Relationship between terrain use and performance of beef cows grazing foothill rangeland.

A study was conducted on foothills rangeland to determine whether grazing patterns differed among cow breeds and to determine whether there was a relationship between individual grazing patterns and performance of beef cows. Hereford (HH), Tarentaise (TT), 3/4 Hereford x 1/4 Tarentaise (3H1T), 1/2 Hereford x 1/2 Tarentaise (HT), and 1/4 Hereford x 3/4 Tarentaise (1H3T) cows were observed during the summers of 1997 (n = 183) and 1998 (n = 159). Locations of individual cows were recorded two to three times per week during 1.5- to 2.5-h periods in the morning by observers on horseback. Statistical models included cow breed, age, and nursing status. Data from each year were analyzed separately. During 1997 and 1998, nonlactating cows were located at greater (P < 0.05) vertical distances from water than lactating cows. In 1998, nonlactating cows used steeper (P < 0.05) slopes than lactating cows. However, nonlactating cows did not travel as far horizontally from water (P < 0.05) as lactating cows in 1997. Younger cows (3 yr) traveled further (P < 0.05) from water both vertically and horizontally than older cows (5+ yr) in 1997, but not during 1998. Tarentaise and 1H3T cows were observed at greater (P < 0.05) vertical distances from water than HH cows during both years of the study. During 1998, TT and 1H3T cows used steeper (P < 0.05) slopes than HH cows. Using residual correlations, there were no consistent relationships between topographic aspects of individual grazing locations and cow weight, height, and body condition score. In 1997, cows with earlier calving dates and correspondingly heavier calf weaning weights used areas that had greater vertical distances to water; however, in 1998 there were no relationships (P > 0.05) of calving date and weaning weight with cow location. During both years, pregnant and nonpregnant cows used terrain similarly (P > 0.05), which suggests that cow reproductive performance was not related to terrain use. Grazing patterns in foothills rangeland varied among cow breeds. Performance of cows that used more rugged topography was similar to cows using gentler terrain.

Genetic evaluation of carcass traits in Simmental-sired cattle at different slaughter end points.

Our objectives were to estimate genetic parameters for carcass traits and evaluate the influence of slaughter end point on estimated breeding values (BV). Data provided by the American Simmental Association were divided into three sets: 1) 9,604 records of hot carcass weight (CW) and percentage retail cuts (PRC), 2) 6,429 records of CW, PRC, and marbling score (MS), and 3) 1,780 records of CW, PRC, MS, fat thickness (FT), and longissimus muscle area (LMA). Weaning weights (WW) from animals with carcass data and from their weaning contemporaries were used. Data were analyzed with a multiple-trait animal model and REML procedures to estimate genetic parameters and BV on an age-, CW-, MS-, or FT-constant basis. The model for carcass traits included fixed contemporary group and covariates for breed, heterozygosity, and slaughter end point and random additive direct genetic and residual effects. Weaning weight was preadjusted for founder effects, direct and maternal heterosis, age of dam, and age of calf. The model for WW included fixed contemporary group and random additive direct genetic, maternal genetic, maternal permanent environment, and residual effects. Heritabilities from data set 1 were 0.34 for CW and 0.25 for PRC on an age-constant basis and 0.25 for PRC on a CW end point. Heritabilities for data set 2 were 0.35, 0.24, and 0.36 for CW, PRC, and MS, respectively, on an age-constant basis. Data set 2 heritabilities were 0.25 for PRC and 0.34 for MS on a CW-constant basis and 0.33 for CW and 0.25 for PRC at a constant MS end point. Heritabilities on an age-constant basis for data set 3 were as follows: CW, 0.32; PRC, 0.09; MS, 0.12; FT, 0.10; and LMA, 0.26. Heritability estimates for data set 3 on a CW-, MS-, and FT-constant basis were similar to those on an age-constant basis. Heritabilities were 0.12 for PRC, 0.12 for MS, 0.14 for FT, and 0.22 for LMA on a CW-constant basis; 0.30 for CW, 0.09 for PRC, 0.10 for FT, and 0.28 for LMA at a constant MS end point; and 0.33, 0.17, 0.13, and 0.29 for CW, PRC, MS, LMA on a FT-constant basis. Genetic correlations among traits varied across groups and end points but suggested that it should be possible to select for improved lean yield without sacrificing quality grade. Correlations were calculated among BV computed at different end points. Adjustment to various end points resulted in some changes in BV and reranking of sires, especially for PRC; however, the number of records available had a larger influence than slaughter end point.

