Do You Understand BV D Virus?

Transcription

1 Volume 8 Issue 1 May 2003 Do You Understand BV D Virus? I just returned from a livestock training in Boise, ID. One of the topics of discussion was Bovine Viral Diarrhea Virus (BVDV). After four decades of vaccinating cattle for BVDV and 130 federally licensed vaccines, losses are still estimated at $35-56 million/million calves. These losses include outright mortality, reduced growth rates, reproductive failure, and increased virulence of other pathogens. What is Bovine Viral Diarrhea? Bovine Viral Diarrhea (BVD) is a disease of cattle caused by the Bovine Viral Diarrhea Virus. The virus is widespread and most herds are at risk for infection. In the susceptible herd, BVD can be a serious, costly disease. Could My Herd Be Infected? The signs of BVD vary, depending on the immune status of the exposed animals, and the strain of the infecting virus. Signs include fever and diarrhea followed by recovery. The incubation period is about three to five days. Other indications of BVDV are: too many open cows, weak dummy calves, ataxic ( drunk looking ) calves, abnormal calves such as crooked legs and domed-shaped heads, calves with white eyes, too many calves with scours and pneumonia, and very small size calves. If susceptible (non-vaccinated) animals are infected with a virulent strain of the virus, the disease will likely appear as an acute, severe sickness, with high fever ( degrees F), offfeed, mouth ulcers, and often pneumonia. Occasionally the BVDV will cause bloody diarrhea. Since BVD is a viral disease, antibiotics are ineffective. Why Does BVDV Cause Such a Multifaceted Disease? BVD is caused by a pestivirus. Previously, there were three pestiviruses affecting livestock; 1) BVD affecting cattle, sheep, and deer, 2) Hog Cholera affecting swine, and 3) Border disease affecting sheep and cattle. Now they have identified a fourth species called BVD Type 2 affecting cattle and sheep. So, BVD is actually two diseases, BVD Type 1 and BVD Type 2, caused by related but separate species of pestivirus. How is the Virus Spread? BVDV typically enters an animal by the oral or nasal route. Acute or persistently infected cattle shed the virus in mucus, saliva, feces, and urine. The virus can also be spread to a much lesser extent by contaminated equipment, semen, fetal calf serum, and biting insects. Persistently infected animals are the primary source of new and continuing herd infections. How Do We Prevent and Control BVD? Colostrum is the first line of defense against BVDV Types 1 and 2. This protection usually lasts 4-8 months. To induce active immunity, all calves should be vaccinated no earlier than one week of age. Vaccination will protect calves from infection and boost the immunity of calves with low (Continued on page 3) Amy Peters, Coos County OSU Extension Service, 290 N. Central, Coquille, OR phone ext.240 or ext.240 Fax amy.peters@oregonstate.edu

2 Coos and Curry Livestock News Page 2 How Much Lime Is Needed? Soil ph is an easily measured soil chemical property used to assess the condition roots experience. Low ph or acidic soil increases the solubility of iron, zinc, manganese, copper, and aluminum. Concentrations of manganese and aluminum can reach levels that are toxic or at least inhibit root growth. Bacteria that assist with nitrification, the conversion of ammonium to nitrate, are also adversely affected by low soil ph. Crop sensitivity to soluble manganese and aluminum varies not only by species but also by variety. This sensitivity can also be soil dependent. Some varieties may show manganese or aluminum toxicity, while others remain productive. The adaptation and selection process sorted plants for tolerance to soil ph. Blueberries and cranberries tolerate high acidity (low soil ph) while garlic and alfalfa grow well in slightly acidic to neutral soil (moderate soil ph). Historically, we plant crops or ornamentals in soil modified to fit the ph requirements of the plant rather than choosing to plant blueberries in a field because the soil ph is appropriate for that crop. When the soil ph is below a suitable level for the species we wish to plant, lime is added to raise the soil ph. Table 1 presents suitable soil ph levels for selected plants. After the need for lime is established, the next question to address is how much lime Table 1. Suitable soil ph for some plants Alfalfa 6.5 Vegetables 6.5 Garlic 6.5 Grass for seed or pasture 5.5 Fruit trees 6.0 Blueberries and cranberries Azaleas and rhododendrons Field or silage corn 5.5 Wheat 5.5 Flowers 6.0 should be applied?. In Oregon, the amount of lime needed to raise soil ph is estimated by a soil test called the SMP Buffer, lime requirement (LR), or buffer ph test. SMP are the initials of Shoemaker, McClean, and Pratt, the people that published the procedure used for rapidly measuring lime requirement. The first step toward understanding the SMP buffer soil test is to understand a buffer. A buffer has the ability to resist change. Let s use a monetary example to explain a buffer. We will use a wallet containing $10 and a bank account containing $100,000. Consider the change if $1 is removed from both the wallet and the bank account. The amount of money in the wallet is reduced by 1/10 while the bank account is relatively unchanged. We could also add money to the wallet, $10, from the bank account. The $10 added to the wallet doubles the amount of money in the wallet, but changes the amount of the bank account relatively little. When $10 is moved from the bank account to the wallet, no change is made in the total amount of the money, but the amount in the wallet is changed dramatically. Our example shows that the bank account is buffered and the wallet is not buffered. Let s apply the concept of a buffer to soil and soil acidity. In the first article of this series, soil ph was defined as the amount of hydrogen ions in soil solution. Using the wallet/bank account analogy, hydrogen in the soil solution would be money in the wallet. Hydrogen ions are also attracted to the soil surface. Think of these hydrogen ions as those in the bank account. The wallet/bank account ration of money is approximately the same ration of hydrogen ions in soil solution to hydrogen ions attracted to the soil particles. The hydrogen ions attracted to soil particles are extremely important, as these ions must be reduced to effectively raise soil ph for plant growth. The number of hydrogen ions attracted to soil particles is primarily a function of clay and organic matter content. A sandy soil low in organic matter would have fewer hydrogen ions (Continued on page 3)

