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Effects of Incubation Humidity and Hatching Time on Heat Tolerance of Neonatal Chicks: Growth Performance After Heat Exposure
Effects of Incubation Humidity and Hatching Time on Heat Tolerance of Neonatal Chicks: Growth Performance After Heat Exposure A.M.M. HAMDY, A. M. HENKEN, and W. VAN DER HEL Department of Animal Husbandry, Agricultural University, P.O. Box 338, 6700 AH Wageningen, The Netherlands A. G. GALAL and A.KJ. ABD-ELMOTY Department of Animal Production, Faculty of Agriculture, El-Minia University, Minia, Egypt
ABSTRACT Three experiments were performed with 300 neonatal Hisex Brown layer chicks in each. The chicks hatched from eggs incubated at a relative humidity (RH) of 55 or 45%. Within each RH group, two groups were separated based on hatching time (early and late hatch groups). After hatch, 60 chicks served as controls. The other chicks were exposed to 35, 37, or 39 C for 48 h. After exposure, a 4-wk experimental growing period started at Day 2 of age. Chicks exposed to the experimental temperature regimens for 2 days had lower body weights at the end of exposure and grew less than controls during the 1st wk afterwards. At Day 2 of age, chicks hatched from eggs incubated at 45% RH had higher body weights than clucks hatched from eggs incubated at 55% RH. These chicks also had higher body weight gain in the 1st and 2nd wk following exposure to 39 C than chicks hatched from eggs incubated at 55% RH. Chicks hatching late were heavier at Day 2 than early-hatching ones, but body weight gain was similar. Chicks exposed to the experimental temperature regimens had lower rectal temperatures than controls at the end of the 1st and 2nd wk. Incubation RH, hatching time, and sex did not affect feed intake, feed conversion, or rectal temperature. After exposure to 39 C, fewer chicks that had hatched from eggs incubated at low RH died compared with chicks that had hatched from the 55% RH group. Early-hatching chicks had a significantly higher risk of dying than late-hatching ones. (Key words: incubation, incubation humidity, hatching time, growth, mortality rate) 1991 Poultry Science 70:1507-1515
the time period between actual hatching and removal from the hatcher. The objective of the Body weight loss and mortality rates of present research was to evaluate the growth neonatal chicks are increased when they are performance of neonatal chicks after heat transported at high temperatures. After arrival exposure early in life. Chicks used hatched at a farm and placement at normal thermal from eggs incubated at one of two relative conditions, chicks that have survived exposure humidities (RH) and had stayed in the hatcher to high temperatures will eat and grow less and for a varying period of time after hatch. may still have a higher risk of dying than those exposed to lower temperatures (Ernst et ah, MATERIALS AND METHODS 1984; Henken et al, 1987). A high heat tolerance is therefore an important attribute. Chicks cope with heat by losing moisture Chicks and Pre-Experimental Conditions through evaporation. Chicks with a high water Three experiments were performed each content may therefore be relatively more heat using 300 neonatal Hisex Brown layer chicks.1 tolerant. Water content of neonatal chicks can chicks were be manipulated in two different ways: 1) by Within each experiment, 150 2 hatched from eggs incubated at 55 ± 2% RH varying incubation humidity and 2) by varying from Day 0 to 19, and the other 150 were hatchedfromeggs incubated at 45 ± 2% RH. At Day 19 all eggs were placed in one hatcher. Hatching time of each chick was recorded. After 'Euribrid, 5830 AA, Boxmeer, The Netherlands. ! Pas Reform, 7038 ZG, Zeddam, The Netherlands. opening the hatcher, two hatch groups were INTRODUCTION
1507
Downloaded from http://ps.oxfordjournals.org/ at University of Hong Kong on May 9, 2015
(Received for publication November 17, 1990)
1508
HAMDY ET AL.
Experimental Procedure After the exposure period of 48 h, the chambers were opened and the chicks collected. During the exposure period, no deaths had occurred. Then, in each experiment, 45 chicks of each group were allocated to one of three subgroups of 15 [an all-male group, an allfemale group, and a mixed-sex group (7 to 8 of each sex)]. Each subgroup (12 groups in total) was placed in a grower cage with feed (commercial starter)3 and water available for ad libitum consumption. These cages and those of the controls belonged to one battery line. Controls had access to feed and water from Day 1 onwards. This was to evaluate the effect of feed and water withdrawal as occurs during transport. Environmental temperature was maintained at 31 C during the 1st wk and was decreased thereafter in a stepwise-fashion by 2 C/wk to 25 C by the 4th wk. Light was on continuously. The vaccination schedule adopted was: Marek's disease (Day 1 of growing period, i.m.), infectious bronchitis [Day 2 of growing period, intraoccularly (i.o.)], infectious bursal disease (Day 12 of growing period, i.o.), and Newcastle disease (Day 18 of growing period, i.o.). The experimental growing period lasted 4 wk. Determinations and Statistics
3 CP = 20.8%; ME = 2,800 kcal/kg; calcium = .99%; and available phosphorus = .45%. 4 Dual Digital thermometer, Lieca B.V., 2280 AB, Rijswijk, The Netherlands.
