reproduction & embryotic development

According to the article "Reproduction in Hens: Is Testosterone Necessary For the Ovulatory Process?", hormones produced by the endocrine system play an important role in reproduction. The endocrine system maintains biological processes and is responsible for producing hormones. Although testosterone is typically thought of as being a male hormone, it is very significant in females too. Testosterone stimulates the production of progesterone, which is another hormone that prepares the female body for pregnancy.

In the study, the researchers observed the effects of administering intramuscular injections of testosterone. These injections were done in vivo (within the body) and in vitro (outside the body). The researchers found that the concentration of testosterone needed to increase prior to ovulation, in order for ovulation to proceed (Rangel et al, 2014).

Another article titled "Chicken Embryo Development: Metabolic and Morphological Basis For in ovo Feeding Technology" compiled and reviewed a variety of studies involving the addition of supplemental nutrients into developing chicken embryos. Naturally, a chicken embryo already has sufficient access to many nutrients within the yolk sac; such as carbohydrates, proteins, lipids, and minerals (Givisiez et al, 2020).

The phrase "in ovo" refers to the technique of injecting supplements into the egg before the chicken hatches. This is commonly done with vaccines at hatcheries, as it reduces stress from animal handling and is less labor-intensive (Zoetis, 2011). A video example of in ovo vaccine injections is linked below.

One of the many studies discussed in the aforementioned article was about the effect of in ovo administration of Asorbic Acid, more commonly known as Vitamin C. The results concluded that the Vitamin C supplement caused improvement to the chickens' immune system and had positive effects on muscle development (Givisiez et al, 2020).