205-d Weight Research Articles

Correlated responses in reproductive and carcass traits to selection for 200-day weight in Duroc swine.

Correlated responses in reproductive and carcass traits from a line of Duroc pigs selected for increased 200-d weight along with a randomly selected control line were studied in 189 litters (116 select, 73 control) and 191 pigs (106 select, 85 control), respectively. Reproductive and maternal traits studied included litter sizes born, born alive, and alive at 21 d and litter weight at birth and at 21 d. Carcass traits studied were carcass length, longissimus muscle area, average backfat thickness, 10th rib backfat thickness, specific gravity, weights of closely trimmed ham, loin, and shoulder, belly weight, subjective scoring of the longissimus muscle for color and marbling, estimated percentage of muscle and lean gain per day. Total weighted cumulative selection differential for 200-d weight was 81.7 kg. The realized heritability for 200-d weight was .18 +/- .08, and the change in 200-d weight was 2.5 +/- 1.2 kg per generation. The regression coefficient of litter size born on generation was -.29 +/- .12 (P less than .10) pigs per generation. None of the other regression coefficients for the reproductive traits differed from zero. Average backfat thickness, 10th rib backfat thickness, and belly weight increased by .093 +/- .016 cm, .122 +/- .029 cm, and .089 +/- .040 kg, respectively, per generation. Specific gravity, ham weight, shoulder weight, color score, and percentage of muscle decreased -.00086 +/- .00024, -.165 +/- .013 kg, -.104 +/- .011 kg, -.035 +/- .015 points, and -.47 +/- .12%, respectively, per generation in response to the selection.(ABSTRACT TRUNCATED AT 250 WORDS)

Prediction of fertility from calfhood traits of Angus and Simmental heifers.

The objectives of this study were to quantify the relationships between traits observed before the first breeding season and fertility of 946 Angus and 351 Simmental heifers and to use those traits to develop prediction equations for heifer fertility. Logistic regression methodology was used. Traits investigated were Julian birth date, age of the heifer's dam, birth weight, actual weaning and yearling weights, weaning and yearling weight ratios, 205-d weight, 365-d weight, and birth-weaning, weaning-yearling, and birth-yearling ADG and relative growth rate (RGR). In both breeds heifers that were younger at the start of the breeding season were less likely to conceive, but this effect was more important for Angus (logistic regression coefficient, b = -.032; P less than .01) than for Simmentals (b = -.015; P = .06). Weaning weight ratio was positively associated with heifer fertility (b = .025; P = .01 and b = .028, P = .04, respectively, for Angus and Simmental), whereas actual weaning weight was related curvilinearly to fertility of Angus heifers. The likelihood of conception was highest for Angus heifers weighing greater than or equal to 240 kg at weaning. The only postweaning trait associated with heifer fertility was weaning-yearling RGR. The likelihood of conception was highest for Angus heifers growing between .15 and .30% per day (P = .01), whereas fertility increased continuously (P = .04) for Simmental heifers as weaning-yearling RGR decreased. The maximum variations in fertility explained by models including all possible explanatory variables were 11.5 and 9.2% for Angus and Simmental, respectively. Results suggested that growth-related traits were relatively more important as a predictor of fertility for Simmental heifers and that age at the start of the breeding season was more important for Angus heifers. The combination of Julian birth date and weaning-yearling RGR produced the best models to predict heifer fertility for both breeds.

Relative Feeding Value of Rhizoma Perennial Peanut Hay as a Supplement to Bahiagrass Hay for Wintering Cows and Heifers