Body weight of each chick (n = 240, 16 groups x 15 in each experiment) was determined every 5 to 7 days beginning at the start of the growing period (Day 2 of age). Feed intake, feed conversion (feed:gain), and rectal temperature4 (5 chicks) were determined each 5- to 7-day period per cage. The mortality rate was determined daily per cage. Gain and feed intake were expressed in grams per day, as weighings were not done each time exactly after 7 days. Gain within a week was calculated using data of chicks still alive at the end of that week. Feed intake was calculated taking into account number of days within each period and chicks alive at each day. The data on body weight at Day 2, gain, feed intake, feed conversion, and rectal temperature were subjected to analysis of variance (SAS Institute, 1985). Exposure history (heat exposure in the chambers, yes or no), incubation RH (low or normal), hatch group (early or late), and sex were included in the model as main factors. Interactions were analyzed initially, but removed from the model if not significant (P>.05). The data were analyzed for each experiment separately. Data on mortality rates were analyzed wifli a chi-square test. RESULTS
Body Weight and Gain Data on body weight at the start of the growing period after exposure and gain in each of the 4 wk are given in Table 1. Chicks having been exposed to the experimental temperature regimens in the chambers for 2 days had a lower (P<.001) body weight at the start of the growing period man control chicks. The largest difference between control and exposed groups was found in the 39 C experiment (an absolute difference in body weight of 8.9 g). In the 1st wk of the growing period exposed chicks had a lower (P<.05) gain than controls (-.3 g on average). In the 2nd wk after exposure, the difference in gain between controls and exposed chicks decreased, however chicks exposed to 39 C during the first 2 days of life still grew less than controls in this 2nd wk In the 3rd and 4th wk, control and exposed chicks had a similar gain (P>.05). Chicks from eggs incubated at low RH had a higher body weight at the start of the growing period in two of the three experiments and had a higher gain in the 1st and 2nd wk of the 39 C experiment. In the 3rd and 4th wk, no effect
Downloaded from http://ps.oxfordjournals.org/ at University of Hong Kong on May 9, 2015
established within each RH group: a group hatched early and a group hatched late. The average difference in hatching time between the two hatch groups was about 9 h. Fifteen of each hatch by RH combination (seven to eight of each sex) served as unexposed controls and were placed in grower cages in a poultry house at a normal temperature of 31 C. The other chicks (240) were placed in one of two identical climate respiration chambers (Verstegen et al., 1987), with chicks hatched early in one chamber and chicks hatched late in the other. Within each chamber, equal numbers of the two humidity groups and each sex were present. The chicks in both chambers were exposed to a constant (SE = ± .01) thermal regimen for 48 h of 35 (Experiment 1), 37 (Experiment 2), or 39 C (Experiment 3).
3
9.8 10.4 9.4 12.1 12.5 11.9
1.8b 2.5b 2.7 Y 6.6 7.4 6.6 Y
36.6 Y 34.5 Y 30.5 Y 1.9 2.6 3.1 a 6.8 7.4 7.6 X 9.9 10.2 9.6 12.1 12.4 11.8
10.1 10.2 9.7 12.6 12.5 11.5
37.6a 35.8 36. l x
Low
yi.9*37.4 X 39.4 X 2.1 a 2.7a 3.1 x 7.0 7.4 7.9X
No 36.9 b 36.0 33.8 Y 2.0 2.6 2.7 b 6.7 7.4 6.9 Y 10.0 10.4 9.5 12.6 12.7 11.6
Normal
Incubation humidity
Means for each factor within a row with no common superscripts differ significantly (P^.01).
Means for each factor within a row with no common superscripts differ significantly (PS.001).
!tr\
12.3 12.7 12.0
10.1 10.2 9.5
7.0 7.2 b 7.2
36.1 Y 34.6 Y 33.3 Y 1.9 2.5 b 3.0*
Early
1 1 1
1
3 3 3
L
Chick hatch
Root mean square error of the statistical model used.
There was a significant interaction (K.05) at 35 and 39 C between incubation humidity and hatch time with respect to body
In each experiment the statistical analysis was based on n = 240 with subtraction of the number of dead chicks we
x,Y
2
(Q 35 37 39 35 37 39 35 37 39 35 37 39 35 37 39
Yes
Exposure
'4deans for each factor within a row with no common superscripts differ significantly (P£.05).
A,B
a
Daily gain in Week 4
Daily gain in Week 3
Daily gain in Week 2
Daily gain in Week 1
Body weight at Day 2
Parameter1,2
Experimental temperature
TABLE 1. Least squares means of body weight at start of the growing period (at Day 2 of life) and dail
ded from http://ps.oxfordjournals.org/ at University of Hong Kong on May 9, 2015
1510
HAMDY BT AL.
