Poultry nutritionists face something of a dichotomy when it comes to broiler breeders.
While the modern hen has the potential to yield at least 145 chicks over its 40-week productive life, it also possesses the same impressive growth potential of its offspring.
Delivering the correct level of nutrients to obtain optimal productivity, while at the same time moderating the bird’s inherent desire for growth, presents a significant challenge.
During rear and the pre-production period, the focus should be on providing the correct volume of nutrients to achieve good flock uniformity, development of the reproductive organs, growth rate and body composition.
See also: Getting the most from broiler breeders
Once in production, the nutritionist must then deliver a ration that balances weight gain, fat reserves, feather cover, egg production, egg size and hatchability, which will maximize the number of high quality chicks.
But the main factors influencing the reproductive performance of the flock must be established in the rearing period, and perhaps one of the most important is determining the correct body composition and crucially the hen’s fat reserves to fuel subsequent egg production.
Nutrient intake, not feed intake
Management decisions concerning feed allocation can only be made if there is a comprehensive appreciation of nutrient intake, rather than simply feed intake. This requires a strong line of communication between flock managers and nutritionists, and a firm understanding of the energy, protein and amino acid content of the diet.
Once established, the correct adjustments in feed allocation can be made based on the status of the flock. For example, uniformity may be low during rear, with three distinct groups forming: heavy, standard and light. If such a situation arises, grading based on weight must be carried out (see box), and then feed adjustments made, so that the differences in body weight between populations are reduced weekly, and flock uniformity is maximized by the point of lay.
Lighter birds require additional nutrient intake each day to try and increase growth if they are to catch up with the rest of the flock. For heavier birds, growth has to be slowed, but not at the cost of skeletal and reproductive development.
Maintenance requirements must also be respected, as severe feed control in heavier birds will result in hens that might never fully mature sexually. Body maintenance may account for up to three-quarters of total energy intake between four and 10 weeks of age.
Good uniformity can be challenging to achieve due to the rapidity of feed intake observed in the modern breeder, and the fact that breeders will deposit protein more readily than fat. Accurate formulation and subsequent daily feed allocations, as well as ensuring a uniform distribution of feed with good physical quality of the mash, crumble or pellet, will help in minimising the variance of body weight through the population.
First grading should be carried out at four weeks, and three groups determined; light (320-400g), normal (420-500g), and heavy (520-600g). A second grading should be carried out at nine weeks, at which time the normal group should receive 141kcal of a 2,800kcal/kg feed a day, the lighter birds should receive on average 11-1 kcal/day more (approximately 4g) and the heavier birds 6-7kcal/day less (approximately 2g). This should be fed in steady increments following the performance objectives.
Development of the flock
The first four to five weeks of age is important in determining the future performance of the birds. Nutrition during this period is concerned with the development of skeletal, intestinal, cardiovascular and immune system, and feather cover.
This must be achieved uniformly throughout the flock. A starter diet with 2,800kcal/kg, 19% of crude protein, 0.95% of digestible lysine, the correct amino acid balance in relation to lysine and vitamin and mineral supplementation, should be adopted.
Thereafter, grower diets are introduced, usually formulated with an energy level in the range of 2,600 to 2,800kcal ME/kg.
When a high energy diet is fed, flock uniformity may be more difficult to achieve because a smaller amount of feed is needed to meet the energy requirement of the bird, and feed clean-up times are short. A lower density diet will inevitably include more fibre rich ingredients, and appropriate steps should be implemented to minimise potential contaminants or anti-nutritive factors.
But if the correct quality control is in place, low density diets have many advantages, including reducing the hen’s stress as a result of a prolonged feeding time. If included at the correct particle size, fibre rich raw materials will provide sufficient structure to stimulate gizzard development which will regulate the flow of nutrients into the small intestine, optimising digestive processes, nutrient utilisation and prolonging satiety.
