A52-75-2007E.pdf - AgroMedia International Inc

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