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Hematological Changes Associated with Divergent Selection for Packed Erythrocyte Volume in Japanese Quail
1298
N. K. ALLEN AND D. H. BAKER
Huston, R. L., and H. M. Scott, 1968. Effect of varying the composition of a crystalline amino acid mixture on weight gain and pattern of free amino acids in chick tissue. Federation Proc. 27: 1204-1209. Klain, G. J., H. M. Scott and B. C. Johnson, 1960. The amino acid requirement of the growing chick fed a crystalline amino acid diet. Poultry Sci. 39: 39-44. Mathieu, D., and H. M. Scott, 1968. Growth depressing effect of excess leucine in relation to
the amino acid composition of the diet. Poultry Sci. 47: 1694. Mitchell, H. H., 1964. Comparative Nutrition of Man and Domestic Animals V. 2. Academic Press, New York, New York, p. 296. Sauberlich, H. E., 1961. Studies on the toxicity and antagonism of amino acids for weanling rats. J. Nutr. 75 : 61-72. Spolter, P. D., and A. E. Harper, 1961. Leucineisoleucine antagonism in the rat. Am. J. Physiol. 200: 513-518.
Department
F. K. R. STINO AND K. W. WASHBURN of Poultry Science, University of Georgia, Athens, Georgia 30601 (Received for publication November 13, 1971)
ABSTRACT Four generations of divergent selection for 15 day packed erythrocyte volume (P.C.V.) in the Japanese quail resulted in a significant corresponding change in 15 day erythrocyte number (R.B.C. count) and hemoglobin content (H.C.) There was no increase in mean corpuscular volume (M.C.V.) in the line selected for high P.C.V., while there was a slight decrease in the M.C.V. of the line selected for low P.C.V. This would indicate that the change in IS day P.C.V. by selection was mainly due to changes in R.B.C. count. The accompanying change in H.C. was also due to the R.B.C. count rather than their mean corpuscular hemoglobin concentration (M.C.H.C.) since the M.C.H.C. was not changed by selection. Selection for 15 day P.C.V. was effective in changing 8-week P.C.V. and similar hematological data obtained at 8 weeks of age showed the same trend observed at 15 days of age. POULTRY SCIENCE 51:
F
OUR generations of divergent selection for high and low packed erythrocyte volume (P.C.V.) at IS days of age in the Japanese quail separated a high P.C.V. line from a low P.C.V. line by a factor of 29% (Stino, 1971). The sole criterion of selection was 15 day P.C.V., determined by the microhematocrit method, although a number of correlated changes in physiological traits were observed (Stino, 1971). The magnitude of a P.C.V. value for which selection was made is determined by both the number and size of erythrocytes, and it will normally decrease or increase with any decrease or increase in number
1298-1301,
1972
and/or size of the erythrocytes. If there is a change in the total number of erythrocytes, a corresponding change will occur in the total hemoglobin content (H.C). Thus the selection pressure applied to P.C.V. could theoretically force a change in either the numbers or the size of the erythrocytes. Previous papers have dealt with the response of P.C.V. of IS day old Japanese quail to selection under stress and nonstress diets, heritabilities of P.C.V. under the two selection regimes, genetic basis of P.C.V. in Japanese quail, and effects of exchanging the environment on P.C.V. and with correlated changes in growth, re-
Downloaded from http://ps.oxfordjournals.org/ at Northern Arizona University on June 8, 2015
Hematological Changes Associated with Divergent Selection for Packed Erythrocyte Volume in Japanese Quail
SELECTION FOR PACKED CELL VOLUME
production and livability (Stino, 1971). The present paper presents data showing that the progress achieved by selection for 15 day P.C.V. in Japanese quail was through changes in erythrocyte numbers with little or no change in size, suggesting a physiological selection threshold for erythrocyte size. MATERIALS AND METHODS
cas, 1955) and the M.C.H.C. was calculated from the H.C. and P.C.V. values. Reciprocal crosses as well as pure line progeny were obtained from the S4 selected high and low P.C.V. lines. Twenty, 15 day old birds from each reciprocal cross, pure line, and randombred controls were used to observe changes, other than in P.C.V., occurring in the 15 day hematological parameters. Blood samples were collected by decapitation (care was taken so that the contents of the crop would not contaminate the blood sample) and the previous hematological parameters were measured for each individual sample. RESULTS AND DISCUSSION
