Sire Index Research Articles

Recent Advances in Sire Evaluation Methods: A Review

This review deals with the various traditional and recent methods of sire evaluation. A sire evaluation is a method of prediction of sire’s next-generation produced by breeding with specified females and creating their records in a specific environment. Breeding worth of progeny tested sires are obtained through sire index method that assigns ranking to each sire based on their genetic merit. Numerous sire indices are broadly classified in two type’s viz., indices which are purely meant for ranking purposes and those which, besides, provide an estimate of the breeding worth of each sire. Sires can be evaluated in single or multiple herds. The statistical equations represent sire evaluation as linear or non-linear methods. Numerous methods can be incorporated as the advances are made in sire evaluation based on data structures, breeding approaches and selection methods. There are various approaches of sire evaluation such as Least Squares Method (LSM), Simple Regressed Least Squares (SRLS), Best Linear Unbiased Prediction (BLUP) and Derivative-Free Restricted Maximum Likelihood (DFREML) for single as well as multiple trait models which can be used to derive genetic worth of an individual. An efficient method of sire evaluation shows minimum within sire variance or error variance.

SELECTION IN HEREFORD CATTLE I. SELECTION INTENSITY, GENERATION INTERVAL AND INDEXES IN RETROSPECT

Selection intensity and generation interval were evaluated in a Hereford cattle herd of 14 inbred lines and 14 linecross groups corresponding to the lines of inbred sire at the San Juan Basin Research Centre, Hesperus, Colorado. Selection indexes practised were calculated in retrospect. The records analysed were weaning weight and postweaning traits in males and females collected from 1946 through 1973. Analyses were performed by line for the inbreds and pooled analyses for the inbred and linecross populations. From records of 1,239 calves weaned, age of sire averaged 3.75 years compared with 4.52 years for age of dam, showing faster generation turnover for sires than for dams. Generation interval determined 98 actual age of midparent was 4.13 years.Selection applied, evaluated as annual selection differentials within inbred lines and then pooled over all lines, averaged .55 standard deviations per generation for sires for weaning weight. Selection of females was much less. Midparent selection differential amounted to .33 standard deviations per generation. Pooled standardized selection differentials per generation over all lines for sires were .49, .46, 40, -.20, -.10, and .69, respectively, for initial weight, final weight, feed consumption, unadjusted feed efficiency, adjusted feed efficiency, and average daily gain. Selection of females for postweaning traits was not intense. Selection Indexes actually practiced in retrospect were: for sires, IS = .4661(WW) -.0092(FE) + .6126(ADG); for inbred dams, ID = .1824(WW) -.0284 (12W) + .0736 (18W) - 1097 (SPW) -.1097 (FAW); for linecross dams, ID= .2693 (WW) - 2960 (12W) + .0147 (18W) + 1185 (SPW) -.0354 (FAW). The corresponding index selection differentials were .818, 203, and .209. Sire index selection differentials represent about 79 percent of the total selection differentials.

Selection for feed efficiency in Duroc pigs with the addition of daily feed intake data in a 2-stage selection procedure

ABSTRACT The objective of this study was to evaluate the effect of including feed intake records of boars on the genetic gain for feed efficiency. Data were obtained from a Duroc nucleus herd within a Chinese company’s breeding system. The data obtained included ADG, feed conversion ratio (FG), ADFI, days to 115 kg, backfat depth, and loin muscle area. The ADG, FG, and ADFI data were obtained from 570 Duroc boars housed in pens with electronic feeders (FIRE, Feed Intake Recording Equipment, Osborne Industries, Osborne, KS). There were 4,984 Duroc boar and 4,809 gilt progeny. Two sets of estimated breeding values for ADG, FG, ADFI, days to 115 kg, backfat depth, and loin muscle area were estimated using a multivariate animal model, with and without data collected from the FIRE feeders. Terminal sire indices were calculated based on the production costs and market prices for the United States and China. A 2-stage selection procedure was applied with the heaviest sound boars (mean age = 130 ± 17 d) being tested in the FIRE feeder and then the top 100 being selected for breeding. The terminal sire index value gain estimated with ADFI data included was 9.3% greater than the estimates that did not include the ADFI data. The estimated genetic gain for FG with ADFI data was 17% greater than the same annual estimated genetic gain without ADFI data. Overall, there is a substantial genetic gain of FG when individual ADFI records of boars were included in the selection index.