early had a significantly higher risk of dying thantihosemat hatched later. Sex did not affect mortality rate. No deaths occurred in the 3rd and 4th wk. DISCUSSION
Chicks that were exposed to 39 C lost more uian 20% of their initial body weight in 48 h (Hamdy et al., 1991). Exposed chicks needed 2 wk to recover afterwards. These results are in agreement with those reported by Henken et al. (1987). Low RH during setting had no negative effect on body weight at two days of age. A low incubation RH seemed to be positive for body weight at Day 2. Chicks hatching late had a higher body weight at the Feed Intake and Feed Conversion start of the growing period than those hatching early. This may be due to the longer dehydraControl chicks ate more than exposed ones tion period in the hatcher of the chicks that (Table 2). After 1 or 2 wk this difference in feed hatched early. Fanguy et al. (1980) also intake between control and exposed groups was reported that delayed placement of chicks up clearly reduced. Incubation humidity, hatching to 64 h from hatching had a clear effect on time, and sex did not affect feed intake (P>.05). body weight gain until Week 4. The significant In die 3rd and 4th wk, male chicks began to eat interactions, on body weight at Day 2 and gain more than females, but not significantly (P>.05). in 1st and 2nd wk, between incubation RH and Exposure period, incubation humidity, hatching hatching time were due to larger weight time, and sex did riot affect (P>.05) feed differences within hatch groups in the 55% RH conversion with two exceptions (Table 3). than in the 45% RH groups. Chicks exposed to 35 C had a lower (P<.05) feed There is some disagreement as to the exact conversion than controls in the 2nd wk of the age at which rectal temperature of neonatal growing period. Incubation RH affected feed conversion significantly only in the 2nd wk, chicks becomes constant. Rectal temperature chicks from eggs from low RH having a lower of the chicks exposed to elevated temperatures feed conversion than chicks hatched from remained relatively low compared with the controls. It might be that neonatal chicks adapt normal RH. themselves relatively quickly when exposed to heat and mobilize all heat dissipation mechanisms. When placed at normal thermal condiRectal Temperature tions, chicks previously exposed to heat for a Chicks exposed to the experimental tempera- period of time still may be focused on heat ture regimens for 48 h had a lower rectal dissipation rather than on heat conservation. It temperature in the 1st (P<.01) and 2nd (PS.05) might also be that early heat exposure has wk of the growing period (Table 4). In the 3rd altered homeostasis or innate mechanisms that and 4th wk, rectal temperature differences were regulate rectal temperature. According to Freenot significant (P>.05). Incubation RH, hatching man (1965) rectal temperature becomes contime, and sex did not affect rectal temperature stant at about 12 days of age. with one exception. The mortality rate was high during the 1st wk after exposure to 39 C. Chicks exposed to 39 C were very weak afterwards and showed Mortality Rate no inclination to eat or drink. Chicks hatched Incubation RH affected mortality rates signif- from eggs incubated at low RH had a lower icantly in the 39 C experiment (Table 5). Chicks mortality rate than those hatched from eggs hatched from eggs incubated at low RH had a incubated at normal RH. Although chicks lower mortality rate during the beginning of the hatched from eggs incubated at 55% RH were 4-wk period than chicks hatched from eggs heavier at hatch than chicks hatched from eggs incubated at normal RH. Chicks that hatched incubated at 45%, this difference disappeared
Downloaded from http://ps.oxfordjournals.org/ at University of Hong Kong on May 9, 2015
of incubation RH on gain was found. Chicks hatched late were heavier (P<.001) than earlyhatched ones at the start of the growing period (2.7 g on average). Gain of the two groups was similar over 4 wk, although in the 1st and 2nd wk, chicks hatched early grew less than latehatched ones in two cases. In die 35 and 39 C experiments, there were significant (PS.05) interactions between relative humidity and hatching time with respect to body weight at Day 2 and gain in the 1st and 2nd wk. Initially, male and female chicks had comparable body weight (except in the 39 C experiment) and gain. After the 1st wk, however, males grew significantly faster than females.
2
6.4 Y 8.2 5.3 Y 14.8b 18.3 15.1 21.2 24.4 23.7 28.2 32.7 30.0
x
32.9 33.7 30.3
19J2a 18.4 16.7 25.5 24.1 25.4
94
8.9*
No 7.6 8.8 75 17.4 18.4 16.0 24.3 24.0 26.1 31.2 32.3 30.6
Low
17.3 18.7 15.9 23.7 24.5 25.1 31.1 33.3 30.7
29.9 33.0 29.5
29.9 34.0 29.7
7.7 9.2 7.7
Late
7.6 8.4 6.8 16.8 18.1 15.9 23.0 24.0 24.1
(el
Early
Chicks hatched
7.8 8.8 7.0 16.7 18.4 15.8 22.4 245 23.1
Normal
Incubation humidity
Means for each factor within a row with no common superscripts differ significantly (K.001).
In each experiment the statistical analysis was based on n = 16.
Root mean square error of the statistical model used.
1
35 37 39
(Q 35 37 39 35 37 39 35 37 39
Yes
Exposure
Means for each factor within a row with no common superscripts differ significantly (K.05).
x,Y
a,b
Daily intake in Week 4
Daily intake in Week 3
Daily intake in Week 2
Daily intake in Week 1
Parameter1
Experimental temperature
TABLE 2. Least squares means of daily feed intake per chick in each week an
ded from http://ps.oxfordjournals.org/ at University of Hong Kong on May 9, 2015
4.8 3.1 3.4 2.4b 2.5 2.4 2.4 2.4 2.5 2.5 2.6 2.5
(Q 35 37 39 35 37 39 35 37 39 35 37 39
2.7a 2.6 2.3 2.4 2.3 2.7 2.5 2.7 2.6
4.0 3.5 3.8
4.5 3.4 3.3 2.5 2.6 2.3 b 2.4 2.4 2.7 2.5 2.7 2.6
Low
2
4.3 32 3.8 2.6 2.5 2.4 a 2.4 2.3 2.4 2.5 2.6 2.5
Incubation hmnMHy Normal
Root mean square error of the statistical model used.
4.4 3.4 3.7 2.6 2.5 2.3 2.4 2.3 2.7 2.5 2.7 2.6
Chicks hatched Late
(g:g) 4.4 32 35 25 2.6 2.4 2.4 2.4 2.6 2.6 2.6 2.5
Early
'°Means for each factor within a row with no common superscripts differ significantly (PS.05).
