Gestational Heat Stress Research Articles

Late gestation heat stress alters O2 regulation in placenta and neonatal heifers.

Maternal hyperthermia (i.e. heat stress) can adversely affect placental development and function, with severity varying based on pregnancy stage. During the last half of pregnancy, cow uterine blood flow increases 4.5-fold, and decreased maternal blood circulation can reduce placental diffusion capacity, impacting fetal growth. Milk removal was discontinued (i.e. dried off) in multiparous pregnant Holstein cows 54±5 days before expected calving and assigned to cooling (CLD) or heat stress (HT) treatments. Oxygen measurements were taken within ±3h after birth (n=7 per group) using the Rad-G Pulse Oximeter. RNA sequencing of cotyledonary tissue examined pathways and genes related to gas and oxygen transport. Heifers exposed to late gestation in utero hypoxia (HT) had significantly lower oxygen saturation at birth compared with those from dams with normal (CLD) oxygen levels (83.4% vs. 90.7%, p=0.03). The peripheral index of oxygen diffusion was also lower in HT-exposed heifers (2.04% vs. 4.84%, p=0.01). Gene enrichment analysis of cotyledonary tissue revealed affected pathways, including response to hypoxia, oxygen transport, and VEGF signaling. Late gestation HT potentially influenced blood circulation and nitric oxide biosynthesis pathways, with various genes showing upregulation and downregulation. The placenta is vital for fetal development, and late gestation hyperthermia can significantly affect its function, reducing fetal oxygen delivery and altering genes regulating placental gas and oxygen transport. These disruptions may result in fetal hypoxemia and growth restriction.

8 Gestational heat stress: Implications for pregnancy success and offspring development in swine

8 Gestational heat stress: Implications for pregnancy success and offspring development in swine

Late gestation heat stress impact on placental morphology and fetal development in ewes

Late gestation heat stress impact on placental morphology and fetal development in ewes

PSIV-2 Gestational heat stress and its impact on placental weight, colostrum production, and milk production on Columbia-Rambouillet ewes

PSIV-2 Gestational heat stress and its impact on placental weight, colostrum production, and milk production on Columbia-Rambouillet ewes

Deciphering the immune responses in late gestation Sahiwal cows under different microclimate and its carryover effect on progenies.

The current investigation aimed to comprehend the inflammatory and related immune responses in intrauterine calves subjected to heat stress (HS) during late gestation. For this purpose, 48 Sahiwal cows in late gestation were chosen and categorized into four equal groups: naturally heat stressed (NHS), cooling-treated (CLT), spring, and winter, and likewise their neonate calves born in summer (IUHS - intrauterine heat stressed and IUCL - intrauterine cooled), spring, and winter seasons. Environmental parameters were recorded, and the temperature-humidity index (THI) was calculated daily throughout the study period. The average THI values ranged between 84.18 (summer-NHS), 73.88 (summer-CLT), 78.92 (spring), and 64.91 (winter). NHS and spring groups exhibited thermal stress based on THI (> 76.00). Various treatments significantly (P < 0.01) impacted parameters like rectal temperature (RT), respiratory rate (RR), pulse rate (PR), and skin temperature (ST) in Sahiwal cows and their calves during the study, except for heart rate (HR). Blood samples collected during different seasons and from cows housed in a climatic chamber were used to extract plasma. Plasma cortisol, interleukin-6 (IL-6), tumour necrosis factor-α (TNF-α), and thiobarbituric acid reactive substances (TBARS) levels were notably higher (P < 0.05) in the NHS compared to the CLT group. Conversely, total antioxidant capacity (TAC) and immunoglobulin G (IgG) levels were higher (P < 0.05) in the CLT and winter groups. IUHS calves exhibited significantly (P < 0.05) lower overall mean plasma TAC and IgG levels but higher inflammatory and oxidative biomarkers, such as IL-6, TNF-α, and TBARS. Additionally, significant impacts on body weight were observed for factors such as interval (P < 0.01) and the interaction between treatment and interval (P < 0.05), exhibiting consistently lower body weight in IUHS calves throughout the study period. These findings suggest that late gestation heat stress may lead to physiological alterations in future calves. Strategies aimed at mitigating heat stress during late gestation should be considered not only for the productivity and well-being of the pregnant dam but also for the development and future performance of the calf.