Heterosis and breed additive effects for Hereford, Tarentaise, and the reciprocal crosses for calf traits.

Records from 595 straightbred Hereford (HH), straightbred Tarentaise (TT), and reciprocal-cross (HT) females, randomly mated to HH, TT, or HT bulls, were analyzed for estimates of heterosis and breed additive effects for calf traits that included birth weight (BWT), calving difficulty (DIFF), prebreeding (PRE) and postbreeding (PST) weight, weaning weight (WWT), weaning condition score (WCS), weaning hip height (WHH), and preweaning average daily gain (ADG). The statistical model included year, age of dam, sex, regression on age at time of measurement, and regressions for the genetic effects of breed individual, breed maternal, breed grandmaternal, individual heterosis, and maternal heterosis. Breed effects were coded to reflect TT- HH differences. Age at the time of measurement, year, age of dam, and sex were significant for most traits. Individual breed effects were important (P < .05) for BWT, PRE, PST, WCS, and WHH but not for WWT, resulting in lower weights, less condition, and taller animals for TT. Maternal breed effects did not influence BWT, but they were important ( P < .05) for PRE, PST, WWT, WCS, WHH, and ADG. Grandmaternal effects were only important for BWT and ADG. Individual and maternal heterosis were important (P < .05) for most traits measured, resulting in increased calf size, weight, and body condition.

Genetic components for milk production of tarentaise, hereford, and tarentaise x hereford cows.

The objective of this study was to estimate genetic components for milk production of Hereford (HH), Tarentaise (TT), and Hereford x Tarentaise or Tarentaise x Hereford (HT) cows under range conditions at the Northern Agricultural Research Center, Havre, MT. Milk production of 494 cow-calf pairs was estimated by the weigh-suckle-weigh procedure from 1989 to 1994. Milk production and cow and calf weights were measured at 40 d (early) and 120 d (late) of lactation. The mating scheme was a 3 x 3 design in which HH, HT, and TT cows were mated with HH, HT, and TT sires, producing calves that were varying percentages of Hereford and Tarentaise. Data were analyzed by least squares procedures according to a model that included year, age of cow, sex of calf, linear regression on calf age, and linear regressions on coefficients that coded for various genetic components. These genetic components were breed individual, breed maternal, breed grand maternal, individual heterosis (calf heterosis), and maternal heterosis (cow heterosis). Coefficients for genetic components were such that breed effects estimated TT-HH and regressions on heterosis values estimated the full effect of heterosis. The breed individual genetic component was significant only for calf early and late weights; Tarentaise calves were lighter. Breed maternal was significant for most traits, and these effects were positive for milk production (2.16 and 3.77 kg/d for early and late, respectively) and calf weights but negative for cow weights. Individual heterosis was not significant for early milk production but was significant for late milk production (1.05 kg/d) and calf weights (2.3 and 8.1 kg for early and late, respectively). Maternal heterosis was significant for most traits and increased early milk production (1.25 kg/d), calf weights (4.5 and 5.8 kg for early and late, respectively), and cow weights (18.1 and 6.0 kg for early and late, respectively).

Factors influencing genetic evaluations of linebred Hereford cattle in diverse environments.

