Identification of sow-specific risk factors for late pregnancy loss during the seasonal infertility period in pigs

Genetic parameters for automatically-measured vaginal temperature, respiration efficiency, and other thermotolerance indicators measured on lactating sows under heat stress conditions

BACKGROUND

Genetic selection based on direct indicators of heat stress could capture additional mechanisms that are involved in heat stress response and enable more accurate selection for more heat-tolerant individuals. Therefore, the main objectives of this study were to estimate genetic parameters for various heat stress indicators in a commercial population of Landrace × Large White lactating sows measured under heat stress conditions. The main indicators evaluated were: skin surface temperatures (SST), automatically-recorded vaginal temperature (TV), respiration rate (RR), panting score (PS), body condition score (BCS), hair density (HD), body size (BS), ear size, and respiration efficiency (Reff).

RESULTS

Traits based on TV presented moderate heritability estimates, ranging from 0.15 ± 0.02 to 0.29 ± 0.05. Low heritability estimates were found for SST traits (from 0.04 ± 0.01 to 0.06 ± 0.01), RR (0.06 ± 0.01), PS (0.05 0.01), and Reff (0.03 ± 0.01). Moderate to high heritability values were estimated for BCS (0.29 ± 0.04 for caliper measurements and 0.25 ± 0.04 for visual assessments), HD (0.25 ± 0.05), BS (0.33 ± 0.05), ear area (EA; 0.40 ± 0.09), and ear length (EL; 0.32 ± 0.07). High genetic correlations were estimated among SST traits (> 0.78) and among TV traits (> 0.75). Similarly, high genetic correlations were also estimated for RR with PS (0.87 ± 0.02), with BCS measures (0.92 ± 0.04), and with ear measures (0.95 ± 0.03). Low to moderate positive genetic correlations were estimated between SST and TV (from 0.25 ± 0.04 to 0.76 ± 0.07). Low genetic correlations were estimated between TV and BCS (from - 0.01 ± 0.08 to 0.06 ± 0.07). Respiration efficiency was estimated to be positively and moderately correlated with RR (0.36 ± 0.04), PS (0.56 ± 0.03), and BCS (0.56 ± 0.05 for caliper measurements and 0.50 ± 0.05 for the visual assessments). All other trait combinations were lowly genetically correlated.

CONCLUSIONS

A comprehensive landscape of heritabilities and genetic correlations for various thermotolerance indicators in lactating sows were estimated. All traits evaluated are under genetic control and heritable, with different magnitudes, indicating that genetic progress is possible for all of them. The genetic correlation estimates provide evidence for the complex relationships between these traits and confirm the importance of a sub-index of thermotolerance traits to improve heat tolerance in pigs.

Heat wave exposure impairs reproductive performance in primiparous sows and gilts in a tropical environment

We studied the effects of heat waves (HW), defined as three consecutive days with an ambient temperature ≥ 25 °C and a temperature and humidity index (THI) > 74, on the reproductive performance of sows. Meteorological data were obtained from the National Institute of Meteorology and reproductive data from a commercial farm with 51,578 inseminations and 49,103 pregnancies from September 5, 2013, to July 12, 2019. Sows were divided into the following groups according to the parity order: group 1 (sows that did not experience HW on the day of insemination) and group 2 (sows exposed to HW on the day of insemination). The percentage of days that pregnant sows were exposed to HW was calculated as 0 to 25% (1), 26 to 50% (2), 51 to 75% (3), and > 75% (4). Out of a total of 2137 days, there were 160 HW and more than 10 HW per month, except in May, June, and July. Gilts in group 2 showed a decrease in the percentage of gestation (98.21% and 98.78%, respectively, P = 0.0267) and the percentage of births compared with those in group 1 (95.53% and 96.61, respectively, P = 0.0065). Primiparous sows in group 2 had a higher percentage of abortions than gilts in group 1 (3.20% and 2.42%, respectively; P = 0.0334). Sows exposed to more than 50% HW during gestation produced more mummified piglets than sows exposed to less than 50% HW. The number of stillborn piglets was higher in sows exposed to temperatures above 25% HW during gestation. The occurrence of heat waves in gilts and primiparous sows impairs reproductive performance.

Context is key: Maternal immune responses to pig allogeneic embryos

Successful establishment of pregnancy includes the achievement of a state of immune tolerance toward the embryos (and placenta), where the well‐coordinated maternal immune system is capable of recognizing conceptus antigens while maintaining maternal defense against pathogens. In physiological pregnancies, following natural mating or artificial insemination (AI), the maternal immune system is exposed to the presence of hemi‐allogeneic embryos, that is, embryos containing maternal self‐antigens and foreign antigens from the paternal side. In this scenario, the hemi‐allogeneic embryo is recognized by the mother, but the immune system is locally modified to facilitate embryo implantation and pregnancy progression. Pig allogeneic pregnancies (with embryos containing both paternal and maternal material foreign to the recipient female), occur during embryo transfer (ET), with conspicuously high rates of embryonic death. Mortality mainly occurs during the peri‐attachment phase, suggesting that immune responses to allogeneic embryos are more complex and less efficient, hindering the conceptuses to survive to term. Reaching a similar maternal tolerance as in conventional breeding would render ET successful. The present review critically summarizes mechanisms of maternal immune recognition of pregnancy and factors associated with impaired maternal immune response to the presence of allogeneic embryos in the porcine species.

