Factors affecting preweaning piglet mortality Part 1

Unraveling these complex interactions to find out the primary cause is an important step in decreasing PWM.

A. Sow factors

The dam provides the fetus/piglet vital resources in-utero, at farrowing, and during lactation and thereby plays a pivotal role in the survival of the piglets till weaning. Sow genotype, parity, nutrition, and physical condition during gestation and lactation can also influence the resource mobilization to the piglet, and thereby can affect PWM.

1. Effect of the intrauterine environment: Embryonic death can happen either before implantation or during the post-implantation phase. The major contributing factors for post-implantation loss are uterine crowding and placental insufficiency (when the placenta is unable to supply the essential nutrients and oxygen to the developing fetus). These conditions can result in an increased number of stillborn piglets or low viability piglets.
2. Prolonged Farrowing: The impact of farrowing duration can influence piglet survival. Prolonged farrowing can cause changes to the behavior and physiology of the sow, which can influence the survival of piglets during farrowing. Prolonged farrowing in turn is caused by several factors, including increased litter size, sow stress and fatigue, farrowing environment, piglet size, and sow body condition.
3. Availability of colostrum: Piglets receive maternal immunoglobulins directly through colostrum, and this is the only way the piglet can acquire short-term immunity. Further, colostrum is an important factor in the piglet’s ability to respond to reduced temperatures and chilling. The piglet can only absorb maternal immunoglobulins for around 48 hours so any delay in the intake of colostrum can impact piglet survival. Intake of colostrum can be limited either by sow factors or piglet factors (discussed below). But studies have shown that in prolific genotypes, the transfer of colostrum is limited more by sow yield rather than piglet acquisition (Devillers et al. 2011)
4. Maternal behavior: Crushing is considered as one of the most important causes of PWM, and sow behavior is a major cause of this. Restless behavior during farrowing not only prevents access to colostrum but also increases the chances of accidental piglet deaths during farrowing. For the piglets to have easy access to milk and colostrum, the sow should be reasonably passive, should lie down laterally exposing the udders, and should emit rhythmic grunting as a signal to newborn piglets. Savaging, which is more prevalent in gilts is another behavioral abnormality that can influence PWM.

B. Piglet factors

These are factors that are caused mainly by physical or behavioral issues with piglets

1. Bodyweight, maturity and vigor: Body weight is considered as the single most important factor that determines piglet survival. A study published by Roehe and Kalm (2000), reported that pre-weaning mortality rates were around 40% for piglets weighing less than 1 kg, 15% for piglets weighing between 1 to 1.2 kg and only 7% for piglets above 1.6 kg. Along with size, degree of development or maturity also plays an important role in survival. Piglets that have undergone intra uterine growth retardation (IUGR), have a lesser chance of survival even if they fall in the higher body weight range. Immature piglets with underdeveloped digestive or other internal organs, even if they can achieve early ingestion of colostrum, can die due to a lack of a piglet’s ability to absorb/digest colostrum. Vigor or vitality of the piglet describes the survival behavior of the piglet, and piglets that are quicker to reach the udder, find a teat and ingest colostrum, have a higher chance of survival.
2. Gender: Baxter et al (2012) reported that even though male piglets were born heavier and with higher body mass index (birth weight/crown-rump length) than females, they tend to suffer more from crushing and have a significantly lower chance of survival until weaning than females.
3. Thermoregulatory abilities: The capability of the newborn piglet to produce metabolic (body) heat depends on the coordinated activities of various organs and is crucial for the survival of piglets. This is vital, especially in colder environments. If the body temperature drops and becomes irreversible, then the piglet will die of hypothermia or will become more susceptible to secondary factors like crushing. The thermoregulatory mechanism is more important for the survival of piglets with low birthweight as heat loss per unit of body weight is inversely proportional to body size (Herpin et al 2002)

C. Environmental factors

1. Thermoregulation of the environment: The thermal comfort zone of piglets and sow are markedly different. The lower critical temperature of a newborn piglet is around 34oC (93.2oF) and the thermal comfort zone for the sow is between 12-22^oC (53.6 – 71.6^oF). Creating an environment in which newborn piglets are above their lower critical temperature provides one of the biggest challenges in the farrowing pen.
2. Competition: This challenge comes from the social environment, and if not managed well by employing strategies like split suckling within the first 24 to 48 hours of birth, low birth weight piglets, regardless of their vigor will be at risk of starvation. The situation is complicated by an increased within litter birth weight variation.
3. Caretaker influence: The person managing the farrowing rooms also plays a role in controlling PWM. Some of these factors are environmental temperature, barn airflow, intervention in farrowing when required, provide assistance to weak piglets with colostrum, proper hygiene, treatment protocols, etc.

All these factors, independently or in combination lead to PWM, and it requires various management, and selection strategies to reduce it. Pre weaning mortality does have a genetic component, and in the last part of this series, we will discuss in detail the genetic selection strategies that Genesus has adopted to reduce it.