Reciprocal crossbreeding of Angus and Hereford cattle 1. Growth of heifers and steers from birth to the yearling stage

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1 New Zealand Journal of Agricultural Research ISSN: (Print) (Online) Journal homepage: Reciprocal crossbreeding of Angus and Hereford cattle 1. Growth of heifers and steers from birth to the yearling stage J. C. Hunter To cite this article: J. C. Hunter (1986) Reciprocal crossbreeding of Angus and Hereford cattle 1. Growth of heifers and steers from birth to the yearling stage, New Zealand Journal of Agricultural Research, 29:3, , DOI: / To link to this article: Published online: 30 Jan Submit your article to this journal Article views: 154 View related articles Citing articles: 13 View citing articles Full Terms & Conditions of access and use can be found at

2 New Zealand Journal of Agricultural Research, 1986, Vol. 29: /86/ $2.50/0 Crown copyright 1986 Reciprocal crossbreeding of Angus and Hereford cattle 1. Growth of heifers and steers from birth to the yearling stage R. L. BAKER A.H.CARTER C. A. MORRIS D. L. JOHNSON J. C. HUNTER Ruakura Agricultural Research Centre, MAF Private Bag, Hamilton, New Zealand Abstract Maternal (dam breed), direct (sire breed), and heterosis effects on growth were estimated from purebred Angus (A x A), purebred Hereford (H x H), and crossbred (H x A and A x H) steers and heifers bred at the Waikite Land Development block near Rotorua over a 4-year period. There were higher losses of calves from Hereford than Angus dams calving at 2 years-of-age, but no differences for older dams. Survival rate, both pre- and post-weaning, was higher for crossbred than purebred calves. Data from 934 calves alive at 5-month weaning and 897 calves alive at 13 months-of-age were analysed for liveweights and liveweight gains from birth to 13 months. Relative to Angus calves, Herefords were born 7 days later and were 3 kg heavier at birth, because of both maternal and direct effects. Both breeds had similar maternal effects on weaning and on subsequent weights. Post-weaning weights and weight gains for the direct effect favoured the Hereford. Comparison of purebred calves with the reciprocal crosses showed significant (P<O.OI) heterosis for all liveweights and liveweight gains, increasing from 3.00/0 at birth to 5.1% at weaning and 8.6% at 13 months-of-age. In general, heterosis was higher in steer than heifer calves, particularly for weights at or close to weaning. Over the 4-year experimental period, 49 Angus and 34 Hereford sires were used. Sire variance components were estimated simultaneously with the breed and heterosis effects and used to derive paternal half-sib genetic parameters. Heritability estimates increased from weaning (0.17) to 10 months-of-age (0.36) and tended to be higher in heifer than steer calves. Heritabilities of pre- and post-weaning gains were low (0.12 and 0.07) with the exception of postweaning gain for steer calves (0.31). Received 16 September 1985; revision 10 March 1986 Keywords Angus; Hereford; breeds; beef cattle; crossbreeding; liveweight; heritability; genetics; heterosis INTRODUCTION There have been relatively few trials in New Zealand comparing the production characteristics of different cattle breeds and crosses. Those that have been published have been reviewed by Carter (1975) and Baker & Carter (1976, 1982). In contrast there have been numerous trials overseas comparing the beef production of different cattle breeds and crosses (e.g., reviews by Mason 1966; Cundiff 1970, 1982; Vis sac et al. 1982; Gregory et al. 1982; Liboriussen 1982). In some countries, crossbreeding has been integral part of beef production for many years (e.g., Great Britain). In other countries - for example New Zealand, Australia, and North America, where beef production has traditionally been based on purebred cattle - it has recently been realised that crossbreeding systems designed to ensure efficient use of breed resources are often a more productive and profitable option (Gregory & Cundiff 1980; Baker 1982). The predominant beef breeds in New Zealand are the Angus and the Hereford. When the present trial was initiated in 1968 no detailed evaluation of their relative merits had been undertaken. The primary objectives of the breeding studies reported here were to compare the productivity of Angus and Hereford cattle, to assess the possible advantages of crosses between them, and to investigate within-sire and between-sire variation to estimate genetic parameters. Results are presented in a series of papers, of which this is the first. MATERIALS AND METHODS Experimental location The experim<:ntal programme was carried out at Waikite, a Department of Lands and Survey block, 30 km south of Rotorua. Waikite is typical of many North Island commercial beef breeding properties. The land is undulating to steep, '''ith average altitude 420 m, but includes some flat

