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Effects of High Temperature on Growth and Efficiency of Male and Female Broilers from Lines Selected for High Weight Gain, Favorable Feed Conversion, and High or Low Fat Content
BREEDING AND GENETICS Effects of High Temperature on Growth and Efficiency of Male and Female Broilers from Lines Selected for High Weight Gain, Favorable Feed Conversion, and High or Low Fat Content AVIGDOR CAHANER1 and FERRY LEENSTRA Spelderholt Centre for Poultry Research and Information Services (COVP-DLO) P.O. Box 15, 7360 AA Beekbergen, The Netherlands
1992 Poultry Science 71:1237-1250
INTRODUCTION
The reduction in weight gain of broilers due to high ambient temperatures is of great concern in regions with hot climates. Heat-stress conditions also occasionally develop in temperate regions during the hot season, especially if broilers are kept at high densities and ventilation is insufficient. Exact heat-stress or hot-climate conditions are difficult to simulate in experi-
Received for publication December 23, 1991. Accepted for publication April 17, 1992. 1 The Hebrew University of Jerusalem, Faculty of Agriculture, P.O. Box 12, Rehovot, Israel.
mental situations. They result from different (and changing) combinations of temperature and its diurnal cycles, relative humidity, and air velocity. Therefore, a constant temperature within the range of 29 to 35 C has been used in most studies to assess the response of broilers to simulated practical high-temperature conditions. If broilers kept under high temperatures grow older and larger, their growth rate is progressively reduced when compared with birds kept at normal temperatures. Adams and Rogler (1968) found that growth rate was more depressed in the heaviest 40% birds from a flock of male broilers than in the lightest 40% birds.
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ABSTRACT Male and female broiler chicks from five different broiler crosses (WI, LF, and HF = Israeli chicks selected for high body weight gain, and low and high abdominal fat, respectively; FC and WN = Dutch chicks selected for favorable feed conversion and high body weight gain, respectively) were raised at a high ambient temperature (32 to 33 C). Weight gain, protein and fat content in the carcass and feed, and protein efficiency were determined at 4,6, and 8 wk of age. The effect of the high temperature was evaluated by comparing these data with those of similar chicks raised at a normal temperature (20 to 33 C) up to 6 wk of age. The reductions in body weight, protein gain, and feed and protein efficiency due to the high temperature increased with age and were much larger in males than in females. This trend was more pronounced in WI and WN chicks than in LF, HF, and FC chicks. Females of WI and WN crosses were as heavy as males at 6 wk and heavier at 8 wk. In LF, HF, and FC crosses, both sexes had similar weights at 8 wk. Growth reduction due to the high temperature was largest in the groups with the highest growth rate at the normal temperature (WI and WN males). Chicks with a lower growth rate and a higher capacity for energy storage in fat depots (all females, HF chicks), or a higher capacity for heat loss (FC chicks), were less affected by the high temperature. The results suggest that females should be preferred over males for broiler production in hot facilities or locations. Broiler genotypes selected for feed efficiency at the expense of fast growth may allow for a more profitable broiler production in high-temperature regions. (Key words: high temperature, genotype, growth rate, feed efficiency, body composition)
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CAHANER AND LEENSTRA
MATERIALS AND METHODS
The data presented in this paper were obtained from an experiment in which performance of chickens kept at high, normal, and suboptimal temperatures were compared. Chickens, diets, housing, and measurements have been described by Leenstra and Cahaner (1991). They reported on the comparisons between normal and suboptimal temperature. The present study concentrated on the effects of the high temperature. The experimental details were as follows.
cross between the fifth generation of broiler sire and broiler dam lines both selected for a low (LF) or high (HF) amount of abdominal fat (Cahaner, 1988), or high body weight gain (WI). For the Dutch chicks, commercial broiler breeder hens were mated to males of the ninth generation of broiler sire lines selected for favorable feed conversion (FC) or fast body weight gain (WN) (Leenstra, 1988). All eggs were incubated and hatched simultaneously at the DLO Centre for Poultry Research and Information Services, Beekbergen, The Netherlands. Housing and Management
The chicks were housed in floor pens of .75 x 1.0 m, each equipped with a separate feeder. Eighteen chicks were housed in each pen up to 4 wk of age, and their number was reduced, by removing chicks randomly, to 15 per pen in the 5th wk, 12 in the 6th wk, and 6 in the 7th and 8th wk. The pens were arranged in rooms. Ten pens per room, one pen for males and one for females from each of the five genotypes, were used. Lighting was continuous during the 1st day after hatch and intermittent (1 h light; 3 h darkness, alternating) thereafter. The chicks received for ad libitum consumption a pelleted broiler diet with 3,203 kcal metabolizable energy and 215 g of crude protein/ kg of diet. Climate
In three rooms the temperature was kept at 33 C from hatch until 2 wk of age and at 32 C thereafter (high temperature). In three other rooms, normal temperatures, i.e., gradually decreasing from 33 C at hatch to 20 C at 6 wk of age (Leenstra and Cahaner, 1991), were applied. Relative humidity was kept at 60% for both temperature schemes. Measurements
Chickens
Five different genetic groups (genotypes) were used in the current experiment. Three were of Israeli origin and two of Dutch origin. All chicks resulted from a cross between Cornish (broiler sire) and White Plymouth Rock (broiler dam) chickens. The Israeli chicks descended from a
Chicks were weighed by pen at hatch and body weight and feed consumption were determined weekly from 2 to 6 wk of age in the normal temperature groups and from 2 to 8 wk (55 days) of age in the hightemperature groups in an attempt to finish the high-temperature groups at a body weight that the normal temperature groups
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Continuous selection for increased growth rate thus might increase sensitivity of broiler stocks to high temperatures, unless specific criteria for efficient performance under high temperatures are identified and applied in selection programs. Although in most studies (i.e., Kubena et al, 1972; Cerniglia et al, 1983; Howlider and Rose, 1989) the magnitude of the effect of high temperature was not dependent on sex, Osman et al. (1989) found that the reduction in weight gain due to high temperatures appeared at a younger age and was larger in males than in females. Whether the more pronounced effect of high temperatures on males is caused by their higher body weight or by other sexspecific factors (i.e., body composition or feed efficiency) is not clear. If the latter is true, the use of female broilers instead of males or mixed sexes might be advantageous when high environmental temperatures cannot be prevented. The present experiment examined the effects of inherent growth rate and sex on broiler performance at a high temperature using males and females of broiler crosses selected for high body weight gain, favorable feed efficiency, and low or high body fat content.
GENOTYPE BY TEMPERATURE INTERACTIONS IN BROILERS
were tested against e p , the between-pens within-room error term. The effects of age (A; 4, 6, and 8 wk), genotype, sex, and their interactions at the high temperature were examined for each trait by ANOVA with the model: Y = n + er + G + S + GS + e p + A + GA + SA + GSA + e w . [2] Each room was considered as a block (er). The effects of age and the interactions with age were tested against the error term within pen due to repeated measurements (ew). Effects of genotype and sex on performance under the high temperature at each age separately, were examined by ANOVA with the model: Y = ^i + e r + G + S + GS + ep.
[3]
To examine the effect of age, specific contrasts between different ages or age periods were analyzed, i.e., 4 versus 6 or 0 to 4 versus 4 to 6 wk of age (4 to 6 wk), and 6 versus 8 or 4 to 6 versus 6 to 8 wk of age (6 to Statistical Analysis 8 wk). Three contrasts between sources of The entire experiment had a split-plot genetic differences were evaluated. The design with temperature regimens assigned effects of selection goal (WT - LN; body to rooms as the main plots, and the weight or leanness) and of genotypes' genotype by sex combinations assigned to origin (IS - NL; Israel or The Netherlands) pens as secondary plots. The temperature and their interactions with other main regimens were distributed randomly over factors were tested by estimating the conthe rooms. In each room, all 10 genotype trasts WI + WN - LF - FC and WI + LF - WN and sex combinations were randomly dis- - FC, respectively. As the HF chicks did not tributed among the pens. have a Dutch counterpart, they were not The effects on pen mean (Y) of tempera- incorporated in these contrasts. The conture (T, high versus normal), genotype (G), trast HF - LF was, however, evaluated to sex (S), and their interactions were exam- examine the effect of carcass fat content in ined for each of the measurements between chicks from the same origin and with 0 and 6 wk of age, by ANOVA with the similar growth rate. model: All statistical analyses were done with the Genstat program (Genstat 5, 1987). Y = u + T + e r + G + S + TG Unless otherwise stated, main effects, con+ TS + GS + GTS + e p . [1] trasts, and interactions were considered significant if P < .05. The effect of T was tested against e r , the between-rooms error term. All other effects RESULTS InfraAlyzer-400, Bran + Luebbe, Maarssen, The Netherlands.
Up to 6 wk of age, mortality at the high temperature (20 chicks, or 4%) was similar to that at the normal temperature (21
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had at 6 wk. The chicks were weighed fullfed, directly after a light period. At 4 and 6 wk (both temperatures) and at 8 wk of age (high temperature), three randomly selected chicks from each pen were used to determine carcass composition. These chicks were fasted overnight, killed by CO2 suffocation, weighed, and defeathered. The defeathered carcasses from each pen were weighed again, chopped, and minced. In the minced product, protein and fat content were determined by near infrared reflection spectroscopy (NIRS)2 (Steverink et ah, 1988). From the body weights and the NIRS readings, fat and protein contents were calculated. In this calculation, weight and composition of the feathers were ignored. Daily weight gain, protein gain, and fat gain were calculated from hatch to 4 wk, from 4 to 6 wk, and from 6 to 8 wk of age. Feed efficiency (weight gain to feed consumption) and protein efficiency (protein deposition to protein consumption) were calculated for each pen from hatch up to 4, 6, and 8 wk, from 4 to 6 wk, and from 6 to 8 wk of age.
