Biomedical subjects

L V Cundiff

Publications and source records attributed to L V Cundiff.

At least 91 records · Page 5Linked to original sources

PubMed1993

Challenges and opportunities for integrating genetically modified animals into traditional animal breeding plans.

Techniques have been developed to introduce specific genes from one species into the germplasm of another, including livestock. This paper reviews reports on evaluation, selection, and breeding procedures for introduction and multiplication of transgenes in breeding populations of livestock. Before transgenes are introduced and multiplied in commercial breeding populations, it is necessary to test transgenics extensively for both favorable and unfavorable transgene effects. Parent stock used to produce transgenic founder animals should be selected to excel in polygenic breeding value for economically important traits, especially if founder animals or their sons are to be used directly by AI in commercial populations. However, polygenic breeding value of founder transgenic animals and inbreeding depression are of negligible importance if a transgene is introgressed into a selection nucleus population from three or four generations of backcrossing. Transgenic development should be economically viable for traits with major effects on net merit, especially in the dairy industry, where transgenic sires can be used extensively by AI. A minimum effect of about 10% of the mean (or one phenotypic standard deviation) is a reasonable approximation of the minimum transgene effect that would be necessary to justify introgression into a nucleus swine population. A transgene effect of 10 to 20% of the mean would be required for most economic traits in beef cattle.

Animals↗

PubMed1992

Genetic effects on beef heifer puberty and subsequent reproduction.

Significant genetic variation exists within and between breeds of beef cattle for age at puberty (AP). In general, faster-gaining breed groups of larger mature size reach puberty at a later age than do slower-gaining breed groups of smaller mature size; breeds selected for milk production reach puberty at younger ages than do those breeds not selected for milk production. Heterosis, independent of heterosis effects on weight, influences most measures of puberty in females and scrotal circumference (SC) in males. Crossbred heifers reach puberty at younger ages and heavier weights than their straightbred counterparts. Scrotal circumference has been shown to be an excellent indicator of AP in yearling bulls. Furthermore, a favorable genetic relationship exists between SC in bulls and AP of female offspring. Beef cattle breeders may take a direct approach to breeding for AP and subsequent reproduction by directly selecting for measures of fertility such as SC. However, an indirect approach, involving selection for an array of traits that provide an appropriate "genetic environment" for the expression of fertility (i.e., size, milk production, calving ease) may be preferred. Although seedstock producers are limited to making change through within-breed selection, commercial producers can take advantage of both within- and between-breed selection as well as crossbreeding to achieve the same goal.

Age Factors↗

PubMed1992

Estimated breeding values for meat characteristics of crossbred cattle with an animal model.

Longissimus muscle area, shear force measure, and sensory panel scores for flavor, juiciness, and tenderness, and marbling score were obtained from 682 steer carcasses, resulting from crosses among five Bos taurus and Bos indicus breeds. The single-trait model used included birth year and as covariates breed fractions, weaning age, and days on feed. The numerator relationship matrix was for 1,350 animals (682 steers, 74 pure breed and 52 F1-cross sires and 542 dams). The coefficient matrix was inverted to examine standard errors of prediction. Estimated breeding value is the sum of the estimate of genetic deviation and the weighted (fractions) sum of estimates of breed effects. Heritabilities used in estimating breeding values were .62, .06, .05, .11, .05, and .43 for longissimus muscle area, shear force, flavor, juiciness, tenderness, and marbling score. Sires within a breed or crossbred group tended to rank similarly due to large differences among breed effects (e.g., the six Sahiwal sires ranked in the highest six places for shear force). These results illustrate that for traits with large breed differences, selection of the proper breed should be done before selection within that breed.

Animals↗

PubMed1992

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

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

Age Factors↗

PubMed1992

Breed effects and heterosis in advanced generations of composite populations on actual weight, adjusted weight, hip height, and condition score of beef cows.

