Effects of a molasses-coated cottonseed product on diet digestibility, performance, and milk fatty acid profile of lactating dairy cattle1

An experiment was conducted to evaluate the effects of a molasses-coated cottonseed product on nutrient digestibility and milk fatty acid (FA) composition of lactating dairy cattle. The effect of a direct-fed microbial (DFM) product was also examined. Twelve Holstein cows (693 ± 85 kg of body weight, 127 ± 39 d in milk, 2.08 ± 0.29 lactations; mean ± SD) were randomly assigned to sequence in a replicated 4 × 4 Latin square design balanced for carryover effects. Cows were fed 1 of 4 treatments during each of the four 14-d periods: a control diet including 11.4% (dry matter basis) reginned cottonseed (CON), a diet with 14.4% molasses-coated cottonseed to match the cottonseed inclusion rate of the control diet (TC), the control diet with the addition of a liquid form of the cotton coating used to produce molasses-coated cottonseed (LC), and the LC diet with the addition of a DFM (LC+DFM). Diets were formulated for equal concentrations of neutral detergent fiber, crude protein, ether extract, and macrominerals. Treatments had no effect on dry matter intake, apparent total-tract nutrient digestibility, or milk production. The molasses coat, in either form, tended to decrease concentrations of odd-chain FA (2.25 and 2.31 vs. 2.35 g/100 g of FA for TC, LC, and CON, respectively) and unsaturated FA (31.4 and 31.1 vs. 32.1 g/100 g of FA) in milk. This could be indicative of a mild shift in ruminal fermentation away from propionate-producing bacteria toward fiber-digesting bacteria responsible for biohydrogenation of FA. The form of the molasses coating had few effects, but LC significantly decreased concentrations of total trans-C18:1 (2.04 vs. 2.30 ± 0.13 g/100 g of FA) and polyunsaturated FA (4.81 vs. 5.01 ± 0.17) compared with TC, implying that the liquid form slightly enhanced ruminal FA biohydrogenation. Furthermore, adding the DFM to the LC diet tended to increase the proportion of long-chain FA (FA >C16) and significantly increased the proportions of trans-C18:1 (2.22 vs. 2.04 ± 0.13 g/100 g of FA) and unsaturated FA (32.4 vs. 31.1 ± 0.7 g/100 g of FA), suggesting an inhibitory effect on ruminal biohydrogenation. Results suggest that coating cottonseed with a hardened molasses product does not significantly depress nutrient digestibility and may provide a convenient method of incorporating these ingredients into dairy rations.