Data from four closely related Line 1 Hereford herds were used to estimate variance components and predict EPD for birth weight (BWT), weaning weight (WWT), and postweaning gain (PWG). Herds were located in diverse environments and differed in level of phenotypic performance. Within-herd BWT analyses considered effects of inbreeding of calf and dam, sex, age of dam (AOD), and contemporary group as fixed and direct and maternal additive genetic effects and permanent environmental effects due to dam as random. The model for WWT included these effects and age of calf. The model for PWG included inbreeding of calf, contemporary group, and direct additive genetic effects. Across-herd analyses were conducted with additional models. The first considered herd-specific inbreeding, sex, and AOD effects. A second model pooled these effects across herds, and a third included pooled sex and AOD effects but ignored inbreeding. Across-herd EPD, including and ignoring inbreeding, were predicted for WWT preadjusted with standard adjustments for Hereford cattle. Within-herd analyses indicated potential for heterogenous genetic and environmental variances across herds. Across-herd variance component estimates were consistent, regardless of the model. Estimates of genetic trends indicated potential for bias in genetic evaluations resulting from choice of model. Differences in magnitude of fixed effects between herds were observed. Genetic evaluations were different when pooled or herd-specific fixed effects were used. Allowance for individual herd differences in fixed effects in across-herd evaluations is suggested.

Tarentaise and Hereford breed effects on cow and calf traits and estimates of individual heterosis.

Preweaning and weaning records on 457 calves and weights and milk production of their dams were used to evaluate breed of dam effects, breed of sire effects, and individual heterosis effects. Hereford and Tarentaise dams were mated to Hereford and Tarentaise sires and calves were born from 1987 to 1991. Calf traits were birth weight, proportion calving difficulty, weaning weight, weaning height, weaning weight:height ratio, and condition score at weaning. Cow traits were milk production four weights during the year, weight changes, height at weaning, condition score, ratio of calf weight:cow weight, proportion calved and weaned, and calf weaning weight per cow exposed to breeding. Breed of sire was nonsignificant for all traits except calf hip height, but breed of dam was significant for calf weaning weight and condition score, late milk production, change in milk production, and the cow traits of all weights, condition score, weight:height ratio, and ratio of calf weight:cow weight. Least squares means for Hereford and Tarentaise dams, respectively, were 216 and 236 kg for calf weaning weight, 6.2 and 9.3 kg for late milk production, 559 and 507 kg for cow weight at weaning, 6.0 and 4.9 for cow condition score, and .39 and .47 for ratio of calf weight at weaning:cow weight at weaning. Heterosis was significant for birth weight (1.05 kg, 3%, P = .01), weaning weight (11.0 kg, 5%, P = .01), and condition score (.13, 2%, P = .06). Thus, Hereford dams weighted more and had higher levels of condition, whereas Tarentaise dams produced more milk late in lactation and weaned heavier calves.

Life cycle evaluation of five biological types of beef cattle in a cow-calf range production system: I. Model development.

Data collected during a 10-yr study at the Northern Agricultural Research Center (NARC), Havre, MT were used in construction of a simulation model to evaluate production systems using different breed groups. Five dam breed groups, straightbred Hereford (HH), 50% Angus-50% Hereford (AH), 25% Simmental-75% Hereford (1S3H), 50% Simmental-50% Hereford (1S1H), and 75% Simmental-25% Hereford (3S1H), were studied. The simulated system was a northern range cow-calf production system with spring calving and fall weaning. Replacement heifers were purchased and all calves were marketed at weaning. All nonpregnant females were sold in the fall. Statistical analyses of the data yielded input values (least squares means for breed group x age x sex subclasses) for cow and calf weights, pregnancy rate, dystocia, and calf survival. Pregnancy, dystocia, calf survival, calf weights, and cow weights were simulated stochastically. Energy requirements for maintenance, growth, gestation, and lactation were predicted from equations adapted from the literature based on body weight, frame size, sex, and breed group. Economic inputs and outputs were computed by accounting for variable input expenses and output revenues associated with animal performance and fixed costs associated with range management. Simulated measures of system performance included measures of energy conversion, break-even prices, and profit.

Life cycle evaluation of five biological types of beef cattle in a cow-calf range production system: II. Biological and economic performance.

