The experiment conducted to investigate the effects of indigstible NDF (iNDF) and forage particle size (PS) on animal response using eight Holstein lactating dairy cows that assigned to four dietary treatments in a 4 × 4 Latin square design with four 21-day periods (14 days for adaptation and 7 days for sampling). Treatments including diet contained: 1) long alfalfa hay-low iNDF, 2) fine alfalfa hay-low iNDF, 3) long alfalfa hay-high iNDF, and 4) fine alfalfa hay-high iNDF. By increasing iNDF, DMI, digestibility of fat and NDF increased, but the consumption of non-fiber carbohydrate (NFC) and starch decreased. Reduction of PS increased intake of DM and NDF. Rumen pH and NH3-N decreased with the reduction of PS. Total VFA, propionate, and butyrate concentration increased by reduction of PS and decreasing iNDF. Chewing activity increased with greater iNDF. Using eating iNDF as a fibrous index is more sensitive than physically effective NDF (peNDF) especially in the high NFC ration. Cows that consume lower iNDF produced more milk yield, milk protein, lactose and solid non-fat (SNF). Decreasing the iNDF increased DMI, rumen propionate and butyrate, milk yield and protein, but decreased digestibility of DM and rumen pH. In addition, reduction of PS increased DMI, effected nutrient digestibility and rumen fermentation, but the effects were not large enough to affect rumen pH and milk production. The results showed that the iNDF as an index to predict chewing behaviour is more sensitive than DM, NDF, and peNDF>1.18, especially in low iNDF ration to prevent ruminal acidosis.
Halako GA, Yansari AT* and Pirsaraei ZA