Nível energético em dietas de vacas leiteiras no período de transição: revisão sistemática e metanálise

Abstract

The objective of this study was to verify the appropriate energy level to decrease the effects of negative energy balance in animals during the transition period. For systematic review, the criteria for the selection of papers were: (1) in vivo experimental evaluation of diets with different energy levels; (2) presentation of initial, final and/or total results; (3) stated treatment period; (4) expressed data of dry matter intake (DM), milk production, and blood data or feed efficiency. Graphical analyses were used to check the distribution of the data and to obtain an overview of their consistency and heterogeneity of variance. Next, correlation hypotheses were formulated to define the statistical models, and thus, preliminary analysis of the data obtained was performed, following a polynomial regression model. The means were organized and evaluated in parameters of dispersion and quality of fit, such as the Q test and residual heterogeneity. Since there was no repeatability of energy levels, the adjustment was made through normality analysis, dividing the data by quartiles. Thus, data were grouped into four energy classes (levels), where quartiles were grouped as follows, 1st - energy consumption from 17,390 to 26,844 Mcal/day; 2nd - energy consumption from 26,845 to 31,868 Mcal/day; 3rd - energy consumption from 31,869 to 35,681 Mcal/day; 4th - energy consumption from 35,682 to 46,838 Mcal/day. The variables milk production, milk production corrected for 4% fat, protein and lactose showed no significant differences (P>0.05). The results of fat percentage showed significant difference (P>0.05). Feed efficiency, postpartum energy balance, prepartum and postpartum body condition and β-hydroxybutyrate showed no significant difference, while prepartum energy balance, glucose level and non-esterified fatty acids were influenced by diet energy level (P>0.05). Intake levels of pre-labour metabolizable energy between 17,390 and 35.681 Mcal/day of metabolizable energy are the most indicated to decrease the effects of negative energetic balance in the animals and maximize milk production.