Endocrine changes during group housing of primiparous sows in early pregnancy.

The effect of group housing sows during early pregnancy on maternal endocrine changes and on embryonic survival was studied. Twenty crossbred (Swedish Yorkshire x Swedish Landrace) primiparous sows were used. On day 11 +/- 1 of pregnancy 3 unacquainted sows were randomly assigned to a single pen measuring 3 m x 3 m in area. A fourth sow in each group was housed in an individual pen and used as a control. This procedure was repeated 5 times to collect data from 5 animals in each rank as well as in a control group. Blood samples were collected from the day before grouping to day 5 after grouping for cortisol, corticosteroid-binding globulin (CBG), progesterone (P4), oestradiol-17 beta (E2) and prostaglandin F2 alpha metabolite (PG-metabolite) analysis. A rank-order test and an ACTH test were performed on day 4 and day 5 of grouping respectively. The sows were slaughtered on day 17 +/- 1 of pregnancy and embryos recovered. Aggression accompanied by elevations (p < 0.05) in cortisol concentrations occurred in all grouped sows on the first day of grouping. The cortisol increase was greater (p < 0.01) in the subordinate than in the other ranked sows. Cortisol concentrations and the level of aggression decreased on subsequent days during grouping, but the cortisol levels were still higher than on the pre-grouping day except for the intermediate ranked sows. Cortisol concentrations after the ACTH test were similar in the grouped as well as the control sows. The dominance hierarchy was confirmed during the rank order test. Concentrations of P4, E2, PG-metabolite and CBG were similar between the group-housed sows and with the controls. Mean embryonic recovery was 66.8% +/- 11.5%, 71.3% +/- 6.0%, 70.0% +/- 16.0%, and 69.9% +/- 5.8% for the dominant, intermediate, subordinate, and control sows respectively. Hence, group housing during early pregnancy did not influence reproductive hormones or embryonic survival.

Patterns of release of oxytocin, prolactin, insulin and LH in lactating sows, studied using continuous blood collection technique.

To describe the patterns of release of oxytocin, prolactin, insulin and LH in relation to suckling and to investigate relationships between them, blood was collected continuously from four sows at a rate of 1 ml per min for 12 h (0900-2100 h) on day 10 (D10) and day 20 (D20) of lactation. The 12-h period was divided into four smaller periods: P1 (0900-1200 h), P2 (1200-1500 h), P3 (1500-1800 h) and P4 (1800-2100 h). The number of nursings occurring during a 12-h period tended to decrease between D10 (17.3 +/- 0.3) and D20 (16.0 +/- 0.3). About 40-50% of all sucklings induced a significant rise in plasma oxytocin, while prolactin gradually increased following each suckling. Decrease in the levels of oxytocin (14.1 +/- 0.4 vs 7.1 +/- 0.4 pmol/l, P < 0.001), prolactin (12.9 +/- 0.3 vs 7.9 +/- 0.1 micrograms/l, P < 0.001) and insulin (24.8 +/- 1.7 vs 14.4 +/- 1.7 mU/l, P < 0.001) were observed between D10 and D20. Average and basal levels of LH and the number of LH pulses increased (P < 0.01) between D10 and D20. A negative correlation between number of sucklings and number of LH pulses was demonstrated on D20 (r = -0.59, P = 0.07). There was a positive correlation between levels of LH and oxytocin on D10 (r = 0.54, P = 0.001) and between prolactin and insulin levels on D20 (r = 0.34, P = 0.05).

Plasma oxytocin, prolactin, insulin and LH after 24 h of fasting and after refeeding in lactating sows.

