The Journal of Heredity 70:273-274. 1979.
Distribution of sexes in cattle ELMER GRAY AND VALINA K. HURT
REATER KNOWLEDGE of sex ratios and distriVjTbutions of sexes within progenies has been sought in an effort to control sexes of domesticated animals for economic gain and to provide a population control measure in humans. In a recent review of sex ratio studies in cattle, Powell et al.7 stated that the sex ratio (percentage of all births that is male) in cattle is near 50 percent with the percentage of males being slightly higher in most reports. In the study conducted by Powell et al.7, the sex ratio was 52.9 percent for a sample consisting of 513,624 single births in dairy cattle. The ratio was 51.4 percent for a carefully edited subset of 14,559 progeny by 94 sires in Holstein herds. Heritability estimates were near zero for sires used in genetic analysis of sex ratios. Several studies of the human sex ratio and the distribution of sexes within families have been reported. In most studies the proportion of males has exceeded the proportion of females, with the most commonly observed human secondary sex ratio being approximately 106:100 (males: females at birth)8. Some investigators1'2'5-6 have found positive correlations between sexes of successive births within families, whereas other workers3-4 have found no associations between sexes of successive births. Generally observed frequencies of combinations of sexes within different family sizes have not differed significantly from expected frequencies obtained by using the observed sex ratio and the binomial expansion4"6. Since associations between sexes within families have not been consistent in subsets of the human population, such studies need to encompass other species. Associations between sexes within progenies of cattle apparently have not been reported. The objective of the present investigation was to study the distribution of sexes of calves within progenies of Holstein dams.
of parities separated by two (calf n vs. calf n + 3 for «= 1 — 9), and for parities separated by three or more (#i=l-9). Each dam's offspring was divided into combinations of sexes. Through expansion of the binomial using the observed sex ratio, the expected frequencies of combinations of sexes in each offspring size (n = 2-5) were calculated. The observed and expected combinations of sexes were compared using chi-square.
Results Sex ratio The overall sex ratio for 4,245 single parities was 52.74 percent. This ratio is similar to the 52.9 percent reported by Powell et al.7for a much larger sample. Ratios by order of parities (Table I) fluctuated around the overall sex ratio with a combined ratio of 51.97 percent for the first five parities. Ratios for all parities except the third indicated a slightly greater proportion of males than females in the progeny. The ratio (48.70 percent) for the third parity differed significantly (0.05 level of probability) from the overall sex ratio (52.74 percent) and from the sex ratio (52.9 percent) reported by Powell et al.7. No biological explanation is evident for this aberrant ratio. Correlations between sexes Correlation coefficients between the sexes of calves of successive and nonsuccessive parities are presented in Table II. Generally the coefficients were low and nonsignificant, indicating no apparent association between sexes of calves of parities that were successive (Table IIA) or separated by one (Table IIB), by two (Table HC), or by three or more parities (Table IID). None of the coefficients for total effects of the successive and various nonsuccessive parities was significant. The correlation between the sexes of the third and fifth calves (Table IIB) was highly significant (P < 0.01). However, this correlation is attributed to chance rather than to a true biological relationship.
Population and Methods Data were obtained from records of 1,046 Holstein cows included in the dairy herd at Cornell University during the period 1940 through 1977. Records were selected to get dams that had at least two parities. Multiparous births, abortions, and calves born dead (no sex recorded) were excluded from the analyses. Sex by order of parity was determined for the calves of each dam. These data were used to calculate a sex ratio for each parity (1 through 5) and to calculate correlation coefficients between sexes of successive calves. Correlation coefficients were computed between the sexes of successive parities (calf n vs. calf n+\ for /j=l-9), of parities separated by one (calf n vs. calf n + 2 for n= 1-9), The authors are, respectively, professor of agriculture and dean of the Graduate College; and graduate assistant, Department of Biology, Western Kentucky University, Bowling Green, KY 42101. Sincere appreciation is expressed to Dr. R. W. Everett and Ms. Susan Herbert, Department of Animal Science, Cornell University, for providing the data for this study.
