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Rectal Temperature and Respiratory Responses of Jersey and Sindhi-Jersey (F1) Crossbred Females to a Standard Hot Atmosphere
R EC TAL T E M P E R A T U R E AND R E S P I R A T O R Y R E S P O N S E S OF J E R S E Y AND S I N D H I - J E R S E Y (F1) CROSSBRED F E T [ A L E S TO A STANDARD HOT A T M O S P H E R E R. E. I~cDOWELL, D. H. K. L E E , 1 1~. H. FOHRMAN, J. F. SYKES, AND R. A. ANDERSON
Dairy t~usbandvy tgeseareh Branch, USDA, Beltsville, Md.
In the course of systematic studies of crossbred cattle resulting from an experimental breeding program made with Jerseys and Red Sindhi as the parent stocks, a number of F1 Sindhi-Jersey females have been subjected to a standard hot atmosphere to determine t h e i r responses to hot atmospheric conditions. The effect of such exposures on rectal temperature and respiratory rate is reported in this paper. :E~XPERIMENTALCONDITIONS Each female produced by the breeding program is subjected to the standard hot atmosphere f o r 6 hours at approximately 2-month intervals from 6 months of age onward except during the first lactation, which is left undisturbed for record purposes, and during the 45 days preceding each expected parturition. The test animals are placed in a climatic chamber on the afternoon preceding the test, but without any heat. Water, grain, and hay are allowed ad libitum during the afternoon. Grain is also offered the following morning, but all feed is withdrawn before the test is started. Water is available to the animal up to the time of starting the test, but no feed or water is offered during the test period. At about seven in the morning, the heaters and humidifiers are switched on, and the air conditions rise fairly rapidly (15 minutes in summer, 20 minutes in winter) to the desired 105 ° F. and 34 ram. Itg vapor pressure (corresponding to a we~ bulb temperature of 92 ° F. and a relative humidity of 60%). They are maintained at these levels, within 2 ° F. dry- and wet-bulb temperatures, for the remainder of the 6-hour test period. Air temperatures near the floor are somewhat lower than 105 ° F. until the end of the first hour. Rectal temperature is measured by a 5-in. clinical thermometer inserted into the rectum and left in position for 3 minutes. Under hot conditions the chance of error from variations in the position of the thermometer is small. Respiratory rate is measured by counting flank movements over an undisturbed period of 1 minute. Readings are made just before the heat is switched on and at hourly intervals thereafter. Other responses measured during the test, such as water loss and skin wetness, will be reported elsewhere. RESULTS
To reduce the numerous individual observations to manageable proportions, the m e a n of the observations during the test has'been taken as the representative datum. The use of the m e a n has the advantage of minimizing the error inherent Received for publication !~arch 21, 1955. 1 Professor of Physiological Climatology, Johns Hopkins University, Baltimore. 1037
1038
R.E.
i~cDOWELL
ET
AL
in single observations and avoids the uncertainty of interpretation attending such criteria as maximum temperatures. The trapezoidal mean has been used in preference to the straight mean, as more representative of the animal's state while u n d e r test, especially when the initial rise of rectal temperature is rapid.
0.5t6)/6
tm = (0.5to + ti + t2 + t~-F t4 + t~ +
where tm is trapezoidal mean temperature ; tl, t2, etc. are temperatures observed after 1, 2, etc. hours of exposure.
Rectal temperature. The results obtained in these studies are illustrated in Figures 1 and 2, and the analyses of variance are given in Table 1. In these analyses the method recommended by Snedecor (6) for dealing with disproportionate subclass numbers was used. Data are given for both the absolute rectal temperature during exposure and the rise of rectal temperature above the initial value. The latter is probably a better indicator of the additional strain developed in the animal by exposure to heat, but the former indicates the total strain experienced by the animal and thus probably comes closer to suggesting the economic consequences of the situation. Exposure to heat results in a marked rise of rectal temperature in all three categories of animals~heifers, d r y cows, and lactating cows. I f final, or maximum, rectal temperatures had been reported instead of the exposure means, the rise would have been even more striking, since the rectal temperature tends to go on increasing throughout the exposure, especially in the less tolerant animals. IO5
--
HATCHING-FIDUCIAL
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12 14 16 AGE ( MONTHS )
|8
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17
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12
13
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FIG. 1. I n i t i a l a n d m e a n rectal t e m p e r a t u r e s of heifers during exposure to a s t a n d a r d h o t atmosphere (6 hours a t 105 ° 1~. with 34 mm. H g vapor pressure). N u m b e r s at foot indicate the n u m b e r of animals, J e r s e y s ( J ) and crossbreds (C), tested at each age.
