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Effects of Low, Normal, and High Temperatures on Slaughter Yield of Broilers from Lines Selected for High Weight Gain, Favorable Feed Conversion, and High or Low Fat Content
Effects of Low, Normal, and High Temperatures on Slaughter Yield of Broilers from Lines Selected for High Weight Gain, Favorable Feed Conversion, and High or Low Fat Content FERRY LEENSTRA Spelderholt, Centre for Poultry Research and Information Services (DLO-COVP), P.O. Box 15, 7360 AA Beekbergen, The Netherlands AVIGDOR CAHANER
ABSTRACT Male and female broiler chicks from five different broiler crosses (WI = Israeli chicks selected for increased body weight; LF and HF = Israeli chicks selected for low and high abdominal fat, respectively; FC and WN = Dutch chicks selected for improved feed conversion and increased body weight, respectively) were raised at low, normal, or high temperature. Slaughter yield, amount of breast meat, and abdominal fat were determined at 6 wk of age in all groups and at a body weight of 2,360 g for males and 1,965 g for females in the low- and normal-temperature groups, and at 8 wk in the hightemperature groups. Temperature, genotype, and sex influenced both absolute and relative weights of carcass, breast meat, and abdominal fat. Temperature had a negative effect on breast meat yield. Males were affected more by high temperature than females. A significant interaction between temperature and sex for breast meat yield was caused by a low yield for males at the high temperature. A similar interaction for proportion of abdominal fat was caused by a high fat content in males reared at the high temperature. Slaughter yield and especially yield of breast meat were highest in FC chickens in all comparisons. (Key words: broilers, genotypes, temperatures, slaughter yield, interactions) 1992 Poultry Science 71:1994-2006
(Howlider and Rose, 1989; Tawfik et ah, 1989). Selection and management of broilers is Leenstra and Cahaner (1991) and Caincreasingly aimed at a high meat yield haner and Leenstra (1992) reported on and low fat deposition. In general, lean- growth rate, feed conversion, and cheminess, higher meat yield, and a favorable cal composition of Dutch and Israeli feed efficiency coincide in selection experi- broiler crosses descending from lines ments (Cahaner, 1988; Leclercq, 1988; selected for increased body weight gain, Leenstra, 1988; Whitehead, 1988). Carcass improved feed conversion, and high or composition and meat yield are also low abdominal fat content, reared at low, dependent on environmental temperature. normal, or high temperature. Genotype At high temperatures, meat yield and and temperature had a significant effect especially yield of breast meat are reduced on weight gain, carcass composition, and feed and protein efficiency. In comparisons at equal age and at equal final body weight, chickens selected for improved Received for publication May 13, 1992. feed conversion had the highest feed and Accepted for publication August 13, 1992. INTRODUCTION
1994
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The Hebrew University of Jerusalem, Faculty of Agriculture, P.O. Box 12, 76100 Rehovot, Israel
GENOTYPE BY TEMPERATURE INTERACTIONS IN BROILERS
MATERIALS AND METHODS The effects of low, normal, and high temperatures on body weight, body composition (protein and fat content), and feed and protein efficiency of the chicks used for the present study, as well as details regarding genetic groups, temperatures, diet, and housing, were presented by Leenstra and Cahaner (1991) and
1 Centre for Poultry Research and Information Services (COVP) "Spelderholt", Agricultural Research Department (DLO), Ministry of Agriculture, Nature Management, and Fisheries, 7360AA Beekbergen, The Netherlands.
Cahaner and Leenstra (1992). The current study concentrates on the effects of genotype, sex, and temperature on yield characteristics. Chickens Five different genetic groups (genotypes) were used. Three were of Israeli origin and two of Dutch origin. All chicks resulted from a cross between Cornish (broiler sire) chickens and White Plymouth Rock (broiler dam) chickens. The Israeli chicks descended from a 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 high body weight gain (WN) (Leenstra, 1988). All eggs were incubated and hatched simultaneously at COVP-DLO.1 Housing and Management The chicks were housed on chopped straw 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 from 6 wk of age onwards. The pens were arranged in rooms. In total, nine rooms were available. Ten pens, one pen for males and one for females from each of the five genotypes, were used per room. Lighting was continuous on the 1st day after hatch and intermittent (1 h light, 3 h darkness alternating) thereafter. The chicks received ad libitum access to a pelleted broiler diet with 3,203 kcal metabolizable energy and 215 g of crude protein/kg of diet. Climate The chicks were reared at three temperature schedules: low (gradually decreasing from 33 C at hatch to 15 C from 5 wk of age onwards); normal (gradually decreasing from 33 C at hatch to 20 C from 6 wk of age onwards (Leenstra and Cahaner, 1991); high (33 C from hatch to 2 wk of age and 32
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protein efficiency regardless of temperature regimen. Interactions between genotype and temperature were clearly present for weight gain, protein deposition, and feed and protein efficiency, but were less evident for fat deposition. At the low temperature, the Dutch chickens had a higher weight gain and protein deposition than those derived from Israeli strains; at the normal temperature, the Israeli chickens gained more weight and protein. Irrespective of country of origin, genotypes with the highest growth rate at the low or normal temperature were most affected by the high temperature, and males were affected more than females. Genotypes selected for a favorable feed conversion or for low or high abdominal fat content were less affected by the high temperature. Broiler production is increasing throughout the world and processing yield and deboned meat yields are becoming important because of market demands with demographic changes. Based on the interactions found between genotype, temperature, and sex for weight gain and carcass composition (Leenstra and Cahaner, 1991; Cahaner and Leenstra, 1992), main effects and interactions can also be expected for slaughter yields. In the present study the effects of environmental temperature, genotype, and sex, and their interactions on slaughter yield, breast yield, and amount of abdominal fat of the Dutch and Israeli genotypes mentioned above were evaluated.
1995
1996
LEENSTRA AND CAHANER
C thereafter). Relative humidity was kept at 60% for all groups throughout the experiment. Three rooms were used for each temperature schedule. Measurements
Statistical Analysis The experiment had a split-plot design, with temperature regimens assigned to rooms as the main plots, and the genotype by sex combinations assigned to pens as
Y = u + T + e r + G + S + TG + TS + GS + GTS + e p + ec. [1] The effect of T was tested against er, the between-rooms error term. All other effects were tested against e p , the between-penswithin-room error term. The expression ec is the between-chicks-within-pen error term, which was not needed to test the effects in the present study. The slaughter yields at EQBW calculated for each of the pens at the low and normal temperature were analyzed by a .similar model, but without e0 as only pen means were available. At the high temperature, the target weight was not reached. The effects of age (A), genotype, sex, and their interactions on chicks sampled at 6 or 8 wk at the high temperature were examined by ANOVA with the model: Y + n + e r + G + S + GS + e p + A + GA + SA + GSA + e s + ec. [2] The effects of age and the interactions with age were tested against the error term between-samples-within-pen (es). The effects of genotype and sex on yields at each temperature-age combination separately were examined by ANOVA with the model: Y = n + e r + G + S + GS + e p + ec.
[3]
Each room was considered as a block (er) and all the effects were tested against e p . The yields at EQBW calculated for each of
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The 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 low- and normal-temperature groups and from 2 to 8 wk (55 days) in the high-temperature groups. Three birds from each pen were used to determine slaughter yields at 6 wk of age. Because within each sex, WN and WI chicks at the low temperature were heavier at 6 wk, the other groups at the low and normal temperature were raised to 7 wk, when again three birds per pen were taken to determine slaughter yields. This procedure allowed estimation of slaughter yields for the low and normal temperature at a similar body weight (EQBW, 2,360 g for males and 1,965 g for females) by interpolation per pen between data for 6 and 7 wk. The chicks reared at the high temperature were kept to 8 wk of age, in an attempt to finish them at a body weight that the groups reared at low or normal temperature had at 6 wk of age, when three birds per pen were slaughtered. The chickens to be slaughtered were deprived of feed for 8 h and weighed individually before slaughter and processing. The chickens were stunned, bled, and plucked in the COVP-DLO pilot plant. Head and feet were removed and afterwards each chicken was packed in a plastic bag and chilled for 10 to 24 h at 0 C. From each chicken, the abdominal fat (fat surrounding the gizzard included), and the breast meat were removed and weighed. Also griller weight (the weight of the empty carcass with neck, but without giblets and abdominal fat) was determined. Absolute weights and griller, breast meat, and abdominal fat as proportion of body weight were subjected to statistical analysis.
