Effects of close-up dietary energy level and supplementing rumen-protected lysine on energy metabolites and milk production in transition cows

摘要

The objective of this study was to investigate theeffects of dietary energy levels and rumen-protectedlysine supplementation on serum free fatty acid levels,β-hydroxybutyrate levels, dry matter (DM) intake, andmilk production and composition. Treatments were arrangedin a 2 × 2 factorial design with 2 dietary energylevels [high net energy for lactation (NE_L) = 1.53 Mcal/kg of DM vs. low NE_L = 1.37 Mcal/kg of DM; HE vs.LE) fed either with rumen-protected lysine (bypass lysine;40 g/cow per day) or without rumen-protected lysine(control). Sixty-eight third-lactation Holstein dairycows entering their fourth lactation were randomlyallocated to 4 treatments groups: HE with bypass lysine,HE without bypass lysine, LE with bypass lysine,and LE without bypass lysine. Groups were balancedbased upon their expected calving date, previous milkyields, and body condition score. All cows were fed thesame diet (NE_L = 1.34 Mcal/kg of DM) during the dryperiod prior to the trial. Rumen-protected lysine wastop-dressed on a total mixed ration to deliver 9.68 g/dof metabolizable lysine to pre- and postpartum cows.After calving, all cows received the same TMR (1.69Mcal/kg of DM). Blood samples were collected at −21,−14, −7, 0, 3, 7, 14, and 21 d relative to calving, andfree fatty acids and β-hydroxybutyrate concentrationswere measured. Amount of feed offered and orts werecollected and measured for individual cows 4 d/wk.Milk samples were collected once per week followingcalving, and milk composition was analyzed. Feedinghigh NE_L to close-up cows decreased the concentrationsof free fatty acid and β-hydroxybutyrate in prepartumcows but not in postpartum cows. Addition of rumenprotectedlysine increased postpartum DM intake, anddecreased serum free fatty acid and β-hydroxybutyrateconcentrations. Neither energy nor rumen-protectedlysine supplementation nor their interaction affectedmilk yield or fat or lactose yields. However, cows inthe group receiving HE with bypass lysine tended toproduce more milk compared with other groups andhad a lower blood β-hydroxybutyrate concentrationpostpartum. These results indicate that feeding ahigh-energy diet together with rumen-protected lysineimproved DM intake and lowered serum free fatty acidand β-hydroxybutyrate concentrations in transitioncows.