3 422 New Zealand Journal of Agricultural Research, 1986, Vol. 29 Table 1 Number of sires used. Angus Calf birth year New Repeat Total 49 3 Hereford Total New Repeat New Repeat areas. The soil is a pumice loam of volcanic origin, moderately fertile but deficient in certain essential elements. The winter season is long and severe, with heavy frosts which limit pasture production and stock performance seriously at this time. Cattle and sheep farming are integrated under an extensive grazing system; paddock size is 20 ha on average but varies up to 80 ha. During the 4-year experimental period reported here (calvings ), steers were not normally finished on the property, which was carrying about 12 ewe equivalents/ha on a total area in pasture of 1140 ha. Experimental design and management procedures The experimental programme was started in 1968 and this paper presents the growth data of calves born during The herd at this time comprised both Angus (A) and Hereford (H) cows joined with bulls of the same 2 breeds to generate purebred and crossbred progeny in a 2 x 2 diallel design. A total of 83 sires, 49 Angus and 34 Hereford, were used (Table 1). Details of the sources of the bulls used have been given by Baker et al. (1975). The majority of bulls were used as 2-year-olds after being purchased at about 20 months-of-age by the Department of Lands and Survey (Rotorua) from a wide range of Angus and Hereford breeders throughout the North Island. Bulls bred at Waikite were also used, and comprised both yearlings (14-15 months-of -age) and 2-year-olds, recorded for growth on the property (Baker & Carter 1976). A new set of bulls was used each year apart from a few which were used again to act as reference sires (Table 1). Each bull was joined with about 20 Angus and 10 Hereford cows. Cows, with their calves at foot, were rerandomised to bulls in November each year. Before 1966 all cows at Waikite were Angus of a wide genetic background, as a result of the bull purchasing policy of the Department of Limds and Survey in the 1950s and 1960s. In 1968 and 1969 about 300 additional Angus cows were purchased from 9 different stud or commercial sources in the North Island to broaden further the genetic base of the cows. The Hereford cows were derived from 7 different stud or commercial sources representative of the breed at the time. For each of the calving years the same Angus and Hereford bulls were used to generate the contemporary purebred and reciprocal crossbred calves for the crossbreeding experiment. At the same time they were also used to sire the foundation purebred Angus and Hereford stock of known pedigree and performance for selection studies initiated in (Baker et al. 1980). About 800 cows were joined in each of the first 3 years, about being Angus and Hereford, but fewer cows were joined in the breeding season (Table 2). The majority of base Angus and Hereford females ranged in age from 1 to 6 years at joining each year, but no yearling heifers were joined in the season. Bulls were joined with cows from the first or second week in November until mid to late January (range, days). Cows were managed in large grazing groups except during the single-sire joining period, in a deliberate attempt to avoid any management biases between breeds. Small quantities of hay were offered to cows in the winter (about 300 kg/cow per year) to supplement the limited amount of available pasture. Calves were weighed, tagged, and identified with respect to their dams within 24 h of birth. In the calving years , bull calves were kept entire until weaning (at an average age of 156 days), when all crossbred and a balanced sample of purebred Angus and Hereford bull calves were castrated. Bull calves born in 1972 were castrated at birth. Purebred Angus and Hereford heifer calves born during were also randomly allocated at weaning to either the crossbreeding or selection experiment. Weights of cows and calves were taken at the beginning (November) and end