Genetic and phenotypic correlations between backfat thickness and weight at 28 weeks of age, and reproductive performance in primiparous Landrace sows raised under tropical conditions

Backfat thickness could reflect the energy reserve of female pigs that is required for their reproductivity, especially gilts that might be selected as replacements. In this study, genetic and phenotypic correlations between backfat thickness (BF) and body weight (BW) at 28 weeks of age, and reproduction traits were estimated. They were considered for the possibility of using BF at the pre-selective stage as an early indicator of sow's reproduction potential. Pedigree information, BF and BW at 28 weeks of age, age at first farrowing (AFF), transformed proportion of piglet loss at birth (tPL), and transformed weaning to first service interval (tWSI) of 806 primiparous Landrace sows were used to estimate the variance components by a restricted maximum likelihood procedure with an average information algorithm for multivariate analysis. The genetic correlation between BF and BW was 0.70 ± 0.13. Both BF and BW had a negative genetic correlation with AFF but not with tWSI. Genetic correlation estimates between tPL and other traits were unclear due to high standard error. The genetic correlation between AFF and tWSI was 0.78 ± 0.36. There were 19.35% of sires, 26.34% of dams, and 25.81% of sows that had preferable estimated breeding values for BF, BW, AFF, and WSI. These values indicated the feasibility of using selection index to improve BF and BW at the pre-selective stage and reduce AFF and tWSI of replacement gilt simultaneously. The estimation of genetic correlation between PL and other traits warrants further study in larger populations.

Timing and temperature thresholds of heat stress effects on fertility performance of different parity sows in Spanish herds

High temperature is an environmental factor that impairs sow fertility. In this study, we identified the critical weeks for heat stress effects on aspects of fertility performance, namely weaning-to-first-service interval (WSI) and farrowing rate (FR). We also examined the threshold temperatures above which the fertility performance deteriorated and whether there were any differences between parities regarding heat stress effects or thresholds. Performance data of sows in 142 herds from 2011 to 2016 were matched to appropriate weekly averaged daily maximum temperatures (Tmax) from weather stations close to the herds. Two types of ratios (i.e., ratio for WSI and odds ratio for FR) were used to identify the critical weeks for heat stress by comparing the respective measures for two sow groups based on Tmax in different weeks around weaning or service events. The ratios for WSI were calculated between groups of sows exposed to Tmax ≥ 27 °C or <27 °C in each week before weaning, with the Tmax cutoff value based on a recent review study. Similarly, the odds ratios for FR for the two groups were calculated in weeks around service. The weeks with the largest differences in the fertility measures between the two Tmax groups (i.e., the highest ratio for WSI and the lowest odds ratio for FR) were considered to be the critical weeks for heat stress. Also, piecewise models with different breakpoints were constructed to identify the threshold Tmax in the critical week. The breakpoint in the best-fit model was considered to be the threshold Tmax. The highest ratios for WSI were obtained at 1 to 3 wk before weaning in parity 1 and 2 or higher sow groups. The threshold Tmax leading to prolonged WSI was 17 °C for parity 1 sows and 25 °C for parity 2 or higher sows. Increasing Tmax by 10 °C above these thresholds increased WSI by 0.65, and 0.33 to 0.35 d, respectively (P < 0.01). For FR, the lowest odds ratios were obtained at 2 to 3 wk before service in parity 0, 1, and 2 or higher sow groups. The threshold Tmax leading to reductions in FR was 20, 21, and 24 to 25 °C for parity 0, 1, and 2 or higher sow groups, respectively. Increasing Tmax by 10 °C above these thresholds decreased FR by 3.0%, 4.3%, and 1.9% to 2.8%, respectively (P < 0.01). These results indicate that the critical weeks for heat stress were 2 to 3 wk before service for FR and 1 to 3 wk before weaning for WSI. The decreases in fertility performance in parity 0 to 1 sows started at temperatures 3 to 8 °C lower than in parity 2 or higher sows.

Controlled elevated temperatures during early-mid gestation cause placental insufficiency and implications for fetal growth in pregnant pigs

It is known that pig offspring born from pregnant pigs exposed to elevated ambient temperatures during gestation have altered phenotypes, possibly due to placental insufficiency and impaired fetal growth. Therefore, the objective of this study was to quantify the effect of maternal heat exposure during early-mid gestation, when pig placentae grow heavily, on placental and fetal development. Fifteen pregnant pigs were allocated to thermoneutral (TN; 20 °C; n = 7) or cyclic elevated temperature conditions (ET; 28 to 33 °C; n = 8) from d40 to d60 of gestation. Following euthanasia of the pigs on d60, placental and fetal morphometry and biochemistry were measured. Compared to TN fetuses, ET fetuses had increased (P = 0.041) placental weights and a lower (P = 0.013) placental efficiency (fetal/placental weight), although fetal weights were not significantly different. Fetuses from ET pigs had reduced (P = 0.032) M. longissimus fibre number density and a thicker (P = 0.017) placental epithelial layer compared to their TN counterparts. Elevated temperatures decreased (P = 0.026) placental mRNA expression of a glucose transporter (GLUT-3) and increased (P = 0.037) placental IGF-2 mRNA expression. In conclusion, controlled elevated temperatures between d40 to d60 of gestation reduced pig placental efficiency, resulting in compensatory growth of the placentae to maintain fetal development. Placental insufficiency during early-mid gestation may have implications for fetal development, possibly causing a long-term phenotypic change of the progeny.

