University o/ Nebraska, Lincoln 68503

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1 THE ROLE OF MATERNAL EFFECTS IN ANIMAL BREEDING: VI. MATERNAL EFFECTS IN BEEF CATTLE 1, 2 ROBERT IV[. KOCH University o/ Nebraska, Lincoln 6853 ATERNAL effects as used in this discus- M sion refer to differences in birth weight or rate of gain from birth to weaning caused by differences in maternal environment provided by cows during gestation and nursing. Although maternal effects are environmental so far as their influence on offspring they are determined by genetic and environmental factors. My discussion attempts to examine evidence for existence of maternal effects, measures of relative size of genetic and environmental components of maternal effects and to determine if covariation exists between maternal ability and other genetic or environmental factors affecting phenotypic expression of birth weight or gain from birth to weaning. Evidence on existence and size of maternal effects generally comes from experiments which (1) measure known components of maternal effects such as milk production from cows suckling their young, (2) from reciprocal crosses or cross-nursing among genetic types and (3) by comparison of observed correlations with theoretical expectations for various kinds of relatives. Milk Production and Crossbreeding Results. Studies relating milk production of beef cows with gain of calves have generally indicated a significant association. Reported correlations /all in the range of.3 to.8 depending on age of calf or length of period measured (Christian, Hauser and Chapman, 1965; Drewry, Brown and Honea, 1959; Gifford, 1953; Gleddie and Berg, 1968; Knapp and Black, 1941; Neville, 1962; Schwulst etal., 1966). Correlations between total or cumulative milk production and gain from birth to weaning were usually high, on the order of.5 to.8, suggesting important 1 Presented at a symposium on The Role of l~aternal Effects in Animal Breeding sponsored by the American Society of Animal Science, August 3, 1971, University of California, Davis. Published as Paper Number 3236, Journal Series, Nebraska Agricultural Experiment Station. Contribution from North Central Regional Project NC-1, Improvement of Beef Cattie Through Breeding Methods differences in maternal ability as measured by milk production. Cross nursing experiments following breeding designs as outlined by Eisen (1967) have not been feasible in beef cattle. However, differences among reciprocal crosses from crossbreeding experiments provide evidence on maternal effects. In crosses among Angus, Hereford and Shorthorn cattle significant differences between reciprocals were found for gain from birth to weaning but generally lacked significance so far as birth weight was concerned in studies reported by Gaines et al., 1966; Gregory er al., 1965; and Pahnish et al., Reciprocal crosses among breeds differing greatly in size such as Holstein, Jersey and Ayrshire crosses reported by Donald, Russell and Taylor (1962) did show significant differences among birth weights of reciprocals. Although reciprocal crosses provide evidence that differences in maternal effects on birth weight and weaning gain are real they are not too helpful in quantifying relative variation attributable to maternal effects. Theoretical Expectation and Observed Correlations Among Relatives. Biometrieal aspects for assessing relative contributions from maternal and individual genetic effects on variation in growth for beef cattle are shown in path coefficient diagrams of figures 1 and 2 for paternal half sibs, maternal half sibs, maternal grand sire sibs, maternal grandsires progeny and grandoffspring, offspring-sire and offspring-dam. Correlation between any two variables in the diagram is equal to the sum of all paths connecting them, without going back along any arrow after going forward and not passing through any variable twice in the same path (Wright, 1967). Theoretical composition of various relationships and average values of observed correlations reported in the literature are given in table 1. The fraction of variation among phenotypic values for birth weight or daily gain to weaning attributable to the additive genetic, dominance, or random environmental differences of individuals are represented by g2o, d2o, e2o, respectively. Simi- JOURNAL OF ANIMAL SCIENCE, vol. 35, no. 6, 1972

