{
 "dataset": "heat-stress",
 "title": "Temperature-humidity index, and how heat load presents by production system",
 "description": "The THI variant Galen publishes, the grid it produces across 22–34 °C and 20–80% relative humidity, the derived statement the article is built around, and what fails first in each production system under heat load.",
 "generated": "2026-09-17",
 "publisher": {
  "name": "Galen",
  "url": "https://galen.vet/",
  "documentation": "https://galen.vet/api/",
  "contact": "hello@galen.vet",
  "byline": {
   "name": "Galen editorial",
   "url": "https://galen.vet/about/",
   "type": "Organization",
   "note": "An organisation byline, deliberately, and not a named expert. Nobody on this masthead is a practising clinician; a named authority who does not exist would be a lie in machine-readable form. Where a veterinarian reviews a page, the name, qualification and date are attached to that page rather than to the site."
  }
 },
 "licence": {
  "id": "CC-BY-4.0",
  "name": "Creative Commons Attribution 4.0 International",
  "url": "https://creativecommons.org/licenses/by/4.0/",
  "attribution": "Galen (https://galen.vet)",
  "covers": "The compilation: the article index, the reference tables as structured here, the source registry and every derived field. Use it commercially, modify it, redistribute it; credit Galen with a link. The underlying standards, guidelines and reference works belong to the bodies that publish them and are cited row by row."
 },
 "scope_limits": {
  "no_dosing": "Galen publishes no doses, dose rates, dose intervals or dose calculations, for any species or any product. The figure that applies is on the approved label of the product in front of you, interpreted by the veterinarian who has examined the animal.",
  "no_diagnosis": "Nothing here diagnoses. A sign is not a disease and a list of signs is not a differential. What is published is what a measurement or a label phrase MEANS, so that a conversation with a veterinarian starts from the right place.",
  "no_products": "No product is named and none is recommended. Which product is appropriate is a clinical decision and, in most jurisdictions, a prescribing one.",
  "no_clearance": "An absent row is never a statement of safety. These tables list what they list; the space around them is unexamined, not cleared.",
  "emergency": "If an animal has swallowed something, is collapsed, is struggling to breathe, is bloated and retching unproductively, or is deteriorating after a bite or sting, the answer is a veterinarian or an animal poison centre immediately — not a reference page and not an agent.",
  "jurisdiction": "Veterinary medicines law is national. Where a figure or a rule belongs to one regime it is named as such; where a page describes a pattern common to several, it says so. Nothing here should be read as the law of a country it does not name."
 },
 "corrections": {
  "how": "Email hello@galen.vet with the URL and the source that contradicts it.",
  "policy": "A correction to a figure is made in the source registry or the reference data and reaches every surface — page, markdown twin, JSON and MCP — on the next build, because there is only one copy of it."
 },
 "source_page": "https://galen.vet/journal/heat-stress-livestock-poultry/",
 "sources": [
  {
   "key": "faoAnimalProduction",
   "title": "Animal production and health",
   "publisher": "Food and Agriculture Organization of the United Nations (FAO)",
   "url": "https://www.fao.org/animal-production/en/"
  },
  {
   "key": "woahCode",
   "title": "Terrestrial Animal Health Code",
   "publisher": "World Organisation for Animal Health (WOAH)",
   "url": "https://www.woah.org/en/what-we-do/standards/codes-and-manuals/terrestrial-code-online-access/"
  },
  {
   "key": "merckManual",
   "title": "The Merck Veterinary Manual",
   "publisher": "MSD/Merck Veterinary Manual",
   "url": "https://www.merckvetmanual.com/"
  }
 ],
 "index": {
  "id": "nrc-1971",
  "formula": "THI = 1.8T + 32 − (0.55 − 0.0055 × RH) × (1.8T − 26)",
  "inputs": {
   "T": "dry-bulb air temperature, degrees Celsius",
   "RH": "relative humidity, per cent (0–100)"
  },
  "note": "One of several published variants. Thresholds differ by species, by index version and by production level, so a THI value must always travel with the variant that produced it and the animal group the threshold was derived for.",
  "ignores": "Air speed and radiant heat load. Two buildings at an identical THI are not equivalent if one has air moving over the animals and shade over the yard and the other does not.",
  "source_page": "https://galen.vet/journal/heat-stress-livestock-poultry/",
  "grid": {
   "temperatures_c": [
    22,
    24,
    26,
    28,
    30,
    32,
    34
   ],
   "humidities_pct": [
    20,
    40,
    60,
    80
   ],
   "rows": [
    {
     "humidityPct": 20,
     "values": [
      {
       "temperatureC": 22,
       "thi": 65.6
      },
      {
       "temperatureC": 24,
       "thi": 67.6
      },
      {
       "temperatureC": 26,
       "thi": 69.6
      },
      {
       "temperatureC": 28,
       "thi": 71.7
      },
      {
       "temperatureC": 30,
       "thi": 73.7
      },
      {
       "temperatureC": 32,
       "thi": 75.7
      },
      {