Biology of heat stress; the nexus between intestinal hyperpermeability and swine reproduction

Unfavorable weather conditions are one of the largest constraints to maximizing farm animal productivity. Heat stress (HS), in particular, compromises almost every metric of profitability and this is especially apparent in the grow-finish and reproductive aspects of the swine industry. Suboptimal production during HS was traditionally thought to result from hypophagia. However, independent of inadequate nutrient consumption, HS affects a plethora of endocrine, physiological, metabolic, circulatory, and immunological variables. Whether these changes are homeorhetic strategies to survive the heat load or are pathological remains unclear, nor is it understood if they temporally occur by coincidence or if they are chronologically causal. However, mounting evidence suggest that the origin of the aforementioned changes lie at the gastrointestinal tract. Heat stress compromises intestinal barrier integrity, and increased appearance of luminal contents in circulation causes local and systemic inflammatory responses. The resulting immune activation is seemingly the epicenter to many, if not most of the negative consequences HS has on reproduction, growth, and lactation. Interestingly, thermoregulatory and production responses to HS are only marginally related. In other words, increased body temperature indices poorly predict decreases in productivity. Further, HS induced malnutrition is also a surprisingly inaccurate predictor of productivity. Thus, selecting animals with a "heat tolerant" phenotype based solely or separately on thermoregulatory capacity or production may not ultimately increase resilience. Describing the physiology and mechanisms that underpin how HS jeopardizes animal performance is critical for developing approaches to ameliorate current production issues and requisite for generating future strategies (genetic, managerial, nutritional, and pharmaceutical) aimed at optimizing animal well-being, and improving the sustainable production of high-quality protein for human consumption.

Measurements of circulating progesterone and estrone sulfate concentrations as a diagnostic and prognostic tool in porcine pregnancy revisited

The main goal of this study was to examine the utility of measuring systemic concentrations of steroid hormones, namely progesterone (P₄) and estrone sulfate (E₁S), for monitoring the progression of porcine pregnancy and predicting sow fertility. There were 3 subsets of artificially inseminated (AI'd) sows used in the present experiments: (i) animals sacrificed on gestational day 20 (gd20; n = 16) or (ii) gd50 (n = 16; Experiment 1), and (iii) animals maintained throughout pregnancy (n = 24; Experiment 2). Blood samples (10 mL) were drawn from the orbital sinus and the endocrine data determined at different time points around ovulation/artificial insemination (gd0 (first AI), gd1 (second AI), and gd2) and maternal recognition of pregnancy (gd11), as well as on gd20 and gd50 (during 2 periods of increased embryonic/fetal mortality in swine) were examined for correlations with the numbers of healthy, arrested, and reabsorbing embryos (Experiment 1) or with the number of live, stillborn, and mummified piglets recorded at farrowing (Experiment 2). No correlations were recorded between circulating concentrations of both steroids and the numbers of healthy, arresting, or reabsorbing conceptuses on gd20 or 50 (Experiment 1). The number of corpora lutea (CL) was directly related to the number of healthy embryos/conceptuses on gd20 and 50 (r = 0.71, P = 0.007 and r = 0.76, P = 0.0007, respectively) and the number of arresting embryos on gd20 (r = 0.54, P = 0.05), and negatively correlated with the number of reabsorbing embryos on gd20 (r = -0.53, P = 0.05). In Experiment 2, circulating P₄ concentrations on gd11 related directly to the number of live-born piglets (r = 0.46, P < 0.04). Systemic E₁S concentrations on gd0, gd1, gd2 and gd50 were correlated with the number of mummified conceptuses recorded at farrowing (r = 0.50, P = 0.03; r = 0.59, P = 0.01; r = 0.48, P = 0.04; and r = 0.56, P = 0.01, respectively) and plasma concentrations of E₁S on gd20 related directly to the number of stillborn piglets (r = 0.60, P = 0.02). In summary, the number of CL on gd20 and 50 is a reliable marker of embryonic/fetal pig status. Measurements of P₄ and E₁S on gd20 and 50 showed limited diagnostic value (ie, were not indicative of the number of healthy and abnormally developing embryos/fetuses). However, measurements of circulating P₄ and E₁S concentrations during the periconceptional period and in the early/mid-pregnancy of sows have the makings of a practical method to predict gestational outcomes.