Results from a 10-yr study of five dam breed groups in a range beef production system were used as inputs to a simulation model to evaluate life cycle biological and economic performance. Dam breed groups were straightbred Herefords (HH), Angus-Hereford and Simmental-Hereford F1 crosses (AH and 1S1H), 75% Hereford-25% Simmental (1S3H), and 25% Hereford-75%. Simmental (3S1H). Biological measures were number of lifetime matings, calves weaned and kilograms of calf weight sold per cow exposed, and metabolizable energy (ME) consumed per kilogram of calf weight sold and per kilogram of total weight sold. Simulated economic measures were break-even steer prices, total production costs, net profit per cow exposed, and net profit for a ranch of fixed size. The HH and 3S1H dams consumed the least ME per kilogram of total weight sold yet had the highest steer break-even prices and lowest profits. The F1 dams yielded consistently higher profits than other dam breed groups. Breed group rankings were not sensitive to prices paid for hay or calf prices relative to cow prices. Regression techniques were used to estimate maternal heterosis and maternal breed substitution effects from the simulated data. Maternal heterosis effects were large and highly significant for all measures of system performance and were desirable for all traits except ME/kilogram of total weight sold. Maternal heterosis for net profit was nearly $70.cow-1.yr-1 and $20,400/yr for a ranch of fixed size (2,700 AUM range forage). Maternal breed substitution effects were generally much smaller than heterosis effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Paternal half-sib heritabilities and genetic, environmental, and phenotypic correlation estimates from randomly selected Hereford cattle.

Growth and carcass data were collected during 10 yr at the Fort Keogh Livestock and Range Research Laboratory in Miles City, MT from a Hereford herd selected at random. The objective was to compare genetic parameter estimates from this randomly selected herd with estimates from published selection studies. Only bulls were included in the data set. Bulls were slaughtered between 14 and 17 mo of age. Genetic parameters were estimated by the paternal half-sib procedure. Data were subdivided into three subgroups: 1) all bulls that had birth weights, 2) bulls with complete records for growth traits, and 3) bulls with complete carcass and growth records. The heritability estimate for birth weight on 736 progeny from 86 sires was .18. The second group included 616 progeny representing 85 sires and heritability estimates were weaning weight, .17; daily gain from birth to weaning, .20; final test weight, .42; and daily gain on test, .47. The third group included 401 progeny from 75 sires and heritability estimates were carcass weight, .38; longissimus muscle area, .51; marbling, .31; slaughter weight, .42; and dressing percentage, .25. Thus, these estimates of heritability were in quite good agreement with previously published values, with a tendency for these estimates to be lower for early growth weights. Phenotypic and environmental correlations were in good agreement and genetic correlations were in general agreement with the data reviewed. Estimates of heritabilities from this herd selected at random were not larger than previous estimates from selected herds.

Effects of selection strategies using heifer pelvic area and sire birth weight expected progeny difference on dystocia in first-calf heifers.

A stochastic computer simulation model was developed to evaluate the effects of selection strategies based on heifer pelvic area and sire birth weight EPD on dystocia in first-calf heifers. Parameters and relationships used were taken from the literature. Unrelated sets of yearling heifers were simulated. Replacement heifer selection was based on breeding the top 40, 60, 80 or 100% (i.e., no selection) of available heifers as determined by yearling pelvic area (YRLGPA). Selected heifers were bred to bulls that were selected based on EPD for birth weight (SEPD). Levels of SEPD were -2.7, -1.8, -.9, 0, .9, and 1.8 kg. Simulated responses included precalving pelvic area, calf birth weight, calving difficulty score (1, 2, 3, 4), and incidence of dystocia (0, 1). Both measures of dystocia were predicted from the ratio of precalving pelvic area to calf birth weight. Simulated data were analyzed using least squares procedures. The effects of SEPD were significant (P < .05) for birth weight, calving difficulty score, and the frequency of dystocia. Differences among levels of heifer selection for YRLGPA were significant for YRLGPA, precalving pelvic area, birth weight, and calving difficulty score but not for the frequency of dystocia. Based on partial regressions calculated from weighted replication means, a 1-kg decrease in SEPD will decrease average calving difficulty score by .12 units and decrease the frequency of dystocia by 4%, whereas each 10% increase in selection pressure on YRLGPA will reduce the average calving difficulty score by only .02 units and have no detectable effect on the frequency of dystocia.(ABSTRACT TRUNCATED AT 250 WORDS)

Performance of crosses among Hereford, Angus, and Simmental cattle with different levels of Simmental breeding: VI. Maternal heterosis of 3- to 8-year-old dams and the dominance model.