Increased genetic gains in multi-trait sheep indices using female reproductive technologies combined with optimal contribution selection and genomic breeding values

Female reproductive technologies such as multiple ovulation and embryo transfer (MOET) and juvenile in vitro fertilisation and embryo transfer (JIVET) can produce multiple offspring per mating in sheep and cattle. In breeding programs this allows for higher female selection intensity and, in the case of JIVET, a reduction in generation interval, resulting in higher rates of genetic gain. Low selection accuracy of young females entering JIVET has often dissuaded producers from using this technology. However, genomic selection (GS) could increase selection accuracy of candidates at a younger age to help increase rates of genetic gain. This increase might vary for different traits in multiple trait breeding programs depending on genetic parameters and the practicality of recording, particularly for hard to measure traits. This study used both stochastic (animals) and deterministic (GS) simulation to evaluate the effect of reproductive technologies on the genetic gain for various traits in sheep breeding programs, both with and without GS. Optimal contribution selection was used to manage inbreeding and to optimally assign reproductive technologies to individual selection candidates. Two Australian sheep industry indexes were used – a terminal sire index that focussed on growth and carcass traits (the ‘Lamb 2020’ index) and a Merino index that focuses on wool traits, bodyweight, and reproduction (MP+). We observed that breeding programs using artificial insemination or natural mating (AI/N) + MOET, compared with AI/N alone, yielded an extra 39% and 27% genetic gain for terminal and Merino indexes without GS, respectively. However, the addition of JIVET to AI/N + MOET without GS only yielded an extra 1% genetic gain for terminal index and no extra gain in the Merino index. When GS was used in breeding programs, we observed AI/N + MOET + JIVET outperformed AI/N + MOET by 21% and 33% for terminal and Merino indexes, respectively. The implementation of GS increased genetic gain where reproductive technologies were used by 9–34% in Lamb 2020 and 37–98% in MP+. Individual trait response to selection varied in each breeding program. The combination of GS and reproductive technologies allowed for greater genetic gain in both indexes especially for hard to measure traits, but had limited effect on the traits that already had a large amount of early age records.

두록 품종에서의 부계 선발지수 개발을 위한 형질별 가중치에 따른 유전적 개량량의 변화

두록 품종에서의 부계 선발지수 개발을 위한 형질별 가중치에 따른 유전적 개량량의 변화

Genetic evaluation of days to harvest in crossbred lambs1

Days to harvest (DTH) is the number of days a lamb is fed before reaching a target level of fatness. Although economically relevant, this trait has not been thoroughly evaluated in sheep. Most lambs harvested in the United Kingdom are crossbreds sired by purebred terminal sires, with Charollais, Suffolk, and Texel most commonly used. Sires from these breeds were selected on an index designed to increase lean growth while constraining fat. The purpose of this research was to 1) evaluate the effects of index selection in terminal sires on DTH and 2) evaluate the feasibility of incorporating DTH into genetic evaluation programs. Charollais, Suffolk, and Texel sheep had participated in sire referencing schemes where genetic links among flocks were established by sharing rams. Rams with high or low index scores were chosen from these schemes and mated to crossbred ewes at 3 farms in the United Kingdom. Lambs were harvested at a target 11% subcutaneous fat. Records on DTH from 6,350 lambs were analyzed in 2 ways: 1) as time to harvest fitting a survival model and 2) as a normally distributed variable in a bivariate analysis with weight at harvest. The survival analysis was stratified by rearing type (single or twin). In both approaches, sires were fitted using a multivariate normal distribution with a relationship matrix. Regardless of model fitted, sire index did not affect DTH (P>0.10). However, Texel-sired lambs reached harvest faster (P<0.01) than either Charollais- or Suffolk-sired lambs although DTH in those 2 breed types did not differ (P>0.1). Ewe lambs reached harvest faster than wethers (P<0.01). Lambs from older ewes were harvested faster (P<0.001). The heritability of DTH was 0.21 from the survival model and 0.20 from the bivariate model. Rank correlation of sire EBV between methods was 0.9, suggesting strong agreement. The use of high or low index sires did not extend DTH in lambs harvested at a target fatness. Importantly, there is no antagonism between improving carcass merit and extending the grazing season. Furthermore, DTH is moderately heritable. If economically justified within a breeding program, it could be reduced through genetic selection.