Heterosis effects were evaluated in three composite populations in F1, F2, and F3 generations separately and combined in 1-yr-old and from 2- through greater than or equal to 7-yr-old beef cows. Traits included actual weight, weight adjusted to a common condition score, hip height, and condition score. Breed effects were evaluated in the nine parental breeds (Red Poll [R], Hereford [H], Angus [A], Limousin [L], Braunvieh [B], Pinzgauer [P], Gelbvieh [G], Simmental [S], and Charolais [C]) that contributed to the three composite populations (MARC I = 1/4 B, 1/4 C, 1/4 L, 1/8 H, 1/8 A; MARC II = 1/4 G, 1/4 S, 1/4 H, 1/4 A; and MARC III = 1/4 R, 1/4 P, 1/4 H, 1/4 A). Breed group (parental breed and composite) effects were significant for all traits analyzed. The effects of heterosis were generally important (P less than .05) for all traits in F1, F2, and F3 generations separately and combined in the three composite populations. Generally, the magnitude of heterosis observed at 1 yr of age did not differ from that observed in cows from 2 through greater than or equal to 7 yr old. Adjusting weight to a common condition score resulted in an average reduction of heterosis effects on actual weight by approximately one-fourth. Thus, approximately one-fourth of the effects of heterosis on weight result from heterosis effects on condition score. Generally, retained heterosis in the F3 generation of either 1-yr-old or from 2-through greater than or equal to 7-yr-old cows of the three composite populations did not differ (P greater than .05) from expectation based on retained heterozygosity for the traits analyzed. These results support the hypothesis that heterosis for weight, hip height, and condition score of cows of these age classes is the result of dominance effects of genes.

Analysis of Variance↗

PubMed1992

Genetic analysis of bovine respiratory disease in beef calves during the first year of life.

The prevalence of bovine respiratory disease (BRD) was assessed in a population of 10,142 beef calves representing nine pure breeds and three composite populations born in 1983 through 1988. Twenty-four percent of the calves experienced at least one episode of respiratory disease during the 1st yr of life; frequencies over the six birth years ranged from 14 to 38%. The timing of respiratory disease outbreaks differed among birth years; in 4 of the 6 yr, more illness occurred in the pasture before weaning than in the feedlot after weaning. Frequencies of BRD during preweaning and postweaning periods were analyzed separately. Pure breeds and composite populations within a single preweaning location differed in frequency of illness during the preweaning period. However, not all possible breed comparisons could be made because preweaning location differed for the breed groups, and preweaning location had a significant effect on the frequency of respiratory disease in the preweaning period. The preweaning location effect did not carry through to the postweaning period. Pinzgauers had the highest BRD frequency within the feedlot (24.6%). The heritability estimates of BRD during the preweaning and postweaning periods did not differ significantly from 0 (.10 +/- .02 and .06 +/- .07, respectively). Although it is likely that response to selection for resistance to BRD would be slight using the animal's history of BRD as the selection criterion, including information on relatives or additional immune traits may improve the accuracy of an estimated breeding value for BRD resistance.

Animals↗

PubMed1992

Economic evaluation of heterosis and culling policies for lifetime productivity in Hereford, Angus, shorthorn, and crossbred cows.

Experimental lifetime performance data obtained from 156 straightbred Hereford, Angus, and Shorthorn and 172 first-cross heifers were used to estimate heterosis for economic efficiency in a 100-cow herd at age equilibrium under three culling policies and at terminal ages from 6 to 12 yr. All nonpregnant heifers and cows greater than 9 yr of age were culled. The culling policy for removal of nonpregnant cows from second parity through 9 yr of age were 1) no culling, 2) after two consecutive years (actual), and 3) all (imposed). Efficiency was calculated as input cost per unit of output value. A 10-yr average was used for costs of replacement heifers, cow units, and the ratio of calf:cull cow prices (PR), plus higher and lower PR. Input included costs for both cow units and purchased replacements. Output value included both weaned calves and cull cows. Optimum terminal age was mainly a function of PR: 9 yr for average and high PR, but 6 through 9 yr when PR was low, regardless of culling policy or breed groups. Efficiency differences among culling policies were small for high or average PR, but more culling for infertility was beneficial when PR was low. Estimated reductions in unit costs of output value under any culling policy or terminal age were approximately 6% from crossbred cows plus another 6% from crossbred calves, or a total of 12% from specific three-breed crossing of these British breeds. Cost reductions would be somewhat less for rotation crossbreeding but greater for mating smaller crossbred cows with sires of superior growth-carcass breeds.

Age Factors↗

PubMed1992

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

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

Analysis of Variance↗

PubMed1992

Heterosis for lifetime production in Hereford, Angus, shorthorn, and crossbred cows.