2 ROLE OF MATERNAL EFFECTS IN ANIMAL BREEDING 1317 E os~ eo "" n I I'~,.1 ""~ =-~ ~, l"oi UOS mo ~ l"os., Go~ ~ P~ / ~Oo~ r~g~: O~ E~c s ~ re. t~-ii/ "~,-~ ~'nl "~' ""x G', o3 G,~3 Po6 ~G ~.s ~ 4 Go-, z Po, Do, do ---~Po. Eo7 Figure 1. Po is phenotypic, Go additive genetic, Do dominance and Eo environmental value of birth weight or daily gain expressed by individuals. Pro, Gin, Dm and Em are corresponding maternal effects. Primes on symbols represent parental values and double primes grand parent values. Path coefficients between symbols (.5, g, d, e, p) are standard partial regression coefficients. Double headed arrows represent residual correlation between traits. P'o~ and P'o~ are paternal half sibs. Po~ and Po~ are maternal half sibs. Po~ and P~ are maternal grand sire sibs. Maternal grandsire's male progeny and grand offspring relationships are typified by P'ol and PoT. larily, p2mg2m, p2md2 m and p2,.e2,~ indicate the fraction of phenotypic differences in birth weight or daily gain attributable to additive genetic, dominance, or "permanent" environmental differences in maternal ability. Additive genetic covariance (in standard measure) between individual and maternal effects is represented by gmpmgorg, while similar covariance between dominance values is represented by dodmpmri~. Environmental covariance is a complex function most easily visualized by checking terms shown at the bottom of table 1 with figure 2. It will be discussed later. Epistatic contributions are assumed to be zero. Relationships usually available in beef cattle data do not provide critical contrasts for separating dominance and environment effects. These contributions are shown jointly, i.e. p2m(d2m+e2m) and (d2o+e2o). The importance of genetic improvement in both individual and maternal effects for growth from birth to weaning has prompted several studies on the magnitude of maternal effects and the genetic correlation with individual genetic effects using comparisons of expected composition of correlations or varia-

3 1318 KOCH ~,. / \ \ / r~,-- i'' ~ /' l,,,r eo Do o L K r2gx ~---7" d,-~./" /I / -.s --,6'o' ~o Figure 2. Definitions of symbols are similar to figure 1. P'o~ and Po3 are dam and offspring phenotypes. 9% and I~o3 are sire and offspring phenotypes. tion with observed values from different types of relatives. Such comparisons are subject to large error due to the generally small number of relatives involved and the multipliers used (i.e., 1/2,, 1/8, 1/16). Errors of estimate in one component tend to cause other compo- nents to differ in the opposite direction since the sum of components is forced to equal the whole. An estimate of total maternally related variation and covariation is derived by comparing maternal half sib with paternal half sib cor- TABLE 1. CAUSAL COMPONENTS AND OBSERVED CORRELATIONS AMONG DIFFERENT TYPES OF RELATIVES Birth weight gmpta psmd~m@ d%+ dodra Envir. Gain, B.-Wean g~o gor~ p2mg2 m p~me2m e2 pmrv cv. Lit a Ft. Rob. Lit a Ft. Rob. Paternal half sibs Offspring and sire 1/2.I1 O. 19.1i O O. 1 Mat. grandsire's progeny and grandoffspring 1/8?... O O. 2 Mat. grandsire's sibs 1/ Offspring and dam t/2 5/4 1/2 1? Offspring and mat. grand dam Maternal half sibs 5/ fm?... O. 29 ~.13.3 ~ b,13 O.S1 b Within maternal half sibs 3/4 1 O. 71 O. 7 O Environmental cnvariance (fi~ure 2 ) = eoreempm+eor~em f'npm+p ~rafm +fro/(2 --fro) (2--fro) (.5 g~ m p2m+ t.25 gogmpmrn) Literature values taken from Brown and Galvez (1969), Deese and Koger (1967) and Petty and Cartwright (1966). Ft. Rob. values are unpublished data from Fort Robinson Beef Cattle Research Station, Nebraska. b Adjacent calves.

