Hipomagnesemia subclínica em vacas leiteiras durante o período de transição: ocorrências hormonais e metabólicas

Abstract

O objetivo, com este estudo, foi investigar as conseqüências da hipomagnesemia subclínica sobre parâmetros metabólicos de vacas leiteiras. Amostras de sangue foram coletadas de 12 animais, a cada dois dias, entre os dias 22 pré e 22 pós-parto, para a realização de análises sanguíneas e determinação do perfil metabólico. Os animais foram categorizados de acordo com os níveis séricos de magnésio: Grupo Hipomagnesêmicas (n=5), com níveis abaixo de 1,8 mg/dL em ao menos dois dias consecutivos, e o Grupo Controle (n=7), com níveis acima de 1,8 mg/dL em todo o período. O grupo hipomagnesêmicas apresentou níveis de glucagon maiores nos dias 10, 18 e 20, e a taxa Glucagon/Insulina foi maior nos dias 6, 8, 10, 12 e 16 após o parto. As concentrações de aspartato amino transferase foram maiores no grupo hipomagnesêmicas nos dias 0, 6, 8, 10, 12 e 14 pós-parto. Os resultados indicaram que níveis reduzidos de magnésio no periparto podem estar relacionados com níveis elevados de aspartato amino transferase e de glucagon. Em geral, a hipomagnesemia subclínica não altera os níveis dos indicadores do metabolismo energético, mas os resultados demonstraram que as vacas com hipomagnesemia apresentaram maior taxa de glucagon/insulina, demonstrando um maior desafio para manter os níveis glicêmicos.

Subclinical hypomagnesemia: Prevalence and causes in dairy cows in the semiarid region of the state of Paraíba, Brazil

“…In a study carried out by Alvarenga et al (2015), of the 12 animals evaluated, one presented subclinical hypomagnesemia (1.67 mg.dL -1 ) five days after calving. Schimitt et al (2016), evaluating 11 cows during the transitional period, found that five presented subclinical hypomagnesemia (blood levels below 1.8 mg.dL -1 ) in both pre-and postpartum episodes, with emphasis on two cows whose Mg concentrations remained below normal serum levels for 60% of the experimental period. For the peripartum cow, the status of the Mg interferes with Ca metabolism.…”

“…According to Lean et al (2006), an increase in Mg concentration of 3 to 4 g.kg -1 dry matter in the animals' diet can reduce the risk of hypocalcemia in the herds by approximately 62%. Of the cows evaluated by Schimitt et al (2016), 41% presented subclinical hypomagnesemia, with the animals under continuous grazing of Brachiaria Decumbens and receiving commercial mineral supplement at will. The data is similar to that found in this study, where the group of cows that received commercial mineral supplement had the lowest levels of Mg in the blood.…”

“…Sudden changes in the metabolic and endocrine functions of the dairy cow that are associated with calving and early lactation make the transition period inherently difficult for the animal (Degaris & Lean, 2009). During this period diet is considered a conditioning element in the satisfactory performance, and when not given due attention, the animals may display reduced production (Sheehy et al, 2016). In nutritional management, mineral supply is essential for maintaining organic homeostasis, and during the preand post-partum period the cows can suffer changes in serum levels, with damage to the metabolism responsible for milk production.…”

“…In most cases, hypomagnesemia does not present clinically, but attacks dairy cows both sub-clinically and chronically, especially after delivery (Mulligan & Doherty, 2008;Pham et al, 2014). The prevalence of subclinical hypomagnesemia has not been adequately quantified in dairy herds, despite being an important risk factor for hypocalcemia usually associated with the development of peripartum metabolic disorders (Schimitt et al, 2016). The aim of this study was to determine the localised prevalence of subclinical hypomagnesemia in pre-and postpartum dairy cows inserted in milkproduction systems in the Sousa microregion and the district of São João do Rio do Peixe, both in the State of Paraíba, Brazil.…”