Effect of rumen fluid inoculation on the rate of adaptation of lambs to forage brassicas : A dissertation submitted in partial fulfilment of the requirements for the degree of Bachelor of Agriculture Science with Honours at Lincoln University

Abstract

The effect of intraruminal inoculation on liveweight change, daily feed intake and blood parameters (Heinz bodies, red blood cells and haemoglobin) were measured over 28 days, using Coopworth wether lambs continuously grazed on forage brassicas. Lambs were inoculated with 200ml of live rumen microorganisms adapted specifically to either forage brassica or tall fescue/white clover pasture. The source of rumen fluid inoculum did not affect liveweight change over the trial period. Mean liveweight gain was high in experiment 1 at 250 g hd⁻¹ d⁻¹ and experiment 2 at 430 g hd⁻¹ d⁻¹.Liveweight change was relatively linear over the duration of the trial. Estimated dry matter intake early in the grazing period using the alkane technique in experiment 1, showed voluntary feed intake was higher (1.6 - 2.2 kg DM/hd/day) for brassica inoculated lambs compared to pasture inoculated lambs (0.7 - 1.5 kg DM/hd/day). However dry matter intake by the end of both experiments estimated by the pre and post grazing yield difference, suggested feed intake was similar between treatments at 0.9 - 1.2 kg DM/hd/day. The length and severity of anaemia was greater for lambs inoculated with rumen fluid previously adapted to forage brassicas. This was indicated by higher Heinz bodies numbers J for brassica inoculated lambs, and a longer time to minimum haemoglobin and red blood cells. Heinz bodies numbers were higher in experiment 2, as a result of higher herbage SMCO levels. The rate and potential DM degradation of forage brassicas and pasture was measured, when incubated with rumen fluid from lambs either previously grazing forage brassicas or tall fescue/white clover pasture. The rate and potential dry matter degradation on both pasture and brassica samples were higher with pasture adapted rumen fluid (3 to 7% higher) compared to brassica adapted rumen fluid. These results suggest specific rumen microorganisms were impeded using brassica adapted rumen fluid. The source of rumen inoculum had no effect on liveweight gain but may have resulted in a greater physiological challenge from plant secondary compounds for lambs ·inoculated with brassica rumen fluid.