Yeast, or single-celled fungi, have been used in animal feed and the human food industry for many years. Brewer's yeast was a common feed ingredient in diets for monogastric animals prior to the identification of all the B-vitamins. Today, some nutritionists still incorporate these inactivated microbes as a source of so-called 'unidentified growth factor'. More recently there has been an interest in the use of live yeast cultures. These cultures most often contain the yeast themselves and the medium upon which they have been grown. Yeast cultures are usually derived from Saccharomyces species, in particular, Saccharomyces cerevisiae. As with probiotics, their mode of action in enhancing animal perform ance is not fully understood. Yeasts may beneficially alter the inherent gut microflora, possibly through controlling pH. The presence of living yeast cells may also act as a reservoir for free oxygen, which could enhance growth of other anaerobes. At the present time, there does not seem to be any move to manipulate yeast for specific purposes related to animal nutrition. To some extent, this relates to scant knowledge on mode of action, and so should more facts be uncovered in this area so-called 'designer' yeast may be considered.
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The first trimester is very important for the mother and the baby. For most women it is common to find out about their pregnancy after they have missed their menstrual cycle. Since, not all women note their menstrual cycle and dates of intercourse, it may cause slight confusion about the exact date of conception. That is why most women find out that they are pregnant only after one month of pregnancy.