Fatores nutricionais e comportamentais associados à dinâmica do pH ruminal em vacas leiteiras

Abstract

This work aimed to integrate different approaches to investigate the occurrence of subacute ruminal acidosis in dairy cows, as well as feeding behavior and nutritional and/or monitoring strategies for its prevention, with potential implications for productivity and animal health in dairy systems. To achieve this, three complementary studies were conducted, combining controlled experimentation, integration of experimental datasets, and evaluation under commercial conditions. In the first study, magnesium phosphate (MgP) was evaluated as a source of magnesium and phosphorus for lactating dairy cows. Supplementation with MgP, either alone or in combination with magnesium oxide, did not affect dry matter intake, milk yield, or ruminal pH and fermentation variables. However, increased dietary magnesium supply increased milk fat concentration, which was associated with greater proportions of preformed fatty acids and higher ether extract digestibility, as well as improved total-tract nutrient digestibility. In the second study, associations among carbohydrate intake, feeding behavior, and ruminal pH dynamics were evaluated using integrated data from two experiments with continuous ruminal pH measurement via bolus sensors. Fiber intake, particularly forage NDF and physically effective NDF relative to body weight, was positively associated with rumination and chewing time and with indicators of greater ruminal pH stability. Rumination modified the relationship between fiber intake and ruminal pH, whereas parity effects indicated greater responsiveness in multiparous cows and increased susceptibility of primiparous cows to unfavorable pH conditions. Ruminal pH variables were also associated with productive performance, milk fatty acid profile, and physiological markers. In the third study, the potential of collar-derived rumination time as a tool for nutritional monitoring at the pen level under commercial conditions was evaluated. Rumination time was positively associated with milk yield and dry matter intake and showed strong relationships with diet composition and nutrient intake variables, particularly lignin. These associations were more pronounced in early lactation, and the results indicate that sensor-derived rumination data can serve as useful indicators of nutritional management in commercial dairy systems. Overall, the results demonstrate that ruminal pH dynamics and their relationship with productive performance depend on the interaction among fiber intake, feeding behavior, and animal characteristics, and that sensor-based tools have potential to support nutritional monitoring and decision-making in dairy production systems.