This slow flow of nutrients into the gut and their subsequent absorption may also be beneficial in delivering gently the required amino acids for feather development, as well as contributing to a steady build-up of abdominal fat.
When offering a low density grower ration, feed allocation must be increased to cover the daily requirements of the bird. But it is also imperative that protein and amino acids should be reduced to maintain the optimal energy:protein ratio. If this is not done, then protein intake will be excessive, leading to overweight birds.
To highlight this point, in a low density grower diet formulated to 2,700kcal/kg with 15% crude protein, the protein cumulative intake from six to 15 weeks will be 20g more than a standard 2,800kcal/kg and 15% CP grower diet. This is the equivalent protein intake expected from 360g of feed. This will clearly have a large impact on body conformation, resulting in over-fleshed birds with low level fat reserves at photostimulation.
The heavier the bird, the greater its maintenance requirement will be during lay, and nutrients will be assigned for this as opposed to maintaining good feather cover and the production of viable eggs. To avoid excessive protein intake, a diet of 2,700kcal/kg should contain around 14.46% crude protein to maintain the correct ratio, and of course the amino acids adjusted accordingly.
Increments in the amount of feed must be aligned with the standard daily energy requirements profile, to allow birds to achieve the correct body weight gain at target age. To help with this, Aviagen proposes daily energy allowances for the rearing period.
Fuel for production
When using a low density grower diet (2,600-2,700kcal/kg), a pre-breeder diet with higher ME content is a necessary transition to the production phase, providing a boost in energy to achieve the necessary fat deposition. A specialist pre-breeder ration should be considered, not simply a grower diet with extra calcium.
The response of the hens to light stimulation is based on the body condition and body weight of the bird. The hen needs the ideal fleshing, fat reserves and pelvic bone movement to respond properly to light stimulation. It is important not to stimulate the flock if the coefficient of variation for body weight is over 10%, usually a result of underweight birds.
By 22-25 weeks of age, if correct feeding and management through rear has been achieved, hens should have a sizable deposit of abdominal fat – the equivalent of 2% of its bodyweight, and this should increase to about 3% by peak production.
If feeding into lay is not adequate, and peak feed is only provided after 70-75% egg production, then the fat reserves will be utilised. This will impact persistency of production after 40 weeks, so it is imperative that feeding into lay provides sufficient energy to meet the demands of production and additional fat deposition.
Fat reserves are negatively correlated with muscle accumulation, but importantly, positively correlated with persistency in production. As feed is withdrawn from the hen, its reliance on reserves increases, so that by 45 weeks of age roughly a third of yolk lipids are being provided by fat reserves.
In addition, there is growing evidence that promoting sufficient fat reserves is linked to a reduction in feather issues post 40 weeks of production. This supports the theory that feather loss is due to a lack of energy in production, and the hen opts for feather loss over a decline in egg production.
In field trials, 40-week birds possessing 2.5-3% abdominal fat and 24% breast muscle exhibited perfect feather coverage, while birds from the same flock with 1.5% abdominal fat and 28% breast muscle displayed significant feather loss.
Key considerations for breeder nutrition
- Optimal production in a breeder flock is determined in rear and pre-production.
- Nutritionists and breeder managers must work together to ensure the correct levels of nutrients are delivered to the hens at the correct phase of development.
- Lower density (2,600-2,700kcal/kg) grower feeds can be effective in ensuring good flock uniformity, as well as improved fat deposition and reduced stress.
- Protein and amino acids must be reduced in line with energy, maintaining the recommended energy:protein ratio, if good results are to be achieved.
- A pre-breeder ration with a standard energy level will help to provide a boost in nutrients prior to production.
- Achieving approximately 2% abdominal fat in hens at 22 weeks of age, and 3% by peak production is strongly correlated with good persistency and feather cover.
Adam Sacranie was appointed to Aviagen’s global nutrition team in July 2014, to assist with the dissemination of practical information and guidance. He has a PhD in poultry nutrition and digestive physiology.