This trial aimed to evaluate the effects of replacing a true protein source (pelleted sunflower meal) with a non-protein nitrogen source (Optigen 61650) in feedlot fed "bolita" calves. The study was carried out on the Don Tomás Farm, located in San Alberto, San Andrés de Giles County, 100 km west of Buenos Aires, Argentina. Forty Aberdeen Angus calves, with an average initial weight of 210 ± 9.6 kg and approximately 10 months of age, were used in the trial. A completely randomized experimental design was used, with 2 treatments and 2 replicates (10 animals/replicate). Treatments were: T1 – Pelleted sunflower meal as a protein source (DM basis: 70.5% corn grain, 26% pelleted sunflower meal, 2% wheat meal and 1.5% vitamin-mineral mixture with monensin); and T2 ¬ Optigen as a protein source (70.5% corn grain, 26.65% pelleted wheat bran, 1.35% Optigen and 1.5% vitamin-mineral mixture with monensin). The experimental period lasted for 95 days, with the first 7 days used for adaptation. The animals were individually weighed at the beginning and at the end of the trial, before the morning feeding. The data were submitted to ANOVA using the GLM procedure (SAS, 2000) and the means were compared by Tukey test (P<0.05). There were no differences between treatments in terms of final live weight (308.5 vs. 309.3 kg for T1 and T2, respectively, SEM= 2.01; P= 0.78), live weight gain (1.16 vs. 1.17 kg/d; SEM= 0.023; P= 0.81), feed conversion (7.64 vs. 7.59 for T1 and T2, respectively), and carcass yield (56.6 vs. 56.4%; SEM= 0.39; P= 0.76). In addition, the feces from the animals fed Optigen showed numerically lower starch concentrations (5.71 vs. 3.81%; SEM= 1.46; P= 0.24), and similar protein and dry matter concentrations (17.9 vs. 18.9%; SEM= 0.93; P= 0.34 and 14.2 vs. 15.0%; SEM= 0.65; P= 0.41 for T1 and T2, and DM and protein, respectively), compared to the animals fed pelleted sunflower meal. It was concluded that under the conditions of this study, Optigen successfully replaced a true protein source in feedlot fed "bolita" calves, typical of an Argentinean feedlot system.

The aquaculture industry has been the fastest growing sector of agriculture over the past thirty years (FAO 2002). During this time the industry has become very reliant on fishmeal as a high quality protein source. However, fishmeal is also a limited resource on the world stage. For future growth to occur in this industry it will be necessary to incorporate larger amount of plant based protein into diets as fishmeal becomes scarcer. When incorporating these plant-based feed ingredients into diets often fish growth is compromised because of insufficient stimulation of the olfactory and gustatory receptors. This lack of stimulation of these receptors means that fish have trouble finding the feed by olfaction and feed palatability may be reduced. To counter this lack of stimulation the addition of feed additives like betaine, thin distiller solubles and more recently soluble canola protein concentrate have been shown to increase feed intake and growth of farmed fish in diets containing low inclusion rates of fishmeal (Kosdella et al., 1993, Thiessen et al. 2000, Scobie 2005).