1039
RESPONSES TO A STANDARD HOT ATMOSPHERE
105.0
I
104.0
103,0
102.0
I01.0 Jersey
I DRY J G
90 42
,
[]
Crosses L ~ HGtchinq~Fiducial limits ( 5 % level) i i I
20 PRODUCTION (LB. 17 14 NO. OF TESTS
30 40 of FCM) 53 3" 35 14
50 + 25 14
FIG. 2. I n i t i a l a n d m e a n rectal t e m p e r a t u r e s d u r i n g e x p o s u r e to a s t a n d a r d h o t a t m o s p h e r e (~i h o u r s a t 105 ° F. w i t h 34 m m . H g v a p o r p r e s s u r e ) b y a v e r a g e level of milk p r o d u c t i o n on t h e five d a y s p r e c e d i n g t h e test. N u m b e r s a t f o o t i n d i c a t e t e s t s p e r f o r m e d on J e r s e y s ( J ) a n d c r o s s b r e d s (C) a t v a r i o u s levels of p r o d u c t i o n .
In all three categories both the mean rectal temperature during exposure and the mean rise in rectal temperature above the initial value are greater to a highly significant degree in the Jerseys than in the Sindhi-Jersey crossbred animals. In heifers, the rectal temperature during exposure is higher in the younger animals, but so is the initial temperature, so that the rise on exposure is substantially the same at all ages (Figure I and Table 1). D ry cows show much the same reaction as do the older heifers (Figure 2). In lactating cows, the stage of lactation has little effect upon the reactions to heat. In Jerseys, the rectal temperature on exposure tends to be higher in the earlier months of lactation, but this is also accompanied by a higher initial temperature, so that the rise is substantially the same at all stages. In Sindhi-Jersey crossbred cows, neither the initial rectal temperature nor the mean obtained during exposure is affected by the stage of lactation. The level of production, in sharp contrast to the stage of lactation, has a highly significant effect upon both the absolute and the relative rectal temperature during exposure (Figure 2). When dry cows are included, a significant difference is seen between the development of this effect in the two groups. The rectal temperature during exposure tends to rise steadily with the production level in the Jerseys, but in the Sindhi-Jersey crossbred cows it rises with the lower levels of production to a value which is not furt her affected by furt her increases in production. This interaction between breed and production level is
R. E. lVIoDOWELL ET AL
1040
TABLE 1 Analyses o f variance o f the initial rectal temperature, mean reveal temperature on exposure, and rise in rectal temperature with exposure Mean squares Source of variation
Degrees of freedom
Initial rectal temp.
Mean rectal temp. on exposure
Mean rise in rectal temp. with exposure
(a) H e i f e r s
Breeds Ages Interaction Error
1 8 8 258
0.325 1.910"* 0.022 0.132
50.289** 3.085 *~ 0.369 0.426
55.472** 0.656 0.382 0.396
0.300 0.640* 0.083 0.165
16.554"* 1.807" 0.654 0.562
20.349** 0.648 1.178 0.527
0.016 0.118
15.307"* 0.502
15.311"* 0.503
(b) L a c t a t i n g cows by months of lactation Breeds l~onths Interaction
Error
1 3 3 130 (e) D r y cows
Breeds Error
1 130
(d) Cows by levels of production (excluding dry cows)
Breeds Levels Interaction Error
1 3 3 201
0.215 0.152 0.126 0.185
35.314"* 2.398** 2.239** 0.408
37.634** 1.656" 1.761" 0.608
Significant at the 5% level of probability. ** Significant a t the 1% level of probability.