Rhizoma perennial peanut (Arachis glabrata Benth.) hay was evaluated as a replacement for purchased concentrate supplement given to cows and heifers being wintered on residual bahiagrass (Paspalumnotatum Fiugge) pasture and bahiagrass hay in central Florida. Data were collected over 2yr from 237 Hereford and 177 Senepol cows and first-calf heifers. Treatments were .9kg·head-1·d-1 of a commercially available 20% CP supplement (CUBE) or 2.3kg·head-1·d-1 of perennial peanut hay (PNUT). Supplements were fed for 16 wk from January through April each year. Response variables evaluated were cow and heifer body weight (BW) change, body condition score (CS) change, pregnancy rate, plasma urea nitrogen concentration (PUN), calf birth weight (CBW), and adjusted 205-d calf weaning weight (AWW). Both years, AWW was higher (P<.01) for calves with Senepol dams than for calves with Hereford dams (year 1: 209 vs. 184kg; year 2: 226 vs. 172kg), but AWW was not affected by treatment. Treatment did not affect pregnancy rate in either year; however, more (P<.05) Hereford (74%) compared to Senepol cows and heifers (62%) were palpated pregnant in year 2. Also in year 2, CBW was heavier (P<.01) for Senepol dams compared with Hereford dams (35.1 vs. 30.3kg), and BW and CS changes were greater (P<.01) in Senepol cows and heifers compared with Hereford (-90 vs. -67kg; -2.6 vs. -1.9). There were a few differences in PUN between treatments and breeds, but the greatest changes in PUN were observed over time through the wintering period. No other treatment or breed effects were observed either year. These data indicate that 2.3kg of the perennial peanut hay used in this study had a replacement value about equal to .9kg of a 20% CP concentrate cube supplement.

Effects of breed and retained heterosis on milk yield and 200-day weight in advanced generations of composite populations of beef cattle.

Retained heterosis in F2 cows nursing F3 progeny was evaluated in 3-, 4-, and greater than or equal to 5-yr-old cows. Traits evaluated included milk yield at three stages of lactation and 200-d weight of progeny. Breed effects were evaluated in the nine parental breeds (Red Poll [R], Hereford [H], Angus [A], Limousin [L], Braunvieh [B], Pinzgauer [P], Gelbvieh [G], Simmental [S], and Charolais [C]) that contributed to the three composite populations (MARC I = 1/4 B, 1/4 C, 1/4 L, 1/8 H, 1/8 A; MARC II = 1/4 G, 1/4 S, 1/4 H, 1/4 A; and MARC III = 1/4 R, 1/4 P, 1/4 H, 1/4 A). Breed effects were significant for 12-h milk yield, estimated 200-d milk yield, and 200-d weight of progeny. Herefords were lowest (P less than .05) for 12-h milk yield and estimated 200-d milk yield, and Braunvieh produced significantly more milk than all breed groups except Pinzgauer and Simmental, for which the difference approached significance. The correlation among breed group means (nine parental breeds and three composites) for 12-h milk yield with 200-d weight of progeny was .91. When 200-d weight was adjusted to a common estimated 200-d milk yield, Hereford, Angus, Red Poll, and Limousin did not differ (P greater than .05); all were significantly lighter than Braunvieh, Pinzgauer, Gelbvieh, Simmental, and Charolais, which did not differ (P greater than .05) from each other.(ABSTRACT TRUNCATED AT 250 WORDS)

Growth and fertility traits of calves sired by Piedmontese, Gelbvieh and Red Angus bulls

Heifer ( n = 72), bull ( n = 22) and steer ( n = 60) calves from matings of Hereford, Hereford x Angus and three-breed crossbred dams to Piedmontese (P), Gelbvieh (G) and Red Angus (RA) bulls were evaluated for growth and fertility traits. Birth weight, calving difficulty and adjusted 205-d weaning weight data were obtained from all calves. Pelvic dimensions, reproductive tract scores and pregnancy percentages were analyzed for heifers at 12 months of age. Breeding soundness examinations compared reproductive traits of bull calves at 12 and 13 months old. Steers were assigned to pens by breed of sire post-weaning to evaluate daily gain and adjusted feed efficiency for growing and finishing periods. Calves sired by P and G sires had heavier birth weights and higher calving difficulty scores ( P < 0.05) as compared to RA sired calves. No breed of sire differences were observed for pelvic dimensions, reproductive tract scores, pregnancy percentages and breeding soundness examination scores ( P∼0.10). The adjusted feed efficiency of P sired steers was similar to G and RA sired steers during the growing and finishing phases. Compared to the P and RA sired steers, the G sired steers gained faster ( P < 0.05) during the finishing period. Results from this study indicated P sired calves were similar to G and RA sired calves for most growth and reproductive traits.

Maternal performance of Hereford, Brangus, and reciprocal crossbred cows under semidesert conditions.

