The effects of cold exposure of pregnant sheep on foetal plasma nutrients, hormones and birth weight

Maternal Exposure to Extreme Cold Events and Risk of Congenital Heart Defects: A Large Multicenter Study in China

Over the past decade, extreme temperature events have become more frequent and longer in duration. Previous studies on the association between extreme cold events (ECEs) and congenital heart defects (CHDs) are few and inconsistent. We conducted a national multicenter study in 1313 hospitals in 26 provinces in China and collected a total of 14 808 high CHD-risk participants from 2013 to 2021. We evaluated the ECEs experienced by each pregnant women during the embryonic period (3-8 weeks). The results indicated that ECEs experienced by pregnant women during the embryonic period were associated with the development of fetal CHD and were more strongly associated with some specific fetal CHD subtypes, such as pulmonary stenosis, pulmonary atresia, and tetralogy of Fallot. Of the CHD burden, 2.21% (95% CI: 1.43, 2.99%)-2.40% (95% CI: 1.26, 3.55%) of fetal CHD cases were attributable to ECEs during the embryonic period. Our findings emphasize the need to pay more attention to pregnant women whose embryonic period falls during the cold season to reduce cold spell detriments to newborns.

Factors influencing ease of whelping and its relationship with maternal behaviour and puppy perinatal mortality in commercially bred dogs

For dog breeders, parturition is a critical stage in the reproductive cycle of the dam. Evidence in other mammals suggests that a difficult labour can influence maternal behaviour and offspring viability during the first hours postpartum. However, the effect of whelping difficulty on the onset of maternal behaviour has not yet been investigated in domestic dogs. Here we developed an ease of whelping (EoW) index in dams maintained within a Commercial dog Breeding Establishment (CBE) environment and investigated the relationship between intrinsic and extrinsic factors (breed group according to size/weight, litter size, parity, whelping season and origin of the dam), EoW, early maternal behaviour and puppy perinatal mortality. The behaviour of 30 dams was observed throughout the whelping process, starting 24 h before delivery of the first puppy until birth of the last puppy. Parturition duration, birth interval, and behaviours indicative of distress, restlessness, and general activity were scored and included in a Principal Component Analysis to construct the EoW index. Subsequently, mother-pup interactions and puppy perinatal mortality were recorded during the first 24 and 72 h postpartum respectively. Results showed that EoW was significantly affected by whelping season, litter size and origin of the dam (whether she was born and raised within the CBE or brought in). Furthermore, mothers that experienced more difficult parturitions (higher EoW score) spent more time lying in contact with their puppies during the first 24 h postpartum. Time in contact with puppies was also significantly affected by breed group. Nursing duration was significantly affected by breed group and origin of the dam. Additionally, medium-size breed (10-20 kg) puppies were significantly less likely to experience perinatal mortality than large breeds (> 20 kg). These findings are particularly relevant for the welfare of breeding dams maintained in large-scale CBEs where the staff-to-dog ratio might be insufficient to adequately manage multiple simultaneous parturitions.

Shearing ewes in the first third of gestation improves offspring performance

The effect of shearing ewes at 50 days of gestation on birth and weaning weight, vigour of the lambs in the first hour of life and the survival of single and twin lambs was investigated. Ultrasound pregnancy diagnosis was used to allocate 140 Polwarth ewes on Day 50 of gestation to one of four treatments, including two factors: shearing time (prepartum (PS) and postpartum (U)) and litter size (single (S) and twin (T)) resulting in the following treatments: single-bearing ewes shorn at 50 days of gestation (SPS, n = 39), single-bearing ewes unshorn (SU, n = 40), twin-bearing ewes shorn at 50 days of gestation (TPS, n = 28) and twin-bearing ewes unshorn (TU, n = 33). All ewes grazed together on improved pastures. Body condition score of the ewes was recorded once every 2 weeks from shearing until weaning, and plasma concentration of NEFA in ewes was measured once every 2 weeks from Day 30 postpartum until weaning (Day 104 ± 7). Gestation length, lamb behaviour during the first hour of life, lamb weight at birth and daily weight gain from birth to weaning and lamb survival were measured. Ewe body condition and plasma non-esterified fatty acids concentration was not affected by shearing time or litter size. Birthweight of the lambs was affected by shearing time (P = 0.0002), litter size (P < 0.0001) and sex of the lamb (P = 0.03). Lambs born to PS ewes had higher daily growth rate (P < 0.0001) than lambs born to U ewes (0.149 ± 0.07 vs 0.141 ± 0.07 kg, respectively). Birthweight affected the number of assisted lambs at birth (P = 0.01). Length of gestation was affected by shearing time (P < 0.0001). Sucking ability was improved by shearing time and litter size. Lambs born to PS ewes tried to suck (P = 0.01) and successfully sucked (P = 0.009) before lambs born to U ewes (23.3 ± 2 vs 28.7 ± 2 and 37.6 ± 1 vs 38.4 ± 1 min, respectively). Attempt and success to suck was affected by litter size (P = 0.004 and P = 0.05). TPS-born lambs tried to suck before (P = 0.004) and successfully sucked earlier (P = 0.0004) than TU lambs (26.1 ± 2.5 vs 33.7 ± 2 and 38 ± 1 vs 42.1 ± 2 min, respectively). Shearing time affected lamb survival at 20 days of age (P = 0.04). The improved survival in these lambs, expressed by a higher birthweight and vigour at birth, may be explained by better nutrition in utero in response to shearing during early pregnancy. In contrast to previous research on prepartum shearing, the present experiment shearing was done at 50 days of gestation. Early shearing in gestation might coincide with a period of high cell proliferation, intense vascular development and increased uterine and umbilical blood flows in the placenta which is in rapid development, and may result in improved outcomes when compared with shearing done on Day 70 or later of gestation.

