Made available in DSpace on 2014-12-17T15:34:47Z (GMT). No. of bitstreams: 1 MayaraLJB_DISSERT.pdf: 1993520 bytes, checksum: a4115cc58db013fd3492bae607af2afe (MD5) Previous issue date: 2013-02-27 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / The direct relationship with the processing, industrial yield and price of milk, the importance of the centesimal composition of milk and their protein fractions has increased for both the dairy industry and for the producers, so it is important to identify the possible causes on variation of these components. The aim of this study was to evaluate the effect of the seasons, order of calving and lactation phase on milk composition and protein fractions in dairy farms in the Agreste and Leste meso-regions, of Rio Grande do Norte State (RN). Milk samples were taken in seven milk farms directly from the bulk tanks except for one farm where samples were taken from higher milking cows producers and heifers. The experiment was done in seven properties with milk samples taken directly from the bulk tanks and in one property were collected from higher production cows and heifers. Composition analyses were carried out for both experiments and sensorial trial was performed for the second experiment only. The data results were submitted to analysis of variance (ANOVA) and Tukey test performed for 5% significance level. In the first experiment was observed response of the seasons, dry and rainy season; while in the second, the effect of the order of calving and lactation phase had influence on milk composition and protein fractions. There was significant response (p < 0.05) for season effects but due to farms. The rainy season had higher averages in the protein, lactose, total solids and nonfat dry extract. Multiparous cows had higher CCS, NUL and PCAS milk contents; while, first calving heifers showed higher average for the sensory attribute, color of milk. The final third of lactation was responsible for the elevation of the levels of almost all milk components and their protein fractions / Mediante a crescente import?ncia da composi??o centesimal do leite e suas fra??es proteicas, para a ind?stria de latic?nios e para os produtores, em fun??o da rela??o direta com o processamento, rendimento industrial e pre?o do leite, torna-se relevante verificar poss?veis causas de varia??o desses componentes. Dessa forma, objetivou-se com este estudo avaliar o efeito das esta??es do ano (seca e chuvosa), da ordem de parto e da fase de lacta??o sobre a composi??o do leite e suas fra??es proteicas em propriedades nas mesorregi?es agreste e leste do Rio Grande do Norte - RN. O experimento foi realizado em sete propriedades, com coleta de leite em tanques de expans?o e em uma destas por amostragem do lote de vacas de maior produ??o e de novilhas. Foram realizadas an?lises de composi??o do leite e sensorial. Os respectivos resultados foram analisados por meio da an?lise de vari?ncia (ANOVA) com as poss?veis diferen?as entre as m?dias (p<0,05) pelo teste de Tukey. N?o houve efeito da esta??o do ano nos componentes do leite. No entanto, houve efeito de intera??o da esta??o do ano com a fazenda na prote?na, lactose, s?lidos totais e no extrato seco desengordurado. Na composi??o do leite a ordem de parto influenciou os teores de CCS, NUL e PCAS e na sensorial o atributo cor. Os est?dios de lacta??o influenciaram os teores todos os componentes do leite, com exce??o do ESD