Index selection in terminal sires improves lamb performance at finishing1

Lamb meat is often perceived by consumers as fatty, and consumption has decreased in recent decades. A lean growth index was developed in the UK for terminal sire breeds to increase carcass lean content and constrain fat content at a constant age end point. The purposes of this study were 1) to evaluate the effects of index selection of terminal sires on their crossbred offspring at finishing and 2) to evaluate its effectiveness within terminal sire breeds. Approximately 70% of lambs marketed in the UK have been sired by rams of breeds typically thought of as specialized terminal sires. The most widely used are Charollais, Suffolk, and Texel. These breeds participated in sire referencing schemes from the early 1990s by sharing rams among flocks selected on the lean growth index. From 1999 to 2002 approximately 15 "high" and 15 "low" lean growth index score rams were selected from within their sire referencing schemes and mated to Welsh and Scottish Mule ewes. Their crossbred offspring were commercially reared on 3 farms in the UK. Lambs were finished to an estimated 11% subcutaneous fat by visual evaluation. At finishing, lambs were weighed, ultrasonically scanned, and assessed for condition score and conformation. Records were obtained for 6356 lambs on finishing BW (FWT), ultrasonic muscle depth (UMD), ultrasonic fat depth, overall condition score (OCS), and conformation of gigot, loin, and shoulder. Ultrasonic fat depth was log transformed (logUFD) to approach normality. High-index-sired lambs were heavier at finishing (1.2±0.2 kg) with thicker UMD (0.7±0.2 mm) and less logUFD (0.08±0.01 mm; P<0.05). There were no differences in OCS or conformation based on the sire index or breed (P>0.08). Suffolk-sired lambs were heavier than Charollais (1.0±0.3 kg), which were heavier than Texel (0.9±0.3 kg; P<0.001). Texel-sired lambs had thicker UMD than Charollais (0.7±0.2 mm; P<0.001) but were not different than Suffolk. Charollais-sired lambs had greater logUFD than both Texel (0.098±0.016 mm) and Suffolk (0.061±0.017 mm) sired lambs (P<0.001). Within a breed, high- and low-index-sired lambs differed in performance with the exceptions of FWT and UMD in Suffolks. Index selection produced heavier and leaner lambs at finishing. Producers have flexibility in choosing the terminal sire that best fits their production system.

Index selection in terminal sires improves early lamb growth1

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.

Gene flow in a national cross-breeding beef population

Future progress in genetic improvement and the monitoring of genetic resources in beef cattle requires a detailed understanding of the population under selection. This study examines the gene flow in the UK beef population with an uncommon breeding structure involving interaction between the beef and dairy populations. British Cattle Movement Service records were used as the primary source of information, and these data were triangulated with UK government statistics, other industry information sources and existing literature to build up a profile of the UK beef industry. Estimates were made of the breed composition of suckler cows, breeding bulls and the prime slaughter population. Cross-bred animals made up 85% and 94%, respectively, of the commercial beef breeding cow and prime slaughter populations. Holstein/Friesian (through cross-breeding) made up the largest proportion of genes in both these populations with 33% and 28%, respectively. The next five most popular breeds were specialist beef breeds: Limousin (22% and 18%), Charolais (11% and 6%), Simmental (9% and 11%), Angus (7% and 8%) and Belgian Blue (6% and 6%). Combined, the top seven beef breeds accounted for 94% of beef genetics in the prime slaughter population, and 80% of this came from non-native breeds. The influence of dairy breeds in the commercial beef breeding population was highlighted by the fact that 44% of replacement commercial beef breeding females were sourced from beef-sired crosses in the dairy herd, and in total 74% of all maternal grand dams of prime slaughter animals were Holstein/Friesian. The use of selection index technology was also investigated by analysing breeding bull sale results, with the correlation between the terminal sire index and sale price of young breeding bulls being generally moderate but significant, ranging from 0.21 to 0.38 across the major beef breeds. The most influential source of genetics in the commercial suckler beef herd was natural service breeding bulls. These were mostly sourced from pedigree breeders, and accounted for 47.8% of the genetics in the prime beef population. Artificial insemination sires were responsible for 16.6% of prime beef genetics, with the remaining 35.6% coming from dairy breeds, 95% of which was Holstein/Friesian.