Birth weight responses to shearing ewes in early to mid gestation

This study compared the effect on foetal growth of shearing ewes in very early pregnancy (day 50) with the effect of shearing later in pregnancy (day 70 or 100). One hundred and sixty ewes were allocated at day 49 of pregnancy to four ‘time of shearing’ treatments — pregnancy day 50 (P50), P70, P100 (no. = 45 ewes per treatment) and unshorn (shearing of this group occurred 43 days after weaning) (no. = 25); two methods of shearing (by standard comb and cover comb); and two levels (1 or 2) of pregnancy/rearing rank. All ewes had been mated over a 28-day period and grazed pasture throughout the trial. The mid point of lambing was 27 August 1996. Live weights of ewes (corrected for fleece weight) were not influenced by shearing time at any stage except at day 45 of lactation when ewes shorn at P50, P70 or P100 were about 3⋅0 kg lighter than unshorn ewes. Shearing method had no effect on ewe live weight. Time of shearing and shearing method had no effect on ewe greasy fleece production or wool tensile strength. Shearing significantly (P < 0⋅05) influenced the birth weight of single- (by 0⋅7 to 0⋅8 kg) but not twin-born lambs. Maternal plasma triiodothyronine concentration increased proportionately by 0⋅47 to 0⋅85 (P < 0⋅05) and lasted for at least 20 days in response to shearing irrespective of time of shearing. No difference in plasma insulin concentration was detected between shearing groups but plasma glucose concentration proportionately increased by 0⋅06 to 0⋅16 (P < 0⋅05) for 10 to 20 days after shearing. These results indicate that shearing between day 50 and 100 of pregnancy can increase lamb birth weights and that the response is associated with an increase in thyroid hormone concentrations in the maternal circulation.

Effect of cold exposure on plasma glucose and acetate turnover rates in sheep

Isotopic dilution methodology of [U-13C]glucose and [1-13C]Na-acetate were performed simultaneously as primed continuous infusions to determine plasma glucose and acetate metabolism in sheep during thermoneutral (TN) and cold exposure (CE, 2−4°C). The experiment was performed using crossbred (Corriedale × Suffolk) sheep (n = 5; 3 male and 2 female; ~2 years old, 38 ± 2.5 kg of initial bodyweight). The animals were offered mixed hay of orchardgrass and reed canarygrass (40 : 60) 62 g/kg0.75/day with ad libitum water access. Concentration of plasma glucose was determined enzymatically using the glucose oxidase method. Plasma concentration of non-esterified fatty acids (NEFA) and glucose were higher (P = 0.01 and P = 0.05 respectively) during CE than TN. Plasma concentration and the turnover rate of acetate were numerically higher (P = 0.09 and P = 0.25 respectively) during CE than during TN. Plasma glucose turnover rate was higher (P = 0.02) during CE than TN. The present findings suggested that plasma acetate turnover rate tended to be elevated during CE, with further more extensive studies required to clarify the significance.

Selective enhancement of growth in twin foetuses by shearing ewes in early gestation

Shearing ewes during pregnancy frequently increases the birth weight of lambs. In housed ewes, the birth weight responses are greatest when shearing occurs relatively early in pregnancy. This study examined the effects of the timing and method of shearing on foetal growth, as measured by birth weight, in ewes at pasture. Border Leicester × Romney ewes were allocated at day 50 of pregnancy to: four ‘time of shearing’ treatments — pregnancy day 70 (P70), P100, P130 (no. = 60 for each treatment) and unshorn (no. = 34); two methods of shearing (by standard comb or cover comb); and two levels of pregnancy/rearing rank All ewes had been mated over a 14-day period and grazed pasture together throughout the trial The mid-point of lambing was 17 August.

At no time during pregnancy or lactation did ewe live weight differences between the groups exceed 4 kg. Ewes shorn by cover comb were heavier prior to lambing and during lactation than standard comb-shorn ewes. Time of shearing, method of shearing and ewe rearing rank had no effect on ewe annual greasy fleece production. There was a highly significant (P < 0·001) interaction between the effects of birth rank and time of shearing on lamb birth weight. Time of shearing did not affect birth weight of single-born lambs but birth weight of twin lambs increased with earlier maternal shearing to a maximum of 0·7 kg (per lamb) in those born to ewes shorn on P70. These results imply that shearing reduced the greater extent of maternal constraint which applies to the growth of twin v. single foetuses in utero. This selective increase in birth weights of twins achieved by early pregnancy shearing may have advantages in reducing lamb mortality.

