Avaliação de tamponantes, metionina rúmen-protegida e Aspergillus spp. como aditivos em dietas para vacas leiteiras: abordagens in vivo, in situ e in vitro

Abstract

This dissertation aimed to address the findings of three distinct studies. The first study, using an in vivo approach, evaluated the inclusion of a buffer blend composed of calcitic limestone, magnesium oxide, calcareous algae, and sodium bicarbonate (BBA), compared with the isolated use of sodium bicarbonate, in the diet of 36 Holstein cows (BBA, n = 18; Sodium Bicarbonate, n = 18). The second study, conducted in vitro, assessed the effects of a formulation containing Aspergillus oryzae and A. niger on ruminal digestibility of three total mixed rations (TMRs), incubated for 12, 30, 48, and 120 hours under simulated ruminal conditions. The third study, using an in situ approach, evaluated the ruminal resistance of a rumen-protected methionine (RPMet) product during 10 hours of incubation in fistulated steers, adopting a 3 × 4 crossover design with three treatments (Control; RPMet; unprotected methionine [UnMet]) and four periods, totaling four animals per group. The results of the first study indicated that cows supplemented with BBA exhibited higher fecal pH (P < 0.05) and greater feed efficiency (P < 0.05) compared with cows receiving sodium bicarbonate alone. In the second study, there was a trend (P = 0.07) toward greater dry matter digestibility and a significant increase in organic matter digestibility (P = 0.04) in a TMR where corn silage was partially replaced by wheat straw. In the third study, it was observed that, after 10 hours of incubation, 94.05 ± 1.42% of the RPMet dose resisted ruminal degradation, whereas only 20.30 ± 1.22% of the UnMet dose remained resistant (P < 0.01). Overall, the findings of this dissertation indicate that the inclusion of buffers and the co-culture of Aspergillus oryzae and Aspergillus niger improve ruminal stability parameters, digestibility, and feed efficiency. Moreover, the evaluated RPMet product demonstrated high resistance to ruminal degradation, highlighting its potential for intestinal absorption.