Body condition during pregnancy and lactation and reproductive efficiency of mares

In Experiment I, 32 mares were equally allotted to the following treatments: mares fed to A) high body condition from 90 days prepartum to foaling and maintained in high body condition to 90 days postpartum, B) high body condition from 90 days prepartum to foaling and allowed to lose body condition to 90 days postpartum, C) lose body condition from 90 days prepartum to foaling and maintained in low body condition to 90 days postpartum, and D) lose body condition from 90 days prepartum to foaling and allowed to gain weight after foaling to attain a high level of body condition by 90 days postpartum. After three cycles, pregnancy rate at 30 days postovulation was lower (P<0.05) in C mares (50%) than in those in the other three groups (100%). Maintenance of pregnancy to 90 days was also reduced (P<0.05) in C mares (25%) when compared with A, D (both 100%) and B mares (88%). Foal growth to 90 days of age was similar in all treatments. In Experiment II, 927 mares were evaluated for body condition and monitored for reproductive performance. Pregnancy rate was lower (P<0.05) and number of cycles/conception was higher (P<0.05) for barren and maiden mares entering the breeding season in thin condition and for pregnant mares foaling in thin condition (condition score less than 5.0) when compared with mares with a higher level of condition. Also, onset of estrus and ovulation appeared to be delayed in barren and maiden mares entering the breeding season in thin condition. Breeding efficiency was enhanced in mares entering the breeding season or foaling at a condition of 5.0 or above. Initial excess stores of body fat enhanced fertility. There were no detrimental effects of excess body fat stored in late gestation.     

Changes in bovine mammary insulin binding during pregnancy and lactation

1. Binding of insulin to microsomes from mammary glands of pregnant and lactating dairy cows was characterized. 2. Binding affinities of the insulin receptor did not change from pregnancy to lactation. 3. Maximal specific binding occurred in microsomes from cows in mid-pregnancy and declined in microsomes from cows in late pregnancy. 4. Insulin binding continued to decrease from early to mid-lactation and increased during late lactation. 5. Results indicate that decreased sensitivity in mammary tissue from lactating dairy cows is at least in part a result of a reduction in insulin receptor number. 6. Results demonstrate further physiological differences between the ruminant and non-ruminant mammary gland.     

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.     

A low-protein diet during pregnancy alters glucose metabolism and insulin secretion

In pancreatic islets, glucose metabolism is a key process for insulin secretion, and pregnancy requires an increase in insulin secretion to compensate for the typical insulin resistance at the end of this period. Because a low-protein diet decreases insulin secretion, this type of diet could impair glucose homeostasis, leading to gestational diabetes. In pancreatic islets, we investigated GLUT2, glucokinase and hexokinase expression patterns as well as glucose uptake, utilization and oxidation rates. Adult control non-pregnant (CNP) and control pregnant (CP) rats were fed a normal protein diet (17%), whereas low-protein non-pregnant (LPNP) and low-protein pregnant (LPP) rats were fed a low-protein diet (6%) from days 1 to 15 of pregnancy. The insulin secretion in 2.8 mmol l(-1) of glucose was higher in islets from LPP rats than that in islets from CP, CNP and LPNP rats. Maximal insulin release was obtained at 8.3 and 16.7 mmol l(-1) of glucose in LPP and CP groups, respectively. The glucose dose-response curve from LPNP group was shifted to the right in relation to the CNP group. In the CP group, the concentration-response curve to glucose was shifted to the left compared with the CNP group. The LPP groups exhibited an "inverted U-shape" dose-response curve. The alterations in the GLUT2, glucokinase and hexokinase expression patterns neither impaired glucose metabolism nor correlated with glucose islet sensitivity, suggesting that β-cell sensitivity to glucose requires secondary events other than the observed metabolic/molecular events.     

Metabolism of sheep adipose tissue during pregnancy and lactation. Adaptation and regulation.