substantiated by a highly significant mean square in Table 1. The initial rectal temperatures of lactating cows are higher than those of d r y cows, but there is no progressive rise with the level of production. Since seasonal variations in the maintenance environment of animals subjected only periodically to testing may influence their reactions to such tests, the responses of animals to the standard hot atmosphere were examined in relation to season. The analysis and results have been discussed at some length in a previous publication (3), and only a summary needs to be given here. I t was found that there was little repeatability in the responses of the animals unless they were first sorted according to season. When the responses of heifers and d r y cows were plotted by months of the year, an unexpected t r e n d was revealed. The responses showed a maximum in F e b r u a r y with a smaller maximum in August, separated by a marked minimum in May-June. The values in November-December were intermediate. This type of fluctuation was easily observed in the Jerseys, which have the greater response, but it was still discernible in the crossbred animals. W h e n the responses for heifers were sorted by season, as suggested by this variation, a fairly high repeatability was found (Table 2). No repeatability was f o u n d with lactating cows, however, as was to be expected in view of the multiplicity of factors which affect lactation and its consequences for the animal. Respiration rate. Respiratory data are given in Figures 3 and 4, and the analyses of variance in Table 3. Exposure to heat results in a very marked rise
1041
RESPONSES TO A STANDARD HOT ATMOSPHERE
TABLE 2 t~epeatabi~ity ~ of mean body temperature responses b of heifers (8-~'2 months of age) to a standard test hot atmosphere (6 hours at 105 ° 1~. and 34 ram. l t g vapor pressure) when sorted by season Repeatability within seasonal group
Breed Jersey
SindhiJersey (1~1) crosses
Item Repeatability No. of animals No. of tests Repeatability No. of animals No. of tests
Apr.-July (low response) 0.93 ~~ 23 60 0.54 ~ 21 48
Aug.-Sept. & l~eb.-l~ar. (high response) 0.72 ~~ 22 53 0.67 ~ 17 38
Oct.-Jan. (intermediate response) 0.60 ~~ 20 48 0.78 ~ 18 44
~ Significant at 0.01 level of probability. i Coefficient of intra-animal correlatiOn (1, 6). b Trapezoidal mean for a period of 6 hours exposure. of respiration rate in all three categories of animals. Observations made throughout the period of exposure indicate that the respiration rate, unlike the rectal temperature, rises rapidly during the first hour and then remains at about the s a m e l e v e l o r f a l l s s o m e w h a t a s e x p o s u r e p r o c e e d s . T h i s is i n a c c o r d a n c e w i t h observations previously reported on cows (5) and sheep (4). In heifers, both the mean respiratory rate during exposure and the mean rise in respiratory rate above the initial value are greater to a highly significant degree in the Jerseys than in the Sindhi-Jersey crossbred animals. (The lower significance in Table 3 TABLE 3 Analyses of variance of the initial respiration rate, mean respiration rate on exposure, and rise in respiration rate with exposure Mean squares
Source of variation Breeds Ages Interaction Error Breeds Months Interaction Error Breeds Error Breeds Levels Interaction Error
Degrees of freedom
Initial respiration rate
Mean respiration rate on exposure
(a) Heifers 1 1,982.829 ~ 16,140.750 ~ 8 200.291 299.784 8 246.127 75.969 258 152.192 822.283 (b) L a c t a t i n g cows by mouths of lactation 1 970.196 ~ 5,802.264 ~ 3 230.999 390.738 3 93.547 10.584 130 241.309 199.478 (c) Dry cows 1 535.759 ~ 1,041.460 130 119.384 357.52 (d) Cows by levels of production (excluding dry cows) 1 15.669 3,805.264 ~ 3 733.186 ~ 262.580 3 577.953 399.170 201 231.041 211.85
Significant a t the 5% level of probability. ~ Significant at the 1 % level of probability.
Mean rise in respiration rate with exposure 4,766.164 ~ 364.463 664.346 413.380 1,631.130 ~ 698.430 69.709 316.618 363.77 404.22 4,776.468 ~ 236.096 48.467 321.141
1042
2. E. MeDOWELL ET A L
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F i e . 3. I n i t i a l a n d m e a n r e s p i r a t o r y r a t e s of h e i f e r s to a s t a n d a r d h o t a t m o s p h e r e (6 h o u r s a t 105 ° F . w i t h 34 ram. t t g v a p o r p r e s s u r e ) . N u m b e r s a t f o o t indicate t h e n u m b e r of a n i m a l s , J e r s e y s ( J ) a n d c r o s s b r e d s (C) t e s t e d a t each age.
for breed differences in cows sorted by stages of lactation is attributed to the smaller number used in this analysis.) In lactating cows, however, the mean respiratory rate during exposure was higher in the crosses. The initial respiration rate of the Jerseys is the greater to a highly significant degree in heifers and to a significant degree in dry cows, but the difference in lactating cows is obscured by the effects of levels of production. The response to heat is not significantly affected by age in heifers, stage of lactation, or level of production. DISCUSSION
I t is clear that cows of the Fz cross between Jersey and Red Sindhi show a smaller rise of rectal temperature when exposed to severe heat than do comparable purebred Jerseys. This is true whether the comparison be made as young heifers, older heifers, dry cows, or lactating cows at the same production level or stage of lactation. It seems reasonable to suppose that all bodily processes, including milk production, will be adversely affected in an animal which shows a marked rise of rectal temperature. But, from a practical point of view, an animal might have such a high productive capacity that it would continue to yield more milk under
1043
RESPONSES TO A STANDARD HOT ATMOSPHERE
