EVALUATION OF THE 1988 NRC REQUIREMENTS FOR ENERGY WHEN MARKET PIGS ARE FED BARLEY-BASED DIETS

Three barley-based diets, without (BRS) or with sufficient added fat to meet the current recommendations for energy content during the growing (NRC-G, < 50 kg liveweight) and finishing (NRC-F) periods, were used to compare I (BRS), II (NRC-G) and III (NRC-G; NRC-F) treatments fed ad libitum over the period from 20 to 104 kg liveweight. Twelve pens, each containing three boar (B), three gilt (G) or three castrate (C) crossbred pigs, were assigned to each treatment using a nested design. Responses of the sex-types followed the expected patterns; favouring B for efficient production of a lean carcass and C for high intake, growth rate and meat quality, while G represented the better attributes of both B and C. The superiority of I (no added fat) over III (NRC recommendation) was evident in the overall growth rate (861 vs. 756 g d-1, P < 0.01) and estimates of carcass lean (e.g. loin eye area 32.4 vs. 27.7 cm2, P < 0.01; leaf fat 1273 vs. 1607 g, P < 0.05). These responses could be related to the more appropriate lysine: energy balance in the BRS diet (i.e. 0.61 g lysine per MJ DE, compared with 0.53 and 0.42 in the NRC-G and NRC-F, respectively). In general, treatment II produced results intermediate to the others but at a higher cost than either. It was concluded that using supplementary fat, to raise the energy level of barley-based diets up to NRC recommended levels, did not enhance the efficiency of production of market pigs. In addition, the amino acid:energy ratios represented by the NRC recommendations appear to be too low for pigs with above-average potential for production of lean carcasses.