Mammary gland amino acid affinity in response to different levels of dietary protein and insulin
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Animal Science Laboratory, Center of Nuclear Energy in Agriculture, University of Sao Paulo, Piracicaba, SP, Brazil.
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The aim of this study was to investigate mammary gland clearance rates for essential (EAA), non-essential (NEAA) and branched-chain (BCAA) amino acids from plasma, in response to different levels of dietary metabolizable protein (MP) and insulin. Six lactating Holsteins cows (590 kg BW; 32.96 kg milk/day), were randomly assigned in a 2×2 factorial arrangement crossover design. The diet was formulated to be either protein sufficient (17.5%/DM; SMP) or deficient (14.0%; DMP). Milk samples were collected daily. Arterial and venous blood was sampled via catheters every hour (h) for 8 h without infused insulin (NI), and after 4 days of an intravenous infusion of 1 μg of insulin/kg of BW per h plus varying glucose to achieve hyperinsulinemic-euglycemic status (HI). Plasma was obtained by centrifugation, and analyzed for EAA and NEAA concentrations by isotope dilution. Clearance rate (CR) was determined as: CR_AALblood/h= ([Artery_AA]umol/Lblood × Blood FlowLblood/h / [Vein_AA]umol/Lblood) – Blood FlowLblood/h. Statistical procedures were performed by R Studio. Milk yield was affected by dietary protein (P=0.03) and the interaction with insulin (P<0.01). There was an effect of insulin on Thr (P<0.01), BCAA (P=0.01) and total NEAA (P<0.01). In addition, an effect on MP for total EAA (P=0.05) was observed, with decreasing CR as MP increases.