Correlation between LH response to challenges with GNRH and naloxone during lactation, and LH secretion and follicular development after weaning in the sows.

The aim of this study was of establishing a correlation between endogenous LH secretion and the magnitude of the LH response to challenges with GnRH and the opioid antagonist naloxone during lactation, and between these characteristics and LH secretion and follicular development after weaning. Sows (n = 9) were sampled for 6 h at day 2 post-partum, for 12 h on day 26 of lactation and for 6 h immediately after weaning at day 27 of lactation. Four hours after the beginning of sampling at day 26 of lactation all sows were injected with 2 mg/kg i.v. of naloxone hydrochloride and 5 h later with 100 microg/sow of GnRH. Follicular development was studied in all sows at slaughter the day after weaning. There was an effect of time (sampling period; P < 0.001) on mean plasma LH, with an increase (P < 0.05) in LH the day after weaning compared to mean LH concentrations during lactation. Naloxone and GnRH treatment both increased (P < 0.05) mean LH concentrations. A positive relationship (r = 0.58, P < 0.01) between mean plasma LH after GnRH and after weaning was established. Although there were differences (P < 0.001) between sows in follicular fluid volume, there were no correlations between mean follicular fluid volume and mean LH concentrations after GnRH or after weaning. These data indicate that the LH response to GnRH during late lactation could be useful predictor of LH activity after weaning. However, none of the measures of endogenous or induced LH secretion were associated with differences in ovarian follicular size after weaning. Direct evidence is therefore still needed for a functional link between differences in LH in lactation and differences in fertility after weaning.     

Timing of lactational oestrus in intermittent suckling regimes: consequences for sow fertility

Three intermittent suckling (IS) regimes were evaluated for their effects on lactational oestrus and subsequent fertility. Control sows were weaned (CW; n = 38) at d 26 ± 2 of lactation. In IS19-7D (n=40) and IS19-14D (n=42) sows, IS started at d 19 ± 1 of lactation and sows were weaned 7 or 14 d later. In IS26-7D (n=41), IS started at d 26 ± 1 of lactation and sows were weaned 7d later. During IS, sows were separated from their piglets for 10h/day. Oestrus detection was performed twice daily without a boar and ovulation was confirmed by ultrasound once a week. In IS19-7D, IS19-14D and IS26-7D, respectively, 50%, 64% and 61% of the sows showed oestrus and ovulation during IS (P>0.05), and, of the remaining sows, 100%, 93%, and 69% showed oestrus in the first week after weaning. In CW sows, 95% showed oestrus in the first week after weaning. Parity 1 sows were considerably less likely than older parities (23% vs. 68%) to show oestrus in lactation. Pregnancy rate of the first post partum oestrus (during lactation or after weaning) was 89% (CW), 92% (IS19-7D), 80% (IS19-14D) and 77% (IS26-7D) (P>0.05) and subsequent litter size was 14.5 ± 0.5, 14.5 ± 0.6, 15.3 ± 0.5 and 15.2 ± 0.8, respectively (P>0.05). Sows mated during lactation had similar pregnancy rate and litter size to those mated after weaning. Hence, ongoing lactation for the first 2-9 d of pregnancy did not negatively affect fertility. A total of 50-64% of IS sows showed lactational oestrus, regardless of the stage of lactation. Pregnancy rates and litter size were similar to control sows, and were not affected by stage of lactation at mating.     

Relationship of vaginal impedance with speed of return to oestrus after weaning, oestrous behaviour, parity and lactation length in cyclic sows

