Estimation of genetic correlations between racing times recorded at different racing distances by restricted maximum likelihood in Thoroughbred racehorses.

SUMMARY: Genetic correlations between racing times on track type (turf and dirt), and at racing distances on turf (1200 m, 1400 m, 1600 m, 1800 m, and/or 2000 m) and dirt (1000 m, 1200 m, 1400 m, 1600 m, 1700 m, and/or 1800 m) tracks, were estimated in Thoroughbred horses. (Co)variance components were estimated using multiple-trait derivative-free restricted maximum likelihood (MTDFREML). The data used were collected by the Japan Racing Association from 1992 to 1993. The generation 2 pedigree information was preferable for (co)variance estimates. The genetic correlations between racing times on turf and dirt tracks ranged from 0.69 to 0.31 (average 0.51). The genetic correlations between racing distances ranged from 0.68 to 1.00 (average 0.85) and from 0.53 to 1.00 (average 0.88) on turf and dirt tracks, respectively. These results suggest that the racing time per 100 m can be used for horse genetic evaluation within one track type. ZUSAMMENFASSUNG: Schätzung genetischer Korrelationen zwischen Rennzeiten von Vollblüternüber verschiednen Distanzen mittels restringierter Genetische Korrelationen zwischen Rennzeiten auf Rasen- und Erdbahnen, Renndistanzen auf Rasen- (1200, 1400, 1600, 1800 und 2000 m) und Erdbahnen (1000, 1200, 1400, 1600, 1700 und 2000 m) wurden für Vollblüter geschätzt. (Co)Varianzkomponenten wurden mittels Mehr-Merkmal Ableitungsfreier Restringierter Maximum Likelihood (MTDFREML) geschätzt. Die Unterlagen wurden von der Japanischen Renn Vereinigung 1992 und 1993 gesammelt. Generation 2 Abstammungsinformation war für die Co-Varianzschätzung günstig. Genetische Korrelationen zwischen Rennzeiten auf Rasen und auf Erdbahnen waren zwischen 0.69 und 0.31 (Durchschnitt 0.51), jene zwischen Distanzen zwischen 0.68 und 1.00 (Durchschnitt 0.85) und zwischen 0.53 und 1.00 (Durchschnitt 0.88) auf Rasen und Erdbahnen. Die Ergebnisse zeigen, daß Rennzeit per 100 m zur Bewertung der Pferde geeignet ist.

Estimation of non-additive genetic variances in three synthetic lines of beef cattle using an animal model.

Dominance and additive x additive genetic variances were estimated for birth and weaning traits of calves from three synthetic lines of beef cattle differing in mature size. Data consisted of 3,992 and 2,877 records from lines of small-, medium-, and large-framed calves in each of two research herds located at Rhodes and McNay, IA, respectively. Variance components were estimated separately by herd and line for birth weight (BWT), birth hip height (BH), 205-d weight (WW), and 205-d hip height (WH) by derivative-free REML with an animal model. Model 1 included fixed effects of year, sex, and age of dam. Random effects were additive direct (a) and additive maternal (m) genetic with covariance (a,m), maternal permanent environmental, and residual. Model 2 also included dominance (d) and model 3 included dominance plus additive x additive (a:a) effects. In general, only slight changes occurred in other variance components estimates when day was included in Model 2. However, large estimates of additive x additive genetic variances obtained with Model 3 for 4 out of 24 analyses were associated with reductions in estimates of direct additive variances. Direct (maternal) heritability estimates averaged across herd-line combinations with Model 2 were .53(.11), .42(.04), .27(.12), and .35(.04) for BWT, BH, WW, and WH, respectively. Corresponding covariance (a,m) estimates as fractions of phenotypic variance (sigma p2) were .00, .01, .01, and .06, respectively. For maternal permanent environmental effects in Model 2, average estimates of variances as fractions of sigma p2 across herd-line combinations were .03, .00, .05, and .02, for BW, BH, WW, and WH, respectively. Dominance effects explained, on average, 18, 26, 28, and 11% of total variance for BWT, BH, WW, and WH, respectively. Most of the estimates for additive x additive variances were negligible, except for one data set for BWT, two for BH, and one for WH, where the relative estimates of this component were high (.21 to .45). These results suggest that most of the non-additive genetic variance in the traits studied is accounted for by dominance genetic effects.