Data from Hereford, 25% Simmental-75% Hereford, 50% Simmental-50% Hereford, and 75% Simmental-25% Hereford dams were used to estimate maternal heterosis and level of agreement with the dominance model. Cows were located at the Northern Agricultural Research Center near Havre, MT and were managed consistent with practices for western range environments. Sample halves of dam breed groups were bred to Charolais and Tarentaise sires to produce calves at 3 to 8 yr of age. There were 766 exposures to breeding that resulted in 581 calves. Breed group means for most traits supported the dominance model. Maternal heterosis was estimated by regression techniques for 22 cow and calf traits. Maternal heterosis was not significant for day of conception, number of services, gestation length, or calving difficulty. Estimates of maternal heterosis for calf growth traits ranged from .7% for weaning height to 5.2% for weaning weight and 7.5% for weaning condition score. Calf weight per unit of cow weight at weaning showed significant maternal heterosis (7.1%). Higher levels of maternal heterosis were exhibited for milk production (8.2 to 11.1%) and the negative, but nonsignificant, estimate of maternal heterosis for early minus late milk production suggested more persistent lactation for crossbred cows. Maternal heterosis was 11.5% for proportion of dams that calved and 10.4% for proportion of dams that weaned calves. Calf weaning weight per cow exposed to breeding, a characteristic combining calf growth and dam reproduction, exhibited 17.9% maternal heterosis.

Correcting bias from the standard linear adjustment of weaning weight to an age-constant basis for beef calves.

Standard linear adjustment of weaning weight to a constant age has been shown to introduce bias in the adjusted weight due to nonlinear growth from birth to weaning of beef calves. Ten years of field records from the five strains of Beefbooster Cattle Alberta Ltd. seed stock herds were used to investigate the use of correction factors to adjust standard 180-d weight (WT180) for this bias. Statistical analyses were performed within strain and followed three steps: 1) the full data set was split into an estimation set (ES) and a validation set (VS), 2) WT180 from the ES was used to develop estimates of correction factors using a model including herd (H), year (YR), age of dam (DA), sex of calf (S), all two and three-way interactions, and any significant linear and quadratic covariates of calf age at weaning deviated from 180 d (DEVCA) and interactions between DEVCA and DA, S or DA x S, and 3) significant DEVCA coefficients were used to correct WT180 from the VS, then WT180 and the corrected weight (WTCOR) from the VS were analyzed with the same model as in Step 2 and significance of DEVCA terms were compared. Two types of data splitting were used. Adjusted R2 was calculated to describe the proportion of total variation of DEVCA terms explained for WT180 from the ES. The DEVCA terms explained .08 to 1.54% of the total variation for the five strains. Linear and quadratic correction factors were both positive and negative. Bias in WT180 from the ES within 180 +/- 35 d of age ranged from 2.8 to 21.7 kg.(ABSTRACT TRUNCATED AT 250 WORDS)

Grazing behavior of rangeland beef cattle differing in biological type.

Grazing behavior exhibited by different biological types (breed groups) of lactating beef cows was evaluated during the summers of 1985 (Trial 1) and 1986 (Trial 2). Animals grazed native Montana foothill grassland. In Trial 1, breed groups consisted of Hereford (HH), 50% Angus-50% Hereford (AH), 50% Simmental-50% Hereford (SH), and 75% Simmental-25% Hereford (3S1H) with six cows per breed group. Daily grazing hours were 11.8 +/- .2, 12.3 +/- .2, 11.6 +/- .2, and 11.6 +/- .5 h/d for HH, AH, SH, and 3S1H, respectively. There was a tendency for AH cows to graze longer than HH and SH cows (P = .10). Bite rates were 52.7 +/- 1.5, 56.2 +/- 1.5, 53.2 +/- 1.4, and 59.0 +/- 1.6 bites/min for HH, AH, SH, and 3S1H, respectively. The AH and 3S1H cows had higher bite rates (P less than .05) than the HH and SH cows. Means for distance traveled were 3.1 +/- .2, 3.4 +/- .2, 4.0 +/- .2, and 2.8 +/- .2 km/d for HH, AH, SH and 3S1H, respectively. The SH cows tended to travel farther (P less than .10) than cows of other breed groups. The AH traveled farther than the 3S1H but did not differ from the HH. In Trial 2, breed groups were Hereford (HH), Tarentaise-Hereford (TH), Tarentaise-Simmental-Hereford (T(SH], and Charolais-Simmental-Hereford (C(SH]; each group included six lactating cows. Means for bite rate were 56.9 +/- 1.1, 58.7 +/- 1.1, 60.9 +/- 1.0, and 59.0 +/- 1.1 bites/min for HH, TH, T(SH), and C(SH), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Genetic parameters by son-sire covariances for growth and carcass traits of Hereford bulls in a nonselected herd.

