Tommy Dugger photo

As a way of actually measuring stress responses, let’s take a slight detour with another game species before addressing whitetails. When I was a research professor at Texas A&M University, my students and I did extensive studies on the physiological causes of the well-known Texas phenomenon of Boom-Bust Cycles in Bobwhite and Blue Quail. Since we are in a sure enough drought cycle in Texas right now, it seems an appropriate time to review those studies and how they related to stress and reproduction (or the lack of it).

Quail are seasonal breeders that begin reproductive activity when daylength exceeds about 14 hours per day (normally in late April or May in the wild) and if other conditions are to their liking. The most obvious natural stimulus after daylength is adequate rainfall, but how do the quail know? Some have postulated that it is their food supply’s response to the moisture; for example more insects or higher plant nutrients. Quail, however, can respond very quickly to rainfall, or almost not at all depending on other factors. We spent many years attempting to measure these variables, and their influence on reproduction.

Both Bobwhites and Blue Scaled Quail were housed in research facilities at the Texas A&M Poultry Science laboratories. These were descendents of many generations of captive reared birds, so their management requirements were well understood and they reproduced well when these requirements were met. A variety of treatments were designed to provide a single stress source, while maintaining all other variables conducive for reproduction. Some were given plenty of food, but not nutritionally satisfactory for reproductive activity. Others were given nutritionally superior food, but insufficient quantities of water (quail are said to be able to create their water needs metabolically). Still others were given boring feeds such as straight milo, or kleingrass, or alfalfa and others were moved from one pen to another daily. Blood samples were taken from quail in each of these groups and analyzed for reproductive and stress hormones. None of the test groups exhibited reproductive activity but the control group did, and all groups appeared to be relatively healthy, didn’t lose weight nor have any significant amount of mortality. All treatment groups did have high blood levels of the stress hormone, corticosterone and low levels of estrogen (hens) and testosterone (cocks).

In the next set of experiments, quail were fed levels of corticosterone in the diet which produced blood levels of this stress hormone similar to levels found in the stressed birds of previous trials. Corticosterone can be ingested much like birth control hormones and transfers to the blood stream where it acts in a natural way to inhibit reproduction. These hormone treated quail were given complete dietary and management regimes which would normally stimulate reproductive activity, but they showed none. Males had testes about half the size of normally active males, and females had ovaries with only partially developed ova, like they would prior to breeding season. When the stress hormone was removed from their feed, normal reproductive activity began in about 7-14 days, much like in nature following a good soaking spring rain. Thus, many environmental stressors act in the same way to cause the body to produce the stress hormone, corticosterone. When stress hormone is present, reproduction is inhibited. When the stress abates, corticosterone levels in the blood fall and reproductive hormone levels rise leading to normal reproductive activity. This same cycle of hormonal activity is common for most animals, man and whitetails included.

How can whitetail breeders put this knowledge to work for better conception rates and more healthy fawns? What about artificially inseminating does and how the stress of multiple handlings affects pregnancy rates? What about shipping bred does at different times after implantation and can stress cause abortions? The answer is yes, stress causes release of the hormone corticosterone, and that inhibits the production of reproductive hormones which can have negative consequences. The key then is what management protocols you can use to reduce the stress on your does (and bucks for that matter).

It is my belief that bottle raised does are less stressed when handled than mother raised does, but we have not measured their circulating levels of corticosterone following handling so it is only my observation. We have successfully artificially inseminated many of both types of does, and not seen a significant difference, but in our facilities we have done everything we know to do to cultivate calm does. We have relatively small pens (100’X200’) with about 10 does per pen and we are in our pens at least once daily walking among the deer. We house our does like we do our bucks, by age group (reducing social dominance stress); older grumpy does can only pick on other old grumpy sisters. While we may move deer from one pen to another occasionally, we normally keep the same does together. This is especially true when it is getting close to rut, and after they have been AI’d, so new social stresses aren’t a factor. Last year Dr. Dennis Gourley suggested we move our backup bucks to our does’ pen, rather than moving does to a buck’s pen and thus reducing another possible source of stress (new pen stress). Our does are periodically allowed into our alleys to graze and check out their surroundings so when it is time to move them to the handling facility, they are used to the drill and are less stressed. The handling facility has a series of hanging walls to move the deer to the tunnel boxes to reduce their handling stress, and darkened conditions also seem to be calming. There isn’t much calming about the floor dropping out from under a deer in a handler, but we try to keep them there a minimum amount of time and after the first two or three times, they seem to tolerate it with little struggle. Most all of our deer (bucks and does alike) have been through the handler several times on practice runs where they aren’t restrained, so maybe that is why they tolerate it so well. If we have a deer that needs some kind of treatment, or an antibiotic shot, we run the whole pen through the facility and only restrain the one needing treatment. The rest just go through for practice and back to their pen. While we use a dart gun occasionally, we find it is far easier, quicker, and less stressful on the deer (and us) to run a pen through the handling facility, even for one deer. It takes us 15-20 minutes total to treat or load one or two deer, and no time to wait for reversal drugs to work.

Regardless of how deer are managed, there will always be some stress in their lives. The key is to identify the various forms of stressors and minimize their affect on the deer we raise. While permitted breeder deer and wild deer may share some of the same stressors, and good management in either high or low fenced properties can reduce stress on deer herds, it is evident that farmed deer must be subjected to less stress in general than their wild counterparts because standard stress measurements like reproductive rate, body weight, viability, longevity, and antler size favor the deer in breeder pens.

BY DR. DICK CAIN
Reproductive Physiologist
Sept/Oct 2006 Issue of Texas Deer Association Tracks