Genetics of racing performance in the Japanese Thoroughbred horse:: I. Description of the data.

SUMMARY: The Japan Racing Association (JRA) operates 10 national racecourses with both turf and dirt tracks. JRA formulates the rules for horseracing; registers owners, colors, and horses using foal registration; and licenses all JRA trainers and jockeys. In 1990, at the 10 racecourses there were 288 racing days, 3,353 races, and some 38,397 horses. Horse breeding is concentrated in 7 locations with 93% of the Thoroughbreds foaled each year coming from Hokkaido. Thoroughbred flat racing comprise 92% of all races held. Two year olds race together and nearly 40% of their races are run at 1200 m. Some 39% of the three year olds races are at 1800 m. For 3 (and 4) year olds, the range in distances is from 1000 m to 3600 m. The average, over years, of the number of race records per race for 2 year olds is 10.0 and for 3 year olds and up is 11.3. The average for race records per horse for 2 year olds is 3.5 and for 3 year olds and up is 6.7. This average for horses raced per year for 2 year olds is 1,164 and 4,240 for 3 year olds and up. Horses raced per sire averaged over years was 4.6 for 2 year olds and 10.5 for the older ages. The linear regression of seconds per 100 m fit the average seconds reported for the several distances run almost perfectly with R(2) values greater than .99 for all horse ages on either turf or dirt. There is selection practiced as indicated by horse numbers registered and their numbers over ages for stallions and mares. Less than .2% of the horses raced are geldings. A high degree of control exists by JRA in horse stabling and distribution of racing by horses over racecourses. Jockeys are trained by JRA, ride at several race courses, and ride for many trainers. ZUSAMMENFASSUNG: Genetik der Rennleistung beim Japanischen Vollblut: I. Beschreibung der Daten Die "Japan Racing Association" (JRA) betreibt in ganz Japan zehn Pferderennbahnen sowohl mit Rasen- als auch mit Sandkursen. JRA legt die Regeln für Pferderennen fest, registriert die Eigentümer, Farben und Pferde mittels Fohlenregistrierung und vergibt die Lizenzen für alle JRA-Trainer und -Jockeys. Im Jahre 1990 verzeichneten die zehn Pferderennbahnen 288 Renntage, 3353 Rennen mit 38 397 Pferden; Pferdezucht ist an sieben Orten konzentriert, wobei 93% der Vollblutfohlen aus Hokkaido stammen. Bei 92% der veranstalteten Rennen handelt es sich um Nichthindernisrennen von Vollblutpferden. Dabei stehen die Zweijährigen im Wettbewerb, und fast 40% der Rennen gehen über 1200 m. Etwa 39% der Dreijährigen nehmen an Rennen über 1800 m teil. Bei den Dreijährigen (und Vierjährigen) liegen die Distanzen zwischen 1000 bis 3600 m. Der Durchschnitt der Zahl der Rennmeldungen über mehrere Jahre für die Zweijährigen beträgt 10,0 und für die dreijährigen und älteren Pferde 11,3. Der Durchschnitt der Rennmeldungen pro Pferd bei den Zweijährigen beträgt 3,5 und den dreijährigen und älteren Pferden 6,7. Durchschnittlich nehmen jährlich an Rennen 1164 zweijährige und 4240 dreijährige und ältere Pferde teil. Die durchschnittliche Zahl der Pferde über mehrere Jahre war 4,6 pro Vatertier für die Zweijährigen und 10,5 für ältere Pferde. Die lineare Regression von Sekunden pro 100 m paßte sich mit R(2) -Werten über 0,99 fast genau den Durchschnittssekunden an, die für die verschiedenen Renndistanzen angegeben wurden, für die Pferde aller Altersgruppen sowohl auf Rasen- als auch Sandbahn. Selektion bei Hengsten und Stuten ergibt sich aus Zahl der registrierten Pferde mit verschiedenem Lebensalter. Unter den an Rennen beteiligten Pferden sind weniger als 0,2% Wallache. Bei JRA herrscht ein hoher Grad an Kontrolle in bezug auf Ställe und die Verteilung über die Pferderennbahnen. Die von JRA ausgebildeten Jockeys reiten auf verschiedenen Pferderennbahnen und für mehrere Trainer.

