Impacts of Animal Welfare on Pig Production

Intensive farming greatly restricts animals’ freedom of movement, reduces their living space, and alters their natural living habits. These factors collectively weaken pigs’ adaptability, increase abnormal behaviors and stress responses, lower their immune resistance, and even compromise the safety and quality of animal-derived food. As more countries recognize and embrace the concept of animal welfare, relevant legislations have been formulated worldwide to regulate livestock production. Therefore, animal welfare deserves sufficient attention in intensive pig farms. It is critical to acknowledge that animal welfare exerts significant impacts on herd health and underpins the sustainable development of the pig industry.

Animal Welfare: Definition and Core Principles

The concept of animal welfare was first proposed by Richard Martin from the United Kingdom, who sponsored the Martin’s Act to safeguard animal welfare. In 1866, the United States enacted its animal welfare legislation, the Act for the Prevention of Cruelty to Animals. A century later, in 1976, American scholar Hughes defined animal welfare as “a state of complete mental and physical health where an animal is in harmony with its environment.” In 2011, Chinese researcher Gu Xianhong put forward that the core tenet of animal welfare is to protect animals from physical and psychological harm and enable them to live in a state of well-being.

There exists no unified global standard for animal welfare. Today, the framework is widely summarized into five fundamental freedoms:

1. Freedom from hunger and thirst;

2. Freedom to live comfortably;

3. Freedom from pain, injury and disease;

4. Freedom from fear and distress;

5. Freedom to express natural behaviors.

1. Physiological Welfare and Pig Production

Physiological welfare corresponds to the freedom from hunger and thirst. In commercial pig production, feed formulas and feed intake targets vary for pigs at different growth stages, tailored to distinct production purposes. Gestating sow feed is formulated to support fetal growth and development, while boar feed sustains bodily functions and ensures high-quality semen output.

For gestating sows in large-scale farms, feed intake is artificially controlled across early, mid and late gestation with low, high and high feeding levels respectively. This practice meets the nutritional demands of sows and fetuses yet restricts their voluntary feeding behavior. Lactating sows are allowed ad libitum feeding, though their daily feed intake is artificially reduced one week before weaning to mitigate the incidence of mastitis.

Water intake requirements differ across pig stages and seasons. Insufficient water consumption suppresses feed intake, hindering grow-finisher development and impairing lactation performance in sows. Water temperature also plays a vital production role: cool drinking water in summer and warm water in winter benefit pig health and improve feed conversion ratio. A 2013 trial conducted by Guangxi University demonstrated that piglets provided with 37 °C warm water in farrowing houses achieved an average daily gain 39.4 grams higher than those receiving ambient-temperature water, with weaning weights increased by 820 grams and diarrhea incidence reduced by 20%.

Numerous factors influence pigs’ feed and water intake, including ambient temperature, feed type, palatability, herd health status, water quality, water flow rate, and the type and installation height of drinkers. With rising domestic awareness of animal welfare, many large-scale pig farms have implemented targeted improvements. For instance, liquid creep feed mimicking maternal milk is supplied to piglets, and lactating sows in farrowing barns are also fed liquid diets.

2. Environmental Welfare and Pig Production

Environmental welfare refers to animals’ freedom to live in comfortable conditions. Key challenges in pig production include gestation stall confinement, overcrowding, narrow farrowing crates, heat and cold stress, and excessive concentrations of harmful gases. Cramped farrowing crates compromise sows’ lying comfort, weaken maternal instincts, raise piglet crushing mortality, and hinder piglet suckling.

The European Union has issued legislation banning gestation stalls for pregnant sows to elevate animal welfare standards. A 2016 study by Fu et al. identified the optimal stocking density for finishing pigs as 1.2 square meters per head. By contrast, domestic finishing pig stocking density currently ranges from 0.6 to 0.8 square meters per head, far below animal welfare benchmarks. Cornale et al. (2015) found that overcrowded housing reduces exploratory behaviors and exacerbates stress responses in pigs.

High summer temperatures and frigid winters pose persistent challenges. As intensive pig barns are increasingly fully enclosed with controlled thermal setpoints, many farms fail to balance enclosure and ventilation, leading to severely overthreshold concentrations of ammonia, hydrogen sulfide and other toxic gases. This commonly results in pigs presenting tear stains and persistent coughing.

Piglets require far higher ambient temperatures than mature sows: newborn piglets need local microclimate temperatures of 32–33 °C, whereas lactating sows thrive at approximately 23 °C. To resolve this temperature conflict, heat preservation boxes and heat lamps are installed within farrowing crates to create localized warm zones for piglets.

3. Health Welfare and Pig Production

Health welfare guarantees animals freedom from pain, injury and disease. Traditional pig farms relied on manual dry manure removal, a labor-intensive practice that compromised barn sanitation, elevated pathogen exposure risks, and failed to maintain hygienic conditions. Modern intensive farms adopt fully slatted flooring, which substantially improves barn cleanliness and lowers disease prevalence; slatted flooring for sows also reduces mastitis occurrences. However, slatted floors must meet strict quality standards: overly wide gaps increase the risk of limb and hoof lesions, while overly narrow gaps prevent proper manure leakage.

All barns undergo thorough washing, disinfection and drying after batch removal to provide clean, comfortable housing for subsequent pig groups, cut pathogen transmission risks, and minimize disease burdens.

In terms of disease control, farms carry out eradication programs for Classical Swine Fever and Pseudorabies, install air filtration systems, establish high-health breeding herds, and optimize immunization schedules to cut vaccination frequency and reduce stress from injections. From an animal welfare perspective, terminally ill pigs with no economic value receive humane euthanasia to eliminate suffering.

4. Psychological Welfare and Pig Production

Psychological welfare ensures animals live free from fear and distress. Modern pig farms frequently feature stressful handling practices: staff driving pigs roughly with iron rods or electric prods, rough assisted farrowing for sows experiencing prolonged labor, restraint with snare hooks for blood collection, and severely overloaded transport vehicles lacking protective measures during live pig shipment. All these practices induce intense fear in pigs and create major barriers to advancing animal welfare standards.

Beyond eliminating fear and distress, farms should cultivate a relaxed, pleasant living environment. Enrichment items such as hemp ropes, rubber balls and chain toys can be placed in pens to enrich pigs’ daily lives. Research by Zhang Xiaojun (2016) confirmed that appropriate musical stimulation improves growth performance, alleviates stress, boosts immunity and optimizes physiological status in pigs. Fan Yao (2016) similarly reported that music serves as an effective tool to enhance animal welfare in experimental pig populations.

5. Behavioral Welfare and Pig Production

Behavioral welfare entitles animals to the freedom to express their natural instincts. Intensive pig farming suppresses many innate pig behaviors. For decades, technologies including artificial insemination, embryo transfer, tooth clipping, tail docking and cloning have been widely adopted to boost production efficiency. While artificial insemination curbs disease transmission, maximizes utilization of semen from superior boars and cuts the number of boars kept on farm, it deprives both boars and sows of natural mating behaviors, shortens boar service life, and suppresses their instinctive reproductive behaviors. Artificial tooth clipping and tail docking inflict severe pain and fear on piglets, while stripping them of natural behaviors including chewing during feeding and tail wagging.

Research indicates that omitting piglet tooth clipping generates no significant increase in teat damage to sows; manual assisted suckling by barn staff does not markedly raise maternal pain levels. Likewise, piglets raised without tail docking exhibit minimal tail-biting and pen-mate aggression when enrichment toys such as chains and rubber balls are provided after grouping.