Yes
Exposure No
*In each experiment the statistical analysis was based on n = 16.
a
Week
Experimental temperature
2 2 2
2 2 2
4
M
TABLE 3. Least squares means of feed conversion (feed:gain) during the growing perio
ded from http://ps.oxfordjournals.org/ at University of Hong Kong on May 9, 2015
4
3
2
1
2
41.25 8 41.08B 40.61 Y 41.44 b 41.59 41.57b 41.62 b 41.62 41.34
41.61 41.57 41.39
(Q 35 37 39 35 37 39 35 37 39
35 37 39
41.65 41.58 41.43
41.50 41.59 41.70* 41.67 41.64 41.41 41.63 41.63 41.41
41.67 41.63 41.46
Normal 41.44 41.33 40.86 41.50 41.66 41.58b 41.67 41.58 41.34
41.31 41.11 40.93
Low
41.51 A 41.36A 41.18 x 41.56a 41.66 41.72 s 41.72" 41.61 41.42
No -(C)
41.58 41.61 41.36
41.44 41.22 40.87 41.46 41.52 41.63 41.64 41.61 41.34
Early
Means for each factor within a row with no common superscripts differ significantly (PS.001).
Means for each factor within a row with no common superscripts differ significantly (K.01).
Root mean square error of the statistical model used.
In each experiment the statistical analysis was based on n = 80.
x,Y
1
Yes
Incubation humidity
Means for each factor within a row with no common superscripts differ significantly (P£.05).
A,B
a,b
Week
Experimental temperature
Exposure
41.70 41.60 41.49
41.54 41.73 41.66 41.70 41.62 41.42
41.32 41.23 40.92
Late
Chicks hatched
TABLE 4. Least squares means of rectal temperature during the growing period an
ded from http://ps.oxfordjournals.org/ at University of Hong Kong on May 9, 2015
(Q 35 37 39 35 37 39 35 37 39
1
1
1
2
3
2
Normal
1
1
1
Low
Incubation humidity
2
2
2
2
Early
1
1
Late
Chicks hatched
1
1
Male
2
2
2
2
Female
Sex
6 4 20 b
1 1
6 3 19
5 2 32 a
2
4 2 30 1
Norm
Incubation humidity
= no deaths.
Control groups were not exposed to the experimental temperatures, but placed in grower cages at normal thermal condit
*No deaths occurred in 3rd and 4th wk.
2
Low • (no.)
"•^Numbers for each factor within a row with no common superscripts differ significantly (FS.05).
Total
2
1
Week
Experimental temperature
Control groups2
TABLE 5. Mortality rate of chicks from control and exposed groups per week
ed from http://ps.oxfordjournals.org/ at University of Hong Kong on May 9, 2015
HEAT TOLERANCE AND GROWTH PERFORMANCE OF NEONATAL CHICKS
ACKNOWLEDGMENTS
The authors wish to thank H. A. Brandsma, J. Buwalda, M.J.W. Heetkamp, J. M. van der Linden, P. Vos, and E. Wientjes for their
technical assistance during the experiments and statistical analyses. The support of Euribrid, Boxmeer, The Netherlands, is gratefully acknowledged. REFERENCES Ernst, R. A., W. W. Weatbers, and J. Smith, 1984. Effects of heat stress on day-old broiler chicks. Poultry Sci. 63:1719-1721. Fanguy, R. C , L. K. Misra, K. V. Vo, C. C. Blohowiak, and W. F. Krueger, 1980. Effect of delayed placement on mortality and growth performance of commercial broilers. Poultry Sci. 59:1215-1220. Freeman, B. M., 1965. The relationship between oxygen consumption, body temperature and surface area in the hatching and young chick. Br. Poult. Sci. 6: 67-72. Hamdy, A.MM., W. van der Hel, A. M. Henken, A. G. GalaL and A.K.I. Abd-Elmoty, 1991. Effects of air humidity during incubation and age after hatch on heat tolerance of neonatal male and female chicks. Poultry Sci. 70:1499-1506. Henken, A. M., W. van der Hel, A. Hoogerbnigge, and C. W. Scheele, 1987. Heat tolerance of one-day old chickens with special reference to conditions during air transport Pages 261-287 in: Energy Metabolism in Farm Animals. M.WA. Verstegen and A. M. Henken, ed. Martinus Nijhoff Publishers, Dordrecht, The Netherlands, Boston, MA, and Lancaster, England. SAS Institute, 1985. SAS® User's Guide: Statistics, Version 5 Edition. SAS Institute, Inc., Cary, NC. Verstegen, M.WA, W. van der HeL H. A. Brandsma, A. M. Henken, and A. M. Bransen, 1987. The Wageningen respiration unit for animal production research: a description of the equipment and its possibilities. Pages 21-48 in: Energy Metabolism in Farm Animals. MW.A. Verstegen and A. M Henken, ed. Martinus Nijhoff Publishers. Dordrecht, The Netherlands, Boston, MA, and Lancaster, England.
Downloaded from http://ps.oxfordjournals.org/ at University of Hong Kong on May 9, 2015
very quickly after hatch. At the start of the exposure period, body weights were already similar. During exposure, chicks hatched from eggs incubated at 55% RH lost more weight than chicks from the 45% RH group. Therefore, chicks from the latter group were heavier at the start of the growing period than those from the 55% RH group. These chicks lost significantly less body water during exposure (Hamdy et a/., 1991). The difference at hatch between the groups with different hatching times was preserved during exposure and part of the growing period. Chicks hatching early had a higher mortality rate than those that hatched late. Chicks hatching early lost more weight in die hatcher, but these chicks lost similarly during exposure as die late-hatched ones. These results are in agreement with those reported by Fanguy et al. (1980). They noted that mortality rate during the first 4 wk of the growing period increased with delayed collection of the chicks from the hatcher. In conclusion, a 10% lower than normal (55%) incubation RH did not negatively affect performance of chicks after heat exposure. Chicks hatching early had a higher risk of dying after exposure to heat man late-hatching ones. Chicks hatching late from eggs incubated at low RH apparently were the most heat tolerant.
