CHARACTERISTICS OF DIGESTION OF LINTED AND LINT-FREE COTTONSEED IN DIETS FOR FEEDLOT CATTLE

Eight Holstein steers (439 kg) with ''T'' cannulas in the rumen and pr oximal duodenum were used to evaluate the characteristics of digestion of Pima cottonseed. Treatments consisted of a basal growing-finishing diet containing (DM basis) 1) 15% tapioca, 2) 15% whole linted cotton seed (Delta Pine 61, DP; 3) 15% whole lint-free cottonseed (Pima, PW), and 4) 15% ground Pima cottonseed (PG). Substitution of tapioca with cottonseed decreased (P <.05) ruminal and total tract digestion of OM (10.8 and 3.5%, respectively). Net ruminal microbial N synthesis was a lso lower (20.5%, P <.10) with cottonseed supplementation. The greater reductions occurred with DP and PG. Characteristics of ruminal and to tal tract digestion of OM and N were similar for DP and PG. Grinding P ima cottonseed increased ruminal digestion of OM (13%; P <.05) and fee d N (18.1%; P <.10). Ruminal digestibility of N in DP, PW, and PG aver aged 50.0, 49.4, and 59.3%, respectively. Postruminal digestion of lip id was similar (P >.10) across cottonseed treatments, averaging 76.9%. The comparative DE value of DP, PW, and PG were 4.13, 3.20, and 3.80 Mcal/kg, respectively. It is concluded that the energy value of lint-f ree Pima cottonseed is similar to that of linted varieties provided th at it is ground before feeding. However,grinding will increase ruminal N degradability 20%. Furthermore, depending on the level of incorpora tion in the diet, grinding Pima cottonseed may decrease ruminal microb ial growth and net ruminal protein efficiency.