Impact of feeding whole Upland cottonseed, with or without cracked Pima cottonseed with increasing addition of iron sulfate, on productivity and plasma gossypol of lactating dairy cattle

Lactating Holstein cows were fed one of four diets containing either whole Upland cottonseed (WCS) or whole Upland cottonseed and cracked Pima cottonseed (CrP) with increasing levels of iron sulfate. Effects of supplemental iron sulfate, and the impact of substitution of two-thirds of the WCS with CrP, on milk yield and dry matter (DM) intake of cows fed these diets containing relatively high levels of gossypol were determined. All diets contained 490 g/kg DM of a grain based concentrate, 100 g/kg DM of cottonseed and 410 g/kg DM of chopped alfalfa hay. The cottonseed portion of the Control diet contained 100 g/kg DM of WCS and the other three diets contained 67 g/kg DM of CrP and 33 g/kg DM of WCS. Cottonseed meats (i.e., the interior of the seeds after decortication) were analyzed for gossypol concentration, and whole cottonseed, whole Pima and CrP contained 6.5, 9.9 and 9.6 g/kg DM of free gossypol and 2.7, 5.2 and 5.2 g/kg DM of the minus (−) isomer of gossypol, respectively, in 'meats'. Diets containing CrP were supplemented with 0, 250 or 500 mg of iron from iron sulfate/kg of diet DM. Eight cows (i.e., four primiparous and four multiparous) were used in a duplicated 4 × 4 Latin square design with periods of 28 d. Milk yield (P = 0.02) and DM intake (P < 0.01) decreased linearly with increasing levels of iron sulfate in the diet. Total plasma gossypol (μg/ml) increased (P < 0.01) with substitution of CrP for WCS, and decreased at an increasing rate (linear P < 0.01; quadratic P = 0.04) with increasing inclusion of iron sulfate in the diet. Substitution of CrP for WCS increased DM intake (P < 0.03) but milk yield was unaffected. Although addition of iron sulfate to the CrP diets reduced plasma gossypol concentrations, the reduced yield of milk and DM intake suggests that this method of reducing plasma gossypol concentrations is not commercially applicable.