My understanding is that the primary use of antibiotics in farm animals is for more rapid animal growth, not to prevent visible symptoms of infection. (It's not clear why antibiotics promote growth, but it's possible they are suppressing minor asymptomatic infections that sap calories.)
In any case, the article is slightly misleading since the overlap between important human antibiotics and the widely used animal antibiotics is modest.
> Increased virginiamycin use in Danish broilers during the mid-1990s correlated with a rise in resistant E. faecium prevalence, from 27% to ∼70% (7). Following the ban, resistance declined to 34% in 2000. Likewise, in Denmark, the 1998 ban on the use of tylosin in swine resulted in a decline in erythromycin (a structurally related macrolide) resistance, from 66% to 30%
> The finding of bacterial cross-resistance between NTAs used in food animals and human drugs was aptly demonstrated with avoparcin (an AGP) and its close relative vancomycin (an important human therapeutic) when vancomycin-resistant enterococci (VRE) emerged as a serious human pathogen. A connecting link between resistance in animals and humans was revealed when Bates et al. found avoparcin- and vancomycin-coresistant enterococci in pigs and small animals from two separate farms. Ribotyping methods showed that some of the patterns from farms and sewage exactly matched those of Enterococcus spp. from the hospital (24). The structures of the two drugs are similar: they are both members of the glycopeptide family
In any case, the article is slightly misleading since the overlap between important human antibiotics and the widely used animal antibiotics is modest.
http://animalantibiotics.org/antibiotics-used-farm-animals/