By Rick Kleyn,
The protein and energy levels that are recommended for use in broiler breeder diets represent an area that is filled with confusion and contradiction. The purpose of this paper is to highlight some of these differences and to attempt to explain how these different recommendations may have come about. The different recommendations may have practical implications and some of these issues are discussed.
At the outset it is important to remind oneself that all broiler breeder nutrition is a function not only of the feed specifications used but also of feeding management. Looking at feed specifications alone is simply not good enough.
Secondly, it must be born in mind that because of their shear size, energy is the most critical component (nutrient) of the diet of the broiler breeder. The maintenance requirement of these large framed birds is far higher than that of a commercial laying hen. In addition, the lower egg output of the broiler breeder relative to commercial layers which means that a far higher proportion of the bird’s energy is used for maintenance purposes.
Not only is the energy level of the diet the most crucial in terms of nutrition, but it also has the most impact on the practical application of the feed and on it’s cost. Leeson and Summers (2000), show how the energy levels recommended by the various suppliers of genetic material differ.
Table 1: Nutrient Specifications for breeder diets (after Leeson and Summers, 2000)
These figures are confounded by the fact that the latest data published by Ross (2001) recommend a value of 11.5 MJ/kg, while Leeson and Summers (2000) show that diets containing 12.3 MJ/kg can be fed.
To the inexperienced, these figures show fairly close agreement with each other. Those who formulate diets will know that the difference in cost between a diet containing 11.5 MJ/kg and 12 MJ/kg of metabolisable energy is of the order of R 45.00 per ton. Those who feed broiler breeders will know that in order for the energy allocation to remain constant, the energy allocation of the low energy diet would need to be increased by 7 g/bird per day. Clearly this has both practical and economic implications.
This problem is not new and Kleyn (1987) conducted an experiment to investigate these aspects. Broiler breeders were offered three different energy allocations at 4 fixed daily feed allocations.
The amino acid levels of the diets were determined in such a way as to ensure that the lysine intake of the birds remained at a constant 920 mg/bird d. Ross birds were housed in 36 open sided pens, each pen housing 55 females and 6 males (at the start of the experiment). Data was collected for 4 weekly periods starting at 28 weeks of age. Separate sex feeding was not used.
Table 2: Dietary treatments and determined metabolisable energy and lysine concentrations used in the experiment.
An examination of the results highlights two issues. Firstly, in the case of the different energy allocations, female mass was significantly lower for those birds on the lowest allocation while body mass of the males remained constant. Secondly, the females on the 175 g/d feed allocation did not gain mass at the same rate as the remaining birds. Males on the 145 g/d allocation were heavier than the remaining birds.
Table 3: Main effects of energy and feed allocation on body mass
Differences in egg output were observed between treatments as time progressed. When examining the effect of increasing energy allocation (Table 4) no trends were seen during the first period of observation. Thereafter, egg output was significantly depressed at the 1800 kJ ME/d allocation. Although not significant, a difference was also observed between the 1900 and 2000 kJ ME/d allocation, with the 2000 kJ ME/d allocation resulting in the highest egg output. This is most noticeable during Period 4 at which stage the birds, because of increased body mass would have required considerably more energy for maintenance and production than during the earlier periods of the experiment.
The pattern, which emerges at the different levels of feed allocation, is not as straight forward. Significant depression in egg output was observed during the first two periods in the case of the 175 g/d allocation. An examination of the rate of production (Table 4) highlights this depression, but in addition it shows increased production for those birds at the 145 g/day allocation during the same period. This observation is difficult to explain as all feed was consumed on each day of the trial period. The onset of sexual maturity may have been slightly retarded, but it was not possible to measure this form the available data.
In the third and subsequent periods the situation had altered. Here the birds at the 145 g/d feed allocation showed significantly depressed egg output. The increased body mass of the males at this level of allocation would suggest that they were perhaps over consuming feed and thus preventing the females from meeting their nutrient requirements. There were no significant differences between the other treatments during the third period, but during period 4, the 165 g/d feed allocation resulted in significantly elevated levels of egg output compared with the other three treatments.