Combinations of sexes Data for dams having a total of 2,3,4, or 5 single parities were used to test the observed frequencies of combinations of sexes against the expected frequencies that were based on the overall observed sex ratio and the binomial expansion. None of the resulting chi-squares was signifTable I. Sex ratio by order of parity Parity
No. calves
First Second Third Fourth Fifth Combined
1,105
273
982 690 455 283
3,422
Sex ratio (percent males) 53.10 51.42 48.70 54.50 53.71 51.97
The Journal of Heredity
274
icant (0.05 level of probability), indicating that the ob- sexes appeared to be independent as evidenced by 1) the served frequencies of combinations of sexes within failure of the sex ratio for different parities to differ conprogenies of 2, 3, 4, or 5 calves appeared as expected. sistently from the overall ratio; 2) the lack of evidence of association between the sexes of successive and various nonsuccessive calves; and 3) the absence of significant deviations of observed and expected frequencies of comDiscussion binations of sexes within progenies. These results support The overall sex ratio of 52.74 percent indicates the oc- those of Powell et al., in which the sex ratio was currence of more male than female calves in the sample 52.9 percent and varied only slightly for progenies of difof Holsteins studied. Other aspects of the distribution of ferent sires. One intent of the present investigation was to compare the results obtained for sex distribution in cattle with the Table II. Correlations between sexes results of sex distribution studies that have been reported for the human population. The sex ratio of 52.74 percent Calf pair df is equal to 111.6:100 (males: females) when expressed in human sex ratio terminology. This ratio is included within A. Successive parities (n = 1-9) the range of sex ratios for different subsets of the human 1 vs. 2 +0.0124 951 population and is comparable to the most widely accepted 2 vs. 3 -0.0307 649 ratio of 106:100 for white Americans8. The failure to find + 0.0187 3 vs. 4 429 a positive association between sexes of successive calves +0.1231 4 vs. 5 259 supports the results reported for some subsets of the hu+ 0.0560 5 vs. 6 160 man population3-4. However, positive associations be+ 0.1429 6 vs. 7 91 tween sexes of successive children have been found in -0.2061 7 vs. 8 51 other subsets1-2-5". The agreement between observed and +0.1985 8 vs. 9 32 expected frequencies of sexes of calves in progenies of +0.0182 Total effect 2636 different sizes is consistent with the agreement between observed and expected frequencies of combinations of B. Parities separated by one ( « = 1-9) sexes of children in families of different sizes4"". 1 vs. 3 +0.0180 818 2 vs. 4 3 vs. 5 4 vs. 6 5 vs. 7 6 vs. 8 7 vs. 9 Total effect
+0.0461 +0.1667* +0.0026 -0.0633 -0.1019 +0.0156 +0.0390
C. Panties separated by two ( / i = l - 9 ) 1 vs. 4 + 0.0092 2 vs. 5 + 0.0149 3 vs. 6 -0.0494 4 vs. 7 + 0.0426 5 vs. 8 -0.1534 6 vs. 9 -0.0221 Total effect -0.0045 D.
435 245 155 88 54 30 1837
437 267
165 93 52 32
Literature Cited
Parities separated by three or more -0.0889 -0.0743 + 0.0196 + 0.1481 + 0.0665
272 161
1 vs. 6 2 vs. 7 3 vs.8 4 vs. 9
-0.0988 +0.0435 +0.0071 +0.1176
167 90 53 34
1 vs. 7 2 vs. 8 3 vs. 9
+ 0.0213 + 0.1481 0.0000
94 54 32
1 vs.8 2 vs. 9
-0.0442 -0.0778
55 33
-0.2067 -0.0254
33 1296
* Significant at the 0.01 level of probability
Data were obtained from records of 1,046 Holstein dams included in the dairy herd at Cornell University during the years 1940 through 1977. Sex by order of parity was determined for the offspring of each dam. The overall sex ratio for 4,245 single parities was 52.74 percent males. Sex ratios for different parities were relatively consistent. Within progenies of the dams, there was no consistent evidence of association between the sexes of successive and various nonsuccessive calves. Frequencies of combinations of sexes in the different sizes of offspring occurred as expected.
1056
1 vs. 5 2 vs. 6 3 vs. 7 4 vs. 8 5 vs. 9
1 vs. 9 Total effect
Summary
102
55 33
1. EDWARDS, A.W.F. Some comments on Schutzenberger's analysis of data on the human sex ratio. Ann. Hum. Genet. 23:233-238. 1959. 2. . A factorial analysis of sex ratio data. Ann. Hum. Genet. 25:117-121. 1961. 3. and M. FRACCARO. Distribution and sequences of sexes in a selected sample of Swedish families. Ann. Hum. Genet. 24:245-252. 1960. 4. GRAY, E. and N.M. MORRISON. Influence of combinations
of sexes of children on family size. J. Hered. 65:169-174. 1974. 5. and J. BORTOLOZZI. Studies of the human sex ratio and factors influencing family size in Botucatu, Brazil. J. Hered. 68:241-244. 1977. 6. LOYD, R.C. and E. GRAY. A statistical study of the human sex ratio. J. Hered. 60:329-331. 1969. 7. P O W E L L , R.L., H.D. N O R M A N , and F.N. DICKINSON. Sire
differences in sex ratio of progeny. J. Dairy Sci. 58:1723-1726. 1975. 8. STERN, C. Principles of Human Genetics, 2nd ed. W.H. Freeman, San Francisco. 1960.