4 ROLE OF MATERNAL EFFECTS IN ANIMAL BREEDING 1319 relations. The amount of "permanent" environmental variation included will vary depending on whether maternal half sibs were adjacent or separated by 2 or more years. The average correlation among paternal half sibs for birth weight was.1t; the average maternal half sib correlation among all calves was.25 and of adjacent calves.29 according to the summary of Petty and Cartwright (1966). Thus, total maternally related variation accounted for 14 to 18% of phenotypic variance in birth weight. Heritability of maternal ability affecting birth weight was estimated as 25 and 3% in Angus and Hereford cattle by Brown and Galvez (1969) while in Holsteins, Everett and Magee (1965) estimated it as 4 to 15 %. The genetic correlation between individual and maternal effects can be estimated from various combinations of relatives. A reanalysis of offspring-sire, paternal half sib, and offspring-dam correlations reported by Koch and Clark (1955) indicated a genetic correlation of zero. Estimates of the genetic correlation using paternal half sibs, maternal grandsire relationships and offspring darn correlations were --.58, --.37, and (Brown and Galvez, 1969; Hill, 1965; Everett and Magee, 1965). The simple average of these estimates is for the genetic correlation between individual and maternal effects. The average paternal half sib correlation for daily gain from birth to weaning was.8. The maternal half sib correlation was.37 among all calves from a cow and.46 between adjacent calves (Petty and Cartwright, 1966). Total maternally related variation and covariation accounted for 29 to 38% of phenotypic variation in gain from birth to weaning. Heritability of maternal effects for weaning weight or gain from birth to weaning was estimated as 15, 46, 5, 34 and 4% by Deese and Koger (1967), Hill (1965) and Hohenboken and Brinks (1971), respectively. The average is 37%. Estimates of the genetic correlation between maternal and individual effects on weaning weight or gain from birth to weaning were --.7, --.46, and to according to Deese and Koger (1967), Hill (1965), Hohenboken and Brinks (1971) and Koch and Clark (1955). The average of these values is Major relationships compared were paternal and maternal half-sibs and offspring-sire or offspring-dam. Paternal half-sibs provide the principal estimate for the additive genetic contribution for individual effects. Correlations between maternal half-sibs contain the maternally related components in addition to individual effects. The fact that maternal half sib correlations generally are much larger than paternal half-sib correlations suggests large maternal effects. The contrast includes covariance of individual and maternal effects. Almost all estimates of correlations between offspring and dam are much lower than expected from paternal and maternal half-sib contrasts. There are several instances in the literature of negative estimates of offspringdam correlations or regressions which were dismissed as sampling error. Either there were negative forces lowering the offspring-dam correlation or paternal half-sib estimates have been biased upwards, causing us to expect higher values than generally observed. Possib e sources of bias in paternal half-sib estimates include environmental correlations among sire progenies, sire-year interactions, or in small herds the possibiiity of a sizeable fraction of offspring being three quarter sibs instead of half sibs. Direct Influen'ce of Dams on Maternal A bility of Daughters. The offspring-dam relationship is a complex function if all possible influences hypothesized in the path diagram (figure 2) are real. In addition to the contribution from individual additive genetic effects, additive genetic differences in maternal ability, and additive genetic covariance between individual and maternal effects, a unique covariance involving the dominance deviations of individual and maternal effects is possible. Environmental covariance between the individual and maternal effects (eoreempm) is also a distinct possibility. If maternal ability of the dam has a direct influence on future maternal ability of female offspring (f,~ in figure 2) additional environmental covariance terms are possible, see footnote, table 1. The last term beginning with fm/(2-fm) represents the summation of a geometric series containing contributions of all previous female ancestors through the direct path (fro) connecting maternal effects (Falconer, 1965). The offspringgrand dam relationship has similar covariance terms but one generation removed and proportional to the magnitude of direct influence between phenotypes for maternal ability (fro). Genetic or environmental covariance terms could be negative and cause the offspring-dam relationship to be lower than anticipated from direct genetic or direct maternal effects. It is significant to note that with one exception (Hohenboken and Brinks, 1971) workers

