Relationship between milk expected progeny differences of polled Hereford sires and actual milk production of their crossbred daughters.

One hundred sixteen spring-calving Polled Hereford x Angus cows were milked using milking machines after receiving 20 IU of oxytocin. Sires of the cows had been divergently selected on yearling weight (YW) and total maternal (MAT) EPD to form four groups: high YW, high MAT EPD; high YW, low MAT EPD; low YW, high MAT EPD; and low YW, low MAT EPD. Average milk production after 12-h calf separation was 3.7 +/- 1.3 kg. Actual milk production of cows was regressed on their sires' milk EPD, where the milk EPD estimates the additive maternal genetic contribution of a sire to the weaning weight of his daughters' calves. The regression of actual 12-h milk production on sire milk EPD was .038 +/- .014 kg/kg, and the correlation was .26 (P less than .006), close to its expected value, based on the accuracy of the prediction, heritability of the trait, and the relationship between sire and daughter. Extension of results of a single milking to an entire lactation is difficult, but over the range of sire milk EPD sampled (-10 to 16 kg), the range in daughters' milk production predicted from the regression analysis was 27% of the mean actual milk production, corresponding to an increase of about 1% more milk per kilogram of milk EPD.     

Across-breed expected progeny differences: use of within-breed expected progeny differences to adjust breed evaluations for sire sampling and genetic trend.

Data on 2,034 F1 calves sired by Angus, Hereford, Polled Hereford, Charolais, Limousin, Simmental, Gelbvieh, and Tarentaise bulls with Hereford or Angus dams and data on 3,686 three-breed-cross calves with 700 F1 dams of the same breed crosses were used for this study. Traits analyzed were birth, weaning, yearling, and 420-d weights (BWT, WW, YW, and W420, respectively) of F1 calves and WW of three-breed-cross calves. Expected progeny differences from national cattle evaluation programs for sires of F1 calves and cows for BWT, WW, YW, and net maternal ability (milk) were used to assess their value in prediction of crossbred performance. Regressions of actual F1 calf performance on sire EPD were positive for BWT (1.09 +/- .12 kg/kg of BWT EPD), WW (.79 +/- .14 kg/kg of WW EPD), YW (1.44 +/- .16 kg/kg of YW EPD), and W420 (1.66 kg/kg of YW EPD). These regression coefficients were similar to the expected value of 1.0 for BWT and WW but were larger than expected for YW and W420. Regressions of actual three-breed-cross calf WW on milk and WW EPD of their maternal grandsires were .95 +/- .14 and .42 +/- .10 kg/kg, respectively, and differed little from their expectations of 1.0 and .5, respectively. Observed breed of sire means for each trait were adjusted for sire sampling by using EPD regressions to adjust them to the average EPD of all sires of each breed born in 1970.(ABSTRACT TRUNCATED AT 250 WORDS)     

Relationships Between Charolais Sire Expected Progeny Differences and Progeny Performance in Commercial Beef Herds

Data on Charolais-sired calves in 31 commercial herds were analyzed to evaluate progeny performance relative to sire expected progeny differences (EPD). The traits analyzed were BW at birth (BBW; n = 3554) and at weaning (WBW; n = 3604) of crossbred progeny from nationally evaluated sires. Sire BBW EPD and WBW EPD were evaluated as predictors of performance in these commercial herds. Published sire BBW EPD and WBW EPD were averaged and weighted on the numeric accuracy published for each EPD. The average weighted sire BBW EPD was 0.4 kg, and the WBW EPD was 7.0 kg with an average accuracy of 0.79 and 0.75, respectively. Random regression coefficients were estimated for progeny BBW on sire EPD of 1.03 ± 0.09 kg/kg of BBW EPD, and for progeny WBW, 0.66 ± 0.11 kg/kg of WBW EPD. Correlations for sire effect solutions in commercial herds with published sire BBW and WBW EPD were 0.59 and 0.39, respectively. Sire BBW EPD and WBW EPD were favorably related to actual progeny performance. Therefore, selection based on sire EPD should result in change of crossbred progeny performance. This further validates use of EPD as a selection tool for BBW and WBW in commercial herds. However, WBW response was less than expected, possibly a result of management practices in commercial herds compared with seedstock herds.     

