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Cited by 19Effects of Environmental Stressors on LivestockThermoregulation and physiological responsesAnimal Behavior and Welfare Studies

Modeling of Heat Stress in Sows—Part 1: Establishment of the Prediction Model for the Equivalent Temperature Index of the Sows

Open access
Cao, Mengbing, Zong, Chao, Wang, Xiaoshuai, Teng, Guanghui, Zhuang, Yanrong, Lei, Kaidong·2021·Animals
DOI 10.3390/ani11051472PMC PMC8161218
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Abstract

Heat stress affects the estrus time and conception rate of sows. Compared with other life stages of pigs, sows are more susceptible to heat stress because of their increased heat production. Various indicators can be found in the literature assessing the level of heat stress in pigs. However, none of them is specific to assess the sows’ thermal condition. Moreover, thermal indices are mainly developed by considering partial environment parameters, and there is no interaction between the index and the animal’s physiological response. Therefore, this study aims to develop a thermal index specified for sows, called equivalent temperature index for sows (ETIS), which includes parameters of air temperature, relative humidity and air velocity. Based on the heat transfer characteristics of sows, multiple regression analysis is used to combine air temperature, relative humidity and air velocity. Environmental data are used as independent variables, and physiological parameters are used as dependent variables. In 1029 sets of data, 70% of the data is used as the training set, and 30% of the data is used as the test set to create and develop a new thermal index. According to the correlation equation between ETIS and temperature-humidity index (THI), combined with the threshold of THI, ETIS was divided into thresholds. The results show that the ETIS heat stress threshold is classified as follows: suitable temperature ETIS < 33.1 °C, mild temperature 33.1 °C ≤ ETIS < 34.5 °C, moderate stress temperature 34.5 °C ≤ ETIS < 35.9 °C, and severe temperature ETIS ≥ 35.9 °C. The ETIS model can predict the sows’ physiological response in a good manner. The correlation coefficients R of skin temperature was 0.82. Compared to early developed thermal indices, ETIS has the best predictive effect on skin temperature. This index could be a useful tool for assessing the thermal environment to ensure thermal comfort for sows.

AI snapshot

Written from the paper’s full text.

TL;DR

This study develops an equivalent temperature index for sows (ETIS) by combining air temperature, relative humidity, air velocity, floor heat conduction, and radiation effects, then validates it against sow skin temperature. ETIS showed the best prediction of skin temperature among compared thermal indices and was divided into heat-stress thresholds based on THI.

Key findings

  • ETIS was defined with thresholds: suitable ETIS < 33.1 °C, mild 33.1 °C ≤ ETIS < 34.5 °C, moderate 34.5 °C ≤ ETIS < 35.9 °C, and severe ETIS ≥ 35.9 °C.
  • ETIS correlated strongly with THI (R² = 0.90) and with sow skin temperature (R² = 0.67 in conclusions; R = 0.82 reported for skin temperature prediction).
  • In model validation, the test data set gave R² = 0.7317 for ETIS versus skin temperature, while training data gave R² = 0.6341.
  • Compared with THI, BGHI, ET, and H, ETIS had the best predictive effect on skin temperature.

Methods

  • The study used data from 30 non-pregnant multiparous sows (Large White × Landrace crossbreeds) in a sow barn at the National Feed Research Center of China Agricultural University from June to August 2018; data were collected on 4 batches of 10 sows.
  • Environmental parameters (air temperature, relative humidity, air velocity) and physiological parameters (rectal temperature, respiration rate, skin temperature) were measured every 2 h from 8:00 to 18:00.
  • A total of 1029 data sets were split into 70% training and 30% test sets; multiple linear regression in Matlab was used to develop ETIS, with skin temperature as the response variable, and Pearson correlations were used to compare ETIS with other thermal indices.

Limitations

  • The paper states that ETIS was created in a fully enclosed sow barn, so applicable conditions should be similar; sow individual differences and regional environmental adaptations may affect its use.
  • The paper states that heat-stress thresholds may differ by region and need future validation or correction using actual production data; genotype, hair thickness, health status, productivity level, and activity level can also change threshold ranges.
  • Evident from the text: the model was developed and validated only with non-pregnant multiparous sows in one North China barn during summer, so its performance for pregnant or lactating sows, other housing systems, or other seasons is not established.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.3390/ani11051472

Cites

47 of 47 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

14 of 69 cited sources checked · 5 supported · 0 flagged · accuracy not yet measured

  • Premisecitation

    Heat stress adversely affects sow reproduction, including estrus time and conception rate.