4 Baker et al.-reciprocal crossbreeding of cattle breeds 423 Table 2 Number of cows joined and herd calving performance each year (all as a percentage of cow numbers joined). Number of cows joined! Calves Calves Joining/Calving year Angus Hereford Total In calf (070 ) born (070) weaned (070 ) Total ! All ages including yearlings. (January) of the joining period and at weaning (February). Weights were then recorded at 4- to 6-weekly intervals from weaning to 13 months-ofage (October), or to slaughter at about 20 months for the steers. Heifer and steer calves were managed in separate grazing groups from weaning onwards, so that sex and grazing group effects were confounded. If possible, all heifer calves were given preferential grazing treatment from 12 to 14 months-of-age (September-November) to facilitate yearling mating. All steers born in were off-grazed on other Lands and Survey blocks from about 9-10 months-of-age (June-July) until slaughter. Slaughter data on the steers are reported in the next paper in this series (Johnson et al. 1986). Statistical methods Liveweights and liveweight gains from birth through to the yearling stage were analysed. Initially a least-squares analysis of variance was carried out to determine an adequate model fit. The fixed effect model included sire breed (Angus, Hereford), dam breed (Angus, Hereford), year of birth ( ), sex (steer, heifer), age of dam (4 groups, 2- to ~ 5-year-old), birth date, all firstorder interactions, and 3 second-order interactions (sex x sire breed x dam breed, age of dam x sire breed x dam breed, and sex x age of dam x dam breed). After deleting non-significant interaction terms, the fixed effects reduced to all main effects plus the sire breed x dam breed, sex x age of dam, year x sex, and dam breed x age of dam interactions. The restricted maximum likelihood (REML) technique (Patterson & Thompson 1971) was then used, with sires included as a random effect, to obtain generalised leastsquares estimates of fixed effects and REML estimates of the sire variance components. Paternal half-sib heritability estimates were derived from these components. Heritability and genetic correlation estimates were also derived using the same model and Method 3 of Henderson (1953). Heterosis (in kg) was derived from the sire breed x dam breed estimates as the mean of the 2 crossbreds minus the mean of the 2 purebred calf groups. Heterosis was also calculated by taking the value in kg as a percentage of the mean of the purebred groups. Direct (sire breed) and maternal (dam breed) differences were derived from the marginal effects. In total, 75 calves (7UJo) were excluded from the data set because of incomplete data. For some liveweights and liveweight gains the sex x sire breed x dam breed interaction term was significant, indicating different heterosis levels in the 2 sexes. To investigate this further and to estimate variance components within each sex, separate analyses were carried out for the steer and heifer calves. RESULTS Breeding performance of foundation cows A total of 2608 cows were joined over the to seasons (Table 2). This included yearling heifers joined in each year except ; the calving performance of cows was poor because of semi-drought conditions in that season (a 64UJo weaning rate v. 77UJo average over the other 3 years). On average, young Hereford cows were 5UJo heavier than Angus cows of the same age; at 3 years-of-age and older, Hereford cows were 15UJo heavier (Table 3). There was little difference in effective calf production between the cow breeds, except for higher losses from birth to weaning for calves from Hereford (18UJo) than Angus (loujo) heifers calving at 2 years. Calf survival from birth to weaning was higher for crossbred (96UJo) than

5 424 New Zealand Journal of Agricultural Research, 1986, Vol. 29 Table 3 Joining weight and calving performance of foundation Angus and Herefords by age group of cow. Angus joined at Hereford joined at 1 year 2 years 2: 3 years 1 year 2 years 2: 3 years Joining weight (kg) ~ ~ In calf' Calves born Calves weaned All as percentage of cow number joined. Table 4 Number of calves analysed for growth performance. Weaning (5 months) July (10 months) October (13 months) Sire Dam breed breed Males Females Total Males Females Total Males Females Total A x A H x A A x H H x H III Total A = Angus, H = Hereford. 200 Heifers Born //::/ ~~ / Steers Born 70 OJ ~ E.Ql OJ ~," {...j I ~/ ' O+-~.-r-,,"-,~-.-.-r-r~ O~~~-.-r-r~,-,-.-~~ Birth Nov Jan Feb Apr Jul Oct Birth Nov Jan Feb Apr Jul Oct Fig. 1 Growth curves of heifers and steers up to,l3 months-of age by year of birth.