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CAHANER AND LEENSTRA
Males
HF
LF
FC WN Wl
HF
LF
Females
FC WN Wl
b. Protein gain
c. Fat gain
LF
FC WN Wl
HF
LF
FC WN Wl
LF
FC WN Wl
LF
FC WN Wl
O to 4 wk
HF
LF
FC WN Wl
4 to 6 wk
FC WN Wl
e. Protein efficiency
d. Feed efficiency
HF
HF LF
HF LF
FC WN Wl
O to 4 wk
HF
LF
FC WN Wl
4 to 6 wk
FIGURE 1. Body weight (a), protein gain (b), fat gain (c), feed efficiency (d), and protein efficiency (e) from 0 to 4 wk and from 4 to 6 wk of age of male and female chicks from five genotypes raised at high temperature expressed as percentage of the performance of their sibs reared at normal temperature (HF and LF = Israeli crosses, selected for a high or a low amount of abdominal fat, respectively; FC = Dutch cross, selected for favorable feed conversion between 3 and 6 wk of age; WN and Wl = crosses originating from The Netherlands and Israel, respectively, selected for high 6-wk body weight).
chicks). Mortality at the high temperature between Weeks 6 and 8 was 10% (18 out of the remaining 180 chicks). It was not possible to attribute these deaths to any specific cause, genotype, or sex. The effect of the high compared with the normal temperature on gains of body weight, protein, and fat, and on feed and protein efficiencies up to 6 wk of age are presented in Figure 1. Levels of signifi-
cance (Model 1) for the effects of temperature and its interaction with sex and with genotype for each of these measurements are given in Table 1. As most of the groups reared at the high temperature had not by 8 wk of age reached the body weight of their sibs reared at the normal temperature, it was decided to analyze the data up to 8 wk of age under the high temperature separately. Levels of signifi-
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fljSO
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.094
T x S x G3 WT - LN x S x T
.058
<.001 .002 .005
<.001 <.001
4 to 6 wk
Gain
_
-
.060
_1
_
.028
6 wk
Content 4 wk
_
.056 .072
<.001 <.001
4 wk
n tr.
Protein
.077
<.001 <.001 .002 .049 .002 .037
4 to 6 wk
Gain
_
.047
_
_
.082
_
.090
-
-
.076
<.001
.004
4 to 6 wk
.008
0 to 4 wk
Gain
-
6 wk
Content 4 wk
Fat
_
.020 .002
.021 <.001 .012
0 to 4 wk
.100
<.001 <.001 <.001 <.001 <.001 .096
4 to 6 wk
]Feed eff iciency
_
.052
<.001
-
0 to 4 wk
_
<.001 <.001 .005 .083 .002 .084
4 to 6 wk
Protein efficiency
P > .1. 2 Interaction between temperature and specific genetic contrasts. WT - LN = selection goal, weight selected versus selection for feed efficiency and low abdominal fat. IS - NL = origin, Israeli versus Dutch selection lines. HF - LF = abdominal fat, high or low. 3 Of the three-way interactions only the interaction between the WT - LN contrast, sex, and temperature approached significance.
X
.094
T x G WT - LN x T 2 IS - NL x T HF - LF x T
.034
<.001 <.001 <.001 <.001 .018 .071
<.001 .002
T T x S
.014 .028
6 wk
4 wk
Variable
Mean
Body weight
TABLE 1. Level of significance (probability values) for the effects of temperature (T, normal versus high), and its interactions with sex (S) and genotype (G) as such and as specific: contrasts
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ia
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g
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o
I
g
1
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tA
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ENOTY
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CAHANER AND LEENSTRA
TABLE 2. Levels of significance (probability values) of the effects of age (A) and interactions of age with sex (S) and genotype (G) on the traits examined as such, and as specific contrasts (high temperature only) Fat
Protein Variable
A x S x G 4 to 6 w k x S x G 6 to 8 wk x S x G A x S x WT - LN A x S x IS - NL A x S x HF - LF
<.001 <.001 -e.OOl <.001 .020 <.001 <.001 .025 <.001 .001 .008 .030 .003 .010 .001
<.001 .003 <.001 <.001 .002
Gain: Content day <.001 <.001 .037 .041
<.001 <.001 .002
.010 .007
.032
.107 <.0Ol
.008 .001
<.001 <.001
.058
.016
.014 .002
-
-
:
<.001 <.0Ol <.001 .046
<.001 _2 <.001 .004 .003
.022 .057
<.001 .005 .027 <.001 .034
Gain: Content day
-
.004 .056
Eff: iciency Feed
Protein
•c.001 <.001 <.001 .077 .025
<.001 <.001 .009 .042 .035 .023
.021
_
_
.002
-
-
-
-
-
-
-
-
-
-
-
_
.064
-
1 Age contrasts: 4 to 6 wk = contrast between 4- and 6-wk body weight, protein content, or fat content, and between 0 to 4 and 4 to 6 wk daily weight, protein and fat gain, and feed and protein efficiency; 6 to 8 wk = see above, but between 6 and 8 wk or 4 to 6 wk and 6 to 8 wk. 2 P > .1. 3 Genetic contrasts: WT - LN = selection goal, weight selected versus selection for feed efficiency and low abdominal fat; IS - NL = origin, Israeli versus Dutch selection lines; and HF - LF = abdominal fat, high or low.
cance (Model 2) for the effects of age under high temperature and its interactions with sex and genotype on each of the traits, and for contrasts between ages and between sources of genetic differences are given in Table 2. Group means by genotype and sex within each age and levels of significance of these main effects, of their interactions, and of contrasts between sources of genetic differences (Model 3), are presented in Tables 3 to 7. Body Weight and Body Weight Gain Body weight gain was decreased at the high temperature. The effect was already significant at 4 wk (Table 1), but was much more clear between 4 to 6 wk (Figure la). Weight gain during these 2 wk under the high temperature was lower especially in males. The effects of temperature and sex were significantly different for the weight-
selected (WT) genotypes WI and WN compared with the lean (LN) genotypes LF and FC (Table 1). Different sex effects were observed within WT or LN genotypes from 6 to 8 wk at the high temperature, resulting in a significant three-way interaction between age, genotype, and sex (Table 2). At 4 wk of age, mean body weight was lower in females by about 10% in all genotypes (Table 3). At 6 wk of age, females still weighed 4% less in the FC and LF genotypes, but both sexes had similar weights in the WN and WI genotypes. At 8 wk of age, the two sexes had a similar body weight in LN genotype, whereas mean body weight of WT males was lower by about 12%. The HF genotype had the highest mean body weight at 6 wk of age, and its advantage increased at 8 wk. The superiority of this genotype was due mainly to the HF males, the only males that were significantly
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A 4 to 6 wk 1 6 to 8 wk A x S 4 to 6 wk x S 6 to 8 wk x S A x G 4 to 6 wk x G 6 to 8 wk x G A x WT - LN 3 A x IS - NL A x HF - LF
Body weight
Weight gain: day
GENOTYPE BY TEMPERATURE INTERACTIONS IN BROILERS
heavier than their female counterparts at 8 wk of age (Table 3). Genetic differences in growth due to origin, i.e., Israel or The Netherlands, were found only from 0 to 4 wk, when the Israeli genotypes WI and LF exceeded the Dutch genotypes WN and FC (Table 3). This difference was larger in males than in females. At 6 and 8 wk, genotypes from both origins had the same mean body weight. Protein Content and Protein Gain
Fat Content and Fat Gain Average body fat content for each line was not affected by the high temperature.
There was, however, a highly significant interaction between temperature and sex on fat content at 6 wk (Table 1). At the high temperature compared with the normal temperature, fat content in males was higher by an average of 13%, whereas in females it was reduced by 6% (data not shown). This interaction resulted in a similar fat content for males and females (within genotypes) at 4, 6, and 8 wk (Table 5). At the high temperature, the 6 to 8 wk age comparison showed a significant interaction (Table 2) with the contrast between the weight-selected genotypes (WI and WN) and the genotypes selected for leanness (LF and FC). This interaction was due to the Israeli lean genotype, LF, which was not lean at all under the high temperature. At all three ages, fat content was much higher in LF than in FC chicks (Table 5). At 8 wk, fat content of the LF genotype increased to the level of HF. Differences between genotypes within age did not interact with sex. The effect of the high temperature on fat gain was, on average, quite similar in both sexes (Figure lc). There was no significant difference between sexes in fat gain between 0 and 6 wk, but males' average fat gain was decreased from 6 wk onward. As males' fat content decreased between 6 and 8 wk in HF, WN, and WI genotypes and body weight gain was considerably decreased in the latter two groups, WN and WI males actually lost fat between 6 and 8 wk (Table 5). Feed Efficiency Feed efficiency was not affected by the high temperature up to 4 wk, but afterward it was reduced compared with normal temperature. The effect was much more pronounced in males than in females (Figure Id), leading to a highly significant interaction between temperature and sex (Table 1). At the high temperature, an interaction was present between sex and the 4 to 6 wk age contrast (Table 2). From 4 to 6 wk, females used feed more efficiently than males in all genetic groups, and this remained so from 6 to 8 wk in the two WT genotypes (Table 6). The differences between genotypes in feed efficiency at the high temperature
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Body protein content was not affected by the high temperature (Table 1). Within the high-temperature groups, age interacted with sex and with genotype, but there was no three-way age by sex by genotype interaction regarding protein content (Table 2). The age by genotype interaction was significant only for the WT - LN contrast. The lean genotypes had a higher protein content at 4 and 6 wk, but at 8 wk the ranking was reversed. Differences between genotypes within age did not interact with sex (Table 4). Because protein content was not affected by the high temperature, the reduction in protein gain was similar to that of body weight gain: larger from 4 to 6 wk than from 0 to 4 wk and more in males than in females (Figures la and lb). The difference between sexes for protein gain under the high temperature was reversed between 0 to 4 and 4 to 6 wk, resulting in a significant interaction between sex and the 4 to 6 wk age contrast (Table 2). As at the normal temperature, males gain more protein than females from 0 to 4 wk. However, in all genotypes except HF, protein gain from 4 to 6 wk as well as from 6 to 8 wk was larger in females than in males (Table 4). The age contrast from 4 to 6 wk interacted also with the WT - LN contrast. From 0 to 4 wk, the WT genotypes gained about 13% more protein than the LN genotypes, but from 4 to 8 wk the latter genotypes gained 25% more protein. The HF chicks gained more protein than LF ones and about the same as the FC chicks (Table 4).
