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The Performance of Broiler Chicks During and Following a Severe Feed Restriction at an Early Age1
METABOLISM AND NUTRITION The Performance of Broiler Chicks During and Following a Severe Feed Restriction at an Early Age1 I. PLAVNIK and S. HURWITZ Institute of Animal Science, Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel (Received for publication December 20, 1983) ABSTRACT Growth, feed efficiency, and abdominal fat were evaluated in broiler chicks that had been subjected to a severe feed restriction at the age of 1 week. The restriction period lasted 6 to 28 days, during which time the birds received 30 to 45 kcal/day in the different experiments. Feed restriction was followed by a period of refeeding which continued up to the age of 8 to 9 weeks. In the restricted birds, weight gain was lower during the first 2 weeks of refeeding but later exceeded that of the controls. In some cases this growth pattern resulted in an almost complete compensation for the weight gain lost during restriction. An improved feed efficiency in restricted groups was observed during refeeding, due in part to their lower body weight. Plots of cumulative feed efficiency vs. body weight indicate that with body weight over 1500 g, cumulative efficiency was improved over the controls. The extent of improvement at final weights was 2 to 3%, 2 to 4%, 5 to 9%, and 5% in the less severe restriction groups of trials 1, 2, 3, and 4, respectively. Abdominal fat at 8 weeks of age was reduced by the early, energy restriction. The possible practical benefit of an early energy restriction regimen is discussed. (Key words.- feed-restriction, compensatory growth, feed efficiency, broilers) 1985 Poultry Science 64:348-355 INTRODUCTION Energy restriction has been shown t o result in a r e d u c t i o n in m e t a b o l i c energy loss (Mitchell, 1962) leading t o a reduced r e q u i r e m e n t for m a i n t e n a n c e . If, during refeeding, this l o w r e q u i r e m e n t was m a i n t a i n e d , and if growth resumed at a n o r m a l or above n o r m a l rate ( c o m p e n s a t o r y g r o w t h ) , feed efficiency would be substantially improved, leading to an economic advantage. It can be further shown t h a t if, by feed restriction, b o d y weight were m a d e to follow a m o r e concave curve, feed efficiency would be improved d u e to t h e reduced exp e n d i t u r e for m a i n t e n a n c e . In rats, feed efficiency was f o u n d t o improve following short-term periods of feed restriction (Meyer and Clawson, 1 9 6 4 ) . However, it is difficult t o d e t e r m i n e w h e t h e r this i m p r o v e m e n t resulted from t h e reduced needs for m a i n t e n a n c e energy d u e t o a lower b o d y weight or reduced basal needs following restriction. T h e potentially improved feed efficiency can b e exploited practically, provided t h a t some c o m p e n s a t o r y g r o w t h occurs t o balance t h e loss
1
Contribution from the Agricultural Research Organization, Bet Dagan, Israel. No. 913-E, 1983 series. The work was supported by the Israel Eggs and Poultry Board.
348
of weight gain during feed restriction. However, t h e existence of c o m p e n s a t o r y g r o w t h in broilers remains controversial (Reid and White, 1 9 7 7 ) . T h i s controversy m a y b e d u e in p a r t t o actual conflicting results, to variable experim e n t a l conditions, or in p a r t to t h e definition of t h e t e r m . T h e present study was designed t o e x a m i n e t h e effects in broiler chicks of b o t h sexes of an early period of severe feed restriction, which results in an almost c o m p l e t e arrest of g r o w t h , o n s u b s e q u e n t p e r f o r m a n c e . Severity a n d duration of feed restriction were evaluated. MATERIALS AND METHODS General. Day-old White R o c k chicks were o b t a i n e d from a commercial h a t c h e r y , placed in t w o d e c k electrical b a t t e r y b r o o d e r s , and fed a standard starter diet (Table 1) for 1 w e e k . A t this age t h e chicks were weighed individually, and t h o s e with weights closest t o t h e m e a n weight ( a b o u t 70% of t h e t o t a l n u m b e r ) were divided into groups of 8 to 11 chicks o n t h e basis of b o d y weight, equalizing b o t h m e a n weight and distribution within t h e groups. Each t r e a t m e n t consisted of four replicate g r o u p s , e x c e p t for Trial 3 in which t h r e e replicate g r o u p s were used. T h e chicks were feed-restricted for a variable period of t i m e in t h e different e x p e r i m e n t s . T h e daily energy al-
EARLY FEED RESTRICTION TABLE 1. Composition of the experimental diets Diet
Starter
Grower
(%) Soybean oil meal (45% protein) 31.4 Fish meal 2.6 Sorghum 31.4 Corn 30.0 Soybean oil, refined 1.0 Dicalcium phosphate 2.0 Limestone .8 DL-Methionine .2 Mineral supplements .4 (with salt) 1 Vitamin mix 1 .25 Calculated analysis Crude protein, % 20.9 Metabolizable energy, kcal/kg 2900 Lysine, % 1.21 Sulfur amino acids, % .85 Calcium, % 1.02 Phosphorus, % .75
29.5 34.4 30.0 2.3 2.0 .8 .11 .35 .25 18.8 3000 1.04 .68 .98 .73
•Bartov
