FACTORS INFLUENCING PIGLET MORTALITY: BIRTH TO WEANING

FACTORS INFLUENCING PIGLET MORTALITY: BIRTH TO WEANING

Vanlalhmangaihsanga*¹ and Sarishti Katwal¹

¹Ph. D Scholar, Department of Livestock Production Management, College of Veterinary Sciences and Animal Husbandry, Guru Angad Dev Veterinary and Animal Sciences University, Ludhiana, Punjab, India.

Abstract

Preweaning piglet mortality in pig production is a major concern, with crushing and starvation accounting for up to 50-80% of piglet deaths. In the field, piglet birth body weight, litter size, birth order, gender, parity, farrowing time, maternal behaviour, sow nutritional status, and environmental temperature all have an impact on piglet mortality. As a result, understanding the factors that influence piglet mortality is critical for improving animal welfare, reducing production loss, and increasing benefits. Farmers must understand the potential causes of piglet mortality and employ several approaches to piglet mortality on farms in order to increase the number of healthy piglets at weaning.

Keywords: Animal welfare, Benefits, piglet mortality, piglet birth body weight, Preweaning.

*Corresponding Author: email: hmangaihatochhong@gmail.com

Introduction

Preweaning piglet mortality in pig production is a major concern, leading to poor piglet welfare and financial losses for the farmers. The high piglet mortality poses a moral and financial challenge to pig production. Piglet mortality is multifactorial because it can be reduced by a combination of several factors. Up to 50-80% of piglet deaths are caused by crushing and starvation, which typically occurs within the first two to three days after farrowing (Fig. 1 & 2). Changes in pre-weaning mortality rates over the past ten years point to temporary success. Piglets’ overall mortality and morbidity are influenced by the size and weight of their litter, the season, their care, and how they are handled during the preweaning stage. A piglet, when compared to the young of other livestock, faces more challenges to its survival, including adjusting to its external environment in the face of hypothermia, being savaged and crushed by its mother, attempting to obtain adequate nutrition while competing with its littermates, and so on, until it is able to feed itself. The improvement in piglet survival is as little as 0.5 per cent, resulting in a 10 kg increase in annual pig meat output per sow, which would improve financial gains and reduce pork production’s environmental impact (per kg of product).

The average pre-weaning mortality rate in swine herds in the world’s top pig-producing nations is between 10% and 20%, despite the increases in litter size caused by genetic selection. Piglet mortality is influenced by a number of factors in the field, including piglet birth body weight, litter size, birth order, gender, parity, farrowing time, maternal behaviour, sow nutritional status, and environmental temperature. The different patterns of piglet’s birth weight, litter size and mortality in various varieties of pig in India is shown in Table 1.

Fig. 1 Factors affecting piglet mortality	Fig. 2 Piglet mortality in First four days

Table 1. Patterns of piglet’s birth weight, litter size and mortality in various varieties of pig in India

Factors influencing piglet mortality

Causes of mortality and morbidity may be multifactorial, including lack of awareness among the farmers and pig breeders regarding management practices, disease prevention and control measures. The predisposing factor of piglet mortality is inextricably linked with other causes, either because they directly lead one to another or have common predisposing factors, for example, prolonged farrowing duration is influenced by increased litter size, and sow stress associated with fatigue, restrictive farrowing environments, and high ambient temperatures. As previously suggested, the cause of death can be influenced by many factors. The current information regarding significant causes of piglet mortality under different farms conditions will be discussed and classified in four major groups, involving the piglet, the sow, handlers and other factors.

1. Sow factors

A piglet must have safe and easy access to the udder to consume colostrum early in life. Thus, the sow must be relatively passive, lying laterally, exposing her udder, and emitting rhythmic grunts as an auditory cue to her new-borns to suckle. Restless maternal behavior, particularly during farrowing, not only prevents early colostrum intake but also prolongs farrowing duration and increases the risk of crushing.