Growth rates and weights at weaning, 365 d, and at slaughter were obtained on 616 bulls in a nonselected Hereford herd over a 10-yr period beginning in 1978. Carcass data were obtained for 401 of these bulls at 16 mo of age and on 101 that were sires or alternates and slaughtered at 30 mo of age. Fifty-five bulls slaughtered at 30 mo of age sired 301 male offspring on which growth data were obtained and 30 sired 169 male offspring on which carcass data were obtained. Bulls gained an average of .75 kg/d preweaning and 1.16 kg/d postweaning on a 168-d feed test. Rate of daily gain from the end of feed test to slaughter ranged from .7 to 1.2 kg/d. Time from the end of the feed test to slaughter ranged from 48 to 140 d. Slaughter weight, marbling score (Small = 12, Traces = 6), longissimus muscle area, fat covering over the 12th rib, percentage of kidney, pelvic and heart fat (KPH), and dressing percentage for bulls slaughtered as yearlings were 470 kg, 7.6 score, 82.5 cm, 8.2 mm, 1.0%, and 58.8%, respectively. The 30-mo-old bulls were slaughtered directly from range pastures. Marbling was devoid or practically devoid and fat covering over the 12th rib and KPH fat were insufficient to measure or estimate accurately. Sufficient variation was not available for statistical analyses of these traits. Slaughter weight, longissimus muscle area, and dressing percentage of 30-mo-old bulls were 583 kg, 91.8 cm, and 54.0%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Performance of crosses among Hereford, Angus and Simmental cattle with different levels of Simmental breeding: V. Calf production, milk production and reproduction of three- to eight-year-old dams.

Measures of maternal productivity and reproduction of Hereford (HH), Angus-Hereford (AH), 25% Simmental-75% Hereford (1S3H), 50% Simmental-50% Hereford (1S1H) and 75% Simmental-25% Hereford (3S1H) dams were studied. Half of each dam breed group was bred to Tartentaise and half to Charolais sires to produce 706 calves at weaning from 930 exposures to breeding in a Montana range environment. Data were analyzed according to a model that included the fixed effects of year, dam breed group, dam age, calf sex, calf sire breed, plus appropriate two-way interactions, linear partial regression on calf birth date and random effects of sire within dam breed group (maternal grandsire of the calf) and sire within calf sire breed. Calf sex interacted with calf sire breed for several traits, but interactions were due to changes of magnitude of differences between sexes. There were no significant interactions of dam breed group with other main effects for calf growth traits, except for the interaction with calf sire breed for some calf growth traits. This interaction was due to a change in magnitude; it suggested that larger sire breeds should be matched to larger dam breeds with greater potential for milk production. The only significant interaction for traits that included reproduction of the dam was dam breed group X age of dam. Ranking of dam breed groups depended on age at measurement. Differences among dam breed groups were significant for most traits. Calf weaning weights for HH, AH, 1S3H, 1S1H and 3S1H dams were 211, 223, 227, 237 and 243 kg, respectively; calf weaning weights per cow exposed were 157, 163, 179, 189 and 169 kg; calf weaning weights per unit of dam weight were .40, .41, .43, .44 and .42, respectively. Thus, dam breed groups that weaned the largest calves were not necessarily the most productive under Montana range conditions.

