There is no single numerical standard for fever in pigs. A pig is considered to have a fever when its temperature exceeds its own baseline and is accompanied by clinical symptoms. Pigs have a higher normal body temperature than humans, and it varies significantly with age, body weight, and physiological stage.
1, Due to the action of endogenous pyrogens, the set point of the thermoregulatory center shifts upward, causing a regulated increase in body temperature. When the body temperature rises more than 0.5℃ above normal, this is called fever.
2, Fever is not an independent disease, but an important clinical symptom.
3, Fever-activating substances are divided by source into two categories: infectious fever activators (including Gram-negative bacteria and their endotoxins, Gram-positive bacteria and their exotoxins, viruses, spirochetes, fungi, protozoa, etc.) and non-infectious fever activators (such as aseptic inflammation, antigen–antibody complexes, and tumors).
4, endogenous pyrogens include interleukin 1, interleukin 6, interferon, tumor necrosis factor, macrophage inflammatory protein 1, etc. They are cytokines.
5, the mechanism of fever can be summarized as 3 basic steps, including information transmission, central regulation, and effector response.
6, the development of fever can be divided into 3 stages: the temperature-rising stage, the high-fever stage, and the fever-reducing stage.
(1) Temperature-rising stage: This is the first stage of fever. It is characterized by heat production exceeding heat dissipation, with warmth accumulating in the body and body temperature rising. At this time, the sick animal shows signs such as agitation and restlessness, reduced appetite, accelerated pulse, lowered skin temperature, chills and shivering, and erect hair.
(2) High fever stage: Heat production and heat dissipation remain balanced at a relatively high level. The sick animal shows increased breathing and pulse rates, congested and flushed visible mucous membranes, increased skin temperature, and reduced urine output; sweating sometimes begins.
3, Defervescence stage: Heat dissipation exceeds heat production, and body temperature decreases. At this time, blood vessels in the sick animal’s body surface dilate, sweating increases significantly, and urine output also increases.
Standard body temperature (rectal temperature) of pigs at each stage
· Piglets: Newborn piglets are approximately 39.0℃, suckling piglets approximately 39.2℃, and nursery piglets (9-18kg) can reach 39.3℃.
· Growing and finishing pigs: Growing pigs (27-45kg) are approximately 39.0℃, and finishing pigs (45-90kg) approximately 38.8℃.
· Breeding pigs: Pregnant sows are approximately 38.7℃, lactating sows approximately 39℃, weaned non-pregnant sows approximately 38.6℃, and breeding boars approximately 38.4℃.
· Physiological fluctuation: A sow’s body temperature may reach 40.0℃ within 24 hours after farrowing. If her mental state and appetite are normal, this is a normal metabolic temperature increase, not a pathological fever.
· Mild fever (above baseline body temperature by 0.5-1℃, approximately 40.0℃):
· Common causes: mild localized infection, chronic inflammation, or latent viruses.
· Management principles: If the animal is alert and eating normally, prioritize observation and treatment of the underlying cause. Avoid blindly using potent antipyretics to suppress the immune response. Chinese herbal remedies for clearing heat, detoxifying, and relieving exterior symptoms, or multivitamin supplements, may be used as adjuncts.
· Moderate fever (above baseline body temperature by 1-2℃, approximately 41.0-42.0℃):
· Common causes: Systemic viral or moderate bacterial infections, such as influenza and Mycoplasma pneumonia.
· Management principles: Prompt intervention is required. Common treatments include antiviral Chinese medicines (such as Shuanghuanglian and Houttuynia cordata) combined with antibiotics to which the pathogen is sensitive, with an emphasis on fluid replacement to prevent dehydration.
· Very high fever (above the baseline body temperature by 2℃, approximately above 42.0℃):
· Common causes: Acute, severe bacterial infections or sepsis, such as pleuropneumonia and streptococcosis.
· Treatment principles: Urgent fever reduction and anti-infection measures are equally important. Use a fast-acting antipyretic and anti-inflammatory drug (such as flunixin meglumine) to rapidly control body temperature and prevent organ failure, while also using antibiotics against the pathogen.
Precautions
1. Accurate temperature measurement: Rectal temperature measurement must be used. Ensure the pig has been resting for at least 15 minutes before measuring to avoid a false increase in temperature after exercise or feeding.
2. Distinguishing heat stress: In hot summer weather, pigs that pant with their mouths open and have an elevated body temperature but remain in fairly good spirits are likely experiencing heat stress. Prioritize improving ventilation and cooling rather than directly administering medication to reduce the fever.
3. Overall assessment: Body temperature is only one indicator; diagnosis must also take into account mental status, appetite, breathing, stool, skin color, and other factors. No fever does not mean there is no illness, and body temperature may also become too low in the late stages of a serious illness.
4. Use medication with caution: Never mix multiple fever-reducing medicines. Fever reducers only treat the symptoms; identifying and treating the underlying cause is key. It is recommended to develop the habit of taking temperatures during routine checks and to take accurate temperatures promptly for pigs showing lethargy or reduced feed intake, so they can receive early intervention and treatment.