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Milk and its derivatives are important foods that contribute to daily nutrient requirements and improve consumers’ health. This study evaluated the effects of supplementing the diet of lactating dairy cows with sunflower oil (SFO), selenium, and vitamin E on the milk’s fatty acid profile and fat oxidative stability as well as the acceptability of the milk by consumers. For this purpose, 32 Jersey dairy cows were allocated to four treatment groups for 60 days, as follows: C (control diet); A (3.5 mg/kg DM (dry matter) organic selenium + 2000 IU vitamin E/cow per day); O (4% SFO DM); OA (equal doses of A and O treatments). The inclusion of SFO decreased the contents of 10:0, 10:1, 11:0, 12:0, 12:1, 14:0, and 9c-14:1 fatty acids as well as odd- and branched-chain fatty acids (13:0, iso 13:0, anteiso 13:0, 15:0, iso 15:0, and 17:0). There was also a tendency for 8:0 and 16:0 fatty acid concentrations to decrease when SFO was included in the cows´ diet. SFO decreased the concentration of 10:0 to 15:0 fatty acids in milk. The sum of the conjugated linoleic acids (CLAs), conjugated alpha-linolenic acid intermediates (CLnAs; 18:3 ω6 + 18:3 ω3), and 22:0 fatty acids in milk tended to increase, and there were significant increases in 18:0 and 9c11t-18:2 with SFO. In terms of the effects of SFO on the health-related lipid indices, the atherogenicity index tended to decrease and h/H tended to increase. When cows were supplemented with antioxidants, the concentration of 20:2 fatty acids decreased, the 6 + 7 + 8 + 9t-18:1, 16t-18:1, 20:0, 22:2, and 24:0 fatty acid concentrations increased, and there was a trend for the 22:1 ω9 fatty acid concentration to increase with antioxidants plus oil. There was a tendency for ω6 fatty acids and ω6/ω3 to increase with milk treated with antioxidants plus oil. The oxidative stability of milk was not influenced by the presence of SFO or antioxidants in the diet of dairy cows. Consumers desired the color and mouthfeel of the milk that was treated with SFO. Cows fed with 4% sunflower oil produced milk with an improved fatty acid profile for human nutrition, containing a higher CLA content and an improved ratio of hypocholesterolemic and hypercholesterolemic fatty acids, without increasing the milk’s susceptibility to oxidation. The milk was also rated as being more acceptable by consumers.

RESUMOAvaliou-se o efeito da variação da qualidade do leite mediante acompanhamento de amostras provenientes de tanques refrigeradores. As 2.970 amostras foram obtidas de outubro/2005 a setembro/2006. Foram realizadas análises de composição, contagem de células somáticas (CCS) e contagem bacteriana total. As condições climáticas foram avaliadas pela temperatura e umidade do ar coletadas em estações meteorológicas distribuídas em todo o estado de São Paulo. No outono, ocorreram os maiores valores para gordura e proteína do leite, 3,65 e 3,21%, respectivamente. Para contagem de células somáticas, foi observado aumento no verão e contagem bacteriana na época da primavera. Foi identificada a influência da época do ano sobre o preço do leite pago dentro de um programa, com valor de bonificação máxima de 7,9% para o outono. Um dos mais importantes itens relacionados com a penalização foi a CCS, a qual pode interferir na qualidade dos produtos finais por meio de alteração da proporção de caseína/proteínas do soro. O efeito da CCS e o da época do ano devem ser considerados na formulação das tabelas de programas de pagamento.

This study investigated the association of electrical conductivity (EC) of milk with milk production and composition traits in Dairy Gyr cows. Monthly milk samples were collected on the official milk recording day for laboratory analysis of somatic cell count, EC and milk composition. A total of 680 samples from 268 cows belonging to eight herds in the southeastern region of Brazil were collected between January and July 2012. Traits were analysed by the restricted maximum likelihood method using mixed models in order to associate EC and somatic cell score (SCS) with the other traits. Mean EC and SCS were 4.90 mS/cm and 4.66, respectively, and the correlation between these traits was 0.41. Linear regression of EC on SCS indicated an increase in EC of 0.094 mS/cm per SCS. Despite the relationship between EC and SCS, the former analysed only on the official recording day may not be a reliable method for the diagnosis of mastitis. However, EC could be used as an auxiliary trait in the analysis of mastitis resistance simultaneously with somatic cell count since, in addition to the association between these two traits, the measurement of EC is an inexpensive, simple and rapid method.

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Among tropical forages, corn silage is largely used by farmers trying to explore the maximum genetic potential from the animals. However, other tropical forages, such as elephant-grass (Pennisetum purpureum), are more productive and therefore cheaper to use than corn silage. Our objective was to compare the in situ degradability of elephant-grass with that from corn hybrids, all harvested at four stages of maturity. The experimental design followed a randomized block design with nested subplots. Two corn hybrids: AG5011, ZN8392 were harvested with 25, 30, 35, and 40% dry matter (DM) in the whole plant, and separated in stem + leaf sheath + leaf blade (stover), and cobs. Elephant-grass was harvested with 30, 40, 50 and 60 days after a leveling cut. Dried and ground samples were incubated in nylon bags inside the rumen for 0, 6, 12, 24, 48 and 72 h to estimate the kinetics of ruminal DM and neutral detergent fiber (NDF) degradation. The advance of maturity increased the NDF and acid detergent fiber (ADF) content in elephant-grass, and reduced its DM degradability. However, maturity had little or no effect on fiber content and DM degradability of corn stover. Elephant-grass had a higher NDF degradability than corn stover, and there was no effect of maturity on NDF degradability of either elephant-grass or corn stover. Fiber degradability of elephantgrass was not worse than that of corn stover, and therefore the choice of forage should be made on economical analysis rather than assuming an intrinsic low production potential for elephant-grass based diets. Key words: Pennisetum purpureum, corn silage, digestibility, rumen, tropical grass DEGRADABILIDADE IN SITU DE HÍBRIDOS DE MILHO E DE CAPIM-ELEFANTE COLHIDOS EM QUATRO ESTÁDIOS DE MATURIDADE

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