Caracterização eletroforética de proteínas e estabilidade do leite em vacas submetidas à restrição alimentar

Abstract

Resumo -O objetivo deste trabalho foi avaliar os efeitos da restrição alimentar sobre a produção de leite bovino e sobre seu perfil eletroforético de proteínas, bem como relacioná-los à estabilidade do leite pelo teste do álcool. Foram conduzidos dois experimentos com vacas Jersey: no primeiro, avaliou-se o efeito da redução de 40% na alimentação fornecida a vacas semiconfinadas; no segundo, avaliou-se o efeito da restrição de 30% do conteúdo de nutrientes digestíveis totais na alimentação de vacas confinadas. As frações proteicas foram determinadas por eletroforese, e sua quantificação por meio de análises de imagens. As amostras de leite foram classificadas conforme estabilidade no teste do álcool a 72°GL. A restrição alimentar de 40% a vacas semiconfinadas reduziu a produção de leite, mas não alterou a composição de proteínas lácteas e a estabilidade do leite; neste caso, o leite instável apresentou maiores teores de β-caseína e de proteínas totais, porém menor proporção de κ-caseína em comparação ao leite estável. A restrição de 30% do aporte energético a vacas confinadas não reduziu a produção leiteira, porém diminuiu a percentagem de albumina sérica bovina e a estabilidade no teste do álcool; neste caso, o leite instável e o estável não diferiram quanto às proteínas lácteas.Termos para indexação: b-caseína, κ-caseína, confinamento, eletroforese, leite instável não ácido, teste do álcool. Electrophoretic characterization of proteins and milk stability of cows submitted to feeding restrictionAbstract -The objective of this work was to evaluate the feeding restriction effects on milk yield and on its electrophoretic protein profile, and to relate them to milk stability to the alcohol test. Two experiments were carried out with Jersey cows: in the first one, the effect of 40% feed restriction was evaluated on semiconfined cows; in the second one, the effect of 30% reduction in total digestive nutrients was evaluated on confined cows. Protein fractions were determined by electrophoresis and their quantification was done by image analysis. Milk samples were classified according to their stability in the 72°GL-alcohol test. The 40% feed restriction for semiconfined cows decreased milk yield, but it did not change milk protein contents and stability; in this case, unstable milk showed larger contents of β-casein and total proteins, but lower κ-casein in comparison to stable milk. The 30% restriction of energy supply for confined cows did not reduce milk yield, but decreased the percentage of serum bovine albumin and milk stability; in this case, unstable and stable milk did not differ as for protein fractions.

Effect of dietary cation-anion difference on performance of lactating dairy cows and stability of milk proteins

“…Also, high raw milk stability is needed to avoid losses to dairy farmers due to price penalty or rejection of milk, to prevent coagulation of milk during heat treatment (Fischer et al, 2012), and also to reduce the age-related gelation of heat-treated milks during storage (García-Risco et al, 1999). Thus, the milk ethanol stability (MES) test is still used worldwide in receiving platforms of dairy plants to predict the stability of milk proteins (Fischer et al, 2012).…”

“…However, κ-CN, which is located in the outer layer of the micelle, is hydrophilic and stable to iCa reaction and therefore protects the micelle hydrophobic core (composed of α-and β-CN) from water contact and iCa ionization (Creamer et al, 1998;Walstra, 1999). Thus, the structural arrangement of α-, β-, and κ-CN in the micelle, the milk concentrations of divalent cations, and the electrostatic repulsion strength between micelles may determine the heat stability (Jeurnink and De Kruif, 1995;Barros et al, 1999;Fischer et al, 2012), the formation of β-LG/κ-CN complexes on heating, and, subsequently, formation of irreversible gel in UHT milk during storage (McMahon, 1995;García-Risco et al, 1999).…”

“…Moreover, most studies reported that the nutritional and metabolic conditions of dairy cows were the main factors that changed the milk stability (Zanela et al, 2006;Marques et al, 2011;Barbosa et al, 2012). Barbosa et al (2012) reported that cows fed with nutrientdeficient diets produced milk with lower concentrations of κ-CN and, consequently, lower ethanol stability when compared with milk from cows fed balanced diets. Alternatively, Marques et al (2011) reported that the metabolic acidosis of dairy cows, through the action of parathyroid and 1,25-dihydroxycholecalciferol hormones, may increase milk concentrations of iCa and reduce the MES.…”

“…Milk constituents associated with milk stability can be changed directly by the nutrition and metabolic status of dairy cows (Marques et al, 2011;Barbosa et al, 2012;Fischer et al, 2012). However, few studies on the individual, nutritional, or metabolic factors that may alter milk protein stability exist, as both deficient and excess nutrients (through metabolic acidosis resulting from ruminal acidosis) can reduce milk stability by different means (Marques et al, 2011;Barbosa et al, 2012;Fischer et al, 2012).…”

“…However, few studies on the individual, nutritional, or metabolic factors that may alter milk protein stability exist, as both deficient and excess nutrients (through metabolic acidosis resulting from ruminal acidosis) can reduce milk stability by different means (Marques et al, 2011;Barbosa et al, 2012;Fischer et al, 2012). The use of anionic diets can be applied to study the effect of metabolic acidosis in lactating dairy cows on milk composition and stability without changing the protein and energy content of the diet (Marques et al, 2011).…”