The performance of brown egg laying hybrids, and similarly white egg layers, has increased significantly through genetic selection over the last quarter century. The increase in productivity has been achieved through advancing sexual maturity, increasing the level and time of peak production, improving persistency and also improving livability. An example of performance development during this time is demonstrated in the breed standards for Shaver 579 from 1985 and 2009.
Today’s performance could have been further improved by continuing advances in early maturity; however it has been recognized that the potential benefit in egg numbers may have come at the cost of ease of management and average egg size. For this reason, most breeding companies have reduced or ceased selection in this characteristic and rely more on the improved post peak persistency to give continuing annual gains in egg number.
There remain two critical times in the life of the pullet which will have the greatest effect on final performance, the first four to six weeks and the time from onset of lay until peak production. During both these times, body weight development is crucial if the flock is to perform to breeder standards.
Despite intensive research in the areas of nutrition, feed presentation and lighting programmes, many producers still encounter difficulties in achieving breeders’ projected target weight at four weeks of age. Areas of advancement have come in improving the nutritional balance, both of amino acids and energy in the early growing period. Research has shown that there is a direct effect between the energy level of the ration and growth rate in the early stages as, at this time, birds are unable to regulate energy intake to the energy level of the diet.
Any reduction in the amino acid content of feed will lead to a reduced early growth rate. With the objective of maximizing growth during this initial period, the amino acid balance of the feed is similar to that of a broiler of the same age. Birds, being primarily seed eaters, require a feed which is of a particulate form rather than a finer mash to improve consumption levels. Feed particle size has a direct impact on early growth rate, not only during the early brooding period but throughout the rearing period.
Natural growth promoters (NGPs) are already widely used in broiler production, and field trials have also shown that the use of probiotics and/or phytogenics to improve gut health can further aid the development of early growth to achieve the early development.
The second critical time for successful performance is the period between onset of lay and reaching peak egg mass production. In nature, a chick hatched in one spring would not come into production until the following year, allowing it time to reach its adult weight before coming into lay. With current management programmes and light stimulation, modern hybrids reach sexual maturity much earlier and, whilst already in egg production, still have to grow a further 20% to reach mature bodyweight. Again, this means that care has to be taken in providing the correct nutrition for body maintenance, egg production and growth.
Growth is the first parameter to suffer when insufficient nutrition is provided, which will result in a lower 30/32 week bodyweight which, in turn, will affect post peak egg weight and total egg mass output. In order to overcome this, early lay feeds have been developed. Nutrient utilization through improving gut function has been seen to improve early egg weights and feed efficiency without loss in growth.
Birds are influenced by day length both during the early brooding period and also during the stage approaching onset of lay. A delay in reaching the rearing day length plateau will result in delaying sexual maturity. Similarly, the time of increasing day length will have an effect on stimulation of sexual maturity.
Despite ongoing developments, birds remain very adaptable to management changes to optimise egg number and egg size. Over the last 25 years, producers have recognized the need to produce the correct egg size to meet market requirements and have altered their management practices accordingly. Body weight at point of light stimulation has a direct influence on the future performance of the flock in regard to average egg size.
One of the consequences of this improved productivity is a reduction in the time between successive ovulations. Traditionally, chickens when in production ovulated approximately every 26-27 hours, however, with modern hybrid production, this period has been reduced to 24-25 hours with high production birds ovulating every 24 hours. The time from ovulation to the time the egg enters the shell gland has remained the same and the reduction in overall time between ovulation and lay has come from a reduced calcification time of the egg in the shell gland from approximately 12-13 hours to 11-12 hours.
Calcium metabolism has needed to improve to counteract the reduced time in egg shell formation. Much research has been carried out in finding the best sources of calcium carbonate for egg production, particularly in regard to solubility. Eggshell production is carried out predominantly at night in brown egg layers, which means that the source of calcium has to be held in the bird’s crop and gizzard at the time of lights off. Faece examination has shown a high percentage of calcium particles of less than 1mm passing through the bird which suggests that the gizzard will only retain particles of a larger size, hence the recommendation that limestone of a size 2-4mm is provided in the feed.
Improved gut function through maintenance of gut structure has a role in the calcium metabolism for eggshell production resulting in improved calcium digestion and absorption. Field trials have shown that the inclusion of either probiotic or phytogenic products results in improved eggshell quality, which could see a reduction in the numbers of eggs being downgraded.
Feed costs amount to approximately 70-75% of the total cost of egg production; therefore any improvements in feed utilisation will have a direct impact on commercial egg production. Breeding companies are continually working in this regard and, as a consequence, final bodyweights have reduced significantly during the last quarter century. This has led to a 13% improvement in feed efficiency. However, in order to maintain the correct egg size to meet market requirements further reductions in final bodyweight are unlikely or will be very small. It is therefore important to look at further ways to enhance feed utilization throughout the production period.
Many pathogens such as Escherichia coli and Salmonella enteritidis can have a negative effect on gut structure, severely damaging the villi in the small intestine which reduces the ability of the gut to absorb nutrients. With S enteritidis this occurs particularly in the first two weeks of life. Control of these pathogens will improve overall feed utilization, and acidification of either feed or water has been seen to be effective in both the control of S enteritidis and also improving overall productivity due to improved nutrient availability.