Crossing beef x beef and beef x Brown Swiss: pregnancy rate, calf survival, weaning age and rate

October pregnancy rate, calf survival to weaning, weaning age, weaning rate and actual kg of calf weaned/cow exposed were determined in a 4-yr study involving 880 matings of Angus (A), Hereford (H) and Charolais (C) sires to A, H, C and Brown Swiss (BS) dams. Cows were mated in single-sire herds for 45 or 60 d under pasture conditions; heifers were bred to produce their first calf at 3 yr of age. Pregnancy rate of lactating dams was 9.4% higher (P less than .01) than for non-lactating dams. Pregnancy rates for straightbred matings were 87.5%, 80.6% and 75.4%, respectively, for A, H and C groups (P less than .05). No differences (P greater than .10) due to sire breed were found for any of the traits studied except for calf age at weaning. Calves from C sires were younger (P less than .01) at weaning than calves from H and A sires. Breed-of-dam differences (P less than .05 to P less than .01) were found for all traits studied except calf survival rate. All BS dams produced crossbred calves and had lower pregnancy and weaning rates (both P less than .01), calves were younger at weaning (P less than .05), had lower kg of calf weaned/cow exposed (P less than .05) than for beef-breed dams producing crossbred calves. Crossbred calves from BS dams were 4.9, 11.0 and 3.4 d younger (P less than .05 to P less than .01) at weaning, respectively, than crossbred calves from H, A and C dams.(ABSTRACT TRUNCATED AT 250 WORDS)     

Sheath area in Brahman and grade Brahman calves and its association with preweaning growth traits

Data from 439 Brahman (B) and grade Brahman (GB; 7/8 Brahman or more) calves born from 1970 through 1975 at the USDA Subtropical Agricultural Research Station were used to estimate least-squares means, heritabilities and genetic correlations for sheath area and preweaning growth traits. Grade Brahman calves weighed more (P less than .01) at birth and gained more (P less than .01) preweaning than B calves, although sheath areas were not different. Males exceeded (P less than .01) heifers in all preweaning growth traits and had larger (P less than .01) sheath areas. Heritabilities were: sheath area, .45 +/- .13; birth weight, .25 +/- .13; average daily gain, .38 +/- .15 and weaning weight, .35 +/- .15. Genetic correlations between sheath area and birth weight, average daily gain and weaning weight were .23 +/- .35, .58 +/- .25 and .52 +/- .27. These results suggest selection could be effective in reducing sheath area in B and B-derivative breeds, but would be antagonistic to preweaning growth traits. Because of relatively low phenotypic correlations between sheath area and preweaning growth rate (.27) and weaning weight (.29), continued emphasis on increasing growth rate or weaning weight could generally be maintained with careful attention to avoiding large sheath areas through independent culling level or index selection procedures.     

Evaluation of crossbred calf and cow types for the coastal plain of North Carolina

Data in this experiment consisted of 418 lactation records, and weaning and birth weight records from 600 crossbred calves. The traits evaluated included birth weight, weaning weight, weaning weight per cow exposed, weaning weight per weight of cow, weaning weight per weight of cow exposed, and predicted milk yield. Angus, Brangus, and Gelbvieh sires were mated to purebred Hereford cows. Yearling and 2-yr-old Angus-Hereford, Brangus-Hereford, and Gelbvieh-Hereford daughters then were bred to Polled Hereford bulls (Data Set 2). Later-parity Angus-Hereford, Brangus-Hereford, and Gelbvieh-Hereford daughters were mated to Salers or Simmental sires (Data Set 3). Differences between Gelbvieh- and Brangus-sired calves or Gelbvieh-Hereford and Brangus-Hereford daughters were never significant for weaning weight, birth weight, or milk yield. Angus crosses had the lowest weaning weight, birth weight, and milk yield, but the highest kilograms of calf weaned per cow exposed in all data sets. Angus-Hereford and Brangus-Hereford dams had higher weaning weight per weight of cow exposed than Gelbvieh-Hereford dams (P < .01) in Data Set 3. There were no other significant differences related to cow weight.     