Heat stress during the luteal phase decreases luteal size but does not affect circulating progesterone in gilts1

Heat stress (HS) occurs when heat dissipation mechanisms are insufficient to maintain euthermia, and it is associated with seasonal infertility (SI), which manifests as smaller litters, longer wean-to-estrus interval, increased abortions, and reduced conception rates. To understand HS-induced mechanisms underlying SI, crossbred post-pubertal gilts (167 ± 10 kg; n = 14) experienced either thermal neutral (TN, 20 ± 1 °C, n = 7) or cyclical HS (35 ± 1 °C for 12 h and 31.6 °C for 12 h, n = 7) conditions from 2 to 12 d post-estrus (dpe). Estrous cycles were synchronized via altrenogest administration for 14 d, phenotypic manifestation of estrus was observed and gilts were assigned to experimental treatment. Gilts were limit fed 2.7 kg daily with ad libitum water access. Blood was collected at 0, 4, 8, and 12 dpe via jugular venipuncture and animals were humanely euthanized at 12 dpe. The corpora lutea (CL) width were measured via digital calipers on both ovaries, and CL from one ovary were excised, weighed, and protein and steroid abundance analyzed via western blotting and ELISA, respectively. Relative to TN, HS increased (P < 0.01) rectal temperature and respiration rates and reduced (P < 0.01) feed intake. The CL from HS ovaries were reduced in diameter (P < 0.05) and weight (P < 0.01) relative to those from TN animals. No difference (P = 0.38) in CL or serum progesterone concentrations between groups was observed at any time point, though at 12 dpe the serum progesterone:CL weight was increased (P < 0.10) by HS. No treatment differences (P = 0.84) in circulating insulin were observed. Luteal protein abundance of steroid acute regulatory protein, 3 beta-hydroxysteroid, or prostaglandin F2α receptor were not different between treatments (P = 0.73). Taken together, these data demonstrate that the CL mass is HS sensitive, but this phenotype does not appear to be explained by the metrics evaluated herein. Regardless, HS-induced decreased CL size may have important implications to pig SI and warrants additional attention.

Relationship between seasons and pregnancy rates during intrauterine insemination. A historical cohort

BACKGROUND

The underlying cause of seasonal infertility in humans is unclear, but is likely to be -multifactorial.

OBJECTIVE

The aim of our study was to compare the pregnancy rates among infertile women who underwent induced ovulation and intrauterine insemination (IUI) with the season in which the fertility treatment was performed.

DESIGN AND SETTING

This retrospective cohort study was conducted on 466 patients who were treated in the reproductive endocrinology and infertility outpatient clinic of a tertiary-level women's healthcare and maternity hospital.

METHODS

Retrospective demographic, hormonal and ultrasonographic data were obtained from the patients' medical records. Clomiphene citrate or gonadotropin medications were used for induced ovulation. The patients were divided into four groups according to the season (spring, winter, autumn and summer) in which fertility treatment was received. Clinical pregnancy rates were calculated and compared between these four groups.

RESULTS

There were no significant differences between the seasonal groups in terms of age, infertility type, ovarian reserve tests, duration of infertility, medications used or length of stimulation. A total of 337 patients (72.3%) were treated with clomiphene citrate and 129 (27.7%) with gonadotropin; no significant difference between these two groups was observed. The clinical pregnancy rates for the spring, winter, autumn and summer groups were 15.6% (n = 24), 8.6% (n = 9), 11.5% (n = 13) and 7.4% (n = 7), respectively (P = 0.174).

CONCLUSIONS

Although the spring group had the highest pregnancy rate, the rates of successful IUI did not differ significantly between the seasonal groups.

Characterizing the acute heat stress response in gilts: II. Assessing repeatability and association with fertility

Mitigating heat stress (HS) in swine production is important as it detrimentally affects multiple aspects of overall animal production efficiency. Study objectives were to determine if gilts characterized as tolerant (TOL) or susceptible (SUS) in response to HS maintain that phenotype later in life and if that phenotype influences reproductive ability during HS. Individual gilts identified as TOL (n = 50) or SUS (n = 50) from a prepubertal HS challenge were selected based on their rectal temperature (TR) during acute HS. The study consisted of 4 experimental periods (P). During P0 (2 d), all pigs were exposed to thermoneutral (TN) conditions (21.1 °C). During P1 (14 d), all gilts received Matrix (15 mg altrenogest per day) to synchronize estrus, and were maintained in TN conditions. During P2 (9 d), Matrix supplementation was terminated and gilts were subjected to diurnal HS with ambient temperatures set at 35 °C from 1000 to 2200 h and 21 °C from 2200 to 1000 h. Also during P2 gilts underwent estrus detection and artificial insemination. During P3 gilts were housed in TN conditions for 41 d at which they were sacrificed and reproductive tracts were collected. During the last 2 d of P1 and throughout the entirety of P2, TR and skin temperature (TS) were recorded. During P2, SUS had increased TR relative to TOL pigs during P2 (0.27 °C; P < 0.01). Overall, uterine wet weight, ovarian weight, corpora lutea (CL) count, and embryo survival were 5.6 ± 0.1 kg, 21.6 ± 0.3 g, 17.8 ± 0.3 CLs, and 79 ± 2%, respectively, and not influenced by prepubertal HS tolerance classification (P ≥ 0.37). Tolerant gilts had a longer return-to-estrus (6.1 vs. 5.5 d, respectively; P = 0.01) following altrenogest withdrawal and tended to have larger CL diameters (10.3 vs. 10.1 mm; P = 0.06) compared to SUS gilts. Fetal weight (25.4 vs. 23.6 g; P = 0.01) and fetal crown-rump length (74.8 vs. 72.8 mm; P < 0.01) were higher in gilts previously classified as SUS compared to those previously classified as TOL. Additionally, neither litter size nor the number of fetuses detected as a percentage of ovulations was influenced by classification. In summary, SUS gilts had a shorter return-to-estrus, increased fetus size, and tended to have smaller CL diameters compared to TOL gilts. Additionally, SUS gilts also retained their inability to maintain euthermia postpubertally relative to TOL gilts. In conclusion, there appeared to be little reproductive advantage of maintaining a lower TR during HS.