lowance during the restriction period was calculated as 1.5 kcal/day X BW 2 / 3 , where BW is the body weight in grams, modified from Hurwitz et al. (1978), intended to support maintenance only. The period of restriction was followed by ad libitum feeding to the age of 8 or 9 weeks. At 5 weeks of age, the birds were transferred to community cages situated in an open shed and were fed the growing diet (Table 1). At the end of the experiment, birds were killed by neck dislocation and the amount of abdominal fat weight was estimated. Individual body weights and feed intake on a group basis were recorded at weekly intervals in all experiments. Replicate group averages were subjected to standard statistical analyses according to Snedecor and Cochran (1967), and means were separated by Duncan's multiple range test. Trial 1. The experiment included three treatments: a) control fed ad libitum; b) energy restriction to 40 kcal/day applied during 7 to 21 days of age (2-week restriction); and c) 40 kcal/day during 7 to 35 days of age (4-week restriction). The experiment was continued up to 9 weeks of age. Trial 2. The experimental treatments consisted of a control, and 2 weeks restrictions to 45, 40, 35, and 30 kcal/day between 1 and 3
349
weeks of age. The experiment was continued up to the age of 8 weeks. Trial 3. The experiment included treatments of feed restriction for durations of 6, 10, and 14 days beginning at 7 days of age and a control group. During this period the birds of the restricted lots received 40 kcal/day. The experiment was continued up to the age of 8 weeks. Trial 4. The four treatment lots included an ad libitum-ied control, and feed restrictions to 35 kcal/day for 6, 10, and 14 days, respectively, at the age of 1 week. The experiment was continued until the age of 8 weeks. RESULTS
Trial 1. The purpose of this trial was to evaluate the effect of duration of a severe feed restriction on the subsequent performance of broilers. The results of this experiment are summarized in Table 2. Despite the fact that feed restriction was calculated to arrest growth completely, a growth rate of about 4 g/day was observed in both lots during the first 2 weeks of restriction, dropping to about 2 g/day in Lot 3 during the following period. In both restricted lots, growth in absolute terms was lower than in the control (Lot 1) during the first 2 weeks of refeeding (age 3 to 5 weeks in Lot 2 and 5 to 7 weeks in Lot 3). However, growth rate of the treatment groups exceeded that of the control (Lot 1) during the next biweekly period, and in Lot 2 growth exceeded that of the control also in the third biweekly period of refeeding. The accelerated growth rate was not sufficiently high to compensate entirely for the growth lost during the period of restriction, so that final body weight was lower in the groups restricted for either 2 or 4 weeks than in the control lot. The overall feed efficiency was higher for either treatment group than in the control. This is the reflection of a higher feed efficiency at all times during the refeeding period. Trial 2. The purpose of this trial was to evaluate the effect of severity of feed restriction on subsequent performance. The results are given in Table 3. Similar to the previous trial, the chicks continued to grow even under the most severe restrictions applied in this experiment of 30 kcal/day, but growth rate was reduced stepwise with each reduction in the energy fed. Following refeeding, final body weight was depressed in all restricted groups in comparison with the control; it
350
PLAVNIK AND HURWITZ TABLE 2. Performance of male broilers subjected to 2 or 4 weeks of severe feed restriction (Trial 1)
Body weight, g 1 week Weight gain, g 1—3 weeks 4—5 weeks 6 - 7 weeks 8 - 9 weeks Body weight, g 9 weeks Feed intake, g 1—9 weeks Gain/feed ratio 1—9 weeks
4—week restriction 1
2—week restriction 1
Control
Treatment
153
153
SE 2
152
444a 347 a 483a 49 3 a
b
66 310 a 523 a 541 a
66b 216 b 392b 555 a
2 8 13 27
2841 a
2563 b
1821 c
50
6579 a
5573b
3814 c
.406
b
A4 3 1 a
.437
92 a
.005
a
' ' c Any two means not having a common superscript letter differ significantly (P<.05).
1
40 kcal/day, starting at 1 week of age.
' Calculated from the analysis of variance.
decreased progressively in the treatment groups in relation to previous restriction history. The small differences in body weight among the groups at the end of the depletion period were considerably amplified in the final body weight. Feed efficiency was higher in the restricted groups than in the control, with no significant differences between them. Abdominal fat was significantly reduced by the restriction-refeeding regimens. Trial 3, The results of Trials 1 and 2 suggested that the weight gain lost during periods
of feed restriction lasting 2 to 4 weeks, could not be regained during the period of refeeding of up to 8 weeks of age. This trial was therefore designed to examine the response of male broilers to shorter periods of restriction. The results of this trial are summarized in Table 4. Feed restriction for 6 days hardly influenced the final body weight at 8 weeks of age. The weight decreased progressively in the 10- and 14-day depletion groups. Overall feed efficiency was improved in all depletion lots compared with the control. However, there
TABLE 3. Effect of feed restriction on performance of male broiler chickens (Trial 2) Energy restriction, kcal/day 1 Regimen Body weight, g 1 week End of restriction 8 weeks Feed intake, g 1—8 weeks Gain/feed ratio 1—8 weeks Abdominal fat, % of body weight
Control
45
40
35
30
SE2
135 585 a 2249 a
134 216 b 1953 b
135 201c 1859 b c
135 183 d 1840bc
135 170 e 1754 c
3 40
5506 a
4435b
4275bc
4149cd
4017 d
62
.384 b 2.07 a
.410 a 1.89 ab
.403ab 1.76 ab
.410 a 1.80 ab
.403ab 1.55b
' ' ' ' Means within measurements with different superscripts are significantly different (P<.05). 1
The restriction period lasted 2 weeks, starting at 1 week of age.
2
See footnote 2, Table 2.
