Preweaning growth traits for Senepol, Hereford, and reciprocal crossbred calves and feedlot performance and carcass characteristics of steers.

We conducted a multiyear study in two phases to determine preweaning performance traits of Senepol (S x S), Hereford (H x H), and reciprocal (S x H and H x S) F1 crossbred calves and feedlot performance and carcass characteristics of steers. In Phase I, from 1985 to 1989, data from S x S (n = 194), H x H (n = 383), and S x H (n = 120) calves were used. Numbers of S x S cows were increased during Phase I so that data from H x S (n = 74) calves could be included in Phase II (1990 to 1992) in addition to S x S (n = 118), H x H (n = 130), and S x H (n = 56) calves. Also during Phase II, feedlot performance and carcass characteristics were determined for S x S (n = 30), H x H (n = 26), H x S (n = 36), and S x H (n = 26) steers. In Phase I, S x S calves had heavier (P < .01) birth weights and heavier (P < .01) 205-d adjusted weaning weights than H x H calves. Birth weights of S x H calves were heavier (P < .01) than the mean of the purebred calves, but 205-d adjusted weaning weights did not differ (P > .10). In phase II, direct heterosis was 3.5% for birth weight (P < .05) and 5.1% for 205-d adjusted weaning weight (P < .01). Senepol maternal breed effects were 1.9 kg for birth weight (P < .10) and 37.9 kg for 205-d adjusted weaning weight (P < .01). Levels of direct heterosis, Senepol maternal breed effects, and Hereford direct breed effects were significant for most feedlot performance traits of steer calves that were fed to a common end point. Breeds did not differ (P > .10) for USDA yield and quality grades, and direct heterosis was not significant for Warner-Bratzler shear force. These results demonstrate significant levels of heterosis in preweaning performance between S x S and H x H calves and in feedlot performance of steers. Levels of heterosis were smaller and nonsignificant for most carcass traits including meat tenderness, which did not differ between S x S and H x H steers in this study.

Growth patterns of two lines of Angus cattle selected using predicted growth parameters.

Linear functions of body weight and condition score at weaning and 18 mo of age were used to predict the mature weight (A) and maturing rate (k) parameters of an asymptotic growth model of Angus cows at the Subtropical Agricultural Research Station, Brooksville, FL. From 1981 through 1988 a heavy-mature-weight line (Line A) and a rapid-maturing line (Line K) were selected based on predicted A and k values. Linear contrasts (A-K) of least squares means for weight at fixed ages indicated that the weight difference between lines increased from birth to maturity during the period of the study. Animals from Line A were heavier (P less than .01) at all ages. A negative response in maternal ability, relative to increased growth potential of their calves, seems to have occurred in the cows of Line A. Mature weight was reached at approximately 4.5 yr of age in Line K and at approximately 5.5 yr in Line A. Brody's three-parameter and Richards' four-parameter functions were fitted to 2,855 quarterly weights of cows, from birth to 6.5 yr of age, to estimate the average growth curve for each line. Brody's model gave better estimates of weights from 18 mo to maturity, but the asymptotic residual mean squares were slightly higher because early weights were overestimated. Linear and nonlinear regression analyses of weight-age data and comparisons of degree of maturity at different premature ages showed differences in the growth patterns of the two lines selected for early predicted values of A and k.

Effects of breed group by location interaction on crossbred cattle in Nebraska and Florida.