In the initial base population (Stino, 1971) the mean P.C.V. was 37.5%. The P.C.V. values based on the $>4 selected lines of the entire population were 41.9 and 32.7% for the high and low lines, respectively. The P.C.V. values as well as other hematological data for a sample (20 birds per group) of the S4 generation selected lines (high P.C.V. line-HH-and low P.C.V. line-LL-) and their reciprocal crosses at 15 days of age (HL and LH) are presented in Table 1. In this subpopulation the mean P.C.V. value for the pure-breeding high P.C.V. line was 43.3% compared to 36.1% for the pure-breeding low-P.C.V. line. These values were significantly different from each other and from the P.C.V. value for the randombred controls (40.2%). The P.C.V. of the reciprocal crosses and the randombred controls were intermediate between both selected lines (Table 1) and significantly different from either pure line. Since the magnitude of P.C.V. is a function of R.B.C. counts and M.C.V. one would expect a change in R.B.C. counts and/or M.C.V. associated with the change in P.C.V. The high P.C.V. line at 15 days of age had 18% more erythrocytes than the
Downloaded from http://ps.oxfordjournals.org/ at Northern Arizona University on June 8, 2015
Data were obtained from two lines of Japanese quail which had been individually selected for four generations in divergent directions for 15 day packed erythrocyte volume (P.C.V.). The base population was the randombred population maintained at the Southern Regional Poultry Genetics Laboratory. Randombred controls were raised intermingled with the high and low P.C.V. lines for each generation and with the various crosses. Selection was on the basis of high or low P.C.V. at 15 days for quail fed a turkey starter diet (2945 M.E., 30% protein) (Stino, 1971). Each generation the birds were selected on the basis of their 15 day P.C.V. and reared to eight weeks of age at which time a 1 ml. blood sample was collected from the brachial vein to measure the following hematological parameters: packed erythrocyte volume (P.C.V.), erthrocyte counts (R.B.C. counts), hemoglobin content (H.C.), mean corpuscular volume (M.C.V.) and mean corpuscular hemoglobin concentration (M.C.H.C). In the determination of the hematological parameters blood was collected into heparinized tubes and within one hour the erythrocyte counts and mean cell volume determined by a Coulter Counter Model F with the Coulter Mean Cell Volume Computer (Mattern et al., 1957). P.C.V. values were calculated from the R.B.C. and M.C.V. values. Hemoglobin was quantitated by the acid hematin method (Denington and Lu-
1299
1300
F. K. R. STINO AND K. W. WASHBURN
TABLE 1.—Means and standard errors of 15 day P.C.V., M.C.V., R.B.C. counts, H.C. and M.C.U.C. of Si selected quail lines, their reciprocal crosses and the randombred controls Lines and Crosses
P.C.V.
M.C.V.
CNTS.
H.C.
M.C.H.C.
HH* LL HL LH RB
43.3" ± . 7 36.1"+. 8 41.0b+.6 40.5b+.7 40.2b+.6
129"+ 1 127"+1 128"+1 127"+1 129"+1
335' + 7 283" + 6 321''= + 5 320bc + 6 313" + 5
10.9d+.3 9.0" + . 2 10.8 c d +.2 10.2 b °+.2 9.9 b + . 2
25.2" b +.5 25.1"b+.6 26.4 b + . 6 25.3" b +.6 24.6" + . 4
* The first letter designates the male and the second the female, i.e., H H means the high line and HL means high line malesXlow line females. Values with different superscripts within each environment and trait differ significantly (Duncan, 1955) from each other ( P < . 0 5 ) .
creased or decreased P.C.V. did not influence the hemoglobin synthesis capacity of the individual erythrocyte. Hematological data at eight weeks of age for each generation of the lines selected for high and low IS day P.C.V. are presented in Figure 1. Changes for 15 day P.C.V. were accompanied by changes in the 8week P.C.V. (Figure 1). After four generations of selection for 15 day P.C.V., the 8-
FIG. 1. Eight week hematological parameters of high and low P.C.V. quail lines expressed as deviation from the randombred controls.