5 132 KOCH evaluating maternal effects have assumed environmental correlations in the offspring-dam covariance were zero to solve for genetic components. Many years ago Dr. H. H. Stonaker suggested the negative genetic correlation involving maternal ability hypothesized by Koch and Clark (1955) could have been due to a direct negative influence of dams on maternal ability of her female offspring through overfeeding. At the time I dismissed this hypothesis as unlikely because our data were from a sparse range environment. It did not seem that milk production was abundant enough to affect future development. I now believe I was wrong. Studies of dairy calves indicate that overfeeding heifers during rearing resulted in lower average milk production than from heifers fed normal standards. Underfeeding heifers was detrimental in some cases to the first lactation, but in later lactations subnormally reared heifers equalled or exceeded milk production from normally reared heifers (Crichton, Aitken and Boyne, 196; Hansson, 1956; Reid et al., 1964; Swanson, 196; Swanson and Hinton, 1964; Thomas, Sykes and Moore, 1959; also see reviews by Schultz, 1969; Swanson, 1967). Application of results from dairy heifers to beef heifers require a clarification of low, normal, and high levels of rearing. Birth weights and daily gains were not presented for all early months of growth, but the data indicate gains in the low level were about.35 to.45 kg/day, normal gains were about.55 kg/day and high levels ranged from.6 to.9 kg/day. In beef herds,.75 kg/day would be a reasonable expectation for average daily gain of British breeds, and under good conditions we might except 1. kg/day with a standard deviation of kilogram. Thus, normal to good gains would be similar to high intensity of rearing reported for daily cattle. The standard deviation of daily gain from birth to weaning is about kg leading to a variation in nutritional level from subnormal to super abundance by dairy calf rearing standards. Actual data from beef herds relating levels of rearing to milk production of cows are limited. Totusek (1968) compared weaning weights of calves out of heifers reared under different systems, e.g. (1) weaned at 14 days of age, (2) weaned at 24 days of age and (3) creep fed and weaned at 24 days of age. Heifers weaned at 14 days of age produced calves that weighed about 1 kg more than those out of creep fed heifers. Similar results were reported by Martin, Srinivasan and Garwood (197). Christian et al. (1965) reported weaning weights of twin Hereford heifers were negatively correlated with measures of their milk production. Plum and Harris (1968) compared milk production from Holstein heifers reared by suckling their dams with heifer mates reared under normal dairy calf management. Milk production from heifers that suckled their dams was only 74% as much as that from heifers reared under usual dairy calf management conditions. A recent study of Mangus and Brinks (1971) indicated heifers out of young aged dams subsequently produced heavier calves at weaning than heifers out of mature aged cows. They interpreted this to mean high levels of milk in dams had a detrimental effect on heifers future productivity or conversely, that low levels of milk from young cows was beneficial to future productivity. They also reported a cyclic trend in weaning weights over four generations that was inversely related to producing ability of dams. Results of dairy calf rearing studies and studies in beef herds strongly suggest maternal environment provided by beef cows from birth to weaning has a direct influence on subsequent maternal ability of heifers and is negatively related to the cow's relative superiority or inferiority in maternal ability. If this conclusion is tenable, we would expect environmental covariance terms in the offspring-dam correlation and direct influence of maternal effects of ancestoral dams to be negative. This could explain all or part of the low offspringdam