Nutrition over the winter period — the breeding female

Due to the wide variation in both the productivity of sheep systems and the quality of the food resources that they utilize, the formulation of successful feeding strategies for individual flocks during pregnancy and lactation is best achieved from a knowledge of how these physiological states affect food digestion and nutrient utilization. This paper reviews recent data on the principles of food digestion and nutrient utilization in the breeding ewe and translates them into practical feeding regimens that take account of forage quality, the amount and quality of the concentrate supplement and the contribution that body and dietary lipids can make to production.

The effect of environmental temperature during pregnancy on thermoregulation in the newborn lamb

Twenty-four pregnant Scottish Blackface ewes were divided into three temperature-treatment groups 14 days before expected lambing: closely shorn and kept at 6°C (cold treatment, CD); in full fleece at 26°C (warm treatment, WM); and in full fleece at 6°C (controls, CL). Food allocation and intakes were similar for each group. Their lambs were tested for cold-induced summit metabolic rate capability (SMR) on the day of birth at a mean age of 12 h using water immersion to provide cooling. On the following day, the calorigenic response to subcutaneous injections of noradrenaline (NA) was measured to assess non-shivering thermogenesis capability. The ewes were blood-sampled during pregnancy and the lambs before and after the SMR test.

In the ewes, blood glucose and free fatty acid levels were higher during cold treatment, but not significantly so. Blood glucose was lower in lambs from CD ewes (CD lambs) before SMR tests; other differences were not significant.

During the cold test, SMR was highest in CD lambs, but not significantly so. Rectal temperature declined least during test in the CD lambs (P < 0·05).

The peak metabolic response (PMR) following NA injection was about 1·5 times greater in CD lambs than in the CL and WM lambs (P < 0·05). The mean elevation of PMR over thermoneutral metabolic rate was respectively: 2·8, 1·8 and 1·7 times in the CD, CL and WM lambs (P < 0·05), and this elevation was sustained for longer in the CD lambs (P < 0·01). Thus, the total metabolic response to NA was markedly greater in CD lambs.

It was concluded that cold exposure during late pregnancy favoured the deposition of (or checked the normal decline in) foetal brown adipose tissue, so raising the neonatal capacity for non-shivering thermogenesis.

Effects of maternal cold exposure and nutrient restriction on the ghrelin receptor, the GH-IGF axis, and metabolic regulation in the postnatal ovine liver

Maternal cold exposure of pregnant sheep promotes fetal growth, whereas nutrient restriction (NR) can reverse this effect. The present study was designed to establish whether cold exposure induced by winter shearing of the mother at 70 days gestation (term=147 days), with or without NR (induced by a 50% reduction in maternal food intake from 110 days gestation), has specific effects on mRNA abundance of hepatic genes related to growth and liver energy metabolism that could regulate postnatal body and liver growth. Measurements of hepatic gene expression for the GH secretagog receptor-1a (GHSR-1A), peroxisome proliferator-activated receptor (PPAR)alpha, phosphoenolpyruvate carboxykinase (PEPCK), and glucose-6-phosphatase activity together with glycogen content were made in the livers of offspring at 1 and 30 days of age. Maternal NR reduced liver mass at day 1, whereas offspring of cold-exposed mothers had larger livers at day 30 irrespective of maternal diet. Cold exposure resulted in the up-regulation of GHSR-1A mRNA abundance and reduced glucose-6-phosphatase activity at 1, but not 30 days of age, whereas IGF-II mRNA was decreased at 1 and 30 days. PPARalpha mRNA abundance was enhanced, while PEPCK was reduced in 30-day old offspring of cold-exposed mothers. NR caused reductions in IGF-I mRNA and, at 1-day postnatal age, down-regulated GHR, while, at 30 days, reduced GHSR-1A gene expression and hepatic glycogen content. In conclusion, we have shown that maternal cold exposure and NR have different effects on the hepatic GH-IGF and metabolic axis that may contribute to changes in liver growth over the first month of life.

Effects of dietary energy intake and cold exposure on kinetics of plasma glucose metabolism in sheep

An isotope dilution method using [U-(13)C]glucose injection was applied to determine the effects of dietary energy intake and cold exposure on plasma glucose metabolism in sheep. The sheep were assigned to two dietary treatments and were fed on diets containing either 100% or 160% of ME and both containing 150% of dietary crude protein intake for maintenance. The sheep were exposed from a thermoneutral environment (23 degrees C) to a cold environment (2-4 degrees C) for 5 days. The isotope dilution method was performed on the 18th day in the thermoneutral environment and on the fifth day of cold exposure. Plasma concentrations of glucose and NEFA increased (p < 0.05) during cold exposure for both diets. Plasma glucose pool size remained unchanged (p = 0.67), but plasma glucose turnover rate tended to increase (p = 0.07) with increased energy intake. Both pool size and turnover rate of plasma glucose increased (p = 0.01 and p = 0.0001, respectively) during cold exposure. No significant diet x environment interaction was detected. It is concluded that plasma glucose metabolism was influenced by both dietary energy intake and cold exposure, and plasma glucose metabolism in response to cold exposure was not modified by energy intake in sheep under the conditions (2-4 degrees C on the fifth day) of the present experiment.