.4
.006 .119
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EARLY FEED RESTRICTION TABLE 4. Effect of feed restriction (40 kcal/day) on performance of male broiler chickens (Trial 3) Restriction period, days Regimen Body weight, g 1 week Body weight, g 8 weeks Weight gain, g 1 —8 weeks Feed intake, g 1—8 weeks Gain/feed ratio 1—8 weeks Abdominal fat, % of body weight
Control
10
6
SE1
14
114
114
114
114
2275 a
2257 a
2095ab
1960 b
47
a
a
ab
b
47
2161
2143
4611a .468 2.28 a
1981
3968bc
4225ab b
.508 1.87 b
1846
ab
.500 1.64 b
3516 c ab
.525 1.54b
98 a
.01 .08
' ' Means within measurements with different superscripts are significantly different (P-C05). 1
See footnote 2, Table 2.
were no significant differences in feed efficiency among the restricted lots. Abdominal fat decreased progressively in the lots which had been on the restricted feed regimen several weeks earlier. Trial 4. In this trial, feed restriction of different durations was examined in female broilers. The results of this trial are given in Table 5. Final body weight declined progressively in proportion to the duration of the restriction, although body weight of the 6-day restricted females was not significantly different from
that of the control. Feed efficiency was improved by the restriction treatments, with no significant differences among them. Abdominal body fat at 8 weeks of age was significantly reduced by the restriction regimens, again with no significant difference among these treatments. DISCUSSION
In the present trials, a full compensation for the weight retardation between 1 and 4 weeks of age was not obtained within a growth period of 8 or 9 weeks. However, in two trials (Tables
TABLE 5. Effect of feed restriction (35 kcal/day) on performance of female broiler chickens (Trial 4) Restriction period, days Regimen Body weight, g 1 week Body weight, g 8 weeks Weight gain, g 1—8 weeks Feed consumption, g 1—8 weeks Gain/feed ratio 1—8 weeks Abdominal fat % of body weight
Control
10
6
SE1
14
111
111
111
111
1916 a
1832 b
1703 c
1505 d
21
a
1721
b
1592
c
d
19
4031
b
3792 c
1805
4493 a .402 2.62 a
c
.427 1.88 b
a
.420 1.81 b
1394
3404 d ab
.410 1.62b
35 bc
' ' ' Means within measurements with different superscripts are significantly different (P<.05). 1
See footnote 2, Table 2.
.005 .16
352
PLAVNIK AND HURWITZ
4 and 5) final body weight of males and females restricted for 6 days beginning at the age of 1 week, to 40 and 35 kcal/day, respectively, did not differ significantly from those of the ad libitum-ied controls, in agreement with results reported by Brody et al. (1980). The trends apparent in the growth curves, however, suggest that complete compensation might have occurred had the experiments been continued to a later age. In similar studies with turkeys, which are kept for longer growing periods, full body weight compensation following a 2 weeks of restriction occurred at the age of 20 weeks (S. Hurwitz, I. Plavnik, and I. Bengal, unpublished results). In Trial 1 (Table 2) and also in other experiments not detailed here, growth rate, in absolute terms, was lower in the restricted lots than in the controls during the first 2-week period of refeeding. However, starting at the 6th week of age, weight gain of the previously restricted lots was somewhat higher than that of the control. Thus, compensatory growth as defined by Reid and White (1977) may be delayed, and some experiments that failed to show any compensatory growth might not have been sufficiently long for that purpose. Thus, Washburn and Bondari (1978) found no evidence for compensatory growth when feed was restricted for a period of 3 to 5 weeks in 3 to 8-week-old birds. Wilson and Osborn (1960) also state that compensatory growth was obtained after short periods of restriction, whereas longer periods diminish recovery and may result in delay in achieving normal weights or in a permanent stunting of the animal. In the present study, growth retardation was caused by restriction using a complete diet. Simple calculations using previous models (Hurwitz et al, 1978) suggest that under such conditions, energy is first limiting. In effect, the regular starter diet contains an excess of protein as a percentage of the diet during the severe feed restriction. The response of the birds to a severe energy restriction may be different from that to protein restriction (Auckland and Morris, 1971; Moran, 1981) or to growth retardation by environmental means (Reece and Deaton, 1968), although some compensatory growth was recorded in turkeys or chicks following such stress conditions. In broilers, the energy required for maintenance was found previously to be 1.9 kcal/ g 2 / 3 of body weight per day, at a temperature of 25°C (Hurwitz et al., 1980). The daily
energy allowance of 40 kcal/day used in this study was calculated using the equation given previously (Hurwitz et al, 1978, 1980), but the coefficient for maintenance was lowered to 1.5 kcal/g 2 / 3 per day in anticipation of the reduced needs during energy restriction. However, the results given in Tables 2 and 3 show that this intake supported a growth rate of about 4 g/day during the first 2 weeks of restriction, indicating that the maintenance requirements of these chicks were even lower than anticipated. The results of Trial 1 were used to calculate the energy expenditure for maintenance during refeeding. A requirement for growth of 2 kcal/g (Hurwitz et al, 1978, 1980) was assumed for this calculation. The coefficient of maintenance requirement (kcal/g 2 / 3 per day) is given by: M=
E I
-2' BW 2 ' 3
G
where EI is the energy intake (kcal/day), G is the average weight gain (g/day), and BWis the average body weight for the period. The results of this calculation are given in Table 6. In the control chicks the maintenance expenditure was lower at 2 to 3 weeks of age than at older ages. As theorized previously (Hurwitz, et al, 1978), the lower needs at the early age may be the result of the external heating to which the young chicks are subjected. After that age, the coefficient varied randomly, and hence, only an average is given. The maintenance expenditure was considerably lower than that of the controls during the severe energy restriction and even declined slightly further as energy restriction progressed into its second week. The reduced energy
TABLE 6. Coefficient of energy requirements for maintenance in chicks during and following energy restriction Restricted1