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TABLE 3. Body weight at 4, 6, and 8 wk of age and daily weight gain from 0 to 4, 4 to 6, and 6 to 8 wk by genotype and sex of chicks reared at high temperature Daily body weight gain Body weight Genoti fpe 1
Sex 2
HF HF LF LF FC FC WN WN WI WI SED HF LF FC WN WI SED
M F M F M F
4 wk
6 wk
953 864
1,472 1,408 1,387 1,311 1,355 1,325
8 wk
0 to 4 wk
4 to 6 wk
6 to 8 wk
32.5 29.2
37.1 38.9 32.9 34.7 36.0 39.8
38.0 33.8 37.9 35.1 28.7
34.1 33.8 27.8 31.1 29.5 33.9 14.7 24.4 7.4 29.7 4.8 34.0 29.5 31.7 19.6 18.6
2.6
3.4
(r*
M + F
13
42
43
926 825 851 767 965 884
M F M F M M M M M
+ + + + +
! Of 'variation
Genot1vpe 3 WT :- LN IS - NL HF -- LF Sex Genotype x sex W T - L N x se> IS - NL x sex HF - LF x sex
<.001 <.001 <.001 .023 <.001 .036
_4 .053 .044
-
.017
31.5 28.0 29.0 26.0 33.1 30.1 36.8 31.1 .8 30.9 29.8 27.5 31.6 34.0 .5 • Probability — 001 <.001 . 1 010 <.001 <.001 . 1 D03 .029 .1027 <.001 . i 009 .038 . i 004 .018
31.5 38.7 24.4 32.9 3.7
-
.012 .040 .010
<.001 <.001
.011
.002 .032 .021
l
ffi and LF = Israeli crosses, selected for a high or a low amount of abdominal fat, respectively; FC = Dutch cross, selected for feed conversion between 3 and 6 wk of age; WN and WI = crosses originating from The Netherlands and Israel, respectively, selected for high 6-wk body weight; SED : : standard error of differences between two means. Z 2v M = male; F = female. 3 Specific contrasts: WT - LN ; WN + WI - FC - LF; IS - NL = WI + LF - WN - FC; HF - LF = HF - LF. 4 P > .1.
changed with age, with a significant interaction between age and the WT - LN contrast (Table 2). Feed efficiency of both groups of genotypes was similar from 0 to 4 wk. It was lower by 21% in the WT genotypes from 4 to 6 wk, and this difference increased to 54% from 6 to 8 wk (Table 6). Feed efficiency from 6 to 8 wk of the HF males was as high as that of FC chicks, and higher than ti\at of LF chicks. Protein Efficiency
The effects of the high temperature on protein efficiency were similar to those on
feed efficiency, but smaller with regard to interactions with genotypes (Table 1). Protein efficiency was not affected by the high temperature up to 4 wk, but afterward it was lower than under normal temperature. The effect of the high temperature was larger for males than females (Figure le), and the differences between sexes for protein efficiency were larger than those for feed efficiency (Figure Id). At the high temperature there was an interaction between sex and age (Table 2). Males and females had a similar efficiency from 0 to 4 wk, but from 4 to 6 wk females
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F F F F F
1,081 919 19 909 876 810 925 1,000
1,406 1,425 1,413 1,380 59 1,440 1,349 1,340 1,416 1,397
1,915 1,848 1,749 1,715 1,739 1,766 1,597 1,742 1,509 1,767 61 1,881 1,732 1,753 1,670 1,638
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GENOTYPE BY TEMPERATURE INTERACTIONS IN BROILERS
TABLE 4. Protein content at 4, 6, and 8 wk of age and daily protein gain from 0 to 4, 4 to 6, and 6 to 8 wk of age by genotype and sex of chicks reared at high temperature Protein gain Protein content Genoti fpe 1
Sex 2
4 wk
6 wk
8 wk
0 to 4 wk
4 to 6 wk
6 to 8 wk
4.59 5.56
5.01 4.07
4.70 4.87 5.24 5.64 4.22 5.39 2.83 4.29 .64
3.57 3.70 4.28 4.74
(r/Vr\ K&i*b>
M F M F M F M F M F M M M M M
+ + + + +
F F F F F
159 157 161 161 166 166 162 161
146 152 155 153 159 156 153 153
147 144 149 145 156 152 157 152
160 160 2.4
150 150 2.7
158 161 166 161 160
149 154 157 153 150 1.9
156 150 4.1 145 147 154 155 153
5.16 4.60 5.07 4.50 4.82 4.33 5.34 4.85 5.93 5.00 .12 4.88 4.79 4.57 5.10 5.46
2.9
.09
M + F
1.7
Source! of variation Genotype 3 WT - LN IS - NL HF - LF
.003 .042 .018
.005 .010 .058 .022
Sex
-
-
Genotype x sex WT - LN x sex IS - NL x sex HF - LF x: sex
-
-
5.08 4.79 5.44 4.80 3.56 .45
.064
<.001 <.001 <.001
.008 .009 .009
.024
<.001
.009
.014 _4
-
.048
2.80 3.64 1.74 4.41 .89 4.54 3.63 4.51 3.22 3.07 .63 .098 .062
-
1 HF and LF = Israeli crosses, selected for a high or a low amount of abdominal fat, respectively; FC = Dutch cross, selected for feed conversion between 3 and 6 wk of age; WN and WI = crosses originating from The Netherlands and Israel, respectively, selected for high 6-wk body weight; SED = standard error of differences between two means. 2x ''M = male; F = female. 3 Specific contrasts: WT - LN = WN + WI • FC - LF; IS - NL = WI + LF - WN - FC; HF - LF = HF - LF. 4 P > .1.
were more efficient than males in all genotypes, and from 6 to 8 wk, sex differences ranged from males' superiority in HF to females' superiority in WI (Table 7). Genotypes differed significantly in protein efficiency during each age period, except when efficiency from 6 to 8 wk was analyzed separately (Table 7). Broilers of the LN genotypes were superior to those of the WT genotypes, and Dutch stocks were superior to the Israeli stocks. Protein efficiency of the HF males from 6 to 8 wk was as
high as that of FC chicks and higher than those of the other genetic groups. DISCUSSION Interactions Between Age, Sex, and Selection Goal
Total weight gain, as well as gain of protein and fat, were reduced by the high temperature, although the magnitude of the reduction varied with genotype, sex, and age. Feed and protein efficiencies were also
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HF HF LF LF FC FC WN WN WI WI SED HF LF FC WN WI SED
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CAHANER AND LEENSTRA
TABLE 5. Fat content at 4, 6, and 8 wk of age and daily fat gain from 0 to 4, 4 to 6, and 6 to 8 wk of age by genotype and sex of chicks reared at high temperature Fat gain Fat content Sex2
4 wk
6 wk
HF HF LF LF
M F
182 196 175 160 133 135 163 173 160 188 16 189 168 134 168 174 11
226 205 180 178 150 174 192 191 192 215 16 216 179 162 191 204
8 wk
0 to 4 wk
(g/kg)
FC FC WN WN WI WI SED HF LF FC WN WI
M F M F M F M F M M M M M
SED M + F Source of variation Genotype 3 WT - LN IS - NL HF - LF Sex Genotype x sex WT - LN x sex IS - NL x sex HF - LF x sex
.001 .008 .010 .069
191 199 183 202 158 159 159 170 158 183 17 195 193 159 165 170 12
11 .001 .002 .059 .004
4 to 6 wk
-4
5.91 5.74 5.51 4.48 3.86 3.53 5.40 5.24 6.38 5.86 .51 5.83 4.99 3.70 5.32 6.12 .36 Probability .019 <.001 <.001 .026 <.001 .033 .066
(g/day) 11.41 8.50 6.28 7.21 6.44 9.06 7.96 8.44 6.44 8.86 1.53 9.96 6.74 7.75 8.20 7.65 1.08 .089
6 to 8 wk 2.56 6.16 5.51 8.66 5.56 3.85 -1.21 1.96 -2.73 2.18 2.72 4.36 7.08 4.71 .38 -.27 1.93 .007 <.001
.008 .048
.093
1
HF and LF = Israeli crosses, selected for a high or a low amount of abdominal fat, respectively; FC = Dutch cross, selected for feed conversion between 3 and 6 wk of age; WN and WI = crosses originating from The Netherlands and Israel, respectively, selected for high 6-wk body weight; SED = standard error of differences between two means. 2
M = male; F = female. 'Specific contrasts: WT - LN = WN + WI - FC - LF; IS - NL = WI + LF - WN - FC; HF - LF = HF - LF. 4 P > .1.
diminished by the high temperature, but to a smaller degree. Body composition (protein and fat percentage), however, was not affected by the high temperature. The only notable change was an increase in males' fat content. Increased fat content due to a high environmental temperature was also found in several previous studies (Kubena et al, 1972; Howlider and Rose, 1989; Chwalibog and Eggum, 1989). The reduction in body weight or protein or fat gain due to the high temperature was much larger from 4 to 6 wk than from 0 to 4
wk, and more pronounced in males than in females (Figure 1). Females gained more weight than males between 6 and 8 wk of age at the higher temperature. Body weights at 8 wk at the high temperature were either similar (for females) or lower (for males) than 6-wk body weights of similar chicks at a normal temperature (Leenstra and Cahaner, 1991). There was a three-way interaction between genotype, sex, and age, because the magnitude of reduction in body weight due to the high temperature was also associated with selec-
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Genotype 1
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GENOTYPE BY TEMPERATURE INTERACTIONS IN BROILERS
TABLE 6. Feed efficiency from 0 to 4, 0 to 6, 0 to 8, 4 to 6, and 6 to 8 wk of age by line and sex of chicks reared at high temperature Feed efficiency Genot'
ml
0 to 4 wk
0 to 6 wk .537 .560 .538 .555 .590 .607
F F F F F
.667 .668 .674 .672 .711 .695 .690 .685 .670 .665 .009 .668 .673 .703 .688 .668
M + F
.006
.008
<.001 .027 <.001
-
Sex.2
0 to 8 wk
4 to 6 wk
6 to 8 wk
O-H
M F M F.