Maternal performance of 134 Hereford (H), Brangus (B), and reciprocal crossbred (H x B and B x H) cows from 2 to 7 yr of age was evaluated under semidesert conditions in this study. Calves produced by 2- and 3-yr-old cows were sired by Brangus and Hereford bulls. Calves produced by 4- to 7-yr-old cows were sired by Charolais bulls. Breed of sire and breed of dam of cow affected kilograms of weaning weight, 205-d weight, weaning weight as a percentage of cow weight, and 205-d weight as a percentage of cow weight produced annually. Brangus (either as sire or dam of cow) was superior to Hereford in all cases. Observed maternal heterosis on 2- to 3-yr-old cows was 23.0, 20.1, 30.0, 29.1, 23.9, and 23.0% for calf birth date, weaning percentage, weaning weight per year, 205-d weight per year, weaning weight as a percentage of cow weight per year, and 205-d weight as a percentage of cow weight per year, respectively (P less than .01). Observed maternal heterosis from mature cows was 19.8, 12.8, 21.0, 18.7, 17.4, and 15.4% for calf birth date, weaning percentage, weaning weight per year, 205-d weight per year, weaning weight as a percentage of cow weight per year, and 205-d weight as a percentage of cow weight per year, respectively (P less than .01). Results indicate large heterotic effects on annual cow productivity and an adaptive advantage for cows with Brangus sires and(or) dams under semidesert conditions.

Breed effects and heterosis in advanced generations of composite populations for reproduction and maternal traits of beef cattle

Heterosis effects in F1 dams producing F2 progeny and retained heterosis in combined F2 and F3 dams producing F3 and F4 progeny were evaluated in dams 2 yr old, in dams greater than or equal to 5 yr old, and in dams of all ages. Traits included pregnant percentage, calf crop born percentage, calf crop weaned percentage, 200-d calf weight per heifer or cow exposed, and 200-d calf weight. Breed effects were evaluated in the nine parental breeds (Red Poll [R], Hereford [H], Angus [A], Limousin [L], Braunvieh [B], Pinzgauer [P], Gelbvieh [G], Simmental [S], and Charolais [C]) that contributed to the three composite populations (MARC I = 1/4 B, 1/4 C, 1/4 L, 1/8 H, 1/8 A; MARC II = 1/4 G, 1/4 S, 1/4 H, 1/4 A; and MARC III = 1/4 R, 1/4 P, 1/4 H, 1/4 A). Breed effects were significant for all traits evaluated in the three age groupings and generally were greatest in 2-yr-old dams and smallest in dams greater than or equal to 5 yr old. Heterosis effects for 200-d calf weight were relatively uniform among age groupings and among the three composite populations and heterosis retained was equal to, or greater than, expectation based on retained heterozygosity. Heterosis effects in animals of all ages for reproductive traits in F1 dams producing F2 progeny differed among the three composite populations, as did heterosis retained in combined F2 and F3 dams producing F3 and F4 progeny. In dams of all ages, heterosis retained for reproductive traits in F2 and F3 dams producing F3 and F4 progeny did not differ (P greater than .05) from expectation based on retained heterozygosity in two of the three composite populations, but loss of heterosis was greater (P less than .05) than expectation based on retained heterozygosity in one of the three composite populations for calf crop born percentage, calf crop weaned percentage, and 200-d calf weight per heifer or cow exposed. This reduction was the result of increased fetal loss between pregnancy diagnosis and parturition.(ABSTRACT TRUNCATED AT 400 WORDS)

Selection for postweaning growth in inbred Hereford cattle: the Fort Keogh, Montana line 1 example.

Demographic characteristics and genetic trends in birth weight and pre- and postweaning ADG were examined in a population of Hereford cattle (Line 1). Line 1 was founded largely from two paternal half-sib sires and has been selected for postweaning growth. There were pedigree records on 951 members of the base population that predated 1935, when data collection began. Numbers of records analyzed using mixed-model methodology were 4,716 birth weight, 4,427 preweaning ADG, and 3,579 postweaning ADG. Birth weight and preweaning ADG were considered to have direct and maternal genetic components. Inbreeding accumulated rapidly from 1935 to 1960 and more slowly (.22%/yr) thereafter. Any reduction in additive genetic variance due to inbreeding and selection may have been offset by a concurrent reduction in generation interval that was observed as time progressed. Expected selection differential for 365-d weight, averaged over sexes, was 31.2 kg per generation. For birth weight, annual genetic trends in direct and maternal effects were 42 +/- 3 g and 15 +/- 3 g, respectively. Annual direct and maternal genetic trends for preweaning ADG were .70 +/- .06 g/d and .63 +/- .06 g/d, respectively. Direct response in postweaning ADG was linear and equal to 5.3 +/- .6 g.d-1.yr-1. As a result, estimated breeding values of birth weight, 200-d weight, and 365-d weight increased by 3.2 kg, 14.5 kg, and 62.4 kg, respectively, from 1935 to 1989. Selection within Line 1 was effective in increasing genetic potential for growth over 13 generations. No selection plateau was observed in any of the traits examined.

