# Calculation of Metabolizable Energy Requirements for the Broiler Breeder Production Period (Part II)

The daily metabolizable energy requirements for broiler breeders are dependent upon maintenance, growth, and egg production. The following guide provides basic formulas for estimation of each. It is reasonable to assume that these numbers are most reliable when birds are receiving feed daily. The original calculations were based on birds receiving relatively unlimited access to feed and the effect of feed restriction is not fully known. Calculation of daily maintenance requirements involves a fractional exponent so the attached table is provided for ease of reference. Daily average temperature fluctuations must also be accounted for and the attached table is so configured. For example purposes the lower end of the thermoneutral zone (65°F/18.3°C) is used as a base temperature to demonstrate a reasonable maximum daily maintenance requirement. Most houses are operated in the thermoneutral zone (65°F to 85°F/18.3°C to 29.4°C) and little adjustment is needed within this range. However, it should be noted that in breeder houses with high speed air movement the "effective temperature" for the bird may be less than the observed dry bulb temperature due to the effect of "wind chill."

Maintenance
1.45 BW0.653 x CF where body weight (BW) is in grams and CF is a correction factor for average house temperature calculated as CF = 1.78 - 0.012 T where T is average house temperature in °F. The CF = 1 at 65°F/18.3°C. The attached table compensates for certain temperatures.

Growth
Each gram of growth requires 3.13 kcal ME. This is equivalent to 14.21 kcal per 0.01 pound of gain (0.01 x 454 g/lbs. = 4.54 x 3.13 = 14.21).

Egg Mass
This is best calculated on a gram basis by first determining egg mass per day and then multiplying by 3.15 kcal.

Calculations based upon: Combs, G. F., 1968.

Proceedings Maryland Nutrition Conference for Feed Manufacturers

Example

Maintenance Requirement
Formula A:
(1.45 BW0.653) x CF where BW is in grams and CF is a correction factor for average house temperature. The CF may be calculated as CF = 1.78 - 0.012 T where T is average house temperature in °F. The CF = 1 at 65°F/18.3°C. The table lists the maintenance requirements for various body weights and house temperatures.

Example 1:
3400 g (7.495 lbs.) = 293 kcal (~30 weeks) at 65°F/18.3°C

Example 2:
3100 g (6.834 lbs.) = 276 kcal (~28 weeks) at 65°F/18.3°C

Growth Requirement
Formula B:
Body weight gain (grams) per day x 3.13 kcal ME per day
Body weight gain (0.1 lbs.) per day x 14.21 kcal ME per day

For a 14-day period from 28 to 32 weeks of age (metric and English units)

Example 3:
3400 g - 3100 g = 300 g ÷ 28 days = 10.7 grams gain per day 10.7 grams x 3.13 kcal/gram gain = 33.5 kcal ME per day

Example 4:
7.495 lbs. - 6.834 lbs. = 0.661 lbs. ÷ 28 days = 0.024 lbs. 2.4 (hundredths of a pound) x 14.21 = 34 kcal ME per day

Egg Mass Requirement

Formula C:
Percentage lay x average egg weight (grams) = average daily egg mass per hen (grams)

Example 5:
80% lay of 53 g eggs 0.80 x 53 g = 42.4 g egg mass per day

Example 6:
85% lay of 52 g eggs 0.85 x 52 g = 44.2 g egg mass per day

Formula D:
Egg mass (grams per day) x 3.15 kcal ME per day

Example 7:
(From Example 5) 42.4 g x 3.15 = 133.6 kcal ME per day

Example 8:
(From Example 6) 44.2 g x 3.15 = 139.2 kcal ME per day

Total Daily Metabolizable Energy Required
Scenario 1: Example 2 + Example 3 + Example 7 276 + 33.5 + 133.6 = 443.1 kcal ME per day
Scenario 2: Example 1 + Example 3 + Example 8 293 + 33.5 + 139.2 = 465.7 kcal ME per day

Calculation Of Daily Feed Requirement At Peak
Scenario 1:
Using diets with 2.75, 2.86, or 2.92 kcal ME/g (metric units) 443.1 ÷ 2.75 = 161.1 grams per hen per day 443.1 ÷ 2.86 = 154.9 grams per hen per day 443.1 ÷ 2.92 = 151.7 grams per hen per day
Scenario 2:
Using diets with 1250, 1300, or 1327 kcal ME/g (English units) 465.7 ÷ 1250 = 0.373 lbs. per hen per day 465.7 ÷ 1300 = 0.358 lbs. per hen per day 465.7 ÷ 1327 = 0.352 lbs. per hen per day

