I know that there was testimony by Dr. Lance B. Price to the House Committee for greater transparency on "why, how and in what animals these vital drugs are used."
http://democrats.energycommerce.house.gov/sites/default/file...
From the abstract (freely translated): "... guessed is that a third to half of resistance encountered in germs within humans is of agricultural origin."
Important is that not the antibiotics are transferred from animals to humans but the already resistant bacteria.
A short summary is here: http://www.upi.com/Science_News/2012/08/31/Antibiotic-resist...
After analyzing the mutations of the MRSA strains in the women and the animals, the researchers concluded that it had been circulating among the livestock before jumping to the people. The researchers' analysis is "so fine-grained," McKenna writes, that it "seems to me to be difficult to challenge."
The Danish study comes on the heels a 2012 paper by a consortium of US and European researchers, which used gene sequencing to show that another common strain of MRSA originated in humans as a common staph infection, jumped to livestock, where it evolved resistance to the common antibiotics tetracycline and methicillin, and then jumped back to humans. Of course, you can also contract antibiotic-resistant pathogens through contact with raw meat—as, for example, more than 100 people did when the agribusiness giant Cargill sent out tens of millions of pounds of ground turkey tainted with antibiotic-resistant salmonella in 2011.
Antibiotics are pretty much a non-renewable resource, the more they're used, the lesser their effectiveness. Using them on livestock, or even excessively on humans would leave humans with a dangerous lack of medical defence against harmful bacteria.
This can happen, but most of the bacteria found in animals are species-specific and don't get "passed" to us in the sense that you could "catch" flu or TB from another human.
The real danger is "horizontal gene transfer" [1], where different kinds of bacteria exchange genes - including those for antibiotic resistance. This is the main mechanism for the spread of resistance to antibiotics.
That effect might even have helped in conquering the Americas, because the conquerors where used to such diseases and the natives where not.
BTW, Chicken Pox affects only humans and some other primates. The virus that causes it, varicella zoster, doesn't infect chickens or other fowl. And, being a virus, it has nothing to do with antibiotic resistance either.