The effects of maternal heterosis and maternal and grandmaternal breed effects on cumulative lifetime number and weight of calves weaned per cow entering the breeding herd were evaluated for 172 reciprocal crossbred and 156 straightbred cows of the Hereford, Angus, and Shorthorn breeds. Cows born in 1960 and 1961 were developed and mated to calve first at 3 yr of age and those born in 1962 and 1963 at 2 yr of age. Performance under actual culling of cows nonpregnant in two consecutive years and imposed culling of any nonpregnant cows were analyzed. Reproductive rates and weaning weight per calf and per cow exposed increased (P less than .05) as cows advanced from 2 through 5 yr of age, peaked at ages 5 through 9 yr, and decreased from 9 through 12 yr. Effects of heterosis did not interact (P greater than .05) with age at first calving management. During the 12-yr span in the 2-yr-old first-calving management system, crossbred cows produced nearly one more calf than straightbred cows under the actual culling policy (.97 calves, P less than .10) and .82 more calves (P less than .10) if all nonpregnant cows were culled. Corresponding cumulative calf weight weaned was 272 kg (P less than .01), or 25% more, and 232 kg (P less than .01), or 30% more, for crossbred cows than for straightbred cows. The 12-yr cumulative calf weight weaned by straightbred Angus cows exceeded that of Shorthorn cows (P less than .05) and tended to be greater than that of Hereford cows.

Animals↗

PubMed1991

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.

Animals↗

PubMed1991

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)

Animals↗

PubMed1991

Determining beef carcass retail product and fat yields within 1 hour postmortem.

Hot carcasses from 220 steers (progeny of Hereford or Angus dams mated to Angus, Charolais, Galloway, Gelbvieh, Hereford, Longhorn, Nellore, Piedmontese, Pinzgauer, Salers, or Shorthorn sires) were used to develop equations to estimate weights and percentages of retail product (RP) and trimmable fat (TF) yields. Independent variables examined were 1) 12-13th rib fat probe (12RFD), 2) 10-11th rib fat probe (10RFD), 3) external fat score (EFS), 4) percentage of internal fat estimated hot (H%KPH), 5) hindquarter muscling score (HQMS), and 6) hot carcass weight (HCW). Right sides of the carcasses were fabricated into boneless retail cuts, trimmed to .76 cm of subcutaneous and visible intermuscular fat, and weighed. Cuts were trimmed to 0 cm of subcutaneous and visible intermuscular fat and reweighed. Multiple linear regression equations containing 12RFD, EFS, H%KPH, and HCW accounted for 95 and 89% of the variation in weight of total RP at .76 and 0 cm of fat trim, respectively. When weights of RP from the four primal cuts (.76 and 0 cm of fat trim) were the dependent variables, equations consisting of 12RFD, EFS, H%KPH, and HCW accounted for 93 to 84% of the variation. Hot carcass equations accounted for 83% of the variation in weight of total TF at both .76 and 0 cm of fat trim. Furthermore, equations from hot carcass data accounted for 54 and 51% of the variation in percentage of total RP and 57 and 50% of the variation in percentage of RP from the four primal cuts at .76 and 0 cm of fat trim, respectively. Hot carcass prediction equations accounted for 72% of the variation in percentage of total TF at both fat trim levels. Hot carcass equations were equivalent or superior to equations formulated from chilled carcass traits.

Abattoirs↗

PubMed1991

Breed effects and heterosis in advanced generations of composite populations for preweaning traits of beef cattle.

The effects of heterosis for gestation length, dystocia, calf survival, birth weight, 200-d weight, and ADG from birth to weaning were evaluated in F1, F2, and combined F3 and F4 generations in three composite populations. Breed effects were evaluated for the nine parental breeds (Red Poll, Hereford, Angus, Limousin, Braunvieh, Pinzgauer, Gelbvieh, Simmental, and Charolais) that contributed to the three composite populations. Breed effects were significant for all traits evaluated except survival at birth. The large differences among breeds in additive direct and additive maternal genetic effects offer a great opportunity to use the genetic differences among breeds to achieve and maintain optimum additive genetic (breed) composition to match genetic resources to a wide range of production-marketing ecosystems. There was no heterosis for gestation length. Mean heterosis for dystocia was significant estimated in F1 but not in F2 or in the combined F3 and F4 generations. Mean heterosis was not significant in any generation for survival at birth, to 72 h, and to weaning for the F1 generation; mean heterosis was significant for survival to weaning for the F2 generation and approached significance (P = .06) for the combined F3 and F4 generations. Mean heterosis over all composite populations and heterosis for each composite population were significant in all generations for weight at birth and at 200 d and for ADG from birth to weaning. Retained heterosis was not less than expected from retained heterozygosity in composite populations for the traits evaluated. These results suggest that heterosis for these traits likely is due to dominance effects and, thus, can be attributed to the recovery of accumulated inbreeding depression in the parental breeds.

