Firstly good implantation at 12 to 24 days from service is vital, says Mr Gadd. Care must be taken during this period to provide rest and quiet for the sow.

Following the final service, it has proved effective to keep the sow free of stress and sexual excitement by separating her from the herd.

In terms of feeding, a high nutrient intake between weaning and service is beneficial. For sows with a birthweight problem, feeding 1.5kg per day extra can often help. Also, as routine, feed sows a lactation diet at this time, i.e. before and across insemination. Both of these may help follicle release synchrony – more follicles are released closer together in time – and/or it enables the womb surface to regain receptivity sooner.

However, it is important not to feed a too rich a diet in pregnancy. It is often best to speak to a nutrition expert for a low lysine (0.55 per cent total) pregnancy feed. This is lower than currently favoured. However, just increasing the feed allowance (1.8 to 3.0kg) of this diet as pregnancy progresses, rather than keeping flat as textbooks suggest, can also help.

Another point to be be made is never to let a sow nose-dive in lactation. Mr Gadd comments that: "Here we are looking at the effect on the next litter of what was done in the preceding breeding cycle."

Another point he makes is not to start feeding more suddenly, just before farrowing if birthweights are low. However, this could be acceptable for other reasons.

Do not worry too much about big litters affecting birth weights as, with the new 'hyperprolific' lines, it is possible to have big litters and big newborns.

In the US, multi–site farmers who have changed from farrow-to-finish mono–site have not reported lower birth weights in the next litter when weaning at 16 days old although their litter size seems to be one pig fewer than in developed pig industries in Europe).

Do not use prostaglandins too early, says Mr Gadd, as foetuses could be growing up to 60g per day just before farrowing.

The latest research indicates that transferring to organic trace elements rather than inorganic (from rocks/soil) will be the future of trace element nutrition in the breeding animal.

In conclusion, genetics are not likely to be involved in affecting birth weights, concludes Mr Gadd. It may only affect weights if the super hyperprolific strains are much in evidence.