secondary plots. The temperature regimens were distributed at random among the rooms. In each room, all 10 genotype and sex combinations were randomly distributed among the pens. Griller, breast meat, and abdominal fat as proportion of body weight were distributed normally, and consequently no arc sine transformations were required. The effects of temperature (T), genotype (G), and sex (S), and their interactions on an individual chick (Y) were examined for each of the measurements at 6 wk of age by ANOVA with the model:
GENOTYPE BY TEMPERATURE INTERACTIONS DM BROILERS
RESULTS Body weight of the slaughtered chicks and the absolute and relative weight of the griller, breast meat, and abdominal fat were analyzed by several models. Levels of significance [Model 1] of the effects of temperature, genotype, and sex and their interactions at 6 wk of age, of contrasts between temperatures, and of contrasts between sources of genetic differences (genetic contrasts), are given in Table 1. Levels of significance [Model 2] of the effects of age (6 versus 8 wk), genotype, and sex, their interactions, and of the genetic contrasts for chicks reared at the high temperature are given in Table 2. Mean body weight by genotype and sex within age, and levels of significance of the main effects, interactions, and the genetic contrasts [Model 3] are presented in Table 3. Griller, breast meat, and abdominal fat as proportion of body weight by genotype and sex at 6 wk, at EQBW (low and normal temperature), and at 8 wk (high temperature), and all levels of significance [Model 3], are presented in
Tables 4 to 6. Absolute weight of griller, breast meat, abdominal fat, and live body weight, for the normal temperature groups (at 6 wk), and the high temperature groups (6 and 8 wk) are presented in Figure 1. Body Weight At 6 wk, a temperature by genotype interaction was found (Table 1), because at the low temperature the difference between the weight-selected groups (WN and WI) and those selected for leanness (FC and LF) was much larger than at the normal or high temperature. The interaction between temperature and sex resulted from the similar BW of males and females at the high temperature versus the usual advantage of about 15% of males over females at the low and normal temperature (Table 3, Figure 1). At the high temperature, the sex effect interacted with age and genotype (Table 2). The WN and WI females maintained an advantage of about 70 g over FC and LN females at both ages, whereas males from all genotypes had a similar BW at 6 wk. At 8 wk, WN and WI males had a lower BW than FC and LF males, and than WN and WI females (Table 3, Figure 1). Within each sex, WN and WI chicks at the low temperature were the heaviest at 6 wk (Table 3). Males averaged 2,360 g and females 1,965 g. These mean body weights were used for comparisons of EQBW. By keeping the other groups at low and normal temperature until 7 wk of age, they almost all reached or surpassed this target weight. Griller Differences in absolute griller weight were almost identical to differences in live BW (Tables 1 and 2). This could be expected, as griller was about 65% (between 631 to 693 g/kg) of live BW (Table 4). The proportion of griller (GRP) at 6 wk was affected by genotype and temperature (Table 1). In the high temperature, age (6 versus 8 wk) did affect GRP (Table 2). Four of the genotypes had a similar GRP, but HF means were lower in all temperature by sex by age combinations. At 6 wk, GRP values were higher at the high than at the low and normal temperatures. From 6 to 8 wk at the
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the pens at the low and normal temperature were analyzed by a similar model, but without ec. Three contrasts between sources of genetic differences were evaluated. The effects of selection goal (WT - LN; body weight or leanness) and of origin of the genotypes (IS - NL; Israel or The Netherlands) and their interactions with other main factors were tested by estimating the contrasts WI + WN - LF - FC and WI + LF WN - FC, respectively. As the HF chicks did not have a Dutch counterpart, they were not incorporated in these contrasts. The contrast HF - LF was evaluated to examine the effect of carcass fat content in chicks from the same origin and with similar growth rate. In ANOVA with Model 1, the contrasts between low and normal temperatures (LT - NT) and between normal and high temperatures (NT - HT) at 6 wk of age were evaluated. All statistical analyses were done with the Genstat program (Genstat, 1987). Main effects, contrasts, and interactions were considered significant if P < .05, unless otherwise stated.
1997
1998
LEENSTRA AND CAHANER
TABLE 1. Level of significance (P values) for the effects of temperature (T), genotype (G), sex (S), their interactions, and of specific contrasts on body weight and on absolute and relative weight of griller (empty carcass with neck and without giblets and abdominal fat), breast meat, and abdominal fat in chickens of 6 wk of age Source of variance1 LT - N T N T - HT G WT - LN IS - NL HF - LF
LT - NT x G NT - HL x G T x WT - LN T x IS - NL T x HF - LF
Breast meat Weight Proportion <.001 <.0Ol .003 .043 <.001 .002 .047 <.001 <.0Ol <.001 .071
<.001
<.001
.016
T x S
<.001
<.001
LT - NT x S NT - HT x S G xS
<.001
<.001
<.001 .061 <.0Ol
.088
.091
.067
WT - L N x S
IS - NL x S HF - LF x S T x G xS LT - NT x G x S NT - HT x G x S T x WT - LN x S T x IS - NL x S T x HF - LF x S
.098
.080 .071
<.001
.014
Abdominal fat Weight Proportion <.001
. . -2
<.001 <.001 <.001
. .. <.001 <.001
<.001 <.001 .002
<.001 <.001 .099
.043 <.001 .069
.011
.078
.002 .006
.073
.083
.. .
.115 .081
.099
.103
.052
.050
.013
.019
.096
a
LT - NT and NT - HT = specific contrasts between low and normal, and between normal and high temperature, respectively. WT - LN, IS - NL, and HF - LF = specific contrasts for selection goal (weight versus feed efficiency and low abdominal fat), origin (Israel versus The Netherlands), and carcass fatness (high versus low abdominal fat). 2 P > .1.
high temperature, GRP increased in all genotype by sex combinations by an average of 23 g/kg (Table 4). The differences between sexes were not consistent, although on average males had a slightly higher GRP. At EQBW (only for the lowand normal-temperature groups), the ranking of genotypes with regard to GRP was not changed, but the advantage of FC chickens over the other genotypes became more evident (Table 4). Breast Meat The main effects and their interactions affected the absolute weight of breast meat
at 6 wk in a way similar to live body weight (Table 1). However, at the high temperature (Table 2), the effects of sex and of the interaction between genotype and age were significant for the absolute weight of breast meat, but they were not significant for body weight. At the high temperature, females had more breast meat than males. Strain WI ranked first and FC ranked last at 6 wk, whereas the order was reversed at 8 wk (Figure 1). With regard to the proportion of breast meat (BMP), the temperature by sex interaction at 6 wk was the only significant interaction (Table 1). The increase in temperature reduced BMP, but the effect on
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S T x G
Griller Body _ weight Weight Proportion <.001 <.001 005 .004 .014 <.001 <.001 005 <.001 <.O01 001 <.001 <.001 .061 .047 001 <.001 <.001 060 <.001 .002 .018 .025
1999
GENOTYPE BY TEMPERATURE INTERACTIONS IN BROILERS
TABLE 2. Level of significance of the effects of genotype (G), sex (S), age (A; 6 versus 8 wk) and their interactions, and of the genetic contrasts for selection goal (WT - LN), origin (IS - NL), and carcass fatness (HF - LF), for body weight, and absolute and relative weight of griller (empty carcass with neck, without giblets, and abdominal fat), breast meat, and abdominal fat of chickens reared at high temperature Source of variance1
Griller Body _ weight Weight Proportion
Breast meat Weight Proportion
<.001 W T - LN IS - NL HF - LF
001
S
.085 .024
.074 .017
<.001 .098 .060 .095
<.001 .087 .062 .046
.064 .031
.068 .026
<.001
.057
001 055 .045
<.001 .033 .023 .020
<.001 .080 .065 .024
<.001
<.001
<001 .012 .013 .009
<.001 .004 .056 .026
<.O01
.050 .046
.088
.028
.063 .018
iWT - LN, IS - NL, and HF - LF = specific contrasts for selection goal (weight versus feed efficiency and low abdominal fat), origin (Israel versus The Netherlands), and carcass fatness (high versus low abdominal fat). 2P > .1.
were similarly affected by temperature, genotype, sex, and their interactions (Tables 1 and 2). At 6 wk, the three-way interaction temperature by genotype by sex had a low probability level, due to a significant interaction between the NT - HT temperature contrast and the IS - NL genetic contrast (Table 1). This interaction was caused mainly by male LF chickens at the high temperature, which had an exceptionally high AFP, even higher than their female counterparts, whereas WN males were the only group with an AFP lower at the high temperature than at the normal and low temperature (Table 6). However, no similar trend was observed in the other pair of Israeli and Dutch genotypes (WI and FC). Females had a similar mean AFP at the low and normal temperature and 10% less at the high temperature. The temperatures had the opposite effect on males; in most Abdominal Fat genotypes the AFP of males increased with temperature. The average AFP in males was Absolute weight of abdominal fat, and the proportion of abdominal fat (AFP), 12% lower than AFP in females at the high
males was much larger than on females (Table 5). At the low temperature both sexes had the same mean BMP (135 g/kg); at the normal temperature, BMP of females was only slightly lower (133 g/kg) but males were down to an average of 129 g/kg. The advantage of females over males in BMP was more pronounced at the high temperature (128 versus 116 g/kg at 6 wk and 138 versus 124 g/kg at 8 wk). The increase of BMP with age at the high temperature was highly significant (Table 2). Within genotype and temperature, the differences between males and females were similar at 6 wk, EQBW, and 8 wk (Table 5). The HF chicks had the lowest BMP at all temperatures and ages, and FC chicks had the highest BMP in most cases. This was most evident at EQBW under normal temperature.
