Relationships between health and weight loss during lactation and between health and ability to return to oestrus after weaning in primiparous sows.

The study comprises observations in 301 Swedish Yorkshire primiparous sows belonging to a research herd. During the 6 weeks of lactation, they were fed according to a conventional feeding regime based on litter size. The sows were weighed at farrowing and at weaning. After weaning the sows were checked daily for standing reflex and blood samples for determination of plasma progesterone were drawn regularly. Diseases occurring during lactation were recorded in 223 sows. A clinical health examination of these sows was also performed on the day of weaning, including body temperature, condition scoring, appetite, locomotor disorders, remarks on legs and mammary glands. A blood sample was drawn 1 week before weaning in 155 sows for analysis of blood haemoglobin concentration, packed cell volume, total white blood cell count, serum concentration of urea, creatinine, triglycerides, free fatty acids, total protein and electrophoretic separation of proteins. Sows with large weight loss had a higher total incidence of diseases during lactation, mastitis being the most common disease, than sows with small weight loss. Sows with large weight loss seemed to be more catabolic during late lactation than sows with small weight loss, according to the blood analyses. The blood analyses did not show any signs of subclinical infection being more common among sows with large weight loss than among sows with small weight loss. There were neither any significant differences in the total incidence of diseases during lactation nor in the health at weaning between sows returning to oestrus within 10 days of weaning and sows not returning within this time.