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hot conditions, in spite of the disability, than a more resistant cow with lower productive capacity. The concept of heat tolerance is a complex one, not to be defined in terms of any one response. The diminution of body temperature response with age is to be expected, since the temperament of t h e animals becomes more placid and they acquire a certain familiarity with the proceedings. It is possible that the reduction in basal metabolic rate, which commonly occurs during the early life of most animals, plays a part in reducing the response of body temperature to heat, as to other stresses. The effect of milk production upon the response of body temperature is most interesting. That the response should increase with lactation and that the degree of rise should bear some relation to the level of production are to be expected. The interest lies in the comparative behavior of the two breeds. It is well known that Zebu types have a lower level of production than do the better European
1044
~. E. M c D O W E L L
ET AL
types, and it is sometimes argued that the superior heat tolerance of the Zebu would be nullified if its production were raised to the European level, especially if this increase in production were effected by introduction of production genes from European stock. It is clear, however, from the curves of Figure 2 that half-breed animals at the same level of production as pure Jerseys still show a greater resistance to heat stress (as judged by rise of body temperature). The greater heat resistance of the Zebu is therefore not entirely due to low production. It will be interesting to see if this superiority is maintained in the F2 generation and at what combination of European and Zebu " b l o o d " the productive superiority of the one will offset the heat resistance of the other. The high repeatability of body temperature response to the test conditions, once biassing factors such as season and milk production are excluded, justifies the continuance of present procedures for measuring comparative responses of rectal temperature to heat stress, but caution must be exercised in identifying such responses with the wider concept of " h e a t tolerance" until more extensive studies have been made. It is interesting to note that the Sindhi-Jersey crossbred animals not only maintain a lower rectal temperature than the Jerseys but do so with a lower respiration rate. This is in full agreement with the contention argued elsewhere (2) that differences in respiratory activity are the result and not the cause of differences in heat tolerance. That age in heifers and level of production in lactating animals should not have any effect on respiration, although they do affect body temperature response, is not surprising when one realizes that most animals are near the ceiling of their respiratory effort under the test conditions used. A decrease in respiratory effort could hardly be expected until a substantial reduction in body temperature had been attained. SUMMARY
Jersey and Red Sindhi-Jersey (F1) crossbred cows are subjected at regular intervals to a standard test atmosphere at 105 ° F. with a vapor pressure of 34 ram. Hg (wet bulb 92 ° F.). The mean response of rectal temperature is less in the crossbred animals than in the Jerseys, whether the comparison be made as young heifers, older heifers, dr y cows, or lactating cows. The difference occurs also when comparisons are made between animals at the same level of production. In heifers, both initial temperature and temperature during exposure are higher in the younger animals, but the rise is similar at all ages. Dry cows show much the same reactions as older heifers. The stage of lactation has little effect on the response of rectal t'emperature to heat, but the level of production has considerable effect. The rectal temperature during exposure tends to increase fairly steadily with production in Jerseys, but in F1 crossbreds it quickly reaches a level which does not rise with further increases in production. There is marked seasonal variation in body temperature response. Repeatability of response is high in heifers when results are sorted by season, but low in lactating cows.
RESPONSES TO A STANDARD HOT ATMOSPHERE
1045
I n h e i f e r s t h e r e s p i r a t o r y r e s p o n s e of th e J e r s e y s to h e a t is g r e a t e r t h a n t h a t o f t h e S i n d h i - J e r s e y c r o s s b r e d a n i m a l s , b u t as l a c t a t i n g cows t h e r e v e r s e w as f o u n d . N o d i f f e r e n c e w a s seen i n d r y cows. T h e c o n t e n t i o n is c o n f i r m e d t h a t diff eren ces i n r e s p i r a t o r y r a t e a r e th e r e s u l t a n d n o t t h e cause of d i f f er en ces i n heat tolerance. REFERENCES (1) LUSH, J. L. Animal Breeding Plans. Iowa State College Press, Ames. 1945. (2) McDowELL, R. E., LEE, D. H. K., FO~B~'~, ~I. H., AN1) ANDF-~S0~, R. S. Respiratory Activity as an Index of Heat Tolerance in Jersey and Sindhi × Jersey (F1) Crossbred Cows. J. Animal Sci., 12: 573. 1953. (8) HcDow~L, R. E., HATTHmVS, C. A., LEE, D. H. K., AND FOHR~'~, H. H. Repeatability of an Experimental Heat Tolerance Test and Influence of Season. J. Animal Sol., 12: 757. 1953. (4) RIEK, R. F., HARDY,M. H., L ~ , D. H. K., AND CARTER,H. B. The Effect of the Dietary Plane upon the Reactions of Two Breeds of Sheep during Short Exposures to Hot Environments. Australian J. Agr. Researeh, 1 : 217. I950. (5) RIEK, R. F., AND LB~., D. H. K. Reactions to Hot Atmospheres of Jersey Cows in Milk. J. Dairy Research, 15: 219. 1948. (6) SNEI)EC0R, G. W. Statistical Methods. 4th ed., p. 289. Iowa State College Press, Ames. 1946.
Dairy t~usbandvy tgeseareh Branch, USDA, Beltsville, Md.