Data on 2,744 calves produced in Clay Center, Nebraska and Brooksville, Florida were used to evaluate the importance of genotype x location interactions on the reproductive and maternal performance of eight breed groups of F1 crossbred cows. A total of 648 F1 crossbred cows included Bos taurus x Bos taurus (Bt x Bt) crosses: Hereford x Angus reciprocal crossbreds (HA and AH), Pinzgauer x Angus (PA), Pinzgauer x Hereford (PH); and Bos indicus x Bos taurus (Bi x Bt) crosses: Brahman x Angus (BA), Brahman x Hereford (BH), Sahiwal x Angus (SA) and Sahiwal x Hereford (SH). The first calf crop was sired by Red Poll bulls. All remaining calf crops were sired by Simmental bulls. Although the pregnancy rate was 9% higher in Nebraska, the rate of unassisted calvings and calf survival rate were both 4.6% lower in Nebraska. Calf birth and weaning weights were 8.0 and 15.6 kg heavier in Nebraska than in Florida. Bi x Bt dams exceeded (P less than .001) Bt x Bt crossbred dams for all traits except age of calf at weaning and calf-survival rates (P greater than .10). Birth weights of calves from Bi x Bt crossbred dams were 3.4 kg lighter than those from the Bt x Bt crossbred dams. The interaction of location with the breed group comparison of Bi x Bt vs Bt x Bt crossbred dams was significant for pregnancy rate, calf age at weaning, rate of unassisted calving and all weight traits. Adjusted weaning weights of calves from HA, AH, PA, PH, BA, BH, SA and SH cows were as follows: HA, 194 and 222; AH, 202 and 230; PA, 213 and 242; PH, 217 and 245; BA, 251 and 254; BH, 252 and 254; SA, 236 and 238; and SH, 238 and 243 kg, respectively, in Florida and Nebraska. Bos indicus-sired cows (BA, BH, SA and SH) weaned essentially equal-weight calves at both locations, whereas calves from Bt x Bt crossbred cows (HA, AH, PA, PH) were about 28 kg lighter in Florida.

Effects of winter nutrition and summer pasture or a feedlot diet on plasma insulin-like growth factor I (IGF-I) and the relationship between circulating concentrations of IGF-I and thyroid hormones in steers.

Effects of two winter nutritional levels (LOW, MOD) and two summer pastures (bahiagrass, BG; perennial peanut, PP) on plasma IGF-I, and the relationship between IGF-I and average daily gain (ADG), thyroid hormones, plasma urea, packed cell volume (PCV) and steer type were determined in 101 steers (217 kg) varying in breed composition, frame size and initial condition. Relationships between body composition or composition of gain and IGF-I were determined in 11 contemporary steers assigned directly to the feedlot. Initial IGF-I (57.9 +/- 3.5 ng/ml) was positively correlated (P less than .05) to initial condition, estimated percentage of Brahman and plasma T3, but not related to subsequent ADG. During the 126-day wintering period, ADG was .21 kg for the LOW winter treatment and .47 kg for the MOD winter treatment. Concentration of IGF-I in the wintering period was affected (P less than .01) by nutritional level (LOW = 71.8 ng/ml, MOD = 150.6 ng/ml) and was positively related to winter ADG in MOD steers (P less than .01) but not in LOW steers. Concentration of IGF-I in winter was also positively related to condition at the end of the winter period (P less than .01), T3 (P less than .05) and T4 (P less than .05). There were no effects of winter treatment on IGF-I during the subsequent summer pasture period. During the 145-d summer period, ADG was .53 kg for BG and .68 kg for PP. Concentration of IGF-I during the summer period was affected (P less than .05) by pasture treatment (BG = 138.6 ng/ml, PP = 181.9 ng/ml), was positively related (P less than .01) to PCV and percentage of Brahman, and was negatively related (P less than .05) to estimated percentage of English breeding. In steers assigned directly to the feedlot, IGF-I was correlated with empty body (EB) weight (r = -.59, P less than .10), EB water (r = -.59, P less than .10) and EB protein (r = -.60, P less than .10) at slaughter, and with days on feed (r = -.65, P less than .05), but was not correlated with ADG or rate of component gain. These data indicate that IGF-I is related to nutritional status in steers as in other species, that there may be significant breed or cattle type differences in circulating concentrations of IGF-I, and that circulating concentration of IGF-I may be functionally related to plasma concentration of thyroid hormones.

Direct and maternal genetic effects due to the introduction of Bos taurus alleles into Brahman cattle in Florida: I. Reproduction and calf survival.

