Runt
A runt is an animal that is unusually small for its species.[1] In veterinary medicine, a runt may also described using terms such as low-birth weight, intrauterine growth restriction,[2] and small for gestational age.[3] An animal may be defined as small for gestational age (SGA) depending on different criteria, such as size in comparison to littermates',[4] as percent of maternal body weight[5] , as a specific neonate weight threshold for the breed or species,[6] and as different body proportions displayed by runts.[2]
Runts face many challenges in comparison to their normal birth weight peers - they are more likely to contract diseases,[7] and die in the neonatal period, have lower glycogen stores, suffer from developmental delays, insulin resistance,[2] hypothermia,[5] and low blood pressure.[8] Runts are also associated with economic losses in farm animals - SGA adult cows give smaller milk yields and suffer from infertility,[7] intrauterine growth restricted (IUGR) piglets have modifications in their muscle tissue that may affect the taste of their meat, adult IUGR sows have smaller litter sizes and lower birth weight piglets in their litters[2] and adult low birth weight ewes may have poorer quality fleeces.[9]
Causes
[edit]SGA has been best studied in pigs, both due to industry pressures of high mortality rates of preweaning piglets and the use of pig as a model organism in science. Runts are caused by interplay between genetics, environment in utero, maternal environment and care. Breeding for larger litter sizes has resulted in there being born more piglets than the teats of the sow, longer birthing times and more hypoxic young. Further causes of fetal malfunctioning can be a circovirus infection, maternal malnutrition or a small or inconveniently placed placenta.[2][6]
In cattle and sheep, an additional reason may be hot weather during pregnancy.[10] [11] In dairy cows, a contributing factor may be lactating while pregnant, which can overtax the cow's ability to provide sufficient nutrients to the fetus. Nulliparous cows are more at risk of giving birth to SGA calves, and on average give birth to calves of a lower birth weight.[11]
In dogs, a larger litter size may cause more low weight puppies to be born.[5] Typically low weight puppies, like piglets, have smaller placentas in comparison to their normal body weight littermates. [12]
In cats, younger mothers are more likely to give birth to kittens with lower body weight. Likelihood of giving birth to low body weight kittens increases if there is at least one stillbirth in the litter. [13]
Management
[edit]For companion animals such as dogs, assisting with whelping, using apgar scoring and monitoring weight to identify at-risk puppies has been proven to lower mortality rates and equalize early growth among littermates.[12]
However, it is the identification of at-risk puppies that presents a unique challenge in dogs, as dog breeds can vary in weight from less than 1 kg to 120 kg. This discrepancy in size can make it hard to create a uniform guideline for care which breeders and veterinarians can implement in practice. Several identifying tools have been proposed, such as puppy weight - mother weight ratio, which can help identify low birth weight mongrel puppies[5] or breed-specific thresholds, which can be more useful in identifying underweight purebred puppies, as the birth weight of puppies can vary quite a bit among same adult size large and giant breeds.[14]
For livestock like swine, labor-intensive birth assistance has been identified as a major mitigating factor in runt mortality and future outcomes, however such a strategy is cost ineffective in intensive animal farming. Instead, the recommended strategy is managing the sow's nutritional intake and not breeding IUGR piglets.[2]
In cows, it has been found that runt calves are less likely to be effective milk producers and also tend to produce smaller calves in turn. It has been suggested that it would be more effective to redirect SGA calves to veal production, and preferentially breed calves of an average size and good productivity.[7]
See also
[edit]References
[edit]- ^ "Merriam-Webster Dictionary on runt". Retrieved July 7, 2025.
- ^ a b c d e f Van Ginneken, Chris; et al. (2022). "Preweaning performance in intrauterine growth-restricted piglets: Characteristics and interventions". Molecular Reproduction and Development. 90 (7). Wiley: 697–707. doi:10.1002/mrd.23614. PMID 35652465.
- ^ Radklowski, Emily C; et al. (2014). "A Neonatal Piglet Model for Investigating Brain and Cognitive Development in Small for Gestational Age Human Infants". PLOS ONE. 9 (3). PLOS: e91951. Bibcode:2014PLoSO...991951R. doi:10.1371/journal.pone.0091951. PMC 3956804. PMID 24637829.
- ^ Wootton, R; et al. (1983). "Intrauterine growth retardation detected in several species by non-normal birthweight distributions". Reproduction. 69 (2). Bioscientifica: 659–663. doi:10.1530/jrf.0.0690659. PMID 6631828.
- ^ a b c d Alonge, Salvatore; et al. (2023). "Neonatal–Maternal Bodyweight Ratio at Birth: An Indicator for First-Week Survival Prognosis in Canine Newborns". Animals. 13 (21). MDPI: 3397. doi:10.3390/ani13213397. PMC 10648073. PMID 37958150.
- ^ a b Ramsay, T G; et al. (2010). "Adipokine gene transcription level in adipose tissue of runt piglets". Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology. 155 (2). MDPI: 97–105. doi:10.1016/j.cbpb.2009.09.006. PMID 19788925.
- ^ a b c Meesters, Maya; et al. (2024). "Small for Gestational Age Calves: Part II-Reduced Fertility, Productive Performance, and Survival in Holstein Friesian Heifers Born Small for Their Gestational Age". Animals. 14 (15). MDPI: 2157. doi:10.3390/ani14152157. PMC 11311054. PMID 39123682.
- ^ Louey, Samantha; et al. (2000). "Placental Insufficiency and Fetal Growth Restriction Lead to Postnatal Hypotension and Altered Postnatal Growth in Sheep". Pediatric Research. 48 (6). Nature: 808–814. doi:10.1203/00006450-200012000-00018. PMID 11102551.
- ^ Greenwod, P L; Bell, A W (2003). "Consequences of intra-uterine growth retardation for postnatal growth, metabolism and pathophysiology". Reproduction Supplement. 61: 195–206. PMID 14635936.
- ^ Galan, H L; et al. (1999). "Relationship of fetal growth to duration of heat stress in an ovine model of placental insufficiency". American Journal of Obstetrics and Gynecology. 180 (5). Elsevier: 1278–1282. doi:10.1016/S0002-9378(99)70629-0. PMID 10329890.
- ^ a b Meesters, Maya; et al. (2024). "Small for Gestational Age Calves: Part I—Concept and Definition, Contributing Prenatal Factors and Neonatal Body Morphometrics in Holstein Friesian Calves". Animals. 14 (14). MDPI: 2125. doi:10.3390/ani14142125. PMC 11273420. PMID 39061587.
- ^ a b Tessi, Mateo; et al. (2020). "Relationship between placental characteristics and puppies' birth weight in toy and small sized dog breeds". Theriogenology. 141. Elsevier: 1–8. doi:10.1016/j.theriogenology.2019.08.017. hdl:11568/1026680. PMID 31479776.
- ^ Mugnier, Amélie; et al. (2022). "Birth weight in the feline species: Description and factors of variation in a large population of purebred kittens". Theriogenology. 190. Elsevier: 32–37. doi:10.1016/j.theriogenology.2022.07.008. PMID 35914349.
- ^ Mugnier, Amélie; et al. (2019). "Birth weight as a risk factor for neonatal mortality: Breed-specific approach to identify at-risk puppies". Preventive Veterinary Medicine. 171 104746. Elsevier. doi:10.1016/j.prevetmed.2019.104746. PMID 31491708.