Timing of nutrient restriction and programming of fetal adipose tissue development

It is apparent from epidemiological studies that the timing of maternal nutrient restriction has a major influence on outcome in terms of predisposing the resulting offspring to adult obesity. The present review will consider the extent to which maternal age, parity and nutritional restriction at defined stages of gestation can have important effects on fat deposition and endocrine sensitivity of adipose tissue in the offspring. For example, in 1-year-old sheep the offspring of juvenile mothers have substantially reduced fat deposition compared with those born to adult mothers. Offspring of primiparous adult mothers, however, show increased adiposity compared with those born to multiparous mothers. These offspring of multiparous ewes show retained abundance of the brown adipose tissue-specific uncoupling protein 1 at 1 month of age. A stimulated rate of metabolism in brown fat of these offspring may act to reduce adipose tissue deposition in later life. In terms of defined windows of development that can programme adipose tissue growth, maternal nutrient restriction targetted over the period of maximal placental growth results in increased adiposity at term in conjunction with enhanced abundance of mRNA for the insulin-like growth factor-I and -II receptors. In contrast, nutrient restriction in late gestation, coincident with the period of maximal fetal growth, has no major effect on adiposity but results in greater abundance of specific mitochondrial proteins, i.e. voltage-dependent anion channel and/or uncoupling protein 2. These adaptations may increase the predisposal of these offspring to adult obesity. Increasing maternal nutrition in late gestation, however, can result in proportionately less fetal adipose tissue deposition in conjunction with enhanced abundance of uncoupling protein 1.

Long-term effects of nutritional programming of the embryo and fetus: mechanisms and critical windows

The maternal nutritional and metabolic environment is critical in determining not only reproduction, but also long-term health and viability. In the present review, the effects of maternal nutritional manipulation at defined stages of gestation coinciding with embryogenesis, maximal placental or fetal growth will be discussed. Long-term outcomes from these three developmental windows appear to be very different, with brain and cardiovascular function being most sensitive to influences in the embryonic period, the kidney during placental development and adipose tissue in the fetal phase. In view of the similarities in fetal development, number and maturity at birth, there are close similarities in these outcomes between findings from epidemiological studies in historical human cohorts and nutritional manipulation of large animals, such as sheep. One key nutrient that may modulate the long-term metabolic effects is the supply of glucose from the mother to the fetus, because this is sensitive to both global changes in food intake, maternal glucocorticoid status and an increase in the carbohydrate content of the diet. The extent to which these dietary-induced changes may reflect epigenetic changes remains to be established, especially when considering the very artificial diets used to induce these types of effects. In summary, the maintenance of a balanced and appropriate supply of glucose from the mother to the fetus may be pivotal in ensuring optimal embryonic, placental and fetal growth. Increased or decreased maternal plasma glucose alone, or in conjunction with other macro- or micronutrients, may result in offspring at increased risk of adult diseases.

Effect of hypobaric hypoxia on lamb intrauterine growth: comparison between high- and low-altitude native ewes

The present studies assessed the effect of hypobaric hypoxia on fetal lamb growth in high-altitude (HA) and low-altitude (LA) native ewes. Growth patterns of fetal biparietal diameter (BPD), abdominal diameter (AD) and thorax height (TH) were described by consecutive ultrasound measurements throughout the entire pregnancy. Three groups of animals were used: (1) pregnant LA ewes kept at LA (control; 'LL' group); (2) pregnant LA ewes moved to HA immediately after confirmation of pregnancy ('LH' group); and (3) pregnant HA ewes kept at HA throughout the entire pregnancy ('HH' group). The slope of the BPD curve was higher in LL fetuses followed by that in LH fetuses. During the last month of pregnancy, TH was higher in LH and HH fetuses, whereas AD was higher in LL than in LH fetuses. The length of gestation was longer in HH ewes (153.2 +/- 4.3 days) than in LH and LL ewes (146.0 +/- 5.5 and 145.0 +/- 3.0 days, respectively). Bodyweight at birth was higher for LL newborns (4.2 +/- 0.3 kg) than for LH and HH newborns (3.0 +/- 0.5 and 3.2 +/- 0.8 kg, respectively), whereas placental weight was higher in the HH group (396 +/- 80 g) than in the LH (303 +/- 64 g) and LL (280 +/- 40 g) groups. In conclusion, an HA environment modifies fetal growth and pregnancy outcome with the magnitude of effects depending on the time of residence at HA.

Animal models of placental angiogenesis

The study of the development of the fetal membranes is an ancient one, and the importance of placental vascular development to placental function has long been recognized. Animal models have been important in these studies, as they allow for controlled experiments and analysis of multiple time-points during pregnancy. Since the demonstration nearly 20 years ago that the placenta produces angiogenic factors, the major factors regulating placental angiogenesis have been identified. These major factors include vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), the angiopoietins (ANG), and their receptors. Recently, sophisticated computerized image analysis methods have been developed to establish the pattern of placental vascular development in sheep. The maternal placental capillary bed develops primarily by increased size of capillaries, with only small increases in capillary number or surface densities. In contrast, the microvasculature of the fetal placenta develops primarily by increased branching, resulting in a large increase in capillary number and surface densities. These observations help to explain the relatively large increase in umbilical blood flow and nutrient delivery to the fetus that occurs during the last half of gestation. In addition, expression of mRNAs for VEGF, bFGF, ANG, and their receptors have recently been correlated with normal placental vascular development in sheep, and further refinement of these mathematical models is warranted. Lastly, the recent development of animal models of compromised pregnancies, including those resulting from maternal nutrition (both restriction and excess), multiple fetuses, environmental stress (heat stress and high altitude), and fetal and maternal breed effects, has already indicated that reductions in placental vascular development and expression of angiogenic factors are probably a root cause of fetal growth restriction. With these methods and models now in place, we should soon be able to establish the mechanisms involved in both normal and abnormal placental angiogenesis.