1. Crushing

Crushing is generally regarded as the ultimate cause of the vast majority of neonatal deaths, and as such, it is a well-studied aspect of the hypothermia-starvation-crushing complex. Lack of piglet-directed pre-lying behaviour, designed to remove piglets from the lying location, frequency and nature of posture changes, and failure to rise in response to a trapped piglet are all sow behaviours that influence the risk of crushing. The latter is influenced by the sow’s body condition, which may be related to parity, as well as her inherent responsiveness and the environment in which she is farrowing. Older sows may experience increased leg weakness, impeding posture changes, whilst the enforced restraint of a farrowing crate can limit the effectiveness of a sow’s response to a crushed piglet.

1. Maternal temperament

Piglet mortality is also affected by the sow’s temperament. Individual differences in maternal ability exist, and sows classified as ‘crushers’ behave differently than ‘non-crushers.’ The consistency of behavioural patterns within individuals, as well as the high variation within populations, suggests that ‘non-crushers’ may be selected. Neophobia and nervousness toward humans were also linked to piglet crushing, most likely due to increased reactivity to disturbance. When litter size exceeds the number of functional teats on a regular basis, there is an increased incidence of teat disputes among siblings, causing an increased disturbance at the udder, which can lead to sow restlessness and a higher number of sow-terminated nursing’s.

Mismothering in the form of maternal aggression or savaging can result in traumatic or fatal injuries and is not the only maternal behaviour that can directly cause piglet death. Savaging is more common in gilts, possibly due to a neophobic reaction to new-borns. When sows are confined in crates and unable to escape the attention of the neonates, savaging is more common, whereas this behaviour is rare in other systems. During parturition, scavenging sows are more restless and overly responsive to their piglets. As a result, even if piglets avoid direct aggression, they are at risk of being crushed, and udder access is delayed. In addition, piglets are at risk of infection and later death if they sustain non-fatal injuries as a result of over-lying or savaging by the mother.

• Colostrum yield

Sow colostrum yield was reduced by a prolonged farrowing period and low haptoglobin levels in sow plasma. Furthermore, sow parity also affects colostrum Ig content, with older sows (parity greater than 5) having more IgG and IgA in their colostrum than younger sows. Colostrum IgA levels were lower in sows with thinner back fat at farrowing. Sow colostrum yield was negatively associated with late gestation loss of back fat resulting in poor body condition.

Colostrum yield and composition can also be influenced by sows’ inadequate nutrition in late gestation. Sows need a lot of energy to grow their mammary glands, so nutrition may affect colostrum production through both mammary gland growth and the mechanisms that regulate colostrum secretion in late gestation. Sows’ energy intake during pregnancy is positively correlated with birth body weight of piglets.

1. Piglet factors

This section will detail the consequences of piglets being born with physical and behavioural detriments, with particular reference to their links with chilling, reduced colostrum intake and crushing.

1. Birth weight

Birth weight is widely regarded as the most important predictor of live-birth survival. Pre-weaning mortality was 40% in pigs with birth weights less than 1 kg, 15% in pigs with birth weights between 1-1.2 kg, and only 7% in pigs with birth weights greater than 1.6 kg. The piglet’s active survival behaviour is described by vitality or vigour, and it can be highly variable at birth. Piglets who reach the udder first, find a functional teat and suck colostrum are more likely to survive. As a result, piglets will fight to gain and keep possession of a preferred teat, and if they do not perform optimal massaging and suckling behaviours at this teat, colostrum and milk yield, as well as piglet survival, may suffer. Piglets failing to establish teat dependability grow more slowly, with inability to gain access to the most productive teats resulting in starvation or a lower milk intake when they do manage to gain access to a teat. Heavier piglets, born earlier in the birth order, won more teat disputes, established teat dependability quicker, suckled more frequently and ultimately were at a distinct advantage over less behaviourally and physically vigorous littermates. The competitive nature of the neonatal environment is the main cause of death in smaller animals.