Impact of heat stress during the follicular phase on porcine ovarian steroidogenic and phosphatidylinositol-3 signaling

Environmental conditions that impede heat dissipation and increase body temperature cause heat stress (HS). The study objective was to evaluate impacts of HS on the follicular phase of the estrous cycle. Postpubertal gilts (126.0 ± 21.6 kg) were orally administered altrenogest to synchronize estrus, and subjected to either 5 d of thermal-neutral (TN; 20.3 ± 0.5 °C; n = 6) or cyclical HS (25.4 - 31.9 °C; n = 6) conditions during the follicular phase preceding behavioral estrus. On d 5, blood samples were obtained, gilts were euthanized, and ovaries collected. Fluid from dominant follicles was aspirated and ovarian protein homogenates prepared for protein abundance analysis. HS decreased feed intake (22%; P = 0.03) and while plasma insulin levels did not differ, the insulin:feed intake ratio was increased 3-fold by HS (P = 0.02). Insulin receptor protein abundance was increased (29%; P < 0.01), but insulin receptor substrate 1, total and phosphorylated protein kinase B, superoxide dismutase 1, and acyloxyacyl hydrolase protein abundance were unaffected by HS (P > 0.05). Plasma and follicular fluid 17β-estradiol, progesterone, and lipopolysaccharide-binding protein concentrations as well as abundance of steroid acute regulatory protein, cytochrome P450 19A1, and multidrug resistance-associated protein 1 were not affected by HS (P > 0.05). HS increased estrogen sulfotransferase protein abundance (44%; P = 0.02), toll-like receptor 4 (36%; P = 0.05), and phosphorylated REL-associated protein (31%; P = 0.02). Regardless of treatment, toll-like receptor 4 protein was localized to mural granulosa cells in the porcine ovary. In conclusion, HS altered ovarian signaling in postpubertal gilts during their follicular phase in ways that likely contributes to seasonal infertility.

Physiological mechanisms through which heat stress compromises reproduction in pigs

Seasonal variations in environmental temperatures impose added stress on domestic species bred for economically important production traits. These heat-mediated stressors vary on a seasonal, daily, or spatial scale, and negatively impact behavior and reduce feed intake and growth rate, which inevitably lead to reduced herd productivity. The seasonal infertility observed in domestic swine is primarily characterized by depressed reproductive performance, which manifests as delayed puberty onset, reduced farrowing rates, and extended weaning-to-estrus intervals. Understanding the effects of heat stress at the organismal, cellular, and molecular level is a prerequisite to identifying mitigation strategies that should reduce the economic burden of compromised reproduction. In this review, we discuss the effect of heat stress on an animal's ability to maintain homeostasis in multiple systems via several hypothalamic-pituitary-end organ axes. Additionally, we discuss our understanding of epigenetic programming and how hyperthermia experienced in utero influences industry-relevant postnatal phenotypes. Further, we highlight the recent recognized mechanisms by which distant tissues and organs may molecularly communicate via extracellular vesicles, a potentially novel mechanism contributing to the heat-stress response.

Culling in served females and farrowed sows at consecutive parities in Spanish pig herds

Background

The objectives of our study were 1) to characterize culling and retention patterns in parities 0 to 6 in served females and farrowed sows in two herd groups, and 2) to quantify the factors associated with by-parity culling risks for both groups in commercial herds. Lifetime data from first-service to removal included 465,947 service records of 94,691 females served between 2008 and 2013 in 98 Spanish herds. Herds were categorized into two groups based on the upper 25th percentile of the herd means of annualized lifetime pigs weaned per sow: high-performing (> 24.7 pigs) and ordinary herds (≤ 24.7 pigs). Two-level log-binomial regression models were used to examine risk factors and relative risk ratios associated with by-parity culling risks.

Results

Mean by-parity culling risks (± SE) for served females and farrowed sows were 5.9 ± 0.03 and 12.4 ± 0.05%, respectively. Increased culling risks were associated with sows that farrowed 8 or fewer pigs born alive (PBA). Also, farrowed sows in high-performing herds in parities 2 to 6 had 1.5–5.6% higher culling risk than equivalent parity sows in ordinary herds (P < 0.05). Furthermore, sows in parities 1 to 6 that farrowed 3 or more stillborn piglets had 2.2–4.8% higher culling risk than for sows that did not farrow any stillborn piglets (P < 0.05). For served sows, culling risk in parity 1 to 6 sows with a weaning-to-first-service interval (WSI) of 7 days or more were 2.2–3.9% higher than equivalent parity sows with WSI 0–6 days (P < 0.05). With regard to relative risk ratios, served sows with WSI 7 days or more were 1.56–1.81 times more likely to be culled than those with WSI 0–6 days.

Conclusion

Producers should reduce non-productive days by culling sows after weaning, instead of after service or during pregnancy. Also, producers should pay special attention to sows farrowing stillborn piglets or having prolonged WSI, and reconsider culling policy for mid-parity sows when they farrow 8 or fewer PBA.