Age
Control
(weeks) 1-2 2-3 3-8
(kcal/g2/3 of body weight) 1.49 1.04 1.75 .89 2.14 2.11
1 Chicks received 40 kcal/day between 1 and 3 weeks of age. Results are given in Table 2.
353
EARLY FEED RESTRICTION
requirement during feed restriction could result from the reduction of both basal metabolic rate and the specific dynamic action (Forsum et al, 1981) and is in agreement with observations in mammals, including man (Mitchell, 1962). The reduction in energy expenditure did not extend beyond the period of feed restriction (Table 6). In all experiments, early severe feed restriction resulted in a somewhat reduced body weight during marketing age of 7 to 9 weeks but considerably improved feed efficiency. Because this improvement in some cases, could have been due to reduced body weights, the system would not be of any practical importance unless broilers could reach market weight with improved feed efficiency. This was tested by plotting the cumulative feed efficiency against body weight rather than against age. The improvement in feed efficiency was taken as the difference between the value of the restricted groups and the value obtained by linear interpolations between the points of the control curve. These plots for Trials 1 to 4 are given in Figures 1 to 4, respectively. In all trials, cumulative feed efficiency in the refed groups, which initially had been lower than in the controls, exceeded that of the latter when body weights exceeded 1500 g. The calculated
—
°
.5 —
improvement in cumulative feed efficiency was 2 and 3% for the last two points of the 40 kcal/day-restricted groups of Trial 1,2, and 4% for the last points of the 40 and 35 kcal/dayrestricted groups of Trial 2, respectively; 5.3 and 9% for the groups restricted for 6, 10, and 14 days, respectively, in Trial 3, and 5% for the last point recorded for females of Trial 4. This would suggest that a severe feed restriction applied at an early age may be of practical benefit. Of the regimens tried in the present study, the most suitable one might be an energy restriction to 35 and 40 kcal in female and male chicks, respectively, given to 1-week-old broilers for 6 days. The improved cumulative feed efficiency during refeeding is explainable by the more concave growth pattern exhibited by the restricted birds (Table 2). It can be estimated that a more concave growth pattern results in a reduction in the integral under the curve of body weight vs. time. Because the maintenance needs are a function of body weight, the intake to satisfy maintenance would be reduced. An additional point of practical importance is the lower percentage of abdominal fat at market age because of the early feed restriction (Tables 3 to 5), which contributes to carcass
^s_
—
•* a
500
1000
1500 B00Y WEIGHT (g)
2000
2500
FIG. 1. The relationship between feed efficiency and body weight as affected by energy restriction, Trial 1. (o) Control fed ad libitum; (•) 40 kcal/day between 1 and 3 weeks of age; (•) 40 kcal/day between 1 and 5 weeks of age.
PLAVNIK AND HURWITZ
354
< a. 2
<
1000 1500 BODY WEIGHT (g)
FIG. 2. The relationship between body weight and feed efficiency as affected by feed restriction, Trial 2. (o) Ad libitum-ied control; and feed restriction between 1 and 3 weeks of age at: 45 (°), 40 (•), 35 A , and 30 * kcal/day.
yield and quality. This lowered quantity of carcass fat probably also contributes to the better feed efficiency of the restricted birds. It appears rather unlikely that the reduced body fat in the restricted and refed birds is the
direct effect of a low energy balance of the body during refeeding, in view of the interval of 6 to 7 weeks that elapsed between the end of the feed restriction period and the measurements which were made around the marketing
< tr o UJ
<
500
1000 1500 BODY WEIGHT ( g )
FIG. 3. The relationship between body weight and feed efficiency as affected by feed restriction of 40 kcal/day at 1 week of age, Trial 3. The restriction period was 6 days •; 10 days • ; and 14 days A ; O denotes the control lot fed ad libitum.
EARLY FEED RESTRICTION
500
1000 BODY WEIGHT (g)
355
1500
2000
FIG. 4. The relationship between body weight and feed efficiency in female broilers as affected by feed restriction of 35 kcal/day at 1 week of age, Trial 4. o, Control; restriction for 6 days •, 10 days •, and 14 days A.
age. More likely, t h e reduced a m o u n t of abd o m i n a l fat m a y be t h e result of t h e reduced n u m b e r of adipocytes d u e t o t h e early inhibition of a d i p o c y t e hyperplasia caused b y t h e severe energy restriction (March and Hensen, 1976). ACKNOWLEDGMENTS This s t u d y was s u p p o r t e d b y grants from t h e Israel Egg and P o u l t r y Board. T h e technical assistance of J . N i s e n b a u m , M. Ben-Moshe, and Y . Lev is gratefully acknowledged.
REFERENCES Auckland, J. N., and T. R. Morris, 1971. Compensatory growth in turkeys: effect of undernutrition on subsequent protein requirements. Br. Poult. Sci. 12:41-48. Bartov, I., N. Paster, and N. Lisker, 1982. The nutritional value of moldy grains for broiler chicks. Poultry Sci. 61:2247-2254. Brody, T., Y. Eitan, M. Soller, I. Nir, and Z. Nitsan, 1980. Compensatory growth and sexual maturity in females reared under severe food restriction from day of hatching. Br. Poult. Sci. 2 1 : 4 3 7 446. Forsum, E., P. E. Hillman, and M. C. Nesheim, 1981. Effect of energy restriction on total heat production, basal metabolic rate and specific dynamic action of food in rats. J. Nutr. I l l : 1691-1697. Hurwitz, S., O. Sklan, and I. Bartov, 1978. Newformal approaches to the determination of energy and amino acid requirements of chicks. Poultry Sci. 57:197-205. Hurwitz, S., M. Weiselberg, U. Eisner, I. Bartov, G.