The effect of weaning to oestrus interval, oestrus duration, parity, lactation length, breed and their interactions on changes of vaginal impedance in sows after weaning and during oestrus was examined. The impedance measurements were carried out by a four-electrode method. The interval from weaning to oestrus was significantly longer in sows with the length of lactation 21-25 days than 26-30 days and 31-36 days and in primiparous than multiparous sows. The interval from weaning to oestrus was negatively correlated with the length of lactation (r=-0.21; P<0.05), parity (r=-0.36; P<0.01) and oestrus duration (r=-0.26; P<0.01). The weaning to oestrus interval, oestrus duration, parity and lactation length had a significant effect and the breed of sows had no influence on the vaginal impedance in peri-oestrus. The decrease of vaginal impedance after weaning was delayed in sows with a longer weaning to oestrus interval and in primiparous than multiparous sows. The decline of vaginal impedance during peri-oestrus was more gradual in sows with a longer interval from weaning to oestrus, shorter lactation, primiparous sows and sows with the length of oestrus 36 h and 72 h and more. The nadir of vaginal impedance occurred earlier before oestrus in sows with a shorter oestrus. The interaction of weaning to oestrus interval with parity and oestrus duration and the interaction of oestrus duration with parity significantly affected the vaginal impedance in weaned sows. In conclusion, the weaning to oestrus interval, oestrus duration, parity and lactation length considerably influence the vaginal impedance in sows during peri-oestrus. The findings indicate that the impedance technique may be a useful method for a study of factors and processes that accelerate or slow down the return to oestrus after weaning and affect oestrus duration in sows.     

Relationships between backfat depth and plasma leptin during lactation and sow reproductive performance after weaning

The aim of this study was to determine relationships between sow backfat depth, plasma leptin concentrations, and reproductive performance after weaning. On the day of farrowing (day 0), and at weaning (day 21), single blood samples were obtained from 120 mixed-parity sows and their backfat depth (P2) measured. Based on backfat depth at day 0, sows were classified as FAT (>24 mm, n = 16), MEDIUM (16-24 mm, n = 54), or THIN (<16 mm, n = 14). Sows were further classified on the basis of P2 backfat changes during lactation of <2 mm, 2-4 mm, or >4 mm. Reproductive performance was measured as weaning-to-oestrous intervals (WOI) of <6 d, 6-9 days, or > or =10 d, and pregnancy rates. There was a positive relationship (P < 0.0001) between backfat depth at day 0 and backfat loss during lactation. The WOI was not associated with backfat depth at day 0 or 21 (P > 0.1 for both). Pregnancy rate was not associated with backfat depth at day 0 (P > 0.1) but pregnant sows had a greater backfat depth at weaning (16.5 +/- 0.3 and 14.9 +/- 0.6 mm, P < 0.04). Backfat loss during lactation was positively associated with WOI (P < 0.01) and negatively associated with pregnancy rate (P < 0.04). Plasma leptin concentrations were higher (P < 0.001) in FAT sows than in MEDIUM or THIN sows on both days but there was no relationship between plasma leptin concentrations and reproductive performances after weaning. It is concluded that plasma leptin is associated with backfat depth and that loss of backfat depth during lactation is associated with reproductive performance. However, there is no direct association between plasma leptin and reproductive performance.     

Body weight loss during lactation and its influence on weaning-to-service interval and ovulation rate in Landrace and Yorkshire sows in the tropical environment of Thailand

The aim of this study was to investigate the ovulation rate and the weaning-to-service interval (WSI) of sows in relation to their body weight loss during lactation in tropical climatic conditions. Effect of lactation length (LL), number of total born piglets, number of live born piglets, litter birth weight, average piglet birth weight, number of pigs weaned, litter weaning weight and average pig weaned weight on sow weight loss during lactation were also studied. This study was conducted in two commercial purebred sow herds (A, B) in the central part of Thailand from August to December 1997. The herds had both Landrace (L) and Yorkshire (Y) sows. The 123 sows (55 L and 68 Y) in herd A and 153 sows (95 L and 58 Y) in herd B, parity 1-4, were weighed within 4 days after farrowing and at weaning. Lactation length, litter size at birth and at weaning, litter weight at birth and at weaning, and WSI were recorded for each of these sows. In herd A, 52 sows (20 L and 32 Y) were examined once by laparoscopy between days 8 and 14 after AI-service. These sows had farrowed at least seven piglets in the previous parturition. The numbers of corpora lutea (CL) in both ovaries were counted, and were assumed to equal the ovulation rate. L-sows had significantly (P < 0.05) higher relative weight loss during lactation (RWL) than Y-sows. The RWL increased by 0.7% for each extra pig weaned. When LL increased by 1 day, within the interval of 17-34 days, RWL decreased by 0.6%. Sows with a high weight loss had significantly (P < 0.05) longer WSI than sows with medium or low weight loss. Weight loss had a significant (P < 0.05) effect on WSI in parity 1 and 2 sows. Y-sows had more CL than L-sows (15.7 versus 14.0) (P < 0.05). RWL, parity and regression on lactation length had no significant effect on number of CL. In conclusion, sows with higher number of pigs weaned lose more weight. Under the restricted feeding regime applied, high weight loss during lactation prolongs WSI in parity 1 and 2 sows, but has no influence on the ovulation rate at first oestrus after weaning. The ovulation rate is higher in Yorkshire than in Landrace sows. The ovulation rate is independent of parity.     