FC FC WN WN WI WI SED HF LF FC WN WI SED
M F M F M F M M M M M
+ + + + +
Source: of variation Genotype 3 WT - LN IS - NL HF - LF Sex Genotype x sex WT - LN x sex IS - NL x sex HF - LF x: sex
\S-S) .506 .494
.368 .445 .287 .395 .027
.428 .361 .390 .365 .418 .425 .245 .293 .147 .354 .072
.425 .410 .492 .406 .341
.395 .377 .421 .269 .250 .051
<.001 <.001 <.001
.019 .010 Probability — •c.001 <.001 <.001 •e.001 _4 <.001
<.001
-
<.001
-
-
.073
.498 .492 .540 .547 .471 .482 .438 .481 .014 .500 .495 .544 .477 .459
.540 .566 .507 .538 .012 .549 .547 .599 .553 .522
-
.399 .450 .387 .433 .464 .521
.077
.010 .001
-
1
HF and LF = Israeli crosses, selected for a high or a low amount of abdominal fat, respectively; FC = Dutch cross, selected for feed conversion between 3 and 6 wk of age; WN and WI = crosses originating from The Netherlands and Israel, respectively, selected for high 6-wk body weight; SED = standard error of differences between two means. 2 M = male; F = female. Specific contrasts: WT - LN = WN + WI - FC - LF; IS - NL = WI + LF - WN - FC; HF - LF = HF - LF. 4 P > .1.
tion goal (WT - LN contrast). The WT genotypes (WN and WI) appeared to be more sensitive to the high temperature than their counterparts selected for leanness (FC and LF). This genetic difference increased with age and was much larger in males than in females. In the weight-selected lines, females were heavier than males at 8 wk. The Role of Fat Content
The smaller effect of the high temperature on the genotypes selected for leanness
(FC and LF), than on the fast-growing genotypes (WN and WI) cannot be attributed to their low fat content. In fact, the opposite was true, i.e., a higher capacity for fat deposition (females in general and HF chicks in particular) appeared advantageous at the high temperature. The HF chicks had the highest mean body weight under the high temperature and gained about the same amount of protein as the lean FC chicks. The HF males were the only ones significantly heavier than their female counterparts. Also in all other genotypes,
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HF HF LF LF
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CAHANER AND LEENSTRA
TABLE 7. Protein efficiency from 0 to 4, 0 to 6, 0 to 8, 4 to 6, and 6 to 8 wk of age by genotype and sex of chicks reared at high temperature Protein efficiency Genotype 1
Sex.2
HF HF LF LF FC FC WI WI WN WN SED HF LF FC WN WI SED
M F M F M F M F M F
0 to 4 wk
0 to 6 wk
0 to 8 wk
.494 .488 .504 .503 .550 .538 .501 .496 .519 .513 .012 .491 .504 .544 .516 .499 .008
.367 .395 .387 .396 .436 .441
.345 .331 .346 .332 .391 .386 .319 .336 .345 .341 .012
<.001 .014 <.001
<.001 <.001 <.001
-
-
4 to 6 wk
6 to 8 wk
ff-H ^b-W
Genotype x sex WT •- LN x sex IS - NL x sex HF -- LF x: sex
+ F + F
+ F + F + F + F
.021
-
.338 .339 .389 .343 .327 .009 Probability <.001 <.001 <.001 <.001 •c.001 <.001
-
<.001
-
.289 .200 .237 .200 .283 .273 .158 .245 .212 .204 .059 .244 .218 .278 .208 .202 .041 _4
-
HF and LF = Israeli crosses, selected for a high or a low amount of abdominal fat, respectively; FC = Dutch cross, selected for feed conversion between 3 and 6 wk of age; WN and WI = crosses originating from The Netherlands and Israel, respectively, selected for high 6-wk body weight; SED = standard error of differences between two means. M = male; F = female. Specific contrasts: WT - LN = WN + WI - FC - LF; IS - NL = WI + LF - WN - FC; HF - LF = HF - LF. 4 ? > .1.
especially LF, fat content at 6 wk was higher in males at the high temperature than at the normal temperature. Chicks having a high capacity to store energy intake in fat depots may have a lower heat increment than chicks having an inherent higher tendency to deposit protein. Thus, relatively fat chicks have less heat to disperse, and consequently their feed consumption and weight gain at the high temperature are less depressed. The FC chicks, however, indicate that this assumption is not generally valid. Their
response was quite different from that of LF chicks, despite their similar weight gain. Under the high temperature, FC chicks maintained their leanness and superiority in feed and protein efficiency, whereas LF chicks were no longer lean. The different selection criteria used to develop these two genotypes, high feed efficiency for FC (Leenstra, 1988) and low abdominal fat percentage for LF (Cahaner, 1988), might be responsible for their different fat gains at the high temperature. It was already evident at normal and low temperatures that
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Source! of variation Genotype 3 WT •- LN IS - NL HF -- LF Sex
M M M M M M
.356 .377 .384 .402 .014 .381 .392 .438 .393 .366 .010
.232 .301 .258 .284 .316 .345 .161 .244 .230 .289 .027 .266 .271 .331 .260 .202 .019
GENOTYPE BY TEMPERATURE INTERACTIONS IN BROILERS
despite the similar carcass composition, these two genetic groups differ in many aspects (Leenstra and Cahaner, 1991). Despite their high feed efficiency, FC chicks have a low energetic efficiency (Leenstra and Pit, 1988). This is only possible if FC chicks have a high capacity for heat loss which, as well as high fat deposition, might help in decreasing the depression in weight gain caused by high temperatures. The Role of Growth Potential
6-wk body weight. From 6 wk onward WN and WI males gained hardly any weight, but all other groups continued to grow. Therefore, it is probably the growth potential of these fast-growing males, rather than their actual growth, that made them more sensitive to the high temperature. The current results indicate that the upper limit of the thermoneutral zone of chickens (or the response of chickens if this upper limit is exceeded) is dependent on sex and genotype and is not related in a straightforward way to body weight or body composition. Practical Considerations
Although a constant temperature of 32 C will not occur in commercial broiler operations, the present results strongly suggest that raising male broilers from the modern, fastest growing stocks at high ambient temperatures might not be advisable. Reducing growth rate of such broilers (by feed restriction, for example) may not fully counteract the cumulative physiological differences resulting from selection for rapid growth. In hot regions, where facilities differ in their cooling capability, males should be placed in the cooler houses, whereas females provide a better chance for reasonable performance under higher temperatures. Selection in a subtropical climate, such as in Israel, did not improve resistance to a constant high temperature of 32 C. Indeed, the effect of origins (Israel or The Netherlands) was significant only for weight gain from 0 to 4 wk, when the difference between the normal and the high temperature regimen was relatively small. Although the chicks selected for feed efficiency (FC) had a lower growth rate at the normal temperature (Leenstra and Cahaner, 1991), at the high temperature they grew better than the weight-selected chicks and also maintained their superior efficiency. This is an additional advantage of applying feed efficiency rather than weight gain as a selection criterion for broilers, and is one of special interest for hot-climate regions.
REFERENCES Adams, R. L., and J. C. Rogler, 1968. The effect of environmental temperature on the protein re-
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The magnitude of reduction in growth due to the high temperature was related mainly to the chicks' growth potential, i.e., their growth rate at a normal temperature. In the present study, the fast-growing genotypes WN and WI were affected more by the high temperature than the other genotypes and males were affected more than females. A larger relative effect of high temperature on males than on females was reported by Osman et d. (1989). In other comparisons between high and normal temperatures found in the literature, chicks from both sexes were affected similarly. The different results in these studies may be explained by the difference in the growth potential of the genotypes used; the higher the potential the larger the possible effect of the high temperature, especially on males. Mean 6-wk body weight of males and females under normal conditions (i.e., temperatures between 18 and 24 C) as a measure of growth potential, was in all reviewed studies lower than that of modern broilers: around 1,250 g for the broilers used by Cerniglia et d. (1983), 1,650 g for those used by Howlider and Rose (1989), and 1,750 g for those used by Osman et al. (1989). The growth potential of the FC and LF genotypes used here was 1,843 g and that of the WN and WI genotypes was 2,035 g (Leenstra and Cahaner, 1991). Six-week body weights of WN + WI and LF + FC males at the normal temperature were 2,214 and 1,963 g, respectively. This difference of 250 g is probably responsible for the normal reduction in weight gain due to the high temperature observed in the LF and FC males, versus the much larger effect on the WN and WI males. The effect is not due to actual body weight, because at the high temperature WN and WI males and females and FC and LF males had a similar
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CAHANER AND LEENSTRA Leanness in Domestic Birds: Genetic, Metabolic and Hormonal Aspects. B. Leclercq and C. C. Whitehead, ed. Butterworths, London, England. Leenstra, F. R., and A. Cahaner, 1991. Genotype by environment interactions using fast-growing, lean or fat broiler chickens, originating from The Netherlands and Israel, raised at normal or low temperature. Poultry Sci. 70:2028-2039. Leenstra, F. R., and R. Pit, 1988. Consequences of selection for feed conversion in broiler chickens. Pages 160-161 in: Advances in Animal Breeding. S. Korver, H.A.M. van der Steen, J.A.M. van Arendonk, H. Bakker, E. W. Brascamp, and J. Dommerholt, ed. Pudoc, Wageningen, The Netherlands. Osman, A.M.A., E. S. Tawfik, F. W. Klein, and W. Hebeler, 1989. Effect of environmental temperature on growth, carcass traits and meat quality of broilers of both sexes and different ages. Arch. GeflUgelkd. 53:158-175. Steverink, A.T.G., H. Steunenberg, R. Frankenhuizen, and M. Tusveld, 1988. Application of NearInfrared Reflection Spectroscopy (NIRS) To Determine Fat Content of Broilers (in Dutch). Spelderholt Report 487, Beekbergen, The Netherlands.