    “Heat stress affects the estrus time and conception rate of sows.”
    • Also stated in: § 1. Introduction · plain
      “Heat stress can affect the reproductive endocrine system in sows and inhibit the ovarian function, which in turn affects estrus activity [1], causing delayed estrus, hidden estrus or even no estrus phenomenon [2].”
    • Also stated in: § 1. Introduction · plain
      “Heat stress can reduce fertility rate [3,4]”
    Quote in the paperSubstantial claim1 of 4 sources checked
    • cites [1] Barb, 1991, Endocrine changes in sows exposed to elevated ambient temperature during lactation, Domest. Anim. Endocrinol. source
    • cites [2] Almond, 2005, Seasonal infertility in large pig production units in an Eastern-European climate, Aust. Vet. J. source
    • cites [3] Bloemhof, 2013, Effect of daily environmental temperature on farrowing rate and total born in dam line sows, J. Anim. Sci. source
    • cites [4] Tummaruk, 2004, Effect of Season and Outdoor Climate on Litter Size at Birth in Purebred Landrace and Yorkshire Sows in Thailand, J. Vet. Med Sci. source

      The Discussion (page not provided) reports that heat stress during days 0–16 of pregnancy decreased conception rate in gilts, citing an experimental study. The paper does not report that heat stress affects estrus time; its mention of oestrus in Materials and Methods concerns when gilts were mated. (LLM, conf=0.86)

      Experimental — accuracy not yet measured
  • Premisecitation

    Following Mellado et al., 74 ≤ THI < 78 indicates mild thermal stress.

    “74 ≤ THI < 78 indicates mild thermal stress”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites Mellado et al. [49] Mellado, 2018, Effect of climate and insemination technique on reproductive performance of gilts and sows in a subtropical zone of Mexico, Austral. J. Vet. Sci. source

      The Statistical Analyses section classifies THI into bands including 74–78, but does not label that band mild thermal stress. The Results mention “mild climatic conditions” without explicitly assigning that description to THI 74–78. The numerical range is supported; the stress designation is not established by our copy. (LLM, conf=0.83)

      Experimental — accuracy not yet measured
  • Premisecitation

    Mellado et al. [49] used THI [10] to analyze the pregnancy rate of sows.

    “Mellado et al. [49] used THI [10] to analyze the pregnancy rate of sows.”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites Mellado et al. [49] Mellado, 2018, Effect of climate and insemination technique on reproductive performance of gilts and sows in a subtropical zone of Mexico, Austral. J. Vet. Sci. source
  • Premisecitation

    Following Mellado et al., THI ≥ 82 indicates severe thermal stress.

    “THI ≥ 82 indicates severe thermal stress”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites Mellado et al. [49] Mellado, 2018, Effect of climate and insemination technique on reproductive performance of gilts and sows in a subtropical zone of Mexico, Austral. J. Vet. Sci. source

      The Results classify THI >82 at insemination as severe heat stress. The claim changes that threshold to ≥82, but the paper does not classify THI exactly equal to 82 as severe. Page numbers are not available in our copy. (LLM, conf=0.88)

      Experimental — accuracy not yet measured
  • Premisecitation

    In Mellado et al., when THI > 82, the sow pregnancy rate was 89.8%.

    “when THI > 82, the sow pregnancy rate was 89.8%”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites Mellado et al. [49] Mellado, 2018, Effect of climate and insemination technique on reproductive performance of gilts and sows in a subtropical zone of Mexico, Austral. J. Vet. Sci. source

      Table 1 (Discussion) reports a pregnancy rate of 89.8% at THI >82 for gilts and sows combined. The Results give the sow-specific rate as 90.1% (and the gilt rate as 88.7%), so 89.8% is not the sow pregnancy rate. (LLM, conf=0.90)

      Experimental — accuracy not yet measured
  • May combine two claims. 10
  • The quote only partly states this claim. 1
  • Classified as probably not a substantial claim. 8

  • May combine two claims.