1. Colostrum intake

Colostrum is essential for a piglet’s development of passive immunity, intestinal maturation, and thermoregulation. The bioactive substances immunoglobulins (IgA, IgM, and particularly IgG), hydrolytic enzymes, hormones, and growth factors are all abundant in the colostrum. There is a limited time after birth when the gut is permeable to macromolecules such as immunoglobulins, which confer passive immunity before gut closure begins (at approximately 48 h). Because colostrum ingestion stimulates the closure process, it is critical for the piglet to obtain and process as much colostrum as possible during this time. Pathogens have two major windows of opportunity to establish themselves in the piglet’s systemic circulation. The first occurs within the first 24 hours of postnatal life and is influenced by delayed colostrum intake, which can cause gut closure to be delayed. The second is the time lag between declining antibody concentrations in sow’s milk and the piglet’s transition from passive to active immunity, which is hampered by low colostrum intake in early postnatal life. When piglets consume less than 200 g colostrum, the mortality rate can rise up to 43.4%.

Colostrum provides highly metabolizable energy as well as a high content of fatty acids and lactose, which the piglet efficiently utilizes to cope with cold-induced stress by increasing its metabolic rate and maintaining homeothermic equilibrium on the first day of life. As a result, colostrum consumption correlates positively with piglet rectal temperature at 24 hours of age. Piglets who consume colostrum within the first hour after birth have a 1°C higher rectal temperature than those who do not have access to colostrum. In other words, the piglet’s body temperature rises because colostrum contains a high percentage of fat (30-40%) and can provide up to 60% of the energy that the neonate requires on its first day of life.

• Low body temperature/Hypothermia

The neonatal piglet is born almost hairless, with no brown adipose tissue, and low glycogen reserves which help in metabolic heat production. The hypothermia gets exaggerated when reduced insulation through heat loss by evaporation (moist skin with placental fluids), cold surface (> 40% on a concrete floor) and heat loss per unit of body weight is inversely related to body size, smaller piglets are more vulnerable to hypothermia. If hypothermia becomes irreversible, the piglet will die either directly from hypothermia or indirectly from a secondary factor such as increased susceptibility to crushing. The intake and metabolism of colostrum are required for the initiation and maintenance of the thermogenic response to cold (i.e., a continuous increase in metabolic rate). The piglet’s body temperature rises because colostrum contains a high percentage of fat (30-40%) and can provide up to 60% of the energy that the neonate requires on its first day of life.

The lower critical temperature of newly born piglets is approximately 34 °C, which is not reached upon exit from the uterine environment (38-40 °C). However, new-borns experience a significant environmental change upon birth as they are only exposed to an environment temperature of 20 to 22 °C (the same temperature as the sow’s thermoneutral zone), which is 15-20 °C less than uterine temperatures renders them more susceptible to stress brought on by cold.  Heating the environment to 34 degrees Celsius would have a negative impact on the sow’s thermal comfort zone, which ranges from 12 to 22 °C and is thus markedly different from that of the newly born piglet. Low birth weight increases relative evaporative losses due to a larger relative body surface area, as do increased air velocity (e.g., draughts from ventilation systems) and low ambient air pressure. Even after the placental fluids have dissipated, evaporative heat loss from mucosal surfaces occurs during respiration.

1. Litter size

Piglet survival has been further hampered by genetic selection for larger litters in pigs, which has an effect on birth weight and inter-piglet weight variance. Nowadays, litter size has increased over the years due to lots of sows breeding techniques implementation. But sows have a limited biological capacity related to the number of functional teats and maternal investment, these larger litters demand more management input from the farmer to keep piglet mortality low. The farrowing period is lengthier and has varying birth intervals in larger litters. As a result, more stillbirths and weak piglets are more likely to pass away soon after birth, which raises the danger of suffocation. So, bad management of higher litter size due to low colostrum intake and pen environment enrichment facilities higher mortality occur.