Analysis of Variance↗

PubMed1991

Heterosis for survival and dentition in Hereford, Angus, Shorthorn, and crossbred cows.

Records of 328 Angus, Hereford, Shorthorn, and first-cross cows produced from 1960 to 1963 were used to estimate heterosis (h) and individual (gI) and maternal (gM) average breed effects on cumulative survival (CS) by ages to 12 yr, longevity (L), and size (SI) and condition of incisors at 10 to 15 yr of age. Reasons for cow disposal were also studied. The 155 cows born in 1960 and 1961 first calved at 3 yr of age, and the 173 born in 1962 and 1963 first calved at 2 yr of age. Analyses for CS and L were done for both actual culling of cows open in two consecutive years (AC) and imposed culling of any open cow (IC). The model for CS and L included cow birth year-breed of cow's sire (Y-S), sires within Y-S, breed of dam (D), and D x Y-S. For SI, the model included breed of cow, year of recording, and quadratic effect of age. Linear contrasts were used to estimate h, gI, and gM for quantitative variables, and chi-square was used for discrete variables. Under both AC (P less than .05) and IC, crossbreds exceeded straightbreds in CS to 12 yr (16.7 and 8.5%) and L (1.36 and .99 yr). Estimates of gI and gM for CS and L were generally small, except for the low (P less than .05) gM of Shorthorn cows under IC. Mortality and culling for emaciation, cancer eye, or prolapse was less for crossbreds than for straightbreds and increased with age. Crossbreds had longer (P less than .01) and better (P less than .001) teeth than straightbreds. The longer productive life of crossbred cows reduces rearing costs for replacements and increases sales of calves and cull cows.

Analysis of Variance↗

PubMed1991

Differences among breed crosses of cattle in the conversion of food energy to calf weight during the preweaning interval.

The objective of this study was to determine whether F1 cows that differ in genetic potential for weight at maturity and milk yield vary in the conversion of food energy to calf weight gain. Food intakes and weight change data were recorded by pen for cows and calves from approximately 45 d postpartum. Cows assigned to the study were 7- to 9-yr-old F1s produced by top-crossing Angus, Hereford, Brown Swiss, Chianina, Gelbvieh; Maine Anjou, and Red Poll sires to either Angus or Hereford dams. Calves were sired by Simmentals. Experimental units were pens (10 to 12 cow/calf pairs); pen was replicated within breed of sire in each of 2 yr (n = 24). Calf weight gain and energy consumed by the dams differed among the F1s, as did the ratio of calf weight gain to energy consumed by the calf and cow. Angus or Hereford (35.8), Red Poll (35.7), or Maine Anjou (35.6) F1s produced more calf weight per unit of energy consumed (g/Mcal) by the cow and calf than Chianina (33.1) or Gelbvieh (33.7) F1 females; Brown Swiss cows were intermediate (34.3). Differences in food conversion efficiency exist among breed crosses. These differences seem to be associated with breed cross differences in genetic potential for milk yield and mature weight; an exception to this trend was the Maine Anjou.

Analysis of Variance↗

PubMed1991

Breed effects and heterosis in advanced generations of composite populations for puberty and scrotal traits of beef cattle.

Heterosis effects were evaluated in F1, F2, and F3 generations of females and in the F1, F2, and combined F3 and F4 generations of males in three composite populations of beef cattle. Traits included weight, height, and condition scores at different ages, percentage of females reaching puberty at 368, 410, and 452 d, adjusted age, and adjusted weight of females at puberty and scrotal circumference and paired testicular volume of males. Breed effects were evaluated for the nine parental breeds (Red Poll [R], Hereford [H], Angus [A], Limousin [L], Braunvieh [B], Pinzgauer [P], Gelbvieh [G], Simmental [S], and Charolais [C]) that contributed to the three composite populations (MARC I = 1/4 C, 1/4 B, 1/4 L, 1/8 H, 1/8 A; MARC II = 1/4 G, 1/4 S, 1/4 H, 1/4 A; and MARC III = 1/4 R, 1/4 P, 1/4 H, 1/4 A). Breed effects were significant for all traits evaluated. Heterosis was significant for weight, height, and condition score at all ages and for most measures of puberty in each generation of each composite and for the mean of the three composite populations. Heterosis for age at puberty was largely independent of heterosis effects on 368-d weight. Heterosis was significant for scrotal circumference and paired testicular volume in each generation of each composite and for the mean of the three composite populations. Heterosis effects on scrotal measurements are mediated both through heterosis effects on growth rate and through factors that are independent of growth rate. Correlation coefficients among breed group means and correlations of breed rank for scrotal measurements with puberty traits of females were greater than or equal to .88 (P less than .01) for all puberty traits except weight at puberty, which was not associated with scrotal measurements. There was close agreement in heterosis observed for most traits and expectation based on retained heterozygosity. These results support the hypothesis that heterosis in cattle for size, puberty, and scrotal measurement traits is due to dominance effects of genes.

