I'm finally circling back to this topic to share some of the info I found interesting.
From
this article on Poultry World:
In breeders the vitamin E supplied in the ration, once absorbed, is transported to the liver and, from there, to the developing oocyte by very low density lipoproteins (VLDL). It has been demonstrated that there is a high efficiency in incorporating α-tocopherol from the maternal feed into the yolk of the chicken egg. The quantity of vitamin E in the egg increases linearly with the consumption of vitamin E by the hen. Supplementation of vitamin E above the minimum requirement improves ovulation during the last phase of the laying period, improving the bird’s defence system and averting negative consequences on egg production also in situations of environmental stress.
Vitamin E protects against oxidation in sperm, egg yolk and embryonic tract. The supply of vitamin E in the ration should be continuous, as the hepatic reserve is insufficient to maintain an adequate vitamin concentration in all eggs, when laying rate is high. Inadequate vitamin E in the diet of breeders is detrimental to fertility, giving rise to the production of eggs with low hatchability and high embryonic mortality in the last phase of incubation due to failures related to the circulatory system.
A snippet from
this study for British Poultry Science ("Effect of selenium and vitamin E content of the maternal diet on the antioxidant system of the yolk and the developing chick"):
There was a positive effect of selenium supplementation of the maternal diet on glutathione concentration in the liver of 1-d-old and 5-d-old chicks. A combination of a dietary selenium supplementation with high vitamin E doses further increased glutathione concentration in the liver. Dietary selenium supplementation significantly increased selenium-dependent glutathione peroxidase (Se-GSH-Px) activity in the liver of the 1-d-old and 5-d-old chicks and decreased liver susceptibility to peroxidation
and
The major finding of this work is a beneficial effect of supplementation of the maternal diet with selenium and vitamin E on the antioxidant protection of the neonatal chick which is maintained well into postnatal development. The data clearly indicate that nutritional status of the laying hen determines the efficiency of the antioxidant system throughout early postnatal development of the offspring. An optimal antioxidant status of the newly hatched chick is an effective means for their protection against damaging effects of free radicals and products of their metabolism. Since natural antioxidants determine the redox potential of the cell, which is responsible for gene regulation (Primi-ano et al., 1997), further research is needed to elucidate mechanisms for relationships between antioxidant compounds in the diet and their accumulation in the tissues and interactions with antioxidant enzymes.
As with most cursory research, it's given me more questions than answers, which isn't necessarily a bad thing.
One take-away is the importance of feeding vitamin E above the minimal requirements, especially during times of heavy laying. The hen stores it in her liver and that can be depleted, meaning some eggs could be deficient.
How much Vitamin E does my feed have? No clue. It's not listed on the tag or the manufacturer website. The benchmark guide for poultry nutrition is the National Research Council's "Nutritional Requirements of Poultry" from 1994. It's in the process of being updated but is still utilized by many feed manufacturers today. I've seen mentioned several times that their recommendations for the fat-soluble vitamins are extremely low, especially when consideration is given to the fact that nutritional value of feed degrades due to age and other environmental factors.
I also supplement with Twin City Poultry's Breeder Solution Plus, but again, no idea what that actually contains.
I wasn't able to find much research regarding wry neck. The "proper" name is torticollis which seems to be an umbrella term. The research I did find was regarding a form of torticollis that is a musculoskeletal deformity instead of what appears to be a spasmodic episode.
So lots of interesting research about the levels of vitamin E and selenium passed from hen to egg, especially as it ties into their nutrition. It doesn't rule out that there's a genetic factor, but it's worth some thought.
My two wry neck chicks have been completely normal since being treated on their hatch day. I'll be interested to see how they develop and if any other issues come up. Those two were from a SplashxBlue cross. During the same hatch, I also had BuffxBuff and BuffxBW eggs. 4 of the 6 BuffxBuff chicks and 3 of the 7 BuffxBW chicks died in the shell after Day 18. Perhaps a coincidence, but it makes me wonder if my breeders had inadequate vitamin E levels.