In Fig.5-8 the components of farrowing rate loss are defined at the best levels of biological efficiency. A 7% failure of repeat matings made up of 5% at a normal interval of 18-22 days and a further 2% outside this would be a good target to achieve. A continuing farrowing rate of 89% for a minimum period of 12 months would be considered excellent and this would give approximately 10 non productive days per sow from the first day of mating to the mating for the next pregnancy. Depending on the lactation length 2.3 to 2.4 litters per sow per year would result. It should be noted however that these figures do not take into account the period from the day of entry of the gilt into the herd to its first mating. Non productive days in this respect often go unrecognised and can be significant.