PSIII-12 Influence of early gestational heat stress on biomarkers of mammary gland development in replacement gilts genomically selected for thermotolerance or thermosensitivity

Abstract Heat stress (HS) alters physiological and metabolic processes in lactating sows leading to decreased milk production, which is a major factor limiting growth and survivability of piglets. While genomic selection for thermotolerance may be a viable solution to alleviate the negative effects of HS on pig welfare, it may be linked to a reduction in milk production and subsequently, litter growth performance. Therefore, the study objective was to evaluate the effects of genomic selection for thermotolerance and its interaction with early gestational HS on biomarkers of mammary gland development in replacement gilts. We hypothesized that HS exposure as well as genomic selection for thermotolerance would negatively affect mammary epithelial proliferation rate. A total of 36 Landrace (33%) × Large White (67%) crossbred gilts divergently selected for thermotolerance (TOL; n = 18) or thermosensitivity (SEN; n = 18) were balanced by body weight, bred to a single Duroc sire, and then exposed to either thermoneutral (TN; constant 17 to 22°C) or cyclical HS (26 to 36°C) conditions until d 65 of gestation. From d 66 of gestation until farrowing, all pregnant gilts were exposed to TN conditions. Of the 36 total gilts bred, only 28 became pregnant yielding 15 HS gilts (n = 8 SEN and 7 TOL) and 13 TN gilts (n = 7 SEN and 6 TOL). On d 105 of gestation, a mammary biopsy was taken from all gilts, mammary tissue was placed into 10% buffered formalin, and KI67 immunohistochemical staining was performed to identify proliferating mammary epithelial cells (MEC). Proliferating and non-proliferating MEC populations were counted using ImageJ tool. Data were analyzed using PROC GLM in SAS 9.4 with individual gilt as the experimental unit. Overall, early gestational HS decreased (P &amp;lt; 0.01; 16.53 ± 2.12%) the percent of proliferating MEC relative to those kept under TN conditions (26.42 ± 2.39%). However, no effect of genomic line divergence was detected with any comparison (P &amp;gt; 0.05). In conclusion, early gestation HS, but not genomic selection for thermotolerance, had a negative impact on biomarkers of mammary gland development in replacement gilts. These data may suggest that early gestation HS could have a reductive effect on milk production capacity, which may negatively affect litter growth.

PSIII-11 Impacts of late gestational in utero heat stress on small intestine dynamics of neonatal dairy calves

Abstract Late gestation heat stress in dairy cows has been shown to negatively affect offspring growth and development. In utero heat stressed calves have altered small intestine morphology and an impaired ability to absorb colostral immunoglobulin G (IgG). Thus, the objective of this study was to characterize potential cellular and molecular alterations in the small intestine of neonatal in utero heat stressed calves. In the last ~56 d of gestation pregnant dams were either heat stressed (shade; n = 41) or cooled (shade, fans, soakers; n = 41) resulting in heifers that were in utero heat stressed (IUHS, n = 15) or in utero cooled (IUCL, n = 15). Heifers were fed 3.78 L of high-quality colostrum within 2 h of birth. Apparent efficiency of absorption (AEA) of IgG was calculated by measuring IgG content fed in colostrum and in 24 h serum. Within 4.6 ± 2.3 h of birth a subset of calves (n = 8/treatment) not fed colostrum were euthanized to collect samples from the ileum. Tissue for histological analysis was placed in 10% neutral buffered formalin before being dehydrated, embedded in paraffin, cut into 5 μm thicknesses, and mounted to glass slides. The TUNEL method was used to identify apoptotic cells using the Keyence BZ-X800 Microscope. Tissue for gene expression analysis was snap-frozen and kept at -80°C before RNA extraction and cDNA synthesis. The transcript abundance of endosomal (FCGRT, DAB2, MAMDC4), tight junction (ZO1, ZO2, ZO3, OCLN, CLDN1), and heat shock (HSP90, HSF1) related genes were measured by qPCR using the CFX96 Real-Time PCR detection System (BIO-RAD). Data were analyzed using PROC MIXED or PROC GLIMMIX depending on the response variable. TUNEL results are expressed as the proportion of positive cells to total cells. Quantitative PCR data were analyzed by assessing the estimates of the model relative to the geometric mean of 3 reference genes (ACTB, GADPH, RSP9; ΔΔCT). The concentration of colostrum IgG fed to calves was not different (136.1 vs. 122.5 g/L; IUHS vs. IUCL, respectively; P = 0.32), but AEA of IgG was reduced in IUHS relative to IUCL calves (23.5 vs. 33.3%; P &amp;lt; 0.01). The proportion of apoptotic cells within the villi of the ileum was increased in IUHS calves compared with IUCL (2.11 vs. 1.57%; P &amp;lt; 0.01). Ileum gene transcript abundance of DAB2 and MAMDC4 were increased (P &amp;lt; 0.01), while FCGRT transcripts tended to increase in IUHS calves (P = 0.08). All tight junction and heat shock-related gene transcripts were increased within the ileum of IUHS calves (P ≤ 0.02) with the exceptions of CLDN1 and HSP90, which were not different between treatments (P ≥ 0.22).These results suggest that exposure to heat stress in utero impact small intestine integrity after birth and affect key IgG transporters, providing insight into underlying mechanisms responsible for reduced IgG absorption in IUHS calves.