Obviously, there can be considerable variation due to body weight, egg weight, and temperature. It is important to maintain a relatively stable house temperature. The objective of these calculations is to make a reasonable estimate of the total daily energy required and provide this to the hens in advance of maximum need. This allows the hens to build nutrient reserves that can be utilized if egg production, egg weight, or body weight is greater than anticipated. This will negate the need for "challenge feeding." These reserves also anticipate the increased needs required for peak egg mass that occurs after peak egg production. If the daily ME required for 85% production of 52 gram eggs is 139.2 kcal (Examples 6 and 8) then that required for the egg mass peak might be 0.83 x 58 grams = 48.1 grams x 3.13 = 150.6 kcal. This represents a daily increase of 11.4 kcal. However, this is not an important consideration as daily body weight gain will have decreased and body reserves are available for utilization. It is more important to begin to again look at body weight control as soon as the rate of lay peaks.

Feeding Broiler Breeder Females To Peak Production
At the onset of significant egg production (~5%) the diet should be changed to a breeder feed containing 2.7 – 3.0% calcium, depending upon circumstances. For some strains the use of the high calcium feed before the onset of egg production will cause higher mortality due to sudden death and peritonitis. Feed should be increased in accordance with egg production so that the hens are neither deficient nor fed in excess. Two suggested approaches are shown below where maximum feed allocation is reached at ~70% egg production. This time is selected as it is ~1-2 weeks prior to peak egg production and closely follows the last photoperiod increase that should normally occur at ~50% rate of lay. With "yield" females it is very important to increase the feed slowly. This will minimize mortality and prevent excessive breast meat development ("fleshing") that will cause birds to consume feed slowly and exhibit poor peak production. The two approaches are either proportional to egg production increases or adjusted to give the feed a little more slowly initially to compensate for the fact that some hens start egg production later. The hens that initiate egg production later should not be overfed for best results. Peak daily feed should typically be about 164 grams (36 lbs./100) (164 g x 2.85 kcal ME/g (1295 kcal ME/lbs.) feed = ~467 kcal ME) per bird. For a flock consuming 118 g per bird (26 lbs./100) at 5% production and peak feed is reached at ~70% production then calculations similar to the following are made.

Examples: 164 g – 118 g = 46 g ÷ 13 = 3.54 (rounded off to 3.5) or 36 lbs./100 – 26 lbs./100 = 10 lbs./100 ÷ 13 = ~0.8 lbs./100. The thirteen (13) in the calculation represents the number of feed increases to be given for each 5% increase in egg production.

The above program will provide a feed increase every two to three days as egg production increases. Once some experience is gained with the approach outlined above it is possible to develop a daily feed increase program, based upon records of previous flock feeding programs, that will simply give small increases every day beginning at 5% rate of lay. This will help avoid calculations and possible confusion. Daily feed increases as egg production increases will also help prevent mortality and excessive body weight gain. Practical experience teaches that this daily feed increase can be about 0.40 lbs./100 or 2 gram per bird per day, assuming that egg production increases normally. Again, it may be beneficial to begin with smaller daily feed increases and increase the daily increment as the number of birds in lay increases. It should be remembered that 25% egg production means that 25% of the flock is in production while 75% of the flock is still not in lay. Excessive feed increases for the hens not yet in lay may lead to excessive fleshing and higher than normal mortality.

The selection of the peak feed amount should be based upon a careful analysis of body weight, body weight gain, egg production, egg weight, dietary metabolizable energy content, and environmental temperature. Daily metabolizable energy needs for maintenance, growth, and egg mass demand the predominant consideration. Please refer to another guide for assistance in calculation of metabolizable energy requirements during the egg production period. The practice of providing feed slightly in excess of requirements at peak egg production, as outlined above, is similar to "challenge" feeding practiced by many broiler breeder managers. With the approach outlined above, feed decreases may begin promptly once the birds reach peak production without concern about a loss of egg production.