Placental angiogenesis in sheep models of compromised pregnancy

Because the placenta is the organ that transports nutrients, respiratory gases and wastes between the maternal and fetal systems, development of its vascular beds is essential to normal placental function, and thus in supporting normal fetal growth. Compromised fetal growth and development have adverse health consequences during the neonatal period and throughout adult life. To establish the role of placental angiogenesis in compromised pregnancies, we first evaluated the pattern of placental angiogenesis and expression of angiogenic factors throughout normal pregnancy. In addition, we and others have established a variety of sheep models to evaluate the effects on fetal growth of various factors including maternal nutrient excess or deprivation and specific nutrients, maternal age, maternal and fetal genotype, increased numbers of fetuses, environmental thermal stress, and high altitude (hypobaric) conditions. Although placental angiogenesis is altered in each of these models in which fetal growth is adversely affected, the specific effect on placental angiogenesis depends on the type of 'stress' to which the pregnancy is subjected, and also differs between the fetal and maternal systems and between genotypes. We believe that the models of compromised pregnancy and the methods described in this review will enable us to develop a much better understanding of the mechanisms responsible for alterations in placental vascular development.

Shearing during pregnancy — review of a policy to increase birthweight and survival of lambs in New Zealand pastoral farming systems

Over the past decade, lambing percentages have risen in conjunction with a rise in the percentage of multiple lambs born. Multiple-born lambs are smaller than their singleton counterparts and are particularly susceptible to starvation-exposure. Any technique that can increase the birthweight or thermoregulatory capability, or both, of otherwise lightweight lambs has the potential to substantially increase survival of multiple-born lambs. In the United Kingdom under housed conditions, shearing during pregnancy has been shown to increase both the birthweight and thermoregulatory capability of newborn lambs. However, shearing during pregnancy under pastoral conditions has failed to consistently affect the newborn lamb's thermoregulatory capability. In contrast, under New Zealand's pastoral conditions shearing during pregnancy has been found to increase birthweight, but results have been inconsistent in both magnitude and birth-rank specificity. Increase in feed intake by the dam, types of shearing comb used and changes in gestation length do not explain the variation observed. When studies involving shearing during pregnancy are collated it becomes apparent that there are two criteria that must be met to achieve a birthweight response. Firstly, the dam must have the potential to respond and secondly, the dam must have the means to respond. Any increase in lamb survival through shearing during pregnancy would be predominantly through an increase in birthweight of otherwise lightweight lambs. However, in the few studies conducted to date, an increase in birthweight has not resulted in a statistically significant increase in survival. For an increase in birthweight to have a positive effect on lamb survival, lambs must be otherwise destined to be born within a birthweight range in which survival rate is below optimum (<4.0 kg), and the increase in birthweight observed must move a significant proportion of otherwise lightweight lambs into a higher range of survival rate.

Metabolic responses to mid-pregnancy shearing that are associated with a selective increase in the birth weight of twin lambs

Previous studies have shown that shearing pregnant ewes at mid- or late-pregnancy is associated with an increase in lamb birth weight. The present study was designed to investigate metabolic responses that may underlie this response. Single- and twin-bearing ewes were either unshorn or shorn at mid-pregnancy (Day 69 of pregnancy; P69), and insulin, glucose and epinephrine challenges were conducted on P109-111 and P132-134. Shearing increased the birth weight of twin lambs by over 1 kg (P < 0.001) without having any effect on singleton birth weight. This response was associated with a 10-20% reduction in the insulin response to a glucose challenge (P < 0.05) without a change in glucose clearance following either glucose or insulin challenges. The lipolytic response to epinephrine challenge increased as pregnancy progressed, but was not associated with the increased birth weight of twin lambs born to shorn ewes. By late pregnancy, a 25% reduction in maternal IGF-I concentration and a two- to threefold increase in maternal IGFBP-1 concentration (P < 0. 05) associated with shearing were observed. The increase in lamb birth weight associated with mid-pregnancy shearing may have been associated with an increase in the non-insulin dependent uptake of glucose by the placental-fetal unit.

