Are Persistently Infected Cattle in Your Herd?Tue, 07 Oct 2014 10:18:42 CDT
Gant Mourer, Oklahoma Beef Value Enhancement Specialist & Barry Whitworth, DVM, Oklahoma State University Area Extension Veterinarian, writes in the latest Cow-Calf Newsletter.
Bovine viral diarrhea virus (BVDV) is a contributor (along with others) to what is known as “shipping fever” complex or bovine respiratory disease (BRD). However, some animals will be persistently infected (PI) as a fetus with BVDV and will carry BVDV their entire life. These are the animals that are particularly harmful to cattle herds as they may show no clinical signs of the disease at all and yet shed the virus continuously to surrounding animals. Infected calves transmit the virus through secretions such as feces, nasal discharge, tears, saliva, urine, milk and semen. BVDV may also be transmitted during examination or palpation of the reproductive tract when gloves or sleeves are not changed between animals. Needles can transfer the virus from animal to animal as well. The virus can also survive several days in cool environments and be transferred from tools such as nose tongs, halters, and other tools if not properly sanitized.
Prevention of BVD involves the implementation of a well-defined biosecurity plan developed by you and your veterinarian and possibly testing of calves with an accredited laboratory. Removing all PI calves and cows after testing may be the first step. Also, testing outside animals or purchasing cattle that have been verified as PI-BVDV negative prior to entry into the herd will aid in preventing of the disease. A strong vaccination plan will also help prevent BVDV; it will not treat an animal that is already infected but will aid in prevention and will give some protection if cattle come in contact with other cattle via a fence line or other methods.
BVDV has a significant impact on the beef industry as a whole. In a 2007-2008 APHIS measured the occurrence of cattle tested on farm and found that 0.12% of 44,150 animals tested were tested positive and 8.8% of all 205 operations tested had at least one positive animal. Reproductive losses by far are the most expensive to cow/calf producers and difficult to measure. Some estimates of BVDV outbreak in 1998 can be as much as $400 per cow. Impacts of BVDV in the feedlot have been measured in several studies over the last few years. Even though calves entering the feedlot may only represent 0.3% of cattle, cattle exposed to a PI calf increase its chance of respiratory disease by 43% and 15.9% of all respiratory tract cases can be attributed to exposure to a PI positive animal (Loneragan et al, 2005). Performance alone of exposed calves can result in losses of $88.26 per animal (Hessman et al, 2009).
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