Riesenfeld, M. Shavit, A. Niv, and S. Bornstein, 1980. The energy requirements and performance of growing chicks and turkeys as affected by environmental temperature. Poultry Sci. 59: 2290-2299. March, B. E., and G. Hensen, 1976. Lipid accumulation and cell multiplication in adipose bodies in White Leghorn and broiler-type chicks. Poultry Sci. 56:886-894. Meyer, J. H., and W. J. Clawson, 1964. Undernutrition and subsequent realimentation in rats and sheep. J.'Anim. Sci. 23:214-224. Mitchell, H. H., 1962. Comparative Nutrition of Man and Domestic Animals. Vol. 1. Academic Press, New York, NY. Moran, E. T. Jr., 1981. Early protein nutrition, compensatory growth and carcass quality of broiler-type torn turkeys. Poultry Sci. 60:401 — 406. Reece, F. N., and J. W. Deaton, 1968. Implications of reduced heat during brooding of broilers. Proc. Assoc. Soc. Agric. Workers 65:218-219. (As quoted by J. W. Deaton, F. N. Reece, L. F. Kubena, B. D. Lott, and J. D. May. Poultry Sci. 52:212-265, 1973.) Reid, J. T., and O. D. White, 1977. The phenomenon of compensatory growth. Proc. Cornell Nutr. Conf. p. 16:27. Snedecor, G. W., and W. G. Cochran, 1967. Statistical Methods. 6th ed. Iowa State Univ. Press, Ames, IA. Washburn, K. W., and K. Bondari, 1978. Effects of timing and duration of restricted feeding on compensatory growth in broilers. Poultry Sci. 57:1013-1021. Wilson, P. N., and D. F. Osborn, 1960. Compensatory growth after undernutrition in mammals and birds. Biol. Rev. 35:325-363.
1
Contribution from the Agricultural Research Organization, Bet Dagan, Israel. No. 913-E, 1983 series. The work was supported by the Israel Eggs and Poultry Board.
348
of weight gain during feed restriction. However, t h e existence of c o m p e n s a t o r y g r o w t h in broilers remains controversial (Reid and White, 1 9 7 7 ) . T h i s controversy m a y b e d u e in p a r t t o actual conflicting results, to variable experim e n t a l conditions, or in p a r t to t h e definition of t h e t e r m . T h e present study was designed t o e x a m i n e t h e effects in broiler chicks of b o t h sexes of an early period of severe feed restriction, which results in an almost c o m p l e t e arrest of g r o w t h , o n s u b s e q u e n t p e r f o r m a n c e . Severity a n d duration of feed restriction were evaluated. MATERIALS AND METHODS General. Day-old White R o c k chicks were o b t a i n e d from a commercial h a t c h e r y , placed in t w o d e c k electrical b a t t e r y b r o o d e r s , and fed a standard starter diet (Table 1) for 1 w e e k . A t this age t h e chicks were weighed individually, and t h o s e with weights closest t o t h e m e a n weight ( a b o u t 70% of t h e t o t a l n u m b e r ) were divided into groups of 8 to 11 chicks o n t h e basis of b o d y weight, equalizing b o t h m e a n weight and distribution within t h e groups. Each t r e a t m e n t consisted of four replicate g r o u p s , e x c e p t for Trial 3 in which t h r e e replicate g r o u p s were used. T h e chicks were feed-restricted for a variable period of t i m e in t h e different e x p e r i m e n t s . T h e daily energy al-
EARLY FEED RESTRICTION TABLE 1. Composition of the experimental diets Diet
Starter
Grower
(%) Soybean oil meal (45% protein) 31.4 Fish meal 2.6 Sorghum 31.4 Corn 30.0 Soybean oil, refined 1.0 Dicalcium phosphate 2.0 Limestone .8 DL-Methionine .2 Mineral supplements .4 (with salt) 1 Vitamin mix 1 .25 Calculated analysis Crude protein, % 20.9 Metabolizable energy, kcal/kg 2900 Lysine, % 1.21 Sulfur amino acids, % .85 Calcium, % 1.02 Phosphorus, % .75
29.5 34.4 30.0 2.3 2.0 .8 .11 .35 .25 18.8 3000 1.04 .68 .98 .73
•Bartov
lowance during the restriction period was calculated as 1.5 kcal/day X BW 2 / 3 , where BW is the body weight in grams, modified from Hurwitz et al. (1978), intended to support maintenance only. The period of restriction was followed by ad libitum feeding to the age of 8 or 9 weeks. At 5 weeks of age, the birds were transferred to community cages situated in an open shed and were fed the growing diet (Table 1). At the end of the experiment, birds were killed by neck dislocation and the amount of abdominal fat weight was estimated. Individual body weights and feed intake on a group basis were recorded at weekly intervals in all experiments. Replicate group averages were subjected to standard statistical analyses according to Snedecor and Cochran (1967), and means were separated by Duncan's multiple range test. Trial 1. The experiment included three treatments: a) control fed ad libitum; b) energy restriction to 40 kcal/day applied during 7 to 21 days of age (2-week restriction); and c) 40 kcal/day during 7 to 35 days of age (4-week restriction). The experiment was continued up to 9 weeks of age. Trial 2. The experimental treatments consisted of a control, and 2 weeks restrictions to 45, 40, 35, and 30 kcal/day between 1 and 3
349
weeks of age. The experiment was continued up to the age of 8 weeks. Trial 3. The experiment included treatments of feed restriction for durations of 6, 10, and 14 days beginning at 7 days of age and a control group. During this period the birds of the restricted lots received 40 kcal/day. The experiment was continued up to the age of 8 weeks. Trial 4. The four treatment lots included an ad libitum-ied control, and feed restrictions to 35 kcal/day for 6, 10, and 14 days, respectively, at the age of 1 week. The experiment was continued until the age of 8 weeks. RESULTS