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.     

Assessment of sows mating efficacy during the low productive period after early weaning: a field study

Data on sows bred after weaning (n = 9,540) and their lactation feed intake records (average lactation length <20 d) were obtained from 16 commercial farms. Weaning-to-first-mating intervals (WMI) at 6 to 12 d and 0 to 6 d after weaning were defined as the low and high productive periods, respectively. Of the 9,192 sows mated, 80.5 and 19.5% were mated at 0 to 6 d and 7 to 12 d, respectively. In logistic regression analysis, lower parity, shorter lactation length, lower average daily feed intake (ADFI) during lactation, and a greater number of weaned pigs were associated with mating at 7 to 12 d after weaning (P < or = 0.045). Exponentiating the coefficients in logistic regression analysis, the odds ratios were 0.79 for parity, 0.84 for ADFI during lactation, 0.85 for lactation length, and 1.05 for weaned pigs, respectively. A sow with a 14-d lactation length is 2.3 (1/0.85(5)) times as likely to mate within a 6- to 12-d WMI as a sow with a 19-d lactation length. Thus, the early weaned sows are more likely to mate during the low productive period than the later weaned sows. The odds for party 0.79 imply that Parity 1 sows were 1.6 (1/0.79(2)) times as likely to mate within a WMI 6 to 12 d as Parity 3 sows. For each 1-kg increase in ADFI, a mating occurrence during the low productive period decreased by 0.84 times. Sows are mated during the low productive period because this period is a part of the distribution of WMI in a herd. However, our research suggests that increasing feed intake during lactation and maintaining parity proportion appropriate to the herd can decrease the proportion of sows mated during the low productivity period.     

Response of sows to oestradiol benzoate treatment after weaning at two stages of lactation

The timing and dosage of oestradiol benzoate injected after weaning was critical with respect to the pattern of behavioural oestrus and the ovarian stimulation achieved; treatment on the day of weaning (Day 0) and Day 1 with 60 micrograms oestradiol benzoate/kg body wt produced poor ovulatory responses and abnormal oestrous behaviour. Treatment on Day 2 with 30 micrograms oestradiol benzoate/kg resulted in consistent oestrus and ovulatory responses although the ovulation rates (10 . 6 +/- 1 . 1 in 3-week and 12 . 2 +/- 1 . 7 in 5-week weaned sows) were below those expected in fertile untreated sows weaned at these times. The timing of the preovulatory LH surge (53 . 6 +/- 2 h after oestradiol benzoate) was closely synchronized in all sows and a similar synchronous rise in plasma progesterone concentrations 100 +/- 4 h after oestradiol benzoate suggests a similar synchrony of ovulation. The magnitude of the LH and FSH responses to oestradiol benzoate were similar to those that occur in untreated sows and similar differences also existed in gonadotrophin secretion related to the length of lactation.     