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G x S WT - LN x S IS - NL x S HF - LF x S A G x A WT - LN x A IS - NL x A HF - LF x A G x Sx A WT - LN x S x A IS-NLxSxA HF-LFxSxA
.003
Abdominal fat Weight Proportion
2000
LEENSTRA AND CAHANER
TABLE 3. Body weight prior to slaughter at 6 wk of age for chickens reared at low, normal, or high temperature, at 7 wk for chickens reared at low and normal temperature, and at 8 wk for chickens reared at high temperatures and results of the analysis of variance
Genolypei
Sex2
HF HF LF LF FC FC WN WN WI WI SED4 HF LF FC WN WI SED
M F M F M F M F M F M M M M M M M
Low
6 wk Normal High
Low
7 wk Normal
2,007 1,697 1,946 1,798 1,898 1,682 2,070 1,774 2,161 1,820 67 1,852 1,872 1,790 1,922 1,991 47
(8) 2,437 1,944 2,439 2,085 2,533 2,007 ND3 ND ND ND ND 2,190 2,262 2,270 ND ND ND
2,375 2,025 2,419 2,003 2,115 1,932 2,547 2,062 ND 2,165 ND 2,200 2,211 2,074 2,305 ND ND
ND ND ND ND ND ND ND ND ND
ND ND ND ND ND ND ND ND ND
8 wk High
1,370 1,328 1,356 1,295 1,259 1,260 1,267 1,382 1,348 1302 100 1,349 1,325 1,260 1,324 1,325 70
<.001 <.001
.006 .001 .036
<.001 .010 .005 .010 .027
<.001 .054 .101
.5
1,887 1,723 1,825 1,625 1,737 1,707 1,639 1,785 1,492 1,710 79 1,805 1,725 1,722 1,712 1,601 56 .033 .107
.005 .002
1
HF and LF = Israeli crosses, selected for a high or a low amount of abdominal fat, respectively; FC = Dutch cross, selected for improved 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. 2 M = male; F = female. 3 ND = not done. 4 SED = standard error of differences between two means. sp > .1. 6 WT - LN, IS - NL, and HF - LF = specific contrasts for selection goal (weight versus feed efficiency and low abdominal fat), origin (Israel versus The Netherlands), and carcass fatness (high versus low abdominal fat).
temperature, whereas at the low and normal temperatures it was lower by 40 to 50% (Table 6), resulting in a significant temperature by sex interaction (Table 1). Genotypes ranked, in general, according to the criteria used for selection (Table 6). The HF birds had the highest AFP, and LF and FC were the leanest genotypes (with the exception of LF males at the high temperature). The differences between
genotypes in AFP at the low and normal temperatures at EQBW were similar to those at 6 wk of age. At the high temperature, a genotype by sex by age interaction was evident. The interaction resulted mainly from the high AFP in LF males compared with LF females at 6 wk, and a similar effect in the HF genotype at 8 wk (Table 6). In WN and WI, the higher AFP in females compared with
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~ e of variation oou Genotype WT - LN« IS - NL HF - L F Sex Genotype x sex W T - LN < sex IS - NL x sex HF - L F x sex
2,035 1,705 1,995 1,822 2,039 1,716 2,393 1,936 2,329 1,992 47 oi F + F 1,869 + F 1,908 + F 1,877 + F 2,165 + F 2,161 + F 33
GENOTYPE BY TEMPERATURE INTERACTIONS IN BROILERS
2001
TABLE 4. Griller (empty carcass, with neck and without giblets and abdominal fat) as proportion of body weight at 6 wk of age for chickens reared at low, normal, or high temperature, at equal body weight (EQBW) for chickens reared at low and normal temperature, and at 8 wk of age for chickens reared at high temperature and results of the analyses of variance within temperature by age combinations
Genoi•ype 1
Sex2
HF HF LF LF FC FC WN WN WI WI SEEP HF LF FC WN WI SED
M F M F M F M F M F
Low
6 wk Normal High
Low
EQBW Normal
8 wk High
635 640 647 652 660 660 647 655 649 652 4.5 637 650 660 651 650 3.2
661 661 686 689 691 682 693 693 690 685 7.9 661 687 687 693 688 5.6
(v /\ev\
of variation Geno!ype WT - LN4 IS - NL HF -- LF Sex Genotype x sex
641 628 646 645 647 653 640 647 649 648 6.5 635 645 650 644 648 4.6
635 634 655 652 655 656 651 631 652 649 7.2 635 653 656 641 651 5.1
650 643 660 666 665 653 662 659 675 667 8.3 646 663 659 660 671 5.9
Sniirr e
.086 . .5
.040
.011
.040
.002
<.001
' !o34
.093 .013
.017
.089 .013
<.001
.101
1HV and T.F -
esnertivelv: FC —
Dutch cross, selected for improved 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. 2 M = male; F = female. 3 SED = standard error of differences between two means. 4 WT - LN, IS - NL, and HF - LF = specific contrasts for selection goal (weight versus feed efficiency and low abdominal fat), origin (Israel versus The Netherlands), and carcass fatness (high versus low abdominal fat). 5 P > .1.
males was more pronounced at 8 than at 6 wk. At 8 wk, HF males had the highest AFP, whereas males from all other genotypes had a similar AFP. Among females, AFP values ranked from HF through WN, WI, LF, and FC with the lowest mean AFP. DISCUSSION At the low and normal temperatures, the genotypes were compared within each
sex at EQBW. The ranking of the genotypes and the differences among them at EQBW were either similar or slightly larger than those at equal age (6 wk) in all three yield measurements. The conclusions to be presented for equal age are thus also valid for EQBW. The relation between GRP and AFP was not symmetric. Griller as proportion of body weight was not higher in the LF and FC genotypes than in the WN and WI genotypes at the low and normal tempera-
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631 632 644 635 652 645 651 631 652 649 9.9 M oi F M + F 632 M + F 639 M + F 649 M + F 641 M + F 651 M+ F 7.0
2002
LEENSTRA AND CAHANER
TABLE 5. Breast meat as proportion of body weight at 6 wk of age for chickens reared at low, normal, or high temperature, at equal body weight (EQBW) for chickens reared at low and normal temperature, and at 8 wk of age for chickens reared at high temperature; results of the analyses of variance within temperature by age combinations
Genotype
1
Sex*
Low
6 wk Normal High
EQBW Normal Low
8 wk High
Co- /Irirl
131 133 134 132 135 144 136 131 141 137 6.2 oi• F + F 132 + F 133 + F 140 + F 134 + F 139 + F 4.4
128 124 129 136 129 139 128 135 129 133 4.5 126 133 134 131 131 3.2
111 126 114 130 120 124 114 130 123 130 6.8 118 122 122 122 127 4.8
132 133 136 137 139 148 136 131 140 137 4.1 133 137 144 134 139 2.9
126 134 132 134 141 147 132 140 131 135 3.4 130 133 144 136 133 2.4
119 135 125 134 130 147 122 141 123 134 5.1 127 130 139 131 129 3.6
.4 .037 .005 .096 Genotype .081 WT - LN5 .029 .006 IS - NL H F - LF !053 <.001 .012 .001 Sex .029 Genotype x sex 1 HF and LF = Israeli crosses, selected for a high or a low amount of abdominal fat, respectively; FC = Dutch cross, selected for improved 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. 2 M = male; F = female. 3SED = standard error of differences between two means. *P > .1. 5 WT - LN, IS - NL, and HF - LF = specific contrasts for selection goal (weight versus feed efficiency and low abdominal fat), origin (Israel versus The Netherlands), and carcass fatness (high versus low abdominal fat).
tures, despite the lower total carcass fat content (Leenstra and Cahaner, 1991) and lower AFP in LF and FC chicks. At the high temperature, FC chicks had the lowest body fat content (Cahaner and Leenstra, 1992), but they did not have the highest GRP. On the other hand, the HF chicks with their high AFP and high body fat content in all temperature by sex by age combinations had the lowest GRP. At the low and normal temperature, AFP in HF chicks compared with WN and WI chicks was higher by about 11 g/kg and
their GRP was lower by about 13 g/kg chicks. Thus, the exclusion of abdominal fat from the griller can account for the differences between HF and the two weight-selected genotypes. The lack of a similar difference in GRP between the weight-selected genotypes (WN and WI) and the lean ones (FC and LF) indicates that AFP is not the only important factor in GRP. Consequently, selection against abdominal fat has an advantage only if lean meat yield and not yield of the complete carcass is the production goal.