6 Baker et al.-reciprocal crossbreeding of cattle breeds 425 purebred (93070) calves out of similar (purebred) dams aged 3 years or older, yielding a heterosis estimate of 4% (P<O.lO). Calf growth The number of calves allocated to the crossbreeding experiment at weaning (with complete birth information and weights between birth and weaning) and surviving to 10 or 13 months-ofage is shown in Table 4. Survival rate from weaning to 13 months was higher for crossbred (97.7%) than purebred (94.3%) calves. Estimates of the fixed environmental effects (age of dam, sex, calf age regression coefficients, and the interactions of sex x age of dam, year x sex, and dam breed x age of dam) are not tabulated in this paper, but were summarised and discussed by Baker et al. (1974). Annual growth curves for heifer and steer calves are shown in Fig. 1. The 1970 season was particularly poor because of semi-drought conditions. This was reflected in a severe depression of post-weaning growth in both steer and heifer calves born in 1969; their October weights were respectively 21 and 25% below the corresponding means of the other 3 calf crops. The reversal of the expected superiority of liveweights of steer over heifer calves at 13 months-of-age (October weight) was caused by the preferential grazing treatment given to the heifer calves from August to October. The steers were not giv,en any favourable grazing treatment at this time (July-October) because of competition with feed requirements of ewes lambing and cows calving. Mean birth weights, liveweights, and liveweight gains for Hie 4 breed groups (generalised leastsquares means) are presented in Table 5 for 4 representative weights and pre- and post-weaning liveweight gains. The actual mean calving date was 16 September. Relative to Angus calves, Herefords and, to a lesser extent, crossbred calves (both H x A and A x H) were born later. This reflects longer gestation periods and/or later conception dates in Hereford cows (maternal effect of 3.3 days) and also a significant direct effect - on average, calves sired by Hereford bulls were born 3.4 days later than those sired by Angus bulls. Calves from Hereford dams were 2 kg heavier at birth than those from Angus dams but this difference had disappeared by weaning and was not significant for all subsequent weights up to 13 months-of-age (October). Calves sired by Hereford bulls were 1 kg heavier at birth than those by Angus sires and this difference increased to 5 kg by the yearling stage. Comparison of the purebred calves with the reciprocal crosses indicated significant heterosis of 0.8 kg (3%) at.-... "0 ClJ ClJ... ClJ [/).0 r-:o;"!c:: MMtrlOO t<'l"t"tt<'l ~-;~o; 0\t--t<'l \Ot'-t "T '" t-- ~~-;~ NOt--O\ t OOMVlN "";"";0-0 t<'l"t"tt<'l Ot<'l"T'",."t-or-:r-: NNNN «:"":«:c:: OONN'" "' NNNN x x x x "TOOOOO NNr..:...; N * CIJ: * z * o;o;~ Nt<'lOOIO v)"",;. oo * en: * Z * o 00 t<'l N-- - "!c::c::~ "'Nt<'lt-- [/) [/) * z z! t<'l * * "T"Tt<'l * 000 0\0\000 0'-:0""; [/) * * Z N "'- '" o o 1\ 0....:[/) 2Z... ClJ"; " ro. "0 0 t::: V z:lo.. en II II ~* * [/)* " o.,-0 1;: V ::eo.. II * ::C*

7 426 New Zealand Journal of Agricultural Research, 1986, Vol. 29 Table 6 Average liveweights and heterosis for steer and heifer calves. Heterosis Liveweight (kg) Trait Steers Heifers Birthweight November weight January weight February weight (weaning) March weight April weight May weight July weight (IO-months) October weight (13-months) Birth-weaning weight gain Weaning-13-month weight gain 3l Steers (S) Heifers (H) Difference (S-H) (kg) (0/0 ) (kg) (%) (kg ±SE) l ± ± l l.8 l ± ± ± ± ± ± ± ± ± 2.0 Fig. 2 Growth curves of all 200 calves up to 13 months-of-age, by breed of calf. 150 E 100 0> ~ 50 o Birth Nov Jan Feb Mar Apr. May Jun Jul Oct birth and 6.8 kg (5.1070) at weaning increasing up to 14.8 kg (8.6%) at 13 months-of-age. Although H x A calves were consistently heavier than A x H calves from weaning (2.9 kg) up to 13 monthsof-age (4.4 kg) this difference was not significant. The consistent and significant liveweight advantage of crossbred calves over purebreds, and Hereford over Angus calves is illustrated in Fig~ 2 for all 9 weights recorded from birth to 13 months-of-age in the form of growth curves. For both pre-weaning (birth to weaning) and post-weaning (weaning to 13 months) liveweight gains, neither the direct nor maternal effects were significant, but heterosis was 6 kg (5.5%) for preweaning gain and 7.8 kg (21.8%) for post-weaning gain. The average pre-weaning liveweight gain of