3 Coos and Curry Livestock News Page 3 BVD continued from page 1 maternal antibody. In addition, recent data reveals that vaccinating young calves with modified live BVDV while maternal antibody is present generates T-cell mediated immunity and establishes a memory that is restimulated on subsequent vaccination. Most vaccines in the US are produced from a Type 1 BVDV. There are currently four to five vaccines that contain Type 2 BVDV. Type 1 vaccines protect against Type 1 BVDV and may provide partial protection against some Type 2 viruses. To provide a broader range of protection, it may be better to use a vaccine with both Types 1 and 2 or alternating use of vaccines produced from different strains of BVDV Type 1 and Type 2. Vaccines are available as modified live or killed. Modified live vaccines generally provide better cross protection against strains of BVD than killed vaccines. It may be better to use a vaccine with both Type 1 and Type 2 Producers can identify persistently infected animals with a blood test or ear notch and cull them to decrease the amount of BVD virus circulating. Ideally, newly purchased cattle should be vaccinated before entering the herd and isolated on the farm for two to three weeks. Sick animals should be quarantined to prevent the spread of infection. Semen from an infected bull can transmit the disease. Most artificial insemination companies screen for this but bulls used for natural service should be tested for the virus. Vaccinated cows exposed to the virus at less than 125 days of pregnancy may still occasionally produce persistently infected carrier calves. The informed producer can successfully meet the BVD challenge by following strict biosecurity guidelines, eliminating persistently infected animals, vaccinating the entire herd, and providing calves with colostrum. Contact me or your local veterinarian for more information on a BVDV control plan. -Amy Peters Lime Needed continued from page 2 attracted to the soil particles (small bank account) than would a clayey soil high in organic matter (large bank account). The sandy soil is not as well buffered as the clayey or high organic matter soil. When a sandy and a clayey soil both have the same ph, the same amount of hydrogen ions are attracted to the soil particles in a sandy soil. Since the hydrogen ions are attracted to the soil surface in a much greater quantity than the hydrogen in soil solution, less hydrogen is found in the sandy soil and less lime is required to raise the ph of the sandy soil than the clayey soil. To change soil ph, hydrogen in a solution and attracted to the soil particles must be reduced. To determine the amount of hydrogen that needs to be reduced, or conversely, the amount of lime to add, the hydrogen buffer needs to be measured. The hydrogen buffer is measured with the SMP buffer. The SMP buffer has an initial ph of 7.5. When soil is added, the ph of the mixture will be lower than 7.5. The lower the ph of the mixture of soil and SMP buffer, the greater the amount of lime needed. The SMP buffer ph usually is approximately 0.6 to 0.8 units higher than the soil ph in Western Oregon. A commonly asked question is if the SMP buffer measures much more hydrogen than does soil ph, why isn t the SMP buffer ph lower than the soil ph?. You can answer this question now that you know the SMP buffer s ph initially is 7.5 and it is a stronger buffer than soil. Let s look at some data. A soil has a ph of 5.1 and SMP buffer ph of 5.9, how much lime is needed? First a target ph is needed. Assume a cool season perennial grass such as tall fescue is being grown. Table 1 shows that the minimum soil ph should be 5.5. We don t want to (Continued on page 6)