The effects of 24 h of fasting and refeeding on the release of oxytocin, prolactin, insulin and LH in three lactating sows were investigated. The sows were starved, but supplied with water ad libitum, from 09.00 h on day 27 of lactation until 15.00 h on day 28 of lactation, when they were refed. Blood samples were collected continuously, using an automatic collection system, at a rate of 1 ml min-1 from 09.00 to 21.00 h on day 28 (P1 = 6 h period after the 24 h fast, P2 = 6 h period after refeeding). For both P1 and P2 the mean number of nursings was 7.0 +/- 1.0. Plasma insulin and glucose decreased to very low levels during fasting and increased (P < 0.001) after refeeding (insulin, 2.5 +/- 0.7 vs. 28.9 +/- 0.7 mU l-1; glucose, 2.6 +/- 0.3 vs. 6.4 +/- 0.3 mmol l-1). Following fasting, levels of prolactin were low (2.8 +/- 0.1 micrograms l-1), and sucking did not induce significant release of prolactin. However, prolactin increased rapidly after refeeding (5.4 +/- 0.1 micrograms l-1, P < 0.001). Neither the 24 h fast nor refeeding had a marked effect on basal levels of oxytocin, the percentage of sucklings with an oxytocin peak or the size of oxytocin peak. LH release (average and basal levels and number of pulses/6 h) during fasting was similar to that measured after refeeding. Plasma CCK increased significantly after feeding. The results indicate that the release of prolactin is also regulated by feed intake.(ABSTRACT TRUNCATED AT 250 WORDS)

Body weight loss during lactation in relation to energy and protein metabolism in standard-fed primiparous sows.

After 5 weeks of lactation 14 standard-fed primiparous sows were divided into a low weight-loss group (L-gr, loss < 25 kg, n = 7) and a high weight-loss group (H-gr, loss > or = 25 kg, n = 7). Body weights of the sows and their litters were recorded on days 2, 7, 14, 21, 28 and 35 of lactation. Blood samples were collected before the morning feeding on each weighing day. Samples were analysed to determine concentrations of insulin, glucagon, glucose, triglycerides, non-esterified fatty acids (NEFA), urea and creatinine. The H-gr sows lost weight throughout lactation, whereas the L-gr sows gained weight during the last week. Weight loss was higher in the H-gr than in the L-gr during weeks 2, 3 and 5 of lactation. Litter size and litter weight gain were higher in the H-gr than in the L-gr. Significant changes in levels of insulin, glucagon, glucose, triglycerides and creatinine were observed over lactation. No significant differences in concentrations of any of the parameters were found between the two groups, except for insulin and cholesterol which were higher in the L-gr. Catabolism of adipose tissue and muscle protein was observed in both groups during the first week of lactation. This catabolic state was more pronounced and tended to be prolonged in the H-gr. Concentrations of all parameters seemed to be stable in both groups during the last two weeks of lactation.

Effects of insulin administration at weaning on hormonal patterns and reproductive performance in primiparous sows.

Twelve primiparous sows were grouped into six pairs. One sow from each pair (T) received subcutaneous injections of porcine insulin as follows: pairs 1 and 2, 0.5 IU/kg at 07.00 h; pairs 3 to 6, 0.5 IU/kg at 07.00 and 15.00 h. Insulin administration was started one day before weaning and continued until the last day of post-weaning oestrus. Control sows (C) received physiological saline solution as a sham treatment. Blood samples were collected every 3 h from 09.00 to 21.00 h and, additionally, at 07.00 h during the period of insulin treatment. Additional blood samples were collected at 15-min intervals for 6 h for 2 days before and for 3 days after weaning, and for 12 h on the day of weaning (D35 of lactation). Exogenous treatment with insulin increased plasma levels of insulin (53 v 36 mU/l, P < 0.001) and decreased plasma levels of glucose (4.6 v 5.5 mmol/l, P < 0.001) in T-sows as compared to C-sows. During the treatment period, the average levels of cortisol (31 v 35 nmol/l, P < 0.001) and non-esterified fatty acids (0.13 v 0.16 mmol/l, P < 0.01) were lower in T-than in C-sows. No differences in glucagon or urea levels were observed between the two groups. Plasma levels of LH were higher in T- than in C-sows both before and during the treatment period. However, no differences in number of LH pulses/6h were found between the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of nutrition on pregnant and lactating sows.