Pregnancy rate, calf survival rate to weaning and calf age at weaning of several types of crossbred cows (2/3 or more Brahman) were compared to those of straightbred Brahman and Angus cows over a 12-yr period at Subtropical Agricultural Research Station near Brooksville, FL. The purpose of this study was to determine the relative importance of additive vs nonadditive genetic effects on reproductive and calf survival traits in a population of cattle whose foundation was selected on the basis of superior reproductive performance under harsh environmental conditions. Best linear unbiased estimates (BLUE) of direct additive effect (measured as the deviation of Brahman additive breed effect from Angus) for pregnancy rate and calf age, measured as traits of the dam, were 6 +/- 3% and -7.2 +/- 2.1 d, respectively. Thus, Bos taurus germ plasm did not increase pregnancy rate but resulted in an earlier calving date. The BLUE of nonadditive (intralocus) direct genetic effects measured as deviations from intralocus group genetic effects in the parental breeds on pregnancy rate and calf age at weaning were 25 +/- 4% and -6.4 +/- 2.5 d. Nonadditive effects on pregnancy rate were the primary cause of the superior reproductive rates observed in Brahman crossbred cows. Calf survival was considered to be a trait of the calf, and BLUE of direct additive, direct nonadditive, maternal additive and maternal nonadditive genetic effects was obtained. Only maternal nonadditive genetic effects were found to have a significant effect on survival rate (9 +/- 4%).

Direct and maternal genetic effects due to the introduction of Bos taurus alleles into Brahman cattle in Florida: II. Preweaning growth traits.

Records of birth weight (BW), weaning weight (WW) and condition score (CS) from 1,467 Brahman and Brahman X Angus crossbred calves from Brahman and crossbred Brahman sires and Brahman, crossbred Brahman and Angus dams were collected at the Subtropical Agricultural Research Station, Brooksville, Florida, from 1971 to 1982. Best linear unbiased estimates (BLUE) of Brahman sire and dam group additive genetic effects (as deviations from Angus) and Brahman X Angus dam and calf group nonadditive (intralocus) genetic effects (as deviations from intralocus group genetic effects in the parental breeds) were obtained. Linear combinations of these were used to compute direct and maternal Brahman additive and Brahman X Angus nonadditive (intralocus) group genetic effects. The respective BLUE of these four effects were 5.99 +/- 2.08, -5.70 +/- 1.91, .52 +/- 1.81 and 2.85 +/- .72 kg for BW; 9.60 +/- 10.29, 8.76 +/- 9.47, 9.47 +/- 8.96 and 20.95 +/- 3.56 kg for WW; and -1.10 +/- .55, 1.64 +/- .50, 1.47 +/- .47 and .05 +/- .19 units for CS. Linear combinations of the BLUE of sire, dam and calf group genetic effects can be used to predict the genetic worth of crossbred groups composed of any combination of Brahman and Angus breeding. Nonadditive maternal group genetic effects were the most important factor for BW and WW, whereas nonadditive direct group genetic effects were the most important for CS.

Prediction of mature cow carcass composition from live animal measurements.

Two trials were conducted with mature cows to develop prediction equations for estimating carcass composition from live animal measurements. Trial 1 involved 82 animals that were used to develop these equations. Subjective criteria (frame and condition scores) also were utilized along with live weight in development of prediction equations. Equations using subjective independent variables predicting energy and carcass tissue weights apparently were slightly more variable in precision (R2 = .69 to .91) than those developed with objective variables (R2 = .74 to .90). Equations predicting percent compositions from subjective variables had lower coefficients of determination (R2 = .49 to .76) than those developed with objective variables (R2 = .63 to .83). Forty-one animals similar to those used in Trial 1 served as a test group in Trial 2. Measured carcass composition was regressed on composition predicted by equations developed in Trial 1. These equations generally had slopes and intercepts with confidence intervals that included 0 and 1, respectively, indicating that most of the prediction equations were unbiased. This work indicates that carcass composition can be predicted from both objective and subjective measurements, with some accuracy and precision.

Genotype X environment interaction in Hereford cattle: IV. Postweaning traits of bulls.

Genotype X environment interactions for postweaning performance traits of bulls produced by different lines of Hereford cattle were investigated in the contrasting environments of Miles City, Montana and Brooksville, Florida. During Phase 1 of the study (1966 to 1973), the performance of bull progeny from two unrelated lines (M1 and F6 previously developed in Montana and Florida, respectively) was compared at each of the two experimental sites. During Phase 2 (1967 to 1974), performance of bulls from two related lines (M1 of Montana origin and F4 derived from an M1 foundation through selection in Florida) was compared at each of the two locations. The line X location interaction effect in Phase 1 was highly significant for weaning weights and average daily gain during the postweaning test, and for end-of-test weight, conformation score, condition score and forecannon circumference. The interaction effect in Phase 2 was highly significant for 205-d and end-of-test weights and significant for all other traits except end-of-test conformation score. These results, consistent with results for traits covered in other papers of the same series (reproductive traits, birth-to-weaning traits of bull and heifer calves combined, and postweaning traits of heifers), indicated the existence of economically important genotype X environment interactions in beef cattle. Results from the series of papers indicated that adaptation to local environment should receive consideration in planning breeding programs, performance tests and interregional transfers of beef cattle.

