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July 2013 Archive for Dairy Today Healthline

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Dairy Today Healthline

Manage Heat Stress and Immunity in Dairy Cows with Nutritional Strategies

Jul 08, 2013

Avoid vitamin and mineral deficiencies, maintain your herd’s immune function when temperatures soar.

By D.L. O’Connor, Prince Agri Products 

Dairy producers, veterinarians and dairy nutritionists understand the impact that heat stress can have in decreasing milk production and dry matter intake, the most common symptoms for cows experiencing moderate heat stress.

Nutrition can play an important role in supporting the dairy cow’s natural immune system to reduce the effects of heat stress, which are estimated to cost the dairy industry $897 million annually (St. Pierre et al., 2003). Primary losses are associated with, but not limited to, lowered milk production, increased metabolic disorders, poor reproduction and reduced immune function (Wheelock et al., 2010).

Temperature Humidity Index (THI)

Heat stress in dairy cows has been defined as the point at which rectal temperature exceeds 102.6 F with breaths exceeding 60 per minute. Temperature Humidity Index (THI) is calculated based on the relationship between environmental temperature and relative humidity.

Lactating dairy cows experience heat stress when THI rises above 72, with severe heat stress occurring when THI exceeds 88 (Thatcher et al., 2010). Higher-producing dairy cows show more profound symptoms of heat stress as they generate more heat while eating more feed to support higher production levels.

Table 1: Temperature and Humidity combinations yielding a THI of 72 (Zwald, A., 2007)

Prince Agri Products table 7 8 13Table 1 illustrates various temperatures and humidity values that yield a THI of 72, the point at which signs of heat stress begin to develop.

For example, a temperature of 80 F, with a relatively low humidity value of 35%, will yield a THI of 72 and create conditions that could impact health and performance. Factors such as the level of milk production, air movement, sun exposure and duration of these conditions may impact THI values, such that animals may experience more severe heat stress at lower temperatures and relative humidity values (Thatcher et al., 2010).

Heat stress and immune dysfunction

Acute exposure to high environmental temperatures has been shown to cause significant increases in a stress hormone called cortisol in dairy cattle (Stott et al., 1970). It also is well documented that increases in circulating levels of cortisol in the blood have a negative impact on the cow’s immune system and leave the cow in a weakened state to respond to disease challenges and fight infections.

This immune-suppressed condition may lead to profit-stealing diseases such as mastitis, metritis, ketosis, displaced abomasum and, in extreme cases, even death. Additionally, heat and other sources of stress faced by dairy cattle throughout their life span may manifest themselves as elevated somatic cell counts, reduced milk production and increased culling rates of low-producing and sick cows.

Management strategies

Nutrition plays a pivotal role in a properly functioning immune system and providing resistance to disease. Vitamins and minerals are essential for hormone production, tissue synthesis, oxygen transport, energy production and many other metabolic activities that contribute to growth, reproduction, milk production and overall health.

Deficiencies in vitamins A or E, for example, or the macro and trace minerals, calcium, zinc, copper or selenium, can impair the function of immune cells and may result in a decrease in resistance to disease in the dairy cow. The correct amounts of energy and protein also are critical to allow immune cells to recognize and kill pathogens associated with bacterial and viral challenges.

There also are other opportunities to help maintain immune function. For example, field research has demonstrated benefits of the nutritional supplement OmniGen-AF®* in helping to support immune function in dairy cattle which aids in the maintenance of good health and production.

Maintaining sustained, proper nutrition, combined with cow-comfort management practices, gives dairy producers the best line of defense against the negative health and economic impacts associated with dairy cattle heat stress.

*OmniGen-AF is a product from Prince Agri Products, Inc., that can be supplemented to all classes of dairy cattle as part of their regular diet.

D.L. O’Connor is a dairy technology manager for Prince Agri Products, Inc. She can be contacted at Deb.OConnor@princeagri.com. Learn more about Prince Agri Products here

References
St. Pierre, N.R., B. Cobanov and G. Schnitkey. 2003. Economic losses from heat stress by U.S. livestock industries. J. Dairy Sci. 86 (E Suppl.):E52–E77.

Stott, G.H. and J.R. Robinson. 1970. Plasma corticosteroids as indicators of gonadotropin secretion and fertility in stressed bovine. Presented at: 65th Annual Meeting, Amer. Dairy Sci. Assoc., Gainesville, Fla.