33 Identification of How Future Climates May Impact the Reproductive Herd and What This May Mean for Nutrition

Abstract Changes in our climate with global warming will translate to an expansion in the seasons and an increased incidence of extreme heat events, such that heat stress (HS) will become a major management issue. This poses particular challenges to the reproductive herd, as by virtue of their increased physical size and pregnancy, they are less resilient to environmental challenges. Recent work from our laboratory has quantified the performance of summer mated piglets on productivity, demonstrating that these litters are lighter at birth, have a lighter placenta weight and are more likely to be stillborn. These piglets also take longer to reach market weight and have increased carcass backfat, which can trigger market penalties. Collectively our studies demonstrate that summer conditions result in developmental abnormalities in piglets, potentially through placental insufficiency. Additionally, HS was challenging sows during the periparturient period, resulting in more stillbirths. Two subsequent climate-controlled studies quantified the effects of HS (cyclic 28 to 33 oC) during early to mid-pregnancy (d 40 to 60), when the placenta is undergoing rapid growth, as well as the effects of HS (cyclic 28 to 30 oC) in the periparturient period (d 110 of pregnancy to farrowing). In the first study, gestational HS did not influence the number or size of the piglets at mid-gestation but increased placental mass by 22% and reduced Longissimus muscle fiber hyperplasia by 16%. The apparent enlargement of the placenta at mid-gestation may reflect an adaptation to a reduction in uterine blood flow. In other species, HS is known to reduce blood flow to the splanchnic bed and reproductive tract organs, as blood is redistributed to the periphery and upper respiratory tract to augment heat dissipation. Therefore, the prioritization of placental growth by the piglet may represent an adaptation against a backdrop of insufficient nutrient supply. Whilst reductions in muscle fiber hyperplasia were associated with reduced vascularity, although it is not clear if this was a cause or effect. In the second study, the effects of periparturient HS resulted in a 30% increase in stillbirths, with surviving piglets having lower umbilical vein blood oxygen saturation and increased meconium staining. This supports the likelihood of HS restricting uterine and umbilical blood flows, resulting in increased periparturient fetal stress. Collectively these studies emphasize the challenges that climate change poses to swine production and that addressing these challenges will require a whole farm approach. In the near term, it is likely that advances in nutrition will form an important component in adjusting to a changing climate and minimize production losses.

PSV-16 Different Late Gestation Heat Stress Time-Windows and Their Effects on Newborn Holstein Calves from Northwest México

Abstract Exposure to heat stress (HS) during the dry period not only exerts negative effects on the welfare of pregnant cows, but also impairs the development of the fetus in the utero. When dams are subjected to late-gestation HS, affectations to their placental function and blood placental flow occur, generating fetal hypoxia and growth retardation of their calves. Since on the last 60 d of gestation bovine fetuses undergo through a phase of accelerated growth where they accrue around 60% of their birth weight, the number of days that their dams become exposed to HS during this period could affect differently their body weight and oxygenation status at birth. Therefore, the objective of this study was to determine the effects of different late-gestation HS time-windows on the birth weight and oxygen saturation of newborn Holstein calves. The study was conducted at the Yaqui valley in northwest México, a semiarid zone where the temperature and humidity index (THI) exceeds the dairy cattle thermal threshold from mid-March to mid-October (~7 months). Under such environmental dynamic, all cows within this geographical zone experience HS at some point during their gestation; nonetheless, depending on the conception date of the cow, different late-gestation HS time-windows arise. To assess the influence of the number of days of intrauterine HS exposure during late gestation (e.g., days with an average THI &amp;gt; 72 units), three intrauterine heat-stressed groups of calves were formed: G1 = calves born to dams exposed to HS less than 20 d within the last 60 d of gestation (n = 30), G2 = calves born to dams exposed to HS between 21 and 40 d within the last 60 d of gestation (n = 20), and G3 = calves born to dams exposed to HS for more than 40 d within the last 60 d of gestation (n = 16). Upon calving, variables such as sex, birth weight (BW, kg) and oxygen saturation (SpO2, %) were recorded. A general linear model that included the effects of sex of the calf and intrauterine HS calves’ group was implemented to analyze BW and SpO2. Harmonic means were compared via the Tukey-Kramer test. Harmonic means (±SE) for BW and SpO2 among groups were 42.42 ± 0.92, 40.84 ± 1.11, and 34.73 ± 1.24 kg, and 78.16 ± 2.71, 82.52 ± 3.28, and 82.29 ± 3.68 %, for G1, G2 and G3, respectively. Significant differences (P &amp;lt; 0.001) were found only for BW, with calves of G3 exhibiting the lowest BW in comparison to calves within G1 and G2, which were not statistically different among themselves (P &amp;gt; 0.05). Results of this study indicated that intrauterine HS exposures of &amp;gt;40 d strive deleterious effects on fetal growth and reduce the BW of newborn Holstein calves from northwest México.

