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#15959 - 02/25/04 10:23 AM Egg Laying Regularity - Innate or Developed?
Anonymous
Unregistered


This post is about egg laying regularity in all breeds of chickens, with a historical interest. Only seriously interested parties may wish to remain. I'm specifically curious to hear from our veterinarians and those who are well versed and experienced in raising chickens.

I've read and witnessed in my own hens that modern hens lay pretty frequently. Typically not every day, but sometimes for periods of time they might lay every day. Some might lay every other day, or every few days. And then there will be periods of time when none of my hens are laying. This is particularly pronounced in the winter. These prolonged egg-less times can be due to anything from a change in weather/temperature conditions to a change in the coop. Conversely, during winter, a season which commonly sees a lowering of egg productions, we as caretakers of chickens have learned that there are things we can do to increase egg-laying during this period of time. I myself swear by the red-lightbulb-in-the-coop thingie, after having used it this past winter.

Please note, I'm not concerned with trying to find explanations for why my or anyone else's hens may have stopped laying. Let me get to the point now:

On another board I frequent, someone posted that modern hens have been "developed" to lay on a regular basis, and that this is "hardly a natural process."

This did not ring true to me - but then, I'm a relative newcomer to the world of chickens. It was my understanding that the chicken is a relatively "primitive" organism that has not changed much - biologically - for, well, millenia. Surely, we have developed chickens with odd characteristics such as crested, featherless, and those with feathered feet, etc. (But of course these characteristics have to have occurred naturally somewhere along the line and were merely "encouraged" or "cultivated," if you will.)

But what about this egg-laying theory? I as a human female was not "developed" to ovulate monthly, or rather, approximately every 28 days. That's a mark of my species and I happen, as a single specimen, to adhere to that mark.

Have modern chickens been "developed" to lay relatively regularly? Or is this a mark of their species?

Thanks.

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#15960 - 02/25/04 11:27 AM Re: Egg Laying Regularity - Innate or Developed?
R. Okimoto Offline
Lord of the Fowl

Registered: 07/18/02
Posts: 1498
Loc: Arkansas
Wild Junglefowl used to have a breeding season. Unlike the feral birds that inhabit the original Red Junglefowl territory that can breed pretty much year round the original birds were sensitive to the seasons. This is probably due to the fact that even though they are in the tropical regions and only a few of them made it into the Northern latitudes the Ice Age only ended around 12,000 years ago and where the birds are now was not very warm. Chickens are photosensitive. Even in domestic breeds a lot of them will still show seasonal egg laying.

When the days get too short they stop laying. To keep them laying all you need to do is provide light for 14 hours a day. Most commercial operations provide even more light than that. Some of them are hitting the bird with 18-20 hours of light.

The birds evolved to lay an egg each day for a short period of time to fill out a "clutch" of eggs. They then go through hormonal changes and broody behavior kicks in and they stop laying and begin brooding. For wild birds like Ostriches that haven't been bred for egg production, you can extend the lay period just by collecting the eggs. You can get 80 eggs from a hen instead of 10 or 20. They bred a lot of Whooping cranes just by removing the first two eggs and making the parents start over with a new clutch.

Modern layers are bred to extend the clutch size and to keep laying and not go broody. The birds often go through a molt when they are raising chicks because you might as well molt and loose the ability to fly when you can't fly and leave your babies behind. Modern layers have the genetics to delay the period to the molt to over 18 months because chickens don't lay eggs when they are molting. Some commercial operations are force molting their birds to start a second cycle of lay.

The difference between the best layers is genetic and physiological. I've been told that they can breed birds that lay more than 1 egg in a 24 hour period but that egg quality suffers. There seems to be a limit. It takes a lot to make an egg each day and put a shell on it. Some birds have to take a break more often than others.

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#15961 - 02/26/04 10:24 AM Re: Egg Laying Regularity - Innate or Developed?
Anonymous
Unregistered


Quote:
Originally posted by rokimoto:
The birds evolved to lay an egg each day for a short period of time to fill out a "clutch" of eggs.

Modern layers are bred to extend the clutch size and to keep laying and not go broody.
How "modern" would you say these characteristics are? For example, chickens from, say 1400 years ago in Northern Europe: can you hazard a guess as to whether or not they would display "modern" characteristics of laying about an egg a day to "extend the clutch size"? For short periods of time or longer periods of time?

