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The Impact of Dietary Crude Protein Level on Growth Performance of Growing-finishing Pigs

McGhee, M., P. Xue, C, Pilcher, Q. Li and B. Frederick

Two experiments were conducted to evaluate the impact of dietary crude protein (CP) levels on growth performance of growing-finishing pigs. In experiment 1, a total of 1,035 pigs (47.53 kg ± 1.12 kg) were allotted to a randomized complete block design with 5 dietary treatments (9 pens/treatment; 23 split sex pigs/pen) and fed experimental diets for 5 wk. The concentration of CP in each diet was 13.35, 14.10, 14.85, 15.60, and 16.35%, respectively, and CP was manipulated by soybean meal and crystalline amino acid inclusion. Diets were formulated to be isocaloric and contained equal provisions of standardized ileal digestible Lys, Met+Cys, Thr, and Trp. Diets met or exceeded NRC (2012) estimated nutrient requirements. In experiment 2, the same pigs as used in experiment 1 were randomly reallotted (initial body weight = 107.56 ± 1.77 kg) by pen following a washout period to 5 dietary treatments containing 10.70, 11.45, 12.20, 12.95, or 13.70% CP, respectively. Experimental diets were fed for 3 wk. Results of both experiments were analyzed using the lme4 package of R 4.0.2, and the statistical models included the fixed effect of CP and the random effect of body weight block. Orthogonal contrasts were used to test linear and quadratic effects of increasing dietary CP. Results of experiment 1 indicated final body weight, average daily gain (ADG), and gain:feed (G:F) linearly increased (P < 0.05) as CP in the diet increased (Table 1). Average daily feed intake (ADFI) did not differ among treatments. In experiment 2, dietary CP did not affect body weight, ADG, nor ADFI. As dietary CP increased, however, G:F tended (P < 0.10) to increase.

In summary, greater dietary CP improved the performance of growing-finishing pigs by increasing ADG and G:F in the grower phase and tended to increase G:F in the finishing phase.