Animals are desexed for selective breeding purposes. Males may also be neutered in order to make them more tractable or meatier. A specialized vocabulary has arisen for neutered animals of given species.
Except where a desexed pet is desirable, entire animals usually fetch much higher prices than castrated ones, mostly because they retain the ability to breed. There are various health effects of the decision to leave an animal intact, or to castrate it. Leaving a female animal intact may lead to such complications as ovarian cysts, uterine infections such as pyometra, and cancer of the reproductive tract. In small animals such as dogs and cats, the ovaries and uterus are removed eliminating the possibility of disease in these organs. By de-sexing or spaying the female, the animal is surgically sterilized and cannot get pregnant; this however, may lead to weight gain in the pet and may not be able to burn as many calories in their daily activities. This can be avoided by reducing the food intake once the female has been surgically sterilized to prevent unnecessary weight gain. In addition to a reduced caloric intake, increasing the animals daily physical activity once recovered from surgery will help reduce the chance of weight gain after being de-sexed.
In the case of livestock, mainly cattle, there are various pros and cons to castrating or leaving the animal intact. Leaving a bull calf (an intact male under the age of six months), allows the animal to gain more weight, and have a higher feed efficiency than compared to a steer (or castrated male calf). Leaving a bull calf intact however, can also have disadvantages. If left intact, bull calves can exhibit aggressive behaviour causing damages to fences, equipment, and handlers leaving an occupational risk for employees. Castrating a bull calf before the age of six months leads to a better performing animal not showing signs of aggression when penned with other males, while intact bulls will tend to fight with male siblings. Castration of bulls is recommended to occur before entering the feed lot as a precaution against infections and the calves are small enough to be handled easily with minimal stress towards the animal.
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