Relationships between traits of cow-calf pairs and a measure of partial efficiency.

Angus cow-calf pairs (N = 114) were individually fed grass silage diets under conditions chosen to approximate nutrient intake under a free grazing, noncreep situation. Postfactum comparison with a subsequently conducted study on pasture indicated that the procedures used produced animal responses similar to those provided by a tall fescue pasture averaging 58% dry matter digestibility. Cow-calf pair efficiency was expressed as the ratio of estimated total digestible nutrient (ETDN) intake of the pair to calf weight at weaning. Initial cow weight per se was unrelated to pair efficiency. When considered jointly with calf weight at weaning, initial cow weight was unfavorably and calf weight was favorably related to pair efficiency. Calf age at weaning and milk production were favorably related to pair efficiency through their relationship with calf weight at weaning. Initial cow fat thickness, estimated ultrasonically, was not related to this measure of efficiency, indicating compensations between the year just completed and the next year in the relationship between cow fat thickness at weaning and pair efficiency. Mating schemes resulting in selection of relatively smaller females and larger males, within the variation available in a straightbred population, would be expected to alter the cow weight-calf weight ratio in a direction favorable to the component of efficiency defined in this study.

Growth patterns of Angus, Hereford and shorthorn cattle. I. Comparison of inbred and noninbred lines, changes in patterns over time and effects of level of inbreeding and reproductive performance.

Mature weight (A) and rate of maturing (K) were estimated for 283 Angus, 140 Hereford and 280 Shorthorn cows utilizing the asymptotic regression equation Yt=A(1-Be-Kt). The Yt was weight of the individual at age t; and B was an estimate related to early life weight changes and provided for a Y-intercept (A-B). Each breed consisted of four inbred and two noninbred lines. Regression of estimated growth curve parameters on levels of inbreeding of the individuals and of their dams and effects of early reproductive performance (EREPRO) were studied as sources of variation in addition to line differences and trends in line values over years. Considered jointly with inbreeding of the dam and with EREPRO, inbreeding of the individual was negatively related (P less than .01) to estimates of A in the three breeds and unrelated (P greater than .10) to estimates of K. Each 1% increase in inbreeding of the individual was associated with about 2 kg decrease in estimated mature weight. An increase in inbreeding of the dam of an individual was negatively related to estimates of K in Angus (P less than .01) and Shorthorns (P less than .05). Inbreeding of dams was positively related to estimates of A in the three breeds, but only in Shorthorns could the relationship be declared significant. Estimates of A were about 46 kg heavier and estimates of K about .010 less for each year an individual failed to produce a calf during her first three opportunities. In general, A values declined in all three breeds during the study. Significant changes were observed in all Hereford analyses and after inbreeding was included in the Angus analysis, while inclusion of inbreeding in the Shorthorn analysis caused the change to become unimportant. The K values increased in all three breeds during the study; however, the change could be declared significant only in Herefords.

Growth patterns of Angus, Hereford and shorthorn cattle. II. Relationship of growth patterns of dams with progeny performance.