1. Changes in the mean volume, the rate of fatty acid and acylglycerol glycerol synthesis, the activity of lipoprotein lipase and the numbers and affinities of insulin receptors of subcutaneous adipocytes are reported for sheep at different stages of pregnancy and lactation. In addition, the serum concentrations of insulin, progesterone, prolactin, choriomammotropin, somatotropin, glucose, acetate, L-lactate, glycerol and unesterified fatty acids are reported for these sheep. 2. A switch from lipid accumulation to net lipid mobilization accompanied by a decline in the capacity for lipid synthesis, occurred at the onset of the last third of pregnancy. Net lipid mobilization continued during lactation. 3. The changes that occurred in the serum concentrations of the various hormones listed above are discussed in relation to their possible roles in the modulation of adipose tissue metabolism in sheep during pregnancy and lactation. The observations are compared with those from previous studies on the hormonal control of adipose tissue metabolism in the rat during pregnancy and lactation.     

A maternal high n-6 fat diet with fish oil supplementation during pregnancy and lactation in rats decreases breast cancer risk in the female offspring

The timing of dietary fat intake may modify breast cancer risk. In addition, n-3 fatty acids reduce, and n-6 fatty acids increase, the risk of breast cancer and a maternal high n-6 fat diet results in a greater risk of breast cancer in the female offspring. We hypothesized that the timing of n-3 fatty acid-enriched fish oil supplementation would be important for reducing the risk of breast cancer. Female rats were fed to a high n-6 fat diet containing 20% of the sunflower oil by weight during pregnancy and lactation, and the female offspring were exposed to fish oil by oral gavage either during the perinatal period via maternal intake or during puberty or adulthood. Exposure during the perinatal period to a maternal high n-6 fat diet with fish oil supplementation significantly reduced the incidence of carcinogen-induced mammary tumors in the female offspring compared to a maternal high n-6 fat diet with no fish oil supplementation or fish oil supplementation later in life (P=.0228 by Cox proportional hazards model). We found that a maternal high n-6 fat diet during pregnancy is more important in increasing the risk of mammary tumors in the female offspring than a maternal high n-6 fat diet during lactation. This study suggests that fish oil supplementation during the perinatal period decreases the effect of a maternal high n-6 fat diet on subsequent carcinogen-induced mammary tumor risk, whereas fish oil supplementation during puberty or adulthood does not.     

High fat diet alters lactation outcomes: possible involvement of inflammatory and serotonergic pathways

Delay in the onset of lactogenesis has been shown to occur in women who are obese, however the mechanism altered within the mammary gland causing the delay remains unknown. Consumption of high fat diets (HFD) has been previously determined to result decreased litters and litter numbers in rodent models due to a decrease in fertility. We examined the effects of feeding a HFD (60% kcal from fat) diet versus a low-fat diet (LFD; 10% kcal from fat) to female Wistar rats on lactation outcomes. Feeding of HFD diet resulted in increased pup weights compared to pups from LFD fed animals for 4 d post-partum. Lactation was delayed in mothers on HFD but they began to produce copious milk volumes beginning 2 d post-partum, and milk yield was similar to LFD by day 3. Mammary glands collected from lactating animals on HFD diet, displayed a disrupted morphologies, with very few and small alveoli. Consistently, there was a significant decrease in the mRNA expression of milk protein genes, glucose transporter 1 (GLUT1) and keratin 5 (K5), a luminobasal cell marker in the mammary glands of HFD lactating animals. Expression of tryptophan hydroxylase 1 (TPH1), the rate-limiting enzyme in serotonin (5-HT) biosynthesis, and the 5-HT(7) receptor (HTR7), which regulates mammary gland involution, were significantly increased in mammary glands of HFD animals. Additionally, we saw elevation of the inflammatory markers interleukin-6 (IL-6) and tumor necrosis factor-α (TNF- α). These results indicate that consumption of HFD impairs mammary parenchymal tissue and impedes its ability to synthesize and secrete milk, possibly through an increase in 5-HT production within the mammary gland leading to an inflammatory process.     

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.     

