Biomedical subjects

T J Lawlor

Publications and source records attributed to T J Lawlor.

13 recordsLinked to original sources

PubMed1999

Supply of genetic information--amount, format, and frequency.

The volume and complexity of genetic information is increasing because of new traits and better models. New traits may include reproduction, health, and carcass. More comprehensive models include the test day model in dairy cattle or a growth model in beef cattle. More complex models, which may include nonadditive effects such as inbreeding and dominance, also provide additional information. The amount of information per animal may increase drastically if DNA marker typing becomes routine and quantitative trait loci information is utilized. In many industries, evaluations are run more frequently. They result in faster genetic progress and improved management and marketing opportunities but also in extra costs and information overload. Adopting new technology and making some organizational changes can help realize all the added benefits of the improvements to the genetic evaluation systems at an acceptable cost. Continuous genetic evaluation, in which new records are accepted and breeding values are updated continuously, will relieve time pressures. An online mating system with access to both genetic and marketing information can result in mating recommendations customized for each user. Such a system could utilize inbreeding and dominance information that cannot efficiently be accommodated in the current sire summaries or off-line mating programs. The new systems will require a new organizational approach in which the task of scientists and technicians will not be simply running the evaluations but also providing the research, design, supervision, and maintenance required in the entire system of evaluation, decision making, and distribution.

Animals↗

PubMed1998

Effect of full sibs on additive breeding values under the dominance model for stature in United States Holsteins.

Differences in breeding values between dominance and additive models were examined theoretically and with field data. Data included 5.2 million records on stature from 3.0 million US Holsteins. The largest full-sib family had 29 animals, and 7% of all animals had at least one full sib. The dominance model, which accounted for dominance covariances, included the following effects: management, age, stage of lactation, permanent environment, animal additive, and parental dominance (one-quarter of dominance variance) as well as a regression coefficient for inbreeding percentage. Two reduced models were also assumed; in the first, the parental dominance effect was removed, and, in the second, the inbreeding regression coefficient was also removed. The correlations between breeding values in the three models were > 0.999, but breeding values of some animals from full-sib families changed > 5 standard deviations of parental dominance. The largest changes were observed for parents with large numbers of full-sib progeny, with limited information from parents, and without individual performance records. On average, the differences were up to four times larger for cows than for bulls and up to five times larger for dams than for sires. The greatest differences in breeding values between the dominance and the additive models were observed for dams with full-sib progeny, female full sibs, and low reliability bulls with full sibs in the extended family. Animals with large amounts of additive information as progeny-tested bulls were influenced little by the inclusion of dominance. Animals with a large proportion of information coming from animals with dominance relationships, such as cows originating via embryo transfer changed the most.

Animals↗

PubMed1998

Blood groups and milk and type traits in dairy cattle: after forty years of research.

This study addresses the utility of 11 blood groups as selection aids in Holstein breeding schemes and considers issues inherent to the approach of resolving quantitative variation into components that are due to quantitative trait loci. The data consisted of predicted transmitting abilities of 22,614 bulls, first lactation information on 1,924,171 cows, and type scores on 447,800 cows. Linear models were fitted under male half-sib designs, female half-sib designs, and granddaughter designs as well as under the assumption of direct effects of the markers. The evolution of allele frequencies through time was determined, and previous research results were synthesized according to criteria of consistency of biological significance. The inconsistency of results across studies and analytical designs alludes to the importance of the intrinsic nonadditivity of genetic and biological phenomena to quantitative trait locus detection and marker-assisted selection. In our analyses, three associations met the criteria of consistency--a C blood group effect on rump angle, an L effect on milk yield and composition traits, and an S effect on milk fat yield. The M locus appears to be directly associated with effects on milk and protein yields. An enhanced understanding of the biochemical and physiological bases of quantitative genetics should be a long-term objective of this type of genetic analysis.

Animals↗

PubMed1998

Trait-based analysis in dairy cattle using blood group polymorphisms.

The potential of trait-based analysis to detect quantitative trait loci was investigated using blood group polymorphisms as the marker systems and milk and type traits in Holstein cattle as the quantitative traits. Within large half-sib families, animals were ranked on their predicted transmitted abilities or phenotypes, and blood group allele frequencies were compared between the upper and lower 5% tails of the distributions. Genotype frequencies within large families were also examined for evidence of selection. All of the major effects that had previously been detected using linear model analyses were identified by the trait-based analyses of a C blood group effect on rump angle, an L effect on milk yield and composition traits, an S effect on milk fat yield, and a direct effect of the M locus on milk and protein yields. These results provide additional support for the biological validity of these associations and also demonstrate the utility of trait-based analysis for the detection of quantitative trait loci within existing dairy breeding programs. However, just as in the linear model analyses, an analytical strategy should be utilized that allows the identification of the effects that are consistent across environments and genetic backgrounds.

