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NUTRITION ▶▶▶


Interventions to better deal with IUGR piglets


With ever-growing litter sizes, the chances increase of some piglets being born with intra-uterine growth retardation (IUGR). The topic has been studied extensively in recent years. How is the phenomenon defined and – more importantly – what can be done to best treat these piglets?


BY DR S.A. EDWARDS, PROFESSOR EMERITA AND DR S.M. MATHESON, NEWCASTLE UNIVERSITY, UK; AND DR E.M. BAXTER, SRUC, UK*


Illustration of the characteris- tic domed or ‘dolphin-shaped’ head morpholo- gy in an IUGR piglet (right) in comparison with a normal piglet of the same birth weight.


O


ne of the greatest challenges raised by the intro- duction of hyperprolific sows has been the associ- ated increase in piglet mortality and morbidity. It has been known for many years that piglet still-


birth and pre-weaning mortality increase with litter size. The introduction of prolific sow lines, with litter sizes now averag- ing more than 16 in some countries, has worsened that prob- lem, which has been alleviated only by concurrent selection for piglet survival traits. Figure 1 shows the relationship be- tween litter size and piglet survival obtained in a recent UK study. The reasons for this association between litter size and piglet mortality encompass a number of factors, including a prolon-


gation of farrowing and associated hypoxia in the offspring and increased competition for teat access and nutrients. The most fundamental problem predisposing increased mortality in litters of hyperprolific sows has been reduced viability of newborn piglets due to intra-uterine growth retardation (IUGR). There have been many reviews of the aetiology and underlying mechanisms of IUGR, which results from deficiencies in both embryo quality and uterine capacity.


Birth weight and IUGR determination First of all, methods for identification of IUGR piglets include various birth weight categorisations. Secondly, IUGR is associated with a long and thin body shape, which can be quantified, as in human neonates, by low ponderal index (PI) or body mass index (BMI). Perhaps the clearest external sign of IUGR relates to head morphology. When foetal nutrient supply is limited, relatively more nutrients are directed to- ward growth of the brain (brain sparing) and heart as part of a foetal adaptive reaction to placental insufficiency. Recent studies have characterised IUGR based on three criteria: • steep, dolphin-like forehead • bulging eyes • wrinkles perpendicular to the mouth. A classification of severe (s-IUGR) is given if two or three of the characteristics are present, and of moderate (m-IUGR) if only one of the characteristics is present. While IUGR piglets are typically smaller than their littermates, these head shape characteristics can be seen in pigs across the birth weight range (see Figure 2).


Challenges for IUGR piglets Some of the survival challenges experienced by IUGR piglets relate specifically to their smaller size. Low birth weight pig- lets display a lower vitality, and are less resistant to cold be- cause of their greater surface area to volume ratio. When born wet with foetal fluids, into an environment where the tem- perature is typically 10–20 degrees less than core body tem- perature, they rapidly lose heat. Since they are born with very limited energy reserves, this negative energy balance can only persist for a short time before becoming fatal. The prob- lem is even greater for low birth weight piglets competing in a litter with larger siblings. Piglets that show IUGR characteristics in their weight or mor-


34 ▶PIG PROGRESS | Volume 36, No. 4, 2020


PHOTO: DR EMMA BAXTER


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