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FEEDING TO MORE PRECISELY MEET THE NUTRIENT REQUIREMENTS OF BROILER BREEDERSJohn D. Summers Major changes have taken place with the feeding of broiler breeders in recent years. One of the most significant of these changes is separate sex feeding. With such an approach to feeding, it is now possible to more closely control the weight of the pullet coming into production and to be confident that, with challenge feeding, the additional feed is being used to maximize egg output rather than put extra weight on already overweight cockerels. By being able to precisely control cockerel weight marked improvements in hatch of total eggs set, with reduced cockerel numbers, is now being attained. With separate sex feeding changes in ration formulation to more closely meet nutrient requirements of males and females is now possible. More attention can now be paid to flock uniformity and by switching to everyday feeding, uniform pullet flocks that reach peak production in 4 to 5 weeks and produce 180 to 190 eggs per breeder, is not uncommon. While there are many points to consider with respect to management, feeding, health care, photoperiod, etc., that can have a marked bearing on the economics of production, this presentation will deal mainly with feeding to more precisely meet the energy and protein requirements of the modern day broiler breeder.
Body Weight And ConditionWhile body weight recommendations are readily available for the various commercial breeds on the market today, often there is very little information given as to how to keep problem flocks close to those suggested weights. A 6-week old commercial female broiler weighs around 1800 g while a weight of around 600 g is the target for a breeder pullet of the same age. Hence it is obvious that overweight, not underweight, is more likely to be a problem during the growing period. Pullets that are overweight during rearing should not have their feed allotment reduced in order to bring their weight in line with suggested target weights. Rather, feed should be held at the same level until body weight comes in line with that recommended for a given age. Then adjustments in feed allowance should be made to hold pullets to the desired weight curve. Another important point is to ensure that pullets, as they approach mature pullet weight, are carrying sufficient body flesh. This can be observed by checking fleshing over the keel. Pullets that are lacking in fleshing are immature birds and will be delayed coming into production. Increase feed intake and delay light stimulation of the flock until proper body condition has been achieved, even though body weight may be slightly in excess of the weight guide.
Nutrient RequirementsTwo of the major and most costly nutrients required by the breeder are energy and protein. While meeting protein requirements have often been the major consideration of producers, it is energy, the most costly dietary nutrient, which in many instances is limiting performance. This is demonstrated in Table 1, where it can be noted that varying energy intake by approximately 40% had a marked effect on production parameters, while a similar change in protein intake had little effect on performance.
EnergyIn developing feeding programs for broiler breeders consideration must be given to body size, environmental temperature and bird activity as these are the main factors influencing maintenance energy requirements. A consideration for growth is also important for the growing pullet and to a lesser extent, the mature hen. For the adult the energy requirement for egg mass output must also be taken into account. A number of prediction equations have been developed to estimate energy requirements. Most give reasonable estimates, but they are only estimates and must be evaluated for each situation.
Energy Requirements For PulletsIn Table 2 predicted energy requirements for breeder pullets to 20 weeks of age are shown. As the bird increases in age (larger body size) the maintenance requirement increases, as a percentage of the total energy requirement, until by the end of the growing period over 80% of the energy consumed is used just to maintain the pullet. Growers should be aware of the high energy cost just to maintain a bird and also to recognize that pen temperature is a significant factor influencing maintenance energy requirements. Thus, pen temperature should be monitored closely and feed intake adjusted accordingly if significant temperature changes result.
Energy Requirement For Broiler BreedersIn Table 3 are shown predicted energy requirements for broiler breeder hens from 20 to 68 weeks of age. Again it can be noted that the maintenance energy requirement is around 80% of the total energy intake. This decreases noticeably at peak production and continues to around peak egg mass during which time the hen would be partitioning a significant proportion of energy intake to meet her requirement for egg mass output. It is important for the producer to recognize that only around 20% of the energy intake of the hen goes into egg production (and any increase in body size). Since the hen will preferentially partition nutrients to meet her requirement for maintenance, if her feed allowance is not sufficient to meet her total energy requirement, egg mass output, thus egg production and/or egg size will be reduced.