Alleles↗

PubMed1998

Use of linear type and production data to supplement early predicted transmitting abilities for productive life.

Genetic evaluations for the length of productive life based on actual DHIA culling data have been available in the US since January 1994. Although substantial genetic variation in productive life exists, the reliability of selection is often low, particularly for recently progeny-tested bulls having daughters that have not yet had an opportunity to be culled. Correlated production and conformation traits, which have higher heritability than productive life and are available earlier in life, may be used to enhance evaluations of productive life for young bulls that have little or no direct culling information available. Genetic correlations between productive life and milk, fat, dairy form, and udder traits ranged from +0.22 to +0.46. The maximum reliability of the indirect prediction of productive life from 16 correlated type and production traits was 0.56, and the maximum reliability from a subset of 10 traits was 0.51. Indirect information about productive life that was derived from type and production traits was combined with actual culling information to increase the total amount of available information for many recently progeny-tested bulls. The procedures described herein for enhancing direct evaluations for the productive life of dairy sires with indirect information about production and type were implemented by the USDA Animal Improvement Programs Laboratory and the Holstein Association USA in July 1994.

Animals↗

PubMed1997

Dominance models with method R for stature of Holsteins.

Estimates of variance components were obtained with method R for several additive and dominance models. The data included 301,960 records for first parity and 280,040 records for later parities of Holsteins. The single-record model included effects of management, regression on inbreeding percentage, age at calving, stage of lactation, and additive and dominance effects. The repeatability model included these effects in addition to permanent environment. For the single-record model, estimates were 46% of the total variance for additive variance, 12% of total variance for dominance variance, and -0.06 for the regression coefficient on inbreeding. In the repeatability model, the variance for permanent environment was estimated at 5%; other estimates were similar. When the dominance effect was eliminated, the estimate of the variance for permanent environment increased to 17% for the repeatability model. Elimination of stage of lactation increased regression on inbreeding to 0.09 and the estimate of dominance variance to 17% in the single-record model. The same change increased the estimate of additive variance to 64% for the repeatability model. Elimination of regression on inbreeding or stage of lactation had a small effect on the estimates. The presence or absence of the dominance effect had little influence on additive variance. In the absence of dominance, the estimate of the permanent environment effect included the dominance effect. Estimates of variances with method R are very sensitive to age adjustments. With the adjustments, the estimates of the dominance and additive variances are consistent.

Aging↗

PubMed1994

Adjustment for heterogeneous variance in genetic evaluations for conformation of United States Holsteins.

A method was developed to account for heterogeneous phenotypic variance for final type (conformation) score within herd-year-month-classifier subclasses for national genetic evaluations of US Holsteins. Phenotypic variances decreased 3.5-fold as within-subclass means increased from 70 to 89 points, and variances increased slightly over time and with increases in subclass size and proportion of registered animals. A model containing known management characteristics was fitted to phenotypic standard deviations within subclass, and resulting solutions were used to estimate the prior variance for each subclass. Prior estimates and phenotypic variance estimates within subclass were combined using Bayesian methods, resulting in posterior estimates that contained more information than either the prior estimates or the within-subclass statistics. Observations were standardized to a common variance using the mean of the posterior density of the phenotypic standard deviation within subclass. Moderate changes in PTA occurred for low reliability bulls, bulls with many progeny in a single herd, and foreign bulls subjected to positive assortative mating. Significant increases occurred in PTA of superior cows in subclasses with high means. Incorporation of a heterogeneous variance adjustment into national genetic evaluations should increase fairness of selection among cows and young bulls and may increase the rate of genetic gain from female selection.

Aging↗

PubMed1992

Genetic parameters of conformation traits, milk yield, and herd life in Holsteins.

Genetic parameters were estimated simultaneously for 5 herd-life traits, 15 conformation (type) traits, and milk yield measured in first lactation for 128,601 Holstein cows. Heritabilities of all traits were higher in registered than in grade cows. Genetic correlations of linear type traits with first lactation yield ranged from -.48 for udder depth to .54 for dairy form. Genetic correlations among milk yield and herd-life traits were all positive except for milk-corrected herd life in grade cows. Udder traits had largest absolute genetic correlations with herd-life traits, followed by body traits and feet and leg traits. Some traits associated with body size and foot angle differed between registered and grade cows. Estimates of genetic trends from obtained parameters revealed greatest progress for milk yield from single-trait selection but also the largest changes for some type traits and milk-corrected herd life in an undesirable direction. Relative milk to type ratios of between 2:1 and 3:1 yielded 90% of the gain in milk yield with no change or slight improvement in type traits and functional herd life. Selection for type traits associated with herd life appears to be warranted to improve days of functional herd life or to decrease involuntary culling of dairy cows.