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HF M HF F LF M LF F FC M F FC WN M F WN M WI WI F SED3 M HF M LF M M FC M WN M WI SED M Source of variation
2003
GENOTYPE BY TEMPERATURE INTERACTIONS IN BROILERS
TABLE 6. Abdominal fat as proportion of body weight at 6 wk of age for chickens reared at low, normal, or high temperature, at equal body weight (EQBW) for chickens reared at low and normal temperature, and at 8 wk of age for chickens reared at high temperature and results of the analyses of variance 6 wk Genoltype 1
Low
Sex*
Normal
EQBW
Low
High
8 wk
Normal
High 47.3 41.7 23.3 31.7 19.5 22.5 20.8 36.0 18.1 34.7
fir /VM
HF LF FC WN WI
SED SOIITCe
+ + + + + +
F
32.1 42.1 14.3 28.1 17.1 23.6 23.3 36.4 22.0 32.8
35.5 46.3 16.5 27.8 19.1 25.0 25.1 33.1 21.9 33.3
39.9 41.7 30.2 24.0 19.4 25.2 20.3 30.4 22.9 27.5
38.1 46.2 18.1 23.8 19.8 23.7 23.3 36.4 22.0 32.8
38.5 49.1 19.5 27.9 19.8 27.8 27.5 36.0 21.9 32.7
4.0
2.0
4.0
1.9
1.5
5.3
F F F F F
37.1 21.2 20.4 29.8 27.4
40.9 22.1 22.0 29.1 27.6
40.8 27.1 22.3 25.4 25.2
42.2 21.0 21.7 29.8 27.4
43.8 23.7 23.8 31.7 27.3
44.5 27.5 21.0 28.4 26.4
M + F
2.8
1.4
2.8
1.3
1.1
3.8
<.001 <.001
<.001 <.001
<.001
<.001 <.001
<.001
<.001
<.001 .090 .102 .075 .043
<.O01
<.001 <.001 .045 <.0Ol <.001
of variation
Genol•ype WT - LN* I S - NL H F - - LF
Sex Genotype x sex WT - LN :< sex IS - NL x sex H F - LF x sex
,5
<.001 <.0Ol
<.001
.043
<.001
<.001 .006 .051 .072 .082
1
HF and LF = Israeli crosses, selected for a high or a low amount of abdominal fat, respectively; FC = Dutch cross, selected for improved feed conversion between 3 and 6 w k of age; WN and WI = crosses originating from The Netherlands and Israel, respectively, selected for high 6-wk body weight. 2 M = male; F = female. 3SED = standard error of differences between two means. 4 WT - LN, IS - NL, and HF - LF = specific contrasts for selection goal (weight versus feed efficiency and low abdominal fat), origin (Israel versus The Netherlands), and carcass fatness (high versus low abdominal fat). sp > .1.
The increased GRP at the high temperature compared with the low and normal temperatures at 6 wk of age, and the further increase in GRP between 6 and 8 wk, could not be attributed to reduced fat deposition because AFP was hardly affected by temperature at 6 wk, nor by age at the high temperature. Also body fat content, although decreased in females at the high temperature, was increased in
males (Cahaner and Leenstra, 1992) and therefore could not account for the higher GRP at the high temperature. The higher GRP at the high temperature was not associated with the reduced BW. At 8 wk of age, mean BW of some high temperature groups was similar to that of groups from the same genotype and sex at the normal temperature at 6 wk, and yet their GRP was higher. It therefore seems that
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M F M F M F M F M F M M M M M M
HF HF LF LF FC FC WN WN WI WI SEE>3
2004
LEENSTRA AND CAHANER
Breast meat
Griller
Abdominal fat
Offals + giblets
2.250 2,000 1,750 1,500 1,250 c
! 1,000
500
n V, V
n
2 2
250 0 HF LF FC WN WI Normal temperature 6 wk
HF LF FC WN WI High temperature 6 wk
HF LF FC WN WI High temperature 8 wk
FIGURE 1. Absolute weights of breast meat, griller (empty carcass with neck and without abdominal fat and giblets), abdominal fat, and the difference between these components and live body weight (offals and giblets) for male (left bar of each set) and female (right bar of each set) chicks of five genetic groups at 6 wk (normal and high rearing temperature) and 8 wk (high temperature) of age. HF and LF = Israeli crosses, selected for a high or a low amount of abdominal fat, respectively; FC = Dutch cross selected for improved feed conversion; WN and WI = crosses originating from The Netherlands and Israel, respectively, selected for high 6-wk body weight.
the proportion of other parts (feathers, intestines, and giblets), which were excluded from GRP, was reduced at the high temperature, especially from 6 to 8 wk of age, resulting in an increased GRP. Unlike griller and breast meat weight, which were highly correlated with body weight, the absolute weight of abdominal fat is almost independent of body weight (Cahaner and Nitsan, 1985; Cahaner et ah, 1986; Leenstra, 1986). Also in the current study, the correlations between pen means for abdominal fat and body weight (data combined over genotypes, sexes and three replicates per genotype and sex, a total of 30 pens per temperature) were very low (r = .08, P > .5) at the low and normal temperatures, and only slightly higher at the high temperature. The correlation coefficients between body weight and breast meat or griller weight were, however, over .95 (P < .001).
Because abdominal fat is independent of body weight, similar results and conclusions were obtained for absolute and relative amount of abdominal fat. The conclusions drawn for abdominal fat are similar to those for total body fat content (Leenstra and Cahaner, 1991; Cahaner and Leenstra, 1992), due to the high correlation between the two traits (Cahaner et ah, 1986; Keren-Zvi et ah, 1990; about .7 between means of independent samples from each pen in the present study; P < .001). At the high temperature, body weight was affected by a three-way interaction between age, sex, and the contrast between genotypes selected for fast growth (WN and WI) and those selected for leanness (FC and LF). From 6 to 8 wk, females gained significantly more weight than males in the WN and WI genotypes, but only slightly more in the FC and LF
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750
P
GENOTYPE BY TEMPERATURE INTERACTIONS IN BROILERS
these genotypes were heavier, females had a similar (LF and HF) or higher (FC) absolute breast meat yield. In the weightselected genotypes (WN and WI), the advantage of females over males in body weight at the high temperature (about 12%), together with a similar advantage in BMP, resulted in 26% more breast meat (240 versus 190 g) in females than in males. Because breast meat is the most valuable part of the broiler's carcass, this further accentuates the economical importance of the conclusion (Cahaner and Leenstra, 1992) that female broilers should be preferred over males when modern commercial broilers are to be raised at high environmental temperatures.
REFERENCES 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. Cahaner, A., and F. R. Leenstra, 1992. 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. Poultry Sci. 71: 1237-1250. Cahaner, A., and Z. Nitsan, 1985. Evaluation of simultaneous selection for live body weight and against abdominal fat in broilers. Poultry Sci. 64: 1257-1263. Cahaner, A., Z. Nitsan, and I. Nir, 1986. Weight and fat content of adipose and non-adipose tissues in broilers selected for or against abdominal adipose tissue. Poultry Sci. 65:215-222. Genstat, 1987. Genstat 5 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. Keren-Zvi, S., I. Nir, Z. Nitsan, and A. Cahaner, 1990. Effect of dietary concentrations of fat and energy on fat deposition in broilers divergently selected for high or low abdominal adipose tissue. Br. Poult. Sci. 31:507-516. Leclercq, B., 1988. Genetic selection of meat-type chickens for high or low abdominal fat content. Pages 25-40 in: Leanness in Domestic Birds: Genetic, Metabolic and Hormonal Aspects. B. Leclercq and C. C. Whitehead, ed. Butterworths, London, England. Leenstra, F. R., 1986. Effect of age, sex, genotype and environment on fat deposition in broiler chickens. World's Poult. Sci. J. 42:12-25. Leenstra, F. R., 1988. Selection for leanness: results of the Spelderholt experiment. Pages 59-69 in: Leanness in Domestic Birds: Genetic, Metabolic and Hormonal Aspects. B. Leclercq and C. C. Whitehead, ed. Butterworths, London, England.
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genotypes (Figure 1; Cahaner and Leenstra, 1992). This interaction became more complex with regard to abdominal fat. Although weight gain of HF chicks was similar to that of LF and FC, AFP was much higher in HF chicks. The interaction also reflected surprisingly higher AFP of LF males than females at 6 wk, and a similarly exceptional situation in the HF genotype at 8 wk. No similar changes were observed at the other two temperatures, nor for the other genotypes. It is possible that the changes due to direct selection on AFP at normal temperatures resulted in different patterns of accumulation of abdominal fat in males and females within the HF and LF genotypes at the high temperature. This is in contrast to the FC genotype, which is lean due to selection for improved feed efficiency. Within each sex, FC chicks had the same AFP at all temperatures and ages. In contrast to the fat measurements, results for BMP were not similar to those obtained for body protein content (Leenstra and Cahaner, 1991; Cahaner and Leenstra, 1992). These traits are almost independent [a correlation of about .2 (P > .3) between means of independent samples from each pen in this study], apparently because BMP is not an indicator of total protein, but rather a reflection of the distribution of muscles, i.e., body conformation. Because breast meat is in general more valuable than other muscle tissues, economical considerations of broiler production should be based on breast yield rather than on body protein content. Moreover, the correlations between BMP and body protein content were lower (.0 to .3, P > .1) than those between BMP and body fat content or AFP, especially among females (.5 to .7, P < .005). Therefore, leanness rather than high body protein content is a good indicator for high breast meat yield. Within each temperature, the sex difference in BMP was independent of age and body weight. It indicates that the increase in the advantage of females over males with regard to BMP when temperature increased was indeed due to higher temperature. Higher BMP in females than in males at the high temperature was found in LF, HF, and FC, and although males of
2005
2006
LEENSTRA AND CAHANER
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. Tawfik, E. S., A.M.A. Osman, M. Ristic, W. Hebeler, and F. W. Klein, 1989. Einfluss der Stalitemperatur auf Mastleistung, Schlachtkorperwert und Fleischbeschaffenheit von Broilern unterschied-
lichen Alters und Geschlechts. 2. Mitteilung: Schlachtkorperwert. Arch. Geflugelkd. 53: 235-244. Whitehead, C. C, 1988. Selection for leanness in broilers using plasma lipoprotein concentration as selection criterion. Pages 41-58 in: Leanness in Domestic Birds: Genetic, Metabolic and Hormonal Aspects. B. Leclercq and C. C. Whitehead, ed. Butterworths, London, England.