Prediction of early race starts in Norwegian-Swedish Coldblooded Trotters

BackgroundLess than a third of Norwegian-Swedish Coldblooded Trotters (NSCTs) have started racing as three year olds since the year 2000 despite the fact that large sums are paid out as price-money in the three year season. Recruitment races are arranged by the Norwegian Trotting Association (NTA) to stimulate early training. The management of young horses varies considerably and a large majority is reared by amateurs. The aim of the present study was to identify predictors of early race starts in young NSCT horses under field conditions.MethodsOf the 801 registered NSCT horses born in 2005, 144 were randomly selected by stratified sampling with gender and paternal progeny as stratification factors. All horses were examined clinically. Further data were collected from NTA and by interviews of breeders, owners and trainers. The set of dependent variables consisted of "passed recruitment race", "start in regular race by the end of the three year season" and "start in regular race by the end of October in the four year season". Univariate and logistic regression analyses were performed.ResultsGenetic performance potential, as indicated by best linear unbiased prediction (BLUP) indices, was the major predictor of the three dependent variables despite large variation in management. Dam's index was a better predictor than sire's index. However, the probability of early race starts in a horse with a low genetic performance potential can be increased by a favourable management. Examples of advantageous management factors in the present study were a flat pasture the first summer and early training. Nearly all horses racing in the three or four year seasons had passed a recruitment race in the two year season.ConclusionsThe results confirm the value of the published BLUP index as an important tool for the NSCT breeding program. Recruitment races stimulate early training.

Economic response that can be achieved from including genomic information to the terminal sire index of beef cattle

Economic response that can be achieved from including genomic information to the terminal sire index of beef cattle

Development of a maternal breeding goal and tools to select for this goal in UK beef production

AbstractA maternal breeding goal for the UK beef industry is described and economic selection indexes are developed to assist in the selection of animals for the goal. The breeding objective is made up of general maternal ability traits, cow size, calving and carcass traits. The general maternal ability traits include calving interval, age at first calving, lifespan, maternal weaning weight and maternal calving difficulty. The calculations of economic values for the traits are outlined and discounted genetic expression coefficients are presented. Three selection indexes are illustrated. The first provides a general dualpurpose index for the selection of bulls to produce replacement heifers in most situations. The second, the hardy breed index, is designed to allow selection for improved maternal performance in extensive and hardy environments. The third, the fertile herd index, allows producers who do not have herd fertility problems to place more selection emphasis on objectives other than fertility. A sample of data from the Limousin breed was used to calculate estimated breeding values (EBVs) which were used to investigate response to the three indexes when the top 20% of sires were selected from either sires with 50 or more grand-maternal progeny or bulls with no recorded progeny. Approximately two thirds of the economic response seen in the selection of heavily used bulls was observed in bulls with no progeny for the hardy and dual-purpose indexes. Bulls were also selected using the existing UK terminal sire index and the resulting bulls assessed in the dual-purpose maternal index. There was found to be a negative economic response to the maternal aspect of the index, though a positive response was seen in the carcass objective. The indexes are presented as the sum of four subindexes emphasizing the contribution of maternal ability, cow size, calving and carcass, respectively to the total index. This further assists commercial producers in selection decisions.

