Usually zinc increases the appetite in humans but I dont know if it does the same regarding the animals; practically the animal feeders(poultry,lambs and other edables) inject them by estrogen to increase their weights or their fat content so they will weigh extra pounds in little time with minimal feedings. Hope my answer is helpful

@ Marcel merz: i think you need to be specific about the kind of animal you are talking about because these drugs and chemicals vary in application and their effect varies from one animal to the other..... an appetizer for poultry birds may not necessarily work for livestock animals. Thanks

Antibiotics have been used in animal feed for about 50 years ever since the discovery not only as an anti-microbial agent, but also as a growth-promoting agent and improvement in performance. Tetracyclines, penicillin, streptomycin and bactrican soon began to be common additives in feed for livestock and poultry. Currently, the following antibiotics are used in livestock and poultry feed: chlortetracycline, procaine penicillin, oxytetracycline, tylosin, bacitracin, neomycin sulfate, streptomycin, erythromycin, linomycin, oleandomycin, virginamycin, and bambermycins. In addition to these antibiotics, which are of microbial origin, there are other chemically synthesized antimicrobial agents that are also sometimes used in animal feeds. These include three major classes of compounds: arsenical, nito-furan, and sulfa compounds. Arsenical compounds include arsanilic acid, 3-nitro-4-hydroxy phenylarsonic acid, and sodium arsanilate; nitro-furan compounds include furazolidone and nitro-furazone; sulfamethazine, sulfathiazole, and sulfaquinoxaline. Other chemicals are also used as antiprotozoal agents to prevent coccidiosis and histomaniasis in chickens and turkeys. Antibiotics are used regularly in animal feed at a rate of 2 to 50 grams per ton for improved performance in the animals. The reasons include a more efficient conversion of feed to animal products, an increased growth rate and a lower morbidity/mortality rate in general. The levels of antibiotics are often increased to 50-200 grams/ton or more when specific diseases are being targeted as when the spread of a particular disease is rampant. The levels are also increased in times of stress. This increased amount is often decreased when the threat of a disease is gone.

Reference: http://www1.udel.edu/chem/C465/senior/fall97/feed/present.html