Ruminal fermentation and degradation patterns, protozoa population, and urinary purine derivatives excretion in goats and wethers fed diets based on two-stage olive cake: effect of PEG supply.

Abstract

Three experiments were conducted in Granadina goats and Segureña wethers fed at maintenance level to evaluate the effect of including a mixture of barley and a new by-product derived from olive oil extraction (two-stage dried olive cake) on ruminal degradation and passage kinetics (Exp. 1), fermentation pattern and protozoa population (Exp. 2), and urinary purine derivatives excretion (Exp. 3). Polyethylene glycol was supplied to the animals to evaluate the effects of tannins contained in the by-product. The experimental diets were as follows: alfalfa hay and alfalfa hay plus a concentrate, formulated with two-stage dried olive cake, barley, and a mineral-vitamin mixture either with or without the addition of polyethylene glycol to the drinking water. The inclusion of two-stage dried olive cake in the diet resulted in an increase of condensed tannins. Ruminal VFA concentration in goats and wethers increased (P < 0.05) and ammonia N (NH3-N) concentration decreased (P < 0.05). The inclusion of two-stage dried olive cake decreased (P < 0.001) urinary allantoin excretion only in wethers. Ruminal degradation profiles and fractional passage rates were similar in goats and wethers. The polyethylene glycol supply increased (P < 0.001) DM and N degradation rates in both animal species but did not modify the fractional passage rate. Ruminal fermentation patterns were also similar in goats and wethers and were affected by polyethylene glycol supply. In general, Entodiniomorphida and Holotricha protozoa counts were higher (P < 0.05) in the rumen of goats than of wethers. Protozoa count in wethers responded more to polyethylene glycol supply than in goats. The present work presents the first data obtained from a comparative study with sheep and goats concerning urinary excretion of purine derivatives. The excretion was similar in both animal species when fed alfalfa hay; however, polyethylene glycol affected only urinary allantoin excretion in wethers. Results suggest a greater sensitivity of wethers than of goats to two-stage olive cake condensed tannins.