Table 4: Main effects of energy and food allocation on egg output.
Clearly this experiment showed that the birds responded to an increase in energy allocation, regardless of the energy level of the diet. As all birds were receiving the same protein allocation, all be it only 920 mg/day of lysine, it would be reasonable to assume that energy was the first limiting nutrient in this experiment.
The more dense feeds (145 g/d allocation) resulted in higher egg output during the earlier periods but this benefit was outweighed by the depression in production during the post peak period of the laying cycle. The most dilute diets (175 g/d allocation) resulted in depressed egg output prior to peak production, but thereafter no negative effects were seen. Despite the influence that the male birds will have had on the results of this experiment, it was concluded however that during the post peak period the decision as to which feed birds should be offered in the range 155 to 175 g/d allocation (approximately 11.5 to 12.7 MJ/kg of ME) is an economic one.
Returning to the discussion about the difference in the cost of a diet containing 11.5 MJ/kg of energy or the diet containing 12 MJ/kg it is clear that we need to calculate what the implications are on our feeding cost per bird per day is.
Table 5: The cost implications of feeding diets of different amino acid and energy allocations
Under the cost structure used above, it would be cost effective to feed slightly more of a cheaper diet. Should the price of wheat bran become prohibitively high or unavailable, then it may well pay to feed a more dense diet. If an ingredient of high energy density such as fishmeal, full fat soya or oil should become freely available at a reasonable price the same would apply.
There are practical implications of feeding diets of different energy densities. High-energy diets will be consumed faster in the breeder house, not only because of a reduced feed allocation, but also because of a reduced physical density. Many producers find it hard to manage diets containing higher energy levels as uniformity problems can arise. In addition, it is easy to end up with overweight birds.
Protein and Amino Acids
The situation with regards the amino acid levels of the diets that are used for broiler breeders are less clear than that of energy. In truth the level in the diet is of secondary importance, rather it is the daily intake of amino acid that should be of concern.
In broad terms two sets of recommendations exist for breeders. These are those published by the scientific community based on the research that has been carried out and those published by the breeding companies which tend to be higher. As we are concerned primarily with amino acids, lysine will be used as an indicator of total amino acid content (protein) throughout. Not only is lysine mostly the first limiting amino acid, but it is relatively easy to analyse for. In addition, it is the most widely researched of the amino acids.
Table 6: Dietary protein and lysine recommendations and intakes of broiler breeders (Management Guide Data) (after Leeson & Summers, 2000)
Leeson & Summers (2000) suggest that the differences shown above could be true breed differences but that it is hard to rationalise considering our knowledge of breed-nutrition interactions. An added confusion is that the Ross company recommends not only the lowest but also the highest g of lysine per MJ of ME, all within a 4-year period.
In 1981 Pearson and Heron suggested that the level of 970 mg lys and 19.5 g protein/hen day supported maximum egg production. Kleyn (1987) used the parameters published by McDonald and Morris (1985) for commercial laying hens to meet the requirement of a 3.1 kg bird producing 70 g/egg per day. He estimated a lysine intake of 920 mg/ bird day. In South African work, Bowmaker and Gous (1991), used the diet dilution technique and the Reading Model to determine coefficients of response when incremental levels of lys were offered to broiler breeders. These were found to be 16.88 E and 11.2 W, where E = egg output, g/bird d, and W = body mass, kg/bird. Thus an average, individual broiler breeder weighing 3 kg and producing 45 g of egg /day would need 793 mg of lys. These workers made no recommendation as to the optimal level to feed the flock.
Harms and Ivey, (1992) showed that the Lys requirement for egg production, egg weight and egg mass was achieved with daily Lysine intakes of 824, 806 and 819 mg/hen/day respectively, when daily protein intake was greater than 18.55 g. The NRC (1994) suggests values of 765 mg of lysine and 19.5 g of protein. Leeson et al. (1997) recommend a lysine intake of 990 mg hen/day but a surprisingly high protein intake of 25.6 g hen/day.