    Premisecitation

    Many thermal indices have been developed and some applied with pigs, including THI, BGHI, ET, and H.

    “Over the past decades, many indices have been developed in the assessment of thermal environment, and some have been applied with pigs, such as the temperature-humidity index (THI) [9,10,11,12,13,14,15,16], the globe-humidity index (BGHI) [17,18], the effective temperature (ET) [19,20] and the enthalpy (H) [21].”
    Quote in the paperSubstantial claim3 of 10 sources checked
    • cites [9] Thom, 1958, Cooling degrees-days air conditioning, heating, and ventilating, Trans. ASAE

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

    • cites [10] Thom, 1959, The discomfort index, Weatherwise source
    • cites [11] Ingram, 1965, The effect of humidity on temperature regulation and cutaneous water loss in the young pig, Res. Vet. Sci. source
    • cites [12] Bond, C.F.K.T.E. (1971). Bioclimatic Factors and Their Measurements. A Guide to Environmental Research in Animals, National Academy of Science Press.

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

    • cites [13] Maust, 1972, Effect of Summer Weather on Performance of Holstein Cows in Three Stages of Lactation, J. Dairy Sci. source

      The Abstract and Results and Discussion describe using THI to assess summer weather and Holstein cow responses, supporting the citation as an example of a thermal index in use. The paper studies cows, not pigs, so it does not support the pig-specific application attributed to the THI citations. BGHI, ET, and H have separate citations in the citing sentence. (LLM, conf=0.88)

      Experimental — accuracy not yet measured
    • cites [14] NOAA (National Oceanic and Atmospheric Administration) (1976). Livestock Hot Weather Stress.

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

    • cites [15] Fehr, 1983, Limiting Swine Stress with Evaporative Cooling in the Southwest, Trans. ASAE source

      The Introduction (page unavailable) describes a wet-bulb/dry-bulb index for swine and reports an effective temperature developed for hogs. It also discusses enthalpy as an environmental-stress measure, but the cited paper does not address the globe-humidity index (BGHI), so it does not support the full list. (LLM, conf=0.85)

      Experimental — accuracy not yet measured
    • cites [16] Wu, 2018, Cooling performance of wet curtain fan-fabric duct ventilation system in house of pregnant sows, Trans. Chin. Soc. Agric. Eng.

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

    • cites [17] Buffington, 1981, Black globe-humidity index (bghi) as comfort equation for dairy cows, Trans. ASAE source
    • cites [18] Ferreira, 2011, Behaviour and performance of lactating sows housed in different types of farrowing rooms during summer, Livestock Sci. source

  • May combine two claims.

    Premisecitation

    When a sow reclines, it often alternates between being awake and asleep, which affects the sow's breathing status.

    “When the sow reclines, it often alternates between being awake and asleep, which affects the sow’s breathing status [52].”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites [52] Li, 2018, Sleep and Wake Classification Based on Heart Rate and Respiration Rate, IOP Conf. Ser. Mater. Sci. Eng. source

      The Introduction says that respiration slows and becomes more stable after people fall asleep, supporting a link between sleep state and breathing in humans. The paper does not study reclining sows, and the Methodology says transitions between waking and sleeping are few under normal circumstances, rather than frequent. (LLM, conf=0.88)

      Experimental — accuracy not yet measured

  • The quote only partly states this claim.

    Findingown data

    The coefficient of determination (R2) between ETIS and sow skin temperature was 0.6341 using the training data set.

    “The coefficient of determination (R2) between ETIS and sow skin temperature was 0.6341.”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim. May combine two claims.

    Findingnone given

    The ETIS heat stress threshold is classified as: suitable temperature ETIS < 33.1 °C, mild temperature 33.1 °C ≤ ETIS < 34.5 °C, moderate stress temperature 34.5 °C ≤ ETIS < 35.9 °C, and severe temperature ETIS ≥ 35.9 °C.

    “the ETIS heat stress threshold is classified as follows: suitable temperature ETIS < 33.1 °C, mild temperature 33.1 °C ≤ ETIS < 34.5 °C, moderate stress temperature 34.5 °C ≤ ETIS < 35.9 °C, and severe temperature ETIS ≥ 35.9 °C.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisecitation

    Existing thermal indices applied with pigs normally include two or three environmental parameters, which are unilateral from the perspective of heat exchange.