Maternal high-fat diet during pregnancy and lactation affects hepatic lipid metabolism in early life of offspring rat

We investigated whether maternal over-nutrition during pregnancy and lactation affects the offspring’s lipid metabolism at weaning by assessing liver lipid metabolic gene expressions and analysing its mechanisms on the development of metabolic abnormalities. Female Sprague–Dawley rats were fed with standard chow diet (CON) or high-fat diet (HFD) for 8 weeks, and then continued feeding during gestation and lactation. The offspring whose dams were fed with HFD had a lower birth weight but an increased body weight with impaired glucose tolerance, higher serum cholesterol, and hepatic steatosis at weaning. Microarray analyses showed that there were 120 genes differently expressed between the two groups. We further verified the results by qRT-PCR. Significant increase of the lipogenesis (Me1, Scd1) gene expression was found in HFD (P<0.05), and up-regulated expression of genes (PPAR-α, Cpt1α, Ehhadh) involved in β-oxidation was also observed (P<0.05), but the Acsl3 gene was down-regulated (P<0.05). Maternal over-nutrition could not only primarily induce lipogenesis, but also promote lipolysis through an oxidation pathway as compensation, eventually leading to an increased body weight, impaired glucose tolerance, elevated serum cholesterol and hepatic steatosis at weaning. This finding may provide some evidence for a healthy maternal diet in order to reduce the risk of metabolic diseases in the early life of the offspring.     

Role of insulin receptors in the changing metabolism of adipose tissue during pregnancy and lactation in the rat.

Changes in the volume, the rates of fatty acid synthesis and synthesis of the glycerol moiety of acylglycerols, the activity of lipoprotein lipase, and the number and affinity of insulin receptors of adipocytes, and concentrations of serum insulin, prolactin and progesterone were determined in virgin rats and in rats at various stages of pregnancy and lactation. Changes in the metabolic activities of adipose tissue appeared to be synchronized and primarily comprised a marked decrease in anabolic activity around parturition. In contrast, the number of insulin receptors (Kd 1.5 nM) per adipocyte doubled during pregnancy before returning to normal values around parturition. It is postulated that the increase in the number of insulin receptors is an adaptation to counteract the effects of insulin-antagonistic hormones during pregnancy and that the decrease in the number of receptors is primarily responsible for the loss of anabolic activity around parturition.     

Urinary selenium and iodine during pregnancy and lactation

The New Zealand environment is low in selenium and iodine, and is therefore ideally suited for the study of these anionic trace elements. The aim of this study was to determine urinary excretion of selenium and iodine during pregnancy and postpartum as part of an investigation of the influence of pregnancy and lactation on selenium metabolism in women of low selenium status. In a double-blind placebo-controlled study, 35 women in the earliest stages of pregnancy and 17 non-pregnant women were recruited in Dunedin, New Zealand. Eighteen pregnant women received 50 μg selenium as L-selenomethionine, while the others received a placebo daily during pregnancy and 12 months postpartum. The non-pregnant women received the supplement, serving as a positive control. Blood samples and twenty-four hour urine samples were collected monthly during pregnancy and at 3, 6, and 12 months postpartum for analysis of selenium and iodine. Selenium content in plasma and urinary excretion of selenium fell during pregnancy; however, total excretion of selenium was greater during pregnancy than postpartum. Urinary iodine excretion was much lower than reported previously in New Zealand. Due to large intra- and inter-subject variability, no trends in iodide excretion were observed. Factors which influence urinary excretion of selenium include dietary intake, but more closely, plasma concentrations of selenium (which is probably related to total selenium pool), creatinine excretion and therefore lean body mass, and glomerular filtration rate. The exact mechanism and sequence of events remains unclear and future studies incorporating new speciation techniques are necessary.     