Correlated responses in reproductive and carcass traits to selection for 70-day weight in Landrace swine.

Correlated responses in reproductive and carcass traits were studied in 181 litters and 218 pigs from a line of Landrace pigs selected six generations for increased weight at 70 d of age and a contemporaneous, randomly selected control line. The reproductive and maternal traits studied included litter sizes born, born alive, and alive at 21 d and litter weight at birth and at 21 d. Carcass traits studied were carcass length, longissimus muscle area, average backfat thickness, 10th-rib backfat thickness, specific gravity, weights of closely trimmed ham, loin, and shoulder, belly weight, subjective scoring of the longissimus muscle for color and marbling, estimated percentage of muscle, and lean gain per day. Total weighted cumulative selection differential for 70-d weight was 30.2 kg. The realized heritability for 70-d weight was .13 +/- .06, and the change in 70-d weight was .65 +/- .29 kg per generation. The regression coefficient of litter size at 21 d on generation was .24 +/- .10 (P less than .10) pigs per generation. None of the other regression coefficients for the reproductive traits differed from zero. Carcass length, specific gravity, and ham weight decreased (P less than .10) -.075 +/- .036 cm, -.00054 +/- .00027, and -.102 +/- .048 kg, respectively, per generation. Color score and lean gain per day increased .046 +/- .021 points and .0032 +/- .0013 kg/d, respectively, each generation in response to the selection.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of including relationships in the estimation of genetic parameters of beef calves.

Variances and covariances for birth weight, gain from birth to weaning (ADG), and 205-d weight were obtained from a sire-dam model and a sire-maternal grandsire model for a herd of Angus and a herd of Hereford cattle. Estimates of direct additive genetic variance (sigma 2A), maternal additive genetic variance (sigma 2M), covariance between direct and maternal additive genetic effects (sigma AM), permanent environmental variance (sigma 2PE), and residual variance (sigma 2e) were obtained both with and without the inverse of the numerator relationship matrix (A-1) included. Estimates of heritability for direct genetic effects (h2A), maternal genetic effects (h2M), and the correlation between direct and maternal effects (rAM) for birth weight were .37, .18, and -.01 in Angus and .53, .23, and -.19 in Herefords, respectively, for the analyses without A-1. For the analyses with A-1, estimates of h2A, h2M, and rAM were .42, .22, and -.12 for Angus and .58, .22, and -.13 for Herefords, respectively. Estimates of h2A, h2M, and rAM for ADG were .43, .15, and -.44 in Angus and .52, .38, and -.03 in Herefords, respectively, without A-1. With A-1, estimates of h2A, h2M, and rAM were .57, .15, and -.32 for Angus and .58, .39, and -.05 for Herefords, respectively. Estimates of h2A, h2M, and rAM for 205-d weight were .49, .15, and -.46 for Angus and .58, .43, and -.06 for Herefords, respectively, without A-1. With A-1, estimates of h2A, h2M, and rAM were .63, .16, and -.36 for Angus and .66, .43, and -.08 for Herefords, respectively. Estimates of h2A were higher with A-1 than without A-1, but estimates of h2M were similar. Using variances and covariances obtained from analyses including A-1 generally gave higher estimates of direct breeding values than using variances and covariances obtained from analyses not including A-1. Both Pearson product-moment and Spearman rank correlations were high (.99) between estimates of breeding values from the two analyses, although some changes in rank did occur.

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.