    “they normally include two or three environmental parameters, which are unilateral from the perspective of heat exchange [22,23]”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [22] Yunus, A.C.D., and Afshin, J.G. (2014). Heat and Mass Transfer: Fundamentals and Applications, McGraw-Hill Education.

      Not checked in the free run.

    • cites [23] Modest, M.F. (2013). Radiative Heat Transfer, Academic Press. source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Heat stress increases death rate.

    “increase death rate [7]”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [7] Drolet, 1996, Sow mortality associated with high ambient temperatures, Can. Vet. J.

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Heat stress increases weight loss through lactation.

    “increase weight loss through lactation [5]”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [5] Quiniou, 1999, Influence of high ambient temperatures on performance of multiparous lactating sows, J. Anim. Sci. source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Heat stress decreases milk production.

    “decrease milk production [6]”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [6] Black, 1993, Lactation in the sow during heat stress, Livest. Prod. Sci. source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Heat stress decreases piglet weight gain.

    “decrease piglet weight gain [5]”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [5] Quiniou, 1999, Influence of high ambient temperatures on performance of multiparous lactating sows, J. Anim. Sci. source

  • May combine two claims.

    Premisecitation

    The total heat dissipation of the sow is affected by convective heat transfer, radiation heat transfer, heat conduction and respiratory heat transfer, and these forms of heat dissipation are affected by environmental factors such as air temperature, relative humidity, and airflow velocity.

    “The total heat dissipation of the sow will be affected by the sow’s convective heat transfer, radiation heat transfer, heat conduction and respiratory heat transfer [22,23,29], and those forms of heat dissipation will be affected by environmental factors such as air temperature, relative humidity airflow velocity and so on.”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites [22] Yunus, A.C.D., and Afshin, J.G. (2014). Heat and Mass Transfer: Fundamentals and Applications, McGraw-Hill Education.

      Not checked in the free run.

    • cites [23] Modest, M.F. (2013). Radiative Heat Transfer, Academic Press. source
    • cites [29] Bond, 1959, Hog house air conditioning and ventilation data, Trans. ASAE source

  • Classified as probably not a substantial claim. May combine two claims.

    Study design and conductnone given

    The experimental data were randomly divided into two data sets, of which 70% were used to create the model and the remaining 30% were used to test the model.

    “The experimental data were randomly divided into two data sets, of which 70% were used to create the model and the remaining 30% were used to test the model.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning

    Heat stress thresholds for ETIS are: ETIS < 33.1 °C suitable, 33.1 °C ≤ ETIS < 34.5 °C mild, 34.5 °C ≤ ETIS < 35.9 °C moderate, and ETIS ≥ 35.9 °C severe.

    “The categories are as follows: ETIS < 33.1 °C is considered to be suitable, 33.1 °C ≤ ETIS < 34.5 °C is considered to be mild, 34.5 °C ≤ ETIS < 35.9 °C is considered to be moderate, and ETIS ≥ 35.9 °C is considered to be severe.”
    • Also stated in: § 4.6. Summary of the Study and Research Perspectives · plain
      “The classification is as follows: suitable temperature ETIS < 33.1 °C, mild temperature 33.1 °C ≤ ETIS < 34.5 °C, moderate stress temperature 34.5 °C ≤ ETIS < 35.9 °C, and severe temperature ETIS ≥ 35.9 °C.”
    • Also stated in: § 5. Conclusions · plain
      “The classification was as follows: suitable temperature ETIS < 33.1 °C, mild temperature 33.1 °C ≤ ETIS < 34.5 °C, moderate stress temperature 34.5 °C ≤ ETIS < 35.9 °C, and severe temperature ETIS ≥ 35.9 °C.”
    Quote in the paperSubstantial claim
    • Rests on an assumption: THI has established heat stress thresholds that can be used to derive ETIS thresholds.

  • May combine two claims.

    Premisecitation

    Conventional rectal thermometers are not precise enough to measure 0.099 °C, and minor changes cannot be accurately monitored.

    “However, conventional rectal thermometers are not precise enough to measure 0.099 °C, and minor changes cannot be accurately monitored [51].”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [51] Schinckel, 2017, Effect of floor cooling on late lactation sows under acute heat stress, Livestock Sci. source

  • May combine two claims.

