|
|
|
|
|
|
|
Stress is a natural part of living for calves, indeed, for all living things. It cannot be eliminated, but it can be minimized. Some of the stress factors encountered by calves are weaning, dehorning, vaccinations, change of ration, change in social group, transportation and handling, inclement weather, flies and diseases. One or two may be manageable, but several in combination present a severe challenge to any calf's health.
|
|
|
|
When a calf is stressed, hormones trigger many changes in blood chemistry and metabolism. It may stop eating, using its own body tissues to generate energy. Immune functions may be sharply curtailed. If high levels of stress continue, many calves will die; if stress is alleviated and treatment begins, most will return to good health. There is ample evidence that preventive action, including good vitamin nutrition, can head off stress-related ailments.
One of the main physiological changes brought by stress is elevation of serum glucocorticoid levels, which has been shown to reduce lymphocyte and antibody production and functions. Also, greater epinephrine secretions lead to higher levels of prostaglandin, lipoxin and other fat-based immunosuppressant enzymes. Stress also leads to the release of arachidonic acid from the membrane phospholipids. Once released, arachidonic acid breaks down into immune function inhibitors.
By-products of these chemical reactions include highly reactive oxygen-derived molecules (ROM), hydrogen peroxide and free radicals--all potential agents of cell destruction. White blood cellsÑimportant in fighting diseaseÑare particularly susceptible to destruction by ROMs because of their high levels of free fatty acids.
Two events can help turn the stressed animal around at this subcellular level:
- The oxidants can be degraded by specific metalloenzymes, but stress increases loss of the necessary metals, so this means is limited.
- These destructive oxidative molecules can be controlled by supplementation with antioxidant nutrients, including vitamins A and E.
|
|
|
|
And selenium are both tissue antioxidants. Vitamin E works in cell membrane fractions. Selenium has its effect in the cystosol fraction. Thus, the functions of selenium and vitamin E are independent and additive.
|
|
|
|
Since the late 1950s, vitamin A has been recognized as a limiting vitamin in ruminant diets, but less was known about vitamin E requirements until the 1980s. Vitamin E supplementation enhanced immune responses in other species. However, since green forages are naturally high in vitamin E, the NRC listed no requirements for cattle until 1984, and these are in a wide range.
Neonatal dairy calves are a special class of cattle that don't have access to green forage, one reason that Reddy, et al., conducted studies at Kansas State University (KSU) to see if additional vitamin E would stimulate the immune systems of such calves.
The studies showed that extremely lightweight calves (1 to 24 weeks old) fed conventional calf starter could become vitamin E-deficient (less than 1.5 milligrams of alpha-tocopherol/dl plasma), and vitamin E supplementation could enhance the immune system through an increase in immunoglobulins. After early trials favored dietary supplementation over weekly injections of vitamin E, the KSU team followed up with a study to determine optimum supplementation levels. Those of 125 and 250 IU/head daily appeared most beneficial in decreasing serum cortisol (an indication of stress), which works to defeat immune response (Figure 1). More recent research (Luhman, C.M., et al., 1989) confirms the practical value of feeding elevated levels of vitamin E to young calves.
|
 |
|
|
|
|
|
|
|
Long-haul beef weanlings typically arrive at feedlots in a stressed condition, but Oklahoma State University (OSU) research shows a rapid turnaround by dietary supplementation of 800 IU vitamin E per lb of supplement fed at 2 lbs per day. Research on this level of supplementation looked promising with other species, and research at KSU's Garden City experiment station had shown that receiving calf performance was enhanced with 400 IU supplemental vitamin E per head daily.
In the Oklahoma State University study, 502 head of 500-pound auction market calves were shipped to Pawhuska, Oklahoma during winter months from five states. In the 28-day study, steers gained 23.2 percent greater than the control when they were supplemented with 1,600 IU/head/day for the first 21 days and 800 IU/head/day for the remaining seven days (Figures 2 and 3).
|
 |
|
|
|
|
|
|
|
 |
|
|
|
|
|
|
|
Vitamin E-supplementation led in every category measured, with 13 percent and 11 percent reduction in morbidity and death loss, respectively, compared to the control. Even excluding those calves pulled at initial processing, gain was 22 percent better for the vitamin E calves. Since intake was not affected, feed efficiency was improved.
|
|
|
|
Other vitamins reportedly work in concert with vitamin E and individually to improve immune responses. Vitamin A's positive effects were demonstrated in a 1980 study, and vitamin C was shown as a possible aid for calves deprived of colostrum, while beta-carotene appeared to play an immunostimulatory role aside from its provitamin A activity.
In a 1993 study, members of the KSU team that had earlier established vitamin E benefits for dairy calves reviewed leukocyte functions with varying concentrations of vitamins A, E and beta-carotene. The study demonstrated the importance of a balance of these vitamins.
Beta-carotene seemed to work with vitamin E to moderate E's antioxidant effect on the bactericidal action of neutrophils.
|
|
|
|
Research on controlling stress points directly toward the benefits of dietary vitamin E supplementation for calf immune systems. This is most critical in the first 36 days of a dairy calf's life and the first 28 days after a beef calf is weaned and/or shipped to a feed yard.
For the 500-pound long-haul beef weanlings, Oklahoma research seems to go beyond NRC guidelines. The results with supplemental vitamin E for the 28-day receiving program made a lasting impression on the principal investigator.
OSU beef scientist Dr. Don Gill was skeptical that vitamin E supplementation at 1,600 and then 800 IU/head/day would be cost effective when he set up the experiment. But he says, "It pays better than anything else you can do for receiving calves."
References:
- Gill, D.R., et al., 1986. The Effect of Vitamin E Supplementation on Health and Performance of Newly Arrived Stocker Cattle. Okla. Ag. Exper. Sta., Research Report MP 118:240.
- Lee, R.W., et al., 1985. Effect of Vitamin Supplementation of Receiving Diets on the Performance of Stressed Beef Calves. Kansas State U., CFD-RP 474:14.
- Luhman, C.M., et al., 1993. The Effect of Vitamin E Addition on Calves Fed Calf Milk Replacer. J. Dairy Sci. 76:221.
- Nockels, Cheryl F. 1993. Stress Impacts of Metabolic-Hormonal Regulation and Immune Function. Current Veterinary Therapy, 3rd Edition.
- Reddy, P.G., et al., 1987. Vitamin E is Immunostimulatory in Calves. J. Dairy Sci. 70:993.
|
|
|
|
|