Mastitis in beef cows and its effects on calf weight gain

Quarter milk samples from 51 purebred (Angus, Polled Hereford, and Simmental) and 69 crossbred (Angus x Simmental x Charolais three-way cross) beef cows were collected aseptically at three times during lactation to determine the prevalence of intramammary infection, milk somatic cell counts (SCC), and effects of infection on calf weight gain. Quarter infection prevalence was 13.1, 14.9, and 27.5% in early, mid, and late lactation; corresponding cow infection prevalence was 25.8, 29.2, and 54.4%. Staphylococcus aureus was isolated from 2.9, 2.7, and 3.2% of quarters in early, mid, and late lactation, respectively. Corynebacterium bovis, generally regarded as a minor pathogen, was isolated from 4.0, 7.6, and 18.2% of quarters at the three respective times. Geometric SCC means (10(3) cells/ml) were 1,522, 344, and 509 for S. aureus-infected quarters; 344, 899, and 221 for Staphylococcus hyicus-infected quarters; 65, 36, and 86 for C. bovis-infected quarters; and 20, 17, and 18 for uninfected quarters in early, mid, and late lactation, respectively. Adjusted 205-d weight gain for calves with S. aureus-infected dams was 9.6 kg less (P less than .05) than for calves with uninfected dams. Adjusted 205-d weight gain for calves with dams infected with any mastitis pathogen did not differ significantly from that of calves with uninfected dams. At weaning half of the infected cows and half of the uninfected cows were given an intramammary infusion product containing 300 mg of cephapirin benzathine in each quarter; the remaining cows were untreated controls. Quarter samples were collected aseptically from all cows 14 to 28 d after subsequent calving. Quarter prevalence of infection after calving was lower (P less than .05) in treated (8.2%) than in control (22.4%) cows. Significantly more infections present at weaning were eliminated in treated than in control cows, but the new infection rate during the dry period and early lactation did not differ between the two groups.

Maternal breed of sire effects on postweaning performance of first-cross heifers and production characteristics of 2-year-old heifers

Postweaning growth rates from weaning to 18 mo, fall condition score, pregnancy rates, and production to 2 yr of age were evaluated in a study of Angus (A)-, Pinzgauer (P)-, Red Poll (R)-, Simmental (S)-, and Tarentaise (T)-sired females from Hereford dams. First-cross heifers from the different sire breeds did not differ (P greater than .10) in initial weight. During a 140-d feed test, S gained 98.6 kg, exceeding (P less than .05) gains of P, 92.3; A, 91.4; and R, 87.3 kg but not T, 94.1 kg. Red Poll-sired heifers weighed less at the end of the 140-d test (P less than .05) than the other crosses, which did not significantly differ from each other. No breed of sire differences were found in gain from 140 d to fall weight. Simmental-sired heifers weighed more (P less than .05) than A- and R-sired heifers at 18 mo. Breed of sire and year interacted to affect pregnancy rate of the yearling heifers when mated to Shorthorn sires for 45 d. Percentage of dystocia varied from a low of 26.3 and 28.9% for T- and A-sired heifers, respectively, to 54.4 and 60.8% for P- and S-sired heifers, respectively (P less than .05). Age of dam of heifers affected (P less than .05) weight at the different period end points but not gains after weaning. Age of dam also affected incidence of dystocia. Two-year-old heifers from young dams had more dystocia than heifers from older dams. Shorthorn-sired calves from 2-yr-old heifers with different sire breeds differed in birth weight (P less than .05) but not survival from birth to weaning, ADG from birth to weaning, weaning age, or weaning condition score. Average 200-d weight of calves from P-, S- and T-sired heifers exceeded those from A- and R-sired heifers by 10.7 kg, or 5.7%.

Genetic improvement programs in livestock: swine testing and genetic evaluation system (stages)

Genetic evaluations for the U.S. swine industry are conducted by the eight purebred associations of the National Association of Swine Records. Within-herd evaluations of the growth traits (days to 105 kg [market] and backfat depth) were first reported in 1986. Analyses of the maternal traits (litter size at birth and weaning, and litter 21-d weight) were inaugurated in 1987. Expected progeny differences (EPD) are reported for all traits and for general, paternal, and maternal bioeconomic indexes. A sow productivity index combining only maternal traits is available. All records are adjusted according to National Swine Improvement Federation (NSIF) guidelines for effects such as number of pigs transferred at crossfostering and age at recorded observation prior to the BLUP evaluation. Within-herd analyses of individual contemporary groups are conducted immediately on receipt of performance records at each breed association office. All parents in the herd and the young pigs in the current group are evaluated. A report is returned to the breeder for use in herd selection and the EPD are placed in the pedigree file. The genetic base of each herd is defined as the first n tested pigs or litters, where n is the number of pigs registered annually within the herd. Change in mean EPD between groups is indicative of genetic trend. Periodic across-herd analyses are used to update interim within-herd analyses and a national sire summary is published.

