Effects of dietary substitution of maize silage by amaranth silage on feed intake, digestibility, microbial nitrogen, blood parameters, milk production and nitrogen retention in lactating Holstein cows

Abstract

The effect of dietary feeding amaranth (Amaranthus hypochondriacus) silage (AS) instead of maize silage (MS) on the feed intake, digestibility, microbial nitrogen (N), blood parameters, milk production and N retention of the lactating Holstein cows, in third lactation (140±13 days in milk) with 38.9±4.7kg milk/day, was assessed in a completely randomized design. Three iso-energetic (NEL=6.37MJ/kg dry matter [DM]) and iso-nitrogenous (crude protein [CP]=164g/kg DM) diets were formulated in which MS was replaced by different rates (0, 105 or 210g/kg diet DM) of AS. The diets were assigned randomly to one of three groups of eight cows each in a completely randomized design for 63 days. Diets were provided as total mixed rations at 07:00 and 19:00h. All the animals had free access to feed ensuring 100g orts/kg of the amount fed daily. The DM intake (DMI), diet digestibility, N retention, microbial N supply (MNS), blood parameters and milk yield and composition were determined using standard procedures. Data were analysed as a mixed model using the PROC MIXED of SAS. The values for DMI, DM digestibility, retained N, MNS, blood concentrations of glucose, urea-N, non-esterified fatty acids, nitrate, nitrite, milk yield and milk fat in the cows fed with the diet without AS were 24.3kg/d, 633g/kg, 47.0g/d, 306g/d, 64.8mg/dL, 14.9mg/dL, 0.303mmol/L, 8.53μg/mL, 0.167μg/mL, 36.9kg/d and 33.8g/kg, respectively. The DMI, diet digestibility, MNS and milk yield were greatest (P<0.05) for the cows fed with the diet containing 105g of AS/kg DM as compared to the others. Increasing the rates of AS in the diet had no effect on milk fat, protein and lactose. The concentration of blood urea-N increased linearly (P=0.03) when the cows were offered diets with the increasing levels of AS. The serum concentrations of calcium, phosphorous, magnesium, nitrate and nitrite were not affected by the dietary treatment. Based on the obtained results, although partial replacement of MS by AS up to 210g/kg DM was possible in the diet of lactating Holstein cows, the maximum values for DMI and milk yield were observed in the cows that were fed with the diet containing 105g of AS/kg DM.