Characterization of summer infertility of sows in large confinement units

Data were from 3119 farrowings in three large swine confinement units in eastern North Carolina. Litters were weaned during April through October. Interval to first estrus after weaning was greater during June through September than during other months. The two-way interactions among farm unit, parity and month weaned all affected weaning-to-estrus interval. Conception rate at first estrus was lower for primiparous than for multiparous sows and declined from April through July. Conception rate at first estrus was affected by farm by parity interaction. Weaning-to-conception interval was longer for primiparous than multiparous sows and was longer during June through October. Weaning-to-conception interval was affected by interactions of unit with parity and unit with month weaned. Total pigs farrowed at the subsequent farrowing was affected by unit, parity, length of the previous lactation and the unit x parity interaction. Overall, reproductive performance varied among farm units, was lower in primiparous than in multiparous sows and was reduced during June through October.     

Luteinizing hormone,total estrogens and progesterone secretion during lactation and after weaning in sows

Two experiments were conducted to determine changes in serum concentrations of LH, total free estrogens and progesterone before and after weaning in sows. Blood was collected either via indwelling anterior vena cava cannula or by venipuncture and serum hormones were measured by radioimmunoassay. In Exp. I, blood was collected at 15-min intervals for 4 hr on day 7 and day 21 postpartum from three sows on each day. In addition, individual samples were collected from 10 sows on days 4 and 14 postpartum and from 11 sows on days 1, 3 and 5 after weaning (day 23 postpartum). Serum LH ranged from .2 to .8 ng/ml during lactation and averaged 1.1 ± .7, 1.1 ± .7 and 2.7 ± .7 on days 1, 3 and 5 after weaning, respectively. Progesterone was low (< 1 ng/ml) during lactation and averaged 1.9 ± .3, .6 ± .3 and 1.2 ± .3 on days 1, 3 and 5 after weaning. Estrogens were variable during lactation, averaged 121 ± 36 pg/ml on day 1 after weaning and decreased thereafter. Estrus began on day 3 after weaning in 1 sow and on day 5 in the remaining 10 sows.In Exp. II, blood was collected from seven sows at 12 to 24 hr intervals from 2 days before until 5 days after weaning (day 26 postpartum). Mean serum LH was .7 ± .1 ng/ml during 48 hr before weaning and remained unchanged after weaning until day 3 when LH increased to 6.1 ± .8 ng/ml. Serum LH concentrations then declined to 1.3 ± .8 and .9 ± .8 ng/ml on days 4 and 5 after weaning. Total estrogens averaged 31 ± 4 pg/ml during 48 hr prior to weaning and 32 ± 4, 43 ± 17, 28 ± 1, 30 ± 2, 16 ± 2 and 18 ± 2 on days 0 to 5 after weaning. Progesterone increased from 1.0 ± .3 ng/ml 24 hr before weaning to 3.0 ± .3 at weaning and then remained low (< 1 ng/ml) until after ovulation when progesterone increased. Estrus began on day 4 after weaning in all seven sows.Results from these two experiments indicate that in sows: (1) LH is suppressed during early lactation (day 7), gradually increases during late lactation (day 21) and then reaches peak concentrations after weaning near the onset of estrus, (2) estrogens increase between weaning and estrus and decline thereafter, and (3) progesterone rises transiently at weaning and then increases after estrus and ovulation.     

Plasma Constituents in the Sow

The concentrations in plasma of total protein, urea-N, Ca, Mg, Na and K and the activity of aspartate aminotransferase (ASAT) and alanine aminotransferase (ALAT) in plasma were studied in 20 sows from one week before weaning until four weeks after weaning. Ten of the sows resumed ovarian activity within 10 days after weaning, while in the other 10 sows the resumption of ovarian activity was delayed. Plasma glucose was studied in 10 sows from one week before weaning until two weeks after weaning, five of these sows had delayed resumption of ovarian function. After weaning the concentration of total protein and the ALAT activity increased, while plasma glucose and Mg decreased. Concerning ASAT, Ca, Na and K no changes were observed. A transient increase in urea-N level took place after weaning in sows with prolonged weaning-to-ovulation period. In sows with normal weaning-to-ovulation period no change in urea-N was observed. This was the only difference in blood chemistry observed between sows with normal weaning-to-ovulation period and sows with prolonged weaning-to-ovulation period.     