Genetics of racing performance in the Japanese Thoroughbred horse:: II. Environmental variation of racing time on turf and dirt tracks and the influence of sex, age, and weight carried on racing time.

SUMMARY: Data collected by the Japan Racing Association (JRA) were individual horse racing times at eight racecourses (Hakodate, Fukushima, Niigata, Tokyo, Nakayama, Chukyo, Kyoto and Hanshin) and at five distances (1000 m, 1200 m, 1400 m, 1600 m, and 1800 m) from 1982 to 1990. Important sources of variation in racing time were examined using a nested model and expressing the variance components as percentages of the total on both turf and dirt. At all racecourses and at all distances where races were on both turf and dirt, racing times were less on turf than dirt. Differences were from 2.09s to 3.91s that increased as distance increased except for 1000 m and 1200 m on dirt where the starting gate are at different locations. The total variance increased with distance on both turf and dirt and at each distance the total variance was larger on dirt than turf, except for 1000 m, as was the residual variance. Racecourse accounted for a small fraction of the variance. Years within racecourses were unimportant. Months within years and courses were important. Months accounted for an average of 12.7% of the total variance on turf and 8.8% on dirt indicating an effect of season that influences racing speed more on turf than dirt. Days within months, years, and courses were important and larger on turf (average was 8.6%) than dirt (average 2.4%). Races within days, months, years, and racecourses accounted for an average of 33.2% on turf and 40.2% on dirt. Clearly races accounted for the largest percentage of the total variance. Racecourse and years within course accounted for less variance than that found in American Quarter horse data, but months, days and races accounted for similar variances. Results suggest that racing speed on turf was more influenced by month and day than speed on dirt in data on Japanese Thoroughbreds. Clearly individual race is the logical contemporary group within which to make genetic predictions among horses. Five distance on turf and dirt were studied to ascertain the importance of sex, age, and sex by age effects and the influence of weight carried on racing times. Individual races having at least to sexes and two ages within each sex were used as incomplete blocks to study the effects. Races were important at all distances on both turf and dirt. The interaction between sex and age was unimportant. The effect of sex and/or age was significant except at 1800 m and 2000 m on turf. Mares were faster than stallions on turf at all distances, but on dirt stallions were faster than mares except at 1200 m. In general, 5 year olds were faster than 3 and 4 year olds except at 1600 m on turf. The partial regression of racing times on weight carried were significant at all distances on turf and dirt. The effects of sex and age were significant statistically and weight carried appears to be important at the distances run in Thoroughbred races. ZUSAMMENFASSUNG: Genetik der Rennleistung beim Japanischen Vollblut: II. Umweltbedingte Variation der Rennzeit auf Rasen- und Sandbahnen und Einfluß von Geschlecht, Alter und getragenem Gezvicht auf die Rennzeit Von 1982 bis 1990 wurden von der "Japan Racing Association" (JRA) auf acht Pferderennbahnen (Hakodate, Fukushima, Niigata, Tokyo, Nakayama, Chukyo, Kyoto und Hanshin) Daten über fünf Renndistanzen (1000, 1200, 1400, 1600 und 1800 m) gesammelt. Die wichtigen Ursachen für die Variation der Rennzeit wurden mit Hilfe eines "Verschachtelungsmodells" untersucht, wobei die Varianzkomponenten als Prozentsätze des Gesamtwerts sowohl auf Rasen- als auch auf Sandbahnen ausgedrückt wurden. Auf alien Pferderennbahnen und über alle Distanzen sowohl auf Rasen- als auch Sandkursen zeigte sich, daß die Rennzeiten auf Rasen kürzer als auf Sand waren. Die Untcrschiede betrugen zwiscnen 2,09 bis 3,91 Sekunden und wuchsen mit der Distanz außer bei 1000 und 1200 m auf Sand, wo sich die Starttore an verschiedenen Stellen befinden. Die Gesamtvarianz stieg mit der Distanz, und bei alien Distanzen außer 1000 m waren die Gesamt- und die Restvarianz jeweils größer auf Sand als auf Rasen. Ein geringer Bruchteil der Varianz war auf die Pferderennbahnen zurückzuführen. Jahre bezogen auf die Pferderennbahnen spielten kcine Rolle. Dagegen waren die Monate bezogen auf Jahre und Pferderennbahnen von Bedeutung. Den Monaten sind auf Rasen ein Durchschnitt von 12,7% der Varianz zuzuschreiben und auf Sand 8,8%, was auf einen jahreszeitlichen Effekt hinweist, der die Renngeschwindigkeit auf Rasen in stärkerem Maße beeinflußt als auf Sand. Tagesbedingte Varianz bezogen auf Monate, Jahre und Pferderennbahnen war signifikant und größer auf Rasen (durch-schnittlich 8,6%) als auf Sand (durchschnittlich 2,4%). Rennen bezogen auf Tage, Monate, Jahre und Pferderennbahnen verursachten 33,2% der Varianz auf Rasen und 40,2% auf Sand. Den Rennen konnte deutlich der größte Prozentsatz an der Gesamtvarianz zugeschrieben werden. Pferderennbahn und Jahre/Pferderennbahn führten zu geringerer Varianz als bei "American Quarter Horse", wobei jedoch Monate, Tage und Rennen ähnliche Varianzen verursachten. Diese Ergebnisse legen die Vermutung nahe, daß Renngeschwindigkeit auf Rasen bei japanischen Vollblütern stärker durch Monat und Tag beeinflußt wurde als auf Sand. Also ist für genetische Voraussagen das Einzelrennen die logische Kategorie. Durch die Untersuchung von fünf Distanzen auf Rasen und Sand wurde die Bedeutung von Geschlecht und Alter sowie Geschlecht nach Alter und der Einfluß des zu tragenden Gewichts auf die Rennzeiten festgestellt. Einzelne Rennen mit wenigstens zwei Geschlechtern und zwei Altersgruppen für jedes Geschlecht wurden als unvollständige Blöckc zur Untersuchung herangezogen. Rennen waren über alle Distanzen sowohl auf Rasen als auch auf Sand signifikant. Die Wechselbeziehung zwischen Geschlecht und Alter war signifikant außer bei 1800 m und 2000 m auf Rasen. Stuten waren schneller als Hengste auf Rasen über alle Distanzen, dagegen auf Sand Hengste schneller außer über 1200 m. Im allgemeinen waren die Fünfjährigen schneller als die Drei- und Vierjährigen außer über 1600 auf Rasen. Die partielle Regression der Rennzeiten auf das getragene Gewicht war signifikant bei alien Distanzen. Die Effekte von Geschlecht und Alter waren statistisch signifikant und das getragene Gewicht für Distanzen, über die Vollblüterrennen ausgetragen werden.

