Effect of increasing dietary inclusion of whole cottonseed on nutrient digestibility and milk production of high-producing dairy cows

We determined the effects of increasing the dietary inclusion of whole cottonseed (WCS) on nutrient digestibility and the milk production responses of high-producing dairy cows. Twenty-four multiparous Holstein cows (mean +/- SD; 52.7 +/- 2.63 kg/d milk; 104 +/- 23 DIM) were randomly assigned to treatment sequences in a replicated 4 x 4 Latin square design with 21-d periods. Treatments were increasing doses of WCS at 0%, 8%, 16%, and 24% DM, with WCS replacing soybean meal and hulls to maintain similar diet nutrient composition (% DM) of NDF (32%), forage NDF (21%), starch (27%), and CP (17%). Total fatty acid (FA) content of each treatment was 1.70%, 2.96%, 4.20%, and 5.40% DM, respectively. Three preplanned contrasts were used to test the linear, quadratic, and cubic effects of increasing dietary WCS. Increasing dietary WCS from 0% to 24% DM quadratically influenced the intake of DM and NDF, with the highest value being the inclusion of 8% WCS, and intakes of 16- and 18-carbon, and total FA, with maximum values obtained up to 24% WCS. Increasing dietary WCS affected digestibility of DM (cubic) and NDF (quadratic), with the lowest values being the inclusion of 8% WCS. Increasing WCS increased 16-carbon digestibility (quadratic) but decreased digestibility of 18-carbon and total FA (both quadratic), with highest and lowest values for the inclusion of 24% WCS, respectively. Increasing dietary WCS quadratically increased absorbed 16- and 18-carbon, and total FA, with maximum values obtained for 24% WCS. Increasing dietary WCS quadratically increased yields of milk, milk fat, milk protein, milk lactose, 3.5% FCM, and ECM, and linearly increased BW gain. The source of milk FA was affected by dietary WCS, with a quadratic decrease in the yield of de novo and mixed milk FA and a quadratic increase in preformed milk FA. Increasing dietary WCS linearly increased trans- 10 C18:1 milk FA content. As dietary WCS in creased, plasma insulin linearly decreased, and plasma gossypol levels linearly increased. Despite the decrease in total FA digestibility, increasing dietary WCS from 0% to 24% DM increased FA absorption. Increasing the dietary inclusion of WCS up to 16% DM increased milk production responses and DM intake. Under the current dietary conditions, high-producing dairy cows benefited best from a diet containing an inclusion of 8% to 16% WCS in DM.