Dairy cows experiencing heat stress have reduced intake and increased reliance on glucose, making feeding strategies capable of improving diet digestibility plausible for improving postrumen nutrient flow and performance. The effect of yeast on digestion and performance of lactating cows during the warm summer months of southeastern Brazil was evaluated. Cows were individually fed in tie stalls and temperature-humidity index was above 68 during 75.6% of the experiment. Twenty-eight Holstein cows (207±87 d in milk) received a standard diet for 14 d and then a treatment for 70 d, in a covariate-adjusted, randomized block design with repeated measures over time. Treatments were yeast (Saccharomyces cerevisiae) or control. Yeast was top dressed to the diet in the morning, equivalent to 25×10(10) cfu of live cells and 5×10(10) cfu of dead cells. The diet contained corn silage (37.7%), Tifton silage (7.1%), raw soybeans (4.1%), soybean meal (16.5%), finely ground corn (20.7%), and citrus pulp (11.9%). Yeast increased milk (26.7 vs. 25.4 kg/d) and solids yield (3.06 vs. 2.92 kg/d), especially lactose. Response in milk yield was consistent over time and started at d 5. The daily intake of digestible OM, total-tract digestibility of nutrients, urinary allantoin excretion, chewing pattern throughout the day, and dry matter intake did not respond to yeast. A trend was observed for increased plasma glucose with yeast (62.9 vs. 57.3mg/dL), lowered respiratory frequency (48 vs. 56 breaths/min), and increased plasma niacin content (1.31 vs. 1.22 µg/mL), though cows had similar rectal temperature. Ruminal lactate and butyrate as proportions of ruminal organic acids were reduced by yeast, but no effects on other organic acids, ruminal pH, or protozoa content were detected. Plasma urea N over 24h was increased by yeast. On d 72 to 74, citrus pulp was abruptly replaced with finely ground corn to induce acidosis. The increased load of starch increased dry matter intake between 0700 and 1300 h, jugular blood partial pressure of CO2, HCO3-, and base excess, and decreased blood pH for both treatments. The yeast treatment had a higher blood pH compared with the control, 7.34, and 7.31, respectively. Yeast supplementation improved lactation performance of dairy cows under heat stress. Improvement in lactation performance apparently involved the regulation of body homeothermia, rather than improved digestibility.

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RESUMO:O Lentinus edodes -cogumelo comestível pertencente à família Agaricaceae e popularmente conhecido como shitake -é apreciado há séculos na culinária e medicina oriental devido ao seu sabor agradável e alto valor nutritivo. Visando destacar os benefícios do L. edodes, o presente trabalho teve como objetivo a realização da análise nutricional desse alimento. A qualidade do L. edodes como fonte protéica também foi avaliada e comparada com a carne bovina, o feijão e a soja, considerando que estes alimentos, assim como os cogumelos, são ricos em proteínas. Para avaliação do valor nutricional protéico do L. edodes, foram calculados os escores químicos de seus aminoácidos essenciais. Para fins de comparação, também foram utilizados os valores de digestibilidade protéica para o L. edodes, carne bovina, feijão e soja. O L. edodes analisado apresentou elevado teor protéico (17,14%), baixo teor de gorduras (1,23%) e baixa digestibilidade comparado à carne bovina. Os valores dos escores químicos para o L. edodes apresentaram-se todos maiores do que 1,0, indicando que suas proteínas possuem alto valor biológico, assim como a carne bovina. Os resultados obtidos mostram que o L. edodes apresenta proteínas de maior valor nutricional do que o feijão e a soja, sendo inferior à carne bovina neste quesito. Palavras-chave: shitake; Lentinus edodes; valor nutricional, aminoácidos ABSTRACT:The Lentinus edodes -an edible mushroom from the Agaricaceae family and popularly known as shiitake -have been appreciated through centuries in Eastern cooking and medicine due to its pleasant flavor and high nutritional value. In order to point out L. edodes beneficts, the present work performed the nutritional analysis of this food. The L. edodes quality as a protein source was also evaluated and compared to beef cattle, beans and soy, considering that these foods, such as mushrooms, are rich in protein.For evaluation of L. edodes protein quality, amino acid score for its indispensable amino acid was calculated. For comparison purposes, the protein digestibility values of L.