In the course of systematic studies of crossbred cattle resulting from an experimental breeding program made with Jerseys and Red Sindhi as the parent stocks, a number of F1 Sindhi-Jersey females have been subjected to a standard hot atmosphere to determine t h e i r responses to hot atmospheric conditions. The effect of such exposures on rectal temperature and respiratory rate is reported in this paper. :E~XPERIMENTALCONDITIONS Each female produced by the breeding program is subjected to the standard hot atmosphere f o r 6 hours at approximately 2-month intervals from 6 months of age onward except during the first lactation, which is left undisturbed for record purposes, and during the 45 days preceding each expected parturition. The test animals are placed in a climatic chamber on the afternoon preceding the test, but without any heat. Water, grain, and hay are allowed ad libitum during the afternoon. Grain is also offered the following morning, but all feed is withdrawn before the test is started. Water is available to the animal up to the time of starting the test, but no feed or water is offered during the test period. At about seven in the morning, the heaters and humidifiers are switched on, and the air conditions rise fairly rapidly (15 minutes in summer, 20 minutes in winter) to the desired 105 ° F. and 34 ram. Itg vapor pressure (corresponding to a we~ bulb temperature of 92 ° F. and a relative humidity of 60%). They are maintained at these levels, within 2 ° F. dry- and wet-bulb temperatures, for the remainder of the 6-hour test period. Air temperatures near the floor are somewhat lower than 105 ° F. until the end of the first hour. Rectal temperature is measured by a 5-in. clinical thermometer inserted into the rectum and left in position for 3 minutes. Under hot conditions the chance of error from variations in the position of the thermometer is small. Respiratory rate is measured by counting flank movements over an undisturbed period of 1 minute. Readings are made just before the heat is switched on and at hourly intervals thereafter. Other responses measured during the test, such as water loss and skin wetness, will be reported elsewhere. RESULTS
To reduce the numerous individual observations to manageable proportions, the m e a n of the observations during the test has'been taken as the representative datum. The use of the m e a n has the advantage of minimizing the error inherent Received for publication !~arch 21, 1955. 1 Professor of Physiological Climatology, Johns Hopkins University, Baltimore. 1037
1038
R.E.
i~cDOWELL
ET
AL
in single observations and avoids the uncertainty of interpretation attending such criteria as maximum temperatures. The trapezoidal mean has been used in preference to the straight mean, as more representative of the animal's state while u n d e r test, especially when the initial rise of rectal temperature is rapid.
0.5t6)/6
tm = (0.5to + ti + t2 + t~-F t4 + t~ +
where tm is trapezoidal mean temperature ; tl, t2, etc. are temperatures observed after 1, 2, etc. hours of exposure.
Rectal temperature. The results obtained in these studies are illustrated in Figures 1 and 2, and the analyses of variance are given in Table 1. In these analyses the method recommended by Snedecor (6) for dealing with disproportionate subclass numbers was used. Data are given for both the absolute rectal temperature during exposure and the rise of rectal temperature above the initial value. The latter is probably a better indicator of the additional strain developed in the animal by exposure to heat, but the former indicates the total strain experienced by the animal and thus probably comes closer to suggesting the economic consequences of the situation. Exposure to heat results in a marked rise of rectal temperature in all three categories of animals~heifers, d r y cows, and lactating cows. I f final, or maximum, rectal temperatures had been reported instead of the exposure means, the rise would have been even more striking, since the rectal temperature tends to go on increasing throughout the exposure, especially in the less tolerant animals. IO5
--
HATCHING-FIDUCIAL
LIMITS
(5%LEVEL]
5 Io4 W
IO3
¢Y uJ
~ 102 .,..3 F0 rw r
.:__. I01
~///~ ~
HOT ROOM , J E R S E Y
-~---
HOT ROOM I C R O S S E S
I
- INITIAL ----
I
INITIAL
I
s JERSEY CROSSES
I
]
I
I
I
]
6
8
IO
12 14 16 AGE ( MONTHS )
|8
20
22
J
17
IT
19
17
17
16
17
21
19
C
12
13
14
13
12
12
12
16
12
FIG. 1. I n i t i a l a n d m e a n rectal t e m p e r a t u r e s of heifers during exposure to a s t a n d a r d h o t atmosphere (6 hours a t 105 ° 1~. with 34 mm. H g vapor pressure). N u m b e r s at foot indicate the n u m b e r of animals, J e r s e y s ( J ) and crossbreds (C), tested at each age.