Biological type effects on gestation length, calving traits and calf growth rate

Gestation length, birth weight calving difficulty, calf mortality rate at birth, calf mortality rate from birth to weaning, preweaning calf growth rate and calf 200-d weight were evaluated in a biological type study in which four sire breeds were bred by AI to Hereford dams. Angus and Red Poll sires represented breeds of medium size, and Pinzgauer and Simmental sires represented large breeds. Angus and Pinzgauer represented breeds with medium milk production, and Red Poll and Simmental represented breeds with high milk production. Dams mated to large sire breeds had longer (P less than .01) gestation lengths (.95 d) and higher calving difficulty scores than dams mated to medium-sized sire breeds. Calves from large sire breeds had heavier birth weight (P less than .01) and 200-d wt (6.1 kg; P less than .01) than calves from medium-sized sire breeds. Calf death loss and ADG to weaning were similar (P greater than .10) for all breeds of sire. Calves from the higher milk level sire breeds exceeded the medium-milk breeds in birth weight (1.3 kg; P less than .01) but did not (P greater than .10) in other traits. Calves from the higher milk level sire breeds exceeded the medium-milk breeds in birth weight (1.3 kg; P less than .01) but not (P greater than .10) in other traits. Interaction between size and milk production of sire breed existed for gestation length, birth weight, ADG from birth to weaning and 200-d calf weight (P less than .01). In general, mature size of sire breed was a good indication of expected performance traits not easily influenced by environment. Not all differences, however, could be explained by size and milk production of the size breed.     

Effects of breeding season length and calving season on range beef cow productivity

A 5-yr study was conducted beginning in 1983 with 460 cows to evaluate the effects of three breeding seasons (30, 45, and 70 d in length) and two times of spring calving, March (early) and April (late), on cattle production under Nebraska Sandhills range conditions. Criteria evaluated included pregnancy and weaning percentages, calving date and distribution, cow weights and body condition at four intervals, calf birth and weaning weights, and cow productivity. The 30-d breeding season included a 10-d estrus synchronization and AI period; in the other breeding seasons only natural breeding was used. The same sires were used over the entire study period. Percentage of cows pregnant and percentage of calves weaned were lower (P less than .01) for cows bred for 30 d than for cows bred for 45 or 70 d. Average calving dates were similar among the breeding groups within the early and late calving herds. Pregnancy rates from AI were higher (P less than .01) for the cows calving in April (64%) than for the cows calving in March (41%). Cows calving in April lost less weight between precalving and prebreeding and were heavier (P less than .05) at prebreeding time than the cows calving in March. Calf weaning weights were not different (P greater than .10) among any of the breeding season groups or between the two calving herds when calves were weaned at a similar age. Cow productivity (calf weaning weight per breeding female) was highest (P less than .05) for the cows bred for 70 d (186 kg), intermediate for the cows bred for 45 d (172 kg), and lowest for cows bred for 30 d (162 kg).(ABSTRACT TRUNCATED AT 250 WORDS)     

Life-cycle evaluation of Bos taurus and Bos indicus X Bos taurus breed types in a dry, temperate climate: performance of mature dams

Mature dams representing Hereford, Red Poll, F1 Hereford x Red Poll, F1 Red Poll x Hereford, F1 Angus x Hereford, F1 Angus x Charolais, F1 Brahman x Hereford and F1 Brahman x Angus breed types were evaluated. All cows were bred to Limousin sires to produce two-way or three-way-cross progeny. Mature Brahman x Hereford dams produced a higher (P less than .05) percentage of live calves than Herefords, but dam breed differences in percentage of calves weaned relative to the number of cows exposed for mating were not statistically significant. Progeny of Angus x Charolais and Red Poll dams were outstanding in weaning weight, but Hereford and Brahman-cross calves were below average. Planned comparisons showed that Angus x Charolais calves were heavier (P less than .01) at weaning than Hereford (23.0 +/- 3.8 kg) or Angus x Hereford (9.6 +/- 3.2 kg) progeny. Mature Angus x Hereford mothers weaned heavier calves than did Brahman x Herefords (7.4 +/- 3.2 kg, P less than .05) or Brahman x Angus (10.9 +/- 3.0 kg, P less than .01). Analysis of the Hereford-Red Poll diallel showed evidence of maternal heterosis in calf weaning weight (4.0 +/- 2.6 kg, P less than .05), but there was no difference in the percentage of calves weaned by crossbred vs straightbred dams.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of crossbred cows containing various proportions of Brahman in spring or fall calving systems: III. Productivity as three-, four-, and five-year olds

