Calcium and Magnesium Urinary Excretion in Dairy Cows with Different Fee of Glucose Metabolization

Background: The post-partum period in dairy cows is accompanied by a low glucose metabolism in adipose tissue and skeletal muscle tissue, being glucose conducted to the milk production. In humans, low glucose metabolism is associated with metabolic syndromes, the high glucose levels reduce tubular reabsorption of Magnesium (Mg) and Calcium (Ca), leading to hypomagnesemia and hypocalcemia. These minerals are important to the dairy cow, as their decrease leads to diseases. The aim of this study was to evaluate the relationship between glucose metabolism rate with the urinary excretion of Ca and Mg in multiparous dairy cows during the post-partum period.Materials, Methods & Results: Twenty dairy cows were used from a commercial farm southern Brazil, in the semi-extensive system. Glucose tolerance tests were performed (TTG) on day 9 relative to calving. The cows were categorized into three groups according to the glucose metabolism rate (area under the glucose curve, glucose half-life and glucose consumption rate): High Glucose Metabolization (GA); Intermediate Glucose Metabolizing (GI); and Low Glucose Metabolization (GL). Blood and urine samples were collected on days 0, + 3, + 6, + 9, +16 and +2 3 in relation to calving for to determine the levels of Ca, Mg, insulin (Ins), non-esterified fatty acids (NEFA) and Glu. In urine was evaluated the excretion of Ca and Mg. The cows were milked twice a day (at 3:00 a.m. and 3:00 p.m.) and the milk yield (kg/cow) was recorded daily and averages were generated every five days from day 15 to day 60 postpartum. The statistical analyses were performed with the MIXED procedure to assess the main effect of group, time (in days) and their interaction by using version 9.2 SAS software. The influence of the different rates of glucose metabolism on milk production was observed, the GB group had a production than GH group (30.88 ± 1.44 kg vs 23.96 ± 1.43 kg, P < 0.01), but did not differ from GI. The GL group showed higher levels of Glu compared to GA (P < 0.05). The plasma Ca levels were higher in GL (P < 0.05) compared with GH. The NEFA, insulin, and excretion of minerals did not differ between groups (P > 0.05).Discussion: The low glucose metabolism in humans causes an increase in the excretion of Ca and Mg urine, however, in the animals studied, these changes were not observed. This result can be attributed to the fact that insulin resistance is transitory in dairy cattle. The higher glucose levels in the GL group are related due to the lower capacity of glucose entry in the peripheral tissues (adipose and skeletal muscle), which reflected in the higher milk production observed this group. However, the higher calcium concentrations were not expected, since the release of insulin by β-pancreatic cells is dependent on calcium. Possibly, these higher calcium levels in GB, are related to higher milk production, requiring a greater amount of calcium for the production of casein, increasing bone mobilization, intestinal absorption. The energy metabolites, non-esterified fatty acids and insulin, did not differ between groups, suggesting that the animals did not present different metabolic conditions. We conclude that multiparous dairy cows with low glucose metabolism rate (GB) have higher levels of glucose after delivery and increased milk production. The metabolism rate of glucose did not influence the excretion of the Ca and Mg minerals