One of the least discussed topics in pig nutrition is how to feed the sow after piglets are weaned and until she shows the first signs of estrous. There are many programs, ideas, and methods! They range from starvation in the first couple days to feeding ad libitum to achieve the so-called 'flushing effect'. Based on my experience, no two farms use the same method, and there is at least more than a few programs that are used successfully.
The area that requires some further discussion here concerns the influence of the amount of feed from weaning to mating on subsequent litter size - and this is to be differentiated for gilts and sows. The following may explain why similar practices lead to different, and quite often disappointing, results in several farms.
Gilts that have been raised on an ad libitum or near ad libitum feed intake program, including those that were raised on a limit-feeding but generous program, end up quite heavy for their age at mating time. Such gilts almost invariably will fail to benefit from increasing their feed intake in the last couple weeks before mating. On the other hand, great results in terms of ovulation and subsequent litter size are to be expected on increasing feed intake (up to twice the normal daily allowance) in gilts that reach mating time on the lean side of body condition.
For sows that have just completed a lactation period, flushing works best when body condition has been allowed to greatly deteriorate during lactation. Here, again up to doubling of normal (maintenance levels) feed intake can speed up ovulation and increase subsequent litter size.
However, this is a 'cheap' method to influence productivity as it will only continue the rapid decline of sow condition and reduce overall lifetime productivity. It is best to address the issues of low feed intake during lactation (in most cases a result of overfeeding during gestation) and keep sows on maintenance levels during weaning-to-mating period.
I would be very interested to read your thoughts on this neglected topic!