| Resumo: | The interpretation of milk metabolites from milk recording can be indicative of nutritional and metabolic disorders. The nutrient imbalances as the relationship between carbohydrates fermentability and protein degradability in the rumen can be diagnosed by milk urea nitrogen (MUN), protein and relation of fat/protein (F/P) in milk. The metabolic imbalances, as the negative energy balance, hyperketonemia, ketosis and acidosis can be diagnosed by β-hydroxybutyrate (BHB), fat and the relation of F/P in milk. Thus, milk metabolites can be indicators of health and welfare of the cow. This study analysed 110,461 individual milk samples of 9,523 lactating dairy cows collected monthly from January 2015 to March 2017 from 27 herds of South of Portugal, with an official milk recording. The mean of lactating cows per herd was 353±270 (mean ± SD) and milk production per cow was 35.08±9.80 kg/day. During the first 30 days of lactation 7.7% of milk recording had BHB concentration over 0.2 mmol/l, indicating that these cows had high possibility of being with clinical ketosis. 44.8% of milk recording had the relation of F/P over 1.4 and 49.3% had milk fat over 4.5% indicating that about 45% of the cows were probability mobilizing body fat. 86.7% of milk recording had MUN concentration between 101 and 299 mg/kg indicating that the relation between carbohydrates and protein of the diet was appropriate. On the other hand, 11.9% of milk recording had the relation of F/P above 1.4 and 21.6% had milk protein above 3% indicating that some animals are ingesting a small proportion of protein in the diet comparing with the quantity of carbohydrates. In conclusion, these non-invasive biomarkers can reflect nutritional and metabolic disorders, but the interrelation between them must be taken into account. The thresholds of this milk metabolites to indicate health disorders are not consensual among the authors.
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