Advances in reducing body fat in broilers by nutritional and chemical means.

Abstract

ADVANCES IN REDUCING BODY FAT IN BROILERS BY NUTRITIONAL AND CHEMICAL MEANS G.P.D. Jones*, A. Yang*, and D.J. Farrell* SUMMAH Increased body fat in broiler chickens and consumer resistance to high dietary fat levels has led to the need to develop methods to reduce the deposition of fat in the chicken. Feed restrictions and chemical feed additives may offer the most-practical short-term solutions and these strategies her-e examined in a series of experiments. Feed restrictions by quantitative feeding, based on the energy content of the diet and the birds bodkwight, as well as dietary dilution wre examined when applied to broilers aged from 7 to 28 days. The conseqences of these restrictions on the metabolism and the rate of fat deposition are discussed. Finisher-feeds treated with chemical additives, when fed to broilers from 25 days of age, were also tested. The most dramatic effects were obtained when feed restrictions wre applied to 7 day old broilers. Dietary dilutions decreased body fat but had detrinlental effects on bodyight. Iodinated casein added to the finisher feed decreased body fat with no effects on bodywight. Theophylline and caffeine, however, depressed feed intake and consequently, growth rate.. The production of chicken meat in Australia increased by 1432% between 1960 and 1987, when 337,100 tonnes were produced (Fairbrother 1987). The liveweight gain of broiler chickens has also increased rapidly over this period and with this increase in growth rate, there has frequently been a concomitant increase in body fat. Recently, however, consumer resistance to high levels of/ dietary fat has intensified and methods need to be established to counteract the increased levels of body fat in broiler chickens. Many factors influence the leve 1 of fat in the chicken, such as the environment I genotype, age and sex of the bird, Howver I the nutrition of the bird appears to be the most critical factor in the rapid development of a program to counteract the increase in body fat. Previous research has centred around the manipulation of the energy: protein ratio of the diet. Although reducing fat levels, bodyight may be adversely affected or the cost of the diet too great to warrant comrcial Two methods that may be commercially successful are the use of practise restricted feeding practices and the addition to the diet of chemicals that pronote lean tissue growth at the expense of fat deposition. l The use of feed restrictions is well known in the layer and broiler breeder industries. Their use in broiler production is relatively new. Research initiated in Israel (Plavnik and Huwitz 1.985) indicated that feed restriction of young chickens reduced the body fat content of the bird wk;ile improving feed conversion efficiency, often with no influence on bodwight. Their results proved to be inconsistent and full corrpensation of lost bodyweight was not often achieved. *Department of Biochemistry, Kicrobioloqy and IWrit ion, University of New Engla.nd I Armidale I' NSW. 2351 o 332 Work in Australia by Jone s and Farrell (1987, 1988) examined a range of feed restrictions, ranging from 7950% ad libitum and for durations of l-10 When irrposed on 7 day old birds, restrictions of less than 4 days had days . no effect on body fat at slaughter. If the duration was too long, fat was reduced but bodyweight failed to recover completely. The optimum restriction, 20% ad lib. for. 4 days, produced consistent results over a range of broiler strains: It reduced body fat, maintained bodyweight and generally improved feed conversion efficiency.. l The use of chemicals in reducing body fat has also been studied only recently. Iodinated casein has been shown to reduce fat levels in the chicken, but at high levels of incorporation it has deleterious effects on carcass composition and dressed weight (Wilson et al 1983). The repartitioning agents or beta-adrenergic agonists have been examined in lambs (Baker et al 19841, steers (Ricks et al 1984) and pigs (Jones et al 1985) and have reduced carcass fat levels. The repartitioning agents decrease protein degradation (Li and Jefferson 19771, stimulate lipolysis (Ricks et al 1984) and appear to operate in conjunction with the growth hormone. Results > obtained in broilers (Dalryq$e et al 1984) are less pronounced and the effect of these chemica3,s in broilers may be sex, strain and dose dependent. This paper examines the use of two strategies to reduce the level of body fat in broilers by nutritional means. Firstly feed restrictions are examined in conjunction with dietary dilution techniques to provide a practical feeding method for broilers, optimum feeding strategies are examined and the conswpences of these strategies explored. Secondly, the use of thyroactive, beta-adrenergic and alkaloid chemicals, when incorporated in the finisher diet of the broiler, is also examined. MATFXUALSfXD MElYKDS Feed restricticn experiments One-day-old unsexed U%periments 1 and 2) or female (Experiment 3) broiler chicks of a corrmercial strain were placed in