Follicular Development in Lactating,Post Weaning and Anoestrous Primiparous Sows

The ovarian follicular system was studied in 4 lactating sows (6 or 8 weeks lactation period), 4 post weaning sows (2 or 4 days after weaning) and 5 post weaning anoestrous sows (22 days after weaning) by macroscopical and microscopical examinations. Blood sampling was performed daily in the post weaning anoestrous sows. The results showed that none of the sows had ovulated during lactation and after weaning. Only small and medium sized follicles were present in the ovaries of the sows. The blood levels of oestradiol-17β and progesterone were low throughout the post weaning period in the anoestrous sows. Microscopical examination showed that all sows had more normal than atretic follicles. In the lactating sows all follicles were below 5 mm in size, the majority being small (1.00–2.99 mm in diameter). The post weaning sows had follicles up to 5.00–5.99 mm and 23–24% of the follicles were medium sized (3.00–5.99 mm in diameter). The post weaning anoestrous sows had no follicles above 5 mm in diameter but many normal medium sized follicles.     

Reproductive endocrinology and postweaning performance in the multiparous sow. Part 2. Influence of nursing behavior

The reason for variation in postweaning reproductive performance among multiparous sows is to a large extent unknown. In the present study, the influence of nursing behavior was explored. Blood samples were collected during lactation and after weaning from 18 multiparous sows for cortisol, LH, estradiol-17beta (E2), and progesterone analysis. Sow and piglet behavior was videotaped. The sows were fed according to litter size and slaughtered after the second postweaning estrus. The sows were divided into two groups based on average values for the different behavioral parameters. Sows with a long average nursing duration (long group) had lower average and basal LH levels on Day 14 and 21 of lactation as compared to the sows having a short average nursing duration (short group). In the long group, concentrations of E2 were lower the day after weaning, but on Day 15 and 21 of lactation no differences were noted between the two groups. Postweaning performance seemed impaired in the long group, though, differences were not significant. The sows in the long group were heavier and tended to lose less weight during lactation. To conclude, nursing duration seems to influence the extent to which reproductive functions are inhibited during lactation.     

Comparative profiles of the hexose monophosphate dehydrogenases in rat tissues over the lactation cycle

The mammary gland tissue hexose monophosphate dehydrogenase activities were low in virgin, pregnant and weaned rats, but increased at the onset of lactation. The muscle and liver glucose 6-phosphate dehydrogenase activity peaked at early and late lactation respectively. The liver 6-phosphogluconate dehydrogenase peaked in late pregnancy and remained elevated through lactation. The muscle 6-phosphogluconate dehydrogenase peaked at the onset of lactation. The adipose tissue hexose monophosphate dehydrogenases exhibited small changes during pregnancy and lactation. The spleen hexose monophosphate dehydrogenases did not respond to lactation An overshoot in both the liver and the adipose tissue hexose monophosphate dehydrogenases was observed on weaning. Serum glucose levels remained unchanged throughout pregnancy, lactation and weaning. Only liver glucose 6-phosphate dehydrogenase activity correlated with plasma insulin, which also correlated positively with food consumption. The results demonstrate that tissue-specific control of the hexose monophosphate dehydrogenases occurs in the female rat during its complete lactation cycle.     

Seasonal differences in function of the hypothalamic-hypophysial-ovarian axis in weaned primiparous sows

Primiparous sows were fed to appetite during lactations that occurred during winter or summer, and 11.4 +/- 0.4 pigs per litter were weaned at 23.5 +/- 0.1 days of age. Sows were slaughtered at 0 or 72 h after weaning or blood samples were collected until 24 h after onset of oestrus. Sows that lactated during summer consumed less food and lost more (P less than 0.05) weight, heartgirth and backfat than those that lactated during winter. Weaning-to-oestrus interval was greater (P less than 0.05) in summer (224 +/- 25 h) than in winter (93 +/- 13 h). Content of GnRH in the hypothalamus and concentrations of LH in the anterior pituitary and serum were lower (P less than 0.05) after weaning in summer than winter. The numbers of visible ovarian follicles less than 5 mm in diameter at weaning were lower (P less than 0.05) in summer than in winter. In contrast to LH, FSH concentration in serum was higher (P less than 0.10) in summer than winter, but FSH values in the anterior pituitary were lower (P less than 0.05) in summer than in winter. Post-weaning patterns of secretion of oestradiol and follicular development differed between winter and summer. For example, in some sows weaned during the summer, transient surges of oestradiol occurred repeatedly during 0 to 280 h after weaning without provoking surges of LH. These results indicate that the period of post-weaning anoestrus in summer is prolonged because of altered activity of the hypothalamic-pituitary axis, possibly because of changes in sensitivity to the feedback of oestradiol. Lower feed intake during lactations that occur during summer may predispose the endocrine system to the aberrations.     