Influence Of Feather Cover On Energy RequirementsWhile pen temperature has a significant effect on maintenance energy requirement, feather condition of the hen is also an important consideration. A significant increase in energy requirement for maintenance takes place if pen temperatures drop with a poorly feathered flock. While the pen temperatures shown in Table 4 are relatively low for tropical conditions, the changes in energy requirements shown demonstrate the importance of feather cover in estimating the energy requirements of broiler breeders.
Reducing Feed Intake Past Peak ProductionIt is common practice to reduce feed intake shortly after peak production is attained. This may be responsible for some of the dips in production noted at this time. The hen "thinks" in terms of egg mass output and thus no reduction in feed allowance should be made until after peak egg mass output is reached, which is usually 3 to 5 weeks after peak production. Another error some producers make is to reduce feed allowance in relation to the drop in egg production (e.g.. if production drops 5% reduce feed by a similar amount). An average egg of 60g requires approximately 120 kcal of metabolizable energy for its production. If feed allowance is 160 g/b/d at peak production, with a diet containing 2800 kcal ME/kg, this will result in a daily intake of 448 kcal of ME. If 120 kcal are required to produce one egg, this means approximately 27% of the hen's energy intake is going toward egg production at this time. Egg mass output for a flock at 85% production, with a 60g egg = 51.0 g/b/d. If production drops to 80% and during this time egg weight increases by 3g, egg mass output would be 50.4 g/b/d. Thus, egg mass output drops 51.0 - 50.4/51.0 x 100 = 1.2%. Hence, the energy required per day to produce the 1.2% less egg mass would be 1.2 x 120/100 = 1.44 less kcal/h/d. Thus, the total dietary energy requirement has only dropped 1.44 x 100/448 = .32%, not the 5% one might estimate from percent production. It should be obvious that decreased feed intake, after peak production, has to be precisely calculated if decreased egg numbers and/or size is to be avoided.
Protein RequirementsSince the maintenance requirement for energy is so high, in relation to total energy requirement, changes in feed allotment are usually made in order to try and maintain an optimum intake of energy. However, often little attention is given to the amount of protein consumed. Most breeder diets contain between 16 to 18% protein. With daily feed allotments as high as 160 g/b/d, protein intake could be 25.6 to 28.8 grams per day.
Protein Required For Egg ProductionUsing values generated for commercial layers, the calculated protein required to produce a 65 g egg (containing 7.8 g of protein) should be around 7.8 ÷ .55 (suggested efficiency of dietary protein utilization for egg production) = 14.2 g.
Protein Required For MaintenanceWith an estimated total endogenous loss of nitrogen, including feather loss of 280 mg/kg of body weight (to the .75 power), a 3.5 kg hen would require 3.5.75 x 280 = 717 mg of nitrogen per day to meet her daily maintenance requirement. Converting this to protein would give (.717 x 6.25) 4.48 g of protein. With the assumption that the hen is 55% efficient in the use of dietary protein for body purposes, would give 4.48 ÷ .55 = 8.15g of protein intake required per day to meet her maintenance requirements. Total daily protein requirement of a broiler breeder considering maintenance and egg production would be 14.2 + 8.15 = 22.4g/b/d. This would be sufficient for a hen to lay a 65g egg every day. While no allowance has been made for weight gain this would be minimal after peak production and besides much of this gain would be fat deposition and thus a minimum of body protein would be deposited. Since every bird is not laying every day the flock average for protein for egg production purposes would be the average percent production times, for example, the 14.2g of protein required for a 65g egg. Thus, the average daily protein required for a flock would be significantly less than 22.4 g/b/d.
Partitioning Of The Breeders' Protein RequirementWhile it was shown that approximately 80% of the energy consumed is partitioned to meet the hen's requirement for maintenance, it can be estimated, from the values generated above for protein requirements, that (14.2 ÷ 22.4 x 100) approximately 63% of the protein intake of the broiler breeder is going to meet it's requirement for egg mass output and thus only 37% for maintenance. Hence, the main factor influencing the protein requirement of the broiler breeder is egg mass output.