Electronic supplementary material

The online version of this article (10.1186/s40813-018-0080-y) contains supplementary material, which is available to authorized users.

Seasonal infertility in pigs: what have we achieved and where are we up to?

The most common manifestations of seasonal infertility are delayed puberty, prolonged weaning to oestrus intervals and a reduced farrowing rate brought about by increased returns to oestrus, including a proportionally higher incidence of irregular returns to oestrus. Over the past 40 years, there has been considerable investment in Australian pig research that has generated extensive knowledge about the physiological mechanisms behind seasonal infertility. While some of the physiological mechanisms allowing the expression of seasonal infertility still remain unclear, a number of possible intervention strategies have been developed and investigated to ameliorate the effects of seasonal infertility in commercial production. For commercial pork producers, there is considerable information available that is based on both research and practical experience, which the farmers can use to identify strategies to minimise the impact of seasonal infertility on the farm. The industry still provides some support to research and development efforts to address seasonal infertility, although, in the future, it may be more targeted to identifying interventions to ameliorate the impact of seasonal infertility in affected herds, rather than undertaking intensive studies into the possible mechanisms and reasons behind this very complex syndrome.

Recurrence patterns and factors associated with regular, irregular, and late return to service of female pigs and their lifetime performance on southern European farms

A return-to-service occurrence increases nonproductive days of female pigs and decreases herd productivity. The objectives of the present study were 1) to characterize 3 return types based on reservice intervals in female pigs on southern European farms, 2) to determine return risks and recurrence patterns for these types of returns, and 3) to assess lifetime performance of females with the 3 types of returns. We analyzed 653,528 service records and lifetime records of 114,906 females on 125 farms between 2008 and 2013. Reservice intervals were categorized into 3 groups: regular returns (RR: 18 to 24 d), irregular returns (IR: 25 to 38 d), and late returns (LR: 39 d or later). Multilevel generalized linear models were applied to the data. There were 64,385 reservice records (9.9%), with mean risks of RR, IR, and LR per service (±SEM) of 3.6% ± 0.06%, 2.5% ± 0.05%, and 3.0% ± 0.06%, respectively. Of the 43,931 first-returned females, 32.7% had a second return in the same or later parity. Also, 18.8%, 10.2%, and 11.6% of females that had RR, IR, and LR first returns, respectively, had a second return of the same return type. Summer servicing was associated with greater RR, IR, and LR risks in gilts. Also, increased gilt age at first mating was associated with RR ( = 0.03) and LR risk ( < 0.01) but not with IR risk ( = 0.53). For sows, factors associated with greater RR, IR, or LR risks were summer servicing, lower parity, farrowing more stillborn piglets, and having a weaning-to-first-mating interval of 7 d or more ( < 0.01). In lifetime, 33.5% of serviced females had 1 or more returns. These returned females had 41.5 more lifetime nonproductive days than nonreturn females but also 1.9 more lifetime pigs born alive ( < 0.01). We recommend that producers closely monitor females in high-risk groups to reduce their return-to-service intervals.

Analysis of reasons for sow culling and seasonal effects on reproductive disorders in Southern China

Sow culling rates have a direct correlation to the economic efficiency of both breeding herd and commercial herd. Analyzing the reasons of sow culling could lead to improve production efficiency of farms. This study, which involved inspections of four farms in Southern China, manifested that the rate of unplanned sow-culling has reached to 78.1% in total culls. In which, reproductive disorders and lameness accounted for 35.3% and 22.5%, respectively. The average parity of culled sows was 4.9, but a high proportion (19.6%) of sows was culled at their first parity. Anestrus, the highest proportion of reproductive disorders, accounting for 47.7%, occurred in July followed by June (17.7% and 11.8% respectively). The frequency of culling due to reproductive disorders in Southern China was higher than others regions, which suffered from the high temperature and humidity in Southern China. The frequency of sow culling reached its peak in the summer, specifically in July (12.3%), which means that hot weather has an adverse effect on sow culling. Pig farmers should take effective measures to reduce heat stress as nutrition strategies or cooling systems in gestation and/or farrowing sow herds between May and July in Southern China.

Physiological consequences of heat stress in pigs

Heat stress negatively influences the global pork industry and undermines genetic, nutritional, management and pharmaceutical advances in management, feed and reproductive efficiency. Specifically, heat stress-induced economic losses result from poor sow performance, reduced and inconsistent growth, decreased carcass quality, mortality, morbidity, and processing issues caused by less rigid adipose tissue (also known as flimsy fat). When environmental conditions exceed the pig’s thermal neutral zone, nutrients are diverted from product synthesis (meat, fetus, milk) to body temperature maintenance thereby compromising efficiency. Unfortunately, genetic selection for both increased litter size and leaner phenotypes decreases pigs’ tolerance to heat, as enhanced fetal development and protein accretion results in increased basal heat production. Additionally, research has demonstrated that in utero heat stress negatively and permanently alters post-natal body temperature and body composition and both variables represent an underappreciated consequence of heat stress. Advances in management (i.e. cooling systems) have partially alleviated the negative impacts of heat stress, but productivity continues to decline during the warm summer months. The detrimental effects of heat stress on animal welfare and production will likely become more of an issue in regions most affected by continued predictions for climate change, with some models forecasting extreme summer conditions in key animal-producing areas of the globe. Therefore, heat stress is likely one of the primary factors limiting profitable animal protein production and will certainly continue to compromise food security (especially in emerging countries) and regionalise pork production in developed countries. Thus, there is an urgent need to have a better understanding of how heat stress reduces animal productivity. Defining the biology of how heat stress jeopardises animal performance is critical in developing approaches (genetic, managerial, nutritional and pharmaceutical) to ameliorate current production issues and improve animal wellbeing and performance.