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#15962 - 02/26/04 08:58 PM Re: Egg Laying Regularity - Innate or Developed?
D. Caveny Offline
Ruler of the Roost

Registered: 07/16/02
Posts: 1102
Loc: Arizona
Speed (number of eggs in a clutch) and persistency (one clutch followed by the next with little or no pause between) are the terms used in the business. If you will read James Dryden's Egg-Laying Characteristics of the Hen, Bulletin No. 180 published August, 1921 by Oregon Agriculture College (now Oregon State University, Corvallis, Oregon) you will learn that hens around the turn of the last century hens layed from very few eggs (less than 10) to 70 or 80 eggs in a year. Dryden selected for egg numbers and utilized crossing of breeds to develop the Oregon (LadyMacDuff 303 eggs in a year) and improved production of Leghorns and Plymouth Rocks and thus founded the modern poultry breeding business. In the 1930's Goodale selected for egg size along with egg numbers and further emphased the fact that high producers produce high producers. In 1939 E.B. Parmenter discovered that by selecting hens which laid eggs prior to 10 am produced hens with 24 rather than the normal 26 hour oviposition interval. After that selected hens with 300 eggs or more per 52 weeks of production became more and more frequent. Now after approximately 60 years of selection flocks of 100,000 or more hens have a hen-housed average of 315+ eggs in 52 weeks of production. There are lots and lots of papers and books written on the subject that just require a little reading and lots of experience to apply. The other part shown in a series of papers by Hutt and Cole from Cornell is that populations which are not much inbred but selected for production will continually improve in production characteristics over time.

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#15963 - 02/27/04 07:42 AM Re: Egg Laying Regularity - Innate or Developed?
R. Okimoto Offline
Lord of the Fowl

Registered: 07/18/02
Posts: 1498
Loc: Arkansas
From what breeders have been able to accomplish in just a few decades it is apparent that a lot of genetic variation for better egg production was already in the chicken population. They just selected the birds that expressed the traits that they wanted.

There are a lot of theory papers on how many new mutations to expect, and extended selection in closed lines likely relies on these new mutations appearing and being selected for, but the bulk of the advance is probably due to genetic variation that chickens had 1400 years ago, and I'd expect that a few fortunate guys back then had some prized birds that they selected. That is how Leghorns and other layer breeds were developed.

I just listened to a seminar where the fellow claimed that the advances in the broiler industry for at least the last decade have been due to new genetic variation (mutation) in the broiler population. His inference was due to the fact that there is no phenotypic overlap between the 1950 broilers and the 1990 broilers. No birds grew as fast and put on as much weight in the 1950s as the run of the mill commercial broiler did in 1990. There was no overlap in phenotype. His claim is that the genetic variation that exists in selected populations today that allow for this rapid growth rate did not exist in 1950. He could be right, but we have other explanations like genetic interactions.

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#15964 - 02/27/04 10:25 AM Re: Egg Laying Regularity - Innate or Developed?
Anonymous
Unregistered


It seems to me that it would be detrimental to the wild birds (chickens) to lay eggs during times when food is scarce. A large egg has about 70 dietary calories which is 70 kilocalories to a scientist. That puts a lot of pressure on the hen and the hen's environment. This is probably why the laying season is/was always in the spring when food is more abundant.

Ron, what is the theoretical rate of mutation? Do different genes mutate at approximately the same rate? Pauling's 'molecular clock' idea assumes that the mutation rate is contant when viewed over a large enough time scale, but some genes could mutate faster than others and there could be 'hot spots' where mutation activity is greatest.

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#15965 - 02/27/04 12:08 PM Re: Egg Laying Regularity - Innate or Developed?
R. Okimoto Offline
Lord of the Fowl

Registered: 07/18/02
Posts: 1498
Loc: Arkansas
The molecular clock idea basically relies on the constant rate of fixation of neutral mutations in the genome. Fixation is when all or nearly all of the members of a population are homozygous for the same allele. A large population is never at total fixation at any locus because there are always variation.

The estimate for humans is that you inherit around 200 new mutations from your parents. The vast majority of these mutations occur in what is called junk or spacer DNA and don't do anything to the individual. When people start with highly inbred strains of mice (these are essentially clones of eachother) they find enough genetic variation due to new mutations to perform significant directional selection for things like body weight or litter size. I think that the estimate for mutations affecting a trait are around 1 in a million for each gene each generation that contributes to the trait.

There are 6 billion base-pairs in the human genome and with 200 mutations that is an average mutation rate of 3 X 10^-7 per base-pair. The average gene has a 1000 base-pair coding region, but a lot of the mutations that occur in the coding region aren't going to do anything.

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