Introduction
Broiler chicken production has undergone drastic changes and developments over the last few decades. Constant improvements in nutrition and genetic selection over the last two decades have led to a fast growth rate in modern broiler strains, to the extent that the average time required to grow a broiler chicken to 2 kg has reduced nearly by half (from 63 days to 37 days). Broiler feeding planners have also come up with new innovations to boost broiler performance efficiency further.
For many producers (and researchers alike) the feeding of chickens starts when the birds get to the farm. However, it could be considered to start before they have even hatched. ‘In-ovo’ feeding deals with the administration of food into the amnion of the late-term embryo. To provide the higher nutritional requirement of modern broiler chickens and/or to combat any delay in access to feed due to hold-ups in the hatchery and in transportation, an early feeding programme is advisable.
Once at the farm, the 3 phases (starter, grower and finisher) feeding plan has been universally applied. However, due to changes in broiler growth rate and pattern, alternative feeding plans such as ‘phase feeding’ and ‘feeding time period’ could be adopted to replace NRC.
Researchers have innovated feeding programs such as ‘sequential’ ‘separate’ and ‘choice’ feeding programs, mainly to monitor broiler metabolism, to understand the specific requirements of the animals, and to recommend diet specifications. Various early restriction feeding programs with a view of compensatory growth have also been advocated by researchers mainly to combat ‘disorders’ and fat accumulation currently observed in fast growing birds.
‘Late feed restriction’ to lower the fat content of the carcass and ‘mineral and vitamin removal’ to lower the cost of final products are occasionally being addressed. On the other hand ‘replacer finisher feed’ or ‘withdrawal supplement feed’ are now being introduced to overcome some of the shortcomings of ‘all-feed withdrawal’ plans prior to live haul, slaughter and processing.
There are outstanding reviews dealing individually with most topics mentioned above However, there is a lack of information which could put varying broiler feeding programs into perspective. It is necessary to have a good understanding of all these different feeding programs to be able to design an effective feeding strategy.
Early life feeding
in-ovo feeding
Approximately 2% to 5% of hatchlings do not survive the critical post-hatch period because of limited body reserves, and many survivors exhibit stunted growth, inefficient feed utilisation, reduced disease resistance or poor meat yield. Thus, Uni and Ferket (Reference UNI and FERKET2004) emphasised that the few days pre- and post-hatch are critical for the development and survival of commercial chickens. The reason for this could be the shift to nutrient uptake during this period, when the yolk is replaced with an exogenous diet and the hatchlings are switching from utilising a yolk nutrient-based diet to a solid external feed.
It has been claimed that this technique has much potential for improving all aspects of broilers’ performance including increased hatchling weights of 3% to 7% (which is sustained at least until 35 days), advanced morphometic development of the intestinal tract, increased breast muscle size at hatch which advances the digestive capacity, energy status, and development of critical tissues of the neonate by about 2 days at the time of hatch (Noy and Uni, Reference NOY and UNI2010). Although this might be true for the early life of broiler chickens, whether such progress is lost at a later stage is not well established. This technique is in its early stages, and further investigation is needed before elaborating on its effectiveness and the extent to which it could influence the following feeding programs.
hatchery feeding
Under natural brooding, birds hatched could have immediate access to feed, but under commercial conditions eggs hatch out over a period of 48 h, and chicks might be held for an additional 24 h prior to being given access to food and water. Although this period might not seem long, it represents approximately 8% of the growing period of modern commercial chicks from an age standpoint as compared to 3% in the 1990s.
Delayed access to feed and water will result in a mortality rate of about 5%, poor growth, decreased disease resistance, and impaired levels of muscle development (Willemsen et al., Reference WILLEMSEN, DEBONNE, SWENNEN, EVERAERT., CAREGHI, HAN, BRUGGEMAN, TONA and DECUYPERE2010). Weight losses of chicks held for 24 to 48 hours were equivalent to lengthening the time taken to reach market age by 1 to 2 days (Nir and Levanon, Reference NIR and LEVANON1993).
It is often thought that the residual yolk found in the chick is sufficient to maintain the bird until feed is offered. However, the initiation of growth may be more dependent on feed consumption than on the nutrients found in the yolk post-hatch (Nir and Levanon, Reference NIR and LEVANON1993). According to Murakami et al. (Reference MURAKAMI, AKIBA and HORIGUCHI1992) when feed consumption starts soon after hatch, the nutrients provided by the feed are complementary to the yolk nutrients. Thus, many researchers insist ‘hatchery feeding’ is of great importance (Willemsen et al., Reference WILLEMSEN, DEBONNE, SWENNEN, EVERAERT., CAREGHI, HAN, BRUGGEMAN, TONA and DECUYPERE2010).