Trial 1. The purpose of this trial was to evaluate the effect of duration of a severe feed restriction on the subsequent performance of broilers. The results of this experiment are summarized in Table 2. Despite the fact that feed restriction was calculated to arrest growth completely, a growth rate of about 4 g/day was observed in both lots during the first 2 weeks of restriction, dropping to about 2 g/day in Lot 3 during the following period. In both restricted lots, growth in absolute terms was lower than in the control (Lot 1) during the first 2 weeks of refeeding (age 3 to 5 weeks in Lot 2 and 5 to 7 weeks in Lot 3). However, growth rate of the treatment groups exceeded that of the control (Lot 1) during the next biweekly period, and in Lot 2 growth exceeded that of the control also in the third biweekly period of refeeding. The accelerated growth rate was not sufficiently high to compensate entirely for the growth lost during the period of restriction, so that final body weight was lower in the groups restricted for either 2 or 4 weeks than in the control lot. The overall feed efficiency was higher for either treatment group than in the control. This is the reflection of a higher feed efficiency at all times during the refeeding period. Trial 2. The purpose of this trial was to evaluate the effect of severity of feed restriction on subsequent performance. The results are given in Table 3. Similar to the previous trial, the chicks continued to grow even under the most severe restrictions applied in this experiment of 30 kcal/day, but growth rate was reduced stepwise with each reduction in the energy fed. Following refeeding, final body weight was depressed in all restricted groups in comparison with the control; it
350
PLAVNIK AND HURWITZ TABLE 2. Performance of male broilers subjected to 2 or 4 weeks of severe feed restriction (Trial 1)
Body weight, g 1 week Weight gain, g 1—3 weeks 4—5 weeks 6 - 7 weeks 8 - 9 weeks Body weight, g 9 weeks Feed intake, g 1—9 weeks Gain/feed ratio 1—9 weeks
4—week restriction 1
2—week restriction 1
Control
Treatment
153
153
SE 2
152
444a 347 a 483a 49 3 a
b
66 310 a 523 a 541 a
66b 216 b 392b 555 a
2 8 13 27
2841 a
2563 b
1821 c
50
6579 a
5573b
3814 c
.406
b
A4 3 1 a
.437
92 a
.005
a
' ' c Any two means not having a common superscript letter differ significantly (P<.05).
1
40 kcal/day, starting at 1 week of age.
' Calculated from the analysis of variance.
decreased progressively in the treatment groups in relation to previous restriction history. The small differences in body weight among the groups at the end of the depletion period were considerably amplified in the final body weight. Feed efficiency was higher in the restricted groups than in the control, with no significant differences between them. Abdominal fat was significantly reduced by the restriction-refeeding regimens. Trial 3, The results of Trials 1 and 2 suggested that the weight gain lost during periods
of feed restriction lasting 2 to 4 weeks, could not be regained during the period of refeeding of up to 8 weeks of age. This trial was therefore designed to examine the response of male broilers to shorter periods of restriction. The results of this trial are summarized in Table 4. Feed restriction for 6 days hardly influenced the final body weight at 8 weeks of age. The weight decreased progressively in the 10- and 14-day depletion groups. Overall feed efficiency was improved in all depletion lots compared with the control. However, there
TABLE 3. Effect of feed restriction on performance of male broiler chickens (Trial 2) Energy restriction, kcal/day 1 Regimen Body weight, g 1 week End of restriction 8 weeks Feed intake, g 1—8 weeks Gain/feed ratio 1—8 weeks Abdominal fat, % of body weight
Control
45
40
35
30
SE2
135 585 a 2249 a
134 216 b 1953 b
135 201c 1859 b c
135 183 d 1840bc
135 170 e 1754 c
3 40
5506 a
4435b
4275bc
4149cd
4017 d
62
.384 b 2.07 a
.410 a 1.89 ab
.403ab 1.76 ab
.410 a 1.80 ab
.403ab 1.55b
' ' ' ' Means within measurements with different superscripts are significantly different (P<.05). 1
The restriction period lasted 2 weeks, starting at 1 week of age.
2
See footnote 2, Table 2.
.4
.006 .119
351
EARLY FEED RESTRICTION TABLE 4. Effect of feed restriction (40 kcal/day) on performance of male broiler chickens (Trial 3) Restriction period, days Regimen Body weight, g 1 week Body weight, g 8 weeks Weight gain, g 1 —8 weeks Feed intake, g 1—8 weeks Gain/feed ratio 1—8 weeks Abdominal fat, % of body weight
Control
10
6
SE1
14
114
114
114
114
2275 a
2257 a
2095ab
1960 b
47
a
a
ab
b
47
2161
2143
4611a .468 2.28 a
1981
3968bc
4225ab b
.508 1.87 b
1846
ab
.500 1.64 b
3516 c ab
.525 1.54b
98 a
.01 .08
' ' Means within measurements with different superscripts are significantly different (P-C05). 1
See footnote 2, Table 2.
were no significant differences in feed efficiency among the restricted lots. Abdominal fat decreased progressively in the lots which had been on the restricted feed regimen several weeks earlier. Trial 4. In this trial, feed restriction of different durations was examined in female broilers. The results of this trial are given in Table 5. Final body weight declined progressively in proportion to the duration of the restriction, although body weight of the 6-day restricted females was not significantly different from
that of the control. Feed efficiency was improved by the restriction treatments, with no significant differences among them. Abdominal body fat at 8 weeks of age was significantly reduced by the restriction regimens, again with no significant difference among these treatments. DISCUSSION
In the present trials, a full compensation for the weight retardation between 1 and 4 weeks of age was not obtained within a growth period of 8 or 9 weeks. However, in two trials (Tables
TABLE 5. Effect of feed restriction (35 kcal/day) on performance of female broiler chickens (Trial 4) Restriction period, days Regimen Body weight, g 1 week Body weight, g 8 weeks Weight gain, g 1—8 weeks Feed consumption, g 1—8 weeks Gain/feed ratio 1—8 weeks Abdominal fat % of body weight
Control
10
6
SE1
14
111
111
111
111
1916 a
1832 b
1703 c
1505 d
21
a
1721
b
1592
c
d
19
4031
b
3792 c
1805
4493 a .402 2.62 a
c
.427 1.88 b
a
.420 1.81 b
1394
3404 d ab
.410 1.62b
35 bc
' ' ' Means within measurements with different superscripts are significantly different (P<.05). 1
See footnote 2, Table 2.