       "temperatureC": 34,
       "thi": 77.7
      }
     ]
    },
    {
     "humidityPct": 40,
     "values": [
      {
       "temperatureC": 22,
       "thi": 67.1
      },
      {
       "temperatureC": 24,
       "thi": 69.5
      },
      {
       "temperatureC": 26,
       "thi": 71.9
      },
      {
       "temperatureC": 28,
       "thi": 74.3
      },
      {
       "temperatureC": 30,
       "thi": 76.8
      },
      {
       "temperatureC": 32,
       "thi": 79.2
      },
      {
       "temperatureC": 34,
       "thi": 81.6
      }
     ]
    },
    {
     "humidityPct": 60,
     "values": [
      {
       "temperatureC": 22,
       "thi": 68.6
      },
      {
       "temperatureC": 24,
       "thi": 71.4
      },
      {
       "temperatureC": 26,
       "thi": 74.2
      },
      {
       "temperatureC": 28,
       "thi": 77
      },
      {
       "temperatureC": 30,
       "thi": 79.8
      },
      {
       "temperatureC": 32,
       "thi": 82.6
      },
      {
       "temperatureC": 34,
       "thi": 85.5
      }
     ]
    },
    {
     "humidityPct": 80,
     "values": [
      {
       "temperatureC": 22,
       "thi": 70.1
      },
      {
       "temperatureC": 24,
       "thi": 73.3
      },
      {
       "temperatureC": 26,
       "thi": 76.5
      },
      {
       "temperatureC": 28,
       "thi": 79.7
      },
      {
       "temperatureC": 30,
       "thi": 82.9
      },
      {
       "temperatureC": 32,
       "thi": 86.1
      },
      {
       "temperatureC": 34,
       "thi": 89.3
      }
     ]
    }
   ]
  },
  "derived": {
   "humidity_effect_at_28c": {
    "temperatureC": 28,
    "from_humidity_pct": 20,
    "to_humidity_pct": 80,
    "thi_low": 71.7,
    "thi_high": 79.7,
    "index_points_added": 8.1,
    "equivalent_dry_air_degrees": 8,
    "source": "https://galen.vet/journal/heat-stress-livestock-poultry/"
   },
   "note": "At a fixed 28 °C, taking relative humidity from 20% to 80% adds as much index as adding several degrees would in dry air. That is the whole argument for using an index rather than a thermometer."
  }
 },
 "thresholds": {
  "published_here": null,
  "why": "Galen publishes no THI threshold. A threshold is specific to the species, the index variant and the production level — a higher-yielding animal reaches it sooner because its own metabolism is part of the load — so a single \"danger figure\" quoted without that context is of little use and is routinely quoted without it.",
  "also": "The index ignores air speed and radiant heat entirely. Two buildings at an identical THI are not equivalent if one has air moving over the animals and shade over the yard."
 },
 "heat_load_by_system": {
  "id": "heat-load-by-system",
  "title": "How heat load presents across production systems",
  "about": "What fails first in each production system under heat load, and what follows if the episode persists. The mechanism — reduced intake plus energy spent on cooling — is common to all.",
  "caveat": "These are consequences, not thresholds. The temperature-humidity index at which each system begins to show them differs by species, by index variant and by production level — a higher- producing animal reaches it sooner because its own metabolism is part of the load — and the index ignores air speed and radiant heat entirely.",
  "row_count": 6,
  "rows": [
   {
    "system": "Dairy cattle",
    "affected_first": "Feed intake, then milk yield and composition",
    "if_it_persists": "Reduced oestrus expression, poorer conception, higher somatic cell counts"
   },
   {
    "system": "Beef and growing stock",
    "affected_first": "Intake and daily gain",
    "if_it_persists": "Feed conversion worsens; finishing dates slip"
   },
   {
    "system": "Pigs",
    "affected_first": "Intake, particularly in heavier animals",
    "if_it_persists": "Reduced growth; sows show poorer farrowing performance and lactation intake"
   },
   {
    "system": "Laying hens",
    "affected_first": "Feed intake and egg output",
    "if_it_persists": "Thinner shells, smaller eggs, higher breakage"
   },
   {
    "system": "Broilers",
    "affected_first": "Intake and gain",
    "if_it_persists": "Rising mortality in severe episodes, especially in the heaviest birds"
   },
   {
    "system": "Breeding males, all species",
    "affected_first": "Semen quality",
    "if_it_persists": "Effects persist for weeks after the hot period, since spermatogenesis takes time to recover"
   }
  ]
 },
 "field_notes": {
  "variant_travels_with_value": "Several THI variants are in circulation and they do not agree. A value without its variant is not a value — `variant` is on every computed result for that reason.",
  "compute_it_yourself": "The formula is published in full so you do not have to trust the grid. The MCP tool `thi` at https://galen.vet/mcp computes it for arbitrary inputs from this same module.",
  "not_advice": "An index figure is an environmental measurement. What to do about it on a particular holding is a management and, where animals are affected, a veterinary question."
 },
 "related": {
  "vital_signs": "https://galen.vet/api/v1/vital-signs.json",
  "articles": "https://galen.vet/api/v1/articles.json",
  "documentation": "https://galen.vet/api/"
 }
}