Published online by Cambridge University Press: 02 September 2010
The effects of level of supplemental carbohydrate from turnips and level of rumen degradable nitrogen on bacterial cellulolysis, food intake, live-weight gain and diet digestibility were examined with 36 300-kg Friesian steers allocated, in a randomized-block design, to one of six dietary treatments: (i) sodium hydroxide treated straw plus a supplement of urea (30 g urea per kg straw dry matter (DM)) (uO); (ii) uO plus turnips (23·5 g DM per kg M0·75); (Hi) uO plus a high level of turnips (47 g DM per kg M0·75); (iv) (v) and (vi), the same three diets, but with additional urea (60 g urea per kg straw DM). In two separate experiments each lasting for 56 days, the turnip allowance was given in either two feeds, or one feed per day and the straw was given to appetite. Rumen fluid was obtained by stomach tube from all steers before feeding (07·30 h) and after feeding (11.00 h) on days 10 and 24 of each experiment.
Weight gains for all groups given straw plus turnips were high (> 0·90 kg/day). Increasing the quantity of turnips gave significantly increased DM intakes and weight gains but then turnips substituted for straw, and the proportion of straw consumed decreased from 0·8 to 0·6 of the dietary DM (P < 0·01) There were no significant interactions between frequency of feeding of turnips and level of urea on the variables food intake and weight gain. Fibre digestibility was not depressed by the addition of turnips to the diet. Rumen fluid pH decreased after the steers ate turnips but tended to remain above 6·7. There were no large changes in the total number of viable cellulolytic bacteria as a result of either addition of urea or turnips to the diet; counts remained in the order of 107 per ml. Steers consumed large quantities of sodium hydroxide treated straw; turnips were therefore only a small proportion of the overall DM intake with relatively little effect on bacterial cellulolysis.