.005 .16
352
PLAVNIK AND HURWITZ
4 and 5) final body weight of males and females restricted for 6 days beginning at the age of 1 week, to 40 and 35 kcal/day, respectively, did not differ significantly from those of the ad libitum-ied controls, in agreement with results reported by Brody et al. (1980). The trends apparent in the growth curves, however, suggest that complete compensation might have occurred had the experiments been continued to a later age. In similar studies with turkeys, which are kept for longer growing periods, full body weight compensation following a 2 weeks of restriction occurred at the age of 20 weeks (S. Hurwitz, I. Plavnik, and I. Bengal, unpublished results). In Trial 1 (Table 2) and also in other experiments not detailed here, growth rate, in absolute terms, was lower in the restricted lots than in the controls during the first 2-week period of refeeding. However, starting at the 6th week of age, weight gain of the previously restricted lots was somewhat higher than that of the control. Thus, compensatory growth as defined by Reid and White (1977) may be delayed, and some experiments that failed to show any compensatory growth might not have been sufficiently long for that purpose. Thus, Washburn and Bondari (1978) found no evidence for compensatory growth when feed was restricted for a period of 3 to 5 weeks in 3 to 8-week-old birds. Wilson and Osborn (1960) also state that compensatory growth was obtained after short periods of restriction, whereas longer periods diminish recovery and may result in delay in achieving normal weights or in a permanent stunting of the animal. In the present study, growth retardation was caused by restriction using a complete diet. Simple calculations using previous models (Hurwitz et al, 1978) suggest that under such conditions, energy is first limiting. In effect, the regular starter diet contains an excess of protein as a percentage of the diet during the severe feed restriction. The response of the birds to a severe energy restriction may be different from that to protein restriction (Auckland and Morris, 1971; Moran, 1981) or to growth retardation by environmental means (Reece and Deaton, 1968), although some compensatory growth was recorded in turkeys or chicks following such stress conditions. In broilers, the energy required for maintenance was found previously to be 1.9 kcal/ g 2 / 3 of body weight per day, at a temperature of 25°C (Hurwitz et al., 1980). The daily
energy allowance of 40 kcal/day used in this study was calculated using the equation given previously (Hurwitz et al, 1978, 1980), but the coefficient for maintenance was lowered to 1.5 kcal/g 2 / 3 per day in anticipation of the reduced needs during energy restriction. However, the results given in Tables 2 and 3 show that this intake supported a growth rate of about 4 g/day during the first 2 weeks of restriction, indicating that the maintenance requirements of these chicks were even lower than anticipated. The results of Trial 1 were used to calculate the energy expenditure for maintenance during refeeding. A requirement for growth of 2 kcal/g (Hurwitz et al, 1978, 1980) was assumed for this calculation. The coefficient of maintenance requirement (kcal/g 2 / 3 per day) is given by: M=
E I
-2' BW 2 ' 3
G
where EI is the energy intake (kcal/day), G is the average weight gain (g/day), and BWis the average body weight for the period. The results of this calculation are given in Table 6. In the control chicks the maintenance expenditure was lower at 2 to 3 weeks of age than at older ages. As theorized previously (Hurwitz, et al, 1978), the lower needs at the early age may be the result of the external heating to which the young chicks are subjected. After that age, the coefficient varied randomly, and hence, only an average is given. The maintenance expenditure was considerably lower than that of the controls during the severe energy restriction and even declined slightly further as energy restriction progressed into its second week. The reduced energy
TABLE 6. Coefficient of energy requirements for maintenance in chicks during and following energy restriction Restricted1
Age
Control
(weeks) 1-2 2-3 3-8
(kcal/g2/3 of body weight) 1.49 1.04 1.75 .89 2.14 2.11
1 Chicks received 40 kcal/day between 1 and 3 weeks of age. Results are given in Table 2.
353
EARLY FEED RESTRICTION
requirement during feed restriction could result from the reduction of both basal metabolic rate and the specific dynamic action (Forsum et al, 1981) and is in agreement with observations in mammals, including man (Mitchell, 1962). The reduction in energy expenditure did not extend beyond the period of feed restriction (Table 6). In all experiments, early severe feed restriction resulted in a somewhat reduced body weight during marketing age of 7 to 9 weeks but considerably improved feed efficiency. Because this improvement in some cases, could have been due to reduced body weights, the system would not be of any practical importance unless broilers could reach market weight with improved feed efficiency. This was tested by plotting the cumulative feed efficiency against body weight rather than against age. The improvement in feed efficiency was taken as the difference between the value of the restricted groups and the value obtained by linear interpolations between the points of the control curve. These plots for Trials 1 to 4 are given in Figures 1 to 4, respectively. In all trials, cumulative feed efficiency in the refed groups, which initially had been lower than in the controls, exceeded that of the latter when body weights exceeded 1500 g. The calculated
—
°
.5 —
improvement in cumulative feed efficiency was 2 and 3% for the last two points of the 40 kcal/day-restricted groups of Trial 1,2, and 4% for the last points of the 40 and 35 kcal/dayrestricted groups of Trial 2, respectively; 5.3 and 9% for the groups restricted for 6, 10, and 14 days, respectively, in Trial 3, and 5% for the last point recorded for females of Trial 4. This would suggest that a severe feed restriction applied at an early age may be of practical benefit. Of the regimens tried in the present study, the most suitable one might be an energy restriction to 35 and 40 kcal in female and male chicks, respectively, given to 1-week-old broilers for 6 days. The improved cumulative feed efficiency during refeeding is explainable by the more concave growth pattern exhibited by the restricted birds (Table 2). It can be estimated that a more concave growth pattern results in a reduction in the integral under the curve of body weight vs. time. Because the maintenance needs are a function of body weight, the intake to satisfy maintenance would be reduced. An additional point of practical importance is the lower percentage of abdominal fat at market age because of the early feed restriction (Tables 3 to 5), which contributes to carcass
^s_
—
•* a
500
1000
1500 B00Y WEIGHT (g)
2000
2500
FIG. 1. The relationship between feed efficiency and body weight as affected by energy restriction, Trial 1. (o) Control fed ad libitum; (•) 40 kcal/day between 1 and 3 weeks of age; (•) 40 kcal/day between 1 and 5 weeks of age.
