mixed concentrates. Six 8-month-old castrated rams from a herd of local breed (short tail Han sheep) fitted with permanent ruminal fistula were fed 150, 250, 350, or 450 g/day mixed concentrate per sheep in a four periods experiment ad libitum. DMI of corn stalk increased with concentrate level until it reached 350 g/day (P < 0.01), but there was no further significant increase when the concentrate level increased to 450 g/day (P > 0.05). Corn stalk DMI expressed as g/(d kg W0.75) fitted well with an exponential model. The ratio of urinary N to digestible N (UN/DN) was the lowest when 350 g/day concentrate was fed (P < 0.01), and the urinary N excreted/day was the lowest when 250 g/day concentrate was fed (P < 0.01). The digestibility of DM (P < 0.01), OM (P < 0.01), CP (P < 0.05), NDF (P < 0.05), and ADF (P < 0.05) of the diet was highest when 350 g/day concentrate was fed. High concentrate level could improve feed efficiency as a lower feed: gain ratio (P < 0.01) was observed with 350 450 g/day concentrate. The difference between these two levels was not significant (P > 0.05). Ruminal outflow rate increased with concentrate level (P < 0.05). Chromium marked feed used had no significant influence on ruminal outflow rate (P > 0.05). Effective ruminal degradability of nutrients of corn decreased with concentrate level, but only the degradability of NDF differed significantly with concentrate level (P < 0.05). Results of present study implied that there was an optimal supplementary concentrate level for a given crop stalk when the DMI and feed efficiency were the highest. For an agricultural by-products based ruminant feeding system, the highest crop stalk DMI could be used as a useful practical index in ascertaining the optimal supplementary concentrate level.