Substitution of soybean meal for cottonseed meal in multiple supplements for grazing beef heifers in the dry season

The objective of this study was to evaluate the effect of substituting soybean meal for cottonseed meal in multiple supplements on the nutritional characteristics and performance of beef heifers in their postweaning phase on Brachiaria decumbens pastures during the dry season. Twenty-four Nellore beef heifers (average initial age and weight of 8 mo and 210±6 kg, respectively) were used. The design was completely randomized, with four treatments and six replicates. Supplements contained approximately 30% crude protein (CP) and a progressive substitution of soybean meal for cottonseed meal (0, 50 and 100%). The control animals received only a mineral mixture ad libitum, and those on the other treatments received supplementation at 1.0 kg/animal/day. No differences were found in ADG between supplemented and control animals (P>0.10). Supplementation increased crude protein (CP) intake only (P<0.10). The level of substitution of soybean meal for cottonseed meal did not affect (P>0.10) the intake of supplemented animals. Supplementation elevated the apparent digestibility coefficients (P<0.10) of OM, CP, NFC and TDN, but not EE or NDFap (P>0.10). A positive linear effect (P<0.10) of the level of substitution of soybean meal for cottonseed cake was observed on the digestibility of OM, NFC and TDN. Supplementation and the level of substitution had an effect (P<0.10) on the serum urea nitrogen and urine urea nitrogen contents. Supplementation or substitution level had no effect on the flow of microbial nitrogen to the intestine (MICN) or efficiency of microbial protein synthesis (EMPS) (P>0.10). Substitution caused a decreasing linear effect (P<0.10) on microbial nitrogen/nitrogen intake ratio (MICNR). In conclusion, substitution of soybean meal for cottonseed meal in multiple supplements during the dry season does not impair the productive performance of beef heifers.