Coon (2001) makes the point that many past research reports have discussed amino acid needs from empirical data without separating the requirements into components for maintenance, body weight gain and egg production. Broiler breeders potentially have more profound changes in these parameters than commercial layers (for which this data is available) which enhance the need for a factorial approach to determining the amino acid requirement of breeding birds. Fisher (1998) predicted the amino acid requirement of the Ross 308 using a factorial equation, known as the Reading Model. This model utilises a correction for variation and adds 1.8 standard deviations in requirement to the mean to establish the flock requirement for amino acids. This would ensure that the requirements of about 97.5% would be met. The values that he determined range from 1080 mg of available lysine per day at 28-29 weeks of age to 975 mg per day at the end of the laying cycle. Making use of a factorial model developed by Waldroup et al. (1976), Leeson et al. (2000) determined that the average bird in the flock requires 15.1 g of protein per day and 742 mg of lysine.
Table 7: Dietary protein and lysine recommendations for broiler breeders.
Interpreting the data above is extremely difficult. The work of Fisher (1998) is not based on experimentation although flock variation has been taken into consideration. Neither Bowmaker et al. (1991) nor Leeson et al. (2000) considered flock variation.
As already discussed, the 920 mg/ day of lysine used as a standard by Kleyn (1987) in all likelihood had no impact on performance and as can clearly be seen in Table 8 Harms et al. (1992) achieved excellent performance at levels as low as 804 mg/lysine per day.
As can be seen the amino acid requirement of breeding hens is still poorly understood. It is probably fair to say though that we are probably over feeding protein to most of our broiler breeders. This has a number of important practical and commercial implications.
When one examines the work reported above, it was clearly shown how female body weights were correlated with amino acid and/or protein intake. This is clearly illustrated by the work of Harms et al. (1982). These workers used isocaloric diets in this experiment and although Coon (2001) has commented that the extra caloric effect of the fats used in the higher protein diets may have been responsible for the additional weight gain observed, the researchers feel that the additional energy requirement of the increased egg production would have more than compensated for this. Bear in mind that in the work published by Kleyn (1987) the difference in energy consumption between to lowest energy allocation (1800 kJ/ME per day) and the highest allocation (2000 kJ/ME per day) was 11% but that difference in body weight was only about 3%.
Table 8: (after Harms et al., 1992).
Lopez and Leeson (1993) were able to show that if the amino acid levels of the diet were maintained at a constant level, in this case 8.2 g/kg of lysine and 5.8 g/kg of methionine + cystine, and the protein levels were varied from as low as 10% to 16% all birds produced a similar number of eggs during their production cycle. They were also able to show that the protein content of the diet had a significant impact on fertility. Ross Breeders (1997) conducted a similar trial and whilst they were able to show a decline in egg number and hatch of set eggs when a diet of 19% protein was offered, they were also able to show a decline when a level of 13% dietary protein was fed. Unfortunately total protein and amino acid intakes were not indicated so it is difficult to make comparisons between the two experiments.
Table 9: Dietary protein and female fertility to 64 weeks of age (Lopez and Leeson, 1995)
Surplus protein has a high heat increment, particularly in the case of birds where surplus nitrogen is excreted in the form of uric acid rather than as urea as is the case with mammals. When high levels of protein are fed to birds already exhibiting signs of heat stress, the heat stress situation is exacerbated.
Obviously the protein and amino acid level if the diet has a major financial implication. The ingredient cost of the Ross (2000) recommendation is R 1073.00 while that of a diet supplying 990 mg of lysine at the same intake but with a minimum protein level of 14% would only cost R 957.00
Bearing in mind all of the above, attention now needs to be paid to what should we do as the birds age. Both Fisher (1998) and Leeson et al. (2000) have shown that the requirement for protein and amino acids decline as the birds get older. As feed intakes decline there is some argument for increasing the amino acid levels of the diet. This is at odds with the recommendation made by the Cobb Breeders (1997) who suggest that the lysine content of the diet be reduced from 7.5 g/kg to 7 g/kg at an age of 246 days.
