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Summer Stress

Posted Aug. 1, 1999

If you are like me, summer temperatures can cause you to daydream about what it must be like to be a snowbird. Any means to escape the relentless temperature during July and August is appealing. However, if you like air conditioning and the great indoors, we do have the means to stay cool. We are also able to stay well fed. Whitetailed deer do not have this luxury.

Most whitetailed deer enthusiasts in our area believe that the winter months are the most nutritionally stressful for deer. Winter can in fact be a stressful time of the year for deer. Especially considering the post-rut condition of mature bucks. However, the average winter in our area produces several cool-season forbs and grasses that deer utilize, in addition to mast (acorns).

On the other hand, those same enthusiasts might not think about the summer months posing a nutritional hardship to deer. Sure, the lush months of April, May and June can provide more nutrition than deer need under good habitat conditions. But what about July and August? Most cattle producers know that grass quality declines during this time and, depending on the class of cattle, manage for nutritional deficiencies. It stands to reason that deer managers should know the quality of deer foods during this same time period and why it is critical to deer.

During July and August, does may still be lactating and bucks are growing antlers. A deer's diet should consist of at least 12% crude protein to meet these physiological demands. There is speculation that in our area, browse quality may not be adequate during July and August. Realize, though, that browse comprises less than 20% of deer's summer diet locally. In the spring of 1998, we began to sample key deer browse plants on The Noble Research Institute Coffey Ranch. These plants include poison ivy, greenbrier, winged elm, hackberry, sumac, bois d'arc, roughleaf dogwood, prickly ash, plum, corralberry, chittamwood, and black oak.

The graph depicts the average crude protein (% CP) content of the above species from April through August 1998. Note that by approximately mid-June, the average CP content of browse species on the Coffey Ranch dropped below 12%.

Keep in mind that the summer of 1998 was a drought and browse comprises a small amount of the summer deer diet. We intend to sample these same plants and many preferred forbs for several years in order to get a better idea of the nutritional quality of summer forage available to deer in this area.

The table depicts the monthly average crude protein content (% CP) of those same plants individually, from April through August. Note that bois d'arc, chittamwood, prickly ash, black oak, and winged elm maintained the highest crude protein content through the July-August period. Again, the drought that we experienced during the 1998 growing season could have significantly influenced these results.

The remaining 80% of a deer's summer diet is comprised of forbs. Many of these may have greater than 12% CP levels. However, several factors may influence the availability and/or quality of these forbs such as drought, severity of livestock grazing, and the deer population in a given area. These factors may cause deer to utilize more browse to attempt to meet their nutritional needs.

So how can we meet this potential deficiency in a deer's diet during July and August? The key is good habitat management. This includes proper grazing management and perhaps prescribed fire. Good grazing management will allow high quality native forbs (including legumes) to persist in pastures. Properly timed burns can encourage forb growth and/or stimulate brush regrowth. Both of these practices, weather permitting, can provide high quality forage for deer much longer into the summer.

What about food plots? As the old saying goes, when it rains you can grow food plots but may not need them and when it does not rain you need food plots but can't grow them. This was certainly true last year on the Coffey Ranch. We could have planted food plots, but they would not have grown. Depending on range conditions, summer food plots may play an important role in supplementing deer diet quality in our area. Some good choices for summer food plots are cowpeas (e.g., iron and clay, catjang, and red ripper), soybeans, American jointvetch, or lablab. These forages are high in protein content and deer love them. If you choose to plant food plots to supplement deer nutrition, they should be at least one acre in size, well distributed throughout the habitat, and comprise at least 1 3% of your total land area.

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