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Virginia Cooperative Extension -
 Knowledge for the CommonWealth

Injection Use and Quality Assured Pork

Livestock Update, May 2000

Allen Harper, Extension Animal Scientist, Swine
Virginia Tech Tidewater AREC

Giving iron dextran injections to nursing piglets, vaccinations to breeder gilts and sows or growing pigs, and antibiotic injections to treat pigs that may become sick are all routine practices on hog farms. As components of a comprehensive herd health program, these practices contribute to the production of quality pork from healthy hogs. But producers and herd technicians must remember that they bear an important responsibility when administering injectable vaccines and medications. Ultimately it is a food product and not just live hogs that is being produced at the farm. Swine producers and herd technicians must recognize this and ensure safe use of injectable medications in accordance with proper procedures. Some key considerations in this process are covered in the following discussion.

The Injection Site. All over-the-counter (OTC) or veterinary prescribed (Rx) injectable medications carry a label or prescription indicating the tissue location that the drug should be deposited into. For producer administered products this will practically always be either intramuscular (IM) meaning in the muscle or subcutaneous (SQ) meaning under the skin. For an injectable drug to perform as intended, it must be placed in the prescribed tissue location.

The preferred site to administer IM injections in small pigs and large hogs is in the neck muscle at a point just behind and below the ear. Large hogs may need to be restrained with a snout cable or in a stall but small pigs may simply be held. The skin at the site should be pulled slightly to one side and the needle placed through the skin and into the muscle. Once the proper dose is placed in the muscle, the needle is extracted and the skin is released to the original position. This helps to prevent back-flow of the medication from the injection site. Although it may be tempting to use the large muscles of the ham area for IM injections, this is not advisable. Physical damage or iron staining of the ham may cause trim losses or blemishes in this high value pork cut.

For larger hogs, SQ injections may be placed under the loose skin behind the ears. With smaller pigs, SQ injection under the loose flaps of skin along the rear flank or behind the elbow works well. The needle should slide under the skin away from the entry point before the medication is deposited.

Needle Selection. Needle selection criteria center primarily on the appropriate diameter and length of hypodermic needle needed for each injection situation. Needle diameter is measured using a standard "gauge" scale. Lower gauge numbers refer to larger needle diameters. For example, a 14-gauge needle is considerably larger in diameter than a 20-gauge needle. Generally, it is recommended that the smallest needle diameter be used that will effectively discharge the drug to be administered. Thicker, more viscous medications will require a larger diameter needle than thinner, free flowing solutions. Also, the size and age of the pigs being injected will influence the gauge of needle needed, with younger smaller pigs requiring smaller needles than older, larger animals.

The needle length selected should be just long enough to reach the intended drug deposition site when the needle is fully inserted. Using needles that are longer than necessary increases the chance of injury to the pig and increases the possibility of bending or breaking the needle. The following Table lists National Pork Producer Council guidelines on the recommended needle gauge and length for giving IM and SQ injections to pigs of various sizes.

Recommended Needle Sizes and Lengths for Swine*
Type of PigIntramuscular (IM)Subcutaneous (SQ)
Needle GaugeNeedle LengthNeedle GaugeNeedle Length
Baby pigs18 or 205/8" or 1/2" ----
Nursery pigs16 or 183/4" or 5/8"16 or 181/2"
Finishing pigs161"163/4"
Breeding stock14 or 161" or 1 1/2" 14 or 16 1"
*Source: NPPC Pork Quality Assurance Guidelines

Avoiding Use of Damaged Needles. High quality disposable needles are the products of choice for routine on-farm injections. These are readily available from veterinary or livestock supply companies. Disposable needles can be used with inexpensive disposable syringes or sophisticated repeating syringes. Under all circumstances any needle used should be "razor" sharp and free of any physical damage. Sharp needles are easier to insert, minimize pain experienced by the pig and produce little or no tissue damage. Needles that have become dull due to extended use or physical damage should be replaced with a fresh, sharp needle.

As with dull needles, any needle with a bent or broken shaft should be removed from the syringe, discarded and replaced with a fresh needle. Under no circumstance should a needle that has become bent be re-straightened and used. Needles that have been bent and re-straightened have a weakened point along the shaft and are likely to break. This creates the risk of the needle shaft breaking off and remaining in the pig's tissue at the injection site. Although the occurrence of this is rare, it does happen. As a result, there have been reports of retail consumers of pork products that have found or even bitten into broken needles when eating pork. Again, the occurrence of this is very rare, but when it happens, it causes a safety hazard for the consumer. Furthermore, such an occurrence is extremely detrimental to the public perception of pork as a healthy, quality assured product.

Preventing Abscesses at Injection Sites. Abscesses are localized sites of infection in the tissues of pigs. They may be located near the surface of the body or in tissues deep within the body. Abscesses near the surface may be seen as an extended or swollen mass of tissue. When palpated, an accumulation of fluid within the cavity of the abscess may be detected. This accumulated fluid, commonly referred to as "pus", results from an immune reaction in response to foreign matter or infectious bacteria within the abscess site. In addition to being a direct health risk to the pig, abscesses have a direct negative impact on pork quality assurance. At pork processing plants, abscesses must be completely trimmed from the hog carcass and discarded as trim loss before the carcass can pass inspection and be further processed. If abscesses are extensive, significant portions of the carcass must be trimmed and discarded or perhaps the entire carcass may be condemned.

The most common way that injection practices can contribute to the occurrence of abscesses is through the use of dirty needles and other unsanitary injection practices. Only clean needles should be used for injection purposes. Between injections, the syringe and needle should not be placed on dirty surfaces. Instead, a clean pan or tray lined with fresh paper towels should be prepared for syringe and needle storage during injection procedure. The protective plastic shield that covers all new disposable needles may also be replaced over the needle when not in use. When in doubt about the cleanliness of a needle, it may be swiped with alcohol using absorbent paper or cotton. However, alcohol should not be drawn into the interior of the injection needle as it may affect the potency of vaccines or antibiotic drugs.

The injection site should be inspected before inserting the needle. If the site is dirty or damp, it should be swiped clean and dry before injection. When the site is dirty, the injection needle may carry contaminants and bacteria from the skin into the tissue, increasing the risk of abscess formation. Steps should also be taken to avoid contamination of medication vials. When reloading a syringe from a multi-dose vial, a separate needle should be used to pass into the rubber vial stopper than the one used to inject the pigs.

The number of pigs treated before changing to a fresh needle is a judgement call for producers and herdsmen. If the needle and injection sites are clean, multiple sets of pigs may be treated with the same needle. However, under dirty conditions, frequent changes to a fresh, sterile needle is advisable. When processing baby pigs, a good practice is to change needles between each litter.

Meeting Withdrawal Times. Many injectable medications, especially those containing an antibiotic as the active ingredient, have a required pre-slaughter clearance time requirement. These pre-slaughter withdrawal periods are specific for each product and are established to insure that all potential drug residues are cleared from the pig before it is slaughtered and processed into pork. For example, pigs treated with an injection of tylosin antibiotic must not be shipped for slaughter within 14 days of the last injection. Pigs treated with ivermectin for control of parasites must not be shipped for slaughter within 18 days of the last injection.

Other swine injectable medications will carry different withdrawal periods ranging from as low as no pre-slaughter withdrawal required to as high as 40 days. Accurate records of the type of medications used, when they are administered and identification of the pigs treated are essential to assure that pre-slaughter withdrawal times are met on hog farms.

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