One of the most difficult management tasks is to control the numbers of sows and gilts mated in any given period of time. If for example the programme requires 20 matings per week and only 10 are carried out followed by 30 in the next week major problems may arise in managing these animals through the housing system. The effects of these are shown in Fig.3-28. Problems first arise through the overuse of boars leading to infertility problems and variable litter size. As stocking densities increase more animals enter the housing system than it is designed for. In the farrowing houses there is a failure of the all-in all-out system resulting in early weaning and more fostering. There is an increased number of pigs to be transferred into the weaner and growers accommodation at any one time with increased stocking densities, permanently populated houses and the movement of pigs from one house to another thus disturbing the status quo. The end result of all these various changes is disease or poor growth depending on the severity of the mating control failure and pathogenic organisms present on the farm.