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ABSTRACT Male and female broiler chicks from five different broiler crosses (WI = Israeli chicks selected for increased body weight; LF and HF = Israeli chicks selected for low and high abdominal fat, respectively; FC and WN = Dutch chicks selected for improved feed conversion and increased body weight, respectively) were raised at low, normal, or high temperature. Slaughter yield, amount of breast meat, and abdominal fat were determined at 6 wk of age in all groups and at a body weight of 2,360 g for males and 1,965 g for females in the low- and normal-temperature groups, and at 8 wk in the hightemperature groups. Temperature, genotype, and sex influenced both absolute and relative weights of carcass, breast meat, and abdominal fat. Temperature had a negative effect on breast meat yield. Males were affected more by high temperature than females. A significant interaction between temperature and sex for breast meat yield was caused by a low yield for males at the high temperature. A similar interaction for proportion of abdominal fat was caused by a high fat content in males reared at the high temperature. Slaughter yield and especially yield of breast meat were highest in FC chickens in all comparisons. (Key words: broilers, genotypes, temperatures, slaughter yield, interactions) 1992 Poultry Science 71:1994-2006
(Howlider and Rose, 1989; Tawfik et ah, 1989). Selection and management of broilers is Leenstra and Cahaner (1991) and Caincreasingly aimed at a high meat yield haner and Leenstra (1992) reported on and low fat deposition. In general, lean- growth rate, feed conversion, and cheminess, higher meat yield, and a favorable cal composition of Dutch and Israeli feed efficiency coincide in selection experi- broiler crosses descending from lines ments (Cahaner, 1988; Leclercq, 1988; selected for increased body weight gain, Leenstra, 1988; Whitehead, 1988). Carcass improved feed conversion, and high or composition and meat yield are also low abdominal fat content, reared at low, dependent on environmental temperature. normal, or high temperature. Genotype At high temperatures, meat yield and and temperature had a significant effect especially yield of breast meat are reduced on weight gain, carcass composition, and feed and protein efficiency. In comparisons at equal age and at equal final body weight, chickens selected for improved Received for publication May 13, 1992. feed conversion had the highest feed and Accepted for publication August 13, 1992. INTRODUCTION
1994
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The Hebrew University of Jerusalem, Faculty of Agriculture, P.O. Box 12, 76100 Rehovot, Israel
GENOTYPE BY TEMPERATURE INTERACTIONS IN BROILERS
MATERIALS AND METHODS The effects of low, normal, and high temperatures on body weight, body composition (protein and fat content), and feed and protein efficiency of the chicks used for the present study, as well as details regarding genetic groups, temperatures, diet, and housing, were presented by Leenstra and Cahaner (1991) and
1 Centre for Poultry Research and Information Services (COVP) "Spelderholt", Agricultural Research Department (DLO), Ministry of Agriculture, Nature Management, and Fisheries, 7360AA Beekbergen, The Netherlands.
Cahaner and Leenstra (1992). The current study concentrates on the effects of genotype, sex, and temperature on yield characteristics. Chickens Five different genetic groups (genotypes) were used. Three were of Israeli origin and two of Dutch origin. All chicks resulted from a cross between Cornish (broiler sire) chickens and White Plymouth Rock (broiler dam) chickens. The Israeli chicks descended from a 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 high body weight gain (WN) (Leenstra, 1988). All eggs were incubated and hatched simultaneously at COVP-DLO.1 Housing and Management The chicks were housed on chopped straw 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 from 6 wk of age onwards. The pens were arranged in rooms. In total, nine rooms were available. Ten pens, one pen for males and one for females from each of the five genotypes, were used per room. Lighting was continuous on the 1st day after hatch and intermittent (1 h light, 3 h darkness alternating) thereafter. The chicks received ad libitum access to a pelleted broiler diet with 3,203 kcal metabolizable energy and 215 g of crude protein/kg of diet. Climate The chicks were reared at three temperature schedules: low (gradually decreasing from 33 C at hatch to 15 C from 5 wk of age onwards); normal (gradually decreasing from 33 C at hatch to 20 C from 6 wk of age onwards (Leenstra and Cahaner, 1991); high (33 C from hatch to 2 wk of age and 32
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protein efficiency regardless of temperature regimen. Interactions between genotype and temperature were clearly present for weight gain, protein deposition, and feed and protein efficiency, but were less evident for fat deposition. At the low temperature, the Dutch chickens had a higher weight gain and protein deposition than those derived from Israeli strains; at the normal temperature, the Israeli chickens gained more weight and protein. Irrespective of country of origin, genotypes with the highest growth rate at the low or normal temperature were most affected by the high temperature, and males were affected more than females. Genotypes selected for a favorable feed conversion or for low or high abdominal fat content were less affected by the high temperature. Broiler production is increasing throughout the world and processing yield and deboned meat yields are becoming important because of market demands with demographic changes. Based on the interactions found between genotype, temperature, and sex for weight gain and carcass composition (Leenstra and Cahaner, 1991; Cahaner and Leenstra, 1992), main effects and interactions can also be expected for slaughter yields. In the present study the effects of environmental temperature, genotype, and sex, and their interactions on slaughter yield, breast yield, and amount of abdominal fat of the Dutch and Israeli genotypes mentioned above were evaluated.
1995
1996
LEENSTRA AND CAHANER
C thereafter). Relative humidity was kept at 60% for all groups throughout the experiment. Three rooms were used for each temperature schedule. Measurements
Statistical Analysis The experiment had a split-plot design, with temperature regimens assigned to rooms as the main plots, and the genotype by sex combinations assigned to pens as
Y = u + T + e r + G + S + TG + TS + GS + GTS + e p + ec. [1] The effect of T was tested against er, the between-rooms error term. All other effects were tested against e p , the between-penswithin-room error term. The expression ec is the between-chicks-within-pen error term, which was not needed to test the effects in the present study. The slaughter yields at EQBW calculated for each of the pens at the low and normal temperature were analyzed by a .similar model, but without e0 as only pen means were available. At the high temperature, the target weight was not reached. The effects of age (A), genotype, sex, and their interactions on chicks sampled at 6 or 8 wk at the high temperature were examined by ANOVA with the model: Y + n + e r + G + S + GS + e p + A + GA + SA + GSA + e s + ec. [2] The effects of age and the interactions with age were tested against the error term between-samples-within-pen (es). The effects of genotype and sex on yields at each temperature-age combination separately were examined by ANOVA with the model: Y = n + e r + G + S + GS + e p + ec.
[3]
Each room was considered as a block (er) and all the effects were tested against e p . The yields at EQBW calculated for each of
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The 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 low- and normal-temperature groups and from 2 to 8 wk (55 days) in the high-temperature groups. Three birds from each pen were used to determine slaughter yields at 6 wk of age. Because within each sex, WN and WI chicks at the low temperature were heavier at 6 wk, the other groups at the low and normal temperature were raised to 7 wk, when again three birds per pen were taken to determine slaughter yields. This procedure allowed estimation of slaughter yields for the low and normal temperature at a similar body weight (EQBW, 2,360 g for males and 1,965 g for females) by interpolation per pen between data for 6 and 7 wk. The chicks reared at the high temperature were kept to 8 wk of age, in an attempt to finish them at a body weight that the groups reared at low or normal temperature had at 6 wk of age, when three birds per pen were slaughtered. The chickens to be slaughtered were deprived of feed for 8 h and weighed individually before slaughter and processing. The chickens were stunned, bled, and plucked in the COVP-DLO pilot plant. Head and feet were removed and afterwards each chicken was packed in a plastic bag and chilled for 10 to 24 h at 0 C. From each chicken, the abdominal fat (fat surrounding the gizzard included), and the breast meat were removed and weighed. Also griller weight (the weight of the empty carcass with neck, but without giblets and abdominal fat) was determined. Absolute weights and griller, breast meat, and abdominal fat as proportion of body weight were subjected to statistical analysis.
