The UK farm-gate price for pigs is currently about 16 per cent lower than a year ago due to a number of factors.

According to Iain Macdonald, economics analyst with Quality Meat Scotland, the most significant factor has been the increase in supplies. At the UK level, 2014 was the fifth consecutive year that there was an increase in pig slaughtering and the number of pigs butchered was at its highest level since 2002.

"Once you factor in heavier carcase weights, at 862,100 tonnes, UK pig-meat production was at its highest level this century. At the start of this year, weekly abattoir throughput was estimated to be running seven percent ahead of last year," said Mr Macdonald.

The increased level of supply has come despite UK census data reporting a contracting breeding herd. In June 2014, sow numbers were down 3.5 per cent year-on-year at 406,000 head and compared with 2002, there were 28 per cent fewer sows. Scotland's share is now about 30,000 and pig production accounts for less than three per cent of Scottish agriculture by value.

These figures show how significant the improvement in pig sector productivity has been. Years of investment in improving herd health and genetics have seen a huge leap forwards.

"With the cost of feeding each sow spread over an increased output of pig-meat, producers are therefore better placed to withstand a reduction in farm-gate prices," observed Mr Macdonald.

There is an old American saying that a pig is "nothing more than fifteen to twenty bushels of corn (maize)". Feed accounts for about two-thirds of the cost of producing pigs, so changes in feed prices has an immediate effect on profit margins. That used to trigger the "pig cycle" where a couple of profitable years were followed by a period of losses. That cycle of boom or bust became so predictable that some producers learned to increase their breeding herds at the bottom of the cycle to take advantage of the expected upturn.

In late January, feed wheat was trading at less than £120/tonne at the farm-gate, compared with £160/t a year earlier and £220/t two years ago.

Two good years of growing conditions in the US Midwest have seen global grain production surge and prices fall back sharply. It has been a similar scenario for soybeans, and this has pushed down the cost of soya meal, an important source of protein in pig rations.

Chinese pig farmers have also benefitted from cheaper feed supplies on world markets. Since the late 1970s, when the Chinese government liberalised agriculture, pork consumption has increased sevenfold in China. It now produces and consumes about 500m pigs a year, half of all the pigs in the world. The average Chinese now eats 39kg of pork a year, about five times more per person than they ate in 1979.

China hasn't enough land to feed its people as well as its pigs, and it's reckoned that in the near future more than half of the world's feed crops will be eaten by Chinese pigs. Already China's soya imports account for more than 50 per cent of the total global soya market. From a low base, grain imports are rising fast as well and it is predicted that by 2022 China will need to import between one fifth and one third of the world's entire current trade in maize.

The Chinese eat so much pork that when its price go up, the cost of other things rise as well. In 2007, for example, an estimated 45m pigs died in China from "blue ear disease". Pork prices rocketed and the annual rate of increase of the consumer price index hit a ten year high. Panic buying ensued and imports doubled.

In response, the Communist Party established the world's first pork reserves, some of it in frozen form and some of it live. This aims to keep pork affordable and reasonably priced. When pigs become too expensive, the government releases some of its stocks onto the market and conversely, if they become too cheap, the reserve buys more of them to keep farmers in profit.

Other pro-pork policies include grants, tax incentives, cheap loans for farms and assistance with veterinary costs - all intended to boost intensive pig farming and to keep the cost of pork down to consumers.

According to Chatham House, the London-based international affairs think-tank, the Chinese government subsidised pork production by $22bn in 2012, which was worth about $47 per pig.