electrically heated brooders until 6 days of age. They were then individually wighed, wing-tagged and allocat&i to groups of 8 (Expt. 1 and 2) or 10 (Expt. 3) in small wire-mesh cages, At 14 days, they were transferred to larger cages, where they were kept until slaughter. Birds were fed a commercial broiler starter crumble to 28d and then a commercial finisher feed. The experiments were conducted in environmentally controlled rooms maintained at 32 0 C, with g&ual reductions in temperature to 20�C by 28 days of age. Continuous lighting was provided. The birds were weighed and fed daily during the restriction phases and at weekly intervals otherwise. Prior to slaughter, the birds were starved for 12h. After slaughter by cervical dislocation, the abdominal fat pad was removed and weighed, Birds used for carcass analysis were frozen in polythene bags ,at -20�C, cut into small pieces by a bandsaw and f iriely ground twice with an electrically-pwered mincer. Moisture was determined by drying in a force draught oven at 70�C for 5d. Protein was determined using a Kjeldahl techniqe with a selenium catalyst (A.O.A.C. 1984) and distillation by the method of Ivan et al (1974). Fat was analysed by measuring the density of a fat-tetrachloroetbylene extract (Usher et al 1973) and ash determined by combustion at 600 C for 4h in a rmffle furness. Experiment 1 used a factorial, randomised block design with 5 treatments and 3 replicates. Treatments were imposed on chicks at 7 days of age using two methods of feeds restriction. The treatments were - ad libitum control, 333 . feed restriction based on bodyweight (i.e. 3SkJ/g #* 67 /d, Jones and Farrell 1987) for 4 days and 3 restrictions using dietary dilution techniqes. These treatments used diets containing 35%:65%; 40%:60% or 45%:55% starter mash: rice hulls for 4, 5 or 6 days duration respectively. After restriction birds were fed ad libitum until sla g&er at 49 days of age. The treatments were equivalent to 20% (3.1 kJ/g is /d; 35%:65% starter mash: rice hulls) , 25% (40%:60%) or 30% (45%:55%) ad libitum intake. l Experiment 2 was of a factorial, randomised block design incorporating 10 treatments and 3 replicates. The experi 7was designed to examine the best /d restriction stragegy given that 3.1 kJ/giiF represented the optimum restriction severity. The treatments were: ad libitum control, feed restriction beginning at 7, 21 or 28 days of age for 4 days continuously, 2 periods of 2 days with 2 days re-aiimentation between restrictions, or 3 periods of 12h starvation followed by 24h restriction with 36h realimentation between restriction periods. Birds were fed ad libitum before and after restriction and slaughtered at 49 days of age. l Three treatments were imposed in Experiment 3 using a factorial, randomised block design with 4 replica e 7 The treatments here - ad libitum /d) control, or feed restriction (3.lkJ/g I@ for 4 or 6 days commencing at 7 days of age. Birds were fed ad libitum after restriction until slaughterat 70 days of age. Total body water and body fat wre estimatea throughout the experiment using tritiated water techniques (Johnson and Farrell, 1988). l Chemical additive exrxr iments Experimental lines of broilers obtained from Dr. R.A.E. Pym, University of aeensland and commercial broiler chickens were housed and maintained as in the feed restriction experiments. Unsexed experimental broiler chicks were used in Experiment 4 and commercial male broiler chicks in Experiments 5, 6 and 7. Birds were allocated to groups of 6 (Experiments 4, 5) or 7 (Experiments 6, 7). They were fed a commercial starter crumble diet until 25 days of age (Experiment 4) or 28 days of age (Experiments 5, 6 and 7) whereupon they were transferred to a commercial finisher mash with the various chemical treatments thoroughly incorporated. Experiment 4 examined the influence of the beta-agonist cinlaterol (5-(l-hydroxy-2-(isopropqrlamine)ethyl)~thr~ilonitile) on the amount of body fat. The experiment was a randomised block design with 4 treatments and 3 replicates. The treatments were 0, 0.2, 0.4 and 0.6 mg/kg cimaterolmixed with the finisher feed. Birds were slaughtered at 56 days of age. The abdominal fat pad was revved and wighed. Fat analysis was conducted as previously described. The influence experiment used 3 The 3 treatments feed. Birds were weighed. of iodinated casein was examined in Experiment 5. The treatments and 4 replicates in a randomis& block design. were 0, 50 and 100 mg/kg iodinated casein in the finisher slaughtered at 49 days and abdom.inal fat pads removed and Experiment 6 used 3 treatments and 3 replicates in a randomised block design. The 3 treatments were 0, 500 and 1000 mg/kg theophylline added to the finisher feed. Birds were slaughtered at 49 days and the abdominal fat pad rerrroved and weighed, Experiment 7 considered the influence of caffeine. Four treatments and 4 replicates Fiere used in a randomised block design. The treatments were 0, 500 334 and l@GO r&kg caffeine added to the finisher feed and a control ( 0 mg/kg caffeine) pair-fed to the 1000 mg/kg group. Birds were slaughtered at 49 days and