1515
ABSTRACT Three experiments were performed with 300 neonatal Hisex Brown layer chicks in each. The chicks hatched from eggs incubated at a relative humidity (RH) of 55 or 45%. Within each RH group, two groups were separated based on hatching time (early and late hatch groups). After hatch, 60 chicks served as controls. The other chicks were exposed to 35, 37, or 39 C for 48 h. After exposure, a 4-wk experimental growing period started at Day 2 of age. Chicks exposed to the experimental temperature regimens for 2 days had lower body weights at the end of exposure and grew less than controls during the 1st wk afterwards. At Day 2 of age, chicks hatched from eggs incubated at 45% RH had higher body weights than clucks hatched from eggs incubated at 55% RH. These chicks also had higher body weight gain in the 1st and 2nd wk following exposure to 39 C than chicks hatched from eggs incubated at 55% RH. Chicks hatching late were heavier at Day 2 than early-hatching ones, but body weight gain was similar. Chicks exposed to the experimental temperature regimens had lower rectal temperatures than controls at the end of the 1st and 2nd wk. Incubation RH, hatching time, and sex did not affect feed intake, feed conversion, or rectal temperature. After exposure to 39 C, fewer chicks that had hatched from eggs incubated at low RH died compared with chicks that had hatched from the 55% RH group. Early-hatching chicks had a significantly higher risk of dying than late-hatching ones. (Key words: incubation, incubation humidity, hatching time, growth, mortality rate) 1991 Poultry Science 70:1507-1515
the time period between actual hatching and removal from the hatcher. The objective of the Body weight loss and mortality rates of present research was to evaluate the growth neonatal chicks are increased when they are performance of neonatal chicks after heat transported at high temperatures. After arrival exposure early in life. Chicks used hatched at a farm and placement at normal thermal from eggs incubated at one of two relative conditions, chicks that have survived exposure humidities (RH) and had stayed in the hatcher to high temperatures will eat and grow less and for a varying period of time after hatch. may still have a higher risk of dying than those exposed to lower temperatures (Ernst et ah, MATERIALS AND METHODS 1984; Henken et al, 1987). A high heat tolerance is therefore an important attribute. Chicks cope with heat by losing moisture Chicks and Pre-Experimental Conditions through evaporation. Chicks with a high water Three experiments were performed each content may therefore be relatively more heat using 300 neonatal Hisex Brown layer chicks.1 tolerant. Water content of neonatal chicks can chicks were be manipulated in two different ways: 1) by Within each experiment, 150 2 hatched from eggs incubated at 55 ± 2% RH varying incubation humidity and 2) by varying from Day 0 to 19, and the other 150 were hatchedfromeggs incubated at 45 ± 2% RH. At Day 19 all eggs were placed in one hatcher. Hatching time of each chick was recorded. After 'Euribrid, 5830 AA, Boxmeer, The Netherlands. ! Pas Reform, 7038 ZG, Zeddam, The Netherlands. opening the hatcher, two hatch groups were INTRODUCTION
1507
Downloaded from http://ps.oxfordjournals.org/ at University of Hong Kong on May 9, 2015
(Received for publication November 17, 1990)
1508
HAMDY ET AL.
Experimental Procedure After the exposure period of 48 h, the chambers were opened and the chicks collected. During the exposure period, no deaths had occurred. Then, in each experiment, 45 chicks of each group were allocated to one of three subgroups of 15 [an all-male group, an allfemale group, and a mixed-sex group (7 to 8 of each sex)]. Each subgroup (12 groups in total) was placed in a grower cage with feed (commercial starter)3 and water available for ad libitum consumption. These cages and those of the controls belonged to one battery line. Controls had access to feed and water from Day 1 onwards. This was to evaluate the effect of feed and water withdrawal as occurs during transport. Environmental temperature was maintained at 31 C during the 1st wk and was decreased thereafter in a stepwise-fashion by 2 C/wk to 25 C by the 4th wk. Light was on continuously. The vaccination schedule adopted was: Marek's disease (Day 1 of growing period, i.m.), infectious bronchitis [Day 2 of growing period, intraoccularly (i.o.)], infectious bursal disease (Day 12 of growing period, i.o.), and Newcastle disease (Day 18 of growing period, i.o.). The experimental growing period lasted 4 wk. Determinations and Statistics
3 CP = 20.8%; ME = 2,800 kcal/kg; calcium = .99%; and available phosphorus = .45%. 4 Dual Digital thermometer, Lieca B.V., 2280 AB, Rijswijk, The Netherlands.
