Abstract
Antibiotics and pharmacological zinc supplementation were commonly used as growth promoters for several decades in the swine industry before being limited because of public health and environmental concerns. Further, the physiological and metabolic responses associated with their growth promotion effects are unclear. To characterize these responses induced by pharmacological zinc supplementation (2500 mg/kg) and carbadox (55 mg/kg), 192 post-weaning pigs were fed basal and test diets for 43 days. Compared with basal, pharmacological zinc and carbadox independently improved growth performance. Pharmacological zinc increased gastric mucosa thickness compared with basal zinc, while carbadox increased intestinal villus:crypt ratio compared with non-carbadox. Pharmacological zinc and carbadox independently reduced interleukin (IL)-1β concentration compared with basal zinc and non-carbadox. Pharmacological zinc increased IL-1RA:IL-1 ratio by 42% compared with basal zinc, while carbadox tended to increase the IL-10 and IL10:IL-12 ratio compared with non-carbadox. Carbadox increased fecal concentrations of histidine and lysine compared with non-carbadox. The independent effect of pharmacological zinc and carbadox on morphology and nutrient metabolism, and their shared effect on immunity may contribute to the additive effect on growth promotion. These results further confirmed the concept that growth promotion is multifactorial intervention. Therefore, elucidating growth-promoting effects and searching for alternatives should include wide-spectrum evaluation.
Highlights
Antibiotic growth promoters (AGP) and pharmacological doses of zinc (Zn, 1000–3000 mg/kg diet) from zinc oxide (ZnO) were the most common approaches to prevent the adverse effects of weaning in piglets
The non-therapeutic use of antibiotics as AGPs and pharmacological doses of Zn in weaned pigs is of concern because they may cause the selection of multi-drug resistant bacteria [1], and enterobacteria have been shown to develop resistant genes [2]
The time effect was significant (p < 0.05) for body weight (BW), average daily gain (ADG), average daily feed intake (ADFI), and gain to feed ratio (G:F), but there were no interactions of Zn × carbadox × time (Table S1)
Summary
Antibiotic growth promoters (AGP) and pharmacological doses of zinc (Zn, 1000–3000 mg/kg diet) from zinc oxide (ZnO) were the most common approaches to prevent the adverse effects of weaning in piglets. The non-therapeutic use of antibiotics as AGPs and pharmacological doses of Zn in weaned pigs is of concern because they may cause the selection of multi-drug resistant bacteria [1], and enterobacteria have been shown to develop resistant genes [2]. With the restriction of using AGPs and pharmacological doses of Zn in diets, various alternatives, such as probiotics, prebiotics, organic acids, enzymes, phytogenic compounds, and trace minerals, have been the subject of evaluation as growth promoters [6]. A recent review summarizing results from more than 2000 published trials showed limited improvements in weight gain of pigs fed diets using these alternative growth promoters [7]. The effects of AGPs and pharmacological doses of Zn on growth performance have been widely reported [8,9,10,11,12], the mechanisms involved in these effects have not been fully identified [13]
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