Effect of grinding size and sunflower oil addition on intake, digestibility, rumen function and microbial protein synthesis in sheep fed a dry total mixed ration

Abstract

An experiment was carried out in which the effect of grinding a dry total mixed ration, based on barley straw, through 6 or 10 mm sieves on intake, digestibility, rumen function and microbial protein synthesis in sheep was assessed. The effect of including 1% sunflower oil as binder was also explored. None of the variables studied was affected by grinding size, hence the 10 mm sieve was recommended due to its lower cost in terms of energy consumed. On the contrary, addition of 1% sunflower oil significantly increased ammonia concentration in the rumen (83 vs. 161 mg L–1; p = 0.002), potential degradabilities (as proportion) of dry matter (0.65 vs. 0.75; p = 0.0037), organic matter (0.68 vs. 0.75; p = 0.0005) and crude protein (0.78 vs. 0.90; p = 0.0004), and fractional rate of degradation (0.066 vs. 0.080 h–1; p = 0.046) and effective degradability, as proportion (0.63 vs. 0.73; p = 0.010), of this latter. Oil addition (1%) is then recommended as binder, although a more economical option than sunflower oil should be explored due to its high cost.