Distribution of sexes in cattle ELMER GRAY AND VALINA K. HURT
REATER KNOWLEDGE of sex ratios and distriVjTbutions of sexes within progenies has been sought in an effort to control sexes of domesticated animals for economic gain and to provide a population control measure in humans. In a recent review of sex ratio studies in cattle, Powell et al.7 stated that the sex ratio (percentage of all births that is male) in cattle is near 50 percent with the percentage of males being slightly higher in most reports. In the study conducted by Powell et al.7, the sex ratio was 52.9 percent for a sample consisting of 513,624 single births in dairy cattle. The ratio was 51.4 percent for a carefully edited subset of 14,559 progeny by 94 sires in Holstein herds. Heritability estimates were near zero for sires used in genetic analysis of sex ratios. Several studies of the human sex ratio and the distribution of sexes within families have been reported. In most studies the proportion of males has exceeded the proportion of females, with the most commonly observed human secondary sex ratio being approximately 106:100 (males: females at birth)8. Some investigators1'2'5-6 have found positive correlations between sexes of successive births within families, whereas other workers3-4 have found no associations between sexes of successive births. Generally observed frequencies of combinations of sexes within different family sizes have not differed significantly from expected frequencies obtained by using the observed sex ratio and the binomial expansion4"6. Since associations between sexes within families have not been consistent in subsets of the human population, such studies need to encompass other species. Associations between sexes within progenies of cattle apparently have not been reported. The objective of the present investigation was to study the distribution of sexes of calves within progenies of Holstein dams.
of parities separated by two (calf n vs. calf n + 3 for «= 1 — 9), and for parities separated by three or more (#i=l-9). Each dam's offspring was divided into combinations of sexes. Through expansion of the binomial using the observed sex ratio, the expected frequencies of combinations of sexes in each offspring size (n = 2-5) were calculated. The observed and expected combinations of sexes were compared using chi-square.
Results Sex ratio The overall sex ratio for 4,245 single parities was 52.74 percent. This ratio is similar to the 52.9 percent reported by Powell et al.7for a much larger sample. Ratios by order of parities (Table I) fluctuated around the overall sex ratio with a combined ratio of 51.97 percent for the first five parities. Ratios for all parities except the third indicated a slightly greater proportion of males than females in the progeny. The ratio (48.70 percent) for the third parity differed significantly (0.05 level of probability) from the overall sex ratio (52.74 percent) and from the sex ratio (52.9 percent) reported by Powell et al.7. No biological explanation is evident for this aberrant ratio. Correlations between sexes Correlation coefficients between the sexes of calves of successive and nonsuccessive parities are presented in Table II. Generally the coefficients were low and nonsignificant, indicating no apparent association between sexes of calves of parities that were successive (Table IIA) or separated by one (Table IIB), by two (Table HC), or by three or more parities (Table IID). None of the coefficients for total effects of the successive and various nonsuccessive parities was significant. The correlation between the sexes of the third and fifth calves (Table IIB) was highly significant (P < 0.01). However, this correlation is attributed to chance rather than to a true biological relationship.
Population and Methods Data were obtained from records of 1,046 Holstein cows included in the dairy herd at Cornell University during the period 1940 through 1977. Records were selected to get dams that had at least two parities. Multiparous births, abortions, and calves born dead (no sex recorded) were excluded from the analyses. Sex by order of parity was determined for the calves of each dam. These data were used to calculate a sex ratio for each parity (1 through 5) and to calculate correlation coefficients between sexes of successive calves. Correlation coefficients were computed between the sexes of successive parities (calf n vs. calf n+\ for /j=l-9), of parities separated by one (calf n vs. calf n + 2 for n= 1-9), The authors are, respectively, professor of agriculture and dean of the Graduate College; and graduate assistant, Department of Biology, Western Kentucky University, Bowling Green, KY 42101. Sincere appreciation is expressed to Dr. R. W. Everett and Ms. Susan Herbert, Department of Animal Science, Cornell University, for providing the data for this study.