Performance of crosses among Hereford, Angus and Simmental cattle with different levels of Simmental breeding: IV. Maternal heterosis and calf production by two-year-old dams.

The performance of 264 contemporary 2-yr-old straightbred and crossbred dams during 1978 to 1981 was studied and maternal heterosis was estimated. Dam breed groups were Hereford (HH), Angus-Hereford (AH), 25% Simmental-75% Hereford (1S3H), 50% Simmental-50% Hereford (1S1H) and 75% Simmental-25% Hereford (3S1H). Differences among dam breed groups were nonsignificant for length of gestation, calving difficulty and late milk production but were important (P less than .01) for calf weights (birth, early and late milking periods and weaning), calf average daily gains during various intervals from conception to weaning, early milk production and other calf traits at weaning (height, weight/height and visual condition score). Dam breed group means (HH, AH, 1S3H, 1S1H and 3S1H, respectively) for representative calf traits were .37, .39, .39, .42 and .42 kg/d for estimated average daily gain the last 3 mo of gestation; 33.6, 34.7, 35.7, 37.6 and 37.1 kg for birth weight; 191, 205, 209, 228 and 228 kg for weaning and 7.5, 8.4, 8.3, 9.5 and 10.0 kg for 24-h early milk production. Therefore, 2-yr-old crossbred dams raised calves that were generally larger for the preweaning gain traits than HH dams. Differences among dam breed groups were significant for traits involving reproduction; means (HH, AH, 1S3H, 1S1H and 3S1H, respectively) were .58, .92, .72, .91 and .79 for proportion calving and 105, 179, 126, 182 and 154 kg for actual calf weaning weight per cow exposed to breeding. Estimates of percentage maternal heterosis were 6.3, 12.9, 9.0 and 7.6% for calf weights at birth, 40 d, 130 d and weaning, respectively; 1.8, 5.7 and 5.7% for calf hip height, height/weight and condition score at weaning, respectively; and 43.1 and 34.6% for proportion calving and actual calf weaning weight per cow exposed to breeding. The dominance model explained most (greater than 95%) of the variation observed among dam breed group means for most traits.

Direct and maternal variances and covariances and maternal phenotypic effects on preweaning growth of beef cattle.

Birth weights (BW) and weaning weights (WW) of 4,423 non-creep-fed Hereford calves were used to estimate direct and maternal sources of variation and maternal phenotypic effects (fm). Seventeen different (co)variances among relatives were estimated through Henderson's Method III and restricted estimated maximum likelihood procedures. Direct and maternal (co)variances and fm were evaluated by multiple regression procedures. Estimates of h2 for BW and WW were .28 and .28 respectively, by the paternal half-sib procedure and .45 and .88, respectively, based on full-sibs. Repeatability estimates were .21 for BW and .30 for WW. Heritabilities based on regression of offspring on dam and offspring on sire were .45 and .21 for BW and .28 and .06 for WW, respectively. Negative correlations were found between solutions for additive genetic direct and additive maternal effects (rG). Estimates of rG ranged from -.86 to -1.05 for BW and from -.57 to -.79 for WW. Estimates of heritability for direct effects (h2o), for maternal effects (h2m) and for total additive genetic effects (h2T) were .16 to .27, .18 to .63 and -.02 to .05 for BW and .26 to .32, .27 to .67 and .10 to .20 for WW. Dominance affected both direct and maternal effects for BW and WW. Values of -.15 (BW) and -.25 (WW) were found for fm (path coefficient between the maternal phenotypes of dam and daughter). These results indicated that selection response would be decreased due to the negative genetic correlation between direct and maternal effects.

Heterosis among closed lines of Hereford cattle. III. Postweaning growth and carcass traits in steers.