1039
RESPONSES TO A STANDARD HOT ATMOSPHERE
105.0
I
104.0
103,0
102.0
I01.0 Jersey
I DRY J G
90 42
,
[]
Crosses L ~ HGtchinq~Fiducial limits ( 5 % level) i i I
20 PRODUCTION (LB. 17 14 NO. OF TESTS
30 40 of FCM) 53 3" 35 14
50 + 25 14
FIG. 2. I n i t i a l a n d m e a n rectal t e m p e r a t u r e s d u r i n g e x p o s u r e to a s t a n d a r d h o t a t m o s p h e r e (~i h o u r s a t 105 ° F. w i t h 34 m m . H g v a p o r p r e s s u r e ) b y a v e r a g e level of milk p r o d u c t i o n on t h e five d a y s p r e c e d i n g t h e test. N u m b e r s a t f o o t i n d i c a t e t e s t s p e r f o r m e d on J e r s e y s ( J ) a n d c r o s s b r e d s (C) a t v a r i o u s levels of p r o d u c t i o n .
In all three categories both the mean rectal temperature during exposure and the mean rise in rectal temperature above the initial value are greater to a highly significant degree in the Jerseys than in the Sindhi-Jersey crossbred animals. In heifers, the rectal temperature during exposure is higher in the younger animals, but so is the initial temperature, so that the rise on exposure is substantially the same at all ages (Figure I and Table 1). D ry cows show much the same reaction as do the older heifers (Figure 2). In lactating cows, the stage of lactation has little effect upon the reactions to heat. In Jerseys, the rectal temperature on exposure tends to be higher in the earlier months of lactation, but this is also accompanied by a higher initial temperature, so that the rise is substantially the same at all stages. In Sindhi-Jersey crossbred cows, neither the initial rectal temperature nor the mean obtained during exposure is affected by the stage of lactation. The level of production, in sharp contrast to the stage of lactation, has a highly significant effect upon both the absolute and the relative rectal temperature during exposure (Figure 2). When dry cows are included, a significant difference is seen between the development of this effect in the two groups. The rectal temperature during exposure tends to rise steadily with the production level in the Jerseys, but in the Sindhi-Jersey crossbred cows it rises with the lower levels of production to a value which is not furt her affected by furt her increases in production. This interaction between breed and production level is
R. E. lVIoDOWELL ET AL
1040
TABLE 1 Analyses o f variance o f the initial rectal temperature, mean reveal temperature on exposure, and rise in rectal temperature with exposure Mean squares Source of variation
Degrees of freedom
Initial rectal temp.
Mean rectal temp. on exposure
Mean rise in rectal temp. with exposure
(a) H e i f e r s
Breeds Ages Interaction Error
1 8 8 258
0.325 1.910"* 0.022 0.132
50.289** 3.085 *~ 0.369 0.426
55.472** 0.656 0.382 0.396
0.300 0.640* 0.083 0.165
16.554"* 1.807" 0.654 0.562
20.349** 0.648 1.178 0.527
0.016 0.118
15.307"* 0.502
15.311"* 0.503
(b) L a c t a t i n g cows by months of lactation Breeds l~onths Interaction
Error
1 3 3 130 (e) D r y cows
Breeds Error
1 130
(d) Cows by levels of production (excluding dry cows)
Breeds Levels Interaction Error
1 3 3 201
0.215 0.152 0.126 0.185
35.314"* 2.398** 2.239** 0.408
37.634** 1.656" 1.761" 0.608
Significant at the 5% level of probability. ** Significant a t the 1% level of probability.
substantiated by a highly significant mean square in Table 1. The initial rectal temperatures of lactating cows are higher than those of d r y cows, but there is no progressive rise with the level of production. Since seasonal variations in the maintenance environment of animals subjected only periodically to testing may influence their reactions to such tests, the responses of animals to the standard hot atmosphere were examined in relation to season. The analysis and results have been discussed at some length in a previous publication (3), and only a summary needs to be given here. I t was found that there was little repeatability in the responses of the animals unless they were first sorted according to season. When the responses of heifers and d r y cows were plotted by months of the year, an unexpected t r e n d was revealed. The responses showed a maximum in F e b r u a r y with a smaller maximum in August, separated by a marked minimum in May-June. The values in November-December were intermediate. This type of fluctuation was easily observed in the Jerseys, which have the greater response, but it was still discernible in the crossbred animals. W h e n the responses for heifers were sorted by season, as suggested by this variation, a fairly high repeatability was found (Table 2). No repeatability was f o u n d with lactating cows, however, as was to be expected in view of the multiplicity of factors which affect lactation and its consequences for the animal. Respiration rate. Respiratory data are given in Figures 3 and 4, and the analyses of variance in Table 3. Exposure to heat results in a very marked rise