Effects of calving season and sire’s breeding value in a dairy herd during conversion to ecological milk production

A Norwegian dairy herd was examined during and after conversion to ecological management and low concentrate feeding (maximum 3 FEm per day and cow) in 1989–1994. Records from 34 Norwegian Red cows representing 81 lactations were subjected to ANOVA. Mean annual milk yields of 4667 kg, 5478 kg and 6155 kg per cow during first, second and later lactations, respectively, were obtained after conversion. A reduction in number of cows and hence, total milk yield resulted from decreased feed import and reduced forage yields. Decreasing milk yield and increasing protein percentage was found during conversion when effects of calving season, lactation month and number, concentrate ration and cow were corrected for. However, years with large deviations from this trend were observed, demonstrating sensitivity to variations in the farm’s feed production. Periods with pasturing showed the highest milk yield and protein percentage for most seasons of calving, and hence spring calvers obtained the highest milk yield for the whole lactation. Lower somatic cell count in milk was also observed for cows calving in spring and summer compared to calving in autumn and winter. With respect to daily milk yield and protein percentage, cows with higher sire index for protein yield and protein percentage were found superior in this production system. Cows sired by high genetic merit bulls for protein yield also showed higher somatic cell counts than cows sired by low genetic merit bulls, but cows sired by bulls with high overall breeding value showed lower somatic cell counts.

Combined crossbred and purebred selection for reproduction traits in a broiler dam line

Combined crossbred and purebred selection for reproduction traits in a broiler dam line

Lameness in three-year-old standardbred trotters —Influence of parameters determined before three years of age

The aim of the study was to use available information about a group of Standardbred trotters collected during the first three years of life to predict the risk of lameness in these horses when they reach three years of age. In a previous study on the same population, a sire index defined as the frequency of lameness within each progeny group and presence of radiographic changes other than palmar/plantar bony fragments in the metacarpo- and metatarsophalangeal joints, were found to be significant predictors of the likelihood of developing lameness. The additional variables used in the present study were training and feeding of the horses, information that was collected retrospectively up to the time of clinical examination. A total of 265 three-year-old Standardbred trotters were randomly sampled for an epidemiological study of lameness. Eighty horses were classified as sound and 185 horses as lame, with moderate and severe signs in 138 and 47 horses, respectively. The sire index was found to be significant for predicting lameness (P<0.01), the risk of lameness increasing approximately 2.0 times for every 10% increase in sire index. Training and dietary parameters did not influence the risk of lameness significantly.

Lameness in three-year-old standardbred trotters—Influence of parameters determined during the first year of life

Summary The aim of the study was to use parameters determined during the first year of life in order to predict risk of lameness at three years of age. A total of 265 Standardbred trotters with previously recorded radiographic changes of the tarsocrural, metacarpo- and metatarsophalangeal joints were randomly examined as three-year-olds for an epidemiologic study of lameness. Eighty horses were classified as sound and 185 horses as lame with moderate and severe symptoms in 138 and 47 horses, respectively. The variables included in the study were gender, radiographic groups, period of birth, feeding rations in the first winter and sire index calculated as the frequency of lame horses in each progeny group. A significant difference in sire index and period of birth was found in the initial statistical analysis between sound, moderately and severely lame horses. All the variables were entered in a multivariate logistic regression model. A stepwise procedure was performed and resulted in contribution of the sire index (p

Prevalence and risk factors in serous arthritis in the carpal joint of Norwegian coldblooded trotters.

Of 508 four-year-old coldblooded trotters examined for carpitis, 135 (27%) had the condition. Thirty horses had unilateral carpitis on the left frontlimb, 52 on the right frontlimb and 53 had bilateral carpitis. Of these horses, 105 were stallions, 135 were geldings and 269 were mares. The prevalence of carpitis in these three groups was 25%, 25% and 28%, respectively. Information was obtained on the training regimes in four periods of the life of 378 horses. The odds ratios for the training variables were of the same order in all four periods. In logistic regression analyses on the training variables for the first period for the variable percentage of carpitis within each progeny group (sire index), the odds ratio corresponding to a 10% increase in sire index was 1.7 (1.4, 2.1) (95% confidence interval of the odds ratio). The odds ratios for leaving the horses out in a paddock, walking in a jogcart and fast training, or not in each case, were 0.4 (0.2, 0.9), 2.5 (1.2, 5.3) and 2.0 (0.9, 4.4), respectively. This implies a decreased risk of developing carpitis for horses left out in a paddock as a two-year-old, and a 2.5 and 2.0 times increased risk of carpitis occuring in horses exposed to walking in a jogcart and fast training, respectively. Information on the feeding regimes during the first, second and third year collected by a questionnaire revealed no association with carpitis beyond that which could be ascribed to chance. The rations offered were within normal ranges except for calcium, which was below recommended levels.

