Biomedical subjects

R M Bourdon

Publications and source records attributed to R M Bourdon.

8 recordsLinked to original sources

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↗

PubMed1991

Variation among twin beef cattle in maintenance energy requirements.

The genetic variation in energy expenditures of cattle at fasting (FHP) and maintenance (MEm) was determined by using 12 pairs of monozygous twins at 20 mo of age. The pairs were of two breed types, eight Angus x Hereford (three steers, five heifers) and four Barzona x Hereford (three steers, one heifer). The heifers were 132 +/- 13 d pregnant at the time of measurement. The pairs were fed at 1.15 x maintenance energy requirements for a minimum of 30 d prior to heat production (HP) measurements in dual indirect respiration calorimetry chambers. The diet fed was cracked corn:alfalfa hay (45:55) with a determined ME of 2.47 +/- .02 Mcal/kg DM. This diet was fed individually for 7 d prior to and during two consecutive 22-h HP measurements. The animals then were fasted for 2 d and fasting heat production measurements (FHP) were made on d 3 and 4 of the fast. Metabolizable energy required for MEm was calculated iteratively by assuming a semi-log relationship between HP and metabolizable energy intake. There were no differences (P greater than .10) in measured energy expenditures due to different breed type. The FHP and efficiency of ME use for MEm (Km) were similar between sexes, although heifers had lower (P less than .025) MEm than steers. Twin pair effects were detected for FHP (P less than .005) and MEm (P less than .05) but not for Km. Broad sense heritability estimates were calculated as the intraclass correlation between members of monozygous twin pairs. Heritability estimates for MEm, FHP, and Km were .52 +/- .22, .75 +/- .13, and .34 +/- .27, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Animal Feed↗

PubMed1991

A performance programmed method for computing inbreeding coefficients from large data sets for use in mixed-model analyses.

Coefficients of inbreeding are commonly used in mixed-model methods for forming inverses of Wright's numerator relationship matrix and transformation matrices used in variance component estimation and national cattle evaluation. Computation of exact coefficients of inbreeding from very large data sets has been believed to be too expensive or too difficult a task to perform. Approximate methods have been used instead. The effects of using approximation methods for inbred data that appear in national cattle data sets are demonstrated. An algorithm is given for the computation of inbreeding coefficients for large data sets. The algorithm feasibly computes inbreeding coefficients for large data sets even on small computing architectures.

Algorithms↗

PubMed1990

Genetic analysis of absolute growth measurements, relative growth rate and restricted selection indices in red Angus cattle.

Performance records on 41,184 Red Angus cattle were analyzed and estimates of parameters calculated for absolute growth rate, relative growth rate and restricted selection indices. Heritability estimates for birth weight, 205-d weight, 365-d weight and postweaning gain were .46 +/- .02, .39 +/- .02, .40 +/- .02 and .36 +/- .02, respectively. Heritability estimates for preweaning, postweaning and postnatal relative growth rates were identical (.33 +/- .02). Heritability estimates for restricted selection indices were .31 +/- .02, .33 +/- .02 and .31 +/- .02 for weaning index, yearling index and postweaning index, respectively. The genetic correlation between preweaning and postweaning absolute growth rate was .15. The genetic correlation between consecutive measurements of relative growth rate (RGR) was -.33. Genetic correlations of birth weight with preweaning RGR and postnatal RGR were -.68 and -.71, respectively. Correlations among measures of relative growth rate using simulated data were similar to correlations of actual data, indicating that these relationships are the result of numerator/denominator relationships and not biological causes. The genetic correlation between weaning and postweaning indices was near zero. Small genetic coefficients of variation for preweaning and postnatal relative growth rates indicate further problems with the expression of growth in this manner. Restricted selection indices exhibited much larger genetic coefficients of variation than measurements of RGR. Genetic standard deviations were 7.8%, 7.2% and 13.7% of the means for weaning, yearling and postweaning indices, respectively.

Animals↗

PubMed1987

Simulated efficiency of range beef production. I. Growth and milk production.

A revised version of the Texas A&M University Beef Cattle Production Model was used to simulate the effects of growth, milk production and management system on biological and economic efficiency of beef production in a northern plains, range environment. Animals varying in genetic potential for birth weight (BWA), yearling weight (YW), mature weight (WMA) and milk production (PMA) were simulated under both a weanling system of management (weaned calves custom-fed in the feedlot) and a yearling system (calves wintered on the ranch, then custom-fed after their second summer). The yearling system of management was biologically less efficient, but economically more efficient than the weanling system due primarily to heavier slaughter weights of fed animals. The advantage of the yearling system was most apparent for smaller genotypes. Herd efficiency improved with decreased BWA and increased YW, but changed little when WMA was varied while other growth traits were held constant. Increased PMA was favored for production of live weight at weaning and for production of slaughter product when feedlot costs were high. Increased PMA was not favored when feed costs for the cow herd were high. Economic weights generated from the simulation indicated the importance of selection for rapid early growth followed by selection for lighter birth weight. While larger genotypes were generally favored in this study, optimal cow size depended on economic conditions. Larger types were more biologically efficient and more economically efficient using standard costs, but medium- and small-size cattle were more efficient when feedlot costs were high. Small cattle were least efficient when feed costs for the cow herd were high.