Feeding Broiler Breeder Females After Peak Production
Female body weight will exhibit an increase 2 to 4 weeks after peak egg production (when peak production is expressed on a percentage, not egg mass, basis) is reached if care is not taken to readjust feed allocation in a timely manner. This body weight increase is most often caused by failure to promptly reduce feed intake to a level commensurate with requirements. However, as it is often wise to provide a peak feed amount that is greater than absolutely needed ("challenge feeding") in order to be certain that all the birds have sufficient nutrients. It is important to remove this excess feed and continue to decrease feed as the flock ages and egg production decreases to help control female body weight. Adequacy of the feed reduction program can be judged by careful and regular monitoring of breast meat ("fleshing") and fat pad to be sure that abrupt changes or excessive losses do not occur. It is desirable to have hens that have an obvious fat pad. It is also important to monitor the flock for normal declines in egg production. Evidence of hens becoming broody at peak is an indication of insufficient peak feed. Initiating molt later in the laying cycle is an indicator of insufficient feed or excessively rapid feed withdrawal for existing conditions (peak feed and weather). A suggested approach is outlined below.

Step 1. Reach ~164 grams of feed (465-475 kcal ME) per hen per day (~36 lbs./100) at ~70% rate of lay.

Step 2. After 5 days at a consistent rate of lay near 80% or greater reduce feed by ~5 grams per hen per day to ~159 grams per hen per day (~35 lbs./100). This will be about 30-32 weeks of age. This initial reduction may need to be less than suggested if the peak feed amount is less than suggested or if the house temperature is cold.

Step 3. Decrease feed 1 gram (0.2 lbs./100) per week until 40 weeks of age. As an example, the feed allocation will reach about 150 grams if the peak feed was 164 grams and feed reductions began at 30 weeks of age.

Step 4. Decrease feed 1 gram (0.2 lbs./100) every other week thereafter to 45 weeks.

Step 5. Feed decreases after 45 weeks of age are optional dependent upon weather and body weight. A very slow monthly reduction is advisable to adjust for declining egg production. It is typical for total feed reduction to be in the range of 10% from the peak feed amount, depending upon how much the peak feed was relative to actual requirement. For a 164 gram peak feed allocation the 10% reduction amount will be 148 grams.

Examine the weekly egg production and weekly body weight and physical handling data that you collect. If there is evidence that egg production was decreased by the feed decreases in Steps #2 to #4 above you need to increase the peak feed amount or reduce the Step #2 decrease for the next flock and repeat the process of evaluation. If the female body weight increased excessively during the 3 to 6 week period after peak, the feed decreases in Steps #2 and #3 need to be increased and the process of evaluation repeated. If egg production and female body weight react as desired then repeat the program on more flocks while performing the above evaluation. Over a period of time, finalize the program with predetermined variations planned for seasonal differences in temperature. Feed should be decreased more rapidly in hot weather than in cold weather. With the onset of cold weather it may be necessary to increase the feed amount.

It is common practice to employ a late (second phase) breeder period diet that has a reduced level of protein and increased level of calcium. As dietary protein intake may influence albumen quality and egg shell quality the use of a lower protein late phase breeder feed must be approached cautiously. Further, excessive calcium intake may strengthen the eggshell by increasing shell thickness but may also result in the closure of some eggshell pores with a negative impact on hatchability. The use of ascorbic acid (Vitamin C) is beneficial in older flocks as it improves albumen and eggshell quality without creating excessively thick shells.

Estimation Of Required Feed Allocations During Rearing And Reproductive Tract Development
For weekly body weight gains of the following amounts the daily feed allocation contains a portion for body weight gain (in addition to amount for maintenance that can be calculated with aid of another guide) approximately as calculated below, assuming diets containing 1325 kcal ME/lbs. (2.915 kcal ME/g)

0.15 lbs. (68.1 g) gain per week
0.15 x 454 g/lbs. x 3.13 kcal/g ÷'d6 7 = 30.45 kcal ME per day or 2.30 lbs./100 (10.44 g/day)

0.20 lbs. (90.8 g) gain per week
0.20 x 454 g/lbs. x 3.13 kcal/g ÷'d6 7 = 40.60 kcal ME per day or 3.06 lbs./100 (13.89 g/day)

0.25 lbs. (113.5 g) gain per week
0.25 x 454 g/lbs. x 3.13 kcal/g ÷'d6 7 = 50.75 kcal ME per day or 3.83 lbs./100 (17.39 g/day)

If it is assumed for female broiler breeders that the daily feed allocation will be ~20 lbs./100/day (90 g/day) at 20 weeks of age. If we commence restricted feeding at ~7.0 lbs./100/day (~32 g/day) at 2 weeks of age we can calculate the approximate average weekly feed increase for females for body weight gain alone to be:

20 lbs. – 7.0 lbs. = 13.0 lbs. ÷ 18 increases = 0.722 lbs./100 pullets per week or 3.3 g/pullet per week.

