Relationships between age at puberty and interval from weaning to estrus and between estrus signs at puberty and after the first weaning in pigs.

The study comprises observations in 464 Swedish Yorkshire pigs at puberty and after the first weaning. The aim was to study relationships between age at puberty and weaning to estrus interval and between estrus signs at puberty and after the first weaning. The estrus signs were checked, and blood samples for progesterone determination were drawn regularly around puberty and after the first weaning. Gilts expressing early puberty (youngest one-third) showed a greater ability to return to estrus and to ovulate within 10 d after weaning than gilts expressing late puberty (oldest one-third) (P = .01). A positive genetic correlation was found between age at puberty and the interval from weaning to the first detected estrus (WEI) (rg = .45). The genetic correlation between age at puberty and the ability to show the standing reflex and to ovulate within 10 d after weaning was negative (rg = -.50). The heritability of the ability to show the standing reflex and to ovulate within 10 d after weaning was .31. Gilts not showing a standing reflex at puberty also had a higher incidence of ovulation without a standing reflex within 10 days after their first weaning (21.4 vs 6.2%, P = .001). There was a significant positive correlation between the total duration and the intensity of the reddening and swelling of the vulva at puberty and after the first weaning. This study demonstrates relationships both between age at puberty and WEI and between some estrus signs at puberty and after the first weaning.

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.

Some factors influencing pregnancy rate and subsequent litter size in primiparous sows.

The pregnancy rate and the subsequent litter size were studied in 332 Swedish Yorkshire primiparous sows, fed according to a commercial Swedish feeding regime during lactation. The sows were weighed and backfat depth was recorded at the first farrowing, at weaning, and at mating. Oestrous detection was performed once daily after weaning, and the interval from weaning to first oestrus (IWO) was recorded. Blood samples for determination of plasma progesterone were drawn regularly after the first weaning. Statistical analyses were only performed on sows with an IWO of 3-8 days. Of these 206 sows were mated on their first (OE1 sows) and 87 sows on their second (87 OE2 sows) oestrus after weaning. The pregnancy rate was 85.4% for OE1 sows and 75.9% for OE2 sows (p = 0.048). There was no significant difference in pregnancy rate between OE1 sows with an IWO of 3-5 days and OE1 sows with an interval of 6-8 days. OE2 sows with an IWO of 6-8 days, on the other hand, had a significantly lower pregnancy rate compared with OE2 sows with an interval of 3-5 days. The pregnancy rate in sows that lost more than 30 kg during the first lactation period did not differ from that of sows losing less than 30 kg. In sows with a first litter size of more than 9 piglets alive at birth, the pregnancy rate decreases significantly if mating is delayed until the second oestrus after weaning. OE2 sows had a significantly larger second litter size at birth than OE1 sows (+2.0). The litter size at six weeks did not, on the other hand, differ significantly (+0.4). There was a positive correlation between the IWO and 2nd litter size, although significant only for OE1 sows between the IWO and litter size alive at birth. In the OE1 group, sows losing 20 kg or less during lactation had significantly larger second litters at birth than the sows losing 21-30 kg, but not significantly larger than the sows losing more than 30 kg. One piglet more, at birth, in the first litter resulted in 0.25 piglet more in the second litter. For sows with a large first litter there was a low probability of also having a large second litter.

A study on primiparous sows of the ability to show standing oestrus and to ovulate after weaning. Influences of loss of body weight and backfat during lactation and of litter size, litter weight gain and season.

The ability to show standing oestrus and to ovulate within 10 days of weaning was studied in 240 purebred Swedish Yorkshire primiparous sows, fed according to a conventional feeding regime during lactation. The sows were weighted and backfat depth was recorded at farrowing and at weaning. Oestrus control was performed daily and blood samples for determination of plasma progesterone were drawn regularly in 205 sows. The distribution among the sows of the first standing oestrus after weaning had 2 peaks. The first peak occurred within 10 days of weaning and the second 24-30 days after weaning. Twelve per cent of the sows ovulated without showing standing oestrus within 10 days of weaning and 4% had an anovulatory first oestrus within the same time. Significant differences in age at farrowing and in loss of weight and backfat during lactation were found between sows which both showed standing oestrus and ovulated within 10 days of weaning and sows which neither showed standing oestrus, nor ovulated within the same time. The season during which weaning occurred significantly influenced the ability to show standing oestrus and ovulate within 10 days of weaning. Among the sows which both showed standing oestrus and ovulated within 10 days of weaning, significant positive correlations were found between weight loss, litter size, litter weight gain and the interval from weaning to first standing oestrus.