Hatchery feed supplements and starter feed are easily added to chick trays in the chick holding rooms in commercial hatcheries. According to Sklan et al. (Reference SKLAN, NOX, HOYZMAN and ROZENBOIM2000) feeding in the hatching trays improves growth and uniformity of birds up to 21 days of age. However, factors such as type and form of feed might affect the performances. Different sources of protein and energy have varying levels of impact on chicks, showing a need for more digestible nutrients (Lilburn, Reference LILBURN1998). Although newly-hatched chicks cannot make use of fat, Turner et al. (Reference TURNER, APPLEGATE and LILBURN1999) reported a commercial synthetic fat (with concentration of medium chain fatty acids containing 75% C 8:0) can in fact be maximally absorbed, utilized and be a valuable energy source for newly- hatched chicks. Kidd et al. (Reference KIDD, TAYLOR, PAGE, LOTT and CHAMBLEE2007) reported that a 5-h hatchery feeding regimen of crumbled starter diets varying in amino acid concentration and moisture used in their experiment did not affect live performance or yields of broilers marketed to 4.6 lb (2 kg).
Although, most of the feeding programs have been shown to produce an initial enhancement in performance and body weight, it decreases with age with no improvement in feed efficiency by market weight. It may be argued the beneficial effects of these methods in terms of immune, metabolic and morphological improvement for newly hatched chicks might justify their application. They might assist birds in time of crises, i.e. illness, stress and high temperature environments. Furthermore, as the growth performance and meat yield of commercial poultry improves linearly each year, the share of the few early days plays a greater role in the final performance. These feeding programs thus might prove to be more beneficial in the near future. Meanwhile, research to evaluate the combined effect of in ovo, hatchery and early feeding methods might prove interesting.
Pre-starter diet
Although the term ‘pre-starter diet’ could also cover hatchery feeding, the term used here solely relates to feed offered in farm. The first week after hatching is an extremely important period for the rearing of broiler chickens. However, the current broiler nutrient recommendation of the National Research Council (Reference NATIONAL RESEARCH COUNCIL1994) of a three-week starter period has long been around. This practice is based on assumption that the digestibility among the nutrients be the same up to 21 days of age. On the other hand, considerable interest and efforts have been made in the precise formulation of a diet for the first week of the broilers’ life, with the objective of reducing initial mortality and improving the uniformity of the flocks. The inclusion of highly digestible ingredient, high protein diet as ‘pre-starter’ is now being widely advised and practiced. Although such diet can be more expensive than a starter diet, according to Lilburn (Reference LILBURN1998) it can be considered an investment, rather than a cost.
However, recent attempt by Ghomes et al. (2006) and Longo et al. (Reference LONGO, J.F.M., PEDROSO, FIGUEIREDO, RACANICCI and SORBARA2007) did not show much beneficial effect. Although they both reported better performance during the earlier growth phase with a highly nutritious (carbohydrate and protein) ‘pre-starter’ diet, it was not maintained in subsequent phases.
‘Growth up’ feeding plans
The classic (traditional) National Research Council (Reference NATIONAL RESEARCH COUNCIL1994) feeding programs usually define the nutrient requirements of broiler chickens based upon their age, and for three fixed periods, namely starter (0-3 weeks), grower (3-6 weeks) and finisher (6-8 weeks). This program has been criticized by some researchers (Shariatmadari, Reference SHARIATMADARI2009). In recent decades many researchers have tried to make some changes or introduce alternatives to the NRC plan of feeding. ‘Feeding time period’ and ‘phase feeding’ are two different types of presentation that are claimed to have some merit. Planners of these new methods argue that their program benefits both the environment, by reducing the nitrogen excretion, and the birds (Roush et al., Reference ROUSH, BOYKIN and BRANTON2004), by reducing some of metabolic disorders, such as sudden death syndrome (SDS), ascites, leg weakness and other problems (Bizeray et al., Reference BIZERAY, LETERRIER, CONSTANTIN, PICARD and FAURE2002). It is also claimed that ‘some of the non-NRC feeding plans could be more beneficial to birds kept at high environmental temperature’ (Pope and Emmert, Reference POPE and EMMERT2002).
