Estratégias para suplementação concentrada de vacas em lactação em pastos de capim tanzânia

Abstract

The objective was to evaluate different levels of concentrate in diets for dairy cows on pasture on the consumption and digestibility of the diet, milk production and composition, microbial protein synthesis, blood urea nitrogen levels and productive performance. Twelve multiparous Holstein x Zebu crossbreed cows were used, with an average initial live weight of 487 ± 54kg, an average initial lactation period of 95.0 ± 42 days and an average milk production of 10 kg of milk/animal.day-1 . The cows were distributed in a design consisting of three 4 x 4 Latin squares, balanced according to order and lactation period. Four levels of isonitrogenous supplements (0; 2.0; 4.0 and 6.0 kg/animal.day-1), with 25% CP (%DM), supplied daily during milking, were evaluated. The area used was a rotated module, of 9 ha of pasture, divided into 9 paddocks of 1.0 ha each, formed with Panicum maximum cv. Tanzania. The total DMI, pasture DMI and intakes of the nutrients NDF, OM, CP, CNF, EE and TDN were significant (P<0.001), the intakes of OM, CP, NFC, EE, TDN and total DMI increased linearly and consumption of NDF and pasture DMI reduced linearly (P<0.05), with a substitutive effect in relation to the addition of concentrate. The digestibility of the nutrients DM, OM, CP, CNF, EE and TDN increased linearly (P<0.001). Forage mass production was 1,117 (kg DM.ha-1) allowing an average forage supply of 2.2 kg DM per 100 kg BW. Milk production, milk production 3.5%G, fat, protein, NUL and CCS also changed significantly (P<0.001), there was a linear increase in milk production (10.70; 12.42; 13 .34; 14.29 kg of milk/animal.day-1) due to concentrated supplementation. The fat concentration reduced (P=0.0285) (4.25; 4.05; 3.91; 3.88 g.100mL-1) as a result of the low NDF consumption. The fat, protein, total solids and SCC contents were within the minimum recommended values (3.0; 2.9; 11.5% and below 400,000 cells/mL). There was an increase (P<0.05) in the levels of allantoin, uric acid, total purines, absorbed purines (mmol.day-1) and microbial N (g.day-1), due to concentrated supplementation at increasing levels. However, there was no effect of concentrated supplementation (P>0.05) on microbial synthesis efficiency (g/Kg of TDN). The total and effective cost-benefit ratios were greater than zero, and presented profitability greater than expenses, confirming the economic viability. Therefore, it is concluded that the production potential of crossbred cows in Tanzania grass pastures without concentrated supplementation is 12 kg per day of milk with 3.5% fat. Providing xvii increasing levels of concentrate (0; 2.0; 4.0 and 6.0 kg/animal.day-1) linearly increases the availability of nutrients for crossbred cows grazing Tanzania grass, in addition to providing greater production, of milk and ruminal microbial protein synthesis.