Downloaded from http://ps.oxfordjournals.org/ at Northern Arizona University on June 8, 2015
low line, a statistically significant (P < .05) difference (Table 1). The R.B.C. count of the randombred controls was intermediate between the two selected lines. However, the R.B.C. count of the reciprocal crosses was closer to that of the high line (Table 1). In contrast to the changes in the R.B.C. values which were comparable to those for P.C.V., there were no significant changes in the M.C.V. due to selection for P.C.V. As shown in Table 1 the M.C.V. values were similar for all lines tested. These results indicate that the change in IS day P.C.V. by selection was through changes in erythrocyte number and not their size. The closer resemblance of the R.B.C. count of the reciprocal crosses to that of the high P.C.V. line would indicate some dominant gene action for the high R.B.C. count. As expected, due to the change in P.C.V., the high P.C.V. line had 2 1 % higher hemoglobin content (H.C.) than the low line (Table 1). In the absence of a hypochromic anemia this statistically significant difference would be expected since the P.C.V. and total R.B.C. counts were different. The H.C. of the randombred controls was intermediate between the selected pure-lines. However, that of the reciprocal crosses was closer to the high line with an apparent paternal effect. There was no significant difference between either selected lines and the randombred controls in their M.C.H.C. (Table 1) indicating that selection for in-
SELECTION FOR PACKED CELL VOLUME
as to the size of the erythrocyte. Stino (1971) reported that the P.C.V. of the adult male Japanese quail was 18% higher than that of the adult female. He contributed 16% of these differences to the R.B.C. count and 2% to the M.C.V. Differences in the P.C.V. due to selection followed the same pattern as the difference between males and females. This suggests the possibility that the selection for P.C.V. was mainly due to the indirect selection of testosterone level. The high or low level of testosterone would influence the erythropoietin levels (Gordon et al., 1968) and consequently the erythrocyte number. Changes in 8-week H.C. correspond with the observed changes in the P.C.V. Selection for increased or decreased 15-day P.C.V. for four generations failed to reveal any association between 15-day P.C.V. and 8-week M.C.H.C. This would indicate that selection to increase or decrease the P.C.V. did not influence the hemoglobin synthesis capability of the individual erythrocyte. Thus, the observed change in hemoglobin content is due to the change in erythrocyte number. REFERENCES Denington, E. M., and A. M. Lucas, 1955. Blood techniques for chickens. Poultry Sci. 34: 360368. Duncan, D. B., 1955. Multiple range and multiple F tests. Biometrics, 11: 1-42. Gordon, A. S., E. A. Mirand, J. Wenig, R. Katz and E. D. Zanjani, 1968. Androgen action on erythropoiesis. Ann. New York Acad. Sci. 149: 318-335. Mattern, C. F. T., F. S. Brackett and B. J. Olson, 1957. Determination of number and size of particles by electrical gating; blood cell. J. Appl. Physiol. 10: 56-70. Stino, F. K. R., 1971. Divergent selection for packed erythrocytes volume in the Japanese quail under two nutritional environments. Ph.D. Dissertation, University of Georgia. 105 pp.
Downloaded from http://ps.oxfordjournals.org/ at Northern Arizona University on June 8, 2015
week P.C.V. of the high P.C.V. line males exceeded that of the low line by 35% While that of the high P.C.V. line females exceeded that of the low line by 24%. These results are expected, since real genetic change in IS day P.C.V. should have a carry-over effect for the life of the individual. Mass selection in divergent directions for IS day P.C.V. resulted in associated changes in the 8-week R.B.C. count. Selection for high IS-day P.C.V. caused an increase in 8-week R.B.C. count and selection for low IS-day P.C.V. caused a decrease in R.B.C. count (Figure 1). After four generations of selection, the R.B.C. count of the high P.C.V. line males was 28% higher than the low line males with the comparable value for the females being 15%. In contrast to the effects of selection for IS-day P.C.V. on 8-week R.B.C. count, four generations of selection for high 15day P.C.V. failed to increase the 8-week M.C.V. of the selected lines over their randombred controls (Figure 1). However, it appears that the M.C.V can be decreased by selection for lowered P.C.V. since selection for 15-day, low P.C.V. resulted in a slight but significant (P < .05) decrease in 8-week M.C.V. (Figure 1). A slight decrease in 15 day M.C.V. in the low P.C.V. line was also observed, but this difference was not significant. These results, with those of the 15-day hematological data, indicate that the mean red blood cell volume of the Japanese quail is at a threshold level. Although selection for decreased P.C.V. may decrease erythrocyte size slightly, it was not possible to increase cell size. This could be due to the limiting factor of the diameter of the microcapillaries through which the blood must pass which might set the upper limit
1301
N. K. ALLEN AND D. H. BAKER
Huston, R. L., and H. M. Scott, 1968. Effect of varying the composition of a crystalline amino acid mixture on weight gain and pattern of free amino acids in chick tissue. Federation Proc. 27: 1204-1209. Klain, G. J., H. M. Scott and B. C. Johnson, 1960. The amino acid requirement of the growing chick fed a crystalline amino acid diet. Poultry Sci. 39: 39-44. Mathieu, D., and H. M. Scott, 1968. Growth depressing effect of excess leucine in relation to
the amino acid composition of the diet. Poultry Sci. 47: 1694. Mitchell, H. H., 1964. Comparative Nutrition of Man and Domestic Animals V. 2. Academic Press, New York, New York, p. 296. Sauberlich, H. E., 1961. Studies on the toxicity and antagonism of amino acids for weanling rats. J. Nutr. 75 : 61-72. Spolter, P. D., and A. E. Harper, 1961. Leucineisoleucine antagonism in the rat. Am. J. Physiol. 200: 513-518.