Body weight of each chick (n = 240, 16 groups x 15 in each experiment) was determined every 5 to 7 days beginning at the start of the growing period (Day 2 of age). Feed intake, feed conversion (feed:gain), and rectal temperature4 (5 chicks) were determined each 5- to 7-day period per cage. The mortality rate was determined daily per cage. Gain and feed intake were expressed in grams per day, as weighings were not done each time exactly after 7 days. Gain within a week was calculated using data of chicks still alive at the end of that week. Feed intake was calculated taking into account number of days within each period and chicks alive at each day. The data on body weight at Day 2, gain, feed intake, feed conversion, and rectal temperature were subjected to analysis of variance (SAS Institute, 1985). Exposure history (heat exposure in the chambers, yes or no), incubation RH (low or normal), hatch group (early or late), and sex were included in the model as main factors. Interactions were analyzed initially, but removed from the model if not significant (P>.05). The data were analyzed for each experiment separately. Data on mortality rates were analyzed wifli a chi-square test. RESULTS
Body Weight and Gain Data on body weight at the start of the growing period after exposure and gain in each of the 4 wk are given in Table 1. Chicks having been exposed to the experimental temperature regimens in the chambers for 2 days had a lower (P<.001) body weight at the start of the growing period man control chicks. The largest difference between control and exposed groups was found in the 39 C experiment (an absolute difference in body weight of 8.9 g). In the 1st wk of the growing period exposed chicks had a lower (P<.05) gain than controls (-.3 g on average). In the 2nd wk after exposure, the difference in gain between controls and exposed chicks decreased, however chicks exposed to 39 C during the first 2 days of life still grew less than controls in this 2nd wk In the 3rd and 4th wk, control and exposed chicks had a similar gain (P>.05). Chicks from eggs incubated at low RH had a higher body weight at the start of the growing period in two of the three experiments and had a higher gain in the 1st and 2nd wk of the 39 C experiment. In the 3rd and 4th wk, no effect
Downloaded from http://ps.oxfordjournals.org/ at University of Hong Kong on May 9, 2015
established within each RH group: a group hatched early and a group hatched late. The average difference in hatching time between the two hatch groups was about 9 h. Fifteen of each hatch by RH combination (seven to eight of each sex) served as unexposed controls and were placed in grower cages in a poultry house at a normal temperature of 31 C. The other chicks (240) were placed in one of two identical climate respiration chambers (Verstegen et al., 1987), with chicks hatched early in one chamber and chicks hatched late in the other. Within each chamber, equal numbers of the two humidity groups and each sex were present. The chicks in both chambers were exposed to a constant (SE = ± .01) thermal regimen for 48 h of 35 (Experiment 1), 37 (Experiment 2), or 39 C (Experiment 3).
3
9.8 10.4 9.4 12.1 12.5 11.9
1.8b 2.5b 2.7 Y 6.6 7.4 6.6 Y
36.6 Y 34.5 Y 30.5 Y 1.9 2.6 3.1 a 6.8 7.4 7.6 X 9.9 10.2 9.6 12.1 12.4 11.8
10.1 10.2 9.7 12.6 12.5 11.5
37.6a 35.8 36. l x
Low
yi.9*37.4 X 39.4 X 2.1 a 2.7a 3.1 x 7.0 7.4 7.9X
No 36.9 b 36.0 33.8 Y 2.0 2.6 2.7 b 6.7 7.4 6.9 Y 10.0 10.4 9.5 12.6 12.7 11.6
Normal
Incubation humidity
Means for each factor within a row with no common superscripts differ significantly (P^.01).
Means for each factor within a row with no common superscripts differ significantly (PS.001).
!tr\
12.3 12.7 12.0
10.1 10.2 9.5
7.0 7.2 b 7.2
36.1 Y 34.6 Y 33.3 Y 1.9 2.5 b 3.0*
Early
1 1 1
1
3 3 3
L
Chick hatch
Root mean square error of the statistical model used.
There was a significant interaction (K.05) at 35 and 39 C between incubation humidity and hatch time with respect to body
In each experiment the statistical analysis was based on n = 240 with subtraction of the number of dead chicks we
x,Y
2
(Q 35 37 39 35 37 39 35 37 39 35 37 39 35 37 39
Yes
Exposure
'4deans for each factor within a row with no common superscripts differ significantly (P£.05).
A,B
a
Daily gain in Week 4
Daily gain in Week 3
Daily gain in Week 2
Daily gain in Week 1
Body weight at Day 2
Parameter1,2
Experimental temperature
TABLE 1. Least squares means of body weight at start of the growing period (at Day 2 of life) and dail
ded from http://ps.oxfordjournals.org/ at University of Hong Kong on May 9, 2015
1510
HAMDY BT AL.
