Avaliação do sistema FDN fisicamente ajustado em vacas em lactação primíparas e multíparas

Abstract

The National Academies of Sciences, Engineering, and Medicine (NASEM, 2021) introduced the concept of physically adjusted neutral detergent fiber (paNDF) to establish recommendations for dietary particle size based on ruminal pH and its interactions with other dietary components. However, this system still requires validation under field conditions. This study aimed to evaluate the application of the paNDF system in primiparous, and multiparous lactating dairy cows fed a total mixed ration. A total of 46 lactating cows were used, including 19 primiparous and 27 multiparous animals, housed in a Compost Barn system. Rumination time was monitored using CowMed® electronic collars, whereas predicted rumination time and the recommended percentage of particles retained on the 8 mm sieve were estimated using the MUNCH application based on the percentage of particles retained on the 19-mm sieve, neutral detergent fiber (NDF), acid detergent fiber (ADF), crude protein (CP), dietary starch content, and body weight. The experiment was conducted in a completely randomized design with repeated measures over time. Multiparous cows showed longer rumination time than primiparous cows; however, both groups remained above 500 minutes of rumination per day. Observed rumination times were greater than those predicted by the paNDF system, indicating discrepancies between model estimates and field responses. No significant correlation was found between rumination time recorded by the electronic collars and that predicted by the paNDF system using the MUNCH application. In contrast, physically effective neutral detergent fiber (peNDF) values were more consistent with the responses observed in the animals. Diets presented peNDF levels compatible with adequate rumination, and the correlations observed between peNDF and rumination time indicated that this parameter more accurately represented the physical effectiveness of fiber under the evaluated conditions. The paNDF system could not adequately predict the rumination behavior of dairy cows. Conversely, the peNDF concept showed a stronger association with the observed responses, suggesting greater applicability for evaluating the physical effectiveness of fiber in diets with a higher proportion of forage and lower starch concentrations. Further studies are required to validate and adjust the paNDF system to the feeding conditions commonly found in Brazilian dairy production systems.