8 Baker et al.-reciprocal crossbreeding of cattle breeds 427 Table 7 Estimates of heritability (± standard error) for liveweights and liveweight gains. Trait All calves Steers Heifers Birthweight 0.31 ± ± ± 0.14 November weight 0.21 ± ± ± 0.16 January weight 0.22 ± ± ± 0.15 February weight (weaning) 0.17 ± ± ± 0.14 March weight 0.22 ± ± ± 0.16 April weight 0.28 ± ± ± 0.17 May weight 0.30 ± ± ± 0.17 July weight (lo-months) 0.36 ± ± ± 0.18 October weight (13-months) 0.29 ± ± ± 0.17 Birth-weaning weight gain 0.12 ± ± ± 0.13 Weaning-13-month weight gain 0.07 ± ± ± 0.12 Table 8 Estimates of genetic correlations ( ± standard error) and phenotypic correlations for 4liveweights and preand post-weaning liveweight gains. 1 Birth to Weaning to Birth- Weaning July October weaning October Trait weight weight weight weight weight gain weight gain Birthweight NS Weaning weight 1.10 ± July weight 0.66 ± ± October weight 0.59 ± ± ± Birth-weaning weight gain l.25 ± ±O ± ± Weaning-October weight gain ± ± l ± ± ± Phenotypic correlations above the diagonal, genetic correlations below. All phenotypic correlations are significant (P< 0.0(1l) except the one non-significant (NS) value shown. 112 kg is equivalent to an average daily gain of 0.72 kg. The average post-weaning liveweight gain of 40 kg can be broken down into a gain of 48 kg for heifers (0.21 kg/day) and 32 kg for steers (0.15 kg/day). Heterosis was greater in steer than heifer calves for all liveweights and for birth to weaning liveweight gain (Table 6). This effect was most marked for weights at or near weaning and preweaning liveweight gain. For post-weaning liveweight gain, higher heterosis was observed in heifer than steer calves which agrees with the greater gain over this period in heifer calves. Heritabilities and phenotypic and genetic correlations Because Henderson Method 3 and REML estimates of heritability were essentially the same, only REML estimates are reported here (Table 7). For all calves analysed (steers plus heifers) the heritability estimates of liveweights increased from weaning (0.17) up to about the yearling stage ( ), with birthweight being moderately heritable (0.31). The heritability estimates of preand post-weaning liveweight gains were low (0.12 and 0.07 respectively). Although not shown in Table 7, the heritability of the liveweight gain from weaning to July (10 months) was 0.22 ± Except for birth weight and weaning weight, heritability estimates of all other live weights were higher for heifer than steer calves. Estimates of genetic and phenotypic correlations shown in Table 8 were derived from variances estimated by Henderson Method 3. Both phenotypic and genetic correlations among the 4 liveweights and pre-weaning liveweight gain were moderate to high in value. DISCUSSION Heterosis Only one other New Zealand trial has been published which has estimated heterosis for

9 428 New Zealand Journal of Agricultural Research, 1986, Vol. 29 growth in cattle. That study involved reciprocal crossbreeding of Friesian and Angus cattle (Hight et al. 1973). Heterosis estimates were 3.5 and for birth weight and weaning weight respectively, and these effects were small in comparison with large maternal and direct effects favouring the Friesian over the Angus. A large New Zealand trial evaluating local and exotic cattle breeds crossed with Angus and Hereford cows (Baker & Carter 1982) included within it an Angus-Hereford diallel carried out at another experimental location (Goudies Lands and Survey block) in the Rotorua district (Morris et al. 1986). Analyses of calves born during 11 years ( and ) were carried out, involving a total of 2033 calves born. Direct heterosis estimates were 2.4,3.1, and for birth, weaning, and yearling weights respectively, somewhat lower than the estimates of 3.0, 5.1, and reported in this paper. North American crossbreeding studies involving breeds of British origin (Angus, Hereford, and Shorthorn) have been reviewed by Cundiff (1970). Weighted average heterosis estimates were (range, 1.1 to ) for calf survival from birth to weaning, and (range, to ) for weaning weight. The estimates reported in this paper of 4 and respectively are very similar. A large, more recent diallel crossbreeding experiment which included the Angus and Hereford breeds (Gregory et al. 1978a) reported heterosis of for calf survival from birth to weaning, and for birthweight and weaning weight, in reasonable agreement with previous estimates and