Estimating Protein Requirements Of a Flock Of BreedersIn Table 5 one can estimate protein requirements at various stages of the egg production cycle, assuming each hen is laying an egg a day. Thus, to get a reasonable estimate of the protein required per day, by a flock of hens, the values calculated from Table 5 should be reduced to take into account percent production (egg mass output per day) e.g.. for a flock laying at 80% with an average egg weight of 60 g and body weight of the flock averaging 3.5 kg the calculation would be .80 x 13.1 = 10.48g of protein for egg mass output + 8.15 g of protein for body maintenance = 18.63g total protein per bird per day.
Percent Dietary Protein Required To Meet RequirementsIn Table 6 is shown the estimated percent dietary protein required to meet the calculated requirements of the breeder, assuming the flock was laying at 70% production. It can be noted that even with a calculated requirement of 26 g/b/d a diet containing only 11.4% protein would meet the flock's requirement if they were consuming 160 g of feed/b/d. While a lot of assumptions and estimates have been made in generating the above values the low levels of dietary protein suggested are not too far removed from the estimates suggested by Bowmaker and Gous (1989), Harms and Ivey (1992) and Lopez and Leeson (1993). Indeed in the work of Lopez and Leeson (1993) the 10% protein diet resulted in similar total production as compared to their 16% protein diet. However, body weight was lower for the low protein diet as was egg size (Table 7). Lower body weights and smaller egg size have also been reported for commercial egg type hens fed low protein diets, even when supplemented with essential amino acids. More work is required to resolve why the low protein diets limit body weight and subsequently egg size. Lopez and Leeson (1993) reported a significant increase in hatchability (approximately 4%) with the 10 versus the 16% protein diet. It is interesting to note the number of reports suggesting the detrimental effects of higher protein intakes on hatchability. In Table 8 the data of Pearson and Herron (1982) show an increase in dead and deformed embryos, thus resulting in decreased percent hatchability, with 27 versus 23.1 g of protein intake per breeder per day. Similarly Whitehead et al. (1985) reported a significant increase in saleable chicks with a 13.7 versus a 16.8% protein diet (Table 9). Pearson and Herron (1981) reported that a ratio of dietary protein to energy of higher than 15 g:1 M Joule resulted in reduced hatchability of broiler breeders. Converting their ratio to protein per 100 carlories gives a value of 6.28 which is in line with the ratio of protein to energy reported by Spratt and Leeson (1987) to maximize chick hatch weight (Fig. 1). There appears to be a lot of evidence to suggest that many broiler breeders are being fed excessive levels of protein. Not only is such a practice detrimental to performance, but it is uneconomical as well as resulting in a greater potential pollution problem with excreted nitrogen. Dietary protein and energy must be kept in proper balance with respect to requirements, if a deficiency or an excess of one or the other is to be avoided. It requires a significant amount of energy to synthesize and excrete uric acid, the nitrogen excretory product for the avian species. Thus, a large excess of dietary protein could result in a deficiency of energy being encountered if a significant proportion of the energy consumed is used for nitrogen excretion purposes. Under such a condition a production response will be noted to what would appear to be an excessive intake of energy. If a flock is not attaining expected egg numbers or size when consuming 150 to 160 grams of feed per bird per day, one should look at possible management problems before changing diet composition or significantly increasing feed allowance. However, there are well managed flocks that are peaking in excess of 85% and holding a good level of production for a sustained period of time. Such flocks may require more than the normal recommended level of feed intake. The intent of the present talk was not to try and compete with the local nutritionists re diet formulation or feeding programs, but rather to try and point out avenues to pursue in searching out reasons why certain flocks may not be achieving optimum performance. It is often stated that seldom is the diet at fault but rather it is the feeding program or the management conditions under which the diet is being fed which is the problem. This is especially true for broiler breeders where the nutrient intake of the birds is very much under the control of the flock manager. Broiler breeders should be fed to maximize the production of saleable chicks per bird. Consideration of some of the points raised in the present article may help producers to increase these numbers.
References
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