Why does my pig have no appetite?

This morning Szilards pig did not eat. An animal that is not interested in eating is always an alarming fact, since it might indicate illness. We checked her behavior, which was quite normal: alert, rooting her nose over the soil, no extreme warm or cold ears, no excessive breathing (normal respiratory rate is 25 –30 per minute), her stool was normal. Her temperature was 39,8C/104F a bit higher than normal range (for a pig this is 38,5 – 39,5 C/101 – 103F). When pressing with our hands hard on her back she stood very still. Relieved we could conclude that she is in heat. Cycle average for pigs is 21 days (18 – 24 days), she was in heat 18 days ago. So a few days of less appetite, restlessness and little temperature elevation is absolutely normal for a sow every three weeks.