Productivity of 3-, 4-, and 5-yr-old crossbred cows containing various proportions (0, 1/4, or 1/2) of Brahman breeding out of Angus or Hereford dams was evaluated using 489 spring-calving and 427 fall-calving records collected over a 4-yr period. Cows were bred to Limousin sires for the first 3 yr and to Limousin and Salers sires the 4th yr. Interactions between crossbred cow group and season of calving were not significant. Percentage of cows exposed to breeding that weaned a calf increased (P less than .01) as proportion Brahman breeding increased, was higher (P less than .01) for cows out of Angus dams than for cows out of Hereford dams, and was higher (P less than .01) for spring-calving cows. As the proportion Brahman increased, the percentage requiring assistance at birth decreased, and cows out of Angus dams required less (P less than .05) assistance than those out of Hereford dams. Preweaning ADG, adjusted weaning weight, weaning conformation, weaning condition, and adjusted weaning hip height increased a proportion Brahman breeding increased. Spring-born calves gained .12 kg/d faster (P less than .01) than fall-born calves. However, weight at weaning was similar for the two groups; spring-born calves were weaned at an average age of 205 d, and fall-born calves were weaned at an average age of 240 d. Fall-calving cows were heavier (P less than .05) than spring-calving cows, and 0 and 1/2 Brahman cows were heavier (P less than .01) than 1/4 Brahman cows. These data indicate that Brahman-cross dams can be used to improve reproductive rate and increase preweaning growth rate, and thus weaning weight.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of using sires selected for yearling weight and crossbreeding with beef and dairy breeds: birth and weaning traits

Data consisting of 948 calf records collected from 1978 to 1982 were analyzed to determine the effects of breeding methods used to improve commercial herds genetically on birth and weaning traits. Four distinct groups were used in the project: Group 1 (G1), an unselected, random mating Hereford control line; Group 2 (G2), a Hereford group using sires selected for yearling growth; Group 3 (G3), a rotational cross with Angus, Hereford, Charolais and Simmental breeds; and Group 4 (G4), a rotational cross with Angus, Hereford, Simmental and Holstein-Friesian breeds. Traits analyzed were birth weight (BW), calving difficulty (CD), percent assisted births (%AB), percent born alive (%BL), preweaning average daily gain (PWDG), relative growth rate (RGR), weaning weight (WWT) and percent weaned (%WND). The use of high yearling weight sires in G2 increased calf size (P less than .01) at birth and weaning by 8.9 and 28.1 kg, respectively, along with increased CD (P less than .01). Use of rotational crossbreeding systems increased calf size and growth from birth to weaning (P less than .01), but decreased CD and %AB (P less than .01) by .17 units and 13.5%, respectively. Including Holstein-Friesian in G4 resulted in further increases in preweaning growth (P less than .01) and calving ease was improved without affecting BWT compared with G3.     

Production characters of straightbred, F1 and F2 cows: birth and weaning characters of terminal-cross calves

Records of 2,449 births and 2,120 weanings of terminal-cross calves were used to characterize maternal productivity of first- and second-generation cows from a diallel of Angus, Brahman, Hereford, Holstein and Jersey when mated to third-breed sires. Third- and later-parity cows were randomly assigned after each parturition to Charolais and Red Poll bulls in multiple-sire pastures. Calves were weaned at approximately 7 mo of age; males were not castrated. A mixed model was assumed for data analysis. Effects included in the model were breed-type of dam, cow within breed-type of dam (random), breed of sire of calf, season of record, year of record, age of dam group, sex of calf and age of calf (covariate). Age of dam groups were 4- and 5-yr-olds, 6- and 7-yr-olds, 8-, 9- and 10-yr-olds, and those greater than 10 yr of age. Dependent variables were calf weight, shoulder width and hip width at birth, weaning weight, weaning height and survival to weaning. Holstein and Holstein crosses tended to produce the largest calves at birth and weaning. Among straightbred dams, the smallest calves were born to Brahman, whereas Hereford weaned the smallest calves. Brahman-Jersey dams produced the smallest calves at birth among crossbreds; Angus-Hereford cows weaned the smallest calves. Average maternal heterosis estimates for birth weight were small and non-significant. Calves of F1 crossbred dams were 17.4 kg heavier (P less than .01) and 1.70 cm taller (P less than .01) at weaning than calves of first-generation straightbred dams.(ABSTRACT TRUNCATED AT 250 WORDS)     

