Effects of Dietary Zinc Source and Concentration on Performance of Growing-Finishing Pigs Reared with Reduced Floor Space.

Reduced floor space allowance (crowding) depresses pig performance; however, evidence suggests that a highly-available source of zinc may partially mitigate these negative effects of stress, when supplemented at the appropriate concentration. Therefore, the objectives of this experiment were to evaluate effects of dietary zinc source (organic vs. inorganic) and increasing zinc concentration on growth performance and carcass composition of growing-finishing pigs housed in crowded conditions. Maternal-line barrows and gilts (636 pigs; initial BW = 28.7 kg) were blocked by initial BW and assigned randomly within block to one of five treatments. Twelve pens were assigned to each treatment over three replicate trials. Treatments were: 1) Control (Con9) – pigs housed in an uncrowded environment (0.73 m²/pig), fed corn-soybean meal based diets containing 50 ppm Zn (Phases 1 and 2), and 60 ppm Zn (Phases 3 and 4); 2) Crowded (Con11) – pigs housed at 0.60 m²/pig, fed the same diets as Con9; 3) AvZn40 – As Con11 + 40 ppm Zn from Availa^®Zn; 4) AvZn80 – As Con11 + 80 ppm Zn from Availa^®Zn; and 5) Inorganic zinc (ZnSO80) – As Con11 + 80 ppm Zn from zinc sulfate monohydrate. Growth characteristics and feed intakes were determined at the end of each dietary phase (28 d). Upon completion of the trial, carcass composition and meat quality were recorded. Overall, crowding decreased ADG (P < 0.05) for Con11 compared with Con9 pigs (Table 1). There were no differences in ADFI or G:F among treatments. Neither zinc source nor concentration affected fat-free lean % (FFL), dressing %, loin muscle area (LMA, cm²), or backfat depth (BF, mm). Altogether, these data indicate that neither supplemental organic nor inorganic zinc influenced growth performance or carcass composition of pigs under crowded conditions.

Table 1. Effect of zinc source and concentration on growth performance and carcass composition of growing-finishing pigs
	Treatment
Trait	Con9	Con11	AvZn40	AvZn80	ZnSO80	SE	P value
ADG, kg	0.97a	0.91b	0.93ab	0.92ab	0.93ab	0.013	0.04
ADFI, kg	2.74	2.66	2.62	2.59	2.65	0.054	0.35
BF, mm	21.9	22.1	22.3	21.4	21.6	0.44	0.54
LMA, cm2	48.5	48.5	48.9	48.3	49.8	0.63	0.43
FFL, %	52.1	52.0	52.1	52.2	52.3	0.65	0.95
Dressing %	75.9	76.0	75.7	76.2	76.4	0.84	0.98
abMeans within a row with different subscripts differ (P < 0.05).