the abdominal fat pad removed and wighed. Respiration calorimetry experiments Respiration calorimetry experiments were designed to exmine the metabolic conseyences of both feed restrictions and chemical additives on female commercial broiler chickens, The calorimetry procdures used were those described by Farrell (1972) and Pym and Farrell (1977). In the feed restriction x riment, the birds were fed either ad libitum or restricted fed to 3.1 kJ/g WgBgdfor4days. Measurenents were ntade prior to, during, and twice after the feed restrictions were imposed. Restricted feeding corrrmenced at 7 days of age, l The inclusion of theophylline, iodinated casein or cimaterol in the finisher feed was examined in the second experinlent. The levels of inclusion were 500 mg/kg, 50 mg/kg and 0.5 mg/kg respectively. The birds were fed untreated finisher mash for 3 days and were then transferred at 24 days of age to the treated feed. Measurements were then taken over a 3 day period. Due to the poor palatability of theophylline, the birds on the other treatments were pair-fed to the theophylline treatment. RESULTS A dietary diluent (rice hulls) allows the energy restriction to be applied commercially. The influence of a range of dietary dilutions on the growth perfornance and body fat of broilers is shown i. !&ble 1 and are compared to a previously successful restriction ie 3.1 kJ/g pd o /d (20% ad libitum). Table 1. The influence of feed restrict ion and dietary dilution on the performance of commercial broiler chickens (Experiment 1). The quantitative restriction (20% ad lib,) for 4 days produced a 3% decrease in bodkwight at 49 days and a 4% decrease in feed intake. Feed conversion efficiency was not affect& but total body fat was reduced by 11%. If considered on a fat-free body weight basis, the weight lost by the restricted birds was 32g non-fat tissue and 43g fat. The three dilution treatments reduced the size of the abdominal fat pad and decreased total body fat but had adverse effects on the growth performance of the birds. Supplementary work (data not presented) indicated that the rice hull diluted diets were less acceptable than expected hence imposing greater restrictions than intended. 335 The data obtained froni Experiment 2 indicate that feed restrictions inpsed at 7 days of age allow full reccvery of body weight to be obtained whilst maximising fat loss. Restrictions inposed at 21 days of age allowed reccvery of bodyweight but tended to increase body fat (as represented by the abdominal fat pad) and decrease feed conversion efficiency, although in both cases not significantly (P>O.O5). Table 2. The influence of the tim of feed restriction on the performance of commercial broiler chickens Experiment 2). Restrict ions in-posed at 28 days (data not presented) .did not allow'full recovery of bodyweight and did not affect fat levels. The use of a non-continuous restriction thereby periods of re-alimentation are followed by further restrictions produced the best results, most noteably when the restrictiorts began at 7 days of age (Table 2). The effects of successful feed restrictions are only transitory, but if too severe, permanent changes in body coqmsition can be obtained. The third experirrent was designed to examine the effect of feed restriction on birds grown beyond normal slaughter weight. The data (Table 3) indicated that, at 70 days, the carcass conposition of feed restricted birds was similar to that of ad libitum fed birds. Table 3, The influence of feed restrictions on the carcass conposition of commerci&!. female broiler chickens at 70 days of age EYxperiment 3). The experiment followed the coume of fat deposition in the birds using tritiated water techniques to estimate body water and then to calculate body fat by correlative procedures. The developrmt of body fat can be described by the use of allometric equations (shown below) which indicate that the developnmt of body fat is delayed by feed restriction, but as shown in Table 3, eventually reaches parity with that of ad libitum fed birds. 336 Increasing the level of cimaterol in the finisher feed had little effect on bodyweight or'feed intake, with slight, non-significant depressions as the level of cir;laterol increased. The size of the abdominal fat pad was decreased by 12%, 19% and 6% by the 0.2, 0.4 and 0.6 mg/kg cimterol treatments, respectively but only at 0.4ng/kg cimaterol was it significantly (P<O.O5) lower than the controls. Tab3.e 4. The effect of cimaterol in the finisher feed on the perfornlance of experimental broiler chickens (Exprinent 4). Table 5. The effect of iodinated casein in the finisher feed on the . perfornance of connrercial male broiI.er chickens (Experirrent 5). The inclusion of iodinated caseir, ir! the finisher diet markedly decreasd the size of the ddorrtinal fat pad (Table 5). !l%e two rates used, 50 and 100 q/kg, decrease the size of the fat pad by 398 and 32% reqectively. Wywcight at slaughter F?'F not affected but ie& intake was depressed by 9% a and 10% respectively. The depression in fed intake whilst bodyeight was maintained was reflected ir! iqroved feed conversion (Table 5) and indicated that t'rte addition of iodinated casein to the finisher diet depressed fat deposition and inproved non-fat accretion. No improvemt in performance was obtain& when the level of iodinated casein was doubled (100 rq/kg). The tslvo alkaloid chemicals, theophylline and caffeine both had adverse offeci-s C:P the g-rowth performance of the birds. Although they reduced the ~5 ze of the abdom.ina3 fat pad, this is an artefact of the depressed feed intakes z& hence bodyweights (Table 6 and 7). In commn with most alkaloid ch.emicals, theophylline and caffeine are bitter to the taste and hence acceptability of the diets was depressed. 