Effect of physical form of a lucerne hay on rumination and the passage of particles from the rumen of sheep

Six 2-year-old Corriedale wethers fitted with rumen and abomasal cannulas were given a lucerne hay,first as chopped ( CH) hay then as ground and pelleted (GP) hay. Intake rate increased as dry matter intake (DMI) increased and was greater on GP hay. The time spent eating and ruminating per unit of DMI decreased as DMI increased and was shorter on GP. Ruminating efficiency increased with DMI but did not differ between CH hay and GP hay. The critical size of particles for passage from the rumen was not affected by either DMI or by grinding and pelleting. Most of the overall digestion of large particles ( LP) occurred during their retention in the LP pool within the rumen, and retention in the medium particle ( MP) pool accounted for much of the rumen mean retention time of particles. The residual digestible material of MP derived from LP by rumination appeared to be less accessible to fermentative activity. Prediction of an animal's response to the grinding and pelleting of forage must take account of all the determining factors and their interactions.