1041
RESPONSES TO A STANDARD HOT ATMOSPHERE
TABLE 2 t~epeatabi~ity ~ of mean body temperature responses b of heifers (8-~'2 months of age) to a standard test hot atmosphere (6 hours at 105 ° 1~. and 34 ram. l t g vapor pressure) when sorted by season Repeatability within seasonal group
Breed Jersey
SindhiJersey (1~1) crosses
Item Repeatability No. of animals No. of tests Repeatability No. of animals No. of tests
Apr.-July (low response) 0.93 ~~ 23 60 0.54 ~ 21 48
Aug.-Sept. & l~eb.-l~ar. (high response) 0.72 ~~ 22 53 0.67 ~ 17 38
Oct.-Jan. (intermediate response) 0.60 ~~ 20 48 0.78 ~ 18 44
~ Significant at 0.01 level of probability. i Coefficient of intra-animal correlatiOn (1, 6). b Trapezoidal mean for a period of 6 hours exposure. of respiration rate in all three categories of animals. Observations made throughout the period of exposure indicate that the respiration rate, unlike the rectal temperature, rises rapidly during the first hour and then remains at about the s a m e l e v e l o r f a l l s s o m e w h a t a s e x p o s u r e p r o c e e d s . T h i s is i n a c c o r d a n c e w i t h observations previously reported on cows (5) and sheep (4). In heifers, both the mean respiratory rate during exposure and the mean rise in respiratory rate above the initial value are greater to a highly significant degree in the Jerseys than in the Sindhi-Jersey crossbred animals. (The lower significance in Table 3 TABLE 3 Analyses of variance of the initial respiration rate, mean respiration rate on exposure, and rise in respiration rate with exposure Mean squares
Source of variation Breeds Ages Interaction Error Breeds Months Interaction Error Breeds Error Breeds Levels Interaction Error
Degrees of freedom
Initial respiration rate
Mean respiration rate on exposure
(a) Heifers 1 1,982.829 ~ 16,140.750 ~ 8 200.291 299.784 8 246.127 75.969 258 152.192 822.283 (b) L a c t a t i n g cows by mouths of lactation 1 970.196 ~ 5,802.264 ~ 3 230.999 390.738 3 93.547 10.584 130 241.309 199.478 (c) Dry cows 1 535.759 ~ 1,041.460 130 119.384 357.52 (d) Cows by levels of production (excluding dry cows) 1 15.669 3,805.264 ~ 3 733.186 ~ 262.580 3 577.953 399.170 201 231.041 211.85
Significant a t the 5% level of probability. ~ Significant at the 1 % level of probability.
Mean rise in respiration rate with exposure 4,766.164 ~ 364.463 664.346 413.380 1,631.130 ~ 698.430 69.709 316.618 363.77 404.22 4,776.468 ~ 236.096 48.467 321.141
1042
2. E. MeDOWELL ET A L
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F i e . 3. I n i t i a l a n d m e a n r e s p i r a t o r y r a t e s of h e i f e r s to a s t a n d a r d h o t a t m o s p h e r e (6 h o u r s a t 105 ° F . w i t h 34 ram. t t g v a p o r p r e s s u r e ) . N u m b e r s a t f o o t indicate t h e n u m b e r of a n i m a l s , J e r s e y s ( J ) a n d c r o s s b r e d s (C) t e s t e d a t each age.
for breed differences in cows sorted by stages of lactation is attributed to the smaller number used in this analysis.) In lactating cows, however, the mean respiratory rate during exposure was higher in the crosses. The initial respiration rate of the Jerseys is the greater to a highly significant degree in heifers and to a significant degree in dry cows, but the difference in lactating cows is obscured by the effects of levels of production. The response to heat is not significantly affected by age in heifers, stage of lactation, or level of production. DISCUSSION
I t is clear that cows of the Fz cross between Jersey and Red Sindhi show a smaller rise of rectal temperature when exposed to severe heat than do comparable purebred Jerseys. This is true whether the comparison be made as young heifers, older heifers, dry cows, or lactating cows at the same production level or stage of lactation. It seems reasonable to suppose that all bodily processes, including milk production, will be adversely affected in an animal which shows a marked rise of rectal temperature. But, from a practical point of view, an animal might have such a high productive capacity that it would continue to yield more milk under
1043
RESPONSES TO A STANDARD HOT ATMOSPHERE
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NO. of TESTS Fro. 4. I n i t i a l a n d m e a n r e s p i r a t o r y r a t e s d u r i n g e x p o s u r e to a s t a n d a r d h o t a t m o s p h e r e (6 h o u r s a t 105 ° F . w i t h 34 ram. H g v a p o r p r e s s u r e ) b y a v e r a g e level o f milk p r o d u c t i o n on t h e five d a y s p r e c e d i n g t h e test. N u m b e r s a t f o o t i n d i c a t e t e s t s p e r f o r m e d on J e r s e y s ( J ) a n d c r o s s b r e d s (C) a t v a r i o u s levels of p r o d u c t i o n .