Relationships between estimated growth curve parameters of dams and performance traits of their progeny were studied in Angus, Hereford and Shorthorn herds, each divided into four inbred and two noninbred lines. Growth curve parameters were calculated from the growth function Yt=A(1-Be-Kt), where Yt was weight at age t, A was estimated mature weight, B was an estimate related to early life weight changes and provided for a Y-intercept term and K was estimated general rate of maturing. Least-squares analyses of progeny variables were calculated separately for each breed and sex. Line differences did not influence any of the progeny variables except weaning type score of Shorthorn males (P less than .01). Birth year exerted a curvilinear effect on birth weights of Angus female progeny (P less than .01), a linear influence on 205-d weights of Shorthorn male progeny (P less than .05) and a curvilinear effect on weaning type scores of Angus and Shorthorn male progeny (P less than .01). Regression coefficients on weaning age indicated that calves born earlier in the calving season had lighter birth weights and that older calves at weaning received higher type scores. Inbreeding of the progeny negatively influenced (P less than .05) birth weights of Angus male and Hereford female progeny. Hereford male and Shorthorn female 205-d weights were negatively affected (P less than .05) by inbreeding, while weaning type scores of Shorthorn female progeny were negatively influenced (P less than .001) by inbreeding. Regression coefficients of all progeny variables on inbreeding in all analyses indicated negative trends.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of preweaning nutrition on growth of Angus calves provided a postweaning nutritional system resulting in discontinuous growth.

Postweaning growth patterns and preweaning milk and forage intake were observed over a 4-yr period for 137 Angus calves allowed either fescue-legume or fescue pastures preweaning. After weaning, calves grazed fescue pasture until spring for a slow growth phase and then fescue, orchard grass, bluegrass and ladino clover pastures for 4 mo. Following this period, the calves were confined and fed shelled corn and a 36% crude protein supplement until they reached 12 mm of fat over the 12th rib. The spring growing period and the finishing period were classified as a rapid growth phase. Calves that were fatter at weaning lost more fat, but gained more in wither height during the slow growth phase, than those that were thinner at weaning. Apparently, fatter calves were more capable of continuous skeletal growth on a low plane of nutrition because they could retrieve fat energy for this growth. In spring, calves that had been relatively fat at weaning held no advantage in fatness, but had larger frames. Therefore, during the rapid growth phase, they were able to fatten more rapidly than those that were thinner at weaning. Also, calves that were more efficient in preweaning growth had more capacity for rapid postweaning growth when restricted to relatively low quality pasture. Preweaning pasture type influenced pattern of postweaning growth. Part of this influence was associated with differences detected at weaning. An additional part was associated with efficiency of forage and milk utilization during the preweaning phase.

Genotype X environment interaction in Hereford cattle: III. Postweaning trait of heifers.

The postweaning performance of heifers from contrasting lines of Hereford cattle was compared simultaneously at Miles City, Montana and at Brooksville, Florida in an experiment designed to evaluate the importance of genotype X environment interactions in beef cattle. During Phase 1 of the study (1964 to 1973), the performance of two unrelated lines, M1 and F6, was compared at the two locations. During Phase 2 (1967 to 1974), two related lines, M1 of Montana origin and F4 derived from M1 by selection in Florida, were compared at each of the two locations. The line X location interaction term was highly significant in either Phase 1, Phase 2 or both for weaning weight, daily gain from weaning to spring, spring yearling weight, daily gain from weaning to fall, fall yearling weight, yearling condition score, conformation score, wither height, body depth, body length, shoulder width, hook width and forecannon circumference. Daily gain of yearlings from spring to fall was the only objective measurement for which the interaction term was nonsignificant in both phases. These results, consistent with the results on performance to weaning age reported previously, indicate the existence of highly significant genotype X environment interactions in beef cattle. The results indicate that genetic adaptation to the local environment is important in beef cattle production and should be considered in designing breeding programs or performance testing procedures and in interregional transfer of breeding stock.

Phenotype x nutritional environment interactions in forage intake and efficiency of Angus cows grazing fescue-legume or fescue pastures.

