Plasma gossypol dynamics in white-tailed deer: Implications for whole cottonseed as a supplemental feed

Whole cottonseed (WCS) is a potential supplemental feed for white-tailed deer (Odocoileus virginianus) in rangeland conditions because of its high digestible energy and protein content, moderate fiber content, and resistance to degradation in moist conditions. WCS also contains the polyphenolic secondary metabolite gossypol, which reduces palatability to non-target monogastric species but may be of concern for deer nutrition. Plasma gossypol stabilization when fed a constant dry matter intake, plasma gossypol depletion after WCS was removed from the diet, and the relationship between WCS consumption and plasma gossypol concentration was studied in 10 mature male (N =5) and female (N =5) captive white-tailed deer. Consumption of WCS by 73 free-ranging white-tailed deer (59 males, 14 females) was estimated using results of the captive study. Plasma gossypol concentrations declined exponentially and averaged 0.74μg/mL 35 days after WCS was removed from the diet. Plasma gossypol concentration was linearly related to WCS consumption (P <0.001), with females having 0.35μg/mL greater (P =0.04) plasma gossypol than males for a given rate of dry matter consumption. All female and 93% of male white-tailed deer captured in WCS supplemented pastures had detectable plasma gossypol. Female averaged 1.88μg/mL of plasma gossypol and males averaged 4.84μg/mL of plasma gossypol. Based on the captive deer data, these plasma values suggest an average WCS consumption of ∼2.6g/kg BW/day for female free-ranging deer and ∼5.6g/kg BW/day for male free-ranging deer. Inferentially, a large proportion of free-ranging white-tailed deer in rangeland conditions will consume WCS, with females consuming 125g WCS/day and males consuming 428g WCS/day. That plasma gossypol levels decrease rapidly after cottonseed is removed from the diet suggests that the long withdrawal periods often used prior to breeding season may not be needed. However, although 93% of gossypol was eliminated from the animals after a five-week withdrawal period, a small amount of gossypol can still be detected. While our preliminary data on these animals suggests that these levels are not detriment to animal health or reproduction, ranch managers may want to take a conservative approach to the feeding of WCS until these questions are answered.