Milk production responses, rumen fermentation, and blood metabolites of dairy cows fed increasing concentrations of forage rape (Brassica napus ssp. Biennis)

摘要

The aim of this study was to determine animalperformance, rumen fermentation, and health-relatedblood metabolites of dairy cows in mid lactation fedwith increasing levels (30 and 45%) of forage rape (FR)in the diet. Twelve pregnant multiparous lactatingHolstein-Friesian dairy cows were randomly allocatedto 1 of 3 dietary treatments in a replicated 3 × 3 Latinsquare design. The experiment was divided into three21-d periods. For the control diet, 13.0 kg (dry matter,DM) of grass silage, 3.0 kg DM of commercial concentrate,2.7 kg of DM cold-pressed extracted canolameal, and 0.45 kg DM of solvent-extracted soybeanmeal were offered daily. For the other two treatments,30 and 45% of the DM from silage, canola meal, andcommercial concentrate were replaced in equal proportionswith FR. Data were analyzed individually usinglinear and quadratic orthogonal polynomials. Ingestivebehavior was altered by the inclusion of FR. We observeda linear increase in eating time at the expenseof rumination time. Nevertheless, total DM intake wasnot affected by dietary treatments, averaging 19.5 ±0.24 kg of DM/d. Milk yield increased linearly with increasingconcentration of FR in the diet. Thus, feed efficiencyof cows (kg of milk/kg of DM intake) increasedlinearly with the percentage of FR in the diet. Inclusionof FR in the diet had no effect on milk composition ormilk sensory characteristics. Mean rumen pH of cowsdecreased linearly from the control to the 45% FR diet;however, dietary treatments had no effect on the dailyamount of time that rumen pH was below 5.8 (252 ±71.4), indicating no risk of subacute ruminal acidosis.Concentrations of total volatile fatty acids in the rumenand molar proportions of acetate and butyrate wereincreased with FR inclusion, whereas the proportion ofpropionate was linearly reduced. Excretion of uric acidand total purine derivatives tended to be greater forcows fed FR, which resulted in a trend toward a linearincrease in estimated microbial N flow. However, N useefficiency was not affected by FR inclusion. Althoughdifferences for some hematological measures (increasedwhite blood cell and neutrophils counts) and a quadraticresponse for glutamate dehydrogenase for cowsfed FR in the diet (decreased with inclusion of 30%and increased with 45% in the diet) were observed, allvalues were within appropriate ranges for dairy cows.These results indicated that including FR to dairy cowdiets, up to 45% of diet DM, improved milk productiondue to changes in volatile fatty acids and predictedmicrobial N flow and had no negative effects on dairycow health or sensory characteristics of milk.