Presence of pharmacological quantities of Zn as a dose does not stimulate growth

The excess of ZnO in weanling diets may have a negative impact on growth performance.
Thursday 9 September 2010 (8 years 4 months 7 days ago)
It was reported that feeding 3000 ppm Zn as Zn oxide resulted in increased metallothionein (Mt) in the mucosa of the intestine, liver and kidney as well as an increase in villus height and crypt depth. However, the exact mechanism for the stimulation of growth in the nursery pig by pharmacological Zn has not been determined. The goal of this research was to determine if a pharmacological dose of Zn at weaning would result in similar growth as feeding 2000 ppm Zn for the first 2 wk in the nursery. In study 1, 5 pigs were killed at weaning for baseline tissue concentrations and 20 pigs were drenched with 2800 mg Zn from a Zn amino acid chelate or with the same amount of liquid without Zn. Half of the drenched pigs were killed at 24 or 48 h post-drench.

Hepatic Zn (239 vs. 91, 83 μg/g, respectively) and mucosal and hepatic Mt concentrations were higher (P < 0.0001) for pigs drenched with 2800 mg Zn at 24 and 48 h than in baseline pigs or those without the Zn drench. Hepatic Zn concentrations at 48 h were significantly greater than those at 24 h (239 vs. 333 μg/g, respectively). In study 2, 24 and 48 pigs were fed 2000 or 150 ppm Zn as Zn oxide, respectively. Half the pigs fed 150 ppm Zn were drenched with 1535 mg Zn in a slurry similar to study 1. After 2 wk, the ADG was greater for pigs fed 2000 ppm Zn (0.27 kg) or 150 ppm Zn (0.23 kg) than those fed 150 ppm Zn plus 1535 mg Zn drench (0.15 kg; P = 0.001). After 2 wk, G:F was greater (P = 0.008) for these same 2 treatments. Utilizing the same treatments in study 3 (n = 32/ treatment) except one half of the pigs fed 2000 ppm Zn were switched to 150 ppm during wk 3. Overall ADG did not differ for pigs on any treatment.
In summary, 2000 ppm dietary Zn from Zn oxide stimulates growth during the first 2 wk following weaning, but a pharmacological Zn dose does not. The presence of Mt holding Zn in the mucosa for rapidly growing cells does not result in improved growth.

GM Hill, JE Link, JA Snedegar, and MJ Dawes, 2010. Journal of Animal Science, 87 (E-Suppl. 3):91.

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