secondary plots. The temperature regimens were distributed at random among the rooms. In each room, all 10 genotype and sex combinations were randomly distributed among the pens. Griller, breast meat, and abdominal fat as proportion of body weight were distributed normally, and consequently no arc sine transformations were required. The effects of temperature (T), genotype (G), and sex (S), and their interactions on an individual chick (Y) were examined for each of the measurements at 6 wk of age by ANOVA with the model:
GENOTYPE BY TEMPERATURE INTERACTIONS DM BROILERS
RESULTS Body weight of the slaughtered chicks and the absolute and relative weight of the griller, breast meat, and abdominal fat were analyzed by several models. Levels of significance [Model 1] of the effects of temperature, genotype, and sex and their interactions at 6 wk of age, of contrasts between temperatures, and of contrasts between sources of genetic differences (genetic contrasts), are given in Table 1. Levels of significance [Model 2] of the effects of age (6 versus 8 wk), genotype, and sex, their interactions, and of the genetic contrasts for chicks reared at the high temperature are given in Table 2. Mean body weight by genotype and sex within age, and levels of significance of the main effects, interactions, and the genetic contrasts [Model 3] are presented in Table 3. Griller, breast meat, and abdominal fat as proportion of body weight by genotype and sex at 6 wk, at EQBW (low and normal temperature), and at 8 wk (high temperature), and all levels of significance [Model 3], are presented in
Tables 4 to 6. Absolute weight of griller, breast meat, abdominal fat, and live body weight, for the normal temperature groups (at 6 wk), and the high temperature groups (6 and 8 wk) are presented in Figure 1. Body Weight At 6 wk, a temperature by genotype interaction was found (Table 1), because at the low temperature the difference between the weight-selected groups (WN and WI) and those selected for leanness (FC and LF) was much larger than at the normal or high temperature. The interaction between temperature and sex resulted from the similar BW of males and females at the high temperature versus the usual advantage of about 15% of males over females at the low and normal temperature (Table 3, Figure 1). At the high temperature, the sex effect interacted with age and genotype (Table 2). The WN and WI females maintained an advantage of about 70 g over FC and LN females at both ages, whereas males from all genotypes had a similar BW at 6 wk. At 8 wk, WN and WI males had a lower BW than FC and LF males, and than WN and WI females (Table 3, Figure 1). Within each sex, WN and WI chicks at the low temperature were the heaviest at 6 wk (Table 3). Males averaged 2,360 g and females 1,965 g. These mean body weights were used for comparisons of EQBW. By keeping the other groups at low and normal temperature until 7 wk of age, they almost all reached or surpassed this target weight. Griller Differences in absolute griller weight were almost identical to differences in live BW (Tables 1 and 2). This could be expected, as griller was about 65% (between 631 to 693 g/kg) of live BW (Table 4). The proportion of griller (GRP) at 6 wk was affected by genotype and temperature (Table 1). In the high temperature, age (6 versus 8 wk) did affect GRP (Table 2). Four of the genotypes had a similar GRP, but HF means were lower in all temperature by sex by age combinations. At 6 wk, GRP values were higher at the high than at the low and normal temperatures. From 6 to 8 wk at the
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the pens at the low and normal temperature were analyzed by a similar model, but without ec. Three contrasts between sources of genetic differences were evaluated. The effects of selection goal (WT - LN; body weight or leanness) and of origin of the genotypes (IS - NL; Israel or The Netherlands) and their interactions with other main factors were tested by estimating the contrasts WI + WN - LF - FC and WI + LF WN - FC, respectively. As the HF chicks did not have a Dutch counterpart, they were not incorporated in these contrasts. The contrast HF - LF was evaluated to examine the effect of carcass fat content in chicks from the same origin and with similar growth rate. In ANOVA with Model 1, the contrasts between low and normal temperatures (LT - NT) and between normal and high temperatures (NT - HT) at 6 wk of age were evaluated. All statistical analyses were done with the Genstat program (Genstat, 1987). Main effects, contrasts, and interactions were considered significant if P < .05, unless otherwise stated.
1997
1998
LEENSTRA AND CAHANER
TABLE 1. Level of significance (P values) for the effects of temperature (T), genotype (G), sex (S), their interactions, and of specific contrasts on body weight and on absolute and relative weight of griller (empty carcass with neck and without giblets and abdominal fat), breast meat, and abdominal fat in chickens of 6 wk of age Source of variance1 LT - N T N T - HT G WT - LN IS - NL HF - LF
LT - NT x G NT - HL x G T x WT - LN T x IS - NL T x HF - LF
Breast meat Weight Proportion <.001 <.0Ol .003 .043 <.001 .002 .047 <.001 <.0Ol <.001 .071
<.001
<.001
.016
T x S
<.001
<.001
LT - NT x S NT - HT x S G xS
<.001
<.001
<.001 .061 <.0Ol
.088
.091
.067
WT - L N x S
IS - NL x S HF - LF x S T x G xS LT - NT x G x S NT - HT x G x S T x WT - LN x S T x IS - NL x S T x HF - LF x S
.098
.080 .071
<.001
.014
Abdominal fat Weight Proportion <.001
. . -2
<.001 <.001 <.001
. .. <.001 <.001
<.001 <.001 .002
<.001 <.001 .099
.043 <.001 .069
.011
.078
.002 .006
.073
.083
.. .
.115 .081
.099
.103
.052
.050
.013
.019
.096
a
LT - NT and NT - HT = specific contrasts between low and normal, and between normal and high temperature, respectively. WT - LN, IS - NL, and HF - LF = specific contrasts for selection goal (weight versus feed efficiency and low abdominal fat), origin (Israel versus The Netherlands), and carcass fatness (high versus low abdominal fat). 2 P > .1.
high temperature, GRP increased in all genotype by sex combinations by an average of 23 g/kg (Table 4). The differences between sexes were not consistent, although on average males had a slightly higher GRP. At EQBW (only for the lowand normal-temperature groups), the ranking of genotypes with regard to GRP was not changed, but the advantage of FC chickens over the other genotypes became more evident (Table 4). Breast Meat The main effects and their interactions affected the absolute weight of breast meat
at 6 wk in a way similar to live body weight (Table 1). However, at the high temperature (Table 2), the effects of sex and of the interaction between genotype and age were significant for the absolute weight of breast meat, but they were not significant for body weight. At the high temperature, females had more breast meat than males. Strain WI ranked first and FC ranked last at 6 wk, whereas the order was reversed at 8 wk (Figure 1). With regard to the proportion of breast meat (BMP), the temperature by sex interaction at 6 wk was the only significant interaction (Table 1). The increase in temperature reduced BMP, but the effect on
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S T x G
Griller Body _ weight Weight Proportion <.001 <.001 005 .004 .014 <.001 <.001 005 <.001 <.O01 001 <.001 <.001 .061 .047 001 <.001 <.001 060 <.001 .002 .018 .025
1999
GENOTYPE BY TEMPERATURE INTERACTIONS IN BROILERS
TABLE 2. Level of significance of the effects of genotype (G), sex (S), age (A; 6 versus 8 wk) and their interactions, and of the genetic contrasts for selection goal (WT - LN), origin (IS - NL), and carcass fatness (HF - LF), for body weight, and absolute and relative weight of griller (empty carcass with neck, without giblets, and abdominal fat), breast meat, and abdominal fat of chickens reared at high temperature Source of variance1
Griller Body _ weight Weight Proportion
Breast meat Weight Proportion
<.001 W T - LN IS - NL HF - LF
001
S
.085 .024
.074 .017
<.001 .098 .060 .095
<.001 .087 .062 .046
.064 .031
.068 .026
<.001
.057
001 055 .045
<.001 .033 .023 .020
<.001 .080 .065 .024
<.001
<.001
<001 .012 .013 .009
<.001 .004 .056 .026
<.O01
.050 .046
.088
.028
.063 .018
iWT - LN, IS - NL, and HF - LF = specific contrasts for selection goal (weight versus feed efficiency and low abdominal fat), origin (Israel versus The Netherlands), and carcass fatness (high versus low abdominal fat). 2P > .1.
were similarly affected by temperature, genotype, sex, and their interactions (Tables 1 and 2). At 6 wk, the three-way interaction temperature by genotype by sex had a low probability level, due to a significant interaction between the NT - HT temperature contrast and the IS - NL genetic contrast (Table 1). This interaction was caused mainly by male LF chickens at the high temperature, which had an exceptionally high AFP, even higher than their female counterparts, whereas WN males were the only group with an AFP lower at the high temperature than at the normal and low temperature (Table 6). However, no similar trend was observed in the other pair of Israeli and Dutch genotypes (WI and FC). Females had a similar mean AFP at the low and normal temperature and 10% less at the high temperature. The temperatures had the opposite effect on males; in most Abdominal Fat genotypes the AFP of males increased with temperature. The average AFP in males was Absolute weight of abdominal fat, and the proportion of abdominal fat (AFP), 12% lower than AFP in females at the high
males was much larger than on females (Table 5). At the low temperature both sexes had the same mean BMP (135 g/kg); at the normal temperature, BMP of females was only slightly lower (133 g/kg) but males were down to an average of 129 g/kg. The advantage of females over males in BMP was more pronounced at the high temperature (128 versus 116 g/kg at 6 wk and 138 versus 124 g/kg at 8 wk). The increase of BMP with age at the high temperature was highly significant (Table 2). Within genotype and temperature, the differences between males and females were similar at 6 wk, EQBW, and 8 wk (Table 5). The HF chicks had the lowest BMP at all temperatures and ages, and FC chicks had the highest BMP in most cases. This was most evident at EQBW under normal temperature.