correlation observed for weaning gain or weaning weight as compared with paternal and maternal half-sib correlations. Alternative explanations include the possibility of a negative genetic correlation between individual and maternal effects or upward bias in paternal half-sib correlations. The apparent antagonistic correlation between level of milk production of dams and future maternal ability of daughters suggests problems for incorporating high milk production as a goal in long term inter-se or rotational cross breeding programs in contrast with programs using specific maternal lines mated to terminal sire breeds and marketing all male and female offspring. Analysis of Fort Robinson Data. Additional evidence was sought by analyzing records from 4,6 Hereford calves and their parents raised at the Fort Robinson Beef Cattle Research Station, Crawford, Nebraska. Calves born from 1957 to 1962 and their parents were

6 ROLE OF MATERNAL EFFECTS IN ANIMAL BREEDING 1321 foundation animals for a selection experiment. Calves born from 1963 to 197 were from three lines selected for (1) weaning weight, or (2) yearling weight, or (3) yearling weight and muscling score. Analyses were conducted separately for each sex and answers averaged. Sire groups within lines and years were examined and where three quarter sibs occurred a random animal was selected for paternal half sib estimates. Diversity of foundation stock kept loss of three quarter sibs to 583 animals. Maternal half sib correlations were derived by pairing adjacent like sexed calves from a dam and regressing later record on earlier record. This method avoids bias from selection among cows and maintains a constant interval between calves for the influence of maternal effects. Differences in maternal ability provided by cows of different ages provide a measurable environmental influence to test the hypothesis of covariance between environmental factors affecting a dam's phenotype for birth weight or gain to weaning and her phenotype for maternal ability. The offspring's record was regressed on the age of dam correction factor associated with age of the maternal grand dam (i.e., the correction to the dam's own record) among calves born in the same year and out of dams of the same age. The average regression was kg/kg for birth weight and.15+~.7 kg/kg for gain from birth to weaning. Thus, cows which had larger age of dam correction to their own records (i.e., out of younger or older cows) had calves which were heavier at birth and gained more to weaning than cows out of dams from ages 6 to 8 years of age. Bias from genetic improvement such that heifers from the youngest cows which required the greatest correction represent more advanced generations of selection might account for part of the positive regression. The positive regression coefficient quantifies and confirms the observations of Mangus and Brinks (1971). The results for birth weight, though not statistically significant, suggest compensation to stress may affect maternal ability in more aspects of expression than milk production. Implications of negative compensation, if real, are worthy of greater examination. Further evidence on evironment covariance through maternal ability can be obtained by comparing offspring-dam with offspring-grand dam regressions. The difference between the regression of offspring on dam and twice the offspring on maternal grand dam is (1-2 fro) (dodmpmrd-~- fmp2m-t- fmpmeoemre,,). No difference can be interpreted as indicating no direct pathway between maternal ability of grand dam and dam or no dominance covariance, or that covariance of dominance effects (pmdodmrd) cancels the environmental covariance terms. A positive difference suggests a positive direct pathway, positive dominance covariance or both. A negative difference can be interpreted as evidence for negative direct effects, negative dominance effects or both. Results of the Fort Robinson analyses are given in table 1. Comparison of regression coefficients indicates the difference is ( z.3) a very small positive value in the case of birth weight. Though not significantly different from zero it is evident for a small positive direct influence or positive dominance covariance which conflicts with evidence provided by the regression reported earlier related to age of dam correction factors. A comparison of the regression coefficients for gain from birth to weaning ( ~ ) yields a large negative value supporting the hypothesis of