Efficiency is a term that is tossed around a lot in industry circles. Producers want efficient machinery to maximize production, accountants and creditors want efficient operations to ensure profit, nutritionists want efficient cows to signal good health – and so on.
While the meaning of efficiency may sometimes seem vague, Dr. Renée Petri proves the key to a healthy gut is not. Petri’s webinar “Diet for healthy gut: The secret for overall health and productivity in dairy cattle” presented on June 4 at the 2020 Animal Nutrition Conference of Canada, facilitated by the Animal Nutrition Association of Canada, affirms that healthy animals are efficient ones.
Understanding a healthy gut and its role
The gut is a dynamic system, which has continuous flow. It is closely linked with diet; this means a dairy cow’s feed, and the management of it, can impact the flow. Petri explained, “Many production-related diseases are diet-associated. That means there are effects from the diet specifically on the gastrointestinal tract.”
In order for a gut to be considered healthy, it must be determined to be in a state of homeostasis. Homeostasis refers to the stable state in which the host and the microbiome are resistant to external disturbances. In the case of the gut, this means an ecosystem is formed and able to maintain structure and function to establish and uphold homeostasis.
Stressors can push the gut ecosystem out of the optimum and tolerable ranges for homeostasis by changing nutrient availability, temperature and gut pH. Movement outside of these ranges is called dysbiosis. Dysbiosis can lead to disturbances related to dry matter intake (DMI), the application of antibiotics and the negative effects of pathogenic bacteria.
Homeostasis is a balance between nutrient absorption, barrier function and fermentation, factors driven by nutrition, the gastrointestinal epithelium and the gut microbiome.
Gut health challenges
Dairy cows are susceptible to gut health challenges during periods of high metabolic demand, usually around early lactation. When elevated metabolic demand occurs, in combination with dietary precursors that create insufficient conditions for glucose production, ketosis and fatty liver disease may result. In this scenario, the common response is to feed the affected cows a rapidly fermentable diet, high in energy. This change in diet impacts the cow’s gut and its health.
Diet has a strong effect on the populations of gastrointestinal microbiota. The diversity of these populations is linked with the type of feed the animal consumes. High-grain diets tend to be linked with lower diversity in microbial populations. The opposite is true for forage. Petri noted, “Higher levels of forage are increasing the microbial diversity.” Understanding this pattern is useful to help explain changes in the relative abundance of microbiota in the gut.
In cases where diet may be responsible for dysbiosis of the gut, specific changes to microbes will take place. Lactic acid-producing and -utilizing microbes will increase; an overgrowth in pathogens and a reduction in fiber degraders may be observed. Beyond causing dysbiosis, dietary changes may lead to inflammation and tissue damage which can, in turn, affect barrier function and may allow for increased permeation of pathogens into the blood.
Petri explained how microbes can produce micro-organism associated molecular patterns (MAMPS). MAMPS may affect the abundance of certain microbial populations in the gut and cause changes to the levels of lipopolysaccharides (LPS), a type of microbial-derived toxic compound which can negatively impact the cow’s immune response and metabolic function. Additional metabolites may be produced and may affect the cow similarly, although more research is needed to fully understand these impacts.
The role of the rumen and gastrointestinal tract in metabolic function
A cow’s largest interface is its gastrointestinal tract (GIT). The GIT provides a nutrient uptake system and barrier function to prevent the uptake of harmful microbes. The rumen functions to facilitate the digestion of nutrients for energy, to control pH and as a further barrier from pathogens.
The GIT and its microbial metabolites are responsible for the control of some gene expression. In this manner, gene expression is related to diet, and the level of relative expression of specific genes can change based upon LPS concentrations caused by different diets. For example, Petri presented a diagram that showed how a forage diet leading to lower concentrations of LPS in the cow can result in greater expression of a specified gene, compared with a high-grain diet.
If a cow’s gut health is not maintained, the interaction between it and metabolism can cause systemic inflammation. The effects of this range but normally include oxidative stress, systemic immune regulation concerns and the increased susceptibility to secondary infections.
Feed management
To maintain or return to a state of homeostasis in a cow’s gut, meals should be smaller and more frequent. This will increase the amount of saliva produced and increase the buffering capacity of the cow’s rumen, raising the rumen pH. To achieve this, total mixed rations (TMRs) should be given regularly, and feed should be well mixed. Adequate feed space is also necessary.
To provide a fermentable diet that can meet the high energy demands of metabolism, feed additives may be required. This has the potential to significantly decrease the risk of nutrition-related diseases in the herd. They may also impact DMI, rumen pH and the presence of rumen microbes. When selecting a feed additive, the entire GIT ecosystem should be considered. This is also true with adaptation length to a new diet. In her webinar, Petri explained, “We’re not only adapting the animal to the diet, we’re adapting the microbes to the diet. We’re adapting the host tissue to changes in the microbes.”
Petri is clear in her webinar that microbes are vital to the cow’s health and that considering them in the feeding process is essential to maintain gut health and overall animal health. When a cow’s gut functions healthily, in homeostasis, it is reflected in their efficiency and in their capacity for milk production. Petri rounded off her webinar with a piece of advice, stating, “It is worth it to work for rumen health.”