Index Selection Using Milk Yield, Somatic Cell Score, Udder Depth, Teat Placement, and Foot Angle

Milk yield, somatic cell score, udder depth, teat placement, and foot angle were evaluated in an index (sire index with 50 daughters) to improve an aggregate genotype that included milk yield, clinical mastitis, milking labor, and laminitis. Parameters and economic values were from the literature when available. Sensitivity analysis was conducted for various parameters. Selection for milk yield, somatic cell score, udder depth, teat placement, and foot angle would improve efficiency of response in the aggregate genotype by 1 to 4% over selection for milk yield alone. Most improvement in efficiency of indexes compared with selection for milk yield alone came from adding either somatic cell score, udder depth, or both. Standardized index coefficients for milk yield were three to four times the sum of the standardized coefficients for somatic cell score, udder depth, teat placement, and foot angle when all were included in the index. Index coefficients were always negative for somatic cell score and positive for udder depth, teat placement, and foot angle. Selection for lower somatic cell scores, higher udders, and closer teat placement would help to reduce or to eliminate undesirable correlated responses in milking labor and mastitis associated with selection for increased milk yield.

Prediction of performance of progeny from test station boars.

Data were obtained from 1,954 Duroc and 2,252 Yorkshire purebred and crossbred progeny sired by 34 Duroc and 32 Yorkshire boars, respectively. Boars were purchased from the North Carolina Swine Evaluation Station during August 1983 to December 1988. Boars were selected to represent high and low indexes at the test station. Progeny were raised and tested under conditions similar to commercial pig production at the Tidewater Research Station. For each breed of boar (Duroc and Yorkshire), breed type (purebred and crossbred), and sex (castrates and gilts) of progeny, regression coefficients of progeny traits on each sire trait were computed. Progeny traits were ADG, days to 104.3 kg BW (DAYS), backfat thickness (BF), and feed conversion ratio (FC). Sire traits were ADG, DAYS, BF, FC, and INDEX. Effects of boar test group and progeny test group were included in the models. Averaged over breed type and sex, a 25-unit (1 SD) increase in sire INDEX resulted in 14.5 g more ADG, 3.2 fewer DAYS, .57 mm more BF, and .017 lower FC in Durocs and 5.6 g more ADG, .01 more DAYS, .81 mm less BF, and .083 lower FC in Yorkshires. The low magnitude and variable signs of some regression coefficients suggested that predictions of progeny performance from performance of individual sires at the North Carolina Swine Evaluation Station were not very reliable. Differences between regressions for purebreds and crossbreds implied small correlations between the two breed types. Differences between Durocs and Yorkshires indicated that genetic parameters might not be the same for the two breeds.

Sire Selection Using Cow Traits to Improve Quadratic Merit in Progeny

Sire selection methods were compared by stochastic simulation for improvement in a three-trait, quadratic merit function. Selection indexes included milk, udder depth, and rear leg set phenotypes recorded on cows and bull progeny. The progeny index predicted progeny total merit from the trait indexes of both sire and mated cow. The sire index predicted progeny total merit from only the trait indexes of the sire. Compared with the sire index, which selects the best sire, the progeny index usually selected a number of different sires. The mean number of sires was 1.2 or 2.0 per 100 cows mated, depending on whether the trait indexes were calculated using normal or unit heritabilities, respectively. Total merit gains were not different using the progeny or sire index methods. Although the gain for improvement in nonlinear merit using the progeny index was expected to exceed that using the sire index, it has errors caused by low accuracy cow trait indexes. The sire index achieved 5% greater milk merit gain than did the progeny index. The progeny index was compared with a two-stage method that first used the sire index for milk merit followed by the progeny index for type merit. The two-stage method produced lower gains: 8% less in total merit and 25% less in milk merit, compared with the progeny index. Methods are needed of constituting portfolios of service sires for mating a cow herd to improve total merit while controlling the risk associated with using one or few sires in a breeding season.