Genetic parameters for carcass traits estimated from Angus field records.

The American Angus Association has sponsored a carcass evaluation since 1974. The carcass data collected as a part of this program are used by the association to conduct a biannual sire evaluation for carcass merit. This paper presents age-adjustment factors and genetic parameter estimates for carcass traits to be used in the Angus carcass genetic evaluation program. Because of the large range in slaughter ages, age classes were defined as all those animals slaughtered at an age of < or = 480 d and those with a slaughter age > 480 d. Linear and quadratic partial regressions on slaughter age for hot carcass weight (HCW), USDA marbling score (MS), 12th rib longissimus muscle area (LMA), and 12th-rib fat thickness (FT) were estimated within sex and age class. Quadratic age regressions were not significant, nor was the linear age regression coefficient for FT in steers in the > 480-d age class. Heritability estimates for age-constant HCW, MS, LMA, and FT were .31, .26, .32, and .26, respectively. The estimated genetic correlation (rg) between HCW and LMA was .47. The estimated rg between HCW and FT was .38 and between MS and FT was -.13. The linear genetic trends for CWT and LMA were significantly positive at .414 kg/yr and .075 cm2/yr, respectively. The genetic trends for FT and MS were very small but significantly negative at -.004 cm/yr and -.003 units/yr, respectively.