The use of oxytocin in liquid semen doses to reduce seasonal fluctuations in the reproductive performance of sows and improve litter parameters--a 2-year study

The objective of the present research was to eliminate seasonal fluctuations in year-round reproductive performance of sows and to improve litter parameters by administration of oxytocin into liquid semen insemination doses. A 2-year experiment was performed on crossbreed sows, Polish Large White × Polish Landrace, which were partitioned into two groups: control, insemination without any modification with 100 mL semen doses and oxytocin, insemination with 100 mL semen doses to which 5 IU of oxytocin was added just before insemination. A total of 10,486 inseminations were made. The farrowing rate and obtained litter parameters, including the effect of season, were analyzed. For each litter, the following factors were defined: average litter size, percentage of fetal death and mummified piglets, average piglet birth weight, percentage of piglet mortality, fecundity index, average number of piglets weaned, weaned piglet weight, and daily gain. Sows presented a positive reaction to the experimental factor. A statistically higher farrowing rate for oxytocin group in summer and autumn seasons was confirmed (P ≤ 0.01). Regardless of the season, a higher average litter size was observed in the oxytocin group with the most evident differences for winter, spring (P ≤ 0.01), and summer (P ≤ 0.05). The effect of oxytocin on the percentage of fetal death and mummified piglets born was not confirmed statistically except for winter. Analyzing the fecundity index, higher values were obtained for the oxytocin group in all seasons (P ≤ 0.01), including the lowest difference between groups for winter (51.43) and the highest for summer (100.61). A higher average birth piglet weight and weaned piglet weight were recorded for the oxytocin group in all seasons. The highest differences in birth piglet weight between groups were noted for spring (0.22 kg; P ≤ 0.01) and winter (0.17 kg; P ≤ 0.05) and in weaned piglet weight for winter and spring (0.58 kg and 0.52 kg; for both, P ≤ 0.01). The greatest daily gains were observed in the winter season (P ≤ 0.05) in favor of oxytocin. On the basis of the presented results, it should be noted that the use of oxytocin into insemination doses improves the farrowing rate and other parameters of the reproductive performance of sows. In the absence of negative effects, year-round insemination with oxytocin addition into seminal doses is recommended, which effectively improves the production performance and reduces the problem of seasonality in reproduction.

Relevance of ovarian follicular development to the seasonal impairment of fertility in weaned sows

A field study was conducted to estimate seasonal differences in follicular development in weaned sows and to evaluate the implication of these differences on seasonal infertility. A total of 110 sows were selected at weaning during winter-spring (WS, n=58) and summer-autumn (SA, n=52). Ovaries were scanned once daily from weaning to the onset of oestrus and twice daily from then until ovulation. Six sows during WS were removed from study for not showing growing follicles at weaning. Oestrus was evaluated twice daily from day 1 after weaning to day 14 post-weaning. One of 52 (1.9%) sows in WS and 9/52 (17.3%) in SA showed no signs of oestrus within 14 days of weaning (P<0.05). The diameters of the follicles at weaning, at the onset of oestrus and just before ovulation were smaller (P<0.01) in SA sows than in WS sows. There were fewer follicles in SA sows than in WS sows just before ovulation (P<0.05). Fifty of 51 (98.0%) sows in WS and 31/43 (72.1%) sows in SA experienced a weaning-to-oestrus interval (WOI) of 3-6 days (P<0.05). Fifty-one of 52 (98.1%) sows in WS and 43/52 (82.7%) sows in SA were inseminated; the percentage of pregnant sows that failed to farrow was lower in WS (1/51, 2.0%) than in SA (5/43, 11.6%; P<0.05). The percentage of farrowed sows was greater in WS (46/51, 90.2%) than in SA (32/43, 74.4%; P<0.05). Sows in WS had on average 1.5 more piglets than sows in SA (P<0.05). Sows with a WOI of 3-6 days had lower rates of pregnancy losses (P<0.05) and higher farrowing percentages (P<0.01) than those with a WOI>6 days, irrespective of season.

