Body Weight Management

Body weight management comes into play at two critical periods during the life of a flock of laying hens, specifically the rearing and the molt periods. During the rearing period it is important to manage the nutrition, vaccination, beak trimming, house ventilation, and general management program so that the pullets meet the recommended body weight for the strain.[3] With the modern layer strains this process can be managementintensive, because it is not recommended to feed-restrict

Threshold for ovary and oviduct development

Pullets moved to laying house

Begin light

Age of the pullet (days)

Fig. 1 Step down/step up lighting program for replacement pullets in light facilities. (Figure courtesy of Ref. [3].) (View this art in color at

the pullets during the rearing period. Therefore, random samples of pullets should be weighed each week to ensure that body weight targets are met throughout the growing period.

Body weight is generally controlled through changes in diet formulation, altering the duration of feeding phases during the pullet-rearing period, or modifications in the lighting program (intensity and day-length), thereby controlling the protein and energy intake. The third factor that affects growth rate is ambient temperature. Low temperatures will cause overeating, and high temperatures can cause reduced consumption of nutrients. Maintaining a thermal neutral temperature (55 75°F) after the initial brooding period usually results in the best growth rate and productivity of layer flocks. Continuous monitoring of pullet body weights is important, because a dietary or management change to control body weight should be made quickly to maintain the flock's recommended average hen weight.

The impact of a dietary or management change may not manifest itself until 3 to 4 weeks later. Thus, one needs to be familiar with the strain characteristics and have an understanding of how pullets grow in the facilities being used. Another component of body weight is the uniformity of pullet body weights within the flock. A uniform flock (high percentage of the pullet weights falling within ± 10% of the mean weight) is one of the best indicators of pullet quality, and flocks with good uniformity have a greater probability of meeting their genetic potential for egg production and feed conversion. Crowding, stress, improper feeder and waterer space allocations, improper nutrition, and disease are some of the factors that can have a negative impact on uniformity.

Molting is the second critical period of body weight management for laying hens. Molting is used as a management tool in the egg industry to extend the productive life of the laying hens over a longer period of time, or to improve egg production and quality during

120 176 232

568 624 680

Fig. 2 Step up lighting program for laying hens, including the molt, in light control facilities. (Figure courtesy of Ref. [3].) (View this art in color at

120 176 232

288 344 400 456 512 Age of the pullet (days)

568 624 680

Fig. 2 Step up lighting program for laying hens, including the molt, in light control facilities. (Figure courtesy of Ref. [3].) (View this art in color at

Table 1 Ambient temperature influence on heat stress


to 75°F (13°

to 24°C)

Thermal neutral zone: the temperature range in which the bird does not need to alter its basic metabolic rate or behavior to maintain its body temperature.


to 75°F (18°

to 24°C)

Ideal temperature range.


to 85°F (24°

to 29°C)

A slight reduction in feed consumption can be expected, but if nutrient intake is adequate, production efficiency is good. Egg size may be reduced and shell quality may suffer as temperatures reach the top of this range.


to 90°F (29°

to 32°C)

Feed consumption falls further. Weight gains are lower. Egg size and shell quality deteriorate. Egg production usually suffers. Cooling procedures should be started before this temperature range is reached.


to 95°F (32°

to 35°C)

Feed consumption continues to drop. There is some danger of heat prostration among layers, especially the heavier birds and those in full production. At these temperatures, cooling procedures must be carried out.


to 100°F (35

° to 38°C)

Heat prostration is probable. Emergency measures may be needed. Egg production and feed consumption are severely reduced. Water consumption escalates.

Over 100°F (38°C)

Emergency measures are needed to cool birds. Survival is the

concern at these temperatures.

periods of high demand.[4] In addition, molting improves the overall health of the flock.[5] The key to a successful molting program is the rapid cessation of egg production and a uniform body weight loss during the molt. Body weight loss and subsequent performance of the flock are dependent upon the strain of the birds being molted. The various commercial laying stocks respond differently to the amount of body weight loss between 25 and 35% that ensures optimal production in the second cycle. If the weight loss is in excess of 35%, mortality may increase beyond acceptable limits and the productivity of the flock may be impaired.

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