those reported here. Variations in feeding and management procedures and sex make an overall summary of heterosis for post-weaning growth difficult, as noted by Cundiff (1970). However, for yearling or slaughter weight of steers, all 6 studies reviewed by Cundiff (1970) favoured crossbreds over purebreds, with a simple average heterosis of (range, ). The New Zealand estimates for steer yearling weight of in this paper and in the Goudies study (Baker & Morris unpublished data) are not consistent, but in both instances were higher than the weaning weight estimates. The Angus-Hereford heterosis estimates in the Goudies study for steers and heifers respectively were 2.3 and 2.7 for birthweight, 2.4 and 3.4 for weaning weight, and 4.0 and 7.0 for yearling weight. The general trend in this study and overseas studies (Cundiff 1970; Preston & Willis 1970) is for heterosis for growth to increase with age at least up to the yearling stage. Cundiff (1970) suggested that heterosis may tend to decrease with age after approximately one year but this was not observed in the steers in this study which were slaughtered at 20 months-of-age (Johnson et al. 1986). Heterosis for all liveweights reported in this study was higher in steers than heifers - the difference was significant for weights at or near weaning. In contrast in the Goudies trial, heterosis was slightly, but not significantly higher in heifers than steers for all liveweights from birth to one year-of-age. The overseas literature is equally confusing and ambiguous on this topic. Preston & Willis (1970) noted that for pre-weaning growth and weaning weight, Stonaker (1963), Cornforth et al. (1965), Brinks et al. (1967), and Urick et al. (1968) all found greater heterosis in females than males. In Stonaker's analysis of 1229 calves, heterosis was almost twice as great in females. In contrast, Gregory et al. (1978a) found that when they partitioned their average heterosis of 7.3 kg for 200-day weight, higher levels were evident in male than female calves (12.7 v. 3.1 kg). Barlow (1981) reviewed the experimental evidence for interaction between heterosis and environment in animals. Considering the nutrition effects on growth and heterosis in cattle he concluded from studies reported by Wiltbank et al. (1969), Lasley et al. (1973), and Long et al. (1979) that there was evidence for a positive relationship between the expression of heterosis for growth and growth rate itself. This type of relationship would explain the higher estimates of heterosis in males than females for growth up to weaning in the present study. However, it would not explain the lower levels of heterosis in the Goudies trial than the present study where pre-weaning average daily gains were 0.89 and 0.72 kg/day respectively and postweaning average daily gains were 0.24 and 0.18 kg/day respectively. Breed and reciprocal effects The finding that foundation Hereford cows were heavier than Angus, with little breed difference in effective calf production for cows 3 years-of-age and older must be interpreted with caution. It is possible that these cow results could have been affected by carryover effects from their farm source. This was investigated in preliminary statistical models and was significant for some years (calving years 1969 and 1970) and some traits (cow weights and reproductive tra.its mainly). It was a relatively minor source of variation affecting offspring growth. However, interpretation of source effects was complicated by confounding with age of cow. To this extent it was then accounted for in the final analysis of growth traits as part of the age of dam effect. Unbiased estimates of the relative ranking of the 2 breeds for cow weight and reproductive performance

10 Baker et al.-reciprocal crossbreeding of cattle breeds 429 were obtained from females born at Waikite and will be summarised in a later paper in this series (Morris & Baker unpublished data). The direct and maternal breed differences between Angus and Hereford cattle for growth were relatively small compared with the heterosis effects (Table 5). Calves sired by Hereford sires were heavier at birth; post-weaning liveweights and liveweight gains also favoured the Hereford over the Angus in a paternal role. Birthweights of calves from Hereford cows were greater than those from Angus cows, at least partly because of the longer gestation periods of Hereford cows (Baker & Carter 1982). Although there was no significant difference between Angus and