Níveis de proteína bruta na suplementação de vacas leiteiras em pastagens de capim Tanzânia

Abstract

The objective of this study was to evaluate the effect of concentrated supplementation with different crude protein levels on intake, apparent digestibility of dry matter and nutrients, ingestive behavior, nitrogen balance, blood plasma urea nitrogen, milk and urine, microbial protein synthesis and microbial protein efficiency of lactating cows under Tanzania grass grazing. Twelve lactating dairy cows (Holstein/Gir) with average initial body weight of 540 ± 44 kg were used, grouped in homogeneous blocks according to the milk production (mean initial MP of 25 kg day-1), lactating weeks (10 weeks) and parity order (primiparous/multiparous), distributed in three 4 x 4 Latin squares, consisting of four treatments (122, 142, 162 and 180 g kg-1 of crude protein) and four experimental subperiods of 21 days. For the total MS intake, pasture DM, EE, NDF, NFC, TC, TDN and feed efficiency (FE), no effect was verified (P>0.05). There was an increase in the intake of concentrate (P=0.003), crude protein in kg day-1 (P=0.005) and crude protein in g kg-1 PC (P=0.01) for protein supplementation with CP levels. The digestibility was not influenced (P>0.05) by the CP contents of the concentrate supplement. The behavioral variables, grazing, ruminating and leisure, did not change (P>0.05) for treatments of PB levels. There was a linear effect on N intake (P=0.005), urine eliminated urea (P = 0.058) and fecal N excretion (P=0.039) for treatments with concentrate CP. A quadratic trend was observed for microbial protein synthesis (Pmic) (P=0.0003) and microbial efficiency (EFmic) (P=0.0073). Protein supplementation with different levels of CP does not alter the intake, apparent digestibility of DM and nutrients (EE, NDF, CNF and CT) and does not modify the patterns of ingestive behavior of lactating cows under Tanzania grass grazing. The different CP levels for lactating dairy cows in Tanzania grass pasture provided an increase in nitrogen excretion in feces and urine, thus contributing to the environmental impact through the release of ammonia and nitrites in the soil. The microbial protein was influenced by CP contents.