337 Table 6. The effect of theophyiline in the finisher feed on the performce of comrcial male broiler chickens (Experimnt 6) . Table 7. The effect of caffeine in the finisher feed on the performance of cormercial male broiler chickens (Experiment 7). Thecphylline at 1000 @kg depressed the size of the abdominal fat pad by 37% I but depressed bodyweight by 35% and feed intake by 29%, The effects at 500 mq/kg inclusion level was similar but less dramatic (Table 6). The incorporation of caffeine shod similar effects (Table 7). In this final experiment a group receiving a caffeine-free diet were pair-fed to birds receiving the 1000 @kg caffeine diet (Table 7). The pair-fed group had 22% lower bodyweight f similar feed intake, a poorer fed conversion ratio and a larger abdominal fat pad indicating tha.t a. caffeine addit ior! to the diet iqroved growth performnce and decreased fat levels but due to poor palatability these effects were masked. ~eq..iratI.~~n calori.r&rl; indicated that the effects of feed restriction at 7 days wwe still apparent at 30 days of age (Table 8) . During the restricti.on phase (7-M days) the metabolisability of the diet and feed in&&e were depressed with subsequent effects on the energy of nits-c~>en ba3.ance of the birds. Some of these effects were maintained imwdiately after the restriction was lifted, however I only heat production and energy retention were affecteCI at 30 days of age. Heat production was higher in restricted-fed birds (Table 8) and consequently, energy retention was depressed. The mairit enx;ce en.ergy r equ r lent of the birds was reduced by 60% due to feed Fp restriction (803 kJ/kg % 1. No effects on the nitrogen economy of the bird were observed. l .l The use of chemical dditives produced no consistent effects on the metabolism of broiler chickens measured by respiration calorimetry (Table 9). 338 Table 8. The influence of feed restriction (3.3.kJ/gFj 0 .6Td : 4 days) on the energy and nitrogen balances of femle cormxcial broiler chicks Table 9, The effect of added theophylline, iodinated casein cx cimterol in the finisher feed on 24 da! old Eermle commercjal broilers Cimaterol reduced slightly the metabolisability of the diet whereas iodinated casein and theophyliine had no effect. ME intake and heat production of birds fed theophylline were reduced but corresponded to a depressed feed intake (Table 9). Energy retention was unaffected although nitrogen retention was depressed by theophylline. DISCUSSION Feed restrictions in broilers, designed to decrease body fat, have been investigated only recently. Various mthods have been tested and have 339 involved altering the energy:protein ratio of the diet, intermittent or meal feeding, limiting water access, changing the environmental temperature or the use of proportionate or quantita.tive feed restrictions. Each strategy has shortcomings. Firds can readily adjust to intermittent or nleai feeding progrm and can increase their intake to %ormal' levels Fn6th a possible increase in body fat. Limited water access produces wet droppings (Ross 1960) and temperature regulation is costly. If the protein content of the diet is increased to high levels, addit ional costs may be incurred. Similarly, birds can adjust feed intake (if the change in ratio is slight> to meet eneryy or protein requirements (Rosebrough and Steele 1985). The use of quantitative feed restrictions, for short periods of timI se- to be the mst successful means of reducing body fat wMlst maintaining bodpight. The recovery from a period of undernutrition, induced by feed restrictions, is influenced by a nu&er of factors W.lson and C&burn 1960). The tw n?ost iprtant of these are the severity and duration ofthe undernutrition, As these increase, the recuperative ability of the animal diminishes. If the restriction is too mild, overcompensation may arise (Clarke and Smith 1938) and fat levels will increase. If too severe, bone growth will be retarded (Brady 1945) and bodyweight will not recover fully. The response to realimentation after a Ejeriod of undernutrition can be smkarised as follows: If the animal loses height during undernutrition I bodyweight will not, or be slow to, recover and fat levels will be depressed. If bodyweight increases, the recovery will be complete and fat levels may rise. If bodyweight is maintained during undernutrition, then recovery will be generally complete and fat levels depressed. The work of Plavnik and Hurwitz (1385) used feed restrictions based on the energy requirement for naintenance, so that birds pg+d not gain weight over the restrictiori phase o When this level (6,3kJ/gb d> was applied to Australian broil.er strains (Jones and Farrell 1987) it was found to be twice the requirement for maintenance and which may explain the variability in t& results obt.ained by Plavnik and Hurwitz (1985). The use of the 3.lkUgWO' d restriction has given more consistent results and is applicable over a range of broiler strains. l The experiments present.