section_path: Production worldwide/Production yields
section_name: Production yields
paragraph_text: Production yields
  
  FAO reports Israel dairy farms are the most productive in the world, with a yield of 12,546 kilograms (27,659 lb) milk per cow per year. This survey over 2001 and 2007 was conducted by ICAR (International Committee for Animal Recording) across 17 developed countries. The survey found that the average herd size in these developed countries increased from 74 to 99 cows per herd between 2001 and 2007. A dairy farm had an average of 19 cows per herd in Norway, and 337 in New Zealand. Annual milk production in the same period increased from 7,726 to 8,550 kg (17,033 to 18,850 lb) per cow in these developed countries. The lowest average production was in New Zealand at 3,974 kg (8,761 lb) per cow. The milk yield per cow depended on production systems, nutrition of the cows, and only to a minor extent different genetic potential of the animals. What the cow ate made the most impact on the production obtained. New Zealand cows with the lowest yield per year grazed all year, in contrast to Israel with the highest yield where the cows ate in barns with an energy-rich mixed diet.
  
  The milk yield per cow in the United States was 9,954 kg (21,945 lb) per year in 2010. In contrast, the milk yields per cow in India and China – the second and third largest producers – were respectively 1,154 kg (2,544 lb) and 2,282 kg (5,031 lb) per year.
  
  The IPCC Sixth Assessment Report mentions the possibility that the already recorded stagnation of dairy production in both China and West Africa can be attributed to persistent increases in heat stress caused by climate change. This is a plausible hypothesis, because even mild heat stress can reduce daily yields: research in Sweden found that average daily temperatures of 20–25 °C (68–77 °F) reduce daily milk yield per cow by 0.2 kg, with the loss reaching 0.54 kg for 25–30 °C (77–86 °F). Research in a humid tropical climate describes a more linear relationship, with every unit of heat stress reducing yield by 2.13%. In the intensive farming systems, daily milk yield per cow declines by 1.8 kg during severe heat stress. In organic farming systems, the effect of heat stress on milk yields is limited, but milk quality suffers substantially, with lower fat and protein content. In China, daily milk production per cow is already lower than the average by between 0.7 and 4 kg in July (the hottest month of the year), and by 2070, it may decline by up to 50% (or 7.2 kg) due to climate change. Heatwaves can also reduce milk yield, with particularly acute impacts if the heatwave lasts for four or more days, as at that point the cow's thermoregulation capacity is usually exhausted, and its core body temperature starts to increase.