Adjusting weight for body condition score in Angus cows.

Weight, height, and body condition score data supplied by the American Angus Association were used to determine the effect of body condition score on cow weight and to compute condition score adjustment factors. Single records on 11,301 cows for weight and 7,769 cows for height were collected at or near weaning, at which time a subjective condition score (9-point scale) was taken. Limited information on extreme scores 1 and 9 allowed only scores 2 through 8 to be included in the analysis. Cows were grouped into age classes corresponding to 2, 3, 4, 5, 6, 7 to 10, and 11+ yr of age. The mathematical model for a weight record included effects of fixed herd, year-month the record was collected, cow age, body condition score, and a random residual error term. The model for height excluded the condition score effect. Effects of herd, year-month, and cow age were highly significant (P less than .0001) for weight and height. Body condition score was a significant source of variation in weight (P less than .0001) and accounted for 16% of the total variation. Adjustment factors for weight (kilograms) by condition score were +116 (score 2), +91 (score 3), +69 (score 4), +39 (score 5), 0 (score 6), -40 (score 7), and -86 (score 8).

Genetic parameters for nuclear and nonnuclear inheritance in three synthetic lines of beef cattle differing in mature size.

Genetic parameters for nuclear and cytoplasmic genetic effects were estimated from preweaning growth data collected on three synthetic lines of beef cattle differing in mature size. Lines of small-, medium-, and large-framed calves were represented in each of two research herds (Rhodes and McNay). Variance components were estimated separately by herd and size line for birth weight and 205-d weight (WW) by REML with an animal mode using an average of 847 and 427 calf records from Rhodes and McNay, respectively. Model 1 included effects of fixed year, sex of calf, age of dam, and random additive direct (a), additive maternal genetic (m), covariance (a,m), permanent environment affecting the dam, and residual error. Model 2 differed from Model 1 by including random cytoplasmic lineage effects and by ignoring permanent environmental effects. Model 1--direct (maternal) heritability estimates for birth weight at Rhodes were .62(.03) for small, .67(.06) for medium, and .30(.11) for large lines. Genetic correlations between direct and maternal effects for birth weight were .67, -.16, and .48 for the respective size groups. For WW at Rhodes, direct (maternal) heritability estimates were .30(.29), .30(.14), and .10(.16) for small, medium, and large lines, respectively, with genetic correlations of -.34 (small), -.12 (medium), and .17 (large). Heritability estimates at McNay were similar to those at Rhodes, except that maternal genetic heritabilities for WW were smaller (.10, small; .01, medium; .00, large). Model 2--estimates for nuclear genetic effects were consistent with the estimates from Model 1. Cytoplasmic variance accounted for 0 to 5% of the total random variance in birth weight. For WW, cytoplasmic variance was negligible at Rhodes and accounted for 4% of the total random variance in the large line at McNay, averaging less than the permanent environment. Results failed to indicate that cytoplasmic variance was important for preweaning performance.

Genetic predictions of racing performance in quarter horses.

Research on the racing performance of quarter horses has been used to develop genetic prediction summaries on all horses with at least one start on record at the American Quarter Horse Association. In the 1987 summary, records from a total of 212,065 horses were used to give genetic predictions on stallions, mares, geldings, fillies, and colts. A reduced animal model was used that incorporated the repeated records of individuals. The individual race was the contemporary group after the data were adjusted for distance, sex, and age. Estimates of heritability of .24 and repeatability of .32 suggest that increased racing performance can be achieved if the predictions are used by breeders. Continued research in variance component estimation includes the genetic covariances among the several distances, maternal influence, and genetic parameters for racing longevity.