For males we can estimate in a similar manner since the early feed intake is limited and we can calculate the required minimum feed at 6.0 – 7.0 pounds (2.72-3.18 kg) body weight at ~20 weeks of age where we will be feeding about 24 lbs./100/day (109 g/day). In this case we can calculate approximate average weekly feed increase for males for body weight gain alone from 14 lbs./100 (63.6 g/day) fed at 4 weeks of age to be:

24 lbs. - 14 lbs. = 10 lbs. ÷ 16 increases = ~0.63 lbs./100 cockerels per week or 2.84 g/cockerel per week.

In both these cases (males and females) the actual amount of feed required for basic maintenance decreases slightly with age and body weight such that the above general estimates are slightly higher than actually required. As a general rule of thumb, it is suggested that females typically receive approximately 70 grams (15.4 lbs./100) during their 15th week of age.

Given that precision feeding of "yield" females is needed to avoid the problems of overfeeding, but still supply sufficient nutrients for proper reproductive development, an obvious question arises. How much feed (metabolizable energy) is actually needed during the prelay period (photostimulation to first egg on an individual bird basis) for reproductive tract development. In other words, how much body weight gain is really associated with reproductive "bloom" apart from normal body weight gain and maintenance. This can be estimated from the weights of important organs and tissues that develop at the time of sexual maturity following photostimulation under blackout rearing conditions. We can estimate the additional body weight associated with each key organ or tissue at sexual maturity as follows:
Ovary 55 g
Oviduct 55 g
Liver 25 g
Fat pad 35 g
170 g 454 g/lbs. = 0.374 lbs. of body weight.

If we assume that, under conditions of blackout rearing, body weight at 21 weeks is 4.6 lbs. (2.09 kg), normal weekly gain is 0.20 lbs. (91 grams), normal weekly feed increase is 4.5 grams, and photostimulation is at 21 weeks (147 days) of age, then the body weight without reproductive tract development will be ~5.4 lbs. (2.45 kg) at 25 weeks of age. If we add the 0.40 lbs. (182 grams) needed for minimal reproductive development, as calculated above, then we have 5.80 lbs. (2.63 kg) at first egg, if that first egg is laid at 25 weeks of age (5% production). This body weight may vary upwards slightly depending upon the feeding program during rearing.

The feed required for reproductive development to the minimum age for onset of lay can be calculated as follows:

170 grams x 3.1 kcal ME/g gain ÷ 2.9 kcal ME/g (1320 kcal ME/lbs.) feed = ~182 grams (0.40 lbs.) of feed.

This calculation assumes that all hens will start to lay at 25 weeks of age. However, it must be remembered that peak feed will not be reached until about 70% hen-day egg production when most hens have started egg production. This will be about 70 days after photostimulation. Providing more feed than is necessary will only result in additional body weight gain and greater "fleshing."

These calculations are shown in a tabular form below.

The important point to remember is that the amount of additional feed required for reproductive tract development is relatively small and that this demand comes when the normal demand is slightly decreasing.

Maximum feed increases in blackout housing for males should never exceed 7 grams per week and 5 grams per week for females prior to photostimulation. After photostimulation, and mixing with females, sexually mature males should have their feed increases limited to about 1 gram per week as a maximum while females should need less than 3.30 + 2.60 = 5.90 g per week. It is suggested that a small additional feed increment (6-7 g for a single week) be given at the time of photostimulation followed by no more than 5 grams per week until 5% rate of lay is reached.

If we give too much feed too fast, we may simply increase body weight, primarily breast meat, and cause reproductive problems such as peritonitis and sudden death. The excess breast meat probably increases maintenance and inhibits reproductive development. This may be why heavy breasts relative to fat pad develop when feed increases are too rapid. The birds with excess breast meat relative to fat pad tend to lay poorly. A conservative feeding approach (minimum shown above) would be advisable until one becomes familiar with the particular strain of broiler breeder in the particular situation. The above guide should be useful in reviewing past flock records to determine why performance varied by flock. To provide some guidance concerning minimum feed requirements for maintenance and growth alone (for the specific male and female body weight programs shown in the examples), charts are available in other guides that show the amount of feed required for males and females at various temperatures and dietary energy combinations. It is also important to have the flock consume sufficient cumulative nutrition prior to photostimulation in order that they are properly prepared to respond to the photostimulation.