Pelvic and Scrotal Measurements in Test Station Bulls

Pelvic measurements, scrotal circumference, birth weight, 365-d weight, and age were obtained on 422 test station bulls representing three breeds. Breed groups were comprised of 175 Angus, 94 Hereford, and 153 Salers bulls that completed the 1990 performance trial at the Midland Bull Test Station at Columbus, MT. Breed effects were evaluated for pelvic height (PH), pelvic width (PW), pelvic area (PA: product of PH and PW), and scrotal circumference (SC). Linear and quadratic covariates for age or 365-d weight (WT365) and their interactions with breed were also evaluated. Salers were analyzed separately to evaluate the effects of percentage (percent) Salers. Residual phenotypic correlations were calculated among PH, PW, PA, SC, birth weight (BW), and WT365. Breed and linear age effects were significant (P<.05) for PA and PW. Salers had the largest PA followed by Angus and Hereford (P<.01). The linear regression of PA on age was .201 cm2/day. The interaction of breed with age was significant only for PH. Linear effects of WT365 were significant (P<.05) for PA and PH, while quadratic effects of WT365 were significant for PW and SC. The linear regression of PA on weight was .100 cm2/kg. Phenotypic correlations between pelvic dimensions and WT365 and SC were low to moderate. Percentage of Salers breeding was only a significant source of variation for SC. In conclusion, differences between breeds existed for pelvic dimensions. Differences among bulls in PA were independent of differences in SC. Differences between different percentage Salers bulls were small.

Effect of Age of Dam and Sex on 205-D Weight of Senepol Calves

Data (3,710 observations) were collected from two farms by the Virgin Islands Agricultural Experiment Station from 1978 to 1987. Data were analyzed to determine the adequacy of standard Beef Improvement Federation (BIF) age of dam (AOD) and calf sex (SEX) adjustment factors for 205-d weaning weight (WWT) for use on Senepol cattle. The mixed model contained the random effect of contemporary group (CG) and the fixed effects of SEX (bull and heifer), AOD (2 to 11+ yr), and SEX by AOD interaction. In the least squares analysis, CG, SEX, and AOD were highly significant for WWT. The interaction of SEX by AOD was not significant. Estimates of AOD adjustment factors indicate that 2-, 3-, 4- and 11 +-yr-old dams are being overadjusted using BIF correction factors. Adjustments developed by this analysis more adequately fit the Senepol data.

Genetic and environmental growth trait parameter estimates for Brahman and Brahman-derivative cattle.

Beefmaster, Brahman, Brangus, and Santa Gertrudis field data records were used to determine genetic and environmental parameter estimates using a multiple-trait, pseudo-expectation approach. Adjusted birth weight, 205-d weight, and postweaning gain records were analyzed for each breed. Also, Brangus weaning sheath and navel scores were both analyzed using a single-trait, pseudo-expectation method to determine genetic parameter estimates. Additive birth weight heritability (h2A) estimates ranged from .22 to .37 and maternal birth weight heritability (h2M) estimates ranged from .12 to .55. Estimates for 205-d weight h2A for the four breeds varied from .21 to .25, and 205-d weight h2M estimates ranged from .15 to .21. Postweaning gain h2A estimates ranged from .16 to .56. The genetic correlation between direct and maternal portions of birth weight was negative for all breeds. This was also true for the genetic correlation between direct and maternal portions of 205-d weight, except in Brahman cattle, for which it was .15. The genetic correlation between additive portions of birth weight and 205-d weight was large and positive in all breeds. A moderately positive correlation between 205-d weight and postweaning gain was found for all breeds except Santa Gertrudis, whereas the environmental correlation between these two traits was a small to moderately negative estimate in all breeds. Brangus weaning sheath and navel score heritabilities indicated that genetic change for the size and shape of the sheath and navel area is possible.

Postweaning growth of unselected Hereford and Angus cattle fed two different diets.