Department
F. K. R. STINO AND K. W. WASHBURN of Poultry Science, University of Georgia, Athens, Georgia 30601 (Received for publication November 13, 1971)
ABSTRACT Four generations of divergent selection for 15 day packed erythrocyte volume (P.C.V.) in the Japanese quail resulted in a significant corresponding change in 15 day erythrocyte number (R.B.C. count) and hemoglobin content (H.C.) There was no increase in mean corpuscular volume (M.C.V.) in the line selected for high P.C.V., while there was a slight decrease in the M.C.V. of the line selected for low P.C.V. This would indicate that the change in IS day P.C.V. by selection was mainly due to changes in R.B.C. count. The accompanying change in H.C. was also due to the R.B.C. count rather than their mean corpuscular hemoglobin concentration (M.C.H.C.) since the M.C.H.C. was not changed by selection. Selection for 15 day P.C.V. was effective in changing 8-week P.C.V. and similar hematological data obtained at 8 weeks of age showed the same trend observed at 15 days of age. POULTRY SCIENCE 51:
F
OUR generations of divergent selection for high and low packed erythrocyte volume (P.C.V.) at IS days of age in the Japanese quail separated a high P.C.V. line from a low P.C.V. line by a factor of 29% (Stino, 1971). The sole criterion of selection was 15 day P.C.V., determined by the microhematocrit method, although a number of correlated changes in physiological traits were observed (Stino, 1971). The magnitude of a P.C.V. value for which selection was made is determined by both the number and size of erythrocytes, and it will normally decrease or increase with any decrease or increase in number
1298-1301,
1972
and/or size of the erythrocytes. If there is a change in the total number of erythrocytes, a corresponding change will occur in the total hemoglobin content (H.C). Thus the selection pressure applied to P.C.V. could theoretically force a change in either the numbers or the size of the erythrocytes. Previous papers have dealt with the response of P.C.V. of IS day old Japanese quail to selection under stress and nonstress diets, heritabilities of P.C.V. under the two selection regimes, genetic basis of P.C.V. in Japanese quail, and effects of exchanging the environment on P.C.V. and with correlated changes in growth, re-
Downloaded from http://ps.oxfordjournals.org/ at Northern Arizona University on June 8, 2015
Hematological Changes Associated with Divergent Selection for Packed Erythrocyte Volume in Japanese Quail
SELECTION FOR PACKED CELL VOLUME
production and livability (Stino, 1971). The present paper presents data showing that the progress achieved by selection for 15 day P.C.V. in Japanese quail was through changes in erythrocyte numbers with little or no change in size, suggesting a physiological selection threshold for erythrocyte size. MATERIALS AND METHODS
cas, 1955) and the M.C.H.C. was calculated from the H.C. and P.C.V. values. Reciprocal crosses as well as pure line progeny were obtained from the S4 selected high and low P.C.V. lines. Twenty, 15 day old birds from each reciprocal cross, pure line, and randombred controls were used to observe changes, other than in P.C.V., occurring in the 15 day hematological parameters. Blood samples were collected by decapitation (care was taken so that the contents of the crop would not contaminate the blood sample) and the previous hematological parameters were measured for each individual sample. RESULTS AND DISCUSSION
