Methods of manipulating the microbial metabolism in the rumen

Abstract

Summary — We now have the means to increase or decrease the importance of the role of the rumen in ruminant digestion. The aim of these manipulations is to provide the animal with end products of digestion that are the best suited to the type of production required. We describe here the main additives and methods used to modify the rumen microbial population or its hydrolytic and fermentative activities: ionophore antibiotics; methane inhibitors; inhibitors of proteolysis or deamination; elimination of protozoa or fungi from the rumen; and probiotics. Some seem to have a welldefined action (inhibitors of methanogenesis and deamination), whereas others act on several targets (ionophore antibiotics, defaunation). The results observed in animal production depend on factors such as diet, type of production and the animal considered. The rumen should be considered as a balanced integrated system in which it is difficult to change only one variable. For example, the increase in the NADH/NAD ratio is related to the decrease in methanogenesis in the rumen but has repercussions on other factors concerning digestion, leading to a decrease in cellulolysis, deamination of amino acids and an increase in propionate or butyrate at the expense of acetate. The mode of action of some additives is not yet fully understood and the efficacy of probiotics has sometimes been openly contested. Studies presently in progress should make it possible to classify the different compounds on the market according to their effectiveness and to establish the conditions under which they should be used. Once the mechanisms of action are elucidated, research into new products will be more closely targeted. Genetic manipulation is an interesting approach to the control of the metabolism of rumen microbes but has so far yielded no concrete results. rumen I microbes I fermentation I manipulation I feed additives I protozoa I defaunation I pro-

The effect of Saccharomyces cerevisiae and Aspergillus oryzae on fermentations in the rumen of faunated and defaunated sheep; protozoal and probiotic interactions

“…The intensity of digestion and the products of fermentation determine the supply of nutrients to the animal and affect, therefore, animal production. For this rea-son, extensive studies have been centered around the control and manipulation of the rumen digestive processes with the aid of additives (Jouany, 1994) . The production responses and digestive effects are, however, generally slight and highly variable.…”

A note on the influence of fat supplementation of sheep rations on the level of purine derivatives in urine and bacterial synthesis in the rumen

“…It is known that fatty acids, particularly unsaturated ones, have a direct inhibitory effect on the rumen microbial population (Broudiscou et al, 1990). According to Jouany (1994) unsaturated fatty acids are particularly active against protozoa and, if present in large quantities, may even defaunate the rumen. This could probably explain the beneficial effect of moderate quantities of lipids on microbial protein synthesis.…”

“…The use of fats as an energy source in cow and sheep rations has been the focus of interest for years (Murphy et al, 1987). Although the addition of large amounts (up to 10%) of lipids to the diet of ruminants with high production potential satisfies the animals' considerable energy requirements, it can cause changes in rumen metabolism (Jouany, 1994), mostly in microbial protein synthesis. The efficiency of microbial synthesis depends on the nature of fatty acids and increases particularly when ruminal digestibility of organic matter is depressed (Doreau and Ferlay, 1995).…”

Arbustivas forrajeras y ácidos grasos: estrategias para disminuir la producción de metano entérico en bovinos.

“…Otros autores han estimado que un bovino adulto puede producir entre 300 a 600 l/CH 4 / animal /día (Jouany, 1994). La síntesis y emisión de CH 4 en bovinos difiere principalmente según el sistema de producción, el tipo de dieta ofrecido y la eficiencia productiva de los animales.…”

“…En países como Australia el aumento de la producción por vaca lechera y el mejoramiento de la eficiencia productiva de los hatos, ha conllevado a que los animales produzcan en promedio 6000 l/leche/animal/año y se estima que han disminuido su emisión de metano a 24 g CH 4 /l/leche producido (600 l CH 4 /animal/día) (Moate, 2010) Emisiones de metano entérico, en vacas lecheras hasta de 793 l/CH 4 /animal/día (Chase, 2007) estimados a partir del sistema de valoración proteica y energética desarrollado por la Universidad de Cornell, conocido como "Cornell net carbohydrate and protein system (CNCPS)". El valor anterior está por debajo de lo indicado en Colombia, donde para vacas lecheras de alta producción en trópico alto, se estimaron valores de hasta 670 l CH 4 /animal/día (Marín, 2013) y el informado por Jouany (1994) para vacas lecheras adultas el cual fue de 600 l CH 4 /animal/día.…”