Here is some hard evidence that certain antibiotics cause weight gain -
for farmers a desirable side effect, but in humans just another
unwanted deleterious effect

Effect of mass medication with antibiotics at feedlot entry on the
health and growth rate of cattle destined for the Australian domestic
market.

Cusack PM.

Australian Livestock Production Services, 102 Darling Street, Cowra,
New South Wales 2794.

OBJECTIVE: To examine the effectiveness of mass medication with long
acting antibiotics at feedlot entry on lot-fed Australian domestic
cattle during a period of high risk for bovine respiratory disease
(BRD). DESIGN: Systematic allocation at feedlot entry of tilmicosin,
long acting oxytetracycline or no antibiotic treatment, to cattle lot
fed for the Australian domestic market. Comparisons of growth rate,
disease occurrence and mortality were made between the groups at the
conclusion of the feeding period. RESULTS: Cattle medicated with
tilmicosin at 10 mg/kg body weight on entry to the feedlot grew 0.08
kg/d faster than cattle medicated with oxytetracycline at 20 mg/kg body
weight and non-medicated cattle. There was no significant difference in
growth rate between oxytetracycline medicated cattle and cattle not
medicated with antibiotic at feedlot entry. Cattle medicated with
tilmicosin at feedlot entry had 8 fewer cases of disease per 100
animals compared with cattle not medicated with antibiotic at feedlot
entry. There was no significant difference in disease occurrence
between oxytetracycline medicated cattle and those not medicated with
antibiotic at feedlot entry. CONCLUSION: Mass medication with
tilmicosin at feedlot entry of cattle destined for the Australian
domestic market may be used to reduce disease occurrence and increase
growth rate during periods of high risk for BRD.

Publication Types:
Clinical Trial
Randomized Controlled Trial

PMID: 15088981 [PubMed - indexed for MEDLINE]