It has been suggested that the long-term reproduction of the sow is best served by minimizing weight and fat loss in lactation. Such a strategy would require only a minimal restoration of weight in the following pregnancy, which would be beneficial, since the greater feed intake and weight gain in pregnancy, the greater the weight loss in lactation. Feeding ad libitum should be practised during lactation while gestation feed intake must be held low. A relationship between feed intake and embryo survival has been demonstrated in several studies, but the data are sometimes difficult to interpret. High energy feeding during the premating period and during early pregnancy, however, are often associated with increased embryo mortality. A short-term starvation in lactation decreased prolactin to post-weaning concentrations, and insulin and glucose to very low concentrations. Prolactin increased very rapidly after refeeding indicating that a neural mechanism might be involved. The increasing levels of cholecystokinin after refeeding and the neural reflex triggered might be related to this increase in prolactin. No changes in LH release were observed during the periods of starvation or refeeding. The catabolic rate during the first week of lactation is higher in sows with higher backfat thickness than in late gestation. As lactation progresses a more balanced metabolism is achieved regardless of backfat thickness before parturition. High-weight-loss primiparous sows need a longer recovery period from their negative energy balance during lactation than do low-weight-loss primiparous sows or multiparous sows. Several investigations have demonstrated that sows losing excessive amounts of body weight have extended weaning to oestrous intervals and an increase in anoestrus. Sows with low body-weight loss during lactation have higher plasma insulin and lower cortisol around weaning than do sows with high body-weight loss. What remains undefined is the degree of weight or condition loss below which an extension in the remating interval will occur and the level of dietary energy intake required to prevent this extension.

Metabolic and reproductive hormones during lactation and the post-weaning period in sows.

There is a great variation in body weight loss during lactation among primiparous sows fed a standard diet that is adjusted based on the number of piglets nursed and the maintenance requirements. Energy and protein catabolism is more pronounced during the first 1 to 3 weeks of lactation and sows with low weight loss recover earlier from their negative energy balance during lactation than sows with high weight loss. Using continuous blood collection a decrease in plasma levels of oxytocin, prolactin, and insulin, and an increase in plasma levels and no of LH pulses during lactation were demonstrated. Prolactin levels gradually increased in response to each suckling while only 40-50% of recorded sucklings induced a significant rise in plasma oxytocin. Following a 24-h fast during lactation, levels of prolactin were very low but increased rapidly after refeeding. Even plasma levels of insulin and glucose decreased to very low levels during fasting, but the release of LH was similar before and after refeeding. Weaning resulted in decrease in plasma levels of prolactin and increase in plasma levels and no. of LH pulses. Plasma levels of cortisol showed a diurnal pattern of change which disappeared on the day of weaning. In response to weaning plasma levels of glucagon and gastrin decreased, whereas insulin and somatostatin increased. At weaning sows with low weight loss during lactation had higher plasma insulin and lower plasma cortisol levels than sows with high weight loss, but no differences in levels or no. of LH pulses were observed between the two groups of sows.

Relationship between lactation-associated body weight loss, levels of metabolic and reproductive hormones and weaning-to-oestrous interval in primiparous sows.

Twelve conventionally fed primiparous sows with a similar number of piglets were divided into 3 groups (n = 4) according to their body weight loss after a 5-week lactation as follows: H-gr (loss greater than 25 kg), M-gr (loss 11-25 kg) and L-gr (loss less than or equal to 10 kg). Blood samples were collected at 9, 12, 15, 18 and 21 h, from 4 days before weaning until 3 days afterwards, and every 15 min for 6 h on the day before and the day after weaning. The group of sows with higher weight loss during lactation tended to have a higher farrowing weight and higher pre-weaning plasma prolactin levels. At weaning, the L-gr sows had higher plasma insulin and lower plasma cortisol concentrations, especially when compared with H-gr sows. Among the ten sows that showed oestrus within 10 days of weaning, no between-group differences were found in the length of the interval from weaning to oestrus. No significant differences between groups were observed in levels of oestradiol-17 beta and LH. The higher level of insulin in L-gr sows might relate to the higher number of corpora lutea observed in this group.

A technique for continuously monitoring hormone levels in lactating sows and results obtained using it to study LH release.