early had a significantly higher risk of dying thantihosemat hatched later. Sex did not affect mortality rate. No deaths occurred in the 3rd and 4th wk. DISCUSSION
Chicks that were exposed to 39 C lost more uian 20% of their initial body weight in 48 h (Hamdy et al., 1991). Exposed chicks needed 2 wk to recover afterwards. These results are in agreement with those reported by Henken et al. (1987). Low RH during setting had no negative effect on body weight at two days of age. A low incubation RH seemed to be positive for body weight at Day 2. Chicks hatching late had a higher body weight at the Feed Intake and Feed Conversion start of the growing period than those hatching early. This may be due to the longer dehydraControl chicks ate more than exposed ones tion period in the hatcher of the chicks that (Table 2). After 1 or 2 wk this difference in feed hatched early. Fanguy et al. (1980) also intake between control and exposed groups was reported that delayed placement of chicks up clearly reduced. Incubation humidity, hatching to 64 h from hatching had a clear effect on time, and sex did not affect feed intake (P>.05). body weight gain until Week 4. The significant In die 3rd and 4th wk, male chicks began to eat interactions, on body weight at Day 2 and gain more than females, but not significantly (P>.05). in 1st and 2nd wk, between incubation RH and Exposure period, incubation humidity, hatching hatching time were due to larger weight time, and sex did riot affect (P>.05) feed differences within hatch groups in the 55% RH conversion with two exceptions (Table 3). than in the 45% RH groups. Chicks exposed to 35 C had a lower (P<.05) feed There is some disagreement as to the exact conversion than controls in the 2nd wk of the age at which rectal temperature of neonatal growing period. Incubation RH affected feed conversion significantly only in the 2nd wk, chicks becomes constant. Rectal temperature chicks from eggs from low RH having a lower of the chicks exposed to elevated temperatures feed conversion than chicks hatched from remained relatively low compared with the controls. It might be that neonatal chicks adapt normal RH. themselves relatively quickly when exposed to heat and mobilize all heat dissipation mechanisms. When placed at normal thermal condiRectal Temperature tions, chicks previously exposed to heat for a Chicks exposed to the experimental tempera- period of time still may be focused on heat ture regimens for 48 h had a lower rectal dissipation rather than on heat conservation. It temperature in the 1st (P<.01) and 2nd (PS.05) might also be that early heat exposure has wk of the growing period (Table 4). In the 3rd altered homeostasis or innate mechanisms that and 4th wk, rectal temperature differences were regulate rectal temperature. According to Freenot significant (P>.05). Incubation RH, hatching man (1965) rectal temperature becomes contime, and sex did not affect rectal temperature stant at about 12 days of age. with one exception. The mortality rate was high during the 1st wk after exposure to 39 C. Chicks exposed to 39 C were very weak afterwards and showed Mortality Rate no inclination to eat or drink. Chicks hatched Incubation RH affected mortality rates signif- from eggs incubated at low RH had a lower icantly in the 39 C experiment (Table 5). Chicks mortality rate than those hatched from eggs hatched from eggs incubated at low RH had a incubated at normal RH. Although chicks lower mortality rate during the beginning of the hatched from eggs incubated at 55% RH were 4-wk period than chicks hatched from eggs heavier at hatch than chicks hatched from eggs incubated at normal RH. Chicks that hatched incubated at 45%, this difference disappeared
Downloaded from http://ps.oxfordjournals.org/ at University of Hong Kong on May 9, 2015
of incubation RH on gain was found. Chicks hatched late were heavier (P<.001) than earlyhatched ones at the start of the growing period (2.7 g on average). Gain of the two groups was similar over 4 wk, although in the 1st and 2nd wk, chicks hatched early grew less than latehatched ones in two cases. In die 35 and 39 C experiments, there were significant (PS.05) interactions between relative humidity and hatching time with respect to body weight at Day 2 and gain in the 1st and 2nd wk. Initially, male and female chicks had comparable body weight (except in the 39 C experiment) and gain. After the 1st wk, however, males grew significantly faster than females.
2
6.4 Y 8.2 5.3 Y 14.8b 18.3 15.1 21.2 24.4 23.7 28.2 32.7 30.0
x
32.9 33.7 30.3
19J2a 18.4 16.7 25.5 24.1 25.4
94
8.9*
No 7.6 8.8 75 17.4 18.4 16.0 24.3 24.0 26.1 31.2 32.3 30.6
Low
17.3 18.7 15.9 23.7 24.5 25.1 31.1 33.3 30.7
29.9 33.0 29.5
29.9 34.0 29.7
7.7 9.2 7.7
Late
7.6 8.4 6.8 16.8 18.1 15.9 23.0 24.0 24.1
(el
Early
Chicks hatched
7.8 8.8 7.0 16.7 18.4 15.8 22.4 245 23.1
Normal
Incubation humidity
Means for each factor within a row with no common superscripts differ significantly (K.001).
In each experiment the statistical analysis was based on n = 16.
Root mean square error of the statistical model used.
1
35 37 39
(Q 35 37 39 35 37 39 35 37 39
Yes
Exposure
Means for each factor within a row with no common superscripts differ significantly (K.05).
x,Y
a,b
Daily intake in Week 4
Daily intake in Week 3
Daily intake in Week 2
Daily intake in Week 1
Parameter1
Experimental temperature
TABLE 2. Least squares means of daily feed intake per chick in each week an
ded from http://ps.oxfordjournals.org/ at University of Hong Kong on May 9, 2015
4.8 3.1 3.4 2.4b 2.5 2.4 2.4 2.4 2.5 2.5 2.6 2.5
(Q 35 37 39 35 37 39 35 37 39 35 37 39
2.7a 2.6 2.3 2.4 2.3 2.7 2.5 2.7 2.6
4.0 3.5 3.8
4.5 3.4 3.3 2.5 2.6 2.3 b 2.4 2.4 2.7 2.5 2.7 2.6
Low
2
4.3 32 3.8 2.6 2.5 2.4 a 2.4 2.3 2.4 2.5 2.6 2.5
Incubation hmnMHy Normal
Root mean square error of the statistical model used.
4.4 3.4 3.7 2.6 2.5 2.3 2.4 2.3 2.7 2.5 2.7 2.6
Chicks hatched Late
(g:g) 4.4 32 35 25 2.6 2.4 2.4 2.4 2.6 2.6 2.6 2.5
Early
'°Means for each factor within a row with no common superscripts differ significantly (PS.05).