PLAVNIK AND HURWITZ
354
< a. 2
<
1000 1500 BODY WEIGHT (g)
FIG. 2. The relationship between body weight and feed efficiency as affected by feed restriction, Trial 2. (o) Ad libitum-ied control; and feed restriction between 1 and 3 weeks of age at: 45 (°), 40 (•), 35 A , and 30 * kcal/day.
yield and quality. This lowered quantity of carcass fat probably also contributes to the better feed efficiency of the restricted birds. It appears rather unlikely that the reduced body fat in the restricted and refed birds is the
direct effect of a low energy balance of the body during refeeding, in view of the interval of 6 to 7 weeks that elapsed between the end of the feed restriction period and the measurements which were made around the marketing
< tr o UJ
<
500
1000 1500 BODY WEIGHT ( g )
FIG. 3. The relationship between body weight and feed efficiency as affected by feed restriction of 40 kcal/day at 1 week of age, Trial 3. The restriction period was 6 days •; 10 days • ; and 14 days A ; O denotes the control lot fed ad libitum.
EARLY FEED RESTRICTION
500
1000 BODY WEIGHT (g)
355
1500
2000
FIG. 4. The relationship between body weight and feed efficiency in female broilers as affected by feed restriction of 35 kcal/day at 1 week of age, Trial 4. o, Control; restriction for 6 days •, 10 days •, and 14 days A.
age. More likely, t h e reduced a m o u n t of abd o m i n a l fat m a y be t h e result of t h e reduced n u m b e r of adipocytes d u e t o t h e early inhibition of a d i p o c y t e hyperplasia caused b y t h e severe energy restriction (March and Hensen, 1976). ACKNOWLEDGMENTS This s t u d y was s u p p o r t e d b y grants from t h e Israel Egg and P o u l t r y Board. T h e technical assistance of J . N i s e n b a u m , M. Ben-Moshe, and Y . Lev is gratefully acknowledged.
REFERENCES Auckland, J. N., and T. R. Morris, 1971. Compensatory growth in turkeys: effect of undernutrition on subsequent protein requirements. Br. Poult. Sci. 12:41-48. Bartov, I., N. Paster, and N. Lisker, 1982. The nutritional value of moldy grains for broiler chicks. Poultry Sci. 61:2247-2254. Brody, T., Y. Eitan, M. Soller, I. Nir, and Z. Nitsan, 1980. Compensatory growth and sexual maturity in females reared under severe food restriction from day of hatching. Br. Poult. Sci. 2 1 : 4 3 7 446. Forsum, E., P. E. Hillman, and M. C. Nesheim, 1981. Effect of energy restriction on total heat production, basal metabolic rate and specific dynamic action of food in rats. J. Nutr. I l l : 1691-1697. Hurwitz, S., O. Sklan, and I. Bartov, 1978. Newformal approaches to the determination of energy and amino acid requirements of chicks. Poultry Sci. 57:197-205. Hurwitz, S., M. Weiselberg, U. Eisner, I. Bartov, G.
Riesenfeld, M. Shavit, A. Niv, and S. Bornstein, 1980. The energy requirements and performance of growing chicks and turkeys as affected by environmental temperature. Poultry Sci. 59: 2290-2299. March, B. E., and G. Hensen, 1976. Lipid accumulation and cell multiplication in adipose bodies in White Leghorn and broiler-type chicks. Poultry Sci. 56:886-894. Meyer, J. H., and W. J. Clawson, 1964. Undernutrition and subsequent realimentation in rats and sheep. J.'Anim. Sci. 23:214-224. Mitchell, H. H., 1962. Comparative Nutrition of Man and Domestic Animals. Vol. 1. Academic Press, New York, NY. Moran, E. T. Jr., 1981. Early protein nutrition, compensatory growth and carcass quality of broiler-type torn turkeys. Poultry Sci. 60:401 — 406. Reece, F. N., and J. W. Deaton, 1968. Implications of reduced heat during brooding of broilers. Proc. Assoc. Soc. Agric. Workers 65:218-219. (As quoted by J. W. Deaton, F. N. Reece, L. F. Kubena, B. D. Lott, and J. D. May. Poultry Sci. 52:212-265, 1973.) Reid, J. T., and O. D. White, 1977. The phenomenon of compensatory growth. Proc. Cornell Nutr. Conf. p. 16:27. Snedecor, G. W., and W. G. Cochran, 1967. Statistical Methods. 6th ed. Iowa State Univ. Press, Ames, IA. Washburn, K. W., and K. Bondari, 1978. Effects of timing and duration of restricted feeding on compensatory growth in broilers. Poultry Sci. 57:1013-1021. Wilson, P. N., and D. F. Osborn, 1960. Compensatory growth after undernutrition in mammals and birds. Biol. Rev. 35:325-363.