In the initial base population (Stino, 1971) the mean P.C.V. was 37.5%. The P.C.V. values based on the $>4 selected lines of the entire population were 41.9 and 32.7% for the high and low lines, respectively. The P.C.V. values as well as other hematological data for a sample (20 birds per group) of the S4 generation selected lines (high P.C.V. line-HH-and low P.C.V. line-LL-) and their reciprocal crosses at 15 days of age (HL and LH) are presented in Table 1. In this subpopulation the mean P.C.V. value for the pure-breeding high P.C.V. line was 43.3% compared to 36.1% for the pure-breeding low-P.C.V. line. These values were significantly different from each other and from the P.C.V. value for the randombred controls (40.2%). The P.C.V. of the reciprocal crosses and the randombred controls were intermediate between both selected lines (Table 1) and significantly different from either pure line. Since the magnitude of P.C.V. is a function of R.B.C. counts and M.C.V. one would expect a change in R.B.C. counts and/or M.C.V. associated with the change in P.C.V. The high P.C.V. line at 15 days of age had 18% more erythrocytes than the
Downloaded from http://ps.oxfordjournals.org/ at Northern Arizona University on June 8, 2015
Data were obtained from two lines of Japanese quail which had been individually selected for four generations in divergent directions for 15 day packed erythrocyte volume (P.C.V.). The base population was the randombred population maintained at the Southern Regional Poultry Genetics Laboratory. Randombred controls were raised intermingled with the high and low P.C.V. lines for each generation and with the various crosses. Selection was on the basis of high or low P.C.V. at 15 days for quail fed a turkey starter diet (2945 M.E., 30% protein) (Stino, 1971). Each generation the birds were selected on the basis of their 15 day P.C.V. and reared to eight weeks of age at which time a 1 ml. blood sample was collected from the brachial vein to measure the following hematological parameters: packed erythrocyte volume (P.C.V.), erthrocyte counts (R.B.C. counts), hemoglobin content (H.C.), mean corpuscular volume (M.C.V.) and mean corpuscular hemoglobin concentration (M.C.H.C). In the determination of the hematological parameters blood was collected into heparinized tubes and within one hour the erythrocyte counts and mean cell volume determined by a Coulter Counter Model F with the Coulter Mean Cell Volume Computer (Mattern et al., 1957). P.C.V. values were calculated from the R.B.C. and M.C.V. values. Hemoglobin was quantitated by the acid hematin method (Denington and Lu-
1299
1300
F. K. R. STINO AND K. W. WASHBURN
TABLE 1.—Means and standard errors of 15 day P.C.V., M.C.V., R.B.C. counts, H.C. and M.C.U.C. of Si selected quail lines, their reciprocal crosses and the randombred controls Lines and Crosses
P.C.V.
M.C.V.
CNTS.
H.C.
M.C.H.C.
HH* LL HL LH RB
43.3" ± . 7 36.1"+. 8 41.0b+.6 40.5b+.7 40.2b+.6
129"+ 1 127"+1 128"+1 127"+1 129"+1
335' + 7 283" + 6 321''= + 5 320bc + 6 313" + 5
10.9d+.3 9.0" + . 2 10.8 c d +.2 10.2 b °+.2 9.9 b + . 2
25.2" b +.5 25.1"b+.6 26.4 b + . 6 25.3" b +.6 24.6" + . 4
* The first letter designates the male and the second the female, i.e., H H means the high line and HL means high line malesXlow line females. Values with different superscripts within each environment and trait differ significantly (Duncan, 1955) from each other ( P < . 0 5 ) .
creased or decreased P.C.V. did not influence the hemoglobin synthesis capacity of the individual erythrocyte. Hematological data at eight weeks of age for each generation of the lines selected for high and low IS day P.C.V. are presented in Figure 1. Changes for 15 day P.C.V. were accompanied by changes in the 8week P.C.V. (Figure 1). After four generations of selection for 15 day P.C.V., the 8-
FIG. 1. Eight week hematological parameters of high and low P.C.V. quail lines expressed as deviation from the randombred controls.