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quirements and response to energy in slow and fast growing chicks. Poultry Sci. 47:579-586. Cahaner, A , 1988. Experimental divergent selection on abdominal fat in broilers—parental female and male type lines and their crosses. Pages 71-86 in: Leanness in Domestic Birds: Genetic, Metabolic and Hormonal Aspects. B. Leclercq and C. C. Whitehead, ed. Butterworths, London, England. Cerniglia, G. J., J. A. Hebert, and A B. Watts, 1983. The effect of constant ambient temperature and ration on the performance of sexed broilers. Poultry Sci. 62:746-754. Chwalibog, A., and B. O. Eggum, 1989. Effect of temperature on performance, heat production, evaporative heat loss and body composition in chickens. Arch. Geflugelkd. 53:179-184. Genstat 5, 1987. Reference Manual. Clarendon Press, Oxford, England. Howlider, M.A.R., and S. P. Rose, 1989. Rearing temperature and the meat yield of broilers. Br. Poult. Sci. 30:61-67. Kubena, L. F., B. D. Lott, J. W. Deaton, F. N. Reece, and J. D. May, 1972. Body composition of chicks as influenced by environmental temperature and selected dietary factors. Poultry Sci. 51:517-522. Leenstra, F. R., 1988. Selection for leanness: Results of the Spelderholt experiment. Pages 59-69 in:
1992 Poultry Science 71:1237-1250
INTRODUCTION
The reduction in weight gain of broilers due to high ambient temperatures is of great concern in regions with hot climates. Heat-stress conditions also occasionally develop in temperate regions during the hot season, especially if broilers are kept at high densities and ventilation is insufficient. Exact heat-stress or hot-climate conditions are difficult to simulate in experi-
Received for publication December 23, 1991. Accepted for publication April 17, 1992. 1 The Hebrew University of Jerusalem, Faculty of Agriculture, P.O. Box 12, Rehovot, Israel.
mental situations. They result from different (and changing) combinations of temperature and its diurnal cycles, relative humidity, and air velocity. Therefore, a constant temperature within the range of 29 to 35 C has been used in most studies to assess the response of broilers to simulated practical high-temperature conditions. If broilers kept under high temperatures grow older and larger, their growth rate is progressively reduced when compared with birds kept at normal temperatures. Adams and Rogler (1968) found that growth rate was more depressed in the heaviest 40% birds from a flock of male broilers than in the lightest 40% birds.
1237
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ABSTRACT Male and female broiler chicks from five different broiler crosses (WI, LF, and HF = Israeli chicks selected for high body weight gain, and low and high abdominal fat, respectively; FC and WN = Dutch chicks selected for favorable feed conversion and high body weight gain, respectively) were raised at a high ambient temperature (32 to 33 C). Weight gain, protein and fat content in the carcass and feed, and protein efficiency were determined at 4,6, and 8 wk of age. The effect of the high temperature was evaluated by comparing these data with those of similar chicks raised at a normal temperature (20 to 33 C) up to 6 wk of age. The reductions in body weight, protein gain, and feed and protein efficiency due to the high temperature increased with age and were much larger in males than in females. This trend was more pronounced in WI and WN chicks than in LF, HF, and FC chicks. Females of WI and WN crosses were as heavy as males at 6 wk and heavier at 8 wk. In LF, HF, and FC crosses, both sexes had similar weights at 8 wk. Growth reduction due to the high temperature was largest in the groups with the highest growth rate at the normal temperature (WI and WN males). Chicks with a lower growth rate and a higher capacity for energy storage in fat depots (all females, HF chicks), or a higher capacity for heat loss (FC chicks), were less affected by the high temperature. The results suggest that females should be preferred over males for broiler production in hot facilities or locations. Broiler genotypes selected for feed efficiency at the expense of fast growth may allow for a more profitable broiler production in high-temperature regions. (Key words: high temperature, genotype, growth rate, feed efficiency, body composition)
1238
CAHANER AND LEENSTRA
MATERIALS AND METHODS
The data presented in this paper were obtained from an experiment in which performance of chickens kept at high, normal, and suboptimal temperatures were compared. Chickens, diets, housing, and measurements have been described by Leenstra and Cahaner (1991). They reported on the comparisons between normal and suboptimal temperature. The present study concentrated on the effects of the high temperature. The experimental details were as follows.
cross between the fifth generation of broiler sire and broiler dam lines both selected for a low (LF) or high (HF) amount of abdominal fat (Cahaner, 1988), or high body weight gain (WI). For the Dutch chicks, commercial broiler breeder hens were mated to males of the ninth generation of broiler sire lines selected for favorable feed conversion (FC) or fast body weight gain (WN) (Leenstra, 1988). All eggs were incubated and hatched simultaneously at the DLO Centre for Poultry Research and Information Services, Beekbergen, The Netherlands. Housing and Management
The chicks were housed in floor pens of .75 x 1.0 m, each equipped with a separate feeder. Eighteen chicks were housed in each pen up to 4 wk of age, and their number was reduced, by removing chicks randomly, to 15 per pen in the 5th wk, 12 in the 6th wk, and 6 in the 7th and 8th wk. The pens were arranged in rooms. Ten pens per room, one pen for males and one for females from each of the five genotypes, were used. Lighting was continuous during the 1st day after hatch and intermittent (1 h light; 3 h darkness, alternating) thereafter. The chicks received for ad libitum consumption a pelleted broiler diet with 3,203 kcal metabolizable energy and 215 g of crude protein/ kg of diet. Climate
In three rooms the temperature was kept at 33 C from hatch until 2 wk of age and at 32 C thereafter (high temperature). In three other rooms, normal temperatures, i.e., gradually decreasing from 33 C at hatch to 20 C at 6 wk of age (Leenstra and Cahaner, 1991), were applied. Relative humidity was kept at 60% for both temperature schemes. Measurements
Chickens
Five different genetic groups (genotypes) were used in the current experiment. Three were of Israeli origin and two of Dutch origin. All chicks resulted from a cross between Cornish (broiler sire) and White Plymouth Rock (broiler dam) chickens. The Israeli chicks descended from a
Chicks were weighed by pen at hatch and body weight and feed consumption were determined weekly from 2 to 6 wk of age in the normal temperature groups and from 2 to 8 wk (55 days) of age in the hightemperature groups in an attempt to finish the high-temperature groups at a body weight that the normal temperature groups
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Continuous selection for increased growth rate thus might increase sensitivity of broiler stocks to high temperatures, unless specific criteria for efficient performance under high temperatures are identified and applied in selection programs. Although in most studies (i.e., Kubena et al, 1972; Cerniglia et al, 1983; Howlider and Rose, 1989) the magnitude of the effect of high temperature was not dependent on sex, Osman et al. (1989) found that the reduction in weight gain due to high temperatures appeared at a younger age and was larger in males than in females. Whether the more pronounced effect of high temperatures on males is caused by their higher body weight or by other sexspecific factors (i.e., body composition or feed efficiency) is not clear. If the latter is true, the use of female broilers instead of males or mixed sexes might be advantageous when high environmental temperatures cannot be prevented. The present experiment examined the effects of inherent growth rate and sex on broiler performance at a high temperature using males and females of broiler crosses selected for high body weight gain, favorable feed efficiency, and low or high body fat content.
GENOTYPE BY TEMPERATURE INTERACTIONS IN BROILERS
were tested against e p , the between-pens within-room error term. The effects of age (A; 4, 6, and 8 wk), genotype, sex, and their interactions at the high temperature were examined for each trait by ANOVA with the model: Y = n + er + G + S + GS + e p + A + GA + SA + GSA + e w . [2] Each room was considered as a block (er). The effects of age and the interactions with age were tested against the error term within pen due to repeated measurements (ew). Effects of genotype and sex on performance under the high temperature at each age separately, were examined by ANOVA with the model: Y = ^i + e r + G + S + GS + ep.
[3]
To examine the effect of age, specific contrasts between different ages or age periods were analyzed, i.e., 4 versus 6 or 0 to 4 versus 4 to 6 wk of age (4 to 6 wk), and 6 versus 8 or 4 to 6 versus 6 to 8 wk of age (6 to Statistical Analysis 8 wk). Three contrasts between sources of The entire experiment had a split-plot genetic differences were evaluated. The design with temperature regimens assigned effects of selection goal (WT - LN; body to rooms as the main plots, and the weight or leanness) and of genotypes' genotype by sex combinations assigned to origin (IS - NL; Israel or The Netherlands) pens as secondary plots. The temperature and their interactions with other main regimens were distributed randomly over factors were tested by estimating the conthe rooms. In each room, all 10 genotype trasts WI + WN - LF - FC and WI + LF - WN and sex combinations were randomly dis- - FC, respectively. As the HF chicks did not tributed among the pens. have a Dutch counterpart, they were not The effects on pen mean (Y) of tempera- incorporated in these contrasts. The conture (T, high versus normal), genotype (G), trast HF - LF was, however, evaluated to sex (S), and their interactions were exam- examine the effect of carcass fat content in ined for each of the measurements between chicks from the same origin and with 0 and 6 wk of age, by ANOVA with the similar growth rate. model: All statistical analyses were done with the Genstat program (Genstat 5, 1987). Y = u + T + e r + G + S + TG Unless otherwise stated, main effects, con+ TS + GS + GTS + e p . [1] trasts, and interactions were considered significant if P < .05. The effect of T was tested against e r , the between-rooms error term. All other effects RESULTS InfraAlyzer-400, Bran + Luebbe, Maarssen, The Netherlands.
Up to 6 wk of age, mortality at the high temperature (20 chicks, or 4%) was similar to that at the normal temperature (21
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had at 6 wk. The chicks were weighed fullfed, directly after a light period. At 4 and 6 wk (both temperatures) and at 8 wk of age (high temperature), three randomly selected chicks from each pen were used to determine carcass composition. These chicks were fasted overnight, killed by CO2 suffocation, weighed, and defeathered. The defeathered carcasses from each pen were weighed again, chopped, and minced. In the minced product, protein and fat content were determined by near infrared reflection spectroscopy (NIRS)2 (Steverink et ah, 1988). From the body weights and the NIRS readings, fat and protein contents were calculated. In this calculation, weight and composition of the feathers were ignored. Daily weight gain, protein gain, and fat gain were calculated from hatch to 4 wk, from 4 to 6 wk, and from 6 to 8 wk of age. Feed efficiency (weight gain to feed consumption) and protein efficiency (protein deposition to protein consumption) were calculated for each pen from hatch up to 4, 6, and 8 wk, from 4 to 6 wk, and from 6 to 8 wk of age.