Effect of Bee Bread on Corticosterone Level in Rat Dams Exposed to Gestational Heat Stress.

Environmental temperature rises are powerful stimuli that can alter both the sympathetic nervous system and the hypothalamic-pituitary-adrenocortical axis (HPA). Heat stress has been shown to harm pregnancy outcomes such as causing spontaneous abortion, low birth weight, growth retardation and stillbirth. Supplementation of bee bread in pregnant rats under heat stress exposure has been shown to improve the pregnancy outcomes. However, whether supplementation of bee bread during heat stress exposure may also reduce the level of the stress hormone, corticosterone has yet been reported. Therefore, this study aims to determine the effect of bee bread on corticosterone level, progesterone level, oestradiol level and zonation of the adrenal cortex of pregnant rats under heat stress exposure. Pregnant rats were randomly categorised into four groups (n = 6): Control (C: standard feeding), Treatment 1 (T1: 0.5 g bee bread/kg body weight/day), Treatment 2 (T2: standard feeding with heat exposure), and Treatment 3 (T3: 0.5 g bee bread/kg body weight/day with heat exposure). Bee bread (0.5 g/kg body weight/day) was force-fed to pregnant rats through oral gavage beginning on day 0 of pregnancy and continuing until delivery. Heat stress was generated experimentally by putting both T2 and T3 rats in an egg incubator for 45 min daily at a temperature of 43°C till delivery. On a postnatal Day 21, dams were euthanised to assess serum corticosterone, progesterone, oestradiol levels and adrenal gland histology. Rats in the T2 group had a significantly (P < 0.05) increase in the zona fasciculata thickness (94.95 ± 1.55 μm) and higher corticosterone levels (49.57 ± 1.57 ng/mL) compared with control. However, supplementation of bee bread during heat stress was able to show an improvement in adrenal zona fasciculata thickness by decreasing to 79.89 ± 3.08 μm and corticosterone level reduced to 35.31 ± 1.73 ng/mL significantly (P < 0.05). Therefore, these findings may imply that bee bread is effective as a neutralizer in lowering the production of stress hormone.

PSXIII-B-5 Early Gestation Heat Stress Improved Measures of sow Growth Performance but did not Impact Fetal Growth

Abstract In utero heat stress negatively impacts fetal development and alters postnatal phenotypes in swine. However, the effects of heat stress (HS) on fetal growth during early gestation is relatively unknown. The study objective was to evaluate the effects of gestational HS on measures of fetal growth in early gestation. Twenty-three gestating gilts were exposed to HS (n = 12; cyclic 26-38°C) or thermoneutral (TN; n = 11; 18.5 ± 1.2°C) conditions from gestation d 6 ± 0.9 to 33 ± 1.7. Vaginal temperature was recorded in 15 min intervals using data loggers. Respiration rates (RR) were recorded daily at 0800, 1200, 1600, and 2000 h. All gilts were individually-housed, and limit-fed 1.82 kg/d. Gilt body weights (BW) were measured weekly and average daily gain and gain:feed were calculated. At gestation d 33 ± 1.7, gilts were harvested and fetal weights and counts were recorded. Data were analyzed using PROC GLIMMIX. Vaginal temperatures and RR were greater (P &amp;lt; 0.01) in HS (38.5 ± 0.1°C and 59 ± 2 bpm, respectively) versus TN gilts (38.0 ± 0.1°C and 29 ± 2 bpm, respectively). Although no initial BW differences were observed (P = 0.39; 148.8 ± 4.1 kg), final BW tended to be greater (P &amp;lt; 0.07) for HS (166.5 ± 3.8 kg) versus TN (156.8 ± 4.0 kg) gilts. Average daily gain was increased (P &amp;lt; 0.01) for HS (0.5 ± 0.1 kg/d) versus TN (0.3 ± 0.1 kg/d) gilts. Gain:feed was greater (P &amp;lt; 0.01) for HS (0.27 ± 0.03) versus TN (0.16 ± 0.03) gilts. No fetal weight (P = 0.23; 4.3 ± 0.2 g/fetus) or count (P = 0.15; 15.2 ± 0.9 fetuses/gilt) differences were detected. In conclusion, HS-exposure during early gestation improved measures of growth performance in gestating gilts but did not impact fetal growth or count.