Animal Husbandry↗

PubMed1987

Simulated efficiency of range beef production. II. Fertility traits.

A modified version of the Texas A&M University Beef Cattle Production Model was used to simulate the effects of changes in potential for age at puberty (AAP), potential for probability of conception (PCA) and winter feed levels on biological and economic efficiency of beed production in a northern plains, range environment. Two management systems were simulated: a weanling system in which all calves except replacement heifers were custom fed in a feedlot immediately post-weaning; and a yearling system in which calves were kept on the ranch through their second summer, then custom-fed. Biological efficiency was defined as the ratio of TDN input to product output, and economic efficiency was defined as the ratio of total dollar cost to 100 kg product output. A simulated increase in AAP from 365 to 425 d resulted in slightly decreased economic efficiency under a yearling system of management. An increase in PCA from .75 to .85 caused decreased biological efficiency under both weanling and yearling management systems, suggesting biological inefficiencies associated with maintaining mature cows. Simulation results indicate that optimal supplementation levels and corresponding levels of observed fertility depend on the value of product derived from cull cows relative to the value of product derived from fed animals and on the costs of developing replacement heifers relative to the costs of maintaining mature cows. Decreased fertility causes change in the sources of products, not product loss per se. For this reason, survivability may be a more important aspect of reproduction than fertility.

Animal Husbandry↗

PubMed1987

Simulated efficiency of range beef production. III. Culling strategies and nontraditional management systems.

A modified version of the Texas A&M Beef Cattle Production Model was used to simulate life-cycle biological and economic efficiency of various culling strategies and non-traditional management systems in a northern plains, range environment. Biological efficiency was defined as the ratio of TDN input (kg) to product output (kg), and economic efficiency was defined as the ratio of cost ($) to product output (100 kg), where products were live weight at weaning (LWW), empty body weight at slaughter (EBW) and fat-free weight at slaughter (FFW). Several economic scenarios were simulated. Culling cows at younger ages increased biological efficiency, but not necessarily economic efficiency. The simulated optimal age at culling was 8 yr, the same age at which simulated feed intake and milk production began to decline. Finishing young cows in the feedlot had little effect on biological efficiency and generally increased economic efficiency, although specific results depended on feed prices and relative values of cull cows vs fed animals. A simulated sex-controlled system in which only heifer calves were produced, while extremely biologically efficient for production of lean, resulted in relatively little output and was not economically efficient in most cases. Sex control combined with feeding of 2-yr-old cows was economically efficient, but not markedly more efficient than a conventional system. Results suggest that sex-controlled systems may be more appropriate where emphasis is on lean product and heifers can be bred at very early ages. General results indicate that producers should pay attention to relative values of cull cows and fed animals in choosing culling strategies and management systems.

Animal Husbandry↗

PubMed1986

Scrotal circumference in yearling Hereford bulls: adjustment factors, heritabilities and genetic, environmental and phenotypic relationships with growth traits.

Field data on 4,233 yearling Hereford bulls were analyzed using fixed and mixed model least-squares procedures to examine factors affecting scrotal circumference; determine appropriate adjustment factors; and study genetic, environmental and phenotypic relationships among scrotal circumference and growth traits. Scrotal circumference was affected by postweaning feed level; contemporary group/feed level; age of dam; and covariates age, weight and height. Of the three covariates, weight had the greatest effect, and any factor which caused an increase in weight tended to increase scrotal circumference. Quadratic effects of age, weight, height and age X age of dam interaction effects were significant or approached significance, but were of minor importance. Large contemporary group effects suggested the need for expressing scrotal circumferences as trait ratios or as deviations from contemporary group means. Scrotal circumference adjustment factors recommended for yearling Hereford bulls were .026 cm X d-1 of age and .8, .2 and .1 for sons of 2-, 3- and 4-yr old dams, respectively. Heritability of weight-adjusted scrotal circumference was .46 +/- .06 compared with .49 +/- .06 for age-adjusted scrotal circumference, indicating considerable additive genetic variation for relative scrotal size. Correlations between scrotal circumference and growth traits were moderate to high. The genetic correlation between scrotal circumference and yearling weight was the highest of these at .44 +/- .16. Potential implications of this relationship are discussed.

Animals↗