Abstract
In this review article we present an overall summary of the role that high-grain/low forage diets have on rumen composition of microbiota and how changes in the diet affect the release of bacterial cell wall components that are toxic to the host. One of these toxic compounds is lipopolysaccharide or endotoxin, a component of the outer membrane of all Gram-negative bacteria. Moreover, data are provided that support the concept that endotoxin translocates into the blood circulation and show that rumen endotoxin is associated with multiple perturbations of blood variables related to carbohydrate, lipid, and mineral metabolism. In addition, endotoxin induces a general, nonspecific immune response known as acute phase response. We also pinpoint the fact that high-grain diets are associated with distinct clusters of plasma metabolites and immune variables suggesting that changing cereal grain to forage ratio in the diet is very important for the health of dairy cattle. Furthermore, we provide information that support the concept that endotoxin is involved in multiple metabolic diseases such as fatty liver, milk fever, laminitis, retained placenta, displaced abomasum, and downer cow syndrome. More research is warranted to clarify the mechanisms by which nutrition, microbiota, and endotoxin contribute to development of metabolic diseases in dairy cattle. It is concluded that besides the aforementioned causal agents other compounds generated in the gastrointestinal tract such as lipoteichoic acid or methylated amines might be involved in the etiology of several metabolic diseases.
Highlights
The productive lifespan of a dairy cow largely depends on her metabolic health status
Recent research has indicated that dairy cows undergoing a moderate energy overfeeding around parturition experience greater incidence of fatty liver and ketosis postpartum, and this event is preceded by activation of an acute phase response (APR; Ametaj et al, 2005a; Loor et al, 2006)
The major source of endotoxin in dairy cows is the gastrointestinal tract, which contains large numbers of Gram-negative bacteria, in particular, when diets are rich in energy, and this provides a potential pool of endotoxin entering into the animal body (Nagaraja et al, 1978)
Summary
ABSTRACT - In this review article we present an overall summary of the role that high-grain/low forage diets have on rumen composition of microbiota and how changes in the diet affect the release of bacterial cell wall components that are toxic to the host. One of these toxic compounds is lipopolysaccharide or endotoxin, a component of the outer membrane of all Gram-negative bacteria. Fornecemos também informações que apoiam o conceito de que a endotoxina está envolvida em múltiplas doenças metabólicas, como fígado gorduroso, febre do leite, laminitis, placenta retida, abomasum deslocado e síndrome downer cow.
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