1239
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CAHANER AND LEENSTRA
Males
HF
LF
FC WN Wl
HF
LF
Females
FC WN Wl
b. Protein gain
c. Fat gain
LF
FC WN Wl
HF
LF
FC WN Wl
LF
FC WN Wl
LF
FC WN Wl
O to 4 wk
HF
LF
FC WN Wl
4 to 6 wk
FC WN Wl
e. Protein efficiency
d. Feed efficiency
HF
HF LF
HF LF
FC WN Wl
O to 4 wk
HF
LF
FC WN Wl
4 to 6 wk
FIGURE 1. Body weight (a), protein gain (b), fat gain (c), feed efficiency (d), and protein efficiency (e) from 0 to 4 wk and from 4 to 6 wk of age of male and female chicks from five genotypes raised at high temperature expressed as percentage of the performance of their sibs reared at normal temperature (HF and LF = Israeli crosses, selected for a high or a low amount of abdominal fat, respectively; FC = Dutch cross, selected for favorable feed conversion between 3 and 6 wk of age; WN and Wl = crosses originating from The Netherlands and Israel, respectively, selected for high 6-wk body weight).
chicks). Mortality at the high temperature between Weeks 6 and 8 was 10% (18 out of the remaining 180 chicks). It was not possible to attribute these deaths to any specific cause, genotype, or sex. The effect of the high compared with the normal temperature on gains of body weight, protein, and fat, and on feed and protein efficiencies up to 6 wk of age are presented in Figure 1. Levels of signifi-
cance (Model 1) for the effects of temperature and its interaction with sex and with genotype for each of these measurements are given in Table 1. As most of the groups reared at the high temperature had not by 8 wk of age reached the body weight of their sibs reared at the normal temperature, it was decided to analyze the data up to 8 wk of age under the high temperature separately. Levels of signifi-
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fljSO
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.094
T x S x G3 WT - LN x S x T
.058
<.001 .002 .005
<.001 <.001
4 to 6 wk
Gain
_
-
.060
_1
_
.028
6 wk
Content 4 wk
_
.056 .072
<.001 <.001
4 wk
n tr.
Protein
.077
<.001 <.001 .002 .049 .002 .037
4 to 6 wk
Gain
_
.047
_
_
.082
_
.090
-
-
.076
<.001
.004
4 to 6 wk
.008
0 to 4 wk
Gain
-
6 wk
Content 4 wk
Fat
_
.020 .002
.021 <.001 .012
0 to 4 wk
.100
<.001 <.001 <.001 <.001 <.001 .096
4 to 6 wk
]Feed eff iciency
_
.052
<.001
-
0 to 4 wk
_
<.001 <.001 .005 .083 .002 .084
4 to 6 wk
Protein efficiency
P > .1. 2 Interaction between temperature and specific genetic contrasts. WT - LN = selection goal, weight selected versus selection for feed efficiency and low abdominal fat. IS - NL = origin, Israeli versus Dutch selection lines. HF - LF = abdominal fat, high or low. 3 Of the three-way interactions only the interaction between the WT - LN contrast, sex, and temperature approached significance.
X
.094
T x G WT - LN x T 2 IS - NL x T HF - LF x T
.034
<.001 <.001 <.001 <.001 .018 .071
<.001 .002
T T x S
.014 .028
6 wk
4 wk
Variable
Mean
Body weight
TABLE 1. Level of significance (probability values) for the effects of temperature (T, normal versus high), and its interactions with sex (S) and genotype (G) as such and as specific: contrasts
tfl
ia
?3
g
to
o
I
g
1
M
tA
£ 3
ENOTY
1242
CAHANER AND LEENSTRA
TABLE 2. Levels of significance (probability values) of the effects of age (A) and interactions of age with sex (S) and genotype (G) on the traits examined as such, and as specific contrasts (high temperature only) Fat
Protein Variable
A x S x G 4 to 6 w k x S x G 6 to 8 wk x S x G A x S x WT - LN A x S x IS - NL A x S x HF - LF
<.001 <.001 -e.OOl <.001 .020 <.001 <.001 .025 <.001 .001 .008 .030 .003 .010 .001
<.001 .003 <.001 <.001 .002
Gain: Content day <.001 <.001 .037 .041
<.001 <.001 .002
.010 .007
.032
.107 <.0Ol
.008 .001
<.001 <.001
.058
.016
.014 .002
-
-
:
<.001 <.0Ol <.001 .046
<.001 _2 <.001 .004 .003
.022 .057
<.001 .005 .027 <.001 .034
Gain: Content day
-
.004 .056
Eff: iciency Feed
Protein
•c.001 <.001 <.001 .077 .025
<.001 <.001 .009 .042 .035 .023
.021
_
_
.002
-
-
-
-
-
-
-
-
-
-
-
_
.064
-
1 Age contrasts: 4 to 6 wk = contrast between 4- and 6-wk body weight, protein content, or fat content, and between 0 to 4 and 4 to 6 wk daily weight, protein and fat gain, and feed and protein efficiency; 6 to 8 wk = see above, but between 6 and 8 wk or 4 to 6 wk and 6 to 8 wk. 2 P > .1. 3 Genetic contrasts: WT - LN = selection goal, weight selected versus selection for feed efficiency and low abdominal fat; IS - NL = origin, Israeli versus Dutch selection lines; and HF - LF = abdominal fat, high or low.
cance (Model 2) for the effects of age under high temperature and its interactions with sex and genotype on each of the traits, and for contrasts between ages and between sources of genetic differences are given in Table 2. Group means by genotype and sex within each age and levels of significance of these main effects, of their interactions, and of contrasts between sources of genetic differences (Model 3), are presented in Tables 3 to 7. Body Weight and Body Weight Gain Body weight gain was decreased at the high temperature. The effect was already significant at 4 wk (Table 1), but was much more clear between 4 to 6 wk (Figure la). Weight gain during these 2 wk under the high temperature was lower especially in males. The effects of temperature and sex were significantly different for the weight-
selected (WT) genotypes WI and WN compared with the lean (LN) genotypes LF and FC (Table 1). Different sex effects were observed within WT or LN genotypes from 6 to 8 wk at the high temperature, resulting in a significant three-way interaction between age, genotype, and sex (Table 2). At 4 wk of age, mean body weight was lower in females by about 10% in all genotypes (Table 3). At 6 wk of age, females still weighed 4% less in the FC and LF genotypes, but both sexes had similar weights in the WN and WI genotypes. At 8 wk of age, the two sexes had a similar body weight in LN genotype, whereas mean body weight of WT males was lower by about 12%. The HF genotype had the highest mean body weight at 6 wk of age, and its advantage increased at 8 wk. The superiority of this genotype was due mainly to the HF males, the only males that were significantly
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A 4 to 6 wk 1 6 to 8 wk A x S 4 to 6 wk x S 6 to 8 wk x S A x G 4 to 6 wk x G 6 to 8 wk x G A x WT - LN 3 A x IS - NL A x HF - LF
Body weight
Weight gain: day
GENOTYPE BY TEMPERATURE INTERACTIONS IN BROILERS
heavier than their female counterparts at 8 wk of age (Table 3). Genetic differences in growth due to origin, i.e., Israel or The Netherlands, were found only from 0 to 4 wk, when the Israeli genotypes WI and LF exceeded the Dutch genotypes WN and FC (Table 3). This difference was larger in males than in females. At 6 and 8 wk, genotypes from both origins had the same mean body weight. Protein Content and Protein Gain
Fat Content and Fat Gain Average body fat content for each line was not affected by the high temperature.
There was, however, a highly significant interaction between temperature and sex on fat content at 6 wk (Table 1). At the high temperature compared with the normal temperature, fat content in males was higher by an average of 13%, whereas in females it was reduced by 6% (data not shown). This interaction resulted in a similar fat content for males and females (within genotypes) at 4, 6, and 8 wk (Table 5). At the high temperature, the 6 to 8 wk age comparison showed a significant interaction (Table 2) with the contrast between the weight-selected genotypes (WI and WN) and the genotypes selected for leanness (LF and FC). This interaction was due to the Israeli lean genotype, LF, which was not lean at all under the high temperature. At all three ages, fat content was much higher in LF than in FC chicks (Table 5). At 8 wk, fat content of the LF genotype increased to the level of HF. Differences between genotypes within age did not interact with sex. The effect of the high temperature on fat gain was, on average, quite similar in both sexes (Figure lc). There was no significant difference between sexes in fat gain between 0 and 6 wk, but males' average fat gain was decreased from 6 wk onward. As males' fat content decreased between 6 and 8 wk in HF, WN, and WI genotypes and body weight gain was considerably decreased in the latter two groups, WN and WI males actually lost fat between 6 and 8 wk (Table 5). Feed Efficiency Feed efficiency was not affected by the high temperature up to 4 wk, but afterward it was reduced compared with normal temperature. The effect was much more pronounced in males than in females (Figure Id), leading to a highly significant interaction between temperature and sex (Table 1). At the high temperature, an interaction was present between sex and the 4 to 6 wk age contrast (Table 2). From 4 to 6 wk, females used feed more efficiently than males in all genetic groups, and this remained so from 6 to 8 wk in the two WT genotypes (Table 6). The differences between genotypes in feed efficiency at the high temperature
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Body protein content was not affected by the high temperature (Table 1). Within the high-temperature groups, age interacted with sex and with genotype, but there was no three-way age by sex by genotype interaction regarding protein content (Table 2). The age by genotype interaction was significant only for the WT - LN contrast. The lean genotypes had a higher protein content at 4 and 6 wk, but at 8 wk the ranking was reversed. Differences between genotypes within age did not interact with sex (Table 4). Because protein content was not affected by the high temperature, the reduction in protein gain was similar to that of body weight gain: larger from 4 to 6 wk than from 0 to 4 wk and more in males than in females (Figures la and lb). The difference between sexes for protein gain under the high temperature was reversed between 0 to 4 and 4 to 6 wk, resulting in a significant interaction between sex and the 4 to 6 wk age contrast (Table 2). As at the normal temperature, males gain more protein than females from 0 to 4 wk. However, in all genotypes except HF, protein gain from 4 to 6 wk as well as from 6 to 8 wk was larger in females than in males (Table 4). The age contrast from 4 to 6 wk interacted also with the WT - LN contrast. From 0 to 4 wk, the WT genotypes gained about 13% more protein than the LN genotypes, but from 4 to 8 wk the latter genotypes gained 25% more protein. The HF chicks gained more protein than LF ones and about the same as the FC chicks (Table 4).
