Characterization of the Physiological Responses to Post-Weaning Diets Containing Growth Promoting Levels of Zinc Oxide and Carbadox Fed to Nursery Pigs

Concerns about antibiotics and high dietary zinc usage compel the industry to identify alternative growth promoters. To investigate the physiological responses of adding antibiotic (Ab) and pharmaceutical levels of ZnO to the diet as growth promoters, and identify biomarkers that may guide the selection of alternatives, pigs (n=48 pigs/treatment; BW=5.87±1.14 kg) were housed individually and blocked by weight, sex, and room in a 2×2 factorial arrangement. Pigs were fed diets supplemented with low or high ZnO (150 vs. 2500 ppm) with or without Ab (0 vs. 55 ppm carbadox) for 7 d. Ten pigs per treatment were randomly selected for liver and ileum sample collection on d 7 to evaluate morphological changes by microscopy, and levels of 13 cytokines by immunoassay using a multiplex bead array. Metabolites in the ileal digesta of euthanized pigs, and feces (n=44 pigs/treatment) were analyzed using liquid chromatography–mass spectrometry (LC-MS) based metabolomic analysis. Data were analyzed using PROC Mixed in SAS, with treatments as fixed effects and block as a random effect. Growth performance data were shown in Table 1. Liver histology was not different among treatments. Pigs fed Ab diet had 12% greater ileal villus to crypt ratio (P<0.05) compared with pigs fed no Ab, while ZnO had no effect. The concentration of TNFα was 25% greater in liver of pigs fed Ab compared with those fed no Ab (P<0.05). In the ileum, the pro-inflammatory cytokine IL-1β was decreased 31% and 45% (P<0.05) in pigs fed high ZnO and Ab diets compared with those receiving low ZnO and no Ab respectively. Multivariate modeling of the LC-MS data showed that the metabolomes of ileal digesta and feces were affected by Ab treatment, but not by ZnO. Multiple metabolites associated with Ab treatment and ADG were identified. Of remark, Val and Leu in ileal digesta were positively correlated (r=0.41; P<0.01, and r=0.34; P<0.05, respectively) with ADG. These results showed that the intestine presented more physiological changes than liver in response to ZnO and Ab supplementation. The identified biomarkers could lead to the development of alternative growth promoters in pigs.

Table 1.

	ZnO, ppm		Antibiotic		SE	P-value
	150	2500	No	Yes		ZnO	Ab	ZnO×Ab
ADG, g	12.84b	65.38a	24.01b	54.21a	7.53	<0.01	<0.01	0.83
ADFI, g	76.63b	96.06a	80.91b	91.77a	4.52	<0.01	0.04	0.97
G:F	0.20b	0.62a	0.31b	0.51a	0.07	<0.01	0.04	0.58

^a,bLeast squares means within a row with different superscript letters were different.