In a human food chain, much of the energy that livestock take in is used in respiration and lost as heat, rather than being stored as meat, milk or eggs. Reducing these respiratory losses increases the animals' net production (N = I − (F + R)), so more of the food they eat becomes food for humans.Methods used in intensive farming include:• Restricting movement: keeping animals in pens or cages means less energy is used in muscle contraction.
• Keeping animals warm: housing them indoors in a controlled environment means these endotherms use less energy maintaining their body temperature.
• Slaughtering animals young: young animals put a larger proportion of their energy into growth, while adults use more for maintenance.
• Selective breeding of fast-growing breeds that convert food into biomass more efficiently.Worked example: Pigs ingest 2000 kJ of food per day. Outdoors, F = 700 kJ and R = 1150 kJ, so N = 2000 − (700 + 1150) = 150 kJ. Kept indoors, R falls to 1000 kJ, so N = 2000 − (700 + 1000) = 300 kJ. Net production doubles with the same food.These methods produce cheaper food and use less land per kilogram of meat. However, there are drawbacks. Restricting movement and crowding raise animal welfare concerns. Crowded animals spread disease more easily, so antibiotics may be used, which can contribute to antibiotic resistance in bacteria. Heating and lighting buildings also uses energy, often from fossil fuels.
• Keeping animals warm: housing them indoors in a controlled environment means these endotherms use less energy maintaining their body temperature.
• Slaughtering animals young: young animals put a larger proportion of their energy into growth, while adults use more for maintenance.
• Selective breeding of fast-growing breeds that convert food into biomass more efficiently.Worked example: Pigs ingest 2000 kJ of food per day. Outdoors, F = 700 kJ and R = 1150 kJ, so N = 2000 − (700 + 1150) = 150 kJ. Kept indoors, R falls to 1000 kJ, so N = 2000 − (700 + 1000) = 300 kJ. Net production doubles with the same food.These methods produce cheaper food and use less land per kilogram of meat. However, there are drawbacks. Restricting movement and crowding raise animal welfare concerns. Crowded animals spread disease more easily, so antibiotics may be used, which can contribute to antibiotic resistance in bacteria. Heating and lighting buildings also uses energy, often from fossil fuels.