Hereford cows in maternal performance after birth, calves from the Angus dams had 2.0 kg higher pre-weaning liveweight gains, suggesting superior milking ability. This finding was confirmed in the Goudies trial where calves out of Angus cows were 3.8 kg heavier at weaning and had a 5.5 kg higher pre-weaning liveweight gain than calves from Hereford cows (Baker & Morris unpublished data). The smaller maternal breed difference at Waikite could have been because Hereford cow weights exceeded Angus by more than expected (Baker & Morris unpublished data, Goudies trial), probably as a result of carryover effects from farm source. The superior maternal performance of the Angus pre-weaning and the superior direct effect of the Hereford post-weaning have also been generally observed in overseas studies (Cundiff 1970; Gregory et al. 1978a, b, c). In many instances the differences observed are larger in the North American studies, suggesting that there may be less difference in breed characteristics for growth between the Angus and Hereford in New Zealand. The reciprocal difference favouring H x A calves over A x H calves for pre-weaning liveweight gain, weaning weight, and 13-month weight in the present study, though nonsignificant, has also been observed in other comparable studies of similar size (e.g., Gregory et al. 1978a, b, c), where a larger, significant difference was reported. In the present study the reported standard errors took into account the sire variability whereas this was not done in the study by Gregory et al. (1978a, b, c). Heritabilities and correlations The heritabilities estimated in this paper agree with those previously published in New Zealand by Carter (1971) using the regression of progeny performance on sire's own performance, and by Jury et al. (1980) and Baker et al. (1975) using paternal half-sib covariances. The last paper included a preliminary and less rigorous analysis of the present data set. It can be concluded from the heritabilities and genetic correlations in this paper that yearling weight is a more effective selection criterion than post-weaning liveweight gain or weaning weight for improving progeny growth performance. Dickerson et al. (1974), in a comprehensive evaluation of selection criteria for efficient beef production, also considered yearling weight to be one of the better selection criteria, and almost as effective as direct selection for improving feed conversion efficiency to slaughter at constant final age. Woldehawariat et al. (1977) summarised most of the numerous estimates of genetic parameters in beef cattle. Their weighted average value for heritability of birthweight was 0.45, birth to weaning weight gain 0.30, weaning weight 0.24, feedlot weight gain 0.34, pasture weight gain 0.30, final feedlot weight 0.46, and yearling pasture weight Koch et al. (1982) reviewed realised heritability estimates exclusively from selection studies undertaken in North America, and reported unweighted averages of 0.45 for birthweight, 0.21 for weaning weight, 0.36 for postweaning liveweight gain, and 0.36 for final feedlot weight (12-15 months-of-age). The estimates by Koch et al. were in excellent agreement with those reported by Woldehawariat et al. which were mainly based on paternal half sib estimates, with the exception of final (yearling) weight where realised heritability estimates were lower (0.36 v. 0.46). The New Zealand heritability estimates reported in this paper, and by Carter (1971) and Baker et al. (1975) are lower for birth weight, similar for weaning and yearling pasture weight, but lower for pasture weight gain from weaning to the yearling stage. The New Zealand results are based on an earlier weaning regime than is common in most overseas beef studies (i.e., 150 v. 200 days of age). Jury et al. (1980) reported higher estimates of heritability of post-weaning liveweight gain on pasture (e.g., days and days) ranging from 0.33 to Higher heritabilities for female than male progeny found in this study have also been reported by Carter & Kincaid (1959), Pahnish et al. (1961), Blackwell et al. (1962), Koch et al. (1973), and Jury et al. (1980). Similar results have been found in sheep (Baker et al. 1979) and in mice (Monteiro & Falconer 1966). The consistency of progeny tests on male and female offspring have been investigated by Baker et al. (1975) and Jury et al. (1980). After taking into account progeny group sizes and heritabilities it was concluded in both

11 430 New Zealand Journal of Agricultural Research, 1986, Vol. 29 studies that sire x sex interactions were not important for growth traits from birth to 20 monthsof-age and could be ignored when predicting breeding values. General Although there were some differences between the Angus and Hereford for additive breed effects on growth performance, these were much smaller than additive breed differences recorded among many more diverse breed types such as Charolais and Simmental (Baker & Carter 1982; Gregory et al. 1982). The main benefit from crossing the Angus and Hereford breeds is a result of nonadditive heterotic effects. Even these effects were quite small ( ) for the components of growth studied here. Heterosis is much larger for the reproductive and maternal traits which are expressed in the performance of crossbred v. purebred cows (Baker & Carter 1976, 1982; Gregory & Cundiff 1980). The data on these aspects will be reported in subsequent papers in this series. The final paper will summarise the overall biological and economic advantages of crossbreeding Angus and Hereford cattle. ACKNOWLEDGMENTS We thank the Department of Lands and Survey (Rotorua), and in particular Mr R. Bedford (Farm Manager) and his farm staff at Waikite for their generous cooperation. We also thank Messrs J. P. E. Muller and H. A. Templer of Ruakura for assistance in establishing and running the experiment. REFERENCES Baker, R. L. 1982: The place of crossbreeding in beef cattle improvement. Proceedings of the 1st World Congress on sheep and beef cattle breeding, Christchurch, New Zealand. Vol. 2. pp Baker, R. L.; Carter, A. H. 1976: The value of on-farm performance selection of Angus and Hereford bulls. Proceedings of the New Zealand Society of Animal Production 36 : : Implications of experimental results with beef cattle in New Zealand. Proceedings of the 1st World Congress on sheep and beef cattle breeding, Palmerston North, New Zealand. Vol. 1 pp Baker, R. L.; Carter, A. H.; Beatson, P. R. 1975: Progeny testing Angus and Hereford bulls for growth performance. Proceedings of the New Zealand Society of Animal Production 35: Baker, R. L.; Carter, A. H.; Cox, E. H.; Templer, H. A. 1974: Influence of birth date and dam's age on early growth in beef cattle. Proceedings of the New Zealand Society of Animal Production 34 : Baker, R. L.; Carter, A. H.; Hunter, J. C. 1980: Preliminary results of selection for yearling or 18-month weight in Angus and Hereford cattle. Proceedings of the New Zealand Society of Animal Production 40 : Baker, R. L.; Clarke, J. N.; Carter, A. H.; Diprose, G. D. 1979: Genetic and phenotypic parameters in New Zealand Romney sheep. 1. Body weights, fleece weights, and oestrous activity. New Zealand journal of agricultural research 22: Barlow, R. 1981: Experimental evidence for interaction between heterosis and environment in animals. Animal breeding abstracts 49: Blackwell, R. L.; Knox, J. H.; Shelby, C. E.; Clark, R. T. 1962: Genetic analysis of economic characteristics of young Hereford cattle. Journal of animal science 21 : Brinks, J. S.; Urick, J. J.; Pahnish, O. F.; Knapp, B. W.; Riley, T. J. 1967: Heterosis in preweaning and weaning traits among lines of Hereford cattle. Journal of animal science 26 : Carter, A. H. 1971: Effectiveness of growth performance selection in cattle. Proceedings of the New Zealand Society of Animal Production 31 : : Evaluation of cattle breeds for beef production in New Zealand - a review. Livestock production science 2 : Carter, R. C.; Kincaid, C. M. 1959: Estimates of genetic and phenotypic parameters in beef cattle. II. Heritability estimates from parent-offspring and half-sib resemblances. Journal of animal science 18 : Cornforth, V. P.; Swanson, V. B.; Sutherland, T. M. 1965: Weaning weights of Herefords, Angus and their reciprocal crosses. Journal of animal science 24 : (abstract). Cundiff, L. V. 1970: Experimental results on crossbreeding cattle for beef production. Journal of animal science 30: : Exploitation and experimental evaluation of breed differences. Proceedings of the 1st World Congress on sheep and beef cattle breeding, Palmerston North, New Zealand. Vol. 1 pp Dickerson, G. E.; Kunzi, N.; Cundiff, L. V.; Koch, R. M.; Arthaud, V. H.; Gregory, K. E. 1974: Selection criteria for efficient beef production. Journal of animal science 39 : Gregory, K. E.; Cundiff, L. V. 1980: Crossbreeding in beef cattle: evaluation of systems. Journal of animal science 51 :

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