negative direct effects between maternal values or large negative dominance covariance. Equating expectations of various combinations of relatives to observed correlations in the Fort Robinson data and solving them step wise or simultaneously leads to causal component estimates for birth weight shown in table 2. Maternally related components account for about 19% of the variation in birth weight. Both positive and negative estimates were obtained for the genetic correlation between individual and maternal effects. The simple average of estimates is.7. Solutions to equations involving gain from birth to weaning are also given in table 2. Maternally related variation accounts for about 4 to 46% of the variance in gain from birth to weaning. The first three solutions which do not include the offspring-dam correlation yielded an average genetic correlation of --.5 between individual and maternal effects. The average of all estimates was Conclusions 1. Genetic and permanent environmental components of maternal ability and covariance of individual and maternal effects accounted for 15 to 2% of variation in birth weight and 35 to 45% of variation in daily gain from birth to weaning. 2. In the case of birth weight, maternal

7 1322 KOCH TABLE 2. CAUSAL COMPONENTS OF VARIATION, ESTIMATED FROM CORRELATIONS OBSERVED AT FORT ROBINSON (EXPRESSED IN PERCENT OF PHENOTYPIC VARIANCE) d~mp~ d*o+ Relatives used gao gogmpmro g2p2 +e~ n~p2m e~o ro Birth weight P/2, OS, MGS, M/ P/2, MGPGO, MGS, M/ OS, MGPGO, MGS, M/ P/2, OS, OD, M/ P/2, MGPGO, OD, M/ OS, MGS, OD, M/ Daily gain, birth to weaning P/2, OS, MGS, M/ P/2, MGPGO, MGS, M/ OS, MGPGO, MGS, M/ P/2, OS, OD, M/ P/2, MGPGO, OD, M/ ~ OS, MGS, OD, M/ P/2=paternal half sib; OS~offspring and sire; ODzoffspring and dam; MGS~-maternal grand sire sibs; MGPGO=rnaternal grandsire's progeny and grandoffspring; M/2~maternal half sibs; rg=additive genetic correlation between individual and maternal effects. a Arithmetic average of geo and g2mp2m used instead of geometric average. ability of dams did not have a significant direct affect on maternal ability in the next generation. Conflicting evidence of small positive and small negative values may indicate the magnitude is low and not likely to seriously bias correlations of birth weight between generations. 3. Maternal environment for gain from birth to weaning seems to be significantly and negatively affected by direct effects of maternal environment from previous generations. Speculation suggests a value of --.1 to --.2 for this direct path. Such values lead to estimates of environmental covariance which satisfy observed correlations and regressions. Negative direct influence between maternal ability of dam and daughter may be cause for examining alternative rearing systems for male and female calves to obtain maximum gains. It also means that selecting for improved maternal ability on the basis of weaning gain will be less effective than if no direct influence existed. 4. The additive genetic component (g2mp2m) of maternal ability likely accounts for 1 to 15% of the variance in birth weight. Maternal dominance plus permanent environmental effects account for about 1% of the variance. 5. The genetic correlation between individual and maternal effects on birth weight is inconclusive. The average value from Fort Robinson data was.7 while the average of literature values was Heritability of maternal ability for gain to weaning was on the order of 3 to 36% in Colorado and Fort Robinson evaluations which did not use off-spring-dam relationships that may contain a large negative bias. 7. The genetic correlation between maternal and individual effects on gain to weaning was negative in most solutions. A negative value of about --.5 was found in the Fort Robinson data. Larger negative values of --.3 to were indicated in the literature and in the Fort Robinson analysis when correlations between dam and offspring were part of the evaluation. Negative bias associated with the dam-offspring correlation should be considered in interpreting these large negative values. Literature Cited Brown, C. J. and V. Galvez Maternal and other effects on birth weight of beef cattle. J. Anita. Sci. 28:162. Christian, L. L., E. K. Hauser and A. B. Chapman Association of preweaning and postweaning traits with weaning weight in cattle. J. Ahem. Sci. 24:652. Crichton, J. A., J. N. Aitken and A. W. Boyne The effect of plane of nutrition during rearing on growth, production, reproduction and health of daily cattle. I. Growth to 24 months. Anita. Prod. 1:145. Deese, R. E. and M. Koger Maternal effects on preweaning growth rate in cattle. J. Anim. Sci. 26:25. Donald, H. P., W. S. Russell and St. C. S. Taylor Birth weights of reciprocally cross-bred calves. 3. Agr. Sci. 58:45. Drewry, K. J., C. 3- Brown and R. S. Honea Relationships among factors associated with mothering ability in beef cattle. J. Anita. Sci. 18:938. Eisen, E Mating designs for estimatin~ direct and malernal genetic variances and direct-

