By Lynn M. Herrmann, Ph.D.
Most producers re-use needles. In fact, according to the 2001 National Animal Health Monitoring System (NAHMS) Report, 81.7 percent of operations used the same needle on more than one animal when giving injections or vaccinations. And, as the size of the flock increased, the average number of animals injected or vaccinated with the same needle increased.
Why do we re-use needles?
Since needles do not cost that much ? pennies on the dollar ? time seems to be the advocate for needle re-use. Depending on the operation, replacement and breeding ewes, nursing lambs and breeding rams are vaccinated for clostridium and tetanus toxoid in late winter and early spring when temperatures are less than optimal. Some operations give bovine vitamin E and selenium by injection as well. Changing needles in freezing temperatures for a flock of more than 500 sheep can cramp up your fingers and slow your vaccination/injection schedule.
Do the benefits of changing needles on every animal outweigh needle re-use?
One of the best examples to stop re-using needles comes from observations at the Animal Disease Research Unit in Pullman, Wash., where a research flock of 10 ovine progressive pneumonia virus (OPPV)-infected sheep is located. These OPPV-infected sheep came from a flock with high OPPV seroprevalence (84 percent) and were pregnant at the time they were transported. These OPPV-infected ewes gave birth to 22 lambs; the virus was detected in the colostrum and milk. The lambs stayed with the ewes for eight months and after that, were separated by a fence.
However, in the course of three years, none of the lambs has become infected. Based upon the textbooks, most ? more than 70 percent ? of these lambs should have become infected by this time.
Were there any management differences between the source flock and the research flock?
One difference is that most research flocks are not bred, and the Pullman flock was no exception. In addition, during those three years, the needles were changed for every animal during vaccinations or injections, whereas the source flock re-used needles.
There has been no evidence to support the transmission of OPPV by either breeding or needle. However, there is abundant evidence for transmission of HIV (human immunodeficiency virus) by sexual contact and needles. And since HIV and OPPV are similar lentiviruses, it is plausible that OPPV could be transmitted by needle. In addition, Corynebacterium psuedotuberculosis, which causes caseous lymphadenitis, results in many adult sheep and lamb condemnations and could also be transmitted by needle re-use.
At this time, there is no direct experimental proof of needle transmission of OPPV, although a significant association between needle re-use and OPPV seroprevalence, when comparing the small to large operations (Fisher exact test P<0.05), has been observed. The data in the figure below was derived from the 2001 NAHMS Report and an information sheet entitled, Ovine Progressive Pneumonia: Awareness, Management, and Seroprevalence, from the U.S. Department of Agriculture, Animal and Plant Health Inspection Agency, Veterinary Services, Center for Epidemiology and Animal Health. It shows as the percent of needle re-use increases from small to large operations, so does the percent of OPPV instances.
Should producers stop re-using needles?
Most sheep producers have extremely tight profit margins. But, by changing needles for each animal, it may ensure the overall health of the animal and the flock by halting possible mechanical spread of infectious diseases, such as OPPV. According to the Maedi-visna Impact on Productivity in Quebec Sheep Flocks (Canada) Report, the presence of OPPV in ewes is associated with a decrease in lamb weaning weights and lamb survival. It is possible that by changing needles, profit margins could be improved. One surviving lamb would easily compensate for the cost of needles.
In human medicine, it is unheard of to re-use needles for the well documented facts that HIV and Hepatitis B and C can be transmitted by needle re-use. To ensure the health of sheep, and possibly lower OPPV and other viral and bacterial infections, buying more needles appears to be a small price to pay.