A total of twelve lactating Jersey cows were used in a 5-week experiment to determine the effects of severe feed restriction on the permeability of mammary gland cell tight junctions (TJs) and its effects on milk stability to the alcohol test. During the first 2 weeks, cows were managed and fed together and received the same diet according to their nutritional requirements (full diet: 15 kg of sugar cane silage; 5.8 kg of alfalfa hay; 0.16 kg of mineral salt and 6.2 kg of concentrate). In the 3rd week, animals were distributed into two groups of six cows each. One group received the full diet and the other a restricted diet (50% of the full diet). In the 4th and 5th weeks, all animals received the full diet again. Milk composition and other attributes, such as titratable acidity, ethanol stability, pH, density and somatic cell count (SCC) were evaluated. Cortisol levels indicated the stress condition of the cows. Plasma lactose and milk sodium were measured to assess mammary TJ leakiness. Principal factor analysis (PFA) showed that the first two principal factors (PFs) contributed with 44.47% and 20.57% of the total variance in the experiment and, as feeding levels increased, milk stability to the ethanol test became higher and plasma lactose levels decreased, which indicates lower permeability of the mammary gland cell TJ. Correspondence analyses were consistent with PFA and also showed that lower feeding levels were related to reduced milk stability, high plasma lactose, high sodium in milk, low milk lactose (another parameter used to assess TJ permeability) and higher cortisol levels, indicating the stress to which animals were submitted. All observations were grouped in three clusters, with some of the above-mentioned patterns. Feeding restriction was associated with higher permeability of TJ, decreasing milk stability to the ethanol test.
Resumo -O objetivo deste trabalho foi caracterizar a produção e a qualidade do leite em sistemas de produção da região Sul do Rio Grande do Sul e verificar a porcentagem de amostras que se enquadram nos limites determinados pela Instrução Normativa 51 (IN 51). De setembro de 2000 a agosto de 2001, exceto janeiro, foram monitoradas, mensalmente, dez unidades de produção leiteira classificadas nos seguintes sistemas de produção: especializado, semi-especializado e não especializado. Em amostras coletadas no tanque resfriador, foram avaliadas características físico-químicas do leite, realizada a contagem de células somáticas e a produção de leite foi corrigida para 4% de gordura. Houve diferença significativa entre os sistemas para produção de leite, porcentagens de gordura, lactose, caseína, sólidos totais, sólidos desengordurados, contagem de células somáticas, acidez titulável e densidade. Consideradas todas as características do leite, apenas 41,8% das amostras se enquadraram nos limites estabelecidos pela IN 51. A maior especialização dos sistemas resultou em aumento da produção de leite e menor contagem de células somáticas, além de maiores valores porcentuais da caseína, lactose e sólidos desengordurados, possivelmente pelo melhor manejo nutricional e higiene na ordenha.Termos para indexação: propriedades físico-químicas do leite, contagem de células somáticas, Instrução Normativa 51, produção de leite. Milk quality in production systems in the Southern region of Rio Grande do Sul, BrazilAbstract -The objective of this work was to characterize milk yield and quality of production systems in the southern region of Rio Grande do Sul, and verify the proportion of samples in the range allowed by Federal Normative Instruction 51 (IN 51), created to establish quality parameters for milk in the country. From September 2000 to August 2001, except January, ten dairy production units were monthly evaluated and then classified into three productions systems: specialized, partially specialized and nonspecialized. Bulk tank milk was sampled to determine physicochemical characteristics, somatic cell count and milk production was corrected to 4% milk fat. Production systems differed statistically for milk production, percentages of fat, lactose, casein, total solids, nonfat solids, somatic cell count, acidity and density. Only 41.8% of samples were in the acceptable range of IN 51 rules. Production systems greatest specialization resulted in higher milk yield, reduced somatic cell count and larger percentages for milk casein, lactose and non-fat solids, probably due to better nutritional management and milking hygiene.
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.
Resumo -O objetivo deste trabalho foi avaliar o efeito da restrição alimentar na incidência do leite instável não-ácido (LINA) e na composição do leite de vacas Jersey. Foi realizado um experimento piloto de indução ao LINA, com oito vacas Jersey em lactação, confinadas e separadas em dois grupos, às quais havia sido fornecida uma dieta equilibrada ad libitum. Em dois períodos de 18 dias, foram fornecidos dois tratamentos com 100 e 60% das exigências nutricionais. Foram realizados os testes de acidez titulável e do álcool 76%; pH, densidade, crioscopia, caseína, gordura, proteína bruta, lactose, extrato seco total, número de células somáticas e produção de leite foram determinados. A restrição alimentar aumenta a ocorrência de LINA e diminui a produção de leite e a quantidade total dos componentes produzidos; entretanto, não altera os teores dos componentes lácteos.Termos para indexação: estabilidade do leite, subnutrição, teste do álcool/etanol, vacas em lactação. Unstable nonacid milk and milk composition of Jersey cows on feed restrictionAbstract -The objective of this work was to evaluate the effects of feed restriction on unstable nonacid milk occurrence and milk composition of Jersey cows. A pilot trial of feed restriction was conducted with eight lactating Jersey cows. Animals were confined and allocated to two groups which received a balanced diet ad libitum. They received sequentially two treatments, at different periods: 100 and 60% of nutritional requirements. Milk was analyzed for titrated acidity and precipitation at alcohol test 76%; pH, density, cryoscopy, casein, fat, crude protein, lactose, total solids, number of somatic cells and milk production were determined. Feed restriction increases unstable nonacid milk occurrence, reduces milk production and amount of components; however, it does not change the concentration of the milky components.
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