Analysis of Variance↗

PubMed1991

Evaluation of between- and within-breed variation in measures of weight-age relationships.

Variation between- and within-breeds was evaluated for accretion of weight from birth to 7 yr of age and hip height at 7 yr for 1,577 cows sired by Angus, Brahman, Brown Swiss, Charolais, Chianina, Gelbvieh, Hereford, Jersey, Limousin, Maine Anjou, Pinzgauer, Sahiwal, Simmental, South Devon, and Tarentaise and from either Angus or Hereford dams. Parameters from Wt = A (1 - Be-kt) were estimated by nonlinear regressions and provided estimates of mature body weight (A) and rate of weight accretion relative to change in age (k) for each cow. Actual weight at birth, linear adjusted weights at 200, 365, and 500 d of age, ratios of these weights to mature weight, and height at the hip at 7 yr were analyzed. Beyond 20 mo, weights were adjusted to a constant condition score within breed of sire. Variance and covariance components were derived for breed (sigma 2 b), sires within breed (sigma 2 s), and progeny within sire (sigma 2 w). For all traits, the sigma 2 b estimate of genetic variance ranged from two to four times greater than the variance component for sigma 2 s. Between-breed heritabilities were .91 +/- .27 and .54 +/- .17 for A and k, respectively. Estimates of within-breed heritability for these two traits were .61 +/- .11 and .27 +/- .09. Estimates, both between- and within-breed, of the genetic correlation between A and k were moderate to large and negative; those between A and weights at 200, 365, and 500 d and height at maturity were large and positive. Selection for immediate change in measures of growth would be most effective among breeds. Sufficient direct genetic variation exists between breeds to enhance breed improvement of growth characters through breed substitution. Greater opportunity to alter the shape of the growth curve exists through selection for within-breed selection than through breed substitution.

Aging↗

PubMed1991

Output/input differences among nonpregnant, lactating Bos indicus-Bos taurus and Bos taurus-Bos taurus F1 cross cows.

Nonpregnant F1 crossbred cows, progeny of either Hereford (H) or Angus (A) dams and sired by Brahman (Bm), Sahiwal (Sw), Pinzgauer (Pz), H, or A sires, were fed to maintain initial weight while rearing Charolais (C)-sired progeny for a period of 126 d in drylot commencing at about 48 d postpartum. Cow-calf pairs were assigned to equalize cow age, calf sex, and breed of cow's dam among three replicate pens of approximately 12 pairs each. Cows and calves were weighed every 2 wk and feed intake was adjusted to minimize change in cow weight. Metabolizable energy (ME) consumption for zero cow weight change was estimated by regression. Milk production was estimated by weight-suckle-weigh at 58, 85, 125, and 170 d of lactation. Calf gain (GAIN, kg) relative to cow weight (CWT1, kg) was higher (P less than .01) for calves from Bm-X (139.5/585) and Sw-X (132.2/534) than for calves from Pz-X (127.2/552) and HA-X (116.9/547) cows. Estimated mean daily production of milk was 7.40, 7.15, 7.28, and 6.37 kg for the Bm-X, Sw-X, Pz-X, and HA-X, respectively. Total cow ME intake (TMEcow) for breed groups ranked (P less than .05) with cow size and milk production, and calf creep-feed intake (FMEcalf) was inversely related to estimated milk intake. Proportion of total feed ME (TMEcow+calf) consumed by calves was higher (P less than .05) for HA-X cows (18%) than for the others (14%). Total efficiency of calf gain in weight (GAIN/TMEcow+calf) was 11% greater (P less than .05) for crossbred cows of Bos indicus X Bos taurus (Bm-X, Sw-X) than for Bos taurus X Bos taurus (Pz-X, HA-X) cows (35 vs 32 g/Mcal) in the 126-d lactation period.

Adipose Tissue↗