MILK-PRODUCTION AND PLASMA GOSSYPOL OF COWS FED COTTONSEED AND OILSEED MEALS WITH OR WITHOUT RUMEN-UNDEGRADABLE PROTEIN

Twenty-four multiparous Holstein cows were randomly assigned at calvin g to treatment diets using a modified split-plot design to determine t he effects of protein source on milk production and composition. The t reatment diets consisted of an 80:20 combination of corn and alfalfa s ilages and whole cottonseed at 12% of the dietary dry matter (DM). The treatment diets were formulated to contain 17% crude protein (CP) and 20% acid detergent fiber on a DM basis. One of the following sources of supplemental CP was included in each treatment diet: 1) cottonseed meal, 2) cottonseed meal plus a rumen-undegradable protein (RUP) suppl ement, 3) soybean meal, and 4) soybean meal plus an RUP supplement. Co ws were fed the initial treatment diet for 6 wk and then were switched to the other oilseed meal source but continued to receive the same am ount of RUP during the second period of the study. Milk production and composition were not affected by treatment diet. Cows fed treatment d iets without RUP supplementation consumed more DM and thus more CP. Su pplementation with RUP resulted in greater milk production efficiency per unit of DM consumed. Cows fed treatment diets containing cottonsee d meal had higher plasma gossypol concentrations than did cows fed tre atment diets containing soybean meal. Plasma gossypol concentrations f or all cows in each group were below the recommended upper limit that is considered to be safe. Data suggest that cottonseed meal in the die t can be substituted for soybean meal, resulting in similar milk produ ction and composition.