Effects of Physiological Development on the Management of Broiler Parent Stock

Poultry Processing Articles >> Broilers

To be successful in the business of broiler chick production, it is necessary to appreciate the genetic progress for growth, feed efficiency and meat yield that has been both continuous and dramatic. We are told by Primary Breeders that the growth rate is increasing by 50 grams per year. These economic improvements are of course welcomed by the broiler industry.

However, we do not get something for nothing and the poultry business is no exception. While Primary Breeders strive to balance reproductive performance with the prime broiler objectives, inevitably it becomes a difficult task to achieve both predictable and consistently good chick numbers from parents of high performance broilers.

It is essential that logical rearing management, based on the sequence of physiological development is followed, which would ensure the desired genotype. However, alter the phenotype to resemble a layer — the main parameter being body weight. All Primary Breeders recommend restricted bodyweight profile, which in reality, is approximately 47-50% of a full fed bird.

To devise a rearing programme, which would ensure physiological development, it is useful to divide the growth period from day-old to sexual maturity, into stages.

1.1 Day-old To 21 Days:
Chicks are just getting “started”, however, the following development is taking place:

a. Feather cover - This could be affected by brooding temperature and stocking density

b. Development of the immune system - In the early period, the chick depends on passive immunity derived from the hen, hence, the composition of the maternal diet is critical (Surai, 1999)

c. Development of supply organs, in particular, the cardiovascular system - The status of the nutrients, particularly selenium, in the yolk is of importance, marginal deficiency could lead to culls and/or higher rearing mortality (Surai, Sparks, 2000; Lanning et al., 2000)

d. Development of Thermoregulatory Mechanism (TRM) - This allows the birds to regulate its body temperature

Management Action Required
a. Sample weigh day-old chicks and calculate average weight. This weight should increase 3 times by 7 days (e.g. day-old weight 40 grams, 7 day weight 120 grams). If the weight does not treble during this 7-day period, then a full audit of brooding management must be done, followed by corrective action.

b. Feed is give ad libitum, however, daily feed intake must be monitored, so that feed can be controlled once the chicks consume 30 grams per bird per day. Thereafter, feed increases are based entirely on bodyweight every week however, two small feed increases in a week are better than one big increase.

c. Weekly sample weighing and monitoring uniformity is necessary to ensure correct decisions on feed increases.

d. Temperature in the brooding area should provide comfort zones, e.g. 31°C under the brooder, 28°C away from the brooder. This will prevent chicks from overheating which would lead to reduced feed intake.

e. Ensure minimum ventilation, i.e. one air exchange every five minutes, Teeter et al., 1998, state 19.6% oxygen is required for adequate development.

f. Feed and water must be fresh and drinker and feeder spacing adequate.

1.2 21 Days To 42 Days:
During this period of increasing growth rate, the aforementioned physiological developments continue. This period is characterized by rapid skeletal development; approximately 75% of adult skeleton is achieved by 56 days. It is worth noting that skeletal size dictates the bodyweight at which the bird achieves sexual maturity.

Management Action Required
a. Ensure adequate feed and water space. It is critical that feed is distributed so that all the birds receive the feed at almost the same time so that the flock remains uniform.

b. Getting the birds to the target bodyweight by 28 days of age is an important benchmark, as it indicates that the birds have received adequate amounts of nutrients, in particular amino acids, hence the birds have received a “good start”.

c. 35 days of age is a good time to improve uniformity, if required, by grading the flock. It is, however, important to redraw target weights for the heavy and light birds, so that they arrive on standard target weight by 10 weeks of age, i.e. gradually. Remember, uniformity of frame size is essential.

1.3 42 Days To 70 Days:
a. Skeletal development continues.
b. Muscle tissue growth is rapid, feed efficiency is at its peak.
c. Tendons and ligaments are strengthening; any decline or stall in weight may result in leg weakness at a later stage.

Management Action Required
Feed increases should be based on bodyweight, preventing stalls or decline. Bodyweight is always increasing.

1.4 70 Days To 105 Days:
a. Skeletal development nearing completion.
b. Slow down in bodyweight gain, as the birds undergo feather change.
c. Period is characterized by increasing hormone production associated with preparation towards sexual maturity.

Management Action Required
a. All birds should be on target weight by 10 weeks. However, if any of the group is above or below target, then redraw target weight so that it runs parallel to standard until 15 weeks and thereafter to be on standard bodyweight by 18 to 19 weeks.
b. Avoid stalls or decline in bodyweight.
c. Do not grade.

1.5 105 Days To Sexual Maturity (Approximately 161 Days):
a. Acceleration of growth rate from 14 weeks.
b. Rapid production of sex hormones, resulting in rapid ovarian and testicular development. Any decline or stall in bodyweight will interrupt sexual maturity.

Management Action Required
a. Positive weekly feed increases will ensure the rate of bodyweight gain. However, if the bodyweight is under or over the target weight, accept the error and keep the bodyweight parallel to standard bodyweight profile and adjust the light stimulation timing. This is particularly important post 20 weeks of age. One is tempted to get the underweight birds to target by giving more feed. This would result in super ovulation: that is, the ovary will have too many large follicles, a problem known as Erratic Oviposition and Defective Egg Syndrome (EODES) is seen (Robinson, 1995). This condition is accompanied by high incidence of double yolked eggs, which can cause prolapse, laying poor quality or shell-less eggs and egg peritonitis.

b. Light stimulation is best given when 95% of the birds are “ready”; this will be after 20 weeks of age. A model that works well is providing the first light stimulation when 95% of the birds are on or above 2,200 grams bodyweight. The photoperiod at this stage is increased to the maximum and held.

Males
A specific physiological development-taking place in males, apart from all of the above, is worth nothing. Kirby, 1998, reported that the males are developing sertolli cells from an early age to 11 to 12 weeks of age and any stress during this period will therefore reduce sertolli cell count, leading to reduced sperm count later on. Hence, male bodyweight needs to be on or slightly above the standard target at 4, 6, 10 and 12 weeks of age, respectively.

Males may be mixed with females prior to light stimulation at 8-9% mating ratio.

This type of logical rearing programme ensures maximum and repeatable breeder performance, as management actions are based on the sequence of physiological development of the bird.

Summary
The logical rearing programme outlined above ensures maximum and repeatable broiler breeder performance, as management actions are precisely correlated with, and based on, the sequence of physiological development of the bird.

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