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G x S WT - LN x S IS - NL x S HF - LF x S A G x A WT - LN x A IS - NL x A HF - LF x A G x Sx A WT - LN x S x A IS-NLxSxA HF-LFxSxA
.003
Abdominal fat Weight Proportion
2000
LEENSTRA AND CAHANER
TABLE 3. Body weight prior to slaughter at 6 wk of age for chickens reared at low, normal, or high temperature, at 7 wk for chickens reared at low and normal temperature, and at 8 wk for chickens reared at high temperatures and results of the analysis of variance
Genolypei
Sex2
HF HF LF LF FC FC WN WN WI WI SED4 HF LF FC WN WI SED
M F M F M F M F M F M M M M M M M
Low
6 wk Normal High
Low
7 wk Normal
2,007 1,697 1,946 1,798 1,898 1,682 2,070 1,774 2,161 1,820 67 1,852 1,872 1,790 1,922 1,991 47
(8) 2,437 1,944 2,439 2,085 2,533 2,007 ND3 ND ND ND ND 2,190 2,262 2,270 ND ND ND
2,375 2,025 2,419 2,003 2,115 1,932 2,547 2,062 ND 2,165 ND 2,200 2,211 2,074 2,305 ND ND
ND ND ND ND ND ND ND ND ND
ND ND ND ND ND ND ND ND ND
8 wk High
1,370 1,328 1,356 1,295 1,259 1,260 1,267 1,382 1,348 1302 100 1,349 1,325 1,260 1,324 1,325 70
<.001 <.001
.006 .001 .036
<.001 .010 .005 .010 .027
<.001 .054 .101
.5
1,887 1,723 1,825 1,625 1,737 1,707 1,639 1,785 1,492 1,710 79 1,805 1,725 1,722 1,712 1,601 56 .033 .107
.005 .002
1
HF and LF = Israeli crosses, selected for a high or a low amount of abdominal fat, respectively; FC = Dutch cross, selected for improved 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. 2 M = male; F = female. 3 ND = not done. 4 SED = standard error of differences between two means. sp > .1. 6 WT - LN, IS - NL, and HF - LF = specific contrasts for selection goal (weight versus feed efficiency and low abdominal fat), origin (Israel versus The Netherlands), and carcass fatness (high versus low abdominal fat).
temperature, whereas at the low and normal temperatures it was lower by 40 to 50% (Table 6), resulting in a significant temperature by sex interaction (Table 1). Genotypes ranked, in general, according to the criteria used for selection (Table 6). The HF birds had the highest AFP, and LF and FC were the leanest genotypes (with the exception of LF males at the high temperature). The differences between
genotypes in AFP at the low and normal temperatures at EQBW were similar to those at 6 wk of age. At the high temperature, a genotype by sex by age interaction was evident. The interaction resulted mainly from the high AFP in LF males compared with LF females at 6 wk, and a similar effect in the HF genotype at 8 wk (Table 6). In WN and WI, the higher AFP in females compared with
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~ e of variation oou Genotype WT - LN« IS - NL HF - L F Sex Genotype x sex W T - LN < sex IS - NL x sex HF - L F x sex
2,035 1,705 1,995 1,822 2,039 1,716 2,393 1,936 2,329 1,992 47 oi F + F 1,869 + F 1,908 + F 1,877 + F 2,165 + F 2,161 + F 33
GENOTYPE BY TEMPERATURE INTERACTIONS IN BROILERS
2001
TABLE 4. Griller (empty carcass, with neck and without giblets and abdominal fat) as proportion of body weight at 6 wk of age for chickens reared at low, normal, or high temperature, at equal body weight (EQBW) for chickens reared at low and normal temperature, and at 8 wk of age for chickens reared at high temperature and results of the analyses of variance within temperature by age combinations
Genoi•ype 1
Sex2
HF HF LF LF FC FC WN WN WI WI SEEP HF LF FC WN WI SED
M F M F M F M F M F
Low
6 wk Normal High
Low
EQBW Normal
8 wk High
635 640 647 652 660 660 647 655 649 652 4.5 637 650 660 651 650 3.2
661 661 686 689 691 682 693 693 690 685 7.9 661 687 687 693 688 5.6
(v /\ev\
of variation Geno!ype WT - LN4 IS - NL HF -- LF Sex Genotype x sex
641 628 646 645 647 653 640 647 649 648 6.5 635 645 650 644 648 4.6
635 634 655 652 655 656 651 631 652 649 7.2 635 653 656 641 651 5.1
650 643 660 666 665 653 662 659 675 667 8.3 646 663 659 660 671 5.9
Sniirr e
.086 . .5
.040
.011
.040
.002
<.001
' !o34
.093 .013
.017
.089 .013
<.001
.101
1HV and T.F -
esnertivelv: FC —
Dutch cross, selected for improved 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. 2 M = male; F = female. 3 SED = standard error of differences between two means. 4 WT - LN, IS - NL, and HF - LF = specific contrasts for selection goal (weight versus feed efficiency and low abdominal fat), origin (Israel versus The Netherlands), and carcass fatness (high versus low abdominal fat). 5 P > .1.
males was more pronounced at 8 than at 6 wk. At 8 wk, HF males had the highest AFP, whereas males from all other genotypes had a similar AFP. Among females, AFP values ranked from HF through WN, WI, LF, and FC with the lowest mean AFP. DISCUSSION At the low and normal temperatures, the genotypes were compared within each
sex at EQBW. The ranking of the genotypes and the differences among them at EQBW were either similar or slightly larger than those at equal age (6 wk) in all three yield measurements. The conclusions to be presented for equal age are thus also valid for EQBW. The relation between GRP and AFP was not symmetric. Griller as proportion of body weight was not higher in the LF and FC genotypes than in the WN and WI genotypes at the low and normal tempera-
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631 632 644 635 652 645 651 631 652 649 9.9 M oi F M + F 632 M + F 639 M + F 649 M + F 641 M + F 651 M+ F 7.0
2002
LEENSTRA AND CAHANER
TABLE 5. Breast meat as proportion of body weight at 6 wk of age for chickens reared at low, normal, or high temperature, at equal body weight (EQBW) for chickens reared at low and normal temperature, and at 8 wk of age for chickens reared at high temperature; results of the analyses of variance within temperature by age combinations
Genotype
1
Sex*
Low
6 wk Normal High
EQBW Normal Low
8 wk High
Co- /Irirl
131 133 134 132 135 144 136 131 141 137 6.2 oi• F + F 132 + F 133 + F 140 + F 134 + F 139 + F 4.4
128 124 129 136 129 139 128 135 129 133 4.5 126 133 134 131 131 3.2
111 126 114 130 120 124 114 130 123 130 6.8 118 122 122 122 127 4.8
132 133 136 137 139 148 136 131 140 137 4.1 133 137 144 134 139 2.9
126 134 132 134 141 147 132 140 131 135 3.4 130 133 144 136 133 2.4
119 135 125 134 130 147 122 141 123 134 5.1 127 130 139 131 129 3.6
.4 .037 .005 .096 Genotype .081 WT - LN5 .029 .006 IS - NL H F - LF !053 <.001 .012 .001 Sex .029 Genotype x sex 1 HF and LF = Israeli crosses, selected for a high or a low amount of abdominal fat, respectively; FC = Dutch cross, selected for improved 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. 2 M = male; F = female. 3SED = standard error of differences between two means. *P > .1. 5 WT - LN, IS - NL, and HF - LF = specific contrasts for selection goal (weight versus feed efficiency and low abdominal fat), origin (Israel versus The Netherlands), and carcass fatness (high versus low abdominal fat).
tures, despite the lower total carcass fat content (Leenstra and Cahaner, 1991) and lower AFP in LF and FC chicks. At the high temperature, FC chicks had the lowest body fat content (Cahaner and Leenstra, 1992), but they did not have the highest GRP. On the other hand, the HF chicks with their high AFP and high body fat content in all temperature by sex by age combinations had the lowest GRP. At the low and normal temperature, AFP in HF chicks compared with WN and WI chicks was higher by about 11 g/kg and
their GRP was lower by about 13 g/kg chicks. Thus, the exclusion of abdominal fat from the griller can account for the differences between HF and the two weight-selected genotypes. The lack of a similar difference in GRP between the weight-selected genotypes (WN and WI) and the lean ones (FC and LF) indicates that AFP is not the only important factor in GRP. Consequently, selection against abdominal fat has an advantage only if lean meat yield and not yield of the complete carcass is the production goal.