Gestational heat stress alters skeletal muscle gene expression profiles and vascularity in fetal pigs in a sexually dimorphic manner

BackgroundThere is evidence that sow heat stress (HS) during gestation affects fetal development with implications for impaired muscle growth. We have previously demonstrated that maternal HS during early to mid-gestation compromised muscle fibre hyperplasia in developing fetal pigs. Thus, we hypothesised these phenotypic changes are associated with a change in expression of genes regulating fetal skeletal muscle development and metabolism. To test this, at d 60 of gestation, RNA sequencing and immunohistochemistry were performed on fetal longissimus dorsi (LD) muscle biopsies collected from pregnant gilts that had experienced either thermoneutral control (CON, 20 °C, n = 7 gilts, 18 LD samples) or controlled HS (cyclic 28 to 33 °C, n = 8 gilts, 23 LD samples) conditions for 3 weeks.ResultsA total of 282 genes were differentially expressed between the HS and CON groups in female LD muscles (false discovery rate (FDR) ≤ 0.05), whereas no differentially expressed genes were detected in male LD muscles between the two groups (FDR > 0.05). Gestational HS increased the expression of genes associated with transcription corepressor activity, adipogenesis cascades, negative regulation of angiogenesis and pro-inflammatory signalling in female LD muscles. Immunohistochemical analyses revealed a decreased muscle vascularity density in fetuses from HS group for both sexes compared to those from the CON group (P = 0.004).ConclusionsThese results reveal gilt HS during early to mid-gestation altered gene expression profiles in fetal LD muscles in a sexually dimorphic manner. The molecular responses, including transcription and angiogenesis repressions and enhanced adipogenesis cascades, were exclusively observed in females. However, the associated reductions in muscle vascularity were observed independently of sexes. Collectively this may indicate female fetal pigs are more adaptive to gestational HS in terms of gene expression changes, and/or there may be sexually dimorphic differences with respect to the timing of muscle molecular responses to gestational HS.

Effects of Exposure to Heat Stress During Late Gestation on the Daily Time Budget of Nulliparous Holstein Heifers

Exposure of dairy cows to heat stress negatively affects welfare and performance during all phases of the lactation cycle. Detrimental effects include decreased milk and reproductive performance, reduced immune status and health, and altered natural behaviors. While we understand how mature cows respond to heat stress, the effects of late gestation heat stress on pregnant heifers is still unknown. Automated monitoring devices were used to document the behavioral activity of heifers during the pre- (final 60 d of gestation) and postpartum (first 60 d of lactation) periods. Twenty-five pregnant Holstein heifers were housed in a free-stall barn and enrolled to heat stress (HT; shade; n = 13) or cooling (CL; shade, soakers and fans; n = 12) treatments during the last 60 days of gestation. All animals were provided active cooling postpartum. Upon enrollment, heifers were fitted with a leg tag, which measured daily lying time, number of steps, and standing bouts, and a neck tag that measured eating and rumination times. Rectal temperatures (RT) and respiration rates (RR) were measured thrice weekly during the prepartum period. Relative to CL, HT heifers had elevated RT (38.8 vs. 38.7 ± 0.04°C) and RR (59.6 vs. 44.4 ± 1.9 breaths/min) during the prepartum period. Heat-stressed heifers tended to spend more time eating (224 vs. 183 min/d) and less time ruminating (465 vs. 518 min/d) during the prepartum period compared to CL, but dry matter intake did not differ. During the postpartum period, HT heifers spent more time eating (209 vs. 180 min/d) during weeks 1–4 of lactation, but rumination time was similar. Lying time was reduced by 59 and 88 min per day during weeks −7 and −6 prepartum and 84 and 50 min per day during weeks 2 and 3 postpartum in HT heifers, relative to CL. The number of steps was greater for HT during the postpartum period, from weeks 2 to 9 (3019 vs. 2681 steps/d). Eating frequency was similar during pre- and postpartum periods, however, based on semi quantitative visualization of the smarttag reports, HT consumed larger meals at night during the pre- and postpartum periods compared with CL heifers. In summary, late-gestation exposure to heat stress affects the daily time budget of first lactation heifers during both the pre- and postpartum periods. Current insights of heat stress effects on behavioral responses of dairy heifers may contribute to the development of more effective management strategies to mitigate heat load.

Programming effects of late gestation heat stress in dairy cattle.

