| dc.description | This study was carried out to evaluate the effects of replacing soybean meal (SM) with castor bean meal supplemented (CBT) or not (CBNT) with calcium oxide on the intake, total, ruminal and intestinal apparent digestibility of dietary contituents, ruminal pH, and nitrogen ammonia concentration (NH3-N), ruminal degradation parameters, and on the ruminal microbial protein synthesis based on urinary purine derivatives excretion or purine bases in the abomasum. Were used 5 Bos indicus crossbreed castrated male cattle were used with average initial body weight of 360 ± 30 kg, fistulated in the rumen and the abomasum, in a 5 × 5 Latin square experimental design. The duration of each experimental period was 14 d, with 8 d of adaptation and 6 d of sampling. The 5 treatments consisted of 4 levels of replacement of SM with CBT (0, 33, 67 and 100% on the DM basis) and one treatment with 100% replacement of SM with CBNT. The diet consisted of 35 and 65% of concentrate and corn silage on the DM basis, respectively. It was verified that DM digestibility was reduced (P < 0.05) by alkaline treatment of the castor bean meal. With the exception to ruminal apparent digestibility of crude protein (RDCP), there was no effect of calcium oxide (P > 0.05) on the digestibility of other constituents. We observed an increase in RDCP of 24.2% (P < 0.05) for the CBNT treatment compared to the CBT. The intestinal digestibility of the dietary constituents was not affected by the percentage of SM replaced with CBT. However, alkaline treatment of the CBNT decreased (P < 0.05) the intestinal apparent digestibility of ether extract. There was no interaction (P > 0.05) between treatment and time for ruminal pH; however, ruminal pH was influenced (P < 0.05) by collection time, with a minimum value of 6.23 estimated at 5.8 h after food delivery. However there was an interaction (P < 0.05) between treatment and collection time for NH3-N concentration. There were no observed differences (P > 0.05) in excretion of nitrogenous compounds in the urine among the different castor bean meal treatments. The N-RNA to total microbial N ratio was not affected by the percentage of CBT, presenting an average of 0.138. No differences were detected (P > 0.05) between the two methods used to estimate the ruminal microbial protein synthesis. We conclude that castor bean meal supplemented with 60 g kg− 1 of calcium oxide can fully replace soybean meal in crossbreed finishing cattle diets. | |
