"Body condition scores remained good and all of them got pregnant," said Dr. Ron Randel, leader of the deer farming research team at the Texas A&M University System Agricultural Research and Extension Center at Overton.
Previous studies have shown feeding even small amounts of whole cottonseed to have severe detrimental effects on male red deer and male fallow deer. Whole cottonseed diets may diminish antler development by as much as 50 percent, lower body condition scores and reduce the animals' sperm motility. This study was with cottonseed meal, Randel emphasized, not whole cottonseed.
Both whole cottonseed and cottonseed meal contain gossypol, a toxic element that naturally occurs in cotton plants. The effects of gossypol on ruminants such as red deer and related species are not so overt as those on non-ruminants, but seem focused on the animal's reproductive physiology.
Whole cottonseed contains tenfold the amount of gossypol than does cottonseed meal. This is assuming the cottonseed meal is produced by a chemical extraction process followed by mechanical extrusion..
Because they are cheap, high energy feedstuffs, whole cottonseed and cottonseed meal are commonly fed to both free-ranging and ranched deer, particularly in West Texas where cottonseed is particularly cheap and plentiful and grazing is at best spartan.
In the study, the most recent gossypol work completed at the Overton center, 66 fallow deer were separated into three groups of 20 does and two bucks each. All groups were contained in individual two-acre Coastal bermudagrass pastures and fed daily.
The control group was fed 0.79 pounds of soybean meal and no cottonseed meal per head, per day. The low-cottonseed-meal group got 0.39 pounds of soybean meal and 0.50 pounds of cottonseed meal. And the high-cottonseed-meal group received 1 pound of cottonseed meal and no soybean meal per day.
The amount of gossypol in the animals' diets ranged from zero for the soybean meal group, 3.95 milligram per kilogram of body weight for the low-cottonseed-meal group, to 8.10 milligram per kilogram of body weight for the high-cottonseed-meal group. In English units of measurement, these gossypol amounts corresponded from about 0.00006 to about .00012 of an ounce per pound of body weight, respectively.
Like most seasonal breeding animals, fallow deer generally lose weight through the fall and winter. All the deer did lose weight during this period as expected, but there were no significant differences between the groups. Concentrations of progesterone were reduced in the high-cottonseed meal group as compared to the other groups. Progesterone is a hormone that prepares the uterus for implantation of the fertilized ovum, helps maintain pregnancy and promotes mammary gland development.
Randel noted that although the study indicates cottonseed meal can be safely included in rations for both male and female deer, careful consideration must be given not only to the amount but the source of the cottonseed meal.
"If the cottonseed meal was produced by chemical extraction alone, the amounts fed should be reduced by half what this study shows to be safe," Randel said. The study was performed by a student under Randel's supervision, Steven Mapel, for his master's degree thesis. No similar studies - either at the Overton center or elsewhere - have been done to date on white-tailed deer, the wild deer species native to Texas. "However, both fallow and red deer are very similar to white-tails in terms of antler and reproductive cycles. As a result, there are good reasons to believe that too much gossypol could also affect white-tailed deer," Randel said.