Animals↗

PubMed1992

Use of reproductive technology to estimate variances and predict effects of gene interactions.

Advanced reproductive techniques are creating the large numbers of close relatives needed to study gene interactions. Identical triplets, a set of 26 full sisters, a family of 4215 three-quarter sisters (same sire and maternal grandsire), a family of 76,698 half sisters, and 1.6 million granddaughters of Round Oak Rag Apple Elevation now have lactation records. Similarity of closest relatives might be explained by similar nonadditive as well as additive genetic merit. The 23,015 families of full sisters with mean family size of 3 provide nearly as much information about dominance variation as do the 55,779 families of three-quarter sisters with mean family size of 13; the 79 families of clones provide little information by comparison. Hypothetically, REML analysis of all US Holstein data could provide estimates of dominance and additive x additive variance with standard errors approximately 1% of phenotypic variance, but estimates of any higher order interactions would have standard errors greater than 10%. The tilde-hat approximation proved to be incompatible with animal models but was used for sire-maternal grandsire analysis of 765,868 first lactation records. Dominance variance was estimated as 3.5% of phenotypic variance for milk and 3.3% for fat with standard error of 4.2%. With constant data set size, variances are estimated most precisely if family sizes equal 1 plus ratio of within-family to between-family variance. An animal model evaluation including dominance relationships for 581,670 animals was computed, but gene interactions from distant ancestor pairs were ignored. Mating advice and improved additive predictions, especially for clones, could be obtained by including dominance in models.

Animals↗

PubMed1991

Correlations among linear type traits and somatic cell counts.

Genetic and phenotypic correlations between linear type traits and SCC were estimated from lactation average SCC from Pennsylvania DHIA and Holstein linear type evaluations from Sire Power, Inc. and Holstein Association using REML. Correlations were estimated between linear type traits and SCC measured in first lactation and between linear type traits measured in first lactation and SCC measured in second or third lactation. Data sets ranged in size from 4294 daughters of 216 sires to 58,235 daughters of 301 sires. Phenotypic and genetic correlations between the linear traits that reflect body and locomotive characteristics and SCC were generally small and unimportant. Phenotypic correlations between udder traits and SCC were variable, but cows with higher udder depth scores (higher udders) had lower SCC. Genetic correlations between udder traits and SCC were also variable. Genetic correlations between SCC and udder depth, SCC and fore udder attachment, and SCC and teat placement were negative (favorable). Genetic correlations between teat length and SCC tended to be positive. Genetic correlations were largest in magnitude between udder depth and SCC and ranged from -.21 to -.64 (weighted mean = -.35). Selection for higher udders and closer teat placement will likely improve resistance to mastitis in dairy cattle.

Animals↗

PubMed1990

Prediction of transmitting abilities for Holstein type traits.

Heritabilities and genetic and phenotypic correlations among 14 linear type traits were estimated from Holstein Association data by multiple trait REML. Data used for parameter estimation were records of 779,391 daughters of 871 sires included in the January 1988 sire evaluation. Each daughter was represented by her appraisal closest to 30 mo of age. Highest heritability was .37 for stature, and lowest was .10 for foot angle. Gains in reliability from using correlated traits in multiple trait prediction were large for some traits (up to 60% for foot angle for cows). Final score variance parameters were estimated from 953,596 records, which were 43% of records included in the national sire evaluation. Sire models that adjusted or did not adjust for merit of mates were compared. Heritability of final score was .27 with adjustment for merit of mates by subtraction of predicted transmitting ability of dam from daughter's record compared with .29 if mate was ignored. Evaluations for type for several popular older sires were reduced moderately by adjustment for merit of mates, but estimated genetic trend increased slightly. An improved genetic grouping procedure that considers group effects as inherited was adapted for use in sire models. Parameter estimates and models presented were implemented by the Holstein Association for computing July 1988 genetic evaluations for linear traits and final score.

Analysis of Variance↗

PubMed1987

Genetic evaluation of dairy goat does for milk and fat as an extension of buck evaluation.

The current procedure for calculating genetic evaluations of dairy goat bucks provides easily accessible information for constructing genetic evaluations for dairy goat does (doe indexes). Relationships among sires are accounted for by using the additive genetic relationship matrix among sires if the doe's sire was evaluated. The sire evaluation plus a portion of residual doe effect is the basis of doe evaluation. Although direct incorporation of maternal relationships among does may be accomplished, it requires extensive computations for large data sets. An approximate procedure based on selection index principles includes information from a doe's dam with only a modest increase in computing expense over that for genetic evaluations of bucks. Doe indexes were computed and adjusted to separate breed bases. Trend in doe indexes was positive for all breeds and ranged from .54 to 1.37 kg/yr for milk yield and from .021 to .052 kg/yr for fat yield.

Animals↗

PubMed1984

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

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

Animal Population Groups↗