Productive and economic performance of cull heifers from different genetic groups fed diets with different sources of non-protein nitrogen in feedlot.

Non-protein nitrogen (NPN) sources can replace true protein sources in ruminant diets. This strategy can reduce production costs and improve the economics and productivity of production systems. We hypothesized that genetic group and non-protein nitrogen sources in the diet would not affect the intake and performance of cull heifers. The objective of this study was to evaluate the effect of genetic group and non-protein nitrogen sources added to the total ration on the productive and economic performance of Angus × Nellore (A × N) and Charolais × Nellore (C × N) cull heifers finished in feedlot. A total of 552 crossbred beef heifers with an initial weight of 374.23 ± 55 kg and 24.0 ± 2 months of age were used. The data were analyzed considering a 2 × 2 factorial scheme (2 genetic groups and 2 diets). The diets had the same protein and energy levels, however, with different sources of non-protein nitrogen (NPN). The first diet (LPU) contained livestock urea and protected urea, while the second diet (EU) contained only extruded urea as a source of NPN. There was no significant interaction between genetic group and diet on nutrient intake and most of the productive performance variables (P > 0.05). However, A × N heifers showed greater dry matter intake (10.33 vs. 9.92 kg/day), average daily gain (1.29 vs. 1.15 kg/day) and heavier carcass (305.73 vs. 279.8 kg) compared to C × N heifers (P < 0.01). Heifers fed the LPU diet had higher final weights (500.04 vs. 488.56 kg), average daily gain (1.31 vs. 1.21 kg) and feed efficiency (0.13 vs. 0.12) (P < 0.01). Greater revenue was observed in A × N heifers (US$ 1,244.30 vs. US$ 1,151.64), which despite the greater total cost (US$ 307.13/animal vs. US$ 295.09), had a greater gross margin (US$ 209.38 vs. US$ 136.09), in relation to C × N heifers (P < 0.05). A × N heifers had greater nutrient intake and were more efficient in feed conversion compared to C × N heifers. The inclusion of fast and slow soluble non-protein nitrogen sources in the diet of beef heifers provides greater performance during finishing in feedlots.