hot conditions, in spite of the disability, than a more resistant cow with lower productive capacity. The concept of heat tolerance is a complex one, not to be defined in terms of any one response. The diminution of body temperature response with age is to be expected, since the temperament of t h e animals becomes more placid and they acquire a certain familiarity with the proceedings. It is possible that the reduction in basal metabolic rate, which commonly occurs during the early life of most animals, plays a part in reducing the response of body temperature to heat, as to other stresses. The effect of milk production upon the response of body temperature is most interesting. That the response should increase with lactation and that the degree of rise should bear some relation to the level of production are to be expected. The interest lies in the comparative behavior of the two breeds. It is well known that Zebu types have a lower level of production than do the better European
1044
~. E. M c D O W E L L
ET AL
types, and it is sometimes argued that the superior heat tolerance of the Zebu would be nullified if its production were raised to the European level, especially if this increase in production were effected by introduction of production genes from European stock. It is clear, however, from the curves of Figure 2 that half-breed animals at the same level of production as pure Jerseys still show a greater resistance to heat stress (as judged by rise of body temperature). The greater heat resistance of the Zebu is therefore not entirely due to low production. It will be interesting to see if this superiority is maintained in the F2 generation and at what combination of European and Zebu " b l o o d " the productive superiority of the one will offset the heat resistance of the other. The high repeatability of body temperature response to the test conditions, once biassing factors such as season and milk production are excluded, justifies the continuance of present procedures for measuring comparative responses of rectal temperature to heat stress, but caution must be exercised in identifying such responses with the wider concept of " h e a t tolerance" until more extensive studies have been made. It is interesting to note that the Sindhi-Jersey crossbred animals not only maintain a lower rectal temperature than the Jerseys but do so with a lower respiration rate. This is in full agreement with the contention argued elsewhere (2) that differences in respiratory activity are the result and not the cause of differences in heat tolerance. That age in heifers and level of production in lactating animals should not have any effect on respiration, although they do affect body temperature response, is not surprising when one realizes that most animals are near the ceiling of their respiratory effort under the test conditions used. A decrease in respiratory effort could hardly be expected until a substantial reduction in body temperature had been attained. SUMMARY
Jersey and Red Sindhi-Jersey (F1) crossbred cows are subjected at regular intervals to a standard test atmosphere at 105 ° F. with a vapor pressure of 34 ram. Hg (wet bulb 92 ° F.). The mean response of rectal temperature is less in the crossbred animals than in the Jerseys, whether the comparison be made as young heifers, older heifers, dr y cows, or lactating cows. The difference occurs also when comparisons are made between animals at the same level of production. In heifers, both initial temperature and temperature during exposure are higher in the younger animals, but the rise is similar at all ages. Dry cows show much the same reactions as older heifers. The stage of lactation has little effect on the response of rectal t'emperature to heat, but the level of production has considerable effect. The rectal temperature during exposure tends to increase fairly steadily with production in Jerseys, but in F1 crossbreds it quickly reaches a level which does not rise with further increases in production. There is marked seasonal variation in body temperature response. Repeatability of response is high in heifers when results are sorted by season, but low in lactating cows.
RESPONSES TO A STANDARD HOT ATMOSPHERE
1045
I n h e i f e r s t h e r e s p i r a t o r y r e s p o n s e of th e J e r s e y s to h e a t is g r e a t e r t h a n t h a t o f t h e S i n d h i - J e r s e y c r o s s b r e d a n i m a l s , b u t as l a c t a t i n g cows t h e r e v e r s e w as f o u n d . N o d i f f e r e n c e w a s seen i n d r y cows. T h e c o n t e n t i o n is c o n f i r m e d t h a t diff eren ces i n r e s p i r a t o r y r a t e a r e th e r e s u l t a n d n o t t h e cause of d i f f er en ces i n heat tolerance. REFERENCES (1) LUSH, J. L. Animal Breeding Plans. Iowa State College Press, Ames. 1945. (2) McDowELL, R. E., LEE, D. H. K., FO~B~'~, ~I. H., AN1) ANDF-~S0~, R. S. Respiratory Activity as an Index of Heat Tolerance in Jersey and Sindhi × Jersey (F1) Crossbred Cows. J. Animal Sci., 12: 573. 1953. (8) HcDow~L, R. E., HATTHmVS, C. A., LEE, D. H. K., AND FOHR~'~, H. H. Repeatability of an Experimental Heat Tolerance Test and Influence of Season. J. Animal Sol., 12: 757. 1953. (4) RIEK, R. F., HARDY,M. H., L ~ , D. H. K., AND CARTER,H. B. The Effect of the Dietary Plane upon the Reactions of Two Breeds of Sheep during Short Exposures to Hot Environments. Australian J. Agr. Researeh, 1 : 217. I950. (5) RIEK, R. F., AND LB~., D. H. K. Reactions to Hot Atmospheres of Jersey Cows in Milk. J. Dairy Research, 15: 219. 1948. (6) SNEI)EC0R, G. W. Statistical Methods. 4th ed., p. 289. Iowa State College Press, Ames. 1946.