Experimental selection for calving ease and postnatal growth in seven cattle populations. I. Changes in estimated breeding values

Selection was used to create select and control lines within 4 purebred and 3 composite cattle populations. Both lines were selected for similar direct yearling weight and maternal weaning weight EBV. Select lines were selected for lower 2-yr-old heifer calving difficulty score EBV and control lines were selected for average birth weight EBV. Select (n = 6,926) and control (n = 2,043) line calves were born from 1993 through 1999 and selection began with the 1992 mating. High replacement rates resulted in 2,188 births to select line and 598 births to control line heifers. Data used to calculate EBV came from these populations and from 15 yr of data preceding the experiment. Calving difficulty was scored from 1 (no assistance) to 7 (cesarean). Calving difficulty scores from all twins, malpresentations, and cows 3 yr old and older were eliminated. Except for the first year, when a single-trait BLUP was used, a multiple-trait BLUP was used to calculate direct and maternal EBV for calving difficulty score, birth weight, and weaning weight, and direct EBV for postweaning gain. Sires (n = 498) were selected from those born in both the preceding populations and the select and control lines. In purebred populations, some industry sires (n = 88) were introduced based on their EPD. Tests of mean select and control line EBV differences of calves born in the final 2 yr were based on population variation. Select line direct EBV were 1.06 lower for heifer calving difficulty score (P < 0.001) and 3.5 kg lower (P < 0.001) for birth weight than controls. Average differences for other EBV were small and not significant. Yearling weight EBV was intentionally increased in both select and control lines of purebred populations. Angus, Hereford, Charolais, and Gelbvieh yearling weight EBV in control lines increased by 32.4, 27.2, 21.0, and 10.5 kg, respectively, from 1991 and 1992 to 1998 and 1999 compared with an average increase of 2.7 kg in composite populations. Birth weight direct EBV in purebred control lines increased by approximately 8% of yearling weight EBV increases. Selection based on a multiple-trait BLUP was able to create lines differing in calving difficulty score and birth weight EBV, but not in weaning weight and postweaning gain EBV. Differences between lines should be useful for evaluating BLUP and other traits and for identifying potential limitations of genetically decreasing calving difficulty score and birth weight.     

Body measurements of newborn calves and relationship of calf shape to sire breeding values for birth weight and calving ease

Body measurements on Angus- (n = 374) and Polled Hereford-sired (n = 438) calves were used to quantify calf shape via multivariate factor analysis, and measurements on Polled Hereford-sired calves were further used to investigate relationships between calf shape and sire expected progeny differences (EPD) for birth weight and first-calf calving ease. Calf birth weight, head circumference, shoulder width, hip width, heart girth, cannon bone circumference and length, and body length were recorded at 24 h postpartum. Sire birth weight EPD was positively associated (P less than .05) with all calf measures but only with head and cannon circumference after adjustment for phenotypic birth weight and gestation length. Thus, at constant birth weight, calves from higher birth weight EPD bulls tended to have larger cannon and head circumferences. Calving ease EPD was negatively related (P less than .05) to all calf measures except shoulder width. After adjustment for birth weight, only cannon circumference was associated with calving ease EPD, and this effect was removed by additional adjustment for birth weight EPD. Thus, at constant birth weight, bulls with higher EPD for calving ease sired calves with smaller cannon circumference, but at constant birth weight EPD, body measures were not associated with calving ease EPD. Factor analysis defined underlying skeletal width and frame components of shape (independent of birth weight) for both sire breeds. Calf shape differed among sires and was in part explained by birth weight EPD. No additional variation in shape was explained by calving ease EPD. Calf shape seemed to add no information for prediction of dystocia to that provided by birth weight EPD.     