According to Pope and Emmert (Reference POPE and EMMERT2001) the NRC program does not meet modern fast growing bird requirements. They reasoned that, due to genetic improvements, the time required to reach market weight has been reduced, and thus the time span for each phase has to be reconsidered based on market weight of the birds to be slaughtered. The advocators of ‘feeding time period’ schedules argue that because the cost of feed generally declines as the protein is reduced, optimising the time for changing diets is of economic importance. These researchers introduced various time schedules for typical starter, grower and finisher diets (Saleh et al., Reference SALEH, WATKINS and WALDROUP1997a; Reference SALEH, WATKINS and WALDROUP1997b). However, no clear pattern immerged to conclude that a shorter starter and/or grower period is beneficial in all circumstances but rather success of such programs depends on market weight.
Another feeding plan called ‘Phase feeding’ as described by Pope et al. (Reference POPE, LOUPE, TOWNSEND and EMMERT2002) is a strategy to change the diet several times (as opposed to a fixed 3 times) in the course of the broiler's life, in order to better match nutritional requirements to specific nutritional need, thereby usually improving feed efficiency. These researchers have argued that, under the standard three-stage feeding system, birds are either underfed or overfed for most of each feeding stage. Thus, the shorter the duration of a feeding period and the more types of feed changes the closer the diet to bird requirement, therefore achieving a better performance.
An experiment comparing the standard NRC three phase feeding schedule to that of five and nine phases showed that increasing the number of feed changes had no effect on the performance of broiler chickens, resulted in improved protein conversion ratio and decreased nitrogen excretion (Mohseni and Shariatmadari, Reference MOHSENI and SHARIATMADARI2008). Nasril (Reference NASRIL2003) adopting an intensive multi-phase feeding (changing every day) program indicated that body weight gain and feed to gain ratio only improved up to weeks five and six, but not during the overall seven-week period. Nitrogen excretion and nitrogen retention were unaffected by the intensive multiphase feeding systems. Economic analysis indicated that intensive multi-phase feeding programs could potentially lower feed costs per kilogram of gain. However, it is necessary to remember that the high cost of implementing a continuous multiphase feeding system may not justify the relatively small savings in lower feed costs
It should be pointed out that many claims about the benefits of two above feeding plans come from individual groups of researchers, and that not all the merits proposed have been confirmed by other researchers or applied commercially.
sequential feeding and separate feeding
Feeding broilers by alternating different diets during the day was named ‘sequential feeding’ has mainly been studied for nutritional purposes (Foote and Rose, Reference FOOTE and ROSE1991; Rose et al., Reference ROSE, FIELDEN, FOOTE and GARDIN1995). However, the sequential use of feeds of different nutritional values is only practiced in Europe when, for example, whole grain wheat is successfully alternated with a complementary protein-rich feed (Noirot et al., Reference NOIROT, BOUVAREL, BARRIER-GUILLOT, CASTAING, ZWICK and PICARD1999). This feeding plan proved to be effective in reducing mortality under acute heat challenge during the finishing period (De Basilio et al., Reference DE BASILIO, VILARINÕ, YAHAV and PICARD2001) and to reduce gait score and increase activity of young broiler chickens (Bizeray et al., Reference BIZERAY, LETERRIER, CONSTANTIN, PICARD and FAURE2002).
Feeding high and low protein feeds on alternate days has been shown to induce a relatively small and non-significant reduction in BW gain compared with complete diets and shorter sequential phases (Forbes and Shariatmadari, Reference FORBES and SHARIATMADARI1994). Rapid adjustments of muscle protein synthesis and lipogenesis were reported after re-feeding or changing the dietary protein concentration of the feed (Aman-Yaman et al., 2000a; 2000b), suggesting that sequential feeding might be an effective technique to monitor broiler metabolism.
According to Bouvarel et al. (Reference BOUVAREL, BARRIER-GUILLOT, LARROUDE, BOUTTEN, LETERRIER, MERLET, VILARIN, ROFFIDAL, TESSERAUD, CASTAING and PICARD2004) two questions arise from this brief survey of published studies:
• Do sequentially fed chickens adjust their intake according to the energy or according to the protein concentration of each feed?
• Would extending the period of each feed up to 24 h be an effective way to enforce the intake of each feed; on the other hand, would an interval that is too long between imbalanced energy-protein nutrient sources hinder effective anabolism and muscle growth?
Certainly, the time gap between two feeds is important, and this is more evident at high environmental temperature (De Basilio et al., Reference DE BASILIO, VILARINÕ, YAHAV and PICARD2001).
