Twin Chick Survival: Making It To Hatching

Twin chicks are a rare occurrence, and even when they do occur, they rarely survive to hatching. This is due to a number of factors, including insufficient space within the egg, malformations, and the inability to break out of the egg. While it is possible for both chicks to survive, it is more common for only one to make it, with the other dying in the egg or shortly after hatching. Conjoined twins are also possible, though they are even rarer and often do not survive due to severe malformations. With human intervention, the chances of twin chick survival increase significantly.

Double yolk eggs can produce two chicks

The survival of twin chicks is also limited by the space within the egg. There is little room for two chicks to develop correctly, and one or both may not grow large enough to hatch. Even if they develop fully, they may be unable to move and break out of the egg, resulting in their death. In some cases, an experienced chicken owner may be able to assist the chicks in hatching if they make it far enough.

The likelihood of twin chicks also depends on the number of egg cells and yolks in the egg. Most double yolk eggs only have one small egg cell, and for twinning to occur, there would need to be two separate egg cells. Additionally, the egg usually needs to be fertilized and create two embryos, or one embryo would need to split to create identical twins. While double yolk eggs can have two chicks, the percentage of hatch rate and survival for twin chicks is very low.

Twin chicks that do hatch are often not both healthy. One is typically normal-sized, while the other is smaller and may not survive to adulthood. Even rarer than two live chicks hatching is two healthy twins. In some cases, the chicks may be conjoined twins, which have severe malformations of the brain and are generally unable to survive.

Conjoined twins occur when two embryos don't fully separate

Conjoined twins are the result of a monozygotic twin pregnancy, which occurs when a single fertilized egg does not fully split during the process of forming identical twins. The embryo typically divides into two identical twins around 13 days after fertilization. However, in the case of conjoined twins, this division is delayed, and the embryo begins to divide between day 13 and day 15 but remains fused in certain areas of the developing bodies. This incomplete separation results in twins that are physically connected, most commonly at the abdomen, chest, or head.

The specific type of conjoined twins is determined by the point of connection. For example, thoracopagus twins are joined at the chest, omphalopagus twins are joined at the abdomen, and craniopagus twins have fused skulls but separate bodies. The survival rate varies depending on the type of conjoined twins, with some types, such as thoracopagus, having a poor survival rate due to shared vital organs.

Conjoined twins are a rare occurrence, estimated to happen in one in 50,000 to one in 200,000 births, with a higher incidence in southwest Asia and Africa. Approximately half of conjoined twins are stillborn, and an additional one-third die within 24 hours. However, advancements in surgical separation have allowed some conjoined twins to live fully functioning lives, while others who cannot be separated can still enjoy a good quality of life with close monitoring.

The decision to attempt separation surgery can be complex and involves ethical considerations. The overall survival rate for conjoined twins is low, with around 25% surviving long enough to be considered for surgery. The success of separation depends on the location of the connection and the sharing of vital organs. In some cases, the designated twin who is allotted a vital organ, such as the heart, may survive if the other twin is sacrificed.

While conjoined twins in chickens are rare, they can occur. The survival rate for twin chicks is very low, and it is uncommon for both chicks to survive due to limited space inside the egg for proper development. However, with human intervention and assistance, twin chickens can have a higher chance of survival.

Parasitic twins occur when one embryo ceases development

The survival rate of twin chicks is very low. In most cases, a double yolker results in the death of both chicks, or the smaller, underdeveloped twin dies while the larger one survives and is healthy. In rare cases, both chicks survive, but one is usually smaller than the other.

Parasitic twins are a specific type of conjoined twins. They occur when one twin embryo begins developing in utero, but the pair does not fully separate, and one embryo maintains dominant development at the expense of the other. This is known as vanishing twin syndrome, where one twin ceases development during gestation and becomes vestigial to the fully formed, otherwise healthy twin. The undeveloped twin is called parasitic because it is either incompletely formed or is completely dependent on the body functions of the complete fetus. In most cases, the phenotype of parasitic twins is one normal functioning individual with extra appendages or organs.

Parasitic twins are thought to be the result of incomplete twinning, where one egg does not fully separate into two eggs. They are also associated with deficient or excessive amounts of the protein Sonic Hedgehog (SHH) during development, which can lead to stunted midline development or disorders such as fused eyes (cyclopia) and duplication of beaks.

In some cases, the parasitic twin becomes an indistinguishable part of the other, requiring medical treatment. A rare form of parasitic twinning is when one zygote becomes cancerous, resulting in unchecked cellular division and a cancerous growth that overtakes the viable fetus.

Twins are rare, but possible with human intervention

While twin chicks are rare, they are possible, especially with human intervention. The occurrence of twin chicks is influenced by several factors, including the age of the eggs, the conditions under which they were stored, the breeding potential and health of the parent stock, and the incubation conditions.

Firstly, the development of twin chicks is influenced by the presence of double yolks in eggs. Double yolks occur when two yolks are released simultaneously into the hen's oviduct and then encased in calcium to form an egg. While double yolks increase the chances of twin chicks, they also present challenges during hatching. The limited space within the egg can hinder the growth of one or both chicks, and they may struggle to break out of the egg, leading to their demise.

Secondly, the survival of twin chicks is often dependent on human intervention. In nature, twin chicks rarely survive without assistance due to the difficulties in positioning themselves correctly to break out of the egg. However, with careful human intervention, the chances of survival for twin chicks increase significantly. This may involve providing specialised care, such as ensuring the chicks are kept warm, fed, and monitored closely during the critical hatching period.

Additionally, certain breeds of hens, such as those in Asia, are specifically bred to produce multiple-yolk eggs, which can increase the likelihood of twin chicks. These hens are typically younger or older and have not yet adjusted their egg-forming mechanisms or are experiencing irregularities in their laying patterns. While this practice may be controversial, it does provide an opportunity to study and support the development of twin chicks.

Lastly, it is important to consider the potential for conjoined or parasitic twins in chickens. Conjoined twins arise from the incomplete separation of two embryos, resulting in physical connections and possible brain malformations. Parasitic twins, on the other hand, occur when one embryo ceases development, becoming dependent on the body functions of the complete fetus. While these occurrences are rare, they further highlight the complexities of twin chick survival and the potential role of human intervention in ensuring their health and well-being.

Twin chicks rarely survive without human help

Twin chicks rarely survive without human intervention. The survival of twin chicks depends on several factors, including the age of the eggs, the conditions under which they were stored before incubation, the breeding potential, health, and diet of the parent stock, and the conditions during incubation.

One significant challenge for twin chicks is the limited space within the egg. In most cases, there is not enough room for both chicks to develop adequately, resulting in their inability to break out of the egg and subsequent death. Even if they manage to hatch, one twin is typically smaller and scrawnier than the other and often does not survive to adulthood.

The position of the chicks within the egg also plays a crucial role in their survival. To hatch successfully, chicks need to break a hole into the air sac and breathe the air within it before pecking a hole to escape. With two chicks in one egg, they may be unable to position themselves correctly to perform these crucial steps, leading to their demise.

Conjoined twins, where the embryos do not fully separate, further reduce the chances of survival due to severe malformations of the brain or other vital organs. Additionally, parasitic twinning occurs when one embryo ceases development, becoming dependent on the body functions of its fully formed twin. These complexities in twinning often hinder the survival of both chicks.

While rare, there are recorded cases of twin chicks surviving with human assistance. In such instances, skilled human caregivers can increase the chances of twin chick survival by providing essential care, such as hourly feedings of crop milk for several weeks, that the parent birds cannot offer.

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