The final weeks of gestation represent a critical period for dairy cows that can determine the success of the subsequent lactation. Many physiological changes take place and additional exogenous stressors can alter the success of the transition into lactation. Moreover, this phase is pivotal for the final stage of intrauterine development of the fetus, which can have negative long-lasting postnatal effects. Heat stress is widely recognised as a threat to dairy cattle welfare, health, and productivity. Specifically, late gestation heat stress impairs the dam's productivity by undermining mammary gland remodelling during the dry period and altering metabolic and immune responses in early lactation. Heat stress also affects placental development and function, with relevant consequences on fetal development and programming. In utero heat stressed newborns have reduced birth weight, growth, and compromised passive immune transfer. Moreover, the liver and mammary DNA of in utero heat stressed calves show a clear divergence in the pattern of methylation relative to that of in utero cooled calves. These alterations in gene regulation might result in depressed immune function, as well as altered thermoregulation, hepatic metabolism, and mammary development jeopardising their survival in the herd and productivity. Furthermore, late gestation heat stress appears to exert multigenerational effects, influencing milk yield and survival up to the third generation.

35 Effect of Late Gestational Heat Stress on Placental Characteristics in Dairy Cattle

Abstract To determine the effects of late gestation heat stress on placental development, dairy cows were exposed to heat stress (HT, shade) or cooled (CL, shade, fans and soakers) during the final 46 d pre-calving on the University of Florida dairy facility (temperature-humidity index; THI &amp;gt;68). We hypothesize heat stress (or lack of heat abatement) will reduce placental efficiency and in turn increase placental weight, surface area, and volume. At expulsion all placentae were collected and total placental weight was determined as well as individual cotyledonary weights, surface areas, and volume. In addition, the total number of total cotyledons was recorded and cotyledonary color and placental growth abnormalities (i.e. teratomas) were recorded and photographed. All data were analyzed using PROC MIXED in SAS. In addition, associations between parameters were determined by calculating Pearson Correlation Coefficients using SAS. Placentae from HT cows had a higher total placental weight, higher non-vascular membrane weight, higher total cotyledonary weight, higher total cotyledonary volume, and a higher incidence of teratomas than those from CL cows (P &amp;lt; 0.05). HT cows also had placentae with a significantly greater average cotyledonary weight and volume (P &amp;lt; 0.05). HT cows tended to have a greater incidence of color abnormalities in the placenta (P &amp;lt; 0.075). In addition, HT cows had significantly lighter calves at birth (P &amp;lt; 0.05). These data demonstrate that heat stress (or lack of heat abatement) impacts placental growth during the final stages of gestation, resulting in heavier placentae, an increase in cotyledonary weight and volume, but not an increase in the total number of cotyledons or total cotyledonary surface area. These placental alterations ultimately resulted in lighter calves at birth.

Endocrine Signals Altered by Heat Stress Impact Dairy Cow Mammary Cellular Processes at Different Stages of the Dry Period.

Simple SummaryLate-gestation heat stress increases blood prolactin and decreases oestrogen concentrations in dry cows. These hormonal alterations may disturb mammary gland remodelling during the dry period, thereby being potentially responsible for the observed production impairments during the subsequent lactation. This project aimed to better understand the molecular mechanisms underlying subsequent impairments in mammary performance after dry period heat stress. For this, we studied the expression of genes encompassing prolactin and oestrogen pathways and key cellular process pathways under different thermal environments and in vitro hormonal milieus. The results of this study revealed that late-gestation heat stress impacted the expression of genes in the mammary gland involved in key cellular processes occurring during the dry period. Furthermore, our results indicated that these modifications are in part modulated by alterations of oestrogen and prolactin signalling.Hormonal alterations occurring under late gestation heat stress may disturb mammary gland remodelling, resulting in a reduced milk yield during the subsequent lactation. We investigated the effects of an altered endocrine environment on mammary gene expression at different stages of the dry period. Mammary gland biopsies from in vivo-cooled (CL) or heat-stressed (HT) cows were collected at d 3 and 35 relative to dry-off and divided into explants. Explants were incubated in vitro for 24 h in one of three media: Basal: no prolactin or estrogen; CL-mimic: Basal + low prolactin + high 17β-estradiol, or HT-mimic: Basal + high prolactin + low 17β-estradiol. Real time qPCR was used to quantify gene expression. We established that late-gestation heat stress changes the expression of prolactin and oestrogen receptors, downregulates genes involved in apoptosis, autophagy and proliferation at d 3 and upregulates genes related to those cellular processes at d 35. Moreover, compared with in vivo treatments, we showed that the expression of fewer genes was impacted by in vitro treatments which aimed to mimic the hormonal response of cows exposed to a different environment. Further research will continue to uncover the mechanisms behind the production impairments caused by late-gestation heat stress.