Yes
Exposure No
*In each experiment the statistical analysis was based on n = 16.
a
Week
Experimental temperature
2 2 2
2 2 2
4
M
TABLE 3. Least squares means of feed conversion (feed:gain) during the growing perio
ded from http://ps.oxfordjournals.org/ at University of Hong Kong on May 9, 2015
4
3
2
1
2
41.25 8 41.08B 40.61 Y 41.44 b 41.59 41.57b 41.62 b 41.62 41.34
41.61 41.57 41.39
(Q 35 37 39 35 37 39 35 37 39
35 37 39
41.65 41.58 41.43
41.50 41.59 41.70* 41.67 41.64 41.41 41.63 41.63 41.41
41.67 41.63 41.46
Normal 41.44 41.33 40.86 41.50 41.66 41.58b 41.67 41.58 41.34
41.31 41.11 40.93
Low
41.51 A 41.36A 41.18 x 41.56a 41.66 41.72 s 41.72" 41.61 41.42
No -(C)
41.58 41.61 41.36
41.44 41.22 40.87 41.46 41.52 41.63 41.64 41.61 41.34
Early
Means for each factor within a row with no common superscripts differ significantly (PS.001).
Means for each factor within a row with no common superscripts differ significantly (K.01).
Root mean square error of the statistical model used.
In each experiment the statistical analysis was based on n = 80.
x,Y
1
Yes
Incubation humidity
Means for each factor within a row with no common superscripts differ significantly (P£.05).
A,B
a,b
Week
Experimental temperature
Exposure
41.70 41.60 41.49
41.54 41.73 41.66 41.70 41.62 41.42
41.32 41.23 40.92
Late
Chicks hatched
TABLE 4. Least squares means of rectal temperature during the growing period an
ded from http://ps.oxfordjournals.org/ at University of Hong Kong on May 9, 2015
(Q 35 37 39 35 37 39 35 37 39
1
1
1
2
3
2
Normal
1
1
1
Low
Incubation humidity
2
2
2
2
Early
1
1
Late
Chicks hatched
1
1
Male
2
2
2
2
Female
Sex
6 4 20 b
1 1
6 3 19
5 2 32 a
2
4 2 30 1
Norm
Incubation humidity
= no deaths.
Control groups were not exposed to the experimental temperatures, but placed in grower cages at normal thermal condit
*No deaths occurred in 3rd and 4th wk.
2
Low • (no.)
"•^Numbers for each factor within a row with no common superscripts differ significantly (FS.05).
Total
2
1
Week
Experimental temperature
Control groups2
TABLE 5. Mortality rate of chicks from control and exposed groups per week
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HEAT TOLERANCE AND GROWTH PERFORMANCE OF NEONATAL CHICKS
ACKNOWLEDGMENTS
The authors wish to thank H. A. Brandsma, J. Buwalda, M.J.W. Heetkamp, J. M. van der Linden, P. Vos, and E. Wientjes for their
technical assistance during the experiments and statistical analyses. The support of Euribrid, Boxmeer, The Netherlands, is gratefully acknowledged. REFERENCES Ernst, R. A., W. W. Weatbers, and J. Smith, 1984. Effects of heat stress on day-old broiler chicks. Poultry Sci. 63:1719-1721. Fanguy, R. C , L. K. Misra, K. V. Vo, C. C. Blohowiak, and W. F. Krueger, 1980. Effect of delayed placement on mortality and growth performance of commercial broilers. Poultry Sci. 59:1215-1220. Freeman, B. M., 1965. The relationship between oxygen consumption, body temperature and surface area in the hatching and young chick. Br. Poult. Sci. 6: 67-72. Hamdy, A.MM., W. van der Hel, A. M. Henken, A. G. GalaL and A.K.I. Abd-Elmoty, 1991. Effects of air humidity during incubation and age after hatch on heat tolerance of neonatal male and female chicks. Poultry Sci. 70:1499-1506. Henken, A. M., W. van der Hel, A. Hoogerbnigge, and C. W. Scheele, 1987. Heat tolerance of one-day old chickens with special reference to conditions during air transport Pages 261-287 in: Energy Metabolism in Farm Animals. M.WA. Verstegen and A. M. Henken, ed. Martinus Nijhoff Publishers, Dordrecht, The Netherlands, Boston, MA, and Lancaster, England. SAS Institute, 1985. SAS® User's Guide: Statistics, Version 5 Edition. SAS Institute, Inc., Cary, NC. Verstegen, M.WA, W. van der HeL H. A. Brandsma, A. M. Henken, and A. M. Bransen, 1987. The Wageningen respiration unit for animal production research: a description of the equipment and its possibilities. Pages 21-48 in: Energy Metabolism in Farm Animals. MW.A. Verstegen and A. M Henken, ed. Martinus Nijhoff Publishers. Dordrecht, The Netherlands, Boston, MA, and Lancaster, England.
Downloaded from http://ps.oxfordjournals.org/ at University of Hong Kong on May 9, 2015
very quickly after hatch. At the start of the exposure period, body weights were already similar. During exposure, chicks hatched from eggs incubated at 55% RH lost more weight than chicks from the 45% RH group. Therefore, chicks from the latter group were heavier at the start of the growing period than those from the 55% RH group. These chicks lost significantly less body water during exposure (Hamdy et a/., 1991). The difference at hatch between the groups with different hatching times was preserved during exposure and part of the growing period. Chicks hatching early had a higher mortality rate than those that hatched late. Chicks hatching early lost more weight in die hatcher, but these chicks lost similarly during exposure as die late-hatched ones. These results are in agreement with those reported by Fanguy et al. (1980). They noted that mortality rate during the first 4 wk of the growing period increased with delayed collection of the chicks from the hatcher. In conclusion, a 10% lower than normal (55%) incubation RH did not negatively affect performance of chicks after heat exposure. Chicks hatching early had a higher risk of dying after exposure to heat man late-hatching ones. Chicks hatching late from eggs incubated at low RH apparently were the most heat tolerant.
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