Size and management effects on reproduction in first-, second- and third-parity beef cows.

The effects of size, management and size x management interactions on reproduction in beef cattle were determined by using 3,126 breeding and calving records from 1980 to 1985. Cows were from three synthetic lines that differed in mature size (small, medium and large). The lines differed also in the percentages of Jersey, Angus and Simmental. Each line was replicated in two herds. One herd (Rhodes) followed a spring calving schedule and weaned calves at about 180 d of age. The other herd (McNay) calved cows in the fall and weaned calves early at about 45 d of age. Cycling rate, conception rate, abortion rate and calving rate were each evaluated for first-, second- and third-parity dams. An important interaction (P less than .05) was found between lines and management in heifers. Cycling rate and calving percentage were almost identical for all three lines in the Rhodes herd, but small heifers in the McNay herd had about 20% higher cycling (83.8 vs 63.1%) and calving rates (73.8 vs 53.0%) than large heifers. Line x management interactions were not significant in second- and third-parity dams, but line did remain a significant source of variation in calving rate. Calving rates in second-parity dams were 85.0, 78.1 and 70.7% for small, medium and large cows, respectively. In third-parity dams, small cows had a higher calving rate (P less than .05) than either medium or large cows (80.9 vs 66.1 or 68.7%, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Selection for the direct and maternal genetic effects for dystocia in Holsteins.

The effects of selection for the direct and maternal components of dystocia were estimated for first, second and later, and all parities. The effect of restricting maternal change to zero and the effect of selection for only the direct component were also examined. Gene flow procedure was used to compute economic weights as 1 and .347 for the direct and maternal effects, respectively. Genetic gain in aggregate genotype was the largest for first parity. For all parities all the gain in the aggregate genotype was accounted for by the direct effects. At the same time, a slight decrease in the genetic maternal effects was observed. For all cases, selection for both traits had almost no loss in aggregate genotype or accuracy compared with when maternal changes were restricted to zero. Total genetic gain and genetic gain for the direct effect of dystocia were greater and accuracy of selection was lower when selection was for the genetic direct effect only versus the index that included both direct and maternal effects. Selection for only the direct effects is not likely to produce any significant change in dystocia as a maternal trait.

Induction of parturition, progesterone secretion, and delivery of placenta in beef heifers given relaxin with cloprostenol or dexamethasone.

Sixty primiparous beef heifers from a crossbreeding study were used to examine the effects of inducing parturition with relaxin (3,000 U/mg) combined with cloprostenol (500 micrograms, i.m., n = 30) or dexamethasone (20 mg, i.m., n = 30) at Day 273, 10 +/- 1 days before expected parturition (Day 283). Heifers were assigned at random within cloprostenol and dexamethasone groups to receive relaxin (1 mg, n = 5/treatment), i.m. or in the cervical os (OS), at 0 h (the same time as cloprostenol and dexamethasone) or 24 h later. Eleven and six first-calving heifers and sixteen and nine second-calving cows also received cloprostenol + relaxin and cloprostenol + phosphate-buffered saline, respectively. Radioimmunoassay of daily plasma samples indicated an abrupt decrease in progesterone with time (p less than 0.001), from 7.5 +/- 0.50 to 1.0 +/- 0.30 ng/ml (mean +/- SE) within 48 h for all groups. The mean rate of progesterone decrease (ng/ml in 24 h) was accelerated (p less than 0.01) in relaxin-treated heifers (5.3 +/- 0.36), in contrast to dexamethasone- and cloprostenol-treated control heifers (2.8 +/- 0.40). Relaxin combined with cloprostenol or dexamethasone shortened the calving period in these heifers by reducing the interval between treatment and calving (33 vs. 56 h; p less than 0.01). The incidence and duration of retained placenta were reduced by 22 vs. 75% and 14 vs. 34 h for relaxin combined with cloprostenol or dexamethasone as compared with cloprostenol- or dexamethasone-treated controls, respectively (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Within-herd phenotypic, genetic and environmental trend lines for beef cattle breeders.