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HF M HF F LF M LF F FC M F FC WN M F WN M WI WI F SED3 M HF M LF M M FC M WN M WI SED M Source of variation
2003
GENOTYPE BY TEMPERATURE INTERACTIONS IN BROILERS
TABLE 6. Abdominal fat as proportion of body weight at 6 wk of age for chickens reared at low, normal, or high temperature, at equal body weight (EQBW) for chickens reared at low and normal temperature, and at 8 wk of age for chickens reared at high temperature and results of the analyses of variance 6 wk Genoltype 1
Low
Sex*
Normal
EQBW
Low
High
8 wk
Normal
High 47.3 41.7 23.3 31.7 19.5 22.5 20.8 36.0 18.1 34.7
fir /VM
HF LF FC WN WI
SED SOIITCe
+ + + + + +
F
32.1 42.1 14.3 28.1 17.1 23.6 23.3 36.4 22.0 32.8
35.5 46.3 16.5 27.8 19.1 25.0 25.1 33.1 21.9 33.3
39.9 41.7 30.2 24.0 19.4 25.2 20.3 30.4 22.9 27.5
38.1 46.2 18.1 23.8 19.8 23.7 23.3 36.4 22.0 32.8
38.5 49.1 19.5 27.9 19.8 27.8 27.5 36.0 21.9 32.7
4.0
2.0
4.0
1.9
1.5
5.3
F F F F F
37.1 21.2 20.4 29.8 27.4
40.9 22.1 22.0 29.1 27.6
40.8 27.1 22.3 25.4 25.2
42.2 21.0 21.7 29.8 27.4
43.8 23.7 23.8 31.7 27.3
44.5 27.5 21.0 28.4 26.4
M + F
2.8
1.4
2.8
1.3
1.1
3.8
<.001 <.001
<.001 <.001
<.001
<.001 <.001
<.001
<.001
<.001 .090 .102 .075 .043
<.O01
<.001 <.001 .045 <.0Ol <.001
of variation
Genol•ype WT - LN* I S - NL H F - - LF
Sex Genotype x sex WT - LN :< sex IS - NL x sex H F - LF x sex
,5
<.001 <.0Ol
<.001
.043
<.001
<.001 .006 .051 .072 .082
1
HF and LF = Israeli crosses, selected for a high or a low amount of abdominal fat, respectively; FC = Dutch cross, selected for improved feed conversion between 3 and 6 w k of age; WN and WI = crosses originating from The Netherlands and Israel, respectively, selected for high 6-wk body weight. 2 M = male; F = female. 3SED = standard error of differences between two means. 4 WT - LN, IS - NL, and HF - LF = specific contrasts for selection goal (weight versus feed efficiency and low abdominal fat), origin (Israel versus The Netherlands), and carcass fatness (high versus low abdominal fat). sp > .1.
The increased GRP at the high temperature compared with the low and normal temperatures at 6 wk of age, and the further increase in GRP between 6 and 8 wk, could not be attributed to reduced fat deposition because AFP was hardly affected by temperature at 6 wk, nor by age at the high temperature. Also body fat content, although decreased in females at the high temperature, was increased in
males (Cahaner and Leenstra, 1992) and therefore could not account for the higher GRP at the high temperature. The higher GRP at the high temperature was not associated with the reduced BW. At 8 wk of age, mean BW of some high temperature groups was similar to that of groups from the same genotype and sex at the normal temperature at 6 wk, and yet their GRP was higher. It therefore seems that
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M F M F M F M F M F M M M M M M
HF HF LF LF FC FC WN WN WI WI SEE>3
2004
LEENSTRA AND CAHANER
Breast meat
Griller
Abdominal fat
Offals + giblets
2.250 2,000 1,750 1,500 1,250 c
! 1,000
500
n V, V
n
2 2
250 0 HF LF FC WN WI Normal temperature 6 wk
HF LF FC WN WI High temperature 6 wk
HF LF FC WN WI High temperature 8 wk
FIGURE 1. Absolute weights of breast meat, griller (empty carcass with neck and without abdominal fat and giblets), abdominal fat, and the difference between these components and live body weight (offals and giblets) for male (left bar of each set) and female (right bar of each set) chicks of five genetic groups at 6 wk (normal and high rearing temperature) and 8 wk (high temperature) of age. HF and LF = Israeli crosses, selected for a high or a low amount of abdominal fat, respectively; FC = Dutch cross selected for improved feed conversion; WN and WI = crosses originating from The Netherlands and Israel, respectively, selected for high 6-wk body weight.
the proportion of other parts (feathers, intestines, and giblets), which were excluded from GRP, was reduced at the high temperature, especially from 6 to 8 wk of age, resulting in an increased GRP. Unlike griller and breast meat weight, which were highly correlated with body weight, the absolute weight of abdominal fat is almost independent of body weight (Cahaner and Nitsan, 1985; Cahaner et ah, 1986; Leenstra, 1986). Also in the current study, the correlations between pen means for abdominal fat and body weight (data combined over genotypes, sexes and three replicates per genotype and sex, a total of 30 pens per temperature) were very low (r = .08, P > .5) at the low and normal temperatures, and only slightly higher at the high temperature. The correlation coefficients between body weight and breast meat or griller weight were, however, over .95 (P < .001).
Because abdominal fat is independent of body weight, similar results and conclusions were obtained for absolute and relative amount of abdominal fat. The conclusions drawn for abdominal fat are similar to those for total body fat content (Leenstra and Cahaner, 1991; Cahaner and Leenstra, 1992), due to the high correlation between the two traits (Cahaner et ah, 1986; Keren-Zvi et ah, 1990; about .7 between means of independent samples from each pen in the present study; P < .001). At the high temperature, body weight was affected by a three-way interaction between age, sex, and the contrast between genotypes selected for fast growth (WN and WI) and those selected for leanness (FC and LF). From 6 to 8 wk, females gained significantly more weight than males in the WN and WI genotypes, but only slightly more in the FC and LF
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750
P
GENOTYPE BY TEMPERATURE INTERACTIONS IN BROILERS
these genotypes were heavier, females had a similar (LF and HF) or higher (FC) absolute breast meat yield. In the weightselected genotypes (WN and WI), the advantage of females over males in body weight at the high temperature (about 12%), together with a similar advantage in BMP, resulted in 26% more breast meat (240 versus 190 g) in females than in males. Because breast meat is the most valuable part of the broiler's carcass, this further accentuates the economical importance of the conclusion (Cahaner and Leenstra, 1992) that female broilers should be preferred over males when modern commercial broilers are to be raised at high environmental temperatures.
REFERENCES 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. Cahaner, A., and F. R. Leenstra, 1992. 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. Poultry Sci. 71: 1237-1250. Cahaner, A., and Z. Nitsan, 1985. Evaluation of simultaneous selection for live body weight and against abdominal fat in broilers. Poultry Sci. 64: 1257-1263. Cahaner, A., Z. Nitsan, and I. Nir, 1986. Weight and fat content of adipose and non-adipose tissues in broilers selected for or against abdominal adipose tissue. Poultry Sci. 65:215-222. Genstat, 1987. Genstat 5 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. Keren-Zvi, S., I. Nir, Z. Nitsan, and A. Cahaner, 1990. Effect of dietary concentrations of fat and energy on fat deposition in broilers divergently selected for high or low abdominal adipose tissue. Br. Poult. Sci. 31:507-516. Leclercq, B., 1988. Genetic selection of meat-type chickens for high or low abdominal fat content. Pages 25-40 in: Leanness in Domestic Birds: Genetic, Metabolic and Hormonal Aspects. B. Leclercq and C. C. Whitehead, ed. Butterworths, London, England. Leenstra, F. R., 1986. Effect of age, sex, genotype and environment on fat deposition in broiler chickens. World's Poult. Sci. J. 42:12-25. Leenstra, F. R., 1988. Selection for leanness: results of the Spelderholt experiment. Pages 59-69 in: Leanness in Domestic Birds: Genetic, Metabolic and Hormonal Aspects. B. Leclercq and C. C. Whitehead, ed. Butterworths, London, England.
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genotypes (Figure 1; Cahaner and Leenstra, 1992). This interaction became more complex with regard to abdominal fat. Although weight gain of HF chicks was similar to that of LF and FC, AFP was much higher in HF chicks. The interaction also reflected surprisingly higher AFP of LF males than females at 6 wk, and a similarly exceptional situation in the HF genotype at 8 wk. No similar changes were observed at the other two temperatures, nor for the other genotypes. It is possible that the changes due to direct selection on AFP at normal temperatures resulted in different patterns of accumulation of abdominal fat in males and females within the HF and LF genotypes at the high temperature. This is in contrast to the FC genotype, which is lean due to selection for improved feed efficiency. Within each sex, FC chicks had the same AFP at all temperatures and ages. In contrast to the fat measurements, results for BMP were not similar to those obtained for body protein content (Leenstra and Cahaner, 1991; Cahaner and Leenstra, 1992). These traits are almost independent [a correlation of about .2 (P > .3) between means of independent samples from each pen in this study], apparently because BMP is not an indicator of total protein, but rather a reflection of the distribution of muscles, i.e., body conformation. Because breast meat is in general more valuable than other muscle tissues, economical considerations of broiler production should be based on breast yield rather than on body protein content. Moreover, the correlations between BMP and body protein content were lower (.0 to .3, P > .1) than those between BMP and body fat content or AFP, especially among females (.5 to .7, P < .005). Therefore, leanness rather than high body protein content is a good indicator for high breast meat yield. Within each temperature, the sex difference in BMP was independent of age and body weight. It indicates that the increase in the advantage of females over males with regard to BMP when temperature increased was indeed due to higher temperature. Higher BMP in females than in males at the high temperature was found in LF, HF, and FC, and although males of
2005
2006
LEENSTRA AND CAHANER
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. Tawfik, E. S., A.M.A. Osman, M. Ristic, W. Hebeler, and F. W. Klein, 1989. Einfluss der Stalitemperatur auf Mastleistung, Schlachtkorperwert und Fleischbeschaffenheit von Broilern unterschied-
lichen Alters und Geschlechts. 2. Mitteilung: Schlachtkorperwert. Arch. Geflugelkd. 53: 235-244. Whitehead, C. C, 1988. Selection for leanness in broilers using plasma lipoprotein concentration as selection criterion. Pages 41-58 in: Leanness in Domestic Birds: Genetic, Metabolic and Hormonal Aspects. B. Leclercq and C. C. Whitehead, ed. Butterworths, London, England.
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