8 ROLE OF MATERNAL EFFECTS IN ANIMAL BREEDING 1323 maternal genetic covariances. Can. J. Genet. Cyto. 9:13. Everett, R. W. and W. T. Magee Maternal ability and genetic ability of birth weight and gestation length. J. Dairy Sci. 48:957. Falconer, D. S Maternal effects and selection response. In S. J. Geerts (Ed.) Genetics Today. Pergamon Press. New York. Gaines, J. A., W. H. McClure, D. W. Vogt, R. C. Carter and C. M. Kincaid Heterosis from crosses among British breeds of beef cattle: fertility and calf performance to weaning. J. Anita. Sci. 25:5. Gifford, Warren Records of performance tests for beef cattle in breeding herds. Ark. Agr. Exp. Sta. Bull Gleddie, G. C. and R. T. Berg Milk production in range beef cows and its relationship to calf gain. Can. J. Anita. Sci. 48:323. Gregory, K. E., L. A. Swiger, R. M. Koch, L. J. Sumption, W. W. Rowden and J. E. Ingalls Heterosis in preweaning traits of beef cattle. I. Anita. Sci. 24:21. Hansson, Arthur Influence of rearing intensity on body development and milk production. Prec. British Soc. Anita. Sci. Prod. p. 5. Hill, James R., Jr The inheritance of maternal effects in beef cattle. Unpublished Ph.D. Thesis, North Carolina State University, Raleigh. Hohenboken, W. D. and J. S. Brinks Relationships between direct and maternal effects on growth in Herefords: II. Partitioning of covariance between relatives. J. Anita. Sci. 32:26. Knapp, Bradford, Jr. and W. H. Black Factors influencing rate of gain of beef calves during the suckling period. J. Agr. Res. 63:249. Koch, Robert M. and R. T. Clark Genetic and environmental relationships among economic characters in beef cattle. III. Evaluating maternal environment. J. Anita. Sci. 14:979. Mangus, W. L. and J. S. Brinks. 197I. Relationships between direct and maternal effects.on growth in Herefords: I. Environmental factors during Drevceaning growth. J. Anita. Sci. 32:17. Martin, T. G., G. Srinivasan and V. A. Garwood Creep feed as a factor affecting cow and calf performance. J. Anim. Sci. 31:166. (Abstr.). Neville, W. E., Jr Influence of dam's milk production and other factors on 12 and 24 day weight of Hereford calves. J. Anim. Sci. 21:315. Pahnish, O. F., J. S. Brinks, J. J. Urick, B. W. Knapp and T. M. Riley Results from crossing beef x beef and beef x dairy breeds: calf performance to weaning. J. Anita. Sci. 28:291. Petty, Robert R., Jr. and T. C. Cartwright A summary of genetic and environmental statistics for growth and conformation traits of young beef cattle. Texas Agr. Exp. Sta. Dept. Anita. Sei. Tech. Rep. 5. Plum, Mogens and Lionel Harris Rearing intensity and milk production. J. Anita. Sci. 27 : (Abstr.). Reid, J. T., J. K. Loosli, G. W. Trimberger, K. L. Turk, S. A. Asdell and S. E. Smith Causes and prevention of reproductive failures in dairy cattle. IV. Effect of plane of nutrition during early life on growth, reproduction, production, health and longevity of Holstein cows. Cornell Bull Schultz, L. H Relationship of rearing rate of dairy heifers to mature performance. J. Dairy Sci. 52:1321. Schwulst, F. J., L. J. Sumption, L. A. Swiger and V. H. Arthaud Use of oxytocin for estimating milk production of beef cows..1. Anita. Sci. 25:145. Swanson, E~ W Effect of rapid growth with fattening of daily heifers on their lactational ability. J. Dairy Sci. 43:377. Swanson, E. W Optimum growth patterns for dairy ca.tile. ~[. Dairy Sci. 5:244. Swanson, E. W. and S. A. Hinton Effect of seriously restricted growth upon lactation. J. Dairy Sci. 47:267. Thomas, J. W., J. F. Sykes and L. A. Moore Comparisons of alfalfa hay and alfalfa silage alone and with supplements of grain, hay or corn silage for growing dairy calves. J. Dairy Sci. 42:651. Totusek, Robert Early weaning vs. normal weaning vs. creep feeding of heifer calves. Okla. Agr. Exp. Sta. Pub. No. MP-8 p. 72. Wright, SewaU Evolution and the Genetics of Populations. Vol. 1. Genetic and Biometric Foundations, p. 32. Univ. of Chicago Press, Chicago.