Abstract A total of 2,024 pigs (initially, 92.5 kg; TN-70 × PIC 800) were used to evaluate the effects of crude protein (CP) level on growth performance of late finishing pigs. Pigs were allotted to 1 of 5 dietary treatments fed in two phases. Phase 1 diets were fed from 92.5 to 106 kg of body weight (BW) followed by phase 2 diets fed until marketing. There were approximately 26 pigs/pen and 16 replications/treatment. Marketing began on d 29 of the trial and continued for 4 consecutive weeks with an equal number of pigs marketed from each pen per marketing event. Treatments included a medium (13%) and a high (15%) CP level fed in phase 9. In phase 10, pigs previously fed the medium CP level were transitioned to either a low (11%), a medium (12.5%), or a high (14%) CP level. Pigs previously fed the high CP level were transitioned to either a medium (12.5%) or a high (14%) CP level. Therefore, total dietary treatments for phases 9 and 10 included: 1) medium-low, 2) medium-medium, 3) medium-high, 4) high-medium, and 5) high-high. Target CP levels were achieved by adjusting soybean meal and synthetic lysine levels. Complete diets were analyzed to confirm dietary formulation. On average, analyzed CP levels were 1.4 percentage points below formulated values, but analyzed CP differences between phases and treatments were consistent with formulation. From d 0 to 13 (phase 9), there were no differences (P 0.10) between pigs fed different CP levels. From d 13 to 28 (phase 10), pigs fed the medium-high and high-high CP levels had improved (P ≤ 0.017) ADG and G:F compared to pigs fed the medium-low CP level with the other treatments intermediate. From d 0 to 28 (pre-marketing period), pigs fed the high-high CP level had increased (P = 0.029) ADG compared to pigs fed the medium-high CP level with the other treatments intermediate. Pigs fed the medium-high, high-medium, and high-high CP levels had improved (P = 0.002) G:F compared to pigs fed the medium-low CP level with pigs fed the other treatment intermediate. Overall (d 0 to 50), there was a tendency observed (P = 0.064) with pigs fed the high-high CP level having the greatest numerical ADG. Pigs fed the medium-high, high-medium, and high-high CP levels had increased (P = 0.009) margin over feed cost (MOFC) compared to pigs fed the medium-low with pigs fed the other treatment intermediate. In summary, at 92.5 kg of BW, growth performance and MOFC is increased by feeding high CP in phase 9, phase 10, or both.
Johnson et al. (Wed,) studied this question.