January 17, 2010 – PZP Administration, part 2: Delivery

As we discussed in the last post, PZP is prepared into a vaccine by combining it with a substance called an adjuvant. The PZP vaccine must then be administered to a mare. There are a couple different ways in which one can administer PZP, each with its own pros and cons.

Remote Field Darting

PZP was first administered to free-roaming wild horses on Assateague Island during an early study there (Kirkpatrick, J.F., Liu, I.K.M., and Turner, J.W., 1990). This PZP was administered with field darts. Since then, field darts have become more technologically advanced as have the methods of delivering them. Today, there are dart guns suitable for many different applications.

Just as there are a variety of dart guns available, there are also a variety of darts that can be used for many different applications. The darts used to administer PZP are simple in concept: Their job is to successfully hit a mare, inject her with a PZP vaccine, and then fall out. These darts have some interesting features that allow them to work so well, though. Here is a simple schematic drawing of a dart:Once the dart is fired and hits the mare, a series of steps leads to the injection of the PZP vaccine and the ejection of the empty dart. This all happens very quickly. Here is a drawing illustrating the sequence of events:

Field darting has obvious benefits in that it allows for mares to be treated without gathering or handling them. Being able to do this does require that the mares are approachable as the longest successful shots one can expect will be 40 to 50 yards. It is also helpful if mares can be identified as individuals so that treatments can be safely and properly given in accordance with management objectives. There has been some concern of lost darts. Because the darts are bright colors, only a very small percentage of darts are never recovered. Those that are not recovered cannot accidentally inject something else that may step on it or find it as injections only result from the impact of hitting a target. Thus, the issue of lost darts is often considered insignificant. Field darting is relatively inexpensive as a full treatment (dart, PZP, adjuvant, etc) costs around $25.00. Most of the expenses involved in a field darting operation are related to the labor needed to locate, approach, and successfully treat target mares.

Jab Stick Injections

There are times when remote field darting is not practical or needed. For example, this is common in areas with unapproachable horses. In these cases, it is possible to administer PZP to mares during gathers. Often, the PZP pellets are used then as they are longer lasting than the one-year vaccines delivered in field darts. (PZP pellets cannot be delivered by field darts at this time, though I have heard that work is being done to develop field darts that can do this.) During the 2009 Pryor gather, and in many other gathers, PZP pellets are administered by hand with syringes used in conjunction with something called a jab stick. Jab sticks are spring loaded devices that can be loaded with the appropriate PZP treatment. Jab sticks are very sensitive, and small impacts cause them to go off which causes the PZP to be expelled from their needle. In this way, they are similar to the darts, except it is the force of pushing a needle into the mare that triggers the PZP to be injected. Below is a photograph from the 2009 Pryor gather; it shows BLM personnel treating a mare with a jab stick. The needle can be seen at the top of the jab stick. Once this needle is pushed into the mare, the device’s mechanism causes the injection to occur almost instantly.

In areas where managers wish to use PZP pellets, jab sticks are again about the only option for administration. Being able to use jab sticks requires mares to be gathered and handled, though; and this presents a number of possible risks to both the animals and the personnel trying to treat them. Jab sticks are designed to be able to used at a maximum distance; it is possible to inject a mare from 1 to 2 meters away. This does reduce the possible risk to personnel. Compared to remote field darting, the use of PZP pellets can also be more expensive. This is because the pellets themselves can cost up to $200 each, and the costs associated with gathering horses can be very high as well. However, this increased cost can still be worth it given the comparative costs of gathering, adoptions, and holding that result from removing horses.

Injection Area

PZP vaccines are given exclusively in the rump of mares. There are a couple reasons for this. For one, the rump is far from sensitive areas like the head. Thus, stray darts do not have a good chance of hitting the head. More importantly, though, is the fact that the rump is full of muscles that are almost constantly at work. When the PZP vaccine is injected into these working muscles, it is able to get mixed around and agitated quickly; this helps to trigger a proper immune reaction. It is often asked why these injections are not given in the mare’s neck; I understand that this is because there is an increased risk of abscesses forming with neck injections. This all applies to the use of jab sticks as well; PZP vaccines are again only given in the rump.

It is very important for PZP vaccines to be properly delivered; this ensures that they work as intended and that no undesired side effects result from treatments. With this post, we have gone through the processes involved in making and ultimately administering PZP to mares. From here, we will be moving into discussions of research done on the effects PZP has (or does not have) on horses.


Kirkpatrick, J.F., Liu, I.K.M., and Turner, J.W., 1990, Remotely delivered immunocontraception in feral horses. Wildlife Society Bulletin: v. 18, p. 326-330

Also, many different examples of the dart guns available can be seen by visiting the websites of Dan-Inject and Pneu-Dart.

Published in: on January 17, 2010 at 11:51 pm  Comments (1)  

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One CommentLeave a comment

  1. Good job on these articles. Very informative and readable!

    Can’t wait for the rest 🙂

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