From en.wikipedia.org:
[Animal unusually small for its species] [Other uses]
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,<ref name = "pigone">[last1 = Van Ginneken ]
and SMALL FOR GESTATIONAL AGE.<ref name = "pigtwo">[last1 = Radklowski ] An
animal may be defined as small for gestational age (SGA) depending on
different criteria, such as size in comparison to littermates',<ref name =
"dogtwo">[last1 = Wootton] as percent of maternal body weight,<ref name =
"dog">[last1 = Alonge ] as a specific neonate weight threshold for the breed
or species,<ref name = "pigthree">[last1 = Ramsay ] and as different body
proportions displayed by runts.<ref name = "pigone">[last1 = Van Ginneken ]
Runts face many challenges in comparison to their normal birth weight peers -
they are more likely to contract diseases,<ref name = "cowtwo">[last1 =
Meesters ] and die in the neonatal period, have lower glycogen stores, suffer
from developmental delays, insulin resistance,<ref name = "pigone">[last1 =
Van Ginneken ] hypothermia,<ref name = "dog">[last1 = Alonge ] and low blood
pressure.<ref name = "lambone">[last1 = Louey] Runts are also associated with
economic losses in farm animals - SGA adult cows give smaller milk yields and
suffer from infertility,<ref name = "cowtwo">[last1 = Meesters ] 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<ref name =
"pigone">[last1 = Van Ginneken ] and adult low birth weight ewes may have
poorer quality fleeces.<ref name = "lambtwo">[last1 = Greenwod ]
** Causes
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.<ref name = "pigone">[last1 = Van Ginneken
]<ref name = "pigthree">[last1 = Ramsay ]
In cattle and sheep, an additional reason may be hot weather during
pregnancy.<ref name = "lambthree">[last1 = Galan ]<ref name = "cowone">[last1
= Meesters ] 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.<ref name
= "cowone">[last1 = Meesters ]
In dogs, a larger litter size may cause more low weight puppies to be
born.<ref name = "dog">[last1 = Alonge ] Typically low weight puppies, like
piglets, have smaller placentas in comparison to their normal body weight
littermates.<ref name = "dogthree">[last1 = Tessi ]
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.<ref name = "cat">[last1 =
Mugnier ]
** Management
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.<ref name =
"dogthree">[last1 = Tessi ]
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<ref name =
"dog">[last1 = Alonge ] 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.<ref name =
"dogfour">[last1 = Mugnier ]
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.<ref name = "pigone">[last1 = Van Ginneken ]
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.<ref name = "cowtwo">[last1 = Meesters ]
** See also
- Small for gestational age
- Low birth weight
- Vanishing twin
** References
[reflist]
** External links
[Animals]
Category:Biology terminology category:Livestock