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Body Weight Uniformity

In addition to body weight averages, the uniformity of body weights within the flock is an indicator of normal flock development. Uniformity is expressed as the percent of individual weights which occur within 10% of the current flock average. The goal at point of lay is minimum 80% uniformity, although uniformities of 90% are often seen. Flocks lacking uniformity at point of lay often exhibit lower and later peaks than expected and are more difficult to design diets for (because there is a mixture of light and heavy birds in the flock). In grow, flocks of low uniformity can be segregated into similar weight groups to reduce feed competition between large, medium, and small birds. These groups should be managed differently to allow the small group to gain weight faster.

Factors, which can adversely affect the uniformity are

  • crowding
  • disease
  • vaccination program
  • poor beak treatment
  • lack of perches (or inadequate perch space) and
  • inadequate nutrient and energy intakes.

In other words, ensure that flocks have adequate feed, light, air (quality), and water (i.e., the acronym 'FLAW') at all times. See also the section on monitoring body weight.

Calculating body weight uniformity
Weigh at least 100 female birds individually. Be sure the weighed birds represent an average of the birds in the house.

Cages

  • Weigh all birds individually in each selected cage.
  • Select cages evenly spread in the house, and select a combination of cages from top, middle, and lower tiers, and from both ends of the house as well as the middle.
  • Weigh all the birds in the same cages every time body weight uniformity is determined.

Floor

  • Select birds from all locations in the house.


Example of uniformity calculation

  • Number of birds weighed = 105
  • Average (mean) body weight = 1.320 kg
  • 10% of the average body weight = 10% × 1.320 kg = 0.1320 kg
  • Upper body weight range = 1.320 kg + 0.1320 kg = 1.452 kg
  • Lower body weight range = 1.320 kg - 0.1320 kg = 1.188 kg
  • Count the number of weighed birds with a body weight between the upper and lower body weight range = 88
  • Body weight uniformity = (88 birds in weight range / 105 birds weighed) × 100 = 84%

Use the spreadsheet shown below to calculate the body weight mean (i.e., average), percent uniformity, and coefficient of variation (CV). Weigh the birds as per the instructions above and enter the body weights in the highlighted yellow fields (starting in cell B5). Leave cells blank if there is no data—do not enter a zero (0).


Screenshot of spreadsheet used to calculate body weight uniformity
 

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