Differences in the metabolomic signatures of porcine follicular fluid collected from environments associated with good and poor oocyte quality

The microenvironment of the developing follicle is critical to the acquisition of oocyte developmental competence, which is influenced by several factors including follicle size and season. The aim of this study was to characterise the metabolomic signatures of porcine follicular fluid (FF) collected from good and poor follicular environments, using high-resolution proton nuclear magnetic resonance (1H-NMR) spectroscopy. Sow ovaries were collected at slaughter, 4 days after weaning, in summer and winter. The contents of small (3–4 mm) and large (5–8 mm) diameter follicles were aspirated and pooled separately for each ovary pair. Groups classified as summer-small (n=8), summer-large (n=15), winter-small (n=9) and winter-large (n=15) were analysed by1H-NMR spectroscopy. The concentrations of 11 metabolites differed due to follicle size alone (P<0.05), including glucose, lactate, hypoxanthine and five amino acids. The concentrations of all these metabolites, except for glucose, were lower in large FF compared with small FF. Significant interaction effects of follicle size and season were found for the concentrations of glutamate, glycine,N-acetyl groups and uridine. Succinate was the only metabolite that differed in concentration due to season alone (P<0.05). The FF levels of progesterone, androstenedione and oestradiol were correlated with the concentrations of most of the metabolites examined. The results indicate that there is a distinct shift in follicular glucose metabolism as follicles increase in diameter and suggest that follicular cells may be more vulnerable to oxidative stress during the summer months. Our findings demonstrate the power of1H-NMR spectroscopy to expand our understanding of the dynamic and complex microenvironment of the developing follicle.

Seasonal variation in the ovarian function of sows

The modern domestic sow exhibits a period of impaired reproductive performance known as seasonal infertility during the late summer and early autumn months. A reduction in farrowing rate due to pregnancy loss is the most economically significant manifestation of this phenomenon. Presently, little is known of the aetiology of seasonal pregnancy loss in the pig. Recent findings represent a major advancement in the understanding of sow reproductive physiology and implicate poor oocyte developmental competence as a contributing factor to pregnancy loss during the seasonal infertility period. It has also been demonstrated that ovarian activity is depressed during the seasonal infertility period. The reduction in oocyte quality is associated with decreased levels of progesterone in follicular fluid during final oocyte maturation in vivo. The recent identification of sow-specific risk factors, such as parity for late pregnancy loss, should improve breeding herd efficiency by allowing producers to tailor management interventions and/or culling protocols that target animals identified as having a greater risk of late pregnancy loss during the seasonal infertility period.

Oocyte developmental competence is reduced in sows during the seasonal infertility period

The modern domestic sow exhibits a period of impaired reproductive performance during the late summer and early autumn months, known as 'seasonal infertility'. A reduction in farrowing rate due to pregnancy loss is the most economically important manifestation of seasonal infertility. The aim of the present study was to determine whether there are changes in oocyte developmental competence associated with season. Ovaries were collected in pairs from sows sourced from commercial piggeries and slaughtered 4 days after weaning during winter and summer-autumn. Following oocyte IVM and parthenogenetic activation, the ability of oocytes from large follicles to form blastocysts was greater in winter (54.94 ± 6.11%) than in summer (21.09 ± 5.59%). During winter, the proportion of oocytes developing to the blastocyst stage from large follicles was significantly higher (54.94 ± 6.11%) than those oocytes from small follicles (23.17 ± 6.02%). There was no effect of season on the proportion of oocytes developing to the blastocyst stage from small follicles. There was no effect of follicle size on blastocyst formation from those oocytes recovered during summer. Blastocysts derived from small follicles during summer had the lowest number of cells (24.25 ± 1.48) compared with blastocysts derived from large follicles during winter (37.5 ± 1.3; P < 0.05). The mean progesterone concentration in follicular fluid collected from small follicles was greater in winter than summer (1235.55 ± 164.47 v. 701.3 ± 115.5 nmol L(-1), respectively; P < 0.001). The mean progesterone concentration in the follicular fluid of large follicles was also greater in winter than in summer (2470.9 ± 169.1 v. 1469.2 ± 156.5 nmol L(-1), respectively; P < 0.001). Regression analysis revealed a positive correlation between progesterone concentration and oocyte developmental competence. The results indicate that porcine oocytes fail to reach their full developmental potential during the period of seasonal infertility, suggesting that the pregnancy losses observed at this time of year may be due to reduced oocyte developmental competence.

Seasonal infertility in sows: a five year field study to analyze the relative roles of heat stress and photoperiod

The objective of this study was to analyze the relative roles of high temperature and photoperiod as environmental factors of seasonal infertility in swine. The results of five years (2003-2007) of ultrasound pregnancy diagnosis carried out in 266 indoor farms were analyzed. For all farms, the data covered the entire study period. The farms were situated in four French regions. The data of 22,773 batches and 610,117 sows were included. Seasonal infertility was defined as the relative difference between the fertility rate in 'summer' (inseminations in weeks 25-42) and 'winter' (inseminations in weeks 1-18 of the same year). In each region, two meteorological variables were defined, based on the data of a reference weather station: the number of hot days (maximum temperature >or= 25 degrees C) and tropical days (maximum temperature >or= 32 degrees C and minimum temperature >or= 18 degrees C). The mean fertility was 85%. The median seasonal infertility was 2.8% and more than 7.1% for a quarter of farms. Seasonal infertility did not vary with areas or baseline fertility (defined for each studied farm as the average winter fertility over five years). Seasonal infertility differed with the year (p<0.001). Seasonal infertility was significantly higher during 2003 than in the other four years, which did not differ among each other. In the four regions, 2003 was the year with the highest number of hot days and 2007 with the least. Our study strengthens the hypothesis of a prominent role of photoperiod in seasonal infertility and of an additional role of heat stress the hottest years.