Effects of balanced protein level on growth performance and carcass composition of growing-finishing pigs

A total of 1,003 barrows and gilts (initial BW of 51.5 kg) were used in a 88-d study to determine the effects of varied levels of balanced protein (BP) on growth performance and carcass characteristics. Balanced protein refers to balancing dietary AA according to the ideal protein ratio at least for the first 4 limiting AA. In a completely randomized design, 3 corn and soybean meal-based experimental diets were tested over 2 phases, including a growing phase (d 0–28; 51–79 kg BW) and a finishing phase (d 29–88; 79–130 kg BW) using 6 replicate gilt and 7 replicate barrow pens per treatment. Dietary treatments included a low BP diet which met the NRC (1998) requirements, a diet which met the new recommendation for lean pigs (NR), and a diet which was formulated to be 10% above the NR recommendations. Diets were formulated to contain identical net energy content.

No gender × BP interactions were observed (P > 0.30) for any of the growth performance and carcass responses. During the growing phase, G:F improved (P = 0.001) and ADG tended to increase (P = 0.07) as the BP level increased in the diet. The greatest improvements were achieved with the highest BP level containing 0.89% standardized ileal digestible Lys. Gilts had improved (P < 0.001) G:F from d 0 to 28 compared with barrows. During the finishing phase, BP levels did not affect (P > 0.05) growth performance which may have been confounded by a relatively long duration (60 d) of the finishing phase. Over the entire 88-d period, ADG and G:F improved (P < 0.02) as the dietary BP levels increased. Gilts had lower ADFI and improved G:F (P < 0.01) than barrows during the entire period. Carcass characteristics (yield, backfat depth, loin depth, lean percentage) and income over feed cost were not affected by feeding varied levels of BP.

These results suggest that today′s pigs with high lean potential respond to a higher BP than current recommendations.