Endocrine changes before and after weaning in response to boar exposure and altered suckling in sows

Eighteen sows (6 primiparous and 12 multiparous) were allotted randomly within parity to two lactational treatments: litter separation (LS; 6 h/day) plus boar exposure (BE; 1 h/day; N = 14) beginning 8 days before weaning (4 weeks) and no LS + no BE (controls; N = 4). Blood was collected from all sows via indwelling venous catheters at 20-min intervals for 5 h on Days -1, 0, 1, 2 and 3 from start of treatment. Control sows and those exposed to LS + BE not exhibiting oestrus during lactation were resampled on Days -1, 0, 1 and 2 from weaning. All 10 multiparous sows receiving LS + BE exhibited oestrus during lactation, whereas none of the 4 primiparous sows exposed to LS + BE or the 2 control multiparous and 2 control primiparous sows exhibited lactational oestrus. Overall concentrations of LH in serum were higher (P less than 0.05) in sows receiving LS + BE than in control sows during lactation, whereas overall FSH was higher (P less than 0.05) in primiparous than multiparous sows. Number and amplitude of pulses of LH were greater (P less than 0.05) for treated primiparous than multiparous sows during lactation. Oestradiol-17 beta increased (P less than 0.05) in sows during LS + BE and was higher (P less than 0.01) in multiparous sows of this group than control multiparous or treated primiparous sows. Preweaning concentrations of cortisol and progesterone in serum were higher (P less than 0.05) in treated than control sows for multiparous and primiparous animals. In sows resampled at weaning, the number of pulses of LH was greater (P less than 0.05) in treated primiparous than in control sows. Postweaning concentrations of FSH in serum were unaffected by preweaning treatments. It was concluded that (1) litter separation and boar exposure increased basal and pulsatile secretion of LH in multiparous and primiparous sows; (2) lack of ovarian follicular development and oestradiol secretion may preclude expression of oestrus in primiparous sows during lactation, despite elevated concentrations of FSH and LH in serum; and (3) if elevated concentrations of cortisol and progesterone inhibit the onset of oestrous cycles, in response to litter separation and boar exposure during lactation, the effect is limited to primiparous sows.     

Intermittent suckling enables estrus and pregnancy during lactation in sows: effects of stage of lactation and lactation during early pregnancy

Previously we demonstrated that pre-ovulatory LH and post-ovulatory progesterone (P4) concentrations in plasma were low and embryo development was retarded when sows were induced to ovulate during lactation by submitting them to intermittent suckling (IS). The present study investigated whether this was due to: (1) stage of lactation when IS was initiated, and (2) continuation of IS post-ovulation. Multiparous Topigs40 sows were studied under three conditions: conventional weaning at Day 21 of lactation (C21; n = 30), intermittent suckling from Day 14 of lactation (IS14; n = 32), and intermittent suckling from Day 21 of lactation (IS21; n = 33). Sows were separated from piglets for 12 h daily during IS. IS sows were either weaned at ovulation or 20 d following ovulation. One-third (21/63) of the IS21 and C21 sows had already ovulated or had large pre-ovulatory follicles at Day 21 and were excluded from further study. Initiation of IS at Day 14 instead of Day 21 of lactation tended to reduce P4 at 7 d post-ovulation (P = 0.07), did not affect pregnancy rate, and tended to reduce embryo survival (P = 0.06). Continuation of IS during pregnancy resulted in lower P4 at 7 and 12 d post-ovulation, tended to reduce embryo weight and pregnancy rate (P < 0.10), whereas embryo survival was not affected. This study presents data for a population of sows in which follicle growth and ovulation are easily triggered under suckling conditions. Further, when these sows are bred during lactation, initiation of IS at 21 rather than 14 d of lactation with weaning at ovulation yields the most desirable reproductive performance.     