    Premisecitation

    ET simply combines air temperature, relative humidity and air velocity, and it uses a small amount of test data based on sensible heat dissipation of 3.4-70 kg pig.

    “ET simply combines air temperature, relative humidity and air velocity, and it uses a small amount of test data based on sensible heat dissipation of 3.4–70 kg pig [19].”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [19] Bjerg, 2018, Computational prediction of the effective temperature in the lying area of pig pens, Comput. Electron. Agric. source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    When air temperature is above 25 °C, every 1 °C increase in air temperature increases rectal temperature by 0.099 °C.

    “Previous studies have shown that when the air temperature is above 25 °C, every 1 °C increase in air temperature will increase the rectal temperature by 0.099 °C [50].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [50] Bjerg, 2020, Sows’ responses to increased heat load—A review, J. Therm. Biol. source

  • May combine two claims.

    Premisecitation

    In previous studies, the monitored frequency of respiration rate was low, or the number of samples was small, so that the influences of the above factors were ignored.

    “In previous studies, the monitored frequency of respiration rate was low [5], or the number of samples was small [51], so that the influences of the above factors were ignored.”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [5] Quiniou, 1999, Influence of high ambient temperatures on performance of multiparous lactating sows, J. Anim. Sci. source
    • cites [51] Schinckel, 2017, Effect of floor cooling on late lactation sows under acute heat stress, Livestock Sci. source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Interpretationnone given

    The index is created in a fully enclosed sow barn, so the applicable conditions should be similar.

    “However, it should be noted that the index is created in a fully enclosed sow barn, so the applicable conditions should be similar.”
    Quote in the paperNot a substantial claim
17 of 17

  • The paper relies on this without support.

    No existing thermal index is specific to assessing sows’ thermal condition.

    “Various indicators can be found in the literature assessing the level of heat stress in pigs, but none of them is specific to assess the sows’ thermal condition.”

  • The paper relies on this without support.

    No study has focused on heat stress in sows so far.

    “In addition, there is no study focusing on heat stress in sows, so far.”

  • The paper relies on this without support.

    Existing thermal indices applied with pigs were mainly developed based on other animals and directly applied in pigs.

    “those indices mainly developed based on other animals, while directly applied in pigs”

  • The paper relies on this without support.

    Existing thermal indices applied with pigs lack consideration of pigs’ real-time physiological and production characteristics.

    “they lack consideration of pigs’ real-time physiological and production characteristics.”

  • The paper relies on this without support.

    Sows are more susceptible to heat stress than other life stages of pigs because of their increased heat production.

    “Compared with other life stages of pigs, sows are more susceptible to heat stress because of their increased heat production.”

  • The paper relies on this without support.

    Animal behavior, performance and most physiological indicators are either invasive or difficult to monitor continuously.

    “However, animal behavior, performance and most physiological indicators are either invasive or difficult to monitor continuously.”

  • The paper relies on this without support.

    Environmental parameters such as air temperature, relative humidity and air velocity are comparatively much easier to measure than animal behavior, performance and most physiological indicators.

    “In contrast, environmental parameters, such as air temperature, relative humidity and air velocity, acting as the influencing factors of heat stress, are comparatively much easier to measure.”

  • The authors state this as an assumption.

    The coefficient a in the relative humidity equivalent temperature equation is positive.

    “a is a coefficient, and expected to be positive.”

  • The authors state this as an assumption.

    The average radiant temperature is equal to the air temperature.

    “Since indoor climate studies usually assume that the average radiant temperature is equal to the air temperature [44,45,46,47,48], Trad is represented here by T”

  • The paper relies on this without support.

    Heat transfer between the sow body and the floor surface is driven by the temperature difference.

    “The heat transfer between the sow body and the floor surface is driven by the temperature difference.”

  • The paper relies on this without support.

    Radiative heat transfer is driven by the difference of the fourth power of the absolute temperatures between two objects.

    “The radiative heat transfer is driven by the difference of the fourth power of the absolute temperatures between two objects.”

  • The authors state this as an assumption.

    The difference between different measuring points in environmental parameters is linear.

    “The research assumed that the difference between different measuring points in environmental parameters is linear, and the environmental parameters were determined at different locations based on this assumption.”

