Breeding companies have been producing increasingly fast growing and more highly efficient broilers for a number of years and like the broiler birds their parents (the broiler breeders) have registered rapid change
Companies which develop and supply broiler breeders have to marry two requirements– selecting for maximum egg number produced by the parent as well as selecting for the all-important traits of the broiler bird which is still the main focus.
Cobb, the international producer of broiler breeders, has set out what they regard as the correct management and nutrition of the parent birds to ensure customers obtain maximum number of eggs from their broiler breeders. One main reason why flocks do not achieve maximum potential egg numbers is the well-established drop in egg production persistency.
Egg production will rise to a good peak but will invariably fall quickly after the parent birds reach 40 weeks of age. The article is based on information written by Paul Welten and published by Cobb Europe* which elucidates the various reasons for drops in post 40-week production and what producers should do to obtain the maximum possible number of eggs right up until the end of the cycle.
Production persistency
Persistency is expressed as a production index number, or “PI”. That is the percentage of production added to the age of the flock, starting at peak production. For example, a flock at 30 weeks of age with an 84 per cent peak has a PI = 114 (30 + 84). The objective should be to maintain this PI of 114 for the whole production period of 40 weeks. This means at 60 weeks of age the weekly production would need to be 54 per cent (60 + 54 =114).
Production persistency is maintained by taking the following management guidelines into consideration
• Ensuring there is a good sexual uniformity at 23 weeks of age to guarantee a good peak production and production persistency of over 80 per cent. Sexual uniformity also includes fleshing and fat uniformity so females are in the best possible condition to continue good egg production.
• By not over-stimulating with artificial light and not exceeding 15 hours of total light (Table 1). Cobb says that production companies using a maximum of 14 hours of total light are rewarded with a general improvement in the livability of females as well as improved production persistency.
• By avoiding over-stimulation with feed going into peak production to avoid excess body weight, says Cobb. They suggest use of the alternative feeding programme shown in Table 2 if excess body weight occurs during this period. Body Weight should not increase more than 18% from start to peak production. Optimum control of body weight going into peak production means more flexibility and sufficient ‘in reserve’ to provide increased body weight towards the end of the production period.
• Broiler breeder farms are advised to avoid bringing their flocks into production too early (23weeks or earlier) and to be extra careful about timing if the females are not properly prepared to start production. Early production will result in a good peak but less persistency, more wear and tear of the feathers and smaller egg size, says Cobb.
• By avoiding over-weight in birds after peak production by reducing the feed regime on time. As a general rule when peak production is achieved feed reduction c
an be implemented by 2 g per week for 2 weeks in a row and then with 1 g per week till 40 weeks of age. After this period reduce feed more slowly by 1 g every 2 weeks. Many flocks in the field become over weight 3 to 5 weeks after peak production, indicating that excess feed was available in peak or just after peak, says Cobb.
• However, producers must not let the females plateau in weight gain because they must register a slow continuous weight gain to ensure that egg production is maintained. In addition, producers should endeavour to avoid any alteration in feed programmes at 40-45 weeks of age which will involve any change to ingredient composition. Every change of this nature is an added stress which can contribute to an irrecoverable fall in egg production.
• Quality and consistency of feed rations are key factors in maintaining production performance. Without consistent quality the feed reduction program is compromised and will fail to control body weight and therefore maintain egg production. Any error in management, whether related to feathering condition, light, watering or feeding program, will destroy uniformity and consistency resulting in erratic and invariably lower production.
Rearing period
Flock management, feeding and nutrition during the rearing stage have significant effects on final performance with farmers failing to produce good uniform pullets from day old chicks. Providing body weight profiles recommended by breeding companies are followed pullets will achieve the required skeletal development. Broiler breeders must achieve the required weekly gain in body weight with good uniformity for fleshing.
Flock uniformity is a key ingredient in the recipe for highly productive flocks, says Cobb because uniform flocks can respond to changing feed allocations as a ‘unit’. The first 10-12 weeks of the rearing period defines the birds’ frame uniformity while the following 12 to 20 weeks defines fleshing uniformity. Both are crucially important but generally more attention to grading is required between 10-12 weeks of age.
General on-going improvements in genetic potential does not mean breeding companies have increased their body weight targets says Cobb because evidence shows higher body weight profiles between the 10 to 16 week window of the rearing period gives poorer production persistency. This means precise body weight control during rearing has become even more important and is therefore subject to even more focus.
The rearing phase can be divided into three distinct periods:
• 0 - 6 weeks - the growth and development phase
• 7 - 16 weeks – the control growth phase which brings birds to the optimum body weight.