Effects of naloxone or transient weaning on secretion of LH and prolactin in lactating sows

Sows (N = 16) were infused intravenously for 8 h with saline or naloxone (200 mg/h) or their litters were transiently weaned for 8 h. Before infusion, 200 mg naloxone were administered to elevate quickly concentrations of naloxone. Blood samples were collected from sows at 15 min intervals for 24 h, beginning 8 h before and continuing until 8 h after imposition of treatments during the middle 8-h segment. Frequency of episodic release of LH and concentrations of prolactin were similar before, during and after infusion of saline. Average concentration of LH was greater during the last than during the middle 8-h segment when sows were given saline. Frequency of episodic release of LH increased and concentrations of prolactin decreased during infusion of naloxone or transient weaning; however, average concentration of LH increased during transient weaning, but not during infusion of naloxone. After transient weaning or infusion of naloxone, frequency of release of LH decreased, returning to pretreatment values in sows infused with naloxone but remaining above pretreatment values in sows subjected to transient weaning. At the resumption of suckling by litters in sows subjected to transient weaning, prolactin increased to levels not different from those observed during the 8-h pretreatment segment. Prolactin did not increase until 4-5 h after cessation of naloxone infusion. We conclude that continuous infusion of naloxone altered secretory patterns of LH and prolactin. Collectively these results provide evidence that the immediate effects of weaning on LH and prolactin in sows are mediated in part through a mechanism involving endogenous opioid peptides.     

Lack of stimulation of relaxin secretion in lactating sows by suckling in vivo or by oxytocin in vitro.

After parturition, eight sows were zero weaned by removing all piglets 6 h after birth; a further 18 sows suckled at least ten piglets each. Blood samples were collected on Day 4 after zero weaning or on Days 4, 14 and 21 of lactation and the sampling frequency increased during suckling bouts. Ovaries were recovered from sows on these days and corpora lutea were either extracted for estimation of relaxin and progesterone concentration, fixed for immunohistochemical analysis or incubated in vitro in the presence or absence of luteinizing hormone (LH) or oxytocin. Luteal weight and progesterone were higher in the zero-weaned sows than in lactating sows (P less than 0.05 and less than 0.001, respectively); relaxin content was below detection by Day 14. This was supported by immunohistochemical staining for relaxin, which showed limited immunostaining in zero-weaned and Day 4 sows, but none in the tissue recovered on Days 14 and 21, which showed typical signs of regression. Secretion of progesterone and relaxin by luteal tissue in vitro was highest in zero-weaned sows (P less than 0.05), decreased as lactation progressed and neither LH nor oxytocin had any significant effect. Concentrations of plasma relaxin were all less than 0.2 ng/ml in three of the four zero-weaned and Day-4-suckled sows assayed; there was no detectable increase during suckling bouts. It was concluded that during lactation the old corpus luteum of pregnancy is not able to release relaxin in response to suckling in vivo or to oxytocin treatment in vitro.     

Effect of the Japanese diet during pregnancy and lactation or post-weaning on the risk of metabolic syndrome in offspring

We examined the effects on offspring of ingestion of the 1975 Japanese diet during pregnancy and lactation and after weaning in mice. Pregnant dams were divided into groups that were fed the Japanese diet or a control diet and raised until offspring were weaned. The offspring after weaning were further divided into groups that were raised on the Japanese diet or the control diet. Ingestion of the Japanese diet after weaning suppressed accumulation of visceral fat in offspring, and reduced the amount of lipids in serum and liver. This effect was weakened if the Japanese diet was only ingested during pregnancy and lactation. Therefore, it was suggested that ingestion of the Japanese diet of mothers during pregnancy and lactation weakens the lipid accumulation inhibitory effect of the Japanese diet in children.