Feed restriction
Although ad libitum feeding is necessary for fast growing broiler chickens to meet their maximum growth potential, it has led to more frequent occurrences of metabolic and skeletal disorders and increased fat deposition (Yu and Robinson, Reference YU and ROBINSON1992). To overcome such adversities, a controlled restriction program to modify growth pattern had been proposed.
early feed restriction and compensatory growth plan
Compensatory growth could be referred to as the accelerated growth noted in animals of the same age that were previously feed-restricted. It is argued that such birds have smaller maintenance requirements and, when allowed free access to feed, will grow faster relative to unrestricted birds and have a better feed efficiency. Scientists were to take advantage of this natural potential in order to produce more economical products.
This subject has been well covered by Zubair and Leeson (Reference ZUBAIR and LEESON1999). There are many variables such as sex, strain, time of enforcing restriction, duration and types that could affect the outcome of any restriction and succession of compensatory plans. Although the scientific basis for such a phenomenon seems solid, reviewing the literature does not indicate a concrete conclusion on the ability of birds to compensate, at least during the available time and for the target weight desired. This seems more apparent with the ever shortening duration of the growth period. Most experiments examining compensatory growth were carried out during the 1980s, when it took birds about 60 days to reach 2 kg. It now takes 37 days or less. Further and continuous investigation is needed to redefine the parameters and various criteria to implement when deciding to adopt this plan.
In contrast, as the production cycle shortens due to improvements in genetic selection and nutrition, the implementation of early restriction (with a view to compensatory growth) is questionable and in fact opposes the necessity and very logic of early feeding. There is a challenge and perhaps new ground to carry out research to compare these different plans. Furthermore the feeding plan during the realimination period is also of importance when deciding to adopt this plan. The outcome of compensatory feeding could be also affected by the nutrition program put in place to encourage compensatory growth. Jones and Farrell (Reference JONES and FARRELL1992) postulated that the nutrient requirement of restricted birds increases during compensatory growth. However, the question as to whether the birds need change during the compensatory program, i.e. where it needs higher nutrition requirement, has not yet been clarified. The few experiments regarding this issue have not shown any clear answers. Studies by Jones and Farrell (Reference JONES and FARRELL1992) showed that dietary supplementation with lysine or methionine during the re-feeding period resulted in inconsistent responses for final body weight and carcass composition. Leeson and Zubair (Reference LEESON and ZUBAIR1997) concluded that there does not seem to be any advantage to manipulating diet formulation during realimentation of birds that were previously nutrient-restricted.
feed restriction during finisher period
Restricted feeding is also applied during the finishing period. During the last 10 days of production (35-45 days of age), commercial broilers exhibit almost 23% of their total growth and consume over 30% of their total feed. However, allowing birds an unlimited supply of food can result in consumption in excess of the birds’ requirements for maintenance and production and in the excess energy being converted into fat.
Attempts to assess the extent to which quantitative food restriction during the finishing period improved feed efficiency ratio, reduced fat content, lowered mortality rate but also reduced final body weight (Benyi and Habi Habi, 1998; Urdaneta-Rincon and Leeson, Reference URDANETA-RINCON and LEESON2002) Leeson et al. (Reference LEESON, SUMMERS and CASTON1996) reported that feeding broilers with a finisher diet diluted with sand and oat hulls from 35 to 49 days affected the percentage of abdominal fat, breast and carcass weight. Sahraei and Shariatmadari (Reference SAHRAEI and SHARIATMADARI2007) showed that allowing birds a diet containing 7% sand and/or wheat bran from 35-45 days resulted in lower abdominal fat without affecting the final carcass weight.
It looks as though both types of restriction have a beneficial effect on the fat content of the carcass, but qualitative feed restriction has a less adverse effect on final body weight.
Nutrition withdrawal
Maiorka et al. (Reference MAIORKA, LAURENTIZ, SANTIN, ARAÚJO and MACARI2002) stated that in practical diets, a total lack of vitamins and minerals is not an issue, as corn and soybean meal provide a portion of the requirements. Further, fat-soluble vitamins are stored in the fatty tissue of the body and can be remobilised when a deficiency occurs. According to Skinner et al. (Reference SKINNER, WALDROUP and WALDROUP1992a) removal of vitamin and mineral mixes during the week prior to slaughter can reduce growing costs with no adverse effects on performance. Skinner et al.(1992b) reported that removing limestone, dicalcium phosphate, or both from the diet of broilers during the 42- to 49-day period had little effect on broiler growth, feed utilisation, or carcass content.