Forage intake, milk production, calf growth and efficiencies of milk production and calf growth were estimated for 198 lactations of 91 mature Angus cows grazing fescue-legume or fescue pastures. Cows calved January through March and calves were weaned in October in each of the 5 yr of the experiment. Cows grazing fescue-legume consumed 1.7 kg/d more (P less than .01) dry matter (DM) that was 4.6 percentage units more (P less than .01) digestible than cows grazing fescue. Cows grazing fescue-legume produced .4 kg/d more (P less than .01) milk and weaned 23.8 kg more (P less than .01) calf than cows grazing fescue. This increased production required an additional intake/cow-calf unit of 2.3 kg of digestible DM for each additional kilogram of calf weaned. Cows grazing fescue-legume were less efficient in calf production at least partially because they gained 33.3 kg more (P less than .01) weight and 1.82 mm more (P less than .01) fat cover at the 12th rib during lactation than cows grazing fescue. Cows producing relatively large amounts of milk consumed more digestible DM, weaned heavier calves, and were more efficient producers of milk and weaned calf regardless of pasture type grazed. The influence of milk production on these variables was more dramatic for cows grazing fescue than for those grazing fescue-legume. Cow type favoring maximum conversion of digestible DM intake by cow and calf to calf gain was different for the two types of pasture. For cows grazing fescue, those having either small amounts of fatness or having small structural sizes, regardless of milk production, were the most efficient. Structural size was not related to efficiency for cows grazing fescue-legume. Fatness had little influence on efficiency of low milking cows. The relationship of structural dimension and efficiency for cows grazing fescue was due to interrelationships of structural dimension, change in cow weight and fatness during lactation, and calf weaning weight: cow weight ratio. Relationships between efficiency and fatness could not be attributed to these variables.

Impact of numbers and frequency of weighings on bovine weight-age curve parameters.

Estimates of mature weight (A) and maturing rate (K), determined by asymptotic regression, were studied to evaluate the effects of using quarterly weights taken in different seasons of the year for estimating growth curve parameters. Quarterly weights of 102 Angus cows were used to calculate eight sets of weight-age curves. Four sets of estimates were calculated from weights from birth to 5 yr of age (FIVE-YEAR curves) and four sets were calculated from all weights collected throughout the life of each cow (LIFETIME curves). Within each age group, one set of parameters was estimated from all weights up to the respective ages (FIVE-YEAR and LIFETIME). The other three sets, within each age, were based on quarterly weights from birth to 1 yr of age plus one weight/year taken during the summer, fall or winter. The symbols A and K were used with the following subscripts: 0 or 5 as a first digit to represent weight-age parameters estimated from all weights taken during the life of the cow and from weights taken before the cow was 5 yr old, respectively; and 0, 2, 3, or 4 as a second digit to represent all quarterly weight, summer, fall or winter weights, respectively. Mean estimates of mature weight were 496, 492, 492, 522, 483, 478, 487 and 508 kg for A00, A02, A03, A04, A50, A52, A53, and A54, respectively. Season of weighing affected both A and K. Coefficients of correlation among the estimates of mature weights were all positive and larger than .70. Coefficients of correlation among estimates of rate of maturing were larger than .50, except those involving the correlation of K00 and FIVE-YEAR estimates. This study indicates that weight-age characteristics estimated from quarterly weights from birth to 1 yr of age and a single annual weight from 1 to 5 yr are adequate for estimating practical weight-age parameters at an early cow age. However, in FIVE-YEAR estimates, the effect of a cow's being nonpregnant at 2, 3 or 5 yr of age and, in LIFETIME estimates, any open year, especially the terminal year, may result in serious bias.

Patterns of change in mature Angus cow weight and fatness during the year.

Postcalving cow weight and subcutaneous fatness change patterns were described for 80 mature spring-calving Angus cows. The cows grazed either high (regularly clipped fescue-legume) or low (fescue clipped once) quality pastures. Forage consumption was estimated continuously by an internal (acid detergent lignin)-external (Cr2O3) indicator technique. Milk production (calf-suckle technique) was estimated seven times during lactation. Wither height was measured during the fall after the period of intensive measurment. Angus cows grazing high quality pasture lost an average of 36 kg postcalving, whereas those grazing low quality pasture lost an average of 22 kilograms. Minimum weights were observed about April 1, prior to the season of large pasture quality differences in digestibility of consumed forage. Taller cows, when allowed increased nutrient density during midlactation (high versus low quality), responded by increasing (P < .05) fatness at a more rapid rate than less tall cows. For cows grazing high quality pasture, weight change was independent of level of milk production. Cows grazing low quality pasture and giving relatively large amounts of milk maintained less weight and fat during the middle and last part of lactation than did those giving smaller amounts of milk. Shapes of the curves depicting change in weight and fatness were closely related (P < .01) to digestible dry matter intake. Cows apparently consumed forage in such a manner that they became more alike in both weight and fatness as the grazing season progressed.