Effect and mode of action of different doses and sources of zinc in weaning pigs using a meta-analytical and systematic review approach

In the European Union, the withdrawal of pharmaceutical zinc oxide (ZnO) poses challenges for post-weaning pigs management. The present work aims to elucidate, using a meta-analytical and a systematic review approach, the effects of different doses and forms of zinc (Zn) on health, performance, and gut health of weaning pigs. A total of 309 articles were identified from a literature research from 2001 to 2021; 85 were selected. Articles were divided in 3 datasets to evaluate: 1) the effects of ZnO doses (ZnO database); 2) the efficacy of ZnO on infection models (challenge database); 3) the effect of different Zn sources (special Zn database). The experimental groups were classified according to their Zn dose: low Zn (LZn: 0–200 ppm); medium (M1Zn: 201–630 ppm; M2Zn: 631–1600 ppm); high (HZn:>1601 ppm). Dataset 2 and 3 were analysed by a systematic review approach. Results showed that M1Zn and M2Zn guarantee comparable average daily gain, villus height and crypt depth to HZn. The HZn group had higher Escherichia coli (p = 0.04) in the small intestine. The ZnO database confirmed that Zn doses between 600 and 1600 ppm had comparable results for intestinal function and growth performance to pharmacological doses of Zn. The challenge dataset confirmed the positive effect of HZn in counteracting infections resulting in higher performance, lower diarrhoea and better intestinal morphology. The special zinc dataset suggested that coated, capsulated and nano Zn represent the most promising alternative sources to reduce the detrimental effects of weaning on pigs.