Effects of dietary n-3 polyunsaturated fatty acids and ... - FINS

1 st WorkshopXIII International Feed Technology Symposiumpropionate ratio, and milk fat content (Grubić et al. 1999). Concept of effective fiberincludes chemical characteristics of forages and their chop length in diet, and expressesvalue of forages for chewing activity and ruminal function. Physically effective fibers(peNDF) are fibers in cows’ diets that effectively stimulate saliva secretion andrumination (Mertens, 1997). Deficit of effective fiber in ration for high-yielding dairycows, the most frequently causes these disturbances: milk fat depression, ruminalacidosis, ruminal parakeratosis, dislocation of abomasum, and laminitis (Stojanović andGrubić, 2008). This is especially characteristic for cows in early lactation with highrequirements for dietary energy and protein concentration, as also for high digestibilityof ration, because of limited ability for DM intake.Forages, first corn silage and alfalfa haylage, with optimal chop length, provide adequateparticle length and distribution of particles’ fractions in total mixed ration (Stojanović etal. 2009). Recommendation for peNDF portion in diets for dairy cows in early andmiddle lactation is 20 % of dietary DM, for maintaining percentage of milk fat at 3.4 %.Concentration of peNDF in dietary DM should be 22 % to achieve pH 6 as ruminalaverage value (Mertens, 1997).A simple method and device (system of sieves, Penn State Particle Separator-PSPS),developed for determination of particle size of total mixed rations for lactating cows, andsome forages-components of TMR (corn silage and alfalfa haylage), as also foroptimization of physical form of rations (Kononoff et al. 2002).Yang and Beauchemin, (2007) researched effects of dietary peNDF concentrationachieved with different chop length of alfalfa haylage (theoretical chop length 7.9 and19.1 mm). Increasing chop length of alfalfa haylage, increased peNDF intake, but notDM intake. Digestibility of NDF was higher, caused by higher ruminal digestibility offiber, and shifting of starch digestion from rumen to intestine. Increasing of forageparticle size in ration, increases ruminal digestibility of NDF by 18 %, and DMdigestibility by 6 %. Increasing particle size of alfalfa haylage, increased ruminal pH(6.36 and 6.16). This is result of higher intake of peNDF, increased total time of chewingactivity and saliva buffer secretion, and shifting of starch digestion from rumen tointestine. Concentration of peNDF in ration is positively correlated with chewing activity(r=0.61), and negatively correlated with total time of ruminal pH value under 5.8 or 5.5(r=-0.46). Larger forage particles form floating rough and dry layer of ruminal contentthat stimulates ruminal contractions. Without these movements, rumen becomes lessdynamic system, with decreased efficiency for removing of VFA through absorption orfluid passage, and increased risk of acidosis appearance. Intake of larger forage particlesreduces ruminal starch digestion, increases extent of intestinal starch digestion, decreasesruminal concentration of VFA, increases acetate to propionate ratio of molarconcentrations. Authors emphasize significance of peNDF intake, more exactly forageNDF intake, for normal ruminal function, than consuming of total dietary NDF.Yang and Beauchemin (2006) researched effects of different peNDF content in diets forlactating cows, with corn silage (theoretical chop length 28.6, 15.9 and 4.8 mm) as onlyforage. Increasing of average particle size of ration, did not affect DM intake, increasedintake of peNDF, increased CP digestibility (65.7 and 61.3 %), showed tendency forincreasing fiber digestibility (NDF-50.5 and 45.7 %, ADF-49.4 and 43.9 %) in wholedigestive tract. Cows fed rations with higher content of peNDF showed tendency for224