Energy Intake Has Clear Impacts on Immune Function – Dr. Noah Litherland, Vita Plus
The immune system needs fuel to function normally and protect the calf from pathogens. The first few weeks of life and the weaning period are two key times when energy intake is often limited, resulting in reduced efficiency of immune function.
Besides water, energy is the most important nutrient and glucose is the currency of energy. Glucose is the primary source of energy for the immune system. When blood glucose is below optimal levels, the immune system is not able to function normally.
Source and form of energy change greatly over the first two months of a calf’s life. In utero, the calf relies on glucose from maternal blood as the primary source of energy. After birth, the calf relies on lactose (glucose and galactose) and fat from milk as the primary sources of energy. As the rumen develops through the nursery phase, the primary source of energy is from fermented feeds in the rumen, yielding volatile fatty acids (VFAs) that are metabolized by the liver into glucose.
All of these key shifts in fuel source and form require intricate adaptation by the calf – and this takes time. We can help the calf navigate through these necessary changes by following the thumb rules outlined in the table below.
Maintaining energy intakes through various stages of calf growth.
|Phase||Commonly observed problems||Strategy||Thumb rules|
|Newborn (d 1-14)||Calves are not gaining well and have low body condition score. Calf scours and treatment rate increase during cold weather.||Minimize energy loss by keeping calves warm and dry, using calf jackets, and providing adequate bedding for nesting. Optmimize ventilation. Provide adequate amounts of nutrition from milk to meet maintenance energy requirements.||Feed 3-4 qt of clean, quality colostrum. Feed 2-3 qt of pastuerized milk per feeding or 1.3-2.0 lb of milk replacer powder mixed to 13% solids. Offer small amount (0.25 lb) of starter grain initially and increase to consistently maintain starter grain intake.|
|Weaning (d 42-60)||Calves are not gainig well and have low body condition score. Calf respiratory treatment rate is >5%. Calves have loose manure for more than one day after moving from individual pens.||Optimize starter and water intake to achieve adequate rumen development and liver function.||Calves should eat 1 lb of starter by d 30 and 6 lb of grain by d 60. Calves should drink 4-6 lb of water for every pound of starter grain consumed.|
Energy and the immune system
Activated immune cells are obligate glucose utilizers, meaning they cannot use other fuels besides glucose. A recent research study at Iowa State University exposed calves to a large bacterial cell wall (lipopolysaccharide) systemic challenge to determine relationships between immune function in calves and energy requirements.
The immune challenge caused calves to have severe decreases in blood glucose, resulting in hypoglycemia. The authors calculated the glucose requirements of an activated immune system are approximately 43 grams per hour in these calves. This glucose requirement converts to about 1.5 ounces per hour or 2.2 pounds of glucose per day. A calf would need to consume 4.8 gallons of whole milk per day to meet the glucose requirement for the immune system operating at this rate.
Results from this experiment aid our understanding of calf energy requirements during a significant immune challenge. We would expect calves with this amount of glucose demand to have extremely lethargic behavior and lose a considerable amount of bodyweight. It is also more probable the calf will experience additional disease challenges due to decreased immune capacity to fight off infections.
Finally, we know some pathogens can sense stress in the calf by picking up on changes of concentrations of blood hormones such as cortisol. Low blood glucose results in increased hormones that stimulate the calf to seek out feed energy. If the necessary energy is not consumed, a stress response occurs, resulting in increased blood cortisol. Upon sensing increased blood cortisol, pathogens increase in numbers and also become more virulent and able to attack the host, often resulting in respiratory disease.
- Plan to challenge calves with no more than one stressor at a time. Pen moves, feed changes, weather changes and dehorning are examples of necessary stressors that should be done separately.
- Feed greater amounts of fat to nursery calves. Whole milk contains about 30-percent fat on a dry matter basis. Fat provides energy available to muscle and spares glucose for use by the immune system.
- Optimize starter grain intake to develop the gastrointestinal tract. A mature rumen and liver can provide the necessary glucose to the immune system.
Calf and heifer nutrition
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