To put the discussion above into perspective it would be a good idea to show exactly what is being done in this country. For commercial reasons not all of the data could be published.
Table 10: Specifications of typical broiler breeder diets used in South Africa
As can clearly be seen a wide range of feed specifications is used in South Africa. Some companies feed lower energy diets in the summer, with an increase in the winter of some 0.5 MJ/kg. On the other hand, there are companies that like to maintain a constant energy level in their diets as they believe it makes for easier management on the farm. During the past few months many producers have experienced an unexplained drop in female body weight. Increasing the energy level of the diet has helped overcome the problem for some producers but has lead to problems for others.
The situation with regards protein is less clear cut. Some companies reduce their protein and amino acid level as the birds age, while other increase these amounts. Experience has shown that increasing amino acid and protein levels as the birds age may lead to a high proportion of eggs too large to set with no additional benefits in performance. Costs though have been excessively high.
Whatever criticism one may or may not have about the various systems, they all, without fail, appear to give reasonable results. Not every flock is perfect, but enough of them are to show that the combination of feed specification and feed allocation is probably correct.
Fisher (1998b) made the comment that any improvements in broiler breeder nutrition in the future are likely to be made through improving feeding programs rather than through changed or improved dietary specifications. Considering the wide range feed specifications used in South Africa with a fair degree of success, this statement is perhaps well founded.
In this authors experience, the interpretation of production graphs is possibly the area that requires the most experience and attention to detail. The decisions that need to be made by farm managers are not always as straightforward as they would appear to be. Inaccurate weighing and/or an inaccurate bird count often complicate this.
Anon, (1997). Review of broiler parent stock nutrition. Ross Tech 97/33. Ross Breeders Limited.
Anon, (1997). Technical Profile: Breeder nutrition. The Cobb Breeding company limited.
Anon, (2001). On www.rossbreeders.com line technical manuals: 308 Parent Stock.
Bowmaker, J.E. and R.M. Gous (1991). The response of broiler breeder hens to dietary lysine and methionine. Br. Poultry Sci. 32: 1069-1088
Coon, C. (2001). Factorial models for amino acid requirements presented. Feedstuffs, May 7:13
Fisher, C. (1998). Amino acid requirements of broiler breeders. Poultry Sci. 77:124-133
Fisher, C. (1998b). Recent developments in broiler breeder nutrition. AFMA Forum 1998.
Harms, R.H and F.J. Ivey, (1992). An evaluation of the protein and lysine requirement of broiler breeder hens. J. Appl. Poultry Res. 1: 308-314
Kleyn F.J. (1987). An application of the systems approach to egg production. MSc thesis, University of Natal.
Leeson, S. and J.D.Summers, (2000). Commercial poultry nutrition. Second Edition. University books, Guelph, Ontario.
Leeson, S. and J.D.Summers, (2000). Broiler breeder production. University books, Guelph, Ontario.
Lopez, G and S Leeson, (1995). Response of broiler breeders to low protein diets 1. Adult breeder performance. Poultry Sci. 74:685-695.
Lopez, G and S Leeson, (1995). Response of broiler breeders to low protein diets 2. Offspring performance. Poultry Sci. 74:696-701.
McDonald, M.W. and T.R. Morris, (1985). Quantitative review of optimum amino acid intakes for young laying pullets. Br. Poultry Sci. 26:253-264.
National Research Council, (1994). Nutrient requirements of poultry. Ninth revised edition. National Academy of Sciences, Washington, DC
Pearson, R.A. and K.M. Heron, (1982). Relationship between energy and protein intakes and laying characteristics of individually caged broiler breeder hens. Br. Poultry Sci. 23:145-159.
Wauldroup.P.W, Z Johnson and Z Bussell, (1976). Estimating daily nutrient requirements for broiler breeder hens. Feedstuffs 48:29