Computational procedures were developed to compute within-herd phenotypic, genetic and environmental trend lines on a breed-wide basis by using best linear unbiased estimates of fixed effects and predictors of random sire and dam genetic effects. Procedures were demonstrated by using weaning weight performance records from 20 herds participating in the American Angus Herd Improvement Program. Current evaluation procedures used by several beef breed associations make it possible to provide such information to breeders on a routine basis, along with within-herd breeding values. The within-herd genetic trends are relative to the national genetic evaluation base. Procedures are summarized in addition to presentation of within-herd trend lines for four of the 20 herds, demonstrating the utility of such information to breeders, along with a discussion of several alternative presentation formats.

Estimates of beef growth trait variances and heritabilities determined from field records.

Variance components were estimated from field-collected performance records for use in national beef sire evaluation mixed-model programs. Estimates of residual error variances (sigma 2e), sire effect variances (sigma 2s) and dam effect variances (sigma 2d) were obtained for the American Hereford and the American Angus breeds for each of three growth traits: birth weight, weaning weight and postweaning gain. Estimates obtained for birth weight were sigma 2e, 8.43 and 9.26 kg2; sigma 2s, 1.34 and .66 kg2; and sigma 2d, 3.24 and 3.70 kg2 for the Hereford and Angus breeds, respectively. Estimates obtained for weaning weight were sigma 2e, 438.09 and 267.38 kg2; sigma 2s, 20.37 and 17.13 kg2; and sigma 2d, 162.25 and 157.28 kg2 for the Hereford and Angus breeds, respectively. Estimates obtained for postweaning gain were sigma 2e, 425.75 and 374.33 kg2; sigma 2s, 20.08 and 16.49 kg2; and sigma 2d, 41.74 and 48.61 kg2 for the Hereford and Angus breeds, respectively.

Relaxin on induction of parturition in beef heifers.

Purified porcine relaxin (3000 U/mg) was administered into the cervical os of primiparous beef heifers on day 278 of gestation (approximately 5 days before parturition normally occurs) to determine its effects on the induction of parturition, changes in progesterone, estrone (E1), 17 beta-estradiol (17 beta-E2), cervical dilation, and pelvic relaxation. Heifers were assigned randomly to 1 of 3 treatments: relaxin-double (two infusions of 3000 U, 12 h apart; n = 17), relaxin-single (3000 U; n = 14), and PBS-gel vehicle (n = 16). Relaxin induced marked earlier calving (P less than 0.002) than PBS-gel vehicle. The intervals between the administration of relaxin or the PBS-gel vehicle and calving were 2.0, 2.5, and 5.3 days for heifers given relaxin-double, relaxin-single, and PBS-gel vehicle, respectively. The duration of gestation was significantly reduced (P less than 0.002) in relaxin-treated heifers compared with that in control heifers. A precipitous decrease in progesterone (7.1 ng/ml) occurred in peripheral blood plasma within 24 h after relaxin treatment. Coincident with a decline in levels of progesterone, E1 and 17 beta-E2 increased by 1700 and 400 pg/ml, respectively, an increase of 35% compared with the 12% increase in these steroids in control heifers. Mean deviations of cervical dilation increased 643%, 526%, and 11% in heifers given relaxin-double, relaxin-single, and PBS-gel vehicle, respectively. Relaxin induced maximum pelvic opening between 12-36 h after treatment. Although relaxin induced significantly earlier calving, there was no incidence (0 of 31 heifers) of retained placenta. We conclude from this study that purified relaxin administered intracervically to primiparous beef heifers during late pregnancy induced premature parturition. Marked shifts of progesterone, E1, 17 beta-E2, pelvic canal expansion, and cervical relaxation reflect the premature parturition induced by relaxin.

Pelvic development as affected by relaxin in three genetically selected frame sizes of beef heifers.