Thatcher, W.W., I. Flamenbaum, J. Block and T.R. Bilby. 2010. Interrelationships of heat stress and reproduction in lactating dairy cows. High Plains Dairy Conference, Amarillo, Texas.

Wheelock, J.B., R.P. Rhoads, M.J. VanBaale, S.R. Sanders and L.H. Baumgard. 2010. Effects of heat stress on energetic metabolism in lactating Holstein cows. J. Dairy Sci. 93:644–655.

Zwald, A., 2007. Heifer Management Blueprints. Department of Dairy Science, University of Wisconsin.

Don’t Risk Pregnancies, Conception Rates

Jul 01, 2013

Peer-reviewed research shows negative effects of modified-live vaccines on reproductive success.

Novartis   Doug Scholz, DVM, director of veterinary services, Novartis Animal HealthBy Doug Scholz, DVM, director of veterinary services, Novartis Animal Health

When dairy producers select a vaccine to protect against infectious bovine rhinotracheitis (IBR), they expect their cows and heifers will produce a healthy calf. Understandably, the health and well-being of breeding stock is paramount in dairy operations. Often the question arises as to whether an inactivated (INV) or modified-live (MLV) vaccine is best suited for use in pregnant cows.

In 2004, some MLV vaccines got the green light for use in pregnant animals, but recent research by university researchers and veterinarians demonstrates that MLVs can put pregnancies and conception rates at risk, unlike their INV counterpart.

Just what are the risks? Researchers at several universities recently reported MLVs can have a detrimental effect on reproduction, resulting in abnormal estrous cycles, reduced conception rates and, potentially, abortions.

Two articles have recently been published in peer-reviewed scientific journals to support these findings. A study published in the January 2013 issue of Theriogenology raises questions about using MLVs in breeding females and naïve heifers.1

Another article published in the Journal of the American Veterinary Medical Association addresses a diagnostic case study following multiple abortions within a University of Wyoming owned herd of replacement heifers after being vaccinated with an IBR MLV. 2

"In this instance, animals in our university herd had been appropriately vaccinated prebreeding with a modified-live vaccine, and they were vaccinated again at about seven months of pregnancy," notes Dr. Donal O’Toole, MVB, PhD, Department of Veterinary Science, University of Wyoming. O’Toole explains that starting around 30 days postvaccination, a series of abortions began which continued out to about 50 days. The total reproductive loss was a disturbing 25 percent.

"What we found at the Wyoming State Vet Lab when we started looking into these recent episodes was an association with recent use of modified-live IBR vaccines, despite the fact they were administered following label directions," O’Toole explains. The heifers had classical lesions caused by IBR, and there was no evidence of any other causes of abortion in the animals.

Dr. Chris Chase, DVM, MS, PhD, South Dakota State University, has conducted extensive studies on reproduction in cattle.

"Producers believe IBR is just about a respiratory disease, but the virus has an important role as a pathogen in the reproductive tract," says Chase. Chase discovered a modified-live IBR vaccine affected conception rates in cattle.

His study, which was published in Theriogenology, noted that IBR from an MLV is more likely to get into the bloodstream than a field strain, affecting follicle development and estrogen level in heifers. In the trial, heifers administered an MLV experienced more abnormal estrous cycles and lower pregnancy success. Chase strongly advocates using an INV, explaining that it has a much higher safety profile than an MLV.

Two large dairy operations in Colorado that were frustrated by high pregnancy losses serve as important case studies. The vaccination programs on the dairies were similar, with heifers getting three or four doses of a five-way IBR MLV. Their abortion rates regularly exceeded 20 percent, and would jump up to 25 to 35 percent at any given time.

Diagnostic tests indicated high IBR titers in blood samples. In another test, a university diagnostic lab confirmed IBR virus in an aborted fetus. Once both dairies replaced the IBR MLV with an inactivated vaccine, there were dramatic improvements in the conception and pregnancy rates.

O’Toole sums it up simply. "If you’re going to vaccinate animals for IBR, use an inactivated vaccine. Inactivated vaccines are very safe, and have a good track record in terms of efficacy. There are several recent papers demonstrating that they offer very good protection. There is no reason to risk using a modified-live product in pregnant cattle."


References
1. Perry, et al. The effects of vaccination on serum hormone concentrations and conception rates in synchronized naïve beef heifers. Theriogenology 2013;79:200-205.
2. 1. O’Toole D, et al, Pathology in Practice: University of Wyoming herd experiences 25 percent pregnancy losses following use of modified-live vaccines. J Am Vet Med Assoc 2012;241:189-191.

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