Effect of corn silage particle size and level of soybean oil on ruminal mat composition, distribution and consistency in Zel sheep
To determine the effects of two corn silage particle size (coarse particle with geometric mean of 5.83 ± 2.47 mm and fine particle with geometric mean of 4.74 ± 2.74 mm) and two levels of soybean oil (0 and 4% of DM) on ruminal mat composition, distribution and consistency, four two years fistulated ruminant Zel ewes (BW = 34 ± 1.4 kg), fed with 50:50 roughage-concentrate diet, were allocated to a 4 × 4 change over design. The experiment was carried out in 4 periods of 28-days trial (adaptation, 14 days; collection period , 5 days; chewing activity measurement, 1 day; rumen evacuation, 8 days). Experimental diets were: 1) basal diet + coarse corn silage and 0% oil; 2) basal diet + coarse corn silage and 4% oil; 3) basal diet + fine corn silage and 0% oil and; 4) basal diet + fine corn silage and 4% oil. Based on calendar time, rumens were evacuated manually at 3, 7.5 and 12 h post-feeding of each period and total ruminal contents were separated into mat and liquids phase. Dry matter (DM) and organic matter (OM) intake were less in treatment 4 and neutral detergent fiber (NDF) intake in treatment 2 was higher than in the other diets. Physically, effective NDF intakes were higher in treatments 1 and 2 than in treatments 3 and 4, but DM and OM digestibility was higher in treatments 1 than in the other diets. The NDF digestibility was higher in coarse silage diets, but the NFC digestibilities were higher in fine corn silage diets. Rumen mat was greater in coarse silage diets than in fine silage diets (1.83 and 1.32 versus 1.06 and 0.76 kg) at 3 h after feeding. Non-escapable pool sizes in rumen content were higher in diets that contained coarse silage. At all time in post feeding, ruminal pH was less in fine silage particle size with oil supplement. Rumen particulate passage rates were higher in fine corn silage diets. However, passage rates from the lower gastrointestinal tract were similar. In addition, ruminal mean retention times were significantly greater in diets that contained coarse silage. Rumination time was shorter in fine corn silage with oil supplement diet but rumination time per kg of NDF and peNDF was longer in fine corn silage diets. In addition, although reduction of particle size decreased size of rumen mat and non-escapable fraction, oil supplementation reduced ruminal digestion and mean retention of ruminal particulate. However, it seems that oil supplementation can be helpful in fine corn silage diets for maintaining ruminal mat.
Key words: Particle size, soybean oil, ruminal mat, Zel sheep.