Conversely, according to Kavita et al. (Reference KAVITA, HARDY and BAKER1997), removal of supplemental vitamins and trace minerals from broiler diets during the period 35 to 42 day post-hatching decreased daily weight gain. The study by Maiorka et al. (Reference MAIORKA, LAURENTIZ, SANTIN, ARAÚJO and MACARI2002) suggested that withdrawal of vitamin mix during the final period of broiler chicken growth is more deleterious than withdrawal of mineral mix, because of its effect on feed conversion.
Kavita et al. (Reference KAVITA, HARDY and BAKER1997) declared that poultry meat is considered a rich source of high quality protein, vitamins, and trace minerals, and any management practice that might reduce the nutritional value of the product deserves attention. The finding of these researchers indicates that the removal of supplemental riboflavin from the finisher diet for seven days pre-slaughter caused only a slight decrease in the riboflavin content of breast muscle, but removal at 14 days pre-slaughter caused a 43% decrease in breast muscle riboflavin.
Skinner et al. (Reference SKINNER, WALDROUP and WALDROUP1992a) stated that, under conditions of heat stress or marginal performance due to aflatoxicosis or other problems, complete supplementation of vitamins and trace minerals should be maintained.
Feed withdrawal (removal) and/or pre-slaughter feeding
Broiler chickens are routinely subjected to a period of feed withdrawal for four to five hours prior to live haul and slaughter processing. This is done to allow time for the birds to void their gastrointestinal tracts and to reduce contamination from GIT contents. Several factors have an effect on gut clearance, including length of the FW period prior to slaughter, temperature, light intensity, activity, water availability, transportation time, holding time, stress, and interruption of feed availability (Bilgili, Reference BILGILI2002). Accordingly the withdrawal duration could vary greatly from one poultry house to another.
On the other hand prolonged feed withdrawal has the potential to increase the incidence of bacterial colonisation in segments of the GIT (Ramirez et al., Reference RAMIREZ, SARLIN, CALDWELL, YEZAK, HUME, CORRIER, DELOACH and HARGIS1997; Corrier et al., Reference CORRIER, BYRD, HAGGIS, HUME, BAILEY and STANKER1999) and can lead to sloughing and liquification of the intestinal mucosa with increased fragility of the intestinal wall (Northcutt et al., Reference NORTHCUTT, SAVAGE and VEST1997), all of which may increase the risk of contamination during evisceration. Broilers without feed for more than 6 h begin to draw moisture and nutrients from their own body tissues and this weight loss may then affect edible yield (Contreras-Castillo et al., Reference CONTRERAS-CASTILLO, PINTO, SOUZA, BERAQUET, AGUIAR, CIPOLLI, MENDES and ORTEGA2007). Buhr and Northcutt (Reference BUHR and NORTHCUTT1998) estimated this weight loss as being up to 6% of body weight.
Because of difficulty in balancing cross contamination rates with live shrink, several attempts have been made to develop a nutritive supplement formulated with an antimicrobial compound included which may also reduce the risk of carcass contamination, by reducing the total bacterial load in the GIT that might be released in the event of a breakage. Nijdam et al. (Reference NIJDAM, DELEZIE., LAMBOOIJ, NABUURSM, DECUYPERE and STEGEMAN2005) noted that feed withdrawal from broilers before transport changes the plasma hormone and metabolite concentration, and suggested research to apply some energy-delivering supplement during the last day of broilers’ lives to cope with stressors, such as catching and transport, would be worthwhile.
‘Replacer finisher feed’ or ‘Withdrawal supplement feed (WSF)’ as described by Northcutt et al. (Reference NORTHCUTT, BUHR, BERRANG and FLETCHER2003) and Farhat et al. (Reference FARHAT, EDWARD, COSTELL, HADLEY, WALKER and VASILATOS-YOUNKEN2002) respectively are feeds claimed to reduce the intestinal contents at slaughter without compromising yield. This feed called ‘Maltodextrin’ consists of a D-glucose polymer with added salts and is offered to birds four to eight hours prior to dispatching them to the slaughter house. WSF also relieves the birds from the stress associated with feed-deprivation. However the quantity of supplement consumed is critical, and requires amplification through improvement in the physical form or palatability.
Conclusions
The universally-applied three phases of broiler feeding that were practiced routinely prior to the new millennium, may not be around for long. Various alternative and/or complementary feeding programs have been introduced in recent decades, though the effectiveness of some of these programs is uncertain. However, as the time taken for meat birds to achieve market size decreases, their role might become more evident. Research to evaluate the combined effect of these feeding methods would prove interesting. Judging by the last decade's developments in feeding plans of broiler chickens, the next decade seems to be even more exciting.