  • The paper relies on this without support.

    Skin temperature is influenced by both the thermal environment and the sow body, acting as the window for transfer heat.

    “Skin temperature was selected as the only response variable because skin temperature is influenced by both the thermal environment and the sow body, acting as the window for transfer heat.”

  • The paper relies on this without support.

    Sows are warm-blooded animals, and their rectal temperatures are relatively stable under normal conditions.

    “Sows are warm-blooded animals, and their rectal temperatures are relatively stable under normal conditions.”

  • The paper relies on this without support.

    Sows have fewer sweat glands, so they dissipate heat differently from other animals.

    “As sows have fewer sweat glands, they dissipate differently from other animals.”

  • The paper relies on this without support.

    Sows are restricted by crates, and they recline or lie most of the time.

    “Meanwhile, sows are restricted by crates, and they recline or lie most of the time.”

  • The paper relies on this without support.

    Individual differences and lying position may affect a sow’s breathing.

    “Individual differences and the lying position may also have an impact on a sow’s breathing.”

  • The paper relies on this without support.

    THI only includes air temperature and relative humidity.

    “As an environmental thermal index, THI only includes air temperature and relative humidity.”

  • The paper relies on this without support.

    Relief of heat stress is essentially a process of heat dissipation, and air temperature and relative humidity are only part of the parameters of the heat dissipation process.

    “Relief of heat stress is essentially a process of heat dissipation, and air temperature and relative humidity are only part of the parameters of the heat dissipation process.”

  • The paper relies on this without support.

    The sow’s skin is directly exposed to the air, so skin temperature is greatly affected by the environment.

    “Since the sow’s skin is directly exposed to the air, skin temperature is greatly affected by the environment.”

  • The paper relies on this without support.

    Skin temperature is also affected by the sow’s internal heat production.

    “Apart from the influence of external conditions, skin temperature is also affected by the sow’s internal heat production.”

  • The paper relies on this without support.

    The skin of the sow is the main channel for heat exchange.

    “The skin of the sow is the main channel for heat exchange.”

  • The paper relies on this without support.

    The respiration rate changes after receiving the thermal sensory signal provided by the brain of the sow.

    “The respiration rate changes after receiving the thermal sensory signal provided by the brain of the sow.”

  • The paper relies on this without support.

    The respiration rate process has a delay compared to the skin.

    “This process can inevitably have a delay compared to the skin.”

  • The paper relies on this without support.

    Skin temperature is not only affected by the environment but also by the sow’s internal factors, and there are individual differences among different sows.

    “Skin temperature is not only affected by the environment but also by the sow’s internal factors, and there are individual differences among different sows.”

  • The paper relies on this without support.

    In a hot environment, sows are affected not only by air temperature and relative humidity, but also by air velocity.

    “In a hot environment, sows will not only be affected by air temperature and relative humidity, but also by air velocity.”

  • The paper relies on this without support.

    When air temperature is lower than sow skin temperature, increasing air velocity is beneficial to alleviate heat stress.

    “When the air temperature is lower than the skin temperature of the sow, increasing the air velocity is beneficial to alleviate heat stress.”

  • The paper relies on this without support.

    Increasing air velocity increases the convective heat transfer coefficient of the sow, which increases convective heat transfer.

    “The main reason is that increasing the air velocity can increase the convective heat transfer coefficient of the sow, which is beneficial to increase the convective heat transfer of the sow.”

  • The paper relies on this without support.

    Sensible heat is an indirect measurement, so errors will inevitably occur.

    “Sensible heat is an indirect measurement, so errors will inevitably occur.”

  • The paper relies on this without support.

    Large pigs tend to avoid heat, and small pigs tend to avoid cold.

    “Moreover, large pigs tend to avoid heat, and little pigs tend to avoid cold.”

  • The paper relies on this without support.

    The characteristic lengths of big pigs and small pigs are different, so their heat dissipation characteristics differ slightly.

    “The characteristic lengths of big pigs and small pigs are different, so the heat dissipation characteristics will be slightly different.”

  • The paper relies on this without support.

    The skin is a window for heat exchange between the sow and the external environment.

    “The skin is a window for heat exchange between the sow and the external environment.”

  • The paper relies on this without support.

    When the thermal environment is severe, the sow skin is stimulated at first.