Two unselected herds of purebred Hereford and Angus cattle were created and their progeny evaluated during a 4-yr period (1964 to 1967) for 168-d postweaning gain when they were fed either a high- or medium-energy diet. Birth weight and 200-d adjusted weaning weight also were measured and the importance of sire x diet interactions for postweaning gain examined. Year effects were significant (P less than .001) for all traits in Herefords and for postweaning gain in Angus. Postweaning gain of both breeds increased in successive years, but no trend was observed for birth and 200-d weights. Bulls were heavier than heifers (P less than .05) for all three traits in both breeds. Hereford and Angus calves receiving the high-energy diet gained more (P less than .001) than their contemporaries fed the medium-energy diet. Sire differences were significant for birth weight in Herefords and for all three traits in Angus. Sire x diet interactions were not significant for postweaning gain in either breed. Genetic correlations were calculated by two methods: the two-way ANOVA approach using sire and sire x diet interaction variance components and the one-way ANOVA approach in which gains by progeny of each sire on each diet were considered to be two distinct traits. The genetic correlations for gain in Herefords could not be estimated by either method because of negative sire variance component estimates. The genetic correlations for gain in Angus were 1.08 for the two-way ANOVA method and 1.43 +/- .64 for the one-way ANOVA method. These results indicate that sires ranked the same based on progeny performance when fed either diet.

Mass selection for increased 200-day weight in a closed line of Duroc pigs.

Mass selection for increased weight at 200 d of age was conducted for six generations in a line of Duroc pigs. A randomly selected contemporary control line was maintained. Our objectives were to observe the response in 200-d weight, to measure correlated responses in weights at earlier ages, daily gains and ultrasound backfat thickness and to compare three methods for estimating responses to selection. Inbreeding coefficients averaged .213 and .202 for the select- and control-line pigs and .200 and .173 for the select- and control-line dams in the sixth generation, respectively. A total of 1,866 pigs were farrowed; 200-d weights were collected on 798 of them. These pigs were sired by 89 boars and were out of 193 sows. Twelve traits were studied: weights at birth and at 21, 35, 70, 154 and 200 d of age, daily gains from birth to 35 d, 35 d to 70 d, 70 d to 154 d and 154 d to 200 d, ultrasound backfat thickness at 200 d and ultrasound backfat thickness adjusted for 200-d weight. Three methods for estimating responses to selection gave similar results; therefore, the estimates were averaged. Total weighted cumulative selection differential for 200-d weight was 81.7 kg with a response in 200-d weight of 2.5 +/- 1.2 kg/generation. This response corresponds to a realized heritability for 200-d weight of .18 +/- .08. Increased weight at 200 d was the result of more rapid growth in the 154- to 200-d period, with decreased growth in the period from birth to 35 d. Growth at other periods was not changed significantly. Ultrasound backfat thickness at 200 d increased in the select line compared to the control line, but not when adjusted for 200-d weight.

Mass selection for increased 200-day weight in a closed line of Landrace pigs.

Mass selection for increased weight at 200 d of age was conducted for six generations in a line of Landrace pigs. In the select line, the heaviest nine boars and 18 gilts were selected from each generation to produce the subsequent generation. A contemporaneous control line was maintained by randomly selecting a son from each sire and a daughter from each dam to attain a line size of five boars and 10 gilts. Inbreeding coefficients averaged .182 and .191 for the select- and control-line pigs and .150 and .162 for the select- and control-line dams, respectively, in the sixth generation. The 200-d weights and ultrasound backfat thickness data were collected from 1,022 pigs of 2,181 pigs farrowed. These pigs were sired by 92 boars and out of 210 sows. The generation interval was 13 mo. Twelve traits were studied: weights at birth and at 21, 35, 70, 154, and 200 d of age; daily gains from birth to 35 d, 35 to 70 d, 70 to 154 d, and 154 to 200 d; ultrasound backfat thickness at 200 d; and ultrasound backfat thickness adjusted for 200-d weight. Total weighted cumulative selection differential for 200-d weight was 88.7 kg. Realized heritability for 200-d weight was .26 +/- .08 with an average response of 4.2 +/- 1.3 kg/generation. Correlated responses resulted in increases for all weights and daily gains evaluated. Although ultrasound backfat thickness at 200 d increased in the select line compared to the control line, it was not altered by selection for 200-d weight when adjusted for 200-d weight.