Downloaded from http://ps.oxfordjournals.org/ at Northern Arizona University on June 8, 2015
low line, a statistically significant (P < .05) difference (Table 1). The R.B.C. count of the randombred controls was intermediate between the two selected lines. However, the R.B.C. count of the reciprocal crosses was closer to that of the high line (Table 1). In contrast to the changes in the R.B.C. values which were comparable to those for P.C.V., there were no significant changes in the M.C.V. due to selection for P.C.V. As shown in Table 1 the M.C.V. values were similar for all lines tested. These results indicate that the change in IS day P.C.V. by selection was through changes in erythrocyte number and not their size. The closer resemblance of the R.B.C. count of the reciprocal crosses to that of the high P.C.V. line would indicate some dominant gene action for the high R.B.C. count. As expected, due to the change in P.C.V., the high P.C.V. line had 2 1 % higher hemoglobin content (H.C.) than the low line (Table 1). In the absence of a hypochromic anemia this statistically significant difference would be expected since the P.C.V. and total R.B.C. counts were different. The H.C. of the randombred controls was intermediate between the selected pure-lines. However, that of the reciprocal crosses was closer to the high line with an apparent paternal effect. There was no significant difference between either selected lines and the randombred controls in their M.C.H.C. (Table 1) indicating that selection for in-
SELECTION FOR PACKED CELL VOLUME
as to the size of the erythrocyte. Stino (1971) reported that the P.C.V. of the adult male Japanese quail was 18% higher than that of the adult female. He contributed 16% of these differences to the R.B.C. count and 2% to the M.C.V. Differences in the P.C.V. due to selection followed the same pattern as the difference between males and females. This suggests the possibility that the selection for P.C.V. was mainly due to the indirect selection of testosterone level. The high or low level of testosterone would influence the erythropoietin levels (Gordon et al., 1968) and consequently the erythrocyte number. Changes in 8-week H.C. correspond with the observed changes in the P.C.V. Selection for increased or decreased 15-day P.C.V. for four generations failed to reveal any association between 15-day P.C.V. and 8-week M.C.H.C. This would indicate that selection to increase or decrease the P.C.V. did not influence the hemoglobin synthesis capability of the individual erythrocyte. Thus, the observed change in hemoglobin content is due to the change in erythrocyte number. REFERENCES Denington, E. M., and A. M. Lucas, 1955. Blood techniques for chickens. Poultry Sci. 34: 360368. Duncan, D. B., 1955. Multiple range and multiple F tests. Biometrics, 11: 1-42. Gordon, A. S., E. A. Mirand, J. Wenig, R. Katz and E. D. Zanjani, 1968. Androgen action on erythropoiesis. Ann. New York Acad. Sci. 149: 318-335. Mattern, C. F. T., F. S. Brackett and B. J. Olson, 1957. Determination of number and size of particles by electrical gating; blood cell. J. Appl. Physiol. 10: 56-70. Stino, F. K. R., 1971. Divergent selection for packed erythrocytes volume in the Japanese quail under two nutritional environments. Ph.D. Dissertation, University of Georgia. 105 pp.
Downloaded from http://ps.oxfordjournals.org/ at Northern Arizona University on June 8, 2015
week P.C.V. of the high P.C.V. line males exceeded that of the low line by 35% While that of the high P.C.V. line females exceeded that of the low line by 24%. These results are expected, since real genetic change in IS day P.C.V. should have a carry-over effect for the life of the individual. Mass selection in divergent directions for IS day P.C.V. resulted in associated changes in the 8-week R.B.C. count. Selection for high IS-day P.C.V. caused an increase in 8-week R.B.C. count and selection for low IS-day P.C.V. caused a decrease in R.B.C. count (Figure 1). After four generations of selection, the R.B.C. count of the high P.C.V. line males was 28% higher than the low line males with the comparable value for the females being 15%. In contrast to the effects of selection for IS-day P.C.V. on 8-week R.B.C. count, four generations of selection for high 15day P.C.V. failed to increase the 8-week M.C.V. of the selected lines over their randombred controls (Figure 1). However, it appears that the M.C.V can be decreased by selection for lowered P.C.V. since selection for 15-day, low P.C.V. resulted in a slight but significant (P < .05) decrease in 8-week M.C.V. (Figure 1). A slight decrease in 15 day M.C.V. in the low P.C.V. line was also observed, but this difference was not significant. These results, with those of the 15-day hematological data, indicate that the mean red blood cell volume of the Japanese quail is at a threshold level. Although selection for decreased P.C.V. may decrease erythrocyte size slightly, it was not possible to increase cell size. This could be due to the limiting factor of the diameter of the microcapillaries through which the blood must pass which might set the upper limit
1301