Reproductive rates, birth weight, calving ease and 24-h calf survival in a four-breed diallel among Simmental, Limousin, Polled Hereford and Brahman beef cattle

Calving and weaning rates, birth weight, calving ease, and 24-h calf survival were evaluated in a four-breed diallel of Simmental (S), Limousin (L), Polled Hereford (H) and Brahman (B) beef cattle in five calf crops. Limousin dams tended to have the highest calving and weaning rates because they were able to have heavier calves with less calving difficulty and higher survival rates. Brahman-sired calves were the heaviest at birth (P less than .05) and B dams produced the lightest calves (P less than .001). Lower birth weights tended to be the limiting factor on survival of these calves. A linear comparison among means to evaluate purebred, additive, maternal and specific combining ability effects showed most of the reduction in birth weight from B dams was due to maternal effects. Breed of dam accounted for a higher proportion of variation in calving ease than did sire breed. Simmental sires had significantly heavier calves at birth and S and H dams tended to have more calving difficulty and lower survival rates. Heterosis for these traits was generally not significant. Correlations were generally positive and significant for birth weight and calving ease, but were more variable for birth weight and survival. Linear regressions of calving ease on birth weight both within years and within dam-breed-year subclasses were very similar in that the association of these two traits was reduced as dam age increased.     

Influence of calving season and stocking rate on birth weight and weaning weight of Simmental-sired calves from Brahman-Hereford F1 dams.

Braham-Hereford F1 dams have been used to evaluate the influence of grazing pressure on forage attributes and animal performance at the Texas A&M University Agricultural Research Center at Overton. Data for this study were compiled from 1,909 records of Simmental-sired calves born to Braham-Hereford F1 cows from 1975 to 1990. Birth weight and weaning weight were analyzed independently to estimate the influence of year, season of birth, dam age, weaning age, and sex of calf. The effect of stocking rate as represented by levels of forage availability on weaning weights and subsequent birth weights was measured. Within the fall and winter calving seasons, lactating dams grazing at a high stocking rate produced calves with the lowest subsequent birth weights. Lactating dams assigned to creep-fed treatments had calves with the heaviest subsequent birth weights. Although dams that were less than 3.5 yr of age had calves with the lightest birth weights, there was no apparent decline in birth weight of calves from dams 12 to 17 yr old. Year, sex of calf, age of dam, stocking rate, season of birth, age at weaning, and birth weight were significant factors affecting weaning weight (P less than .01). Fall-born calves grazing cool-season annual pastures were heavier at weaning (267.6 kg) than either winter- (252.0 kg) or spring-born calves (240.9 kg). A stocking rate x season-of-birth interaction was observed for birth weight and weaning weight (P less than .05). Differences in weaning weight from low- vs high-stocked pastures were greater for fall-born calves (61.6 kg) than for winter-born calves (48.7).(ABSTRACT TRUNCATED AT 250 WORDS)     

Maternal birth weight breeding value as an additional factor to predict calf birth weight in beef cattle

A total of 1,028 birth weight (BWT) and gestation length (GL) records were collected for calves from 1994 to 1997 in five U.S. Angus herds. Parental BWT EPD and dam BWT maternal breeding values (MBV) computed from the entire U.S. Angus data base after each breeding season were also available. A full model was fit to BWT that contained contemporary group (CG), sire BWT EPD, dam BWT EPD, and dam BWT MBV. A reduced model that dropped dam BWT MBV was also fit. The full model had smaller (P < .01) sum of squares for error than the reduced model. Calf BWT records were then adjusted for CG. Two data sets were formed to include adjusted BWT progeny records from sires with BWT EPD > or = .75 or > or = 1.0 SD above the mean of sires in the data set. Adjusted birth weights were assigned to either > or = .75 or other < .75 SD and > or = 1.0 or < 1.0 SD categories based on the mean BWT of calves in the entire data set. Dams were assigned to either > or =2 .75 or < .75 SD and > or = 1.0 or < 1.0 SD categories based on dam BWT EPD, MBV, or total maternal genetic contribution (TMGC = EPD + MBV). Chi-square analyses showed that dam BWT EPD, MBV, or TMGC categories were not independent (P < .10) of BWT SD categories, indicating that both dam BWT EPD and BWT MBV provide useful information to attenuate calf BWT. Calf BWT records were then adjusted for the overall mean, CG, sire and dam BWT EPD, and dam BWT MBV. Dams were then assigned to five categories: high dam EPD and MBV (HH), high dam EPD and low MBV (HL), low dam EPD and high MBV (LH), low dam EPD and MBV (LL), and other (OTH). High was > or = .75 or > or = 1.0 SD and low was < .75 or < 1.0 SD based on the mean BWT EPD or MBV of dams in the data set. In all adjusted BWT analyses, HH, HL, and LH categories did not differ (P > .05) from each other; however, the LL category was less (P < .05) than all other categories, indicating that calves from LL dams were lighter at birth than expected. For GL, LL was significantly different (P < .05) from only HH. The large differences in birth weight for the LL dams compared to other groups did not seem to be primarily due to shorter GL. Results showed that MBV provided additional information to control BWT; however, when both dam MBV and EPD were low, birth weight of calves was less than expected. Future research should focus on explanations for this interaction.     