Feedlot and carcass characteristics of 276 steers from five closed lines of Hereford cattle and reciprocal crosses among these lines were studied. The traits studied were initial weight, final weight, 224-d gain, days on test, hot carcass weight, marbling score, longissimus muscle area, fat thickness, yield grade, dressing percentage and shear force. Year of record was a significant source of variation for most traits. Age of dam was a significant source of variation for growth traits but not carcass traits. Line of sire affected initial weight, final weight, 224-d gain, days on test, marbling score and dressing percentage. Significant heterosis was observed only for hot carcass weight. Heterosis estimates were 1.9% for initial weight, 2.2% for final weight, 2.5% for 224-d gain, -2.1% for days on test, .6% for hot carcass weight, -.6% for marbling score, 0 for carcass grade, .6% for longissimus muscle area, 2.3% for backfat thickness, .9% for yield grade, -.9% for dressing percent and -10.9% for shear force. Initial age on test affected only hot carcass weight. Hot carcass weight, dressing percentage, marbling score, longissimus muscle area and fat thickness were affected by slaughter weight. Slaughter age affected dressing percent and marbling score.

Performance of crosses among Hereford, Angus and Simmental cattle with different levels of Simmental breeding. III. Heifer postweaning growth and early reproductive traits.

Postweaning growth and early reproductive traits in heifers whose potential for milk production differed were studied during the years 1976 through 1979. Data were collected on 230 heifers raised by greater than or equal to 3-yr-old Hereford dams. Heifers were comprised of the following breed groups: Hereford (HH), Angus-Hereford (AH), 25% Simmental-75% Hereford (1S3H) and Simmental-Hereford (SH). Postweaning growth rate during a 140-d period was greatest for SH heifers (.75 kg/d), intermediate for AH and 1S3H groups (.70 and .68 kg/d, respectively) and slowest for HH heifers (.64 kg/d). At 1 yr of age, SH heifers were heavier, taller and had larger pelvic areas than all other groups (P less than .01). Least-squares means for yearling weight, hip height and pelvic area for HH, AH, 1S3H and SH heifers were 283, 303, 298 and 317 kg; 111, 112, 114 and 118 cm, and 132, 136, 139 and 148 cm2, respectively. Ninety-one percent of the heifers reached puberty by the end of the breeding period. Crossbred heifers reached puberty at younger ages and had higher pregnancy rates than HH heifers (P less than .01). Least-squares means for pubertal age, weight and height for HH, AH, 1S3H and SH breed groups were, respectively, 407, 371, 382 and 368 d; 300, 302, 305 and 313 kg, and 115, 114, 117 and 119 cm. Percentage of heifers reaching puberty by 14 mo of age was 64, 99, 85 and 94 for HH, AH, 1S3H and SH, respectively. Respective pregnancy rates were 59, 90, 77 and 86%, but were not significantly different among breed groups when only heifers reaching puberty by the end of the breeding period were studied. No differences among breed groups were found for date of pregnancy.

Performance of crosses among Hereford, Angus and Simmental cattle with different levels of Simmental breeding. I. Preweaning growth and survival.

Performance through weaning of 543 calves raised on 3-yr-old and older Hereford dams was studied. Calf breed groups were straightbred Hereford, 50% Angus-50% Hereford, 25% Simmental-75% Hereford and 50% Simmental-50% Hereford. Breed group was a significant source of variation for gestation length, birth weight, calving difficulty, late survival (from 24 h to weaning), percentage of calves weaned per cow calving, 180-d weight, 180-d withers height and 180-d weight:height ratio. Breed group differences were not significant for early survival or weaning condition score and approached significance (P less than .10) for net kilograms weaned (zero if no calf was weaned and 180-d weight if a calf was weaned). Fifty percent Simmental calves had the heaviest birth weight (41.4 kg), most calving difficulty (1.19 score), heaviest 180-d weight (200.5 kg) and tallest 180-d height (101.3 cm). Fifty percent Simmental calves also had the longest gestation length (287.5 d), lowest late survival rate (95%) and largest weight:height ratio (2.00), although they did not differ significantly in the first two traits from 25% Simmentals and in the latter trait from 50% Angus. Herefords differed (P less than .05) from 50% Simmentals in all traits for which breed group was significant except for percentage of calves weaned. Fifty percent Angus and 25% Simmental calves were similar to Herefords for many traits.(ABSTRACT TRUNCATED AT 250 WORDS)