Combinations of sexes Data for dams having a total of 2,3,4, or 5 single parities were used to test the observed frequencies of combinations of sexes against the expected frequencies that were based on the overall observed sex ratio and the binomial expansion. None of the resulting chi-squares was signifTable I. Sex ratio by order of parity Parity
No. calves
First Second Third Fourth Fifth Combined
1,105
273
982 690 455 283
3,422
Sex ratio (percent males) 53.10 51.42 48.70 54.50 53.71 51.97
The Journal of Heredity
274
icant (0.05 level of probability), indicating that the ob- sexes appeared to be independent as evidenced by 1) the served frequencies of combinations of sexes within failure of the sex ratio for different parities to differ conprogenies of 2, 3, 4, or 5 calves appeared as expected. sistently from the overall ratio; 2) the lack of evidence of association between the sexes of successive and various nonsuccessive calves; and 3) the absence of significant deviations of observed and expected frequencies of comDiscussion binations of sexes within progenies. These results support The overall sex ratio of 52.74 percent indicates the oc- those of Powell et al., in which the sex ratio was currence of more male than female calves in the sample 52.9 percent and varied only slightly for progenies of difof Holsteins studied. Other aspects of the distribution of ferent sires. One intent of the present investigation was to compare the results obtained for sex distribution in cattle with the Table II. Correlations between sexes results of sex distribution studies that have been reported for the human population. The sex ratio of 52.74 percent Calf pair df is equal to 111.6:100 (males: females) when expressed in human sex ratio terminology. This ratio is included within A. Successive parities (n = 1-9) the range of sex ratios for different subsets of the human 1 vs. 2 +0.0124 951 population and is comparable to the most widely accepted 2 vs. 3 -0.0307 649 ratio of 106:100 for white Americans8. The failure to find + 0.0187 3 vs. 4 429 a positive association between sexes of successive calves +0.1231 4 vs. 5 259 supports the results reported for some subsets of the hu+ 0.0560 5 vs. 6 160 man population3-4. However, positive associations be+ 0.1429 6 vs. 7 91 tween sexes of successive children have been found in -0.2061 7 vs. 8 51 other subsets1-2-5". The agreement between observed and +0.1985 8 vs. 9 32 expected frequencies of sexes of calves in progenies of +0.0182 Total effect 2636 different sizes is consistent with the agreement between observed and expected frequencies of combinations of B. Parities separated by one ( « = 1-9) sexes of children in families of different sizes4"". 1 vs. 3 +0.0180 818 2 vs. 4 3 vs. 5 4 vs. 6 5 vs. 7 6 vs. 8 7 vs. 9 Total effect
+0.0461 +0.1667* +0.0026 -0.0633 -0.1019 +0.0156 +0.0390
C. Panties separated by two ( / i = l - 9 ) 1 vs. 4 + 0.0092 2 vs. 5 + 0.0149 3 vs. 6 -0.0494 4 vs. 7 + 0.0426 5 vs. 8 -0.1534 6 vs. 9 -0.0221 Total effect -0.0045 D.
435 245 155 88 54 30 1837
437 267
165 93 52 32
Literature Cited
Parities separated by three or more -0.0889 -0.0743 + 0.0196 + 0.1481 + 0.0665
272 161
1 vs. 6 2 vs. 7 3 vs.8 4 vs. 9
-0.0988 +0.0435 +0.0071 +0.1176
167 90 53 34
1 vs. 7 2 vs. 8 3 vs. 9
+ 0.0213 + 0.1481 0.0000
94 54 32
1 vs.8 2 vs. 9
-0.0442 -0.0778
55 33
-0.2067 -0.0254
33 1296
* Significant at the 0.01 level of probability
Data were obtained from records of 1,046 Holstein dams included in the dairy herd at Cornell University during the years 1940 through 1977. Sex by order of parity was determined for the offspring of each dam. The overall sex ratio for 4,245 single parities was 52.74 percent males. Sex ratios for different parities were relatively consistent. Within progenies of the dams, there was no consistent evidence of association between the sexes of successive and various nonsuccessive calves. Frequencies of combinations of sexes in the different sizes of offspring occurred as expected.
1056
1 vs. 5 2 vs. 6 3 vs. 7 4 vs. 8 5 vs. 9
1 vs. 9 Total effect
Summary
102
55 33
1. EDWARDS, A.W.F. Some comments on Schutzenberger's analysis of data on the human sex ratio. Ann. Hum. Genet. 23:233-238. 1959. 2. . A factorial analysis of sex ratio data. Ann. Hum. Genet. 25:117-121. 1961. 3. and M. FRACCARO. Distribution and sequences of sexes in a selected sample of Swedish families. Ann. Hum. Genet. 24:245-252. 1960. 4. GRAY, E. and N.M. MORRISON. Influence of combinations
of sexes of children on family size. J. Hered. 65:169-174. 1974. 5. and J. BORTOLOZZI. Studies of the human sex ratio and factors influencing family size in Botucatu, Brazil. J. Hered. 68:241-244. 1977. 6. LOYD, R.C. and E. GRAY. A statistical study of the human sex ratio. J. Hered. 60:329-331. 1969. 7. P O W E L L , R.L., H.D. N O R M A N , and F.N. DICKINSON. Sire
differences in sex ratio of progeny. J. Dairy Sci. 58:1723-1726. 1975. 8. STERN, C. Principles of Human Genetics, 2nd ed. W.H. Freeman, San Francisco. 1960.