Growth and sexual characteristics of suckling beef calves as influenced by age at castration and growth implants

A 2-yr study using crossbred male calves (n = 228) evaluated castrating at birth or at 4 mo of age and use of anabolic growth implants (none, zeranol or estradiol-17 beta). Angus, Hereford and Brahman crossbred calves produced in seven cow-calf units that varied by breed component, stocking rate and calving season were allotted to treatment at birth in a 2 x 3 factorial arrangement. Growth implants decreased (P less than .01) testicular weight and expression (P less than .05) of male secondary sex characteristics in suckling bull calves at 4 mo. Implanted calves were shorter (P less than .05) at the hips and had shorter front legs (P less than .01) at both 4 mo and at weaning. Cannon bone circumference at weaning was increased (P less than .05) by growth implants. Age at castration did not affect (P greater than .05) calf performance or body characteristics. Calves given growth implants had higher (P less than .05) rates of gain from birth to 4 mo than did nonimplanted calves (.75 vs .71 kg/d). Implanted calves were heavier (P less than .01) at weaning and had higher (P less than .01) ADG from 4 mo to weaning than did nonimplanted calves. These data indicate no benefit from delaying age at castration, but implanting increased weaning weight an average of 8.2 kg.     

Preweaning breed-of-sire comparisons involving the Senepol breed of cattle

Preweaning data collected at two locations (Kentucky, Louisiana) were utilized to evaluate breed-of-sire comparisons involving the Senepol breed of cattle. For the Kentucky study, calves sired by Senepol bulls were 1.3 kg heavier (P less than .05) at birth than calves sired by Hereford bulls; however, weaning weights were similar for the two sire groups. For the Louisiana study, calves sired by Longhorn bulls were 5.3 kg lighter (P less than .01) at birth, 20 kg lighter (P less than .01) at weaning and had weaning condition scores .5 unit less (P less than .01) than the average of calves sired by Red Poll and Senepol bulls. Also, heifers exposed to Longhorn bulls weaned 23 kg less (P less than .01) calf per heifer exposed than the average of heifers exposed to Red Poll and Senepol bulls. Calves sired by Red Poll bulls were 1.2 kg heavier (P less than .01) at birth and 12 kg heavier (P less than .01) at weaning than those sired by Senepol bulls; however, the Senepol-sired calves received higher (P less than .01) condition scores at weaning. Heifers exposed to Red Poll bulls weaned 20 kg more (P less than .05) calf per heifer exposed than did heifers exposed to Senepol bulls.     

An evaluation of bias in estimated breeding values for weaning weight in Angus beef cattle field records. I. Estimates of within herd genetic trend

Genetic trends for weaning weight were evaluated in 15 purebred herds in the United States participating in the Angus Herd Improvement. Records production testing program. Regression techniques were used for separate estimates of sire and dam contributions that were summed to estimate total herd trend. Sire contributions, calculated as the pooled within sire regression of weaning weight ratio on year of calf birth, ranged from .01 +/- .23 to 1.30 +/- .24 across the herds and average .51 ratio units/yr. Dam contributions, estimated as the pooled within dam regression of offspring weaning weight ratio, deviated from the contemporary paternal half-sib average ratio, on year of calf birth, ranged from .06 +/- .06 to .68 +/- .11 and averaged .34 ratio units/yr. A positive trend in direct effects was associated with a possible negative trend in maternal effects. The annual trend within herds ranged from .21 to 1.50 ratio units and averaged .85 units over all herds, representing 1.8 kg annual genetic gain in weaning weight.