Now you know why modern, commercial, pigs were developed......but who wants to eat that sort of meat ?
Genetics will always mean that traditional breeds tend to "run to fat".
What can you do to minimise this ?
1. Restrict feed to a maximum of 1.8kgs/day, some would say even less
2. Don't keep the pigs too long. The more mature they get - the more fat they tend to put on (just like us humans)
3. Consider a higher protein, lower energy (carbohydrate) diet that has a high Lysine content. Again, in human nutrition, a high protein/low carb diet will result in weight (fat) loss (thinks Atkins, etc). Now Atkins, and the others are extreme but feeding a higher protein diet will assist in reducing fat content
4. Be realistic in your expectations. You are not going to get pork with only 8mm backfat from traditional breeds