4 Coos and Curry Livestock News Page 4 Revised Hay Quality Guidelines Livestock and Grain Market News branch has revised the hay quality guidelines for use in the nationwide Market News reporting program. These revised guidelines establish specific objective measurements of value attributes for each quality category of alfalfa and grass hay. Nationwide uniformity of price information is the goal of revising these guidelines for quality designations. It is important for hay buyers in any part of the US to be able to read any of USDA s hay reports and know the hay prices quoted are consistent from area to area for quality. Table 1. Alfalfa Hay Guidelines Hay Quality Descriptions Supreme: Very early maturity, pre-bloom, soft, fine stemmed, extra leafy. Factors indicative of very high nutritive content. Hay has excellent color and is free of damage. Premium: Early maturity, prebloom in legumes and pre-head in grass hays, extra leafy and fine stemmed factors indicative of a high nutritive content. Hay is green and free of damage. Good: Early to average maturity, early to mid-bloom in legumes and early head in grass hays, leafy, fine to medium stemmed, free of damage other than slight discoloration. Fair: Late maturity, mid to late bloom in legumes, head-in in grass hays, moderate or below leaf content, and generally coarse stemmed. Hay may show light damage. Utility: Hay in very late maturity, such as mature seed pods in legumes or mature head in grass hays, coarse stemmed. This category could include hay discounted due to excessive damage and heavy weed content or mold. -Amy Peters Quality ADF NDF RFV TDN 100%DM TDN 90%DM Supreme <27 <34 >185 >62 >55.9 >22 Premium Good Fair Utility >35 >44 <130 <56 <50.5 <16 CP Table 2. Grass Hay Guidelines Quality Crude Protein % Premium Over 13 Good 9-13 Fair 5-9 Utility Under 5

5 Coos and Curry Livestock News Page 5 Announcements We re Moving Coos County OSU Extension will be moving to our new building in early July. The new address and phone number are: 631 Alder St. Myrtle Point, OR Phone OSU Extension Dairy Tour June 17, :30 am Meet at OSU Dairy in Corvallis Tour an on-farm digester, farmstead cheese making facility, and manure injector. Lunch & BBQ dinner provided. Cost is $20. Call to reserve your place. Coos County Livestock Association Summer Picnic August 2003 A ranch tour will precede the picnic. Watch for more details. Amy Peters Livestock Agent Oregon State University Extension Service offers educational programs, activities, and materials - without regard to race, color, religion, sex, sexual orientation, national origin, age, marital status, disability, and disabled veteran or Vietnam-era veteran status - as required by Title VI of the Civil Rights Act of 1964, Title IX of the Education Amendments of 1972, and Section 504 of the Rehabilitation Act of Oregon State University Extension Service is an Equal Opportunity Employer.

6 Coos and Curry Livestock News Page 6 Lime continued from page 3 Table 2. Estimation of lime requirements in t/a using the SMP buffer. SMP Buffer Tons/acre of 100-score lime needed to raise ph of surface 6 soil to the following ph ph add just enough lime to raise the ph to 5.5, but have a slightly higher soil ph after adding lime. So let s use 6.0 as our target soil ph. We estimate the amount of lime needed to raise the soil ph from 5.1 to 6.0 when the SMP buffer ph is 5.9 from Table 2. The amount of 100 score lime needed is 3.3 tons/acre. To find the lime rate using Table 2, follow the left-hand column, SMP Buffer until you find 5.9. For this example, 5.9 is in bold type. Now move horizontally to the right to the column with 6.0 on the top. Remember that a soil ph of 6 was our target soil ph. In bold, 3.3 is found. The rate of lime to raise the soil ph from 5.1 to 6 with an SMP Buffer of 5.9 is 3.3 tons/acre. The table heading tells us that the lime rate is for 100 score lime. An explanation of lime score and sources can be found in an extension publication FG 52, Fertilizer and Lime Materials. It is available electronically at agcomwebfile/edmat/html/fg/ fg52/fg52.html Soil ph indicates if lime is needed and the SMP Buffer is used to estimate how much lime should be applied to raise soil ph to a target level. -John Hart and Don Horneck