A technique for collecting continuously blood was successfully applied for the first time in lactating sows. A double-lumen catheter consisted of an internal tubing for delivering an anticoagulant (heparin-saline) and an outer tubing for blood collection. An automatic system, composed of a blood withdrawal pump, an anticoagulant infusion pump and a fraction collector, was connected to the catheter and operated for 12 h on Days 10 and 20 of lactation. Blood samples were collected continuously at a rate of 1 ml per min from four sows. Each fraction consisted of 4 ml blood except during nursing periods when 1 ml blood per fraction was collected. In this study, aliquots of plasma were combined to form pooled 8-min samples for the measurement of the concentrations of LH. Average and base levels of LH, number of LH pulse(s)/12 h and pulse durations were calculated for all pooled samples, all even-numbered samples and all odd-numbered samples. Average and base levels of LH and the number of LH pulses were slightly higher on Day 20 than on Day 10 of lactation. The LH-pulse duration varied between animals, with the value for one of the sows diverging greatly from those of the others. When only every second sample was considered, the LH-pulse rate appeared to be slightly lower.

Effects of weaning on plasma levels of prolactin, oxytocin, insulin, glucagon, glucose, gastrin and somatostatin in sows.

The effect of total weaning (all piglets were weaned at 35 days of lactation) and fractionated weaning (the heavier half of the litter was weaned on day 33 of lactation and the remainder 2 days later) on plasma levels of prolactin, oxytocin, insulin, glucagon, glucose, gastrin and somatostatin in primiparous sows was studied. Twelve crossbred sows were grouped into six pairs according to farrowing data and litter size. The litter of one sow in each pair was weaned in two stages (treatment), and the other was conventionally weaned (control). Blood samples were collected via a permanent jugular vein catheter every 3 hours from 9 a.m. to 9 p.m. from day 31 of lactation until the third day of final weaning. In response to total weaning (studied in the six control sows), plasma prolactin, glucagon and gastrin decreased significantly, whereas plasma insulin and somatostatin significantly increased. Basal concentrations of plasma oxytocin and glucose remained unchanged after weaning. Fractionated weaning did not result in any significant differences in the hormonal and glucose levels as compared with the total weaning. The possible role of prolactin in modulating insulin, glucagon and glucose concentrations as well as the possibility that oxytocin affects gastrin and somatostatin levels following weaning are discussed.

Effect of fractionated weaning on hormonal patterns and weaning to oestrus interval in primiparous sows.

The effect of weaning the 4-5 heaviest piglets in the litter on day 33 of lactation and the remainder 2 days later (fractionated weaning) on plasma levels of prolactin, cortisol, oestradiol-17 beta (E2), progesterone (P4) and LH, as well as on the weaning to oestrus interval in primiparous sows was studied. Twelve crossbred sows were grouped into 6 pairs according to farrowing date and litter size. The litter of 1 sow in each pair (F) was weaned in 2 stages, and the other conventionally weaned at 35 days (C). Blood samples were collected via a permanent jugular vein catheter every 3 h from 9 a m to 9 p m daily throughout the experimental period, and intensively at 15 min intervals for 12 h on the day of first and final weaning and for 6 h on the day after each weaning. All sows were slaughtered following their first post-weaning oestrus and the reproductive organs were macroscopically examined. Lactational oestrus was not observed in any of the sows. Sows from 5 out of 6 pairs showed oestrus within 8 days of weaning and post-mortem examination showed normal ovulation. There was a tendency for the F sows to have a shorter weaning to oestrus interval, as compared with the C sows (5 of 6 pairs, 4.8 days v 5.6 days). The plasma levels of prolactin around weaning were not significantly different between the 2 groups. Within 6 h after final weaning, the prolactin concentrations decreased gradually from 7.6 and 8.7 to 1.6 and 1.7 microgram/l in the control and treatment groups, respectively. The plasma levels of cortisol, showing a diurnal rhythm (with the lowest level at 6 and/or 9 p m), did on no occasion differ between the 2 groups. On the day of final weaning, no diurnal rhythm was observed, with cortisol remaining high at 6 and 9 p m. The plasma levels of E2 and P4 were low until final weaning in both groups. After final weaning the E2 levels rose faster in the F sows than in the C sows, to 44.3 and 34.8 pmol/l, respectively, on day 2 (p less than 0.01). No significant differences in levels of plasma LH and the number of LH pulses were observed between the groups. After final weaning the average and base levels of LH and the number of LH pulse(s) increased significantly.