5 Heat stress during pregnancy compromises intrauterine development and reproductive parameters of female progeny in C57BL/6J mice

Heat stress (HS) affects the reproduction of many species, causing subfertility by reducing gametogenesis. This study assessed the effect of HS at different stages of pregnancy in C57BL/6J mice on the somatic development and reproductive parameters of F1 females. A total of 40 females and 40 males aged between 5 and 6 weeks old were mated (1:1). After mating confirmation (vaginal plug presence) the females were subjected to HS during pregnancy in the first half (FP, from Day 1 to 10; n=10), the second half (SP, from Day 11 to delivery; n=10), or the total pregnancy (TP, n=10). A control group (C, n=10) was maintained in normothermic conditions (25°C, 45% relative humidity) throughout the experiment. The HS was induced (41°C for 2h daily) in an environmental chamber heated by 2 red lamps. After delivery, birthweight was recorded and somatic development of the F1 females was monitored weekly until 8 weeks of age. They were superovulated with 5IU of equine chorionic gonadotrophin (eCG) and 5IU of human chorionic gonadotrophin (hCG) 48h later and mated with control F1 males in four groups: FP×C; SP×C; TP×C; and C×C, female and male, respectively. At 72h after mating confirmation, uterine flushing was performed with 0.5mL of phosphate-buffered saline + 0.4% bovine serum albumin and embryos classified. Ovaries were collected for histological analysis of the follicular population with the formula: follicles per ovary×n section×section thickness/n section observed×average diameter of the oocyte nucleus. Pregnancy rate was analysed by chi-squared test. Data of pups born per female, birthweight, somatic development, follicular population, total and viable structures recovered by female were tested for normality by the Shapiro-Wilk test, before ANOVA and Tukey test. Values of P&amp;lt;0.05 were considered to indicate a difference and P&amp;lt;0.10a tendency. No difference (P&amp;gt;0.05) among groups was detected in pregnancy rate (C=80; FP=40; SP=60; TP=60%) or in the number of pups born per female (C=7.0±1.0; FP=6.0±1.5; SP=6.5±1.5; TP=5.1±1.5). Birthweight was lower (P&amp;lt;0.05) for FP (1.1g) and TP (1.2g) than for C (2.2g) and SP (1.8g). However, this difference disappeared (P&amp;gt;0.05) in the third week of development and remained similar until the eighth week (C=21.0; FP=20.4, SP=20.3, TP=20.0g). Similar (P&amp;gt;0.05) follicular population by ovary (total, primordial, primary, secondary, and antral) was observed between the C and HS groups. However, among HS groups, the total number of follicles and number of primordial follicles, respectively, were lower (P&amp;lt;0.05) in the FP (1623; 942) compared with SP (2735; 1918) and TP (2626; 2352); with no difference in primary, secondary, and antral follicles. This resulted in similar (P&amp;gt;0.05) total number of structures recovered by females (C=11.8±5.0, FP=7.6±2.4, SP=10.8±5.5, TP=6.9±3.1), with a tendency (P=0.06) to fewer viable embryos in TP (4.3±2.7) compared with C (9.5±4.6). Considering the increasing global temperature, it is imperative to understand the effects of HS on animal reproductive capacity. In conclusion, gestational HS impaired mice intrauterine development and changed the ovarian follicular population in the F1 generation.

Reproduction and reproductive tract morphology of male and female pigs whose mothers were heat stressed during the second month of gestation.

