Metabolic Profile of Holstein Cows: Reference Values in Herds of Rio Grande do Sul - Brazil

Background: Assessing data from metabolic profile is a complex task depending on individual factors such as breed, age, sex and physiological status and environmental factors such as climate and management. Therefore, reference intervals produced in herds from different geographic regions are not always precise in the local reality. The aim of this study is to compile results of values of the most used parameters in the metabolic profile of healthy Holstein cows, grouped by lactation stage, obtained from studies in Rio Grande do Sul, Brazil, as an effort for the elaboration of regional reference intervals for dairy cattle in this geographic area. Materials, Methods & Results: The research was defined through the PICO strategy, considering multiparous Holstein cows from scientific studies carried out in Rio Grande do Sul, during the period 1996-2021, in which the nitrogen, glycidic, lipidic, enzymatic or mineral metabolic profile was determined. Goggle Scholar, Scientific Electronic Library and PubMed were the electronic databases selected for the search, using the following descriptors: "profile" and "metabolic" and "metabolic profile" and "dairy" or "cattle" or "cow" and "Brazil" and "southern" or "Rio Grande do Sul". Studies in Portuguese, English and Spanish languages were considered. The references of the articles initially selected were also verified, through ResearchGate and Google Scholar, in addition to unpublished data, unfinished studies or data in the so called "gray literature". It was possible to identify a total of 34 publications, which were tabulated to assess the scientific quality and bias risk. Studies were evaluated by a pair of independent reviewers, in order to compare results. Eligibility confirmation was given after the complete reading of the articles, evaluating the presence of all the inclusion selection criteria, such as adequate population and the intervention made. Examples of exclusion criteria for studies were studies or data duplication and methodological flaws that could compromise reliability. Thus, of the 34 studies selected in the initial screening, 14 remained. Thereafter, observational studies were preferably sought for data extraction. In the case of clinical trials, only data from control groups were used, in order to avoid disturbances due to interventions or treatments that could be applied. The reference intervals or means of the evaluated metabolites extracted from these studies were grouped in tables, in order to facilitate the comparison with research results obtained in different regions or even for comparison with future studies in the region of interest. Discussion: This retrospective study obtained mean values and standard deviation of the most used parameters in the metabolic profile of Holstein cows, grouped by lactation stage, obtained from studies performed in the state of Rio Grande do Sul, Brazil. Divergences were observed in several evaluations, especially in values of albumin, beta-hydroxybutyrate, aspartate transaminase and calcium, in spite of all data represented healthy animals from research trials with adequate environment and diet. It is important to consider the risk of time bias in this study, as within this 25-year period there was a very large evolution in dairy farming and some values may not be fully representative of current management systems in Holstein herds. Nevertheless, the results reinforce the importance of using regional reference values for the proper interpretation of metabolic profile results in dairy cows. In addition, the proposing of database index for regional averages or reference intervals, is useful for comparing results of metabolic profiles carried out in different geographic regions, in future studies to be performed in this particular region, or even to be utilized by field practitioners of this particular region.