• 17 - 20 weeks – a dual function period - preparation for lay and growth acceleration
Development of sexual maturity speeds up from 15 weeks and from this point on the birds must achieve growth increases according to the standard specified curve. With body weight on target at 15 weeks of age the curve can be safely followed. However, if birds are already 100 g above target at 15 weeks then this should be maintained until 20 weeks, before using the light programme to gradually bring back body weight ‘into line’ before onset of production.
Pullets should be reared in dark out-houses where the light regime can be manipulated and controlled. During the rearing period, the light is reduced from 24 hours in 2-3 weeks to just 8 hours with light intensity raised from 3 lux to a maximum of 10 lux so that birds have a clear night and day pattern. Between rearing and production the light intensity should increase a minimum of 10 times so there is a direct and determined influence on the hypothalamus and the pituitary gland.
Production
Pre-pubertal period
The period from photo-stimulation to peak production is perhaps the most critical ‘window’ in broiler breeder management. Birds’ register relatively fast weight gains and ‘life-changing’ internal events due to the production of hormones by the newly physiologically active ovary.
Photo-stimulation timing plays a crucial role in flock development and future egg production. After lighting the very small ovarian follicles start to increase in size and produce large amounts of estrogen hormone that influence the production of egg yolk precursors in the liver. The bird’s liver assumes a paler colour due to increases in fat content to cope with and facilitate production of the egg yolk liquids. The oviduct increases in size so it is ready to receive the ovulated follicles, while the estrogen influences changes in the bone tissue so that calcium can mobilised on a daily basis to make egg shells.
Light stimulation
Age at which photo-stimulation occurs influences sexual maturity, egg production, egg persistency and egg weight. Birds are most sensitive to circulating estrogen levels between 2 to 4 weeks after photo-stimulation and overfeeding during this period leads to many follicles developing in the ovary. This in turn will increase the proportion of non-settable eggs, such as double yolks and soft-shell eggs as well as reducing production persistency. Flocks showing good egg production persistency are invariably those having a light program which does not over-stimulate the birds into production and one that gives a good balance between production and rest (Table 1).
A field trial comprising two different lighting programmes (high and light period increases) and two different feeding periods (slow fed treatment [SFT] and fast fed treatment [FFT]) showed clear results. FFT with the lower light regime produced greater ovary weight. Birds came into lay quicker with the higher light regime but showed poorer egg production post peak resulting in up to 10 less eggs. FFT birds exhibited higher embryo mortality and therefore fewer chicks compared with SFT birds. Overall this shows how both egg and chick production can be compromised by overfeeding early into lay and how over-stimulation with light too early can lower production persistency.
Cobb says the decision to stimulate the birds with light depends on the following:
• Whether body weight of the birds is on or above standard around 2250 g dry body weight
• Less than 5 per cent of birds weigh under 1900 g
• Body weight uniformity is greater than 75 per cent
• Birds have the correct body composition i.e. flesh/ fat score of 3-4.
Incorrect light intensity can also impact negatively on egg production with very low light intensity levels limiting ovary development, follicle production and egg production. Conversely, high light intensity can cause birds to become photo-sensitive much too early.
Feed and feed allocation
Getting the correct amount of feed to the birds at the right time is one of the most important factors in the successful raising of broiler breeders. Maintenance of vital organs, bone and muscle has the highest priority followed by reproduction. Over-supply of nutrients results in excess fat and excess follicle production which may lead to problems relating to SDS (Sudden Death Syndrome) and Haemorrhagic Liver Syndrome.
Feed allocation is at its most critical when broiler breeders are coming into production. Hens need the energy from feed conversion to maintain their body weight, growth and egg production but too many nutrients allows the production of more body fat, more follicle development and excess muscle. Overfeeding is linked to reproductive disorders and poor persistency of lay. Part of the extra nutrients utilised leads to excess fat which impacts negatively on egg production.
As a general rule of thumb, for every 200 g more of body weight after peak egg production the bird needs 5 g more feed for maintenance. Females can rapidly become 200 g overweight after peak if the feed amount is too high which means feed reduction should generally begin within 1 week of peak production or even during the peak production period. Total feed reduction from peak egg production should be between 8-14 per cent depending on the time of the year, production persistency and body weight of the females.
Nutrient shortage will result in smaller and /or fewer eggs. When broiler breeders don’t get enough nutrients, body weight and production correspondingly decreases with eggs smaller and/or lower in number. Both body weight and egg weight are good indicators of birds receiving the right amount, quality and balance of nutrients and both should therefore be monitored on a regular basis.
Dr Terry Mabbett