The primary objective was to assess the development of fetal gonads and measure the subsequent reproductive capacity of boars and gilts whose mother was either subjected to gestational heat stress (GHS) or thermoneutral (GTN; control) conditions during pregnancy. Gilts were subjected to either GHS (28 to 38 °C; 65% to 88% relative humidity [RH]; n = 30) or GTN (17 to 22 °C; 56% to 65% RH; n = 29) for the second month of gestation (a period that coincides with a critical window of gonadal development). A subset of GHS (n = 12) and GTN (n = 11) gilts was sacrificed immediately following treatment for the collection of pregnancy data. The remaining gilts (n = 18 GHS and n = 18 GTN) were allowed to farrow. Female offspring from the farrowed gilts were studied through puberty, first insemination, and early pregnancy when fetal tissues were again collected. During the treatment period, GHS gilts had greater (P < 0.001) rectal temperature and respiration rate at both measurement time points (morning and afternoon) compared with GTN gilts. When assessed at the end of the second month of gestation, the total number of viable fetuses did not differ (P > 0.10) for GHS vs. GTN. Likewise, the weight of the fetus, placenta, fetal testes, and fetal ovaries were similar (P > 0.10) for GHS and GTN pregnancies. There was a tendency for an effect of treatment (63.3 ± 2.3 vs. 70.1 ± 2.6; GHS vs. GTN; P < 0.073) on the number of oogonia per histological section in the fetal ovaries. There was no effect of treatment on the number of prespermatogonia per histological section in the fetal testis. For gilts farrowing after treatment, litter size, piglet birth weight, and weaning weight were similar (P > 0.10) for the GHS and GTN gilts. Testes collected from castrated GHS boars had fewer prespermatogonia per seminiferous tubule cross section (P < 0.049). Female offspring from the GHS (n = 30) or GTN (n = 37) sows reached puberty at a similar age, and their pregnancies (ninth week of gestation) had fewer corpora lutea (15.6 ± 0.5 vs. 17.1 ± 0.4; GHS vs. GTN; P < 0.038) but the number of fetuses was similar for GHS and GTN. In summary, compared with GTN, GHS during a critical window of gonadal development tended to reduce the number of oogonia in the fetal ovary, reduced the number of prespermatogonia in the neonatal testes, and reduced ovulation rate at first pregnancy in gilts.

Late gestation heat stress in dairy cows: Effects on dam and daughter

In dairy cattle, the final weeks before parturition are physiologically challenging and an important determinant of subsequent production performance. External stressors should be carefully managed during this period to avoid adding strain on the animals. Late-gestation heat stress impairs productivity in the dam and exerts transgenerational effects on progeny. Physiological responses are complex and detriments to performance are multifaceted. Late-gestation heat stress blunts mammary gland involution in the first half of the dry period and impairs cell proliferation as calving approaches. Moreover, cows that were exposed to prepartum heat-stress exhibit reduced adipose tissue mobilization and a lower degree of insulin resistance during early lactation. Prepartum heat exposure also depresses immune function and evidence links this decrease to altered prolactin signaling under heat stress. Placental functions are also impaired as reflected in a higher cotyledon mass but lower maternal circulating estrone sulfate concentrations, potentially resulting in lower nutrient supply and reduced calf birth weight. In addition, calves born to heat-stressed dams show impaired immune function and therefore higher disease susceptibly. Novel evidence reported that intrauterine heat stress alters the methylation profile of liver and mammary DNA, which may also contribute to the poorer performance during adulthood of calves exposed to heat stress in utero. Understanding the contribution of all altered biological systems during late-gestation heat stress can be used as a basis for improving cow management during the dry period. This article provides a review of the impacts of late-gestation heat stress and of the emerging understanding of the biological mechanisms that underlie the observed impairments of performance.

TRIENNIAL LACTATION SYMPOSIUM/BOLFA: Late gestation heat stress of dairy cattle programs dam and daughter milk production.

Anticipated increases in the world population to 9 billion people will lead to increased demand for food. Dairy products represent one of the most sustainable animal sources of food protein because ruminants can utilize byproduct and forage feeds unsuitable for human consumption. Continued improvements in productivity will depend on deeper understanding of the biology of lactation, including developmental programming of tissues critical to that process. Although prenatal programming of postnatal phenotype is well documented for growth, behavior, and disease, there may also be instances of "programming" that last for a specific physiological stage (e.g., lactation). We distinguish between these 2 terms by the use of developmental programming to describe a permanent effect, whereas the more general term is used to describe nonpermanent impacts on the mammary gland. Despite this complexity, here we review the evidence that exposure to elevated temperature and humidity during late gestation can program reduced yields in the subsequent lactation, largely through effects at the mammary gland. Furthermore, we provide emerging evidence that adult capacity for milk synthesis can be programmed in the calf that dam is carrying by events during fetal life occurring 2 yr before. Specifically, calves born to dams that are heat stressed for the final 6 wk of gestation produce 19% less milk in lactation relative to calves from dams provided with evaporative cooling. Importantly, the increased milk yield in animals derived from dams under evaporative cooling occurred without a greater decline in BW that accompanies negative energy balance during early lactation. Therefore, the increase in milk production suggests an increase in the efficiency of conversion of feed to milk. These data indicate that a brief period of heat stress late in development reduces the physiological efficiency of the cow in a coordinated manner to result in a substantial decline in productivity. It is likely that this programming effect would be observed across genetic lines and result in poor sustainability of milk production. Milk will continue to be an important source of high-quality, human-edible food and technologies that improve the efficiency of production will be critical to enhance sustainability. These data provide compelling support for the concept that programming impacts on the dam and the developing fetus will play a role in optimizing the efficiency of production.