Some estimates above based upon G. F. Combs, 1968, page 86 in Proceedings Maryland Nutrition Conference for Feed Manufacturers. These estimates may need to be adjusted slightly for strain, age, and local effects and should be used with some caution.

Broiler Breeder Flock Management Case Histories

1. Management Of Females
Situation: Results had been mixed during recent years with a general lack of consistency in egg production and hatchability with "Classic Regular Strain" in this company. Experiences with a yield strain had been very disappointing. The general management philosophy had been to follow a body weight management approach. With the use of blackout rearing it had been generally believed that an "in-season" type of body weight standard could be followed.

Comment: It is my belief that the real reason for the difference between "in-season" and "out-ofseason" birds is environmental temperature. It has been my experience that birds reared in hot weather (out-of-season) will perform poorly if they do not consume the same amount of feed as the birds that are grown in cool weather (in-season). There will be a higher body weight as a result. This is absolutely necessary if the flocks are to consume sufficient feed during rearing to be able to perform optimally during the laying period. I have found that females require about 23,000 kcal ME and 1200 grams of crude protein at 20 weeks of age (140 days) as absolute minimums.

Field Observations: By comparison I found that some of the commercial flocks had cumulative ME near 20,000 kcal at 20 weeks of age. It has also been my experience that feed increases between 15 and 25 weeks of age should be in the 5 gram per week range to avoid development of excessive breast meat. Excessive breast meat is associated with slow feed consumption at peak, a typical problem. The only exception to this slow feeding pattern is immediately following photostimulation when a slightly larger feed increase is needed to supply the nutrients required for reproductive development. Following an initial visit and discussion a few houses were placed onto a feeding program rather than a body weight program. The flocks produced peaks of 80% - 84% using the female feeding program outlined below that produced heavier than normal body weights (BW) that are similar to an out-of-season standard rather than an in-season standard.

Comments: I also show above my suggestions for a Female Feeding and Body Weight Standard to the right. I developed this guide from data from within the company. This proposed body weight standard is to be assumed to be an out-of-season (high side reference) standard for the hotter growing season. The normal in-season (low side reference) standard, for the respective strain, may be used as the minimum BW guide if cool weather growing conditions prevail. I would suggest that both low and high references be posted as part of the records and body weights be generally maintained between these two reference points with an emphasis on the feeding program and achievement of the necessary cumulative nutrient targets.

Observations: The feeding program to peak egg production for this flock is shown below along with my suggestions for a revised program that will provide additional peak feed to the flocks, assuming that the flocks will consume the feed, and they will if the breast meat is not excessive. Some of the houses in this flock consumed 161 grams of feed at peak with no problem. Comments: If feed consumption time remains acceptable (less than 3-4 hours) the peak feed may be increased to 166 grams (464 kcal ME) at 75% lay. This can be considered a type of "challenge feeding." This should be followed by an immediate decrease in feed at peak egg production (5 days at similar egg production) to prevent excessive body weight gain following peak production. I should state that I generally overfeed at peak ("challenge feed") to be certain that all birds have sufficient feed to support maximum egg production and then reduce feed quickly to control the female body weight.

2. Management Of Males And Females
Situation: This company has had excellent results with some flocks (>160 chicks per hen) and poorer results with other flocks on supposedly the same body weight program and with very good uniformity achieved through a series of "grading" exercises.

Field Observations: By comparison among the good and bad flocks for egg production and fertility I found differences in feeding programs as shown in the table below. An important factor in this problem was the fact that the feed before 18 weeks was 2.65 kcal ME/g while the feed after 18 weeks was 2.75 kcal ME/g. This represents the equivalent of a large feed increase in and of itself.

It is very important to keep weekly feed records for the purpose of comparisons such as those shown above.

It is important to remember that there was a ME increase from 18 to 19 weeks that acted like a feed increase itself and no large feed increase should have occurred at the same time. The flocks with excessively large feed increases from 15 to 25 weeks seem to have the most difficulties in females. Males that are fed too much feed after mixing with females also seem to have difficulties.

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