Feeding30<strong>Inc</strong>reasing the physically effective fiber content of dairy cow dietsmay lower efficiency of feed useCorresponding AuthorBeauchemin, K.A.AAFC Lethbridge Research CentreCollaboratorYang, W.Z.AAFC Lethbridge Research CentreJournal of Dairy Science (2006) Vol. 89 p. 2694-2704.Rapid production of volatile fatty acids from the microbial degradation ofhighly fermentable feed puts the early lactation cow at risk of subacuteruminal acidosis. To counteract the effect of these acids on ruminal pH, sufficient‘physically effective’ (pe) fibre must be fed to stimulate active chewingwhich, in turn, provokes the secretion of saliva containing acid-neutralizingbuffers. However, the optimal level of pe fibre in lactation diets isuncertain. While some studies have demonstrated its benefits, others haveshown that increasing dietary pe fibre concentration may reduce nutrientdigestibility. The present study examined the effects of varying dietary levelsof pe fibre on intake, digestion and production in mid to late lactationdairy cows. The measure of pe fibre used was pe neutral detergent fibre(peNDF), calculated by multiplying the proportion of particles retainedon the screens of the original 2-screen Penn State Particle Separator bythe ration NDF concentration. Cows were fed one of three different totalmixed rations (TMRs) containing 10.5, 11.8 or 13.8% peNDF, achieved byincluding barley silage of varying chop lengths. TMR dry matter intake washighest for cows offered the 11.8% peNDF diet. Whole digestive tract fibreand organic matter digestibility decreased as peNDF increased but starchand crude protein digestibility were not affected. The efficiency of rumenmicrobial digestion also declined as peNDF increased. Milk production andcomposition were similar on all 3 diets.50 Highlights in Canadian Dairy Cattle Research - 2007
Feeding31Lower pregnancy losses in lactating dairy cows fed a diet enrichedin α-linolenic acidCorresponding AuthorAmbrose, D.J.AAF EdmontonCollaboratorsKastelic, J.P.AAFC Lethbridge Research CentreCorbett, R.AAF EdmontonPitney, P.A.University of AlbertaPetit, H.V.AAFC Dairy and Swine Researchand Development CentreSmall, J.A.AAFC Brandon Research CentreZalkovic, P.University of AlbertaJournal of Dairy Science (2006) Vol. 89 p. 3066-3074.In early lactation, dairy cows are frequently unable to consume enoughfeed to supply the energy demanded by high levels of milk production.The resulting loss of body weight has been shown to inhibit the resumptionof normal reproductive function. In an attempt to limit weight loss,supplementary fats and oils (lipids) are often fed at this time to increasedietary energy intake. It has also been demonstrated that certain dietarylipids can have positive effects on reproduction, independent of theircontribution to energy balance. In particular, long chain, polyunsaturatedfatty acids found primarily in fish oils have been shown to be effective indelaying luteolysis and improving pregnancy rates. These observationshave raised the possibility that feeding flaxseed might have similar effectssince flaxseed contains high concentrations of alpha-linolenic acid (αLA),a metabolic precursor of the beneficial fatty acids found in fish oils. In thepresent study, reproductive parameters in early lactation cows fed dietscontaining rolled flaxseed (56.7% αLA) or rolled sunflower seed (0.1% αLA)were compared. The average diameter of ovulatory follicles, determined byultrasound, was larger in the cows fed flaxseed although follicle numbers,corpus luteum size, and plasma progesterone concentrations were not affectedby lipid source. At 32 days after artificial insemination, 48.4% of thecows fed flaxseed were confirmed pregnant versus 32.2% of the cows fedsunflower seed. Pregnancy losses (between 32 d of gestation and calving)were 9.8% in cows fed flaxseed; 27.3% in cows fed sunflower seed.32Evaluation of models to describe ruminal degradation kinetics fromin situ ruminal incubation of whole soybeansCorresponding AuthorKebreab, E.University of GuelphCollaboratorsNasri, M.H.F.Ferdowsi UniversityMesgaran, M.D.Ferdowsi UniversityFrance, J.University of GuelphCant, J.P.University of GuelphJournal of Dairy Science (2006) Vol. 89 p. 3087-3095.The most commonly used method for estimating the rumen degradabilityof feeds and feed fractions is the ‘in situ polyester bag technique’. Samplesof finely ground feed, sealed in multiple small polyester or nylon bags aresuspended in the rumen of a rumen-cannulated animal. At predeterminedtime intervals during the incubation, individual bags are withdrawn, rinsedand dried. Analysis of bag contents determines the amount of feed orfeed fraction that has disappeared. For most feeds, disappearance is veryrapid in the first few hours, slowing as the incubation progresses. Whendisappearance at each withdrawal time is plotted on a graph, a curvilinearrelationship is seen. Degradation rates and degradability estimates arecalculated from this data by fitting mathematical equations to the curve.In this study, the authors evaluated several different equations to determinewhich proved the best fit to data derived from incubations of groundsamples of raw and roasted whole soybeans. Although estimates of the extentof degradability were similar for all equations, there were differencesin calculated values of undegradable feed fractions.Feeding 51
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