Maternal manipulation of brown adipose tissue and liver development in the ovine fetus during late gestation

We examined the effect of maternal chronic cold exposure, induced by winter-shearing ewes 4 weeks before their predicted lambing date, on brown adipose tissue (BAT) and liver development in lambs. Fetuses were sampled from under-fed (60% of energy requirements for maintenance and pregnancy of an unshorn ewe) shorn or unshorn ewes at 126, 140 and 145 d of gestation. Lambs were sampled from ewes within 2 h of birth. Throughout gestation fetal body, BAT and liver weights were similar in shorn and unshorn groups. The level of GDP binding to mitochondrial uncoupling protein remained low throughout gestation, but increased dramatically after birth. Lambs born to shorn ewes possessed more mitochondrial protein and exhibited a significantly higher total thermogenic activity in BAT. Type I iodothyronine 5' deiodinase (EC 3.8.1.4) activity in BAT peaked at birth, as did hepatic iodothyronine 5' deiodinase activity and was significantly greater in lambs born to under-fed shorn ewes, which exhibited a higher plasma triiodothyronine concentration. Chronic maternal adaptations to prolonged cold exposure appear to enable pregnant ewes to compensate for the negative effects of under-feeding on fetal growth and development.

Effect of mild cold exposure on whole-body and net hindquarters glucose metabolism in sheep

Isotope dilution using [U-13C]glucose was combined with measurement of hindquarters arteriovenous difference and blood flow to examine the effect of mild cold exposure on whole-body and net hindquarters glucose metabolism in sheep. Determinations were carried out in a thermoneutral environment (20 +/- 1 degrees C) and on day 5 of mild cold exposure (4 +/- 1 degrees C). Whole-body blood glucose turnover rate was 1.56 and 1.91 mg kg-1 min-1 in the thermoneutral environment and during mild cold exposure, respectively. Net hindquarters glucose uptake was 0.79 and 1.19 mg kg-1 min-1, corresponding to 50 and 61% of whole-body turnover rate, respectively. These results suggest that in sheep the contribution of glucose uptake by the hindquarters tended to increase during mild cold exposure, even though whole-body blood glucose turnover rate did not increase significantly.

Cold thermoregulation in the newborn calf

During the fetal to neonatal transition, the newborn calf encounters severe thermolysis due to an abrupt change in thermal environment that is compounded by evaporation of fetal fluids and severe weather conditions. Maintenance of homeothermy during the neonatal period necessitates an acute and sustained thermogenic response by the newborn calf. It is now widely accepted that this thermogenic response is derived from both shivering thermogenesis in muscle tissue and nonshivering thermogenesis in brown adipose tissue (BAT). It is critical that newborn calves possess functional BAT during the neonatal period. This article focuses on the pre- and postnatal factors that influence nonshivering thermogenesis of BAT in the neonatal calf.

Effect of maternal cold exposure on brown adipose tissue and thermogenesis in the neonatal lamb

1. This study examines the effect of chronic cold exposure during pregnancy, induced by winter shearing twin-bearing ewes 4 weeks before predicted lambing date, on O2 consumption and CO2 production during non-rapid-eye-movement (REM) sleep in lambs maintained for at least 1 h at warm (28-18 degrees C) and cold (14-5 degrees C) ambient temperatures at 1, 4, 14 and 30 days of age. This was combined with measurement of the thermogenic activity (GDP binding to uncoupling protein in mitochondrial preparations) of perirenal adipose tissue from lambs immediately after birth and at 33 days of age. 2. Lambs born from shorn (cold-exposed) ewes were 15% heavier (P < 0.01) and possessed 21% (P < 0.01) more perirenal adipose tissue that contained 40% more protein and mitochondrial protein than unshorn (P < 0.05) controls. Total GDP binding in perirenal adipose tissue was 40% greater (P < 0.05) in lambs born from shorn ewes but there was no difference in lipid content of this tissue between the two groups. 3. At 1 day of age, lambs born from shorn ewes exhibited a 16% higher (P < 0.05) rate of O2 consumption (per kilogram bodyweight) at the warm temperature and a 40% greater metabolic response to the cold ambient temperature. All lambs born from shorn ewes responded to cold exposure without shivering (i.e. via non-shivering thermogenesis) whilst shivering was measured in four out of seven lambs in the unshorn group. These differences had disappeared by 4 days of age as a result of a 25% increased (P < 0.01) rate of O2 consumption in the warm in lambs born from unshorn ewes and a 20% decrease (P < 0.05) in the response to the cold in lambs from shorn ewes. Shivering during cold exposure was measured in six out of nine lambs born from shorn ewes indicating a rapid alteration in thermoregulatory responses to cold during the first few days of life. 4. The levels of GDP binding and mitochondrial protein in perirenal adipose tissue fell by one-third in both groups of lambs during the first 33 days of life whereas lipid content either increased or was unchanged. This indicated that brown adipose tissue (BAT) was developing the characteristics of white adipose tissue.(ABSTRACT TRUNCATED AT 400 WORDS)

Psychogenic pregnancy disruptions in mammals

Evidence scattered over the literatures of zoology, psychology, agricultural science, and medicine indicates that diverse stressors will interfere with pregnancy in its early stages. It is probable that the most sensitive period is around the point of intrauterine implantation of fertilized ova. Although there is some indication that conventional "stress" hormones of the pituitary-adrenal axis can inhibit implantation, this evidence is too weak and inconsistent to suggest that these hormones are primary mediators of early pregnancy disruptions. Increasingly, evidence indicates that the balance of ovarian steroids is most important for pregnancy maintenance. It is well known that minute amounts of exogenous estrogens can completely disrupt pregnancy, and some new evidence suggests that endogenous estrogens may be released from the adrenals and/or ovaries during psychological stress.