    “When the thermal environment is severe, the sow skin is stimulated at first.”

  • The paper relies on this without support.

    Sows have individual differences, and sows in different regions have different environmental adaptations.

    “Sows have individual differences, and sows in different regions have different environmental adaptations.”

  • The paper relies on this without support.

    The balance between heat dissipation and heat production is affected by factors related to the sow itself and management, such as genotype, hair thickness, health status, productivity level, activity level, etc.

    “However, the balance between heat dissipation and heat production is not only affected by environmental parameters, but also by other factors related to the sow itself and management, such as sow genotype, hair thickness, health status, productivity level, activity level, etc.”

  • The paper relies on this without support.

    These animal or management-related factors change the range of threshold and heat stress categories.

    “These animal or management-related factors change the range of threshold and heat stress categories.”

  • The paper relies on this without support.

    THI has established heat stress thresholds that can be used to derive ETIS thresholds.

    “Based on the linear regression model in Figure 7, heat stress threshold for ETIS can be developed based on thresholds developed for THI.”
37 of 37

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

  • ETIS thresholds do not follow the stated regression equation

    Major

    Substituting the stated THI cutoffs of 74, 78 and 82 into the ETIS-THI equation gives ETIS values of approximately 19.2, 20.6 and 22.0 °C, not the reported thresholds of 33.1, 34.5 and 35.9 °C. The reported thresholds instead match an equation with a positive intercept.

1 of 1

Cites

Flagged first, then by citations

3 of the 50 references couldn’t be matched to a known paper.

Research works printed but not linked: 6

  1. Thom, 1958, Cooling degrees-days air conditioning, heating, and ventilating, Trans. ASAE, 55, 65
  2. Bond, C.F.K.T.E. (1971). Bioclimatic Factors and Their Measurements. A Guide to Environmental Research in Animals, National Academy of Science Press.
  3. Wu, 2018, Cooling performance of wet curtain fan-fabric duct ventilation system in house of pregnant sows, Trans. Chin. Soc. Agric. Eng., 34, 268
  4. Yunus, A.C.D., and Afshin, J.G. (2014). Heat and Mass Transfer: Fundamentals and Applications, McGraw-Hill Education.
  5. Patience, 1991, Physiological and nutritional effects of heat-stress in the pig, FASEB J., 5, A768
  6. Bergman, T.L., Lavine, A.S., Incropera, F.P., and DeWitt, D.P. (2011). Fundamentals of Heat and Mass Transfer, John Wiley & Sons.

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Authors
Cao, M., Zong, C., Wang, X., Teng, G., Zhuang, Y., & Lei, K.
Affiliations
  • Ministry of Agriculture and Rural Affairs (CN)
  • Zhejiang University (CN)
Corresponding author
Zong, Chao
ORCID
Venue
Animals
Publisher
MDPI AG
Published
2021-05-20
Volume
11
Issue
5
Pages
1472
ISSN
2076-2615 (ISSN-L)
DOI
10.3390/ani11051472
PMC
PMC8161218
OpenAlex
W3163056724
Semantic Scholar
9ac0a6641b413ec0cfe96c6a0313f90fceeb3f21
Cited by
19
References
50
Citations by year
2026: 6 · 2025: 4 · 2024: 3 · 2023: 1 · 2022: 3 · 2021: 2
FWCI
1.50
Type
journal article
Language
en
Open access
Licence
Locations
  • Animals (publishedVersion, cc-by)
  • PubMed Central (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
Funders
National Key Research and Development Plan of China (2016YFD0700204)
Topics
  • Life Sciences › Agricultural and Biological Sciences › Animal Science and Zoology › Effects of Environmental Stressors on Livestock
  • Health Sciences › Medicine › Physiology › Thermoregulation and physiological responses
  • Health Sciences › Veterinary › Small Animals › Animal Behavior and Welfare Studies
Keywords
heat stress, sows, thermal comfort, thermal index, temperature-humidity index, skin temperature, air temperature, relative humidity, air velocity, heat stress threshold, estrus, conception rate

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Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.

Claims read by deepseek-v4.1-flash under definition version 3 (extract-v3) on 2026-10-06.

Classified by jev-1.13-20260917 (gold-guideline-v0.2) on 2026-10-06.

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