Purified porcine relaxin was administered into the cervical os on Day 278 of gestation to determine its effects on pelvic development in three genetically selected frame sizes of primiparous beef heifers. Heifers were categorized as small, medium and large frame based upon their genetic composition. Pelvic height, pelvic width and cervical dilatation were determined from Day 270 to 2 days postpartum. On Day 270, heifers were assigned at random to one of three treatments: vehicle control, n = 16; relaxin once (3,000 U), n = 14; and relaxin twice (2 times 3,000 U 12 h apart), n = 17. Each heifer-frame size was represented in each treatment. Relaxin caused marked increases in pelvic height and width, as well as in the rate of linear increase (cm/day) of these parameters (p less than 0.05). These linear increases in pelvic height were 510, 264 and 204%, and pelvic width, were 280, 213 and 204% of the respective pretreatment rates for small, medium and large heifers. The rate of linear increase in pelvic width was greater than pelvic height in all heifers, but maximal in small-frame heifers; relaxin attenuated these intrinsic differences. For small heifers, the rate of linear increase in pelvic width was 121 and 145% of increases for medium and large heifers, respectively, before treatment, and 160 and 200% after treatment. The rate of postpartum involution of pelvic width was -0.03, -0.36 and -0.50 cm/day and, for pelvic height, -0.02, -0.27 and -0.29 cm/day in small, medium and large heifers, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Sire X environment interactions in beef cattle weaning weight field data.

Weaning weight field records, supplied by the American Polled Hereford Association, were used to examine sire X environment interactions. Sire X herd/region and sire X contemporary group/herd interactions were evaluated from a data set containing 19,503 records. Sire X region interaction was evaluated from a data set containing 8,659 records. The genetic correlations of sire progeny performance across contemporary groups/herd were .59 and .37 across herds and contemporary groups/region. The average genetic correlation of sire progeny performance across regions was .64. Heritability of weaning weight was .11 across regions, .17 within region and .28 within herd. Mixed-model sire analyses of Polled Hereford weaning weight field records should include sire X herd/region and sire X contemporary group/herd random effects to reduce the sire X environment effects particular to any herd or contemporary group, and to account for the distribution of sire progeny across herds and contemporary groups in the estimation of prediction error variance. It may be necessary to perform separate sire analyses for some regions to evaluate the breeding values of sires in regions where rank changes are likely to occur.

Genetic improvement of beef cattle in the United States: cattle, people and their interaction.

The purpose of this essay is to develop a historic perspective of the beef cattle population and the legion of people directing its genetic change so that future leadership can increase the rate of breeding technology assimilation. Use of cattle for beef to feed millions is relatively recent. The beef industry of the United States has a rich, romantic heritage that combined Spanish exploitation with British tradition. Spanish cattle became adapted as the Texas longhorn and the European cattle became indigenous. Breeds developed in Britain replaced both. The Zebu was introduced to produce cattle adapted to the Gulf Coast. Selection for early maturity in the British breeds promoted by livestock shows was ended by the dwarf gene. The Charolais breed demonstrated growth potential. Then in 1967, Continental European breeds were imported, given an array of biological types from which to select. Beef cattle breeding research expanded after the second world war through the three regional projects. Performance Registry International was the focal point for performance. The Beef Improvement Federation produced guidelines for recording beef performance including those for national sire evaluation. U.S. Meat Animal Research Center evaluated the several newly introduced breeds. To date, breeding researchers have developed breeding technology for the use by breeder. The major breed association are keeping and utilizing performance records. The genetic structure of the beef breeds is being altered by the use of AI such that genetic change can be made rapidly by the use of superior sires evaluated on their progeny in many herds.

Beef production efficiency.

In the production of high quality protein, feed grains will continue to be used to finish cattle for market as long as economics dictates. Production systems could be developed that would make ruminant animals less competitive with humans for feed grains, but the costs of instituting such programs would be prohibitive. Sufficient genetic variation exists either between or within breeds for the cattle population to be adapted to new management programs and for current methods of beef production to be significantly improved.