Fetal lung growth: influence of maternal exposure to cold and exercise in rats

The consequences of maternal exposure to low ambient temperature and exercise on maternal and fetal lung growth and in particular on the relationship between the three gas exchange organs (lungs and placenta) were studied in albino rats. Pregnant rats were subjected to 10 degrees C ambient temperature or to daily 10 min swimming exercise beginning at day 3 or day 11 of pregnancy till day 21 when they were sacrificed. Maternal lung growth was assessed by measuring the lung weight, lung air volume and lung DNA content, and the fetal lung growth by lung DNA content. Comparisons were made in rats with litter sizes of 9-14. The major findings were as follows. Cold increased: (1) the maternal lung, liver, kidney and heart size, and fetal body weight, in both groups, but to a greater degree in rats exposed to cold at day 3; and (2) fetal lung DNA content in rats subjected to cold at late gestation. It abolished the relationship between maternal and fetal lung DNA content which exists in large litter size pregnancies. Exercise did not enlarge the maternal lungs; it decreased the placental weight and fetal lung DNA content and abolished the relationship between maternal and fetal lung DNA content in rats subjected to exercise at early gestation. Neither cold nor exercise had an effect on fetal lung maturation. It is postulated that reduction in fetal lung DNA content with maternal exercise may result from the effects of hypoxemia which may be the consequence of reduced uterine blood flow; and that abolition of normally existing direct relationship between maternal and fetal lung DNA content may be the outcome of the effects of alterations in metabolic and endocrine functions, in both the mother and the fetus, in response to cold temperature and exercise, offsetting the influence the growing maternal lung may have on fetal lung growth.

Glucose metabolism in shorn and unshorn pregnant sheep

1. Whole-body, hind-limb and uterine tissue metabolism of glucose was studied using a combination of isotopic and arterio-venous difference techniques in shorn and unshorn pregnant sheep over the final 4 weeks of pregnancy. This was combined with the measurement of the concentrations of oxygen and carbon dioxide in arterial blood and plasma concentrations of lactate, acetate, non-esterified fatty acids, 3-hydroxybutyrate, glycerol, growth hormone (GH), insulin, glucagon, cortisol, thyroxine and 3,5,3'-triiodothyronine (T3). 2. Glucose entry rate was 28% higher in shorn ewes compared with unshorn controls, even though there was no difference in the arterial plasma concentration of glucose. This effect may have been caused by a decrease in the molar rate, insulin: glucagon (I:G), which was 40% lower in shorn ewes as a result of a significant decrease in the plasma concentration of insulin. There was no difference in the plasma concentration of cortisol or GH. 3. Blood flow across the hind-limb or uterine tissues was not significantly different between shorn and unshorn groups, neither were the net glucose uptake, glucose oxidation rate or contribution of glucose to O2 consumption across these tissues. 4. Insulin-tolerance tests performed on a separate group of shorn and unshorn ewes showed an increased sensitivity to the hypoglycaemic effects of insulin in the shorn group. 5. There was no significant difference between shorn and unshorn animals in the contribution of glucose to CO2 output or in the proportion of glucose entry rate oxidized. CO2 entry rate was 18% higher in shorn ewes compared with unshorn controls which resulted in a 26% higher estimated value for heat production. There was a 47% increase in glucose oxidation rate in shorn ewes but there was no significant difference in the proportion of total heat production which was derived from glucose. The arterial concentrations of O2 and CO2 were significantly higher in shorn ewes, which may be an indication of the higher metabolic rate in these animals. This effect may be mediated via a significant rise in plasma T3 concentration in the shorn group. 6. It is concluded that as a result of long-term cold exposure there is a significant increase in whole-body glucose entry and oxidation rates in the shorn pregnant ewe. The increase in insulin sensitivity at the same time as a decrease in plasma insulin concentration may represent a mechanism to ensure continued glucose supply to insulin-sensitive tissues while the concomitant decrease in plasma I:G stimulates hepatic gluconeogenesis.

Influence of prepartum exposure of beef heifers to winter weather on concentrations of plasma energy-yielding substrates, serum hormones and birth weight of calves

The influence of exposure to ambient winter weather conditions (WW) during the final 90 d of gestation on serum hormones, plasma substrates, and birth weight of calves was evaluated in spring-calving, primiparous beef heifers. At of 192+/-14 d of gestation, heifers were assigned by expected calving date, breed, and sire of fetus to one of two treatments. Thirteen heifers were assigned to thermoneutral environment (TN; 12 degrees C) and housed in temperature-controlled rooms. Heifers in WW (n=16) were maintained outdoors in drylots without access to shelter and given additional dietary energy when average weekly windchill fell below -6.7 degrees C. Body weights, hip-heights and samples of serum and plasma were obtained biweekly until heifers were relocated, approximately 7 d prior to expected calving. Polynomial response curves for concentrations of glucose and nonesterified fatty acids (NEFA) in plasma and cortisol in serum were not influenced by treatment. However, average concentrations of NEFA in plasma were increased (P<0.02) and glucose tended to be higher (P=0.13) in WW heifers compared to TN heifers (172.5+/-8.9 vs 136.9+/-7.7 micromol/L and 87.8+/-2.4 vs 83.3+/-2.7 mg/100ml for NEFA and glucose, respectively). Time trends of concentrations of estradiol in serum (P<0.01) and hip-height to weight ratios were different (P<0.05) for WW and TN. Birth weights of calves from TN heifers were greater (P<0.06) than calves from WW heifers (42.3+/-2.0 vs 36.9+/-1.8 kg), but average calving difficulty scores were similar for both heifer groups (3.2+/-0.5 vs 2.7+/-0.4). These data suggest that exposing spring-calving cows to reduced effective ambient temperatures during the final 90 d of pregnancy may elevate energy-yielding metabolites in plasma and alter endocrine function. These changes may contribute to reduced birth weight of calves.

