A PIGFARM WITH CHRONIC FERTILITY PROBLEM

A herd with 320 sows with chronic fertility problems is described. Abo ut 20 to 30 % of the inseminated sows returned to oestrus, For unknown reasons. When the interval from insemination to return to oestrus was analysed, it appeared that 20 % of the sows returned between 24 and 2 8 days. A thorough and extensive control of the herdman's oestrus dete ction technique revealed that nearly all sows were inseminated between 4 to 6 days post-weaning. However, this was too early fora number of sows. These sows showed optimal oestrus symptoms 6 - 8 days post-weani ng. This was also the explanation for the high number of sows returnin g to oestrus 'irregularly' between 24 and 28 days. Thus when analysing insemination intervals, the interval between 24 and 35 days should no t be considered as one period but should be divided into the periods, 24 - 28 days and 29 - 35 days. In this way it is possible to distingui sh between sows inseminated too early and sows returning to oestrus ir regularly.