Breeding
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The breeding of farm animals seldom occurs spontaneously but is managed by farmers with a view to encouraging traits seen as desirable. These include hardiness, fertility, docility, mothering abilities, fast growth rates, low feed consumption per unit of growth, better body proportions, higher yields, and better fibre qualities. Undesirable traits such as health defects and aggressiveness are selected against.[36][37]
Selective breeding has been responsible for large increases in productivity. For example, in 2007, a typical broiler chicken at eight weeks old was 4.8 times as heavy as a bird of similar age in 1957,[36] while in the thirty years to 2007, the average milk yield of a dairy cow in the United States nearly doubled.[36]
Animal health
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Good husbandry, proper feeding, and hygiene are the main contributors to animal health on the farm, bringing economic benefits through maximised production. When, despite these precautions, animals still become sick, they are treated with veterinary medicines, by the farmer and the veterinarian. In the European Union, when farmers treat their own animals, they are required to follow the guidelines for treatment and to record the treatments given.[38] Animals are susceptible to a number of diseases and conditions that may affect their health. Some, like classical swine fever[39] and scrapie[40] are specific to one type of stock, while others, like foot-and-mouth disease affect all cloven-hoofed animals.[41] Animals living under intensive conditions are prone to internal and external parasites; increasing numbers of sea lice are affecting farmed salmon in Scotland.[42] Reducing the parasite burdens of livestock results in increased productivity and profitability.[43]