& here were designed restrictions that could be applied in commercial effects of feed restrictions on body composition undernutrition imsed. me of the strains used favourable results were still obtained. to examine the use of feed industry and to clarify some and the recovery from the was particularly lean yet The use of rice hulls to dilute conlr;ercial diets has some potential al.though this potential was not fully realised in the experiment conducted. As pr&iously mentioned, acceptability of the rice hulls produced mre severe restrictions than intended and hence decreased final bodyweights. Fat levels were mrkediy depressed, but without full bodpight recovery, the results are not satisfactory - especially when no premium is paid for lean birds. The 4@:6G starter mash: rice hull diet, Qhen applied for 4 days may produce better results ie decreased body fat while maintaining bodyweight, Feed restrictions applied to birds at later ages (21 and 28 days) had either no effect or increased fat levels. The relative stage of maturity of the birds, and -especially the maturity of the body components, therefore, has 340 a bearing on the success of the feed restrictions. The restrictions examined have been-applied to birds that were slaughtered at 49 days, regardless of bodyweight. If the birds were to be gram for shorter periods or to heavier bodyweights, then the restrictions muld have to be tiified to obtain the best results. The restriction used by Plavnik ad Hurwitz (1985) &en applied to turkeys grown to 168 days of age (Plavnik and Eurwitz 1988) were not successful. If the restriction was more severe or for a longer duration, then success may have been achieved. The application of two short periods of restriction at an early age appears to hold great promise both in reducing body fat as well as iqroving feed efficiency. The ~&&olic consewencec-3 of feed restrictions and the delay in fat deposition are not clearly understood. Ilowever, feed restrictions have been shown to affect lipoprotein lipase activity (Pearce and Johnson 1984) and influence the levels of two enzymes involved in fatty acid synthesis Kalabotta et al 19851, The use of respiration calorimetry allows changes in the bird's slism to be observed. The use of feed restrictions alters the use and partitioning of the energy coqqnent of the diet. Heat production was increased in restricted-fed birds and consequently energy retention, as fat, was decreased. Again, the reasons for this change in energy use are not clearly understood, The chemicals examined in the experiments presented here produce metabolic changes analogous to the changes produced by restrcited feeding. Iodinated casein alters thyroid activity which is obtained by restricted feeding (Cohn and Joseph 1960). The addition of iodinated casein to the finisher the amount of abdominal fat (representative of total inyroved the feed conversion efficiency. Wethli and lipid levels were correlated to thyroid activity and observed here. diet not only decreased body fat) 8 but also Wessels (1973) noted that this effect has been . The exact erode of action of the beta-adrenergic agonists is unknown but it has been proposed that these chemicals act in both mscle and adipose tissue and affect fatty acid synthesis Wicks et al 1984). The effects on chickens have been less pronounced than expected (Dalryrrple et al 1984) and may be due to the chicken liver being the major site of fatty acidsynthesis, rather than the adipocyte. Chicken adipose tissue is unaffected by noradrenalin or porcine ACTH Karlson et al 1964) which are catecholamines similar to the beta-agonists. Similarly, the level of oestrogen has an influence on the success of these chemicals (Stiles et al 1984) and all previous studies using l&s, steers or pigs have used fmxr castrated males. Hence the *poor' effects obtained in broilers may be a result of either of the above factors. Caffeine and theophylline act within the adipocyte and are reputed to alter the activity of the enzymes, phosphodiesterase and, in turn, lipoprotein lipase, The use of these chemicals may have advantages in reducing fat levels, The present studies show that they are unpalatable at high levels, typical of most alkaloids, but at lower levels, they may reduce fat but not feed intake or bodyweight. The lack of change in the energy and nitrogen balance aen chemicals are added to the finisher feed was unexpected. The birds were fed the treated diets for 3 days only and it is possible that critical levels of each chemical need to be reached before any effect is observed. As both cimaterol and 341