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CAHANER AND LEENSTRA
TABLE 3. Body weight at 4, 6, and 8 wk of age and daily weight gain from 0 to 4, 4 to 6, and 6 to 8 wk by genotype and sex of chicks reared at high temperature Daily body weight gain Body weight Genoti fpe 1
Sex 2
HF HF LF LF FC FC WN WN WI WI SED HF LF FC WN WI SED
M F M F M F
4 wk
6 wk
953 864
1,472 1,408 1,387 1,311 1,355 1,325
8 wk
0 to 4 wk
4 to 6 wk
6 to 8 wk
32.5 29.2
37.1 38.9 32.9 34.7 36.0 39.8
38.0 33.8 37.9 35.1 28.7
34.1 33.8 27.8 31.1 29.5 33.9 14.7 24.4 7.4 29.7 4.8 34.0 29.5 31.7 19.6 18.6
2.6
3.4
(r*
M + F
13
42
43
926 825 851 767 965 884
M F M F M M M M M
+ + + + +
! Of 'variation
Genot1vpe 3 WT :- LN IS - NL HF -- LF Sex Genotype x sex W T - L N x se> IS - NL x sex HF - LF x sex
<.001 <.001 <.001 .023 <.001 .036
_4 .053 .044
-
.017
31.5 28.0 29.0 26.0 33.1 30.1 36.8 31.1 .8 30.9 29.8 27.5 31.6 34.0 .5 • Probability — 001 <.001 . 1 010 <.001 <.001 . 1 D03 .029 .1027 <.001 . i 009 .038 . i 004 .018
31.5 38.7 24.4 32.9 3.7
-
.012 .040 .010
<.001 <.001
.011
.002 .032 .021
l
ffi and LF = Israeli crosses, selected for a high or a low amount of abdominal fat, respectively; FC = Dutch cross, selected for feed conversion between 3 and 6 wk of age; WN and WI = crosses originating from The Netherlands and Israel, respectively, selected for high 6-wk body weight; SED : : standard error of differences between two means. Z 2v M = male; F = female. 3 Specific contrasts: WT - LN ; WN + WI - FC - LF; IS - NL = WI + LF - WN - FC; HF - LF = HF - LF. 4 P > .1.
changed with age, with a significant interaction between age and the WT - LN contrast (Table 2). Feed efficiency of both groups of genotypes was similar from 0 to 4 wk. It was lower by 21% in the WT genotypes from 4 to 6 wk, and this difference increased to 54% from 6 to 8 wk (Table 6). Feed efficiency from 6 to 8 wk of the HF males was as high as that of FC chicks, and higher than ti\at of LF chicks. Protein Efficiency
The effects of the high temperature on protein efficiency were similar to those on
feed efficiency, but smaller with regard to interactions with genotypes (Table 1). Protein efficiency was not affected by the high temperature up to 4 wk, but afterward it was lower than under normal temperature. The effect of the high temperature was larger for males than females (Figure le), and the differences between sexes for protein efficiency were larger than those for feed efficiency (Figure Id). At the high temperature there was an interaction between sex and age (Table 2). Males and females had a similar efficiency from 0 to 4 wk, but from 4 to 6 wk females
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F F F F F
1,081 919 19 909 876 810 925 1,000
1,406 1,425 1,413 1,380 59 1,440 1,349 1,340 1,416 1,397
1,915 1,848 1,749 1,715 1,739 1,766 1,597 1,742 1,509 1,767 61 1,881 1,732 1,753 1,670 1,638
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GENOTYPE BY TEMPERATURE INTERACTIONS IN BROILERS
TABLE 4. Protein content at 4, 6, and 8 wk of age and daily protein gain from 0 to 4, 4 to 6, and 6 to 8 wk of age by genotype and sex of chicks reared at high temperature Protein gain Protein content Genoti fpe 1
Sex 2
4 wk
6 wk
8 wk
0 to 4 wk
4 to 6 wk
6 to 8 wk
4.59 5.56
5.01 4.07
4.70 4.87 5.24 5.64 4.22 5.39 2.83 4.29 .64
3.57 3.70 4.28 4.74
(r/Vr\ K&i*b>
M F M F M F M F M F M M M M M
+ + + + +
F F F F F
159 157 161 161 166 166 162 161
146 152 155 153 159 156 153 153
147 144 149 145 156 152 157 152
160 160 2.4
150 150 2.7
158 161 166 161 160
149 154 157 153 150 1.9
156 150 4.1 145 147 154 155 153
5.16 4.60 5.07 4.50 4.82 4.33 5.34 4.85 5.93 5.00 .12 4.88 4.79 4.57 5.10 5.46
2.9
.09
M + F
1.7
Source! of variation Genotype 3 WT - LN IS - NL HF - LF
.003 .042 .018
.005 .010 .058 .022
Sex
-
-
Genotype x sex WT - LN x sex IS - NL x sex HF - LF x: sex
-
-
5.08 4.79 5.44 4.80 3.56 .45
.064
<.001 <.001 <.001
.008 .009 .009
.024
<.001
.009
.014 _4
-
.048
2.80 3.64 1.74 4.41 .89 4.54 3.63 4.51 3.22 3.07 .63 .098 .062
-
1 HF and LF = Israeli crosses, selected for a high or a low amount of abdominal fat, respectively; FC = Dutch cross, selected for feed conversion between 3 and 6 wk of age; WN and WI = crosses originating from The Netherlands and Israel, respectively, selected for high 6-wk body weight; SED = standard error of differences between two means. 2x ''M = male; F = female. 3 Specific contrasts: WT - LN = WN + WI • FC - LF; IS - NL = WI + LF - WN - FC; HF - LF = HF - LF. 4 P > .1.
were more efficient than males in all genotypes, and from 6 to 8 wk, sex differences ranged from males' superiority in HF to females' superiority in WI (Table 7). Genotypes differed significantly in protein efficiency during each age period, except when efficiency from 6 to 8 wk was analyzed separately (Table 7). Broilers of the LN genotypes were superior to those of the WT genotypes, and Dutch stocks were superior to the Israeli stocks. Protein efficiency of the HF males from 6 to 8 wk was as
high as that of FC chicks and higher than those of the other genetic groups. DISCUSSION Interactions Between Age, Sex, and Selection Goal
Total weight gain, as well as gain of protein and fat, were reduced by the high temperature, although the magnitude of the reduction varied with genotype, sex, and age. Feed and protein efficiencies were also
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HF HF LF LF FC FC WN WN WI WI SED HF LF FC WN WI SED
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CAHANER AND LEENSTRA
TABLE 5. Fat content at 4, 6, and 8 wk of age and daily fat gain from 0 to 4, 4 to 6, and 6 to 8 wk of age by genotype and sex of chicks reared at high temperature Fat gain Fat content Sex2
4 wk
6 wk
HF HF LF LF
M F
182 196 175 160 133 135 163 173 160 188 16 189 168 134 168 174 11
226 205 180 178 150 174 192 191 192 215 16 216 179 162 191 204
8 wk
0 to 4 wk
(g/kg)
FC FC WN WN WI WI SED HF LF FC WN WI
M F M F M F M F M M M M M
SED M + F Source of variation Genotype 3 WT - LN IS - NL HF - LF Sex Genotype x sex WT - LN x sex IS - NL x sex HF - LF x sex
.001 .008 .010 .069
191 199 183 202 158 159 159 170 158 183 17 195 193 159 165 170 12
11 .001 .002 .059 .004
4 to 6 wk
-4
5.91 5.74 5.51 4.48 3.86 3.53 5.40 5.24 6.38 5.86 .51 5.83 4.99 3.70 5.32 6.12 .36 Probability .019 <.001 <.001 .026 <.001 .033 .066
(g/day) 11.41 8.50 6.28 7.21 6.44 9.06 7.96 8.44 6.44 8.86 1.53 9.96 6.74 7.75 8.20 7.65 1.08 .089
6 to 8 wk 2.56 6.16 5.51 8.66 5.56 3.85 -1.21 1.96 -2.73 2.18 2.72 4.36 7.08 4.71 .38 -.27 1.93 .007 <.001
.008 .048
.093
1
HF and LF = Israeli crosses, selected for a high or a low amount of abdominal fat, respectively; FC = Dutch cross, selected for feed conversion between 3 and 6 wk of age; WN and WI = crosses originating from The Netherlands and Israel, respectively, selected for high 6-wk body weight; SED = standard error of differences between two means. 2
M = male; F = female. 'Specific contrasts: WT - LN = WN + WI - FC - LF; IS - NL = WI + LF - WN - FC; HF - LF = HF - LF. 4 P > .1.
diminished by the high temperature, but to a smaller degree. Body composition (protein and fat percentage), however, was not affected by the high temperature. The only notable change was an increase in males' fat content. Increased fat content due to a high environmental temperature was also found in several previous studies (Kubena et al, 1972; Howlider and Rose, 1989; Chwalibog and Eggum, 1989). The reduction in body weight or protein or fat gain due to the high temperature was much larger from 4 to 6 wk than from 0 to 4
wk, and more pronounced in males than in females (Figure 1). Females gained more weight than males between 6 and 8 wk of age at the higher temperature. Body weights at 8 wk at the high temperature were either similar (for females) or lower (for males) than 6-wk body weights of similar chicks at a normal temperature (Leenstra and Cahaner, 1991). There was a three-way interaction between genotype, sex, and age, because the magnitude of reduction in body weight due to the high temperature was also associated with selec-
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Genotype 1
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GENOTYPE BY TEMPERATURE INTERACTIONS IN BROILERS
TABLE 6. Feed efficiency from 0 to 4, 0 to 6, 0 to 8, 4 to 6, and 6 to 8 wk of age by line and sex of chicks reared at high temperature Feed efficiency Genot'
ml
0 to 4 wk
0 to 6 wk .537 .560 .538 .555 .590 .607
F F F F F
.667 .668 .674 .672 .711 .695 .690 .685 .670 .665 .009 .668 .673 .703 .688 .668
M + F
.006
.008
<.001 .027 <.001
-
Sex.2
0 to 8 wk
4 to 6 wk
6 to 8 wk
O-H
M F M F.