The effect of shearing on the energy metabolism of the pregnant ewe

1. Metabolizable energy (ME) intakes, heat production, non-protein respiratory quotient (NPRQ) and the plasma concentrations of glucose, non-esterified fatty acids (NEFA), 3-hydroxybutyrate, insulin, growth hormone (GH) and cortisol were measured in shorn and unshorn pregnant ewes. 2. Lamb birth-weight was 17% higher from shorn ewes despite similar ME intakes in the two groups. Shearing resulted in a significant decrease in the digestibility of dry matter and energy. 3. Both shorn and unshorn ewes were found to be in positive nitrogen balance and negative energy balance. Heat production was 28% higher in shorn ewes. This increase in heat production in the shorn group could be completely accounted for by an increase in the oxidation of fatty acids as measured using the NPRQ values. 4. Despite an apparent increase in the use of fat as an energy source there were no effects of shearing on the mean plasma concentrations of NEFA, 3-hydroxybutyrate, GH and cortisol. 5. Measurements made at 1 h intervals for 24 h indicated a tendency for the concentrations of glucose to be increased and insulin decreased in shorn ewes, particularly, between 6 and 11 h after feeding. 6. It is concluded that shearing pregnant ewes at 8 weeks before lambing results in a chronic increase in energy requirements which are met by oxidizing body fat depots. The cold stress induced by shearing may also inhibit insulin secretion resulting in increased plasma glucose concentrations. The effects of shearing on energy metabolism in the ewe are discussed in relation to the nutrient supply for the developing fetus.

Effects of undernutrition and exercise during late pregnancy on uterine, fetal and uteroplacental metabolism in the ewe

Uterine, umbilical and, by difference, uteroplacental net uptakes of oxygen, glucose, lactate and 3-hydroxybutyrate (uterine uptake only) were measured in single-pregnant ewes which were either well-fed throughout, or severely undernourished for 8-20 d during late pregnancy. All animals were studied while standing at rest and then while walking on a treadmill at 0.7 m/s on a 10 degrees slope for 60 min. Undernutrition did not significantly affect fetal or placental weights at 143 d gestation but caused a 14% decrease in maternal live weight. Uterine blood flow was decreased by 32% and was associated with a significant decrease in uteroplacental oxygen uptake; neither umbilical blood flow nor fetal O2 uptake were affected by maternal plane of nutrition. Maternal and fetal hypoglycaemia in underfed ewes was accompanied by 46-63% decreases in uterine, umbilical and uteroplacental net uptakes of glucose, and similar declines in uterine and umbilical glucose/O2 quotients. Moderate maternal hyperketonaemia was associated with 2.5-fold and 3-fold increases in uterine net uptake of 3-hydroxybutyrate and 3-hydroxybutyrate/O2 quotient respectively. Exercise caused significant decreases in uterine blood flow in fed and underfed ewes but did not affect uterine or umbilical O2 uptakes; uterine net glucose uptake increased in most ewes but umbilical uptake was not significantly affected. Umbilical net uptake of lactate was significantly reduced. In underfed ewes, the extent of hyperketonaemia was significantly reduced by exercise. Contrary to earlier proposals, the ovine pregnant uterus is sensitive and adaptable to long- and short-term alterations in maternal energy balance, as achieved by chronic undernutrition and exercise respectively. Thus, the fetus and placenta significantly add to, but do not necessarily have priority over the energy demands of other tissues of the ewe.

The intake of milk by suckled, newborn lambs and the effects of twinning and cold exposure

Clun Forest ewes with single and twin lambs were exposed to neutral (20 degrees) or cold (-1 degree) environmental temperatures, beginning soon after parturition, for 4 d. The intakes of milk, lactose and glycerides by the lambs were calculated from measurements of the rate of displacement of tritiated water (injected into the lambs) by non-radioactive water in milk from the ewes, and measurements of the concentration of lactose and glyceride glycerol in small samples of milk. The yield of milk from ewes bearing twin lambs was greater than the yield from single-bearing ewes in the neutral environment but, in both environments, twin lambs had lower intakes of milk and milk lactose and glycerides, and gained body-weight more slowly, than single lambs. Milk from twin-bearing ewes had a lower lactose concentration than milk from single-bearing ewes. Cold exposure reduced the intake of milk and milk lactose, and reduced the rate of weight gain, of single and twin lambs. Glyceride intake was not different in the two environments. There appears to be a conflict between reduced supply of milk by the ewe and increased demand for milk by the lamb in cold temperatures. Such a conflict is sharpened when twin lambs are born.