After many generations of selection, breeders have now developed layers which mature at a young age. The rate in advancing onset of sexual maturity corresponds to a half day earlier each year. Changes in egg weight from initial production to maturity have increased by as much as 0.35 g. per year.
The first egg which once weighed 40 g. now weighs 47 g., and a mature 60 g. egg weight (47.5 lb. case weight) is now attained between 30 and 36 weeks of age. This has all happened while mature body weights have been declining. Mature weight of Leghorn strains has decreased by 5 to 15 g. per generation, but this has had a negative influence on the weight of immature pullets.
Breeders have now adopted quantitative methods which allow the body weight curve of hens to be described statistically. One way to do this is to use random regression models, which have been applied to changing the shape of the curve in egg weight in breeding programs for many years.
The goal of breeders today is to increase immature pullet weight. Targets at Hy-Line are to increase pullet weight by 5 to 20 g. while controlling or still lowering mature hen size. This will enable the mature flocks to have low maintenance costs. The immature pullet will be able to achieve the needed body size to enter production at the correct age and weight to maintain high levels of peak production and persistence.
Pullets are now subjected to more intensive vaccination programs which impose stress and divert nutrients from accretion of body mass to developing an immune response. As pullets are prepared for cage-free egg production, demands on muscle development are very high. This requires the selection of more robust pullets which then enter lay and continue growing to 32 weeks of age.
Increasing performance, wellbeing
Geneticists are continuing in their efforts to achieve improvements in both performance and wellbeing. Some of the considerations in contemporary selection programs include:
- Upgrading flock wellbeing through enhanced livability;
- Improved social interactions within the flock, for both non-confined and caged egg hens;
- Selection for improved feather cover; and
- Appropriate nest egg laying behavior.
All of these traits are characterized by moderate to low but sustainable rates of progress. The overall goal is to continue to improve feed and water utilization to increase saleable egg mass.
Currently, commercial hens have the lowest carbon footprint of all farm animals with 2.1 lbs. of carbon used to produce 1.0 lb. of eggs. The rate of improvement in feed conversion has attained a consistent improvement of 1.3 % per annum.
More efficient feed conversion is due to consistent advances in rates of lay, egg mass produced, lower adult maintenance cost, better feather cover, and superior egg quality. This translates into a higher percentage of eggs, which are marketable for each successive generation.