1. Handlers/Worker’s influences

There are several obvious areas within the farrowing house where a handler can influence piglet mortality. In one farm survey, it is concluded that the handler’s factors constitute 26-27% of the variance in pre-weaning mortality. Failure to assist weak piglets with colostrum intake or thermoregulation, as well as failure to intervene when a sow has more piglets than functional teats, will inevitably result in piglet losses. Furthermore, poor management practices in terms of hygiene and disease treatment increase the risk of neonatal diseases and infections becoming fatal. However, it should be acknowledged that care standards at all stages of the reproductive cycle, beginning with gilt rearing, can have an indirect impact on piglet survival. Over many years of research, some scientists have demonstrated the sequential links between stock handler attitudes toward pigs, their subsequent behaviour toward pigs, the impact this has on fear levels in the pigs, and the consequences of increased fear for productive and reproductive performance.  Human behaviour and pig fear levels interact in the farrowing house to influence piglet mortality. For example, when a sow’s fear and nervousness are high, the presence of humans may be a risk factor for stillbirth and savaging deaths.

Stressful experiences during pregnancy not only affect the sow’s behaviour, but they can also have long-term negative effects on the developing offspring, including transgenerational effects. Some researchers subjected primiparous sows to the stress of social mixing during mid-gestation in a study. Neurobiological research found that female offspring of stressed sows were more anxious, and those females who went on to become mothers displayed abnormal maternal behaviour. When compared to control sows, they were also more reactive to their piglets and spent more time visually attending to them; these differences had a negative impact on piglet survival.

1. Other factors
2. Infectious diseases

About 4% of piglet deaths are attributable to infectious illnesses, with gastroenteritis and pneumonia being the main causes. Different causes of mortality of pigs in the age group (0-42) days were enteritis (37.50%), pneumonia (36.11%), pneumonia with enteritis (6.94%), Classical swine fever (4.16%) and 1.38% of other causes i.e. diarrhoea, liver abscess, general poor health with debility, hypovolemic shock, spleen rupture, fibrinous polyserositis, trauma, liver rupture, and physical wound. 29.17% of deaths were due to gastroenteritis, 20.83% to pneumonia and gastroenteritis, 4.17% to mother-child abuse, 8.33% to iron poisoning, 29.17% to pneumonia, and 8.33% to other causes of pneumonia (15.82%), gastroenteritis (42.09%), weakness and debility (10.10%), and traumatic injury (4.04%) were identified to be the most prevalent conditions. Gastroenteritis-40.91%, Pneumonia-9.15%, Weakness, debility, and inanition-12.15%, Traumatic injury-6.32%, Foot and Mouth Disease-1.94%, Urinary Tract Infection-1.26% and others-28.28%.

1. Season

Piglets’ mortality was significantly impacted by the farrowing season. In India, winter seasons had the greatest mortality rates, followed by rainy and spring seasons due to low ambient temperature and cold stress. Winter (47.36%) had the highest fatality rate, followed by summer (27.19%) and monsoon (25.43%). However, various seasonal piglet mortality patterns are also observed. The significantly highest mortality was recorded in rainy season which did not differ significantly from autumn which is related to disease incidence in Landrace, Desi and their halberds in Jharkhand.

• Farrowing pens vs farrowing crates

The relative risk of pre-weaning mortality was 14% higher in farrowing pens when compared with crates. The number of piglets born dead was comparable between the crates and pens with enrichment, but the relative risk of stillbirth was increased by 22% in crates versus pens without enrichment. The floor characteristics of the farrowing pen or the creep area might influence piglet PWM. Floors with rigid physical features (i.e. slatted iron floor, partial concrete and partial round-weld mesh floor) increase the incidence of foreleg skin lesions in piglets with a negative effect on piglets’ pre-weaning growth.

Conclusions

The small size of piglets at birth, low energy storage, and the immature immune system make them susceptible to chilling, starvation, or being crushed by the sow, all of which contribute to pre-weaning mortality. Information on factors that impact piglet mortality is critical to improving animal welfare, reducing production loss and raising benefits. In order to increase the number of healthy piglets at weaning, farmers must understand the potential causes of piglet mortality and employ several approaches to piglet mortality on farms.

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