The primary objective of a swine breeding herd is to achieve an optimal number of piglets weaned per litter. Over the past decade, advances in sow genetics have significantly increased litter size at birth [1,2]. However, preweaning piglet mortality rates remain persistently high [2,3]. Preweaning mortality is influenced by a complex interplay of genetic factors and both intrauterine and extrauterine environmental conditions [4]. Larger litter sizes are associated with prolonged farrowing durations, resulting in higher rates of stillbirths and liveborn piglets suffering from hypoxia [[5], [6], [7]]. In large litters, a greater proportion of piglets are born with low birthweights [8]. The placenta, a critical organ for the transfer of oxygen and nutrients from sow to fetus, plays a vital role in fetal growth and development [[9], [10], [11], [12]]. Genetic selection for highly prolific sows has increased the number of fetuses within the uterus, reducing placental space and adversely affecting piglet quality [9,13]. This placental insufficiency contributes to fetal intrauterine growth restriction (IUGR) [10]. The high preweaning mortality rate is not solely due to low-birthweight piglets but is also linked to the occurrence of IUGR in newborns [14].

Intrauterine growth restriction is a condition observed in newborn piglets, particularly those from prolific sows, due to inadequate placental transfer of oxygen and nutrients [14]. Intrauterine growth restriction refers to the impaired growth of the fetus and its organs during gestation, resulting in development below the genetic potential [15]. Contributing factors include toxins, Circovirus infections, placental dysfunction, and maternal malnutrition [16]. Fetal weight relative to gestational age is often used to define IUGR [16]; however, piglet morphology provides an additional criterion for identifying IUGR piglets and predicting their subsequent performance [17]. Head morphology has been widely accepted as a reliable indicator for identifying IUGR piglets. Characteristics include a dolphin-like forehead, bulging eyes, and wrinkles perpendicular to the mouth [18,19]. Furthermore, adequate colostrum intake during the first 24 h postnatally is crucial for newborn piglets to acquire passive immunity before gut closure occurs. Juthamanee and Tummaruk [20] reported that, under field conditions, the average colostrum intake per piglet was 416 ± 176 g, with 26.6 % of piglets consuming less than 300 g. Similarly, Nuntapaitoon et al. [21] observed a pre-weaning mortality rate of 88.8 % in piglets consuming 0–100 g of colostrum, compared to just 6.3 % in those consuming more than 300 g. These findings highlight the importance of ensuring a minimum colostrum intake of 300 g per piglet to reduce pre-weaning mortality. Amdi et al. [19] further demonstrated that IUGR piglets have significantly lower colostrum intake within the first 12 h after birth compared to normal piglets. To better understand the factors contributing to IUGR in newborn piglets, a clinical study under field conditions is essential, focusing on piglets exhibiting IUGR characteristics. This study aimed to investigate the incidence of IUGR in newborn piglets within a commercial swine herd under tropical conditions and to examine its association with piglet characteristics, birth order, litter size, sow parity, colostrum intake, and mortality rate during the first 24 h of life.