FC FC WN WN WI WI SED HF LF FC WN WI SED
M F M F M F M M M M M
+ + + + +
Source: of variation Genotype 3 WT - LN IS - NL HF - LF Sex Genotype x sex WT - LN x sex IS - NL x sex HF - LF x: sex
\S-S) .506 .494
.368 .445 .287 .395 .027
.428 .361 .390 .365 .418 .425 .245 .293 .147 .354 .072
.425 .410 .492 .406 .341
.395 .377 .421 .269 .250 .051
<.001 <.001 <.001
.019 .010 Probability — •c.001 <.001 <.001 •e.001 _4 <.001
<.001
-
<.001
-
-
.073
.498 .492 .540 .547 .471 .482 .438 .481 .014 .500 .495 .544 .477 .459
.540 .566 .507 .538 .012 .549 .547 .599 .553 .522
-
.399 .450 .387 .433 .464 .521
.077
.010 .001
-
1
HF and LF = Israeli crosses, selected for a high or a low amount of abdominal fat, respectively; FC = Dutch cross, selected for feed conversion between 3 and 6 wk of age; WN and WI = crosses originating from The Netherlands and Israel, respectively, selected for high 6-wk body weight; SED = standard error of differences between two means. 2 M = male; F = female. Specific contrasts: WT - LN = WN + WI - FC - LF; IS - NL = WI + LF - WN - FC; HF - LF = HF - LF. 4 P > .1.
tion goal (WT - LN contrast). The WT genotypes (WN and WI) appeared to be more sensitive to the high temperature than their counterparts selected for leanness (FC and LF). This genetic difference increased with age and was much larger in males than in females. In the weight-selected lines, females were heavier than males at 8 wk. The Role of Fat Content
The smaller effect of the high temperature on the genotypes selected for leanness
(FC and LF), than on the fast-growing genotypes (WN and WI) cannot be attributed to their low fat content. In fact, the opposite was true, i.e., a higher capacity for fat deposition (females in general and HF chicks in particular) appeared advantageous at the high temperature. The HF chicks had the highest mean body weight under the high temperature and gained about the same amount of protein as the lean FC chicks. The HF males were the only ones significantly heavier than their female counterparts. Also in all other genotypes,
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HF HF LF LF
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CAHANER AND LEENSTRA
TABLE 7. Protein efficiency from 0 to 4, 0 to 6, 0 to 8, 4 to 6, and 6 to 8 wk of age by genotype and sex of chicks reared at high temperature Protein efficiency Genotype 1
Sex.2
HF HF LF LF FC FC WI WI WN WN SED HF LF FC WN WI SED
M F M F M F M F M F
0 to 4 wk
0 to 6 wk
0 to 8 wk
.494 .488 .504 .503 .550 .538 .501 .496 .519 .513 .012 .491 .504 .544 .516 .499 .008
.367 .395 .387 .396 .436 .441
.345 .331 .346 .332 .391 .386 .319 .336 .345 .341 .012
<.001 .014 <.001
<.001 <.001 <.001
-
-
4 to 6 wk
6 to 8 wk
ff-H ^b-W
Genotype x sex WT •- LN x sex IS - NL x sex HF -- LF x: sex
+ F + F
+ F + F + F + F
.021
-
.338 .339 .389 .343 .327 .009 Probability <.001 <.001 <.001 <.001 •c.001 <.001
-
<.001
-
.289 .200 .237 .200 .283 .273 .158 .245 .212 .204 .059 .244 .218 .278 .208 .202 .041 _4
-
HF and LF = Israeli crosses, selected for a high or a low amount of abdominal fat, respectively; FC = Dutch cross, selected for feed conversion between 3 and 6 wk of age; WN and WI = crosses originating from The Netherlands and Israel, respectively, selected for high 6-wk body weight; SED = standard error of differences between two means. M = male; F = female. Specific contrasts: WT - LN = WN + WI - FC - LF; IS - NL = WI + LF - WN - FC; HF - LF = HF - LF. 4 ? > .1.
especially LF, fat content at 6 wk was higher in males at the high temperature than at the normal temperature. Chicks having a high capacity to store energy intake in fat depots may have a lower heat increment than chicks having an inherent higher tendency to deposit protein. Thus, relatively fat chicks have less heat to disperse, and consequently their feed consumption and weight gain at the high temperature are less depressed. The FC chicks, however, indicate that this assumption is not generally valid. Their
response was quite different from that of LF chicks, despite their similar weight gain. Under the high temperature, FC chicks maintained their leanness and superiority in feed and protein efficiency, whereas LF chicks were no longer lean. The different selection criteria used to develop these two genotypes, high feed efficiency for FC (Leenstra, 1988) and low abdominal fat percentage for LF (Cahaner, 1988), might be responsible for their different fat gains at the high temperature. It was already evident at normal and low temperatures that
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Source! of variation Genotype 3 WT •- LN IS - NL HF -- LF Sex
M M M M M M
.356 .377 .384 .402 .014 .381 .392 .438 .393 .366 .010
.232 .301 .258 .284 .316 .345 .161 .244 .230 .289 .027 .266 .271 .331 .260 .202 .019
GENOTYPE BY TEMPERATURE INTERACTIONS IN BROILERS
despite the similar carcass composition, these two genetic groups differ in many aspects (Leenstra and Cahaner, 1991). Despite their high feed efficiency, FC chicks have a low energetic efficiency (Leenstra and Pit, 1988). This is only possible if FC chicks have a high capacity for heat loss which, as well as high fat deposition, might help in decreasing the depression in weight gain caused by high temperatures. The Role of Growth Potential
6-wk body weight. From 6 wk onward WN and WI males gained hardly any weight, but all other groups continued to grow. Therefore, it is probably the growth potential of these fast-growing males, rather than their actual growth, that made them more sensitive to the high temperature. The current results indicate that the upper limit of the thermoneutral zone of chickens (or the response of chickens if this upper limit is exceeded) is dependent on sex and genotype and is not related in a straightforward way to body weight or body composition. Practical Considerations
Although a constant temperature of 32 C will not occur in commercial broiler operations, the present results strongly suggest that raising male broilers from the modern, fastest growing stocks at high ambient temperatures might not be advisable. Reducing growth rate of such broilers (by feed restriction, for example) may not fully counteract the cumulative physiological differences resulting from selection for rapid growth. In hot regions, where facilities differ in their cooling capability, males should be placed in the cooler houses, whereas females provide a better chance for reasonable performance under higher temperatures. Selection in a subtropical climate, such as in Israel, did not improve resistance to a constant high temperature of 32 C. Indeed, the effect of origins (Israel or The Netherlands) was significant only for weight gain from 0 to 4 wk, when the difference between the normal and the high temperature regimen was relatively small. Although the chicks selected for feed efficiency (FC) had a lower growth rate at the normal temperature (Leenstra and Cahaner, 1991), at the high temperature they grew better than the weight-selected chicks and also maintained their superior efficiency. This is an additional advantage of applying feed efficiency rather than weight gain as a selection criterion for broilers, and is one of special interest for hot-climate regions.
REFERENCES Adams, R. L., and J. C. Rogler, 1968. The effect of environmental temperature on the protein re-
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The magnitude of reduction in growth due to the high temperature was related mainly to the chicks' growth potential, i.e., their growth rate at a normal temperature. In the present study, the fast-growing genotypes WN and WI were affected more by the high temperature than the other genotypes and males were affected more than females. A larger relative effect of high temperature on males than on females was reported by Osman et d. (1989). In other comparisons between high and normal temperatures found in the literature, chicks from both sexes were affected similarly. The different results in these studies may be explained by the difference in the growth potential of the genotypes used; the higher the potential the larger the possible effect of the high temperature, especially on males. Mean 6-wk body weight of males and females under normal conditions (i.e., temperatures between 18 and 24 C) as a measure of growth potential, was in all reviewed studies lower than that of modern broilers: around 1,250 g for the broilers used by Cerniglia et d. (1983), 1,650 g for those used by Howlider and Rose (1989), and 1,750 g for those used by Osman et al. (1989). The growth potential of the FC and LF genotypes used here was 1,843 g and that of the WN and WI genotypes was 2,035 g (Leenstra and Cahaner, 1991). Six-week body weights of WN + WI and LF + FC males at the normal temperature were 2,214 and 1,963 g, respectively. This difference of 250 g is probably responsible for the normal reduction in weight gain due to the high temperature observed in the LF and FC males, versus the much larger effect on the WN and WI males. The effect is not due to actual body weight, because at the high temperature WN and WI males and females and FC and LF males had a similar
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CAHANER AND LEENSTRA Leanness in Domestic Birds: Genetic, Metabolic and Hormonal Aspects. B. Leclercq and C. C. Whitehead, ed. Butterworths, London, England. Leenstra, F. R., and A. Cahaner, 1991. Genotype by environment interactions using fast-growing, lean or fat broiler chickens, originating from The Netherlands and Israel, raised at normal or low temperature. Poultry Sci. 70:2028-2039. Leenstra, F. R., and R. Pit, 1988. Consequences of selection for feed conversion in broiler chickens. Pages 160-161 in: Advances in Animal Breeding. S. Korver, H.A.M. van der Steen, J.A.M. van Arendonk, H. Bakker, E. W. Brascamp, and J. Dommerholt, ed. Pudoc, Wageningen, The Netherlands. Osman, A.M.A., E. S. Tawfik, F. W. Klein, and W. Hebeler, 1989. Effect of environmental temperature on growth, carcass traits and meat quality of broilers of both sexes and different ages. Arch. GeflUgelkd. 53:158-175. Steverink, A.T.G., H. Steunenberg, R. Frankenhuizen, and M. Tusveld, 1988. Application of NearInfrared Reflection Spectroscopy (NIRS) To Determine Fat Content of Broilers (in Dutch). Spelderholt Report 487, Beekbergen, The Netherlands.
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quirements and response to energy in slow and fast growing chicks. Poultry Sci. 47:579-586. Cahaner, A , 1988. Experimental divergent selection on abdominal fat in broilers—parental female and male type lines and their crosses. Pages 71-86 in: Leanness in Domestic Birds: Genetic, Metabolic and Hormonal Aspects. B. Leclercq and C. C. Whitehead, ed. Butterworths, London, England. Cerniglia, G. J., J. A. Hebert, and A B. Watts, 1983. The effect of constant ambient temperature and ration on the performance of sexed broilers. Poultry Sci. 62:746-754. Chwalibog, A., and B. O. Eggum, 1989. Effect of temperature on performance, heat production, evaporative heat loss and body composition in chickens. Arch. Geflugelkd. 53:179-184. Genstat 5, 1987. Reference Manual. Clarendon Press, Oxford, England. Howlider, M.A.R., and S. P. Rose, 1989. Rearing temperature and the meat yield of broilers. Br. Poult. Sci. 30:61-67. Kubena, L. F., B. D. Lott, J. W. Deaton, F. N. Reece, and J. D. May, 1972. Body composition of chicks as influenced by environmental temperature and selected dietary factors. Poultry Sci. 51:517-522. Leenstra, F. R., 1988. Selection for leanness: Results of the Spelderholt experiment. Pages 59-69 in: