Synthesis of direct and maternal genetic components of economically important traits from beef breed-cross evaluations

Published information on relative performance of beef breed crosses was used to derive combined estimates of purebred breed values for predominant temperate beef breeds. The sources of information were largely from the United States, Canada, and New Zealand, although some European estimates were also included. Emphasis was on maternal traits of potential economic importance to the suckler beef production system, but some postweaning traits were also considered. The estimates were taken from comparison studies undertaken in the 1970s, 1980s and 1990s, each with representative samples of beef breeds used in temperate agriculture. Weighting factors for breed-cross estimates were derived using the number of sires and offspring that contributed to that estimate. These weights were then used in a weighted multiple regression analysis to obtain single purebred breed effects. Both direct additive and maternal additive genetic effects were estimated for preweaning traits. Important genetic differences between the breeds were shown for many of the traits. Significant regression coefficients were estimated for the effect of mature weight on calving ease, both maternal and direct additive genetic, survival to weaning direct, and birth weight direct. The breeds with greater mature weight were found to have greater maternal genetic effects for calving ease but negative direct genetic effects on calving ease. A negative effect of mature weight on the direct genetic effect of survival to weaning was observed. A cluster analysis was done using 17 breeds for which information existed on nine maternal traits. Regression was used to predict breed-cross-specific heterosis using genetic distance. Only five traits, birth weight, survival to weaning, cow fertility, and preweaning and postweaning growth rate had enough breed-cross-specific heterosis estimates to develop a prediction model. The breed biological values estimated provide a basis to predict the biological value of crossbred suckler cows and their offspring.     

Evaluation of Dorset, Finnsheep, Romanov, Texel, and Montadale breeds of sheep: I. Effects of ram breed on productivity of ewes of two crossbred populations

Effects of Dorset, Finnsheep, Romanov, Texel, and Montadale breeds for performance as sires were estimated in the initial phase of a comprehensive evaluation of these breeds as contributors to sheep crossbreeding systems. Objectives were to evaluate the effects of ram breed, ewe breed, season of mating, and two-way interactions. Rams from the five breeds were single-sire-mated with ewes from two breed types to produce lambs over a 3-yr period. Ewes were assigned to one of three distinct 35-d mating seasons initiated each year in August, October, and December. A different sample of six rams per breed was used each year across all three seasons, and each ram was penned with ewes of both breeds. Traits evaluated and number of ewe records were conception rate and litter weaning weight per ewe exposed (n = 3,261) and number born, litter birth weight, average birth weight, number weaned, and litter weaning weight per ewe lambing (n = 2,751). Ram breed and ewe breed interacted (P < .01) for conception rate and litter weaning weight per ewe exposed, implicating mating preferences, particularly of Romanov rams. In mixed groups of ewes exposed to Romanov rams, conception rate was 12.7% lower and litter weight weaned was 8.4 kg lower in the ewe breed presumably less preferred for mating by the rams. On a per ewe exposed basis, Romanov-sired litters produced either the largest or the smallest values for litter weaning weight, depending on the breed of ewe. Effects of ram breed on number born and litter birth weight interacted (P < .05) with season of mating. The largest litters within each ram breed were associated with the October mating season. Montadale and Romanov rams sired larger and heavier litters from August matings than from December matings, whereas the opposite was true for Dorset-sired litters. Texel- and Finnsheep-sired litters were similar in size and weight from August and December matings. Breed of ram differences affected per ewe lambing productivity measurements (P < .01). Differences between ram breeds for ewe productivity were noted, with increased number born and improved survival of crossbred progeny to weaning for Romanov-sired litters. These results may have implications for using these ram breeds as sires in different crossbreeding systems. Structured mating systems or the creation of new composite populations involving these breeds could be used to match the resources, environment, and market of specific production situations.     

Model definition for genetic evaluation of purebred and crossbred lambs including heterosis

Crossbreeding is a common practice among commercial sheep producers to improve animal performance. However, genetic evaluation of U.S. sheep is performed within breed type (terminal sire, semi-prolific, and western range). While incorporating crossbred records may improve assessment of purebreds, it requires accounting for heterotic and breed effects in the evaluation. The objectives of this study were to: 1) describe the development of a paternal composite (PC) line, 2) determine the effect of direct and maternal heterosis on growth traits of crossbred lambs, 3) estimate (co)variance components for direct and maternal additive, and uncorrelated maternal environmental, effects, and 4) provide an interpretation of the estimates of random effects of genetic groups, and to use those solutions to compare the genetic merit of founding breed subpopulations. Data included purebred and crossbred records on birth weight (BN; n = 14,536), pre-weaning weight measured at 39 or 84 d (WN; n = 9,362) depending on year, weaning weight measured at 123 d (WW; n = 9,297), and post-weaning weight measured at 252 d (PW; n = 1,614). Mean (SD) body weights were 5.3 (1.1), 16.8 (3.9) and 28.0 (7.6), 39.1 (7.2), and 54.2 (8.7) kg for BN, WN (at the two ages), WW, and PW, respectively. In designed experiments, the Siremax, Suffolk, Texel, Polypay, Columbia, Rambouillet, and Targhee breeds were compared within the same environment. Estimates of heterotic effects and covariance components were obtained using a multiple trait animal model. Genetic effects based on founders’ breeds were significant and included in the model. Percent estimates of direct heterosis were 2.89 ± 0.61, 2.60 ± 0.65, 4.24 ± 0.56, and 6.09 ± 0.86, and estimates of maternal heterosis were 1.92 ± 0.87, 4.64 ± 0.80, 3.95 ± 0.66, and 4.04 ± 0.91, for BN, WN, WW, and PW, respectively. Correspondingly, direct heritability estimates were 0.17 ± 0.02, 0.13 ± 0.02, 0.17 ± 0.02, and 0.46 ± 0.04 for BN, WN, WW, and PW. Additive maternal effects accounted for trivial variation in PW. For BN, WN, and WW, respectively, maternal heritability estimates were 0.16 ± 0.02, 0.10 ± 0.02, and 0.07 ± 0.01. Uncorrelated maternal environmental effects accounted for little variation in any trait. Direct and maternal heterosis had considerable impact on growth traits, emphasizing the value of crossbreeding and the need to account for heterosis, in addition to breed effects, if crossbred lamb information is included in genetic evaluation.     

Crossbreeding among British and continental European dual-purpose breeds in the coastal Pacific Northwest

From 1979 through 1987, British breed and crossbred cows were mated to Simmental, Pinzgauer or Tarentaise bulls or to Hereford-Angus crossbred bulls. Beginning in 1982, continental European crossbred females also entered the herd, to be mated for first calving to Hereford-Angus or Angus bulls and as cows to continental European or Hereford-Angus bulls. In progeny of British breed and crossbred cows, dam breed effects on birth and weaning weight were not important, but continental European crossbred calves were heavier than British crossbred contemporaries at birth and weaning. Pinzgauer- and Simmental-sired calves were heavier at birth than Tarentaise crosses, but calves sired by each of the continental breeds had similar weaning weights. Maternal heterosis was greater than direct heterosis effects on weaning weight (8% vs 5%), but only direct heterosis (13%) influenced birth weight. Within progeny of continental European crossbred cows, calves with a Tarentaise maternal grandsire were lighter at birth, with no significant difference among other maternal grandsire breeds. Maternal breed effects on weaning weight were not significant. Nevertheless, in contemporary years, continental European crossbred cows reared calves that were 10% heavier than calves reared by British crossbred cows. Pacific Northwestern cattle producers could achieve substantial increases in weaning weight from introducing inheritance from continental European dual-purpose breeds into cow herds and calf crops of British ancestry.     

Performance of purebred and crossbred progeny of White Leghorn and New Hampshire sires

Data from a reciprocal recurrent selection (RRS) programme involving a White Leghorn and a New Hampshire flock were analysed to determine whether there were genetic differences in the purebred population that came to expression primarily in the crossbred progeny. The RRS programme had been in use for four years. The White Leghorn flock had previously been the subject of long‐continued and intensive family selection. The New Hampshire flock was less highly selected. Egg number, egg weight and body weight were the primary traits under selection. Each year the programme involved about 10 sires and 80 females of each breed, and about 400 offspring of each type of cross.

The overall economic value of the crossbreds consistently exceeded the mid‐parent mean, the difference increased steadily during the RRS programme. Heritabilities of the various traits were higher when calculated on the basis of crossbred offspring than when calculated on the basis of purebred offspring. For egg production in the White Leghorns there was a fairly low correlation between purebred and crossbred offspring of the same male. For other traits in both breeds the correlation between purebred and crossbred offspring was moderately high. There was a significant interaction between males and breed of females for all traits and breeds, except for egg number in the New Hampshire. These results are consistent with the notion that there were genetic differences between the purebred males (particularly the White Leghorn males) that affected the production characteristics of their crossbred progeny differently than their purebred progeny.     

Index selection in terminal sires improves early lamb growth

The use of terminal sires (TS) for crossbreeding is integral to the UK sheep industry where approximately 71% of market lambs are sired by TS rams. Early growth of these crossbred lambs affects profitability. The objectives of this study were i) to evaluate the effectiveness of index selection among TS on BW and ADG of their crossbred offspring; and ii) to compare the efficacy of that selection within TS breeds. The most widely used TS breeds in the United Kingdom are Charollais, Suffolk, and Texel. These participated in sire referencing schemes in which they were evaluated on a lean growth index designed to increase carcass lean weight at a given age. From 1999 to 2002, approximately 15 high and 15 low lean growth index rams per breed (93 in total, differing in index on average by 4.6 SD) were selected from within their sire referencing schemes and mated to Welsh and Scottish Mule ewes. Their crossbred offspring were reared commercially on 3 experimental farms in England, Scotland, and Wales. A total of 6,515 lambs were born between 2000 and 2003. Lambs were weighed at birth (BWT), 5 wk (5WT), and 10 wk (10WT), and their ADG from birth to 10 wk was calculated. Lambs sired by high index rams were on average, across breeds, heavier at all ages (P < 0.01) with 0.07 ± 0.03, 0.3 ± 0.1, and 0.4 ± 0.1 kg greater BWT, 5WT, and 10WT, respectively. Their ADG was 5.1 ± 1.9 g/d greater than low-index-sired lambs (P < 0.01). Suffolk-sired lambs were on average heavier at all ages, with greater ADG, whereas Charollais-sired lambs were lightest with smallest ADG. Overall, there was no significant interaction between sire index and sire breed (P > 0.10). Within Suffolk-sired lambs, there was little difference between high and low index sires for the traits studied (P > 0.3). High and low index Charollais-sired lambs differed in BWT (0.09 ± 0.04 kg) and 5WT (0.3 ± 0.1 kg), and Texel-sired lambs differed in 5WT (0.5 ± 0.1 kg), 10WT (0.9 ± 0.2 kg), and ADG (10.2 ± 3.3 g/d; P < 0.01). Lambs from Scottish Mule dams were heavier, with greater ADG, than lambs born to Welsh Mules (P < 0.01). Lambs reared in Scotland were heavier at all ages (P < 0.01). The results suggest that using index selection in TS can improve the growth of their commercial offspring reared on grass.     

新疆细毛羊与澳州美利奴杂交的杂交优势

利用19只公羊和5群母羊来测定初生、断奶和周岁时的杂交优势水平。公羊的基因型包括:纯种新疆细毛羊(XX)、纯种澳州美利奴(AA)和它们的一代杂种(F_1):母羊的基因型只有两个,即(XX)和(F_1)。试验于1987—1989年在新疆维吾尔自治区南山种羊场进行,试验设计了一个不同基因型之间的随机交配,以便估计性状的遗传参数和杂交优势水平。 用计算机分析了552个后代的记录。初生重、断奶重、周岁体重、断奶毛长、周岁毛长和周岁剪毛量的杂交优势分别是4.0％、2％、11.55％、0.4％、6.05％和3.49％。生长发育性状的杂交优势水平明显地高于羊毛生长性状的杂交优势水平。     

Evaluation of Columbia, USMARC-Composite, Suffolk, and Texel rams as terminal sires in an extensive rangeland production system: I. Ewe productivity and crossbred lamb survival and preweaning growth

A 3-yr study was conducted to comprehensively evaluate columbia, suffolk, usmarc-composite (composite), and texel breeds as terminal sires in an extensive rangeland production system. The objective was to estimate breed-of-ram effects on ewe fertility, prolificacy, and dystocia, and sire breed effects on lamb survival and growth until weaning at approximately 132 d of age. Data were from 22 columbia, 22 composite, 21 suffolk, and 17 texel rams with 957 exposures to 574 adult rambouillet ewes (3- to 7-yr-old at lambing), 908 lambings, and 1,834 lambs. Ram breed did not affect ewe fertility (mean = 94.9%; p = 0.73), total number born per ewe lambing (mean = 2.02 lambs; p = 0.20), number born alive per ewe lambing (mean = 1.90 lambs; p = 0.24), or number weaned per ewe lambing (mean = 1.45 lambs, p = 0.94). Dystocia rates were different (p = 0.01) for ewes mated to columbia (12.2%), composite (13.5%), suffolk (25.7%), and texel rams (31.9%) during 1 yr of the study, but differences among ram breeds were not repeatable (p ≥ 0.38) during the other 2 yr. Suffolk-sired lambs were heavier (p ≥ 0.02) at birth (5.5 kg) and weaning (40.3 kg) than lambs sired by the other breeds, which did not differ (p ≥ 0.34) for birth weight (mean = 5.3 kg). Texel-sired lambs (37.4 kg) were lighter (p ≥ 0.02) at weaning than columbia- (38.8 kg) and composite-sired (38.4 kg) lambs, which did not differ (p = 0.40) for weaning weight. Sire breed effect approached significance (p = 0.06) for lamb survival to weaning; estimated survival probabilities were 0.87 (columbia), 0.89 (composite), 0.93 (suffolk), and 0.86 (texel) for lambs reared by their birth dam. Interaction between sire breeds and birth weight affected (p < 0.001) lamb survival and revealed that lightweight columbia- and suffolk-sired lambs had a greater risk of death than lightweight lambs sired by composite and texel rams, but risk of death did not increase substantially for heavyweight lambs from any of the breeds. When mated to adult rambouillet ewes in an extensive rangeland production system, the use of suffolk rams is warranted to improve preweaning growth of market lambs and is not predicted to affect ewe fertility, ewe prolificacy, dystocia, or lamb survival compared with the other sire breeds we tested.     

The crossbred sire: theory

Favorable effects of heterosis on performance of the crossbred market animal and the crossbred dam have been well documented and breeding plans have been developed to utilize these effects. However, a similar mandate for use of the crossbred sire does not exist. Given the common developmental factors involved in reproduction in both sexes, it appears likely that the same nonadditive effects that lead to improved reproductive fitness in the female would also have an effect in the male. Most studies that have evaluated heterotic effects in the male have observed heterosis for at least some components of male reproduction, but have been unable to document consistently favorable effects of the crossbred male on overall conception rate. This result may reflect the categorical nature of conception and possible limiting effects of the female on expression of male differences. Important effects of true paternal heterosis, parallel to maternal heterotic effects acting through the maternal environment provided by the dam, appear unlikely because of the less-intimate relationship between offspring and sire. However, if the relationship between underlying breeding value and realized phenotypic merit is not linear, substantial realized paternal heterosis may be observed due to optimization of gene frequencies through use of the crossbred male. This result is likely for categorical traits or traits with an intermediate optimum breeding value. At the production system level, the appropriate unit of evaluation is the cohort composed of a male and the set of females that are exposed to the male for breeding. At this level, potential advantages of the crossbred male may accrue due to both heterosis for male fertility and optimization of gene frequency.     

Breed and heterotic effects on postweaning traits in Altex and New Zealand White straightbred and crossbred rabbits

Postweaning data from 1,111 straightbred and reciprocally crossbred rabbits were analyzed to evaluate Altex and New Zealand White (NZW) breeds for individual growth and litter traits. The Altex is a recently developed sire breed, whereas the NZW is a popular commercial dam breed. Individual fryer growth traits were weaning (28 d; WW) and market (70 d; MW) weights and ADG. Litter traits included litter size (LSW) and total weight of litter at weaning (LWW), 28 to 70 d total feed intake (LFI), feed efficiency (LFE = total litter gain/LFI), survival rate, and within-litter MW uniformity. Least squares models consisted of fixed effects of sire breed, dam breed, season of weaning, doe parity, two- and three-way interactions, and random effects of sire within sire breed, litter within sire x dam breed, and(or) residual error (depending on whether an individual or a litter trait was analyzed). Crossbreeding parameters (direct breed additive, maternal breed, and individual heterosis) were estimated. Altex sires increased WW, ADG, and MW by 40 g (P < 0.10), 2.5 g/d, and 152 g (P < 0.001), respectively. Individual growth traits were not significantly influenced by the maternal breed effect. Litter size at weaning and LWW means were numerically similar for Altex and NZW dams. Direct heterosis increased ADG (1.7 g/d; P < 0.01) and MW (66 g; P < 0.10). In straightbred Altex compared to NZW fryers, ADG and MW were increased by 3.6 g/d and 216 g, respectively (P < 0.001). In Altex (sire) x NZW (dam) crossbred compared to NZW straightbred fryers, WW and MW were heavier (55 and 218 g; P < 0.10 and < 0.001) and ADG was more rapid (4.2 g/d; P < 0.001). For litter traits, Altex compared to NZW sires increased LFI by 1.28 kg (P < 0.10). Individual crossbreeding parameters did not affect (P > 0.05) other litter traits. No relationship existed between breed type of fryer and survival status (chi2 = 2.81; P > 0.25). For litter traits, straightbred Altex had significantly greater LFI by 2.45 kg and increased LFE by 0.015 units relative to NZW. Combined direct breed additive and heterosis effects increased LFI by 1.84 kg (P < 0.05) in Altex (sire) x NZW (dam) crossbreds compared to NZW straightbreds. Also, 25% more Altex (sire) x NZW (dam) crossbred fryers were marketable (body weight > or = 1.8 kg) by 63 d of age than NZW straightbred fryers. These data suggest that crossing Altex bucks to NZW enhanced breeding efficiency of fryer growth performance.     

Genetic evaluation of growth in a multibreed beef cattle population using random regression-linear spline models

The objective of this study was to examine the feasibility of using random regression-spline (RR-spline) models for fitting growth traits in a multibreed beef cattle population. To meet the objective, the results from the RR-spline model were compared with the widely used multitrait (MT) model when both were fit to a data set (1.8 million records and 1.1 million animals) provided by the American Gelbvieh Association. The effect of prior information on the EBV of sires was also investigated. In both RR-spline and MT models, the following effects were considered: individual direct and maternal additive genetic effects, contemporary group, age of the animal at measurement, direct and maternal heterosis, and direct and maternal additive genetic mean effect of the breed. Additionally, the RR-spline model included an individual direct permanent environmental effect. When both MT and RR-spline models were applied to a data set containing records for weaning weight (WWT) and yearling weight (YWT) within specified age ranges, the rankings of bulls' direct EBV (as measured via Pearson correlations) provided by both models were comparable, with slightly greater differences in the reranking of bulls observed for YWT evaluations (>or=0.99 for BWT and WWT and >or=0.98 for YWT); also, some bulls dropped from the top 100 list when these lists were compared across methods. For maternal effects, the estimated correlations were slightly smaller, particularly for YWT; again, some drops from the top 100 animals were observed. As in regular MT multibreed genetic evaluations, the heterosis effects and the additive genetic effects of the breed could not be estimated from field data, because there were not enough contemporary groups with the proper composition of purebred and crossbred animals; thus, prior information based on literature values had to be included. The inclusion of prior information had a negligible effect in the overall ranking for bulls with greater than 20 birth weight progeny records; however, the effect of prior information for breeds or groups poorly represented in the data was important. The Pearson correlations for direct and maternal WWT and YWT ranged from 0.95 to 0.98 when comparing evaluations of data sets for which the out-of-range age records were removed or retained. Random regression allows for avoiding the discarding of records that are outside the usual age ranges of measurement; thus, greater accuracies are achieved, and greater genetic progress could be expected.     

Economic evaluation of alternative crossbreeding systems involving four breeds of swine. I. The simulation model

A static, deterministic computer model, programmed in Microsoft Basic for IBM PC and Apple Macintosh computers, was developed to calculate production efficiency (cost per kg of product) for nine alternative types of crossbreeding system involving four breeds of swine. The model simulates efficiencies for four purebred and 60 alternative two-, three- and four-breed rotation, rotaterminal, backcross and static cross systems. Crossbreeding systems were defined as including all purebred, crossbred and commercial matings necessary to maintain a total of 10,000 farrowings. Driving variables for the model are mean conception rate at first service and for an 8-wk breeding season, litter size born, preweaning survival rate, postweaning average daily gain, feed-to-gain ratio and carcass backfat. Predictions are computed using breed direct genetic and maternal effects for the four breeds, plus individual, maternal and paternal specific heterosis values, input by the user. Inputs required to calculate the number of females farrowing in each sub-system include the proportion of males and females replaced each breeding cycle in purebred and crossbred populations, the proportion of male and female offspring in seedstock herds that become breeding animals, and the number of females per boar. Inputs required to calculate the efficiency of terminal production (cost-to-product ratio) for each sub-system include breeding herd feed intake, gilt development costs, feed costs and labor and overhead costs. Crossbreeding system efficiency is calculated as the weighted average of sub-system cost-to-product ratio values, weighting by the number of females farrowing in each sub-system.     

Characterization of breeds of Bos indicus and Bos taurus cattle for maternal and individual traits

Angus, Boran and Red Poll sires were mated to Ankole, Boran and small East African Zebu (Zebu) females to produce the cows characterized in this study, which produced calves by Friesian, Brown Swiss, Simmental, Boran and Red Poll sires. Individual traits included cow parturition weight, cow weight at weaning, cow mean weight and cow weight change from parturition to weaning; maternal traits included calf crop born percentage, preweaning viability percentage, overall viability percentage, birth weight, weaning weight, weight at 12, 18 and 24 mo and calf weight weaned per cow exposed to breeding (productivity index). Cows by Angus and Red Poll sires significantly exceeded cows by Boran sires (all cows in this comparison had Ankole and Zebu dams) in weaning weight of progeny and in cow weight at parturition and at weaning. Cows by Red Poll sires significantly exceeded cows by Boran sires in birth weight of progeny. Progeny of cows by Boran sires significantly exceeded progeny of cows by Angus and Red Poll sires in 24-mo weight. Cows by Angus and Red Poll sires did not differ (P greater than .05) in any of the traits analyzed. Cows with Ankole and Boran dams significantly exceeded cows with Zebu dams (all cows in this comparison had Angus and Red Poll sires) in progeny weight at birth, 18 mo and 24 mo and in cow weight at parturition and at weaning. Cows with Boran dams significantly exceeded cows with Zebu dams in weaning and 12-mo weight of progeny and significantly exceeded cows with Ankole dams in weaning weight of progeny. The significantly heavier weaning weight and significantly lighter 24-mo weight of the 3/4 Bos taurus progeny of cows with Angus and Red Poll sires relative to the 1/2 Bos taurus progeny of cows with Boran sires suggest that cattle that are 1/2 Bos taurus breed composition have greater general adaptation than cattle with 3/4 Bos taurus breed composition in the postweaning nutritive and climatic environment under which this experiment was conducted. Significantly heavier weights of Angus and Red Poll crossbred cows relative to Boran crossbred cows (all breeds crossed on Ankole and Zebu cows) indicate that the two Bos taurus breeds exceed the Boran (Bos indicus) breed in additive direct genetic effects for size when they have general adaptation to the environment.     

Lamb production performance of 14 sire breeds mated to New Zealand Bomney ewes

From an extensive series of trials involving approximately 15 000 Romney ewes mated with 435 rams, provisional results are presented on the comparative performance of 14 sire breeds for lamb meat production. The breeds, each represented by ten or more rams, were Southdown, Suffolk, South Suffolk, Hampshire, Dorset Down, South Dorset Down, Poll or Horn Dorset, Border Leicester, English Leicester, Ryeland, Cheviot, Lincoln, Merino and Romney.Important differences exist between sire breeds in progeny survival, with the Southdown being best and the Romney poorest. Progeny of long-wool sires, and particularly the Lincoln, clip more wool at post-weaning shearing than of the Down breeds, which exhibit quite small variation.Sire breeds vary in average live-weight and carcass growth of their progeny, the Suffolk, Hampshire and Dorset breeds producing the heaviest and Merino and Romney the lightest lambs. In terms of lamb live-weight or carcass production per Romney ewe mated, Romney, Merino, Lincoln, Ryeland, Cheviot and English Leicester sires are inferior to the Southdown while Dorset, Suffolk, South Suffolk and Dorset Down are superior.Within any breed, wide differences exist between progeny growth rates of the best and poorest sires, emphasising the importance of sound selection of rams and of adequate genetic sampling in breed comparisons.     

Economic evaluation of alternative crossbreeding systems involving four breeds of swine. II. System efficiency

A static, deterministic computer model was used to calculate production efficiency (cost per kg of product) for four purebred and 69 alternative crossbreeding systems involving the Duroc, Yorkshire, Landrace and Spotted breeds of swine. Crossbreeding systems were defined as including all purebred, crossbred and commercial matings necessary to maintain a total of 10,000 farrowings. Driving variables for the model were predicted mean conception rates, litter size born, preweaning survival rate, postweaning average daily gain, feed-to-gain ratio and carcass backfat. Predictions were computed using breed effect and heterosis estimates obtained from experimental data involving the four breeds collected at the Oklahoma Agricultural Experiment Station between 1976 and 1979. The most efficient breed combinations for each of the nine types of crossbreeding systems evaluated were predicted to reduce cost per kg of product by 6.7 to 10.5%, relative to the most efficient purebred (Duroc). The Duroc X (Yorkshire, Landrace, Spotted) four-breed rotaterminal was predicted to be the most efficient system, followed by the Duroc X (Yorkshire, Landrace) rotaterminal. Duroc X (Spotted X Landrace) and Duroc X (Spotted X Yorkshire) static systems ranked third and fourth overall, respectively. Sensitivity analysis indicated that ranking of systems predicted to be most efficient under the default model was reasonably robust to varying input economic, genetic and management parameter values. Results of this study suggested that three- or four-breed rotaterminal or static systems should maximize effective use of heterosis and breed complementarity in swine production systems.     

Heterosis and recombination effects on pig growth and carcass traits

The primary objective was to estimate breed, heterosis, and recombination effects on growth and carcass traits of two different four-breed composite populations of pigs. Experiment 1 (Exp. 1) included purebred and crossbred pigs originating from Yorkshire, Landrace, Large White, and Chester White breeds, and Experiment 2 (Exp. 2) included pigs from Duroc, Hampshire, Pietrain, and Spot breeds. Data were recorded on purebred pigs, two-breed cross pigs, and pigs from generations F1 through F6, where F1 pigs were the first generation of a four-breed cross. Pig weights were recorded at birth and at 14, 28, 56, 70, and 154 d of age. Average daily gain was calculated for intervals between weights, and ultrasonic backfat measurements (A-mode) were taken at 154 d of age. Feed intake was measured between 70 and 154 d of age on mixed pens of boars and barrows. Carcass backfat, length, and loin muscle area were measured on barrows at slaughter. Mixed-model analyses were done separately by experiment, fitting an animal model. Fixed effects included farrowing group and sex for growth traits and farrowing group for carcass traits. For ADFI, a weighted mixed-model analysis was done fitting farrowing group as a fixed effect, sire nested within farrowing group as a random effect, and weighting each observation by the number of pigs in each pen. To test feed efficiency, a second analysis of ADFI was done adding ADG as a covariate in the previous model. Included as covariates in all models were direct, maternal, and maternal grandam breed effects, direct and maternal heterosis effects, and a direct recombination effect. Recombination is the breakup of additive x additive epistatic effects present in purebreds during gamete formation by crossbred parents. Effects of direct heterosis significantly increased weights at birth, 14, 56, 70, and 154 d of age in Exp. 1. Effects of direct heterosis significantly increased ADG from birth to 14, 28 to 56, and 70 to 154 d of age in Exp. 1. In Exp. 2, effect of direct heterosis significantly increased weights and ADG at all ages. In Exp. 1, recombination significantly reduced loin muscle area. In Exp. 2, recombination significantly increased weights at birth, 14, 28, and 56 d, ADFI from 70 to 154 d, and ADFI adjusted for ADG. The correlation between maternal heterosis and recombination effects for all traits in Exp. 1 and Exp. 2 was approximately -0.90. Maternal heterosis and recombination effects were estimable, but greatly confounded.     

Direct and maternal genetic effects due to the introduction of Bos taurus alleles into Brahman cattle in Florida: II. Preweaning growth traits

Records of birth weight (BW), weaning weight (WW) and condition score (CS) from 1,467 Brahman and Brahman X Angus crossbred calves from Brahman and crossbred Brahman sires and Brahman, crossbred Brahman and Angus dams were collected at the Subtropical Agricultural Research Station, Brooksville, Florida, from 1971 to 1982. Best linear unbiased estimates (BLUE) of Brahman sire and dam group additive genetic effects (as deviations from Angus) and Brahman X Angus dam and calf group nonadditive (intralocus) genetic effects (as deviations from intralocus group genetic effects in the parental breeds) were obtained. Linear combinations of these were used to compute direct and maternal Brahman additive and Brahman X Angus nonadditive (intralocus) group genetic effects. The respective BLUE of these four effects were 5.99 +/- 2.08, -5.70 +/- 1.91, .52 +/- 1.81 and 2.85 +/- .72 kg for BW; 9.60 +/- 10.29, 8.76 +/- 9.47, 9.47 +/- 8.96 and 20.95 +/- 3.56 kg for WW; and -1.10 +/- .55, 1.64 +/- .50, 1.47 +/- .47 and .05 +/- .19 units for CS. Linear combinations of the BLUE of sire, dam and calf group genetic effects can be used to predict the genetic worth of crossbred groups composed of any combination of Brahman and Angus breeding. Nonadditive maternal group genetic effects were the most important factor for BW and WW, whereas nonadditive direct group genetic effects were the most important for CS.     

Reproductive performance and genetic parameters in first cross ewes from different maternal genotypes

The reproduction of 2,846 crossbreed ewes with 7,899 records is reported. The ewes were progeny of mainly Merino dams and 91 sires from several maternal sire breeds including Border Leicester, East Friesian, Finnsheep, Coopworth, Corriedale, Booroola Leicester, and several others. There were 3 cohorts of ewes at each of 3 sites that were bred naturally to meat-type rams for each of 3 yr to evaluate reproduction and lamb production. At 2 sites, the ewes were mated in the autumn, first at 7 mo of age, and at 2 sites the ewes were mated in the spring, first at 14 or 17 mo of age. The cohorts of ewes and sites were genetically linked by 3 common sires. Mixed linear models were used to analyze ultrasound scanned pregnancy rate, fetal number, fertility (ewes lambing), litter size, lamb survival, number of lambs born (NLBj), number of lambs weaned (NLWj), and total weight of lamb weaned (TWWj) per ewe bred. Fixed effects included sire breed (1 to 10), environment (1 to 4, site and season of breeding: autumn, spring), breeding (1 to 3), cohort (1 to 3), and their interactions. The REML procedures were used to estimate (co)variance components. Ewe sire breed effects were significant (P < 0.01) for all the reproductive traits and breed means ranged from 0.75 to 0.96 for fertility, 1.22 to 2.08 for litter size, 0.70 to 0.90 for lamb survival, 0.99 to 1.66 for NLBj, 0.87 to 1.26 for NLWj, and 22.9 to 33.8 kg for TWWj, with the ranking of sire breeds varying for different traits. For all traits except lamb survival, the contrast between breeding 1 vs. 2 and 3 was considerably greater than the contrast between breeding 2 vs. 3, with significant environment x breeding interactions (P < 0.01). Estimates of heritability for the components of reproduction ranged from 0.03 +/- 0.02 for lamb survival to 0.19 +/- 0.05 for litter size, and those for the composite traits were 0.17 +/- 0.04 for NLBj, 0.13 +/- 0.04 for NLWj, and 0.17 +/- 0.04 for TWWj, with repeatability ranging from 0.10 to 0.19. Genetic and phenotypic correlations among the traits are reported. The significant variation among sire breeds of the crossbred ewes can be used to improve reproduction, although there was a change in the rank of the breeds for the various traits. There was considerable overlap between the breeds, and additional improvement could be achieved by exploiting the genetic variation between sires within breeds for all the ewe reproductive traits.     

杜泊绵羊对我国本地绵羊杂交改良的初步效果

目前我国绵羊无论存栏数还是产肉量均居世界首位,但各地方品种众多,与世界优良肉用绵羊相比普遍体重较小、生长慢。2001年以来我国引进了著名肉用绵羊—杜泊绵羊,各地相继开展了杜泊绵羊对本地绵羊的杂交改良,都取得了显著效果,杂交后代在生长速度及产肉性能方面都有很大的提高,为加速我国肉用绵羊业的发展开创了新的途径。     

Maternal heterosis and grandmaternal effects in beef cattle: postweaning growth and carcass traits

Crossbred steer and heifer progeny from 5-, 6- and 7-yr-old dams produced in a four-breed diallel crossing experiment involving the Brown Swiss, Red Poll, Hereford and Angus maternal grandsires and maternal granddams were evaluated for postweaning growth and carcass traits to estimate breed mean maternal heterosis, maternal heterosis for specific breed cross females, average maternal heterosis for all crosses, breed grandmaternal effects and net breed effects in crosses. All progeny evaluated were born in 1979 and 1980 and were sired by 7/8 or 15/16 Simmental bulls. Average maternal heterosis was significant for 200-d weight in heifers but not in steers and was not significant for final weight (444-d) in either heifers or steers. The effects of maternal heterosis on postweaning growth were not important. Differences among breeds in mean maternal heterosis values were small for growth-related traits. Breeds did not differ (P greater than .05) in grandmaternal effects for growth-related traits; Brown Swiss tended to be highest, Red Poll lowest, with Hereford and Angus intermediate. Differences in net breed effects in crosses favored Brown Swiss over the three other breeds and were generally significant for growth traits. Average maternal heterosis, though generally positive, was not significant for carcass traits on either an age-constant or weight-constant basis. Differences among breeds were small in grandmaternal effects, specific heterosis and net effects in crosses for carcass traits associated with both weight or composition; generally the Brown Swiss breed was favored on carcass traits associated with weight in the age-constant analysis and generally had a higher lean-to-fat ratio than the three other breeds in both the age-constant and weight-constant analyses.