the quantity or quality of the native forage is in some way lacking. Results of deer carrying capacity studies at Texas A&M University-Kingsville indicate that late summer is the most stressful time of the year for deer in south Texas. These researchers found that the carrying capacity of the habitat reaches its low point, or “bottleneck,” during July and August. In other words, the native habitat will support only a certain number of deer. This “maximum” number of deer is set by the number that can be supported when the habitat reaches it’s lowest nutritional point, which is late summer. Therefore, this two-month period is a critical time to provide supplemental feed.
The study conducted by Zaiglin and DeYoung verified the importance of supplemental feeding during late summer, which is when they found that consumption, peaked. In their study, supplemental feed consumption was also inversely related to the crude protein levels of the native habitat. Larry Varner, Lytle Blankenship, and Greg Lynch collected and analyzed the nutritive content of 26 different plant species eaten by deer on the Chaparral Wildlife Management Area. They found that crude protein levels were highest in spring, at intermediate levels during fall and winter, and at lowest levels during summer. In a study conducted on the Welder Wildlife Refuge, Thadis Box found that the two periods of lowest forage production were winter (January-February) and late summer (July-September).
Based on the above, ranchers and managers in south Texas should provide supplement during January through February and again during July through September in order to cover the two times of the year when the native vegetation is most likely to be lacking in quantity or quality. Obviously, droughts can also result in less than optimum forage conditions at other times. Therefore, your supplemental feeding program should include periods of drought as well.
The second stress period is based on the deer themselves and occurs when deer are physiologically stressed due to increased nutrient requirements. In the case of bucks, this occurs at two different times of the year. The first period is the post-rut (January-March) when bucks are reeling from the rigors of the rut and trying to recover the 25-35% of body weight they lost while chasing does. Previous telemetry research through Texas A&M University-Kingsville indicates that nearly 80% of all buck mortalities occur during the post-rut. Obviously, the post-rut period is a very stressful time for bucks. The second period of physiological stress for bucks occurs when they are growing antlers (March-August). If your goal is to maximize antler growth, then as a minimum, you should provide supplementation during January-August.
The most physiologically stressful time for does occurs when they are pregnant (January-July) and later when they are nursing fawns (July-September). If one of your goals is to increase fawn production and survival, than supplementation should be continued through September.
It also takes time to get deer used to eating supplemental feed, especially the first year that the feeding program is initiated. If managers are not feeding on a year-round basis, they should begin supplemental feeding at least several weeks before the period they wish to cover with supplementation. In order to cover all of the different critical months for deer of both sexes, as a minimum, supplementation should be provided from December through September.
If a rancher or manager cannot afford to provide supplement year-round, than the “best” time not to provide supplemental feed is probably during late September through early December. The pre-rut and rut are possible times to stop supplementation because bucks at this time of the year greatly reduce feed intake in their endless pursuit of does. In fact, penned studies have shown that even when bucks are individually isolated in small pens, they will still voluntarily restrain from eating feed that is placed into their pen during the rut!
Look for part three of this six-part series on supple