Fat transfer and energetics during lactation in the hooded seal: the roles of tissue lipoprotein lipase in milk fat secretion and pup blubber deposition

Hooded seals (Cystophora cristata) lactate for 3.6 days during which females simultaneously fast and transfer large amounts of energy to their pups through fat-rich milk. Pups grow rapidly, principally due to blubber deposition. Lipoprotein lipase (LPL), the primary enzyme responsible for tissue uptake of triglyceride fatty acids, may strongly influence both maternal milk fat secretion and pup blubber deposition. We measured the energetic costs of lactation (using hydrogen isotope dilution, ³H₂0), milk composition, prolactin, and LPL activity (post-heparin plasma LPL [PH LPL], blubber, mammary gland and milk; U) in six females. PH LPL and blubber LPL were measured in their pups. Females depleted 216.3 MJ · day⁻¹ of body energy and fat accounted for 59% of maternal mass loss and 90% of postpartum body energy loss, but maternal body composition changed little. Maternal blubber LPL was negligible (0.0–0.2 U), while mammary LPL was elevated (1.8–2.5 U) and was paralleled by changes in prolactin. Estimated total mammary LPL activity was high (up to 20,000 U · animal⁻¹) effectively favoring the mammary gland for lipid uptake. Levels of total blubber LPL in pups increased seven-fold over lactation. Pups with higher PH LPL at birth had greater relative growth rates (P = 0.025). Pups with greater blubber stores and total blubber LPL activity had elevated rates of fat deposition (P = 0.035). Accepted: 4 May 1999     

Coprophagy in female mice during pregnancy and lactation

Coprophagy in female mice was observed predominantly in the reproductive stage. Female mice exhibited coprophagy more frequently during pregnancy and ingested larger amounts of feces during pregnancy and lactation than when they were not pregnant. Feces were found to be rich in vitamin B12 and folic acid. However, there were no marked fluctuations in the levels of either vitamin in the feces during pregnancy or lactation as compared with levels when animals were not pregnant. Acceleration of coprophagy during pregnancy and lactation seemed to correlate with the increased nutritional requirements of females during the reproductive stage.     

Thermoregulatory control during pregnancy and lactation in rats

Eliason, Heather L., and James E. Fewell.Thermoregulatory control during pregnancy and lactation in rats.J. Appl. Physiol. 83(3): 837-844, 1997.Although the mechanisms remain unknown, maternal coretemperature (T_c) decreases nearterm of pregnancy and is increased throughout lactation in rats. Thepurpose of our present experiments was to determine whether pregnancy and lactation shift the thermoneutral zone of rats and to investigate whether the changes in maternal T_cduring pregnancy and lactation result from "forced" or"regulated" thermoregulatory responses. Conscious, chronicallyinstrumented nonpregnant and pregnant and lactating rats were studiedboth in a thermocline (a chamber with a linear temperature gradientfrom 12 to 36°C) and in a metabolic chamber to determine theinfluence of pregnancy and lactation on selected ambient temperature aswell as the thermoregulatory response to changes in ambienttemperature. We found that selected ambient temperature, oxygenconsumption, and thermal conductance did not change in rats studied ina thermocline as T_c decreased nearterm of pregnancy. There was, however, a downward shift in thethermoneutral zone of rats studied in a metabolic chamber near term ofpregnancy. During lactation, selected ambient temperature decreased inrats studied in a thermocline as oxygen consumption andT_c increased. The thermoneutralzone of lactating rats was not different from that of nonpregnantanimals. Thus our data provide evidence that the decrease inT_c near term of pregnancy in ratsresults from a regulated thermoregulatory response,whereas the increase in T_c duringlactation results from a forced thermoregulatory response.

     

The endocrine pancreas during pregnancy and lactation in the rat

The percentage of endocrine tissue in the whole pancreas, the volume density of the insulin producing beta-cells, the non-fasting plasma glucose level and the plasma insulin level were studied in pregnant rats and in puerperal lactating and non-lactating rats. During pregnancy there was a progressive rise in the percentage of endocrine tissue, in the volume density of the beta-cells and in the insulin level in peripheral blood. Plasma glucose levels declined during pregnancy. A lower plasma glucose level, a lower plasma insulin level, a lower percentage of endocrine tissue and a lower volume density of the beta-cells was found in lactating compared to non-lactating rats.