Biomedical subjects

J I Weller

Publications and source records attributed to J I Weller.

52 records · Page 3Linked to original sources

PubMed1993

Effects of recombinant bovine somatotropin under conditions of high production and heat stress.

The effect of bST injection on milk production of Israeli Holsteins was tested under conditions of mean production > 9000 kg/yr and climatic stress; mean maximum and minimum summer temperatures are 38 and 25 degrees C, respectively, in the Jordan Valley, located 200 m below sea level. In 1989, 111 cows were injected, and 115 cows were recorded as controls. In 1990, 108 cows were injected, and 93 cows were included as controls. Fifty-nine of the cows injected in 1990 were also injected in 1989. Production records were corrected for parity, calving month, days to first injection, and days in milk. Injection with bST increased total lactation milk production by 12%, fat production by 15%, and protein production by 13%. Injection also resulted in slight increases in fat and protein percentages. Daily milk production during the injection period was increased by 4.4 kg. Injection during the previous lactation slightly decreased production of cows injected during the following lactation. Advancing the commencement of injection from the 4th to the 2nd mo in milk did not affect total lactation production. Weight gains and dry matter intake were higher for injected cows, but body condition score was higher for the control group. Injection had no discernible effect on fertility variables.

Animals↗

PubMed1992

On the use of the moments method of estimation to obtain approximate maximum likelihood estimates of linkage between a genetic marker and a quantitative locus.

The approximate maximum likelihood method of Luo & Kearsey (1989) to determine the parameters of a segregating quantitative trait locus (QTL) in an F2 population by linkage to a genetic marker is compared to the 'true' maximum likelihood estimates derived by scanning the seven parameter likelihood space. The two methods did not yield identical results, and diverged markedly for a dominant QTL loosely linked to the genetic marker. Further study is suggested to evaluate other methods that do not simultaneously maximize the likelihood for all parameters.

Genetic Linkage↗

PubMed1992

Genetic and environmental relationships among somatic cell count, bacterial infection, and clinical mastitis.

Incidence of bacterial infection in 9784 lactations of 7763 cows in 31 herds, SCC in 32,448 lactations of 19,764 cows from 54 herds, and incidence of first parity mastitis recorded in the first lactations of 148,143 cows in 828 herds were analyzed. Bacterial infection was analyzed dichotomously by both threshold and linear models. The effects of parity, season, stage of lactation, and parity by stage of lactation interaction on SCC were estimated. Heritability of mean lactation log SCC--corrected for the effects of parity, season, and stage of lactation--varied from .13 to .27 for all parities in different data sets. Heritability of bacterial infection was .04 for the threshold model and .02 for the linear models. Heritability of field-recorded mastitis was .01. The genetic correlation between bacterial infection and SCC was near unity, but the genetic correlation between SCC and mastitis was .3. Selection for lowered SCC should reduce incidence of bacterial infection by 2% per unit of selection intensity.

Animals↗

PubMed1992

Genetic analysis of fertility traits in Israeli Holsteins by linear and threshold models.

Conception rates of Israeli Holstein cows and heifers were analyzed separately by linear and threshold models. Fixed effects for both data files were insemination number, AI institute, geographical region, and calendar month. Analysis of cows also included the fixed effects of parity, calving status, and DIM at insemination. Random effects included in the models were herd-year-season, insemination technician, sire of cow, and service sire. Fixed effect solutions for heifers and cows were not similar. For cows, insemination month had the greatest effect on conception rate. Heritability of conception rate ranged from 2 to 3.5% for heifers and from 1 to 2% for cows. Correlations between corresponding threshold and linear model random effect solutions were all greater than or equal to .99. Correlations between heifer and cow analyses for sire and service sire solutions were less than .4. Analysis with an incorrect herd-year-season variance component affected only the technician solutions.

Animals↗

PubMed1990

Power of daughter and granddaughter designs for determining linkage between marker loci and quantitative trait loci in dairy cattle.

There is considerable interest in bovine DNA-level polymorphic marker loci as a means of mapping quantitative trait loci (QTL) of economic importance in cattle. Progeny of a sire heterozygous for both a marker locus and a linked QTL, which inherit different alleles for the marker, will have different trait means. Based on this, power to detect QTL, as a function of QTL effect, heritability of the trait, and number of animals tested was determined for 1) daughter design, marker genotype and quantitative trait values assessed on daughters of sires heterozygous for the markers; and 2) granddaughter design, a newly devised alternative design in which marker genotype is determined on sons of heterozygous sires and quantitative trait value measured on daughters of the sons. For equal numbers of assays, power increased with the number of daughters per sire (design 1) and sons per grandsire (design 2). For equal power and heritability less than or equal to .2, design 2 required half as many marker assays as design 1, e.g., with heritability of .2, QTL effect of .2 SD units, and type 1 error of .01, power was .70 if 400 daughters of each of 10 sires were assayed for the markers and .95 if markers were assayed on 100 sons of each of 20 sires with 50 granddaughters per son.

Alleles↗

PubMed1989

Models for genetic analysis of dystocia and calf mortality.

Calvings of 106,750 Israeli Holstein heifers were analyzed for dystocia and calf mortality, which were scored dichotomously. Models fitted included herd-year-season, sex of calf, calving age, calving month, sire of cow, sire of calf, and groups of sire of cow and calf. Herd-year-season, sire of cow and of calf, and residuals were random with diagonal variance-covariance matrices. Traits were analyzed with and without a herd-year-season effect, and dystocia was analyzed separately for male and female calvings and with both sexes combined. Variance components were estimated by REML for linear models and by the counterpart of REML for threshold models. Heritability estimates were two to four times larger in threshold than in linear models, but correlations between corresponding sire evaluations were all greater than .9. Correlations between evaluations computed with and without herd-year-season effects were .9 for sire of calf evaluations for dystocia and greater than .97 for all other evaluations. Correlations between sire evaluations computed separately for male and female calvings were between .3 and .7. Thus, calving difficulty is expressed differently in male and female calvings. Genetic trends were unfavorable for dystocia but favorable for calf mortality. Phenotypic trends were curvilinear with maxima in 1982 and 1983 for calf mortality and dystocia.

Age Factors↗

PubMed1989

Genetic analysis of fertility traits in Israeli dairy cattle.

First through third parity lactation records of 91,770 Israeli Holsteins inseminated between 1980 and 1986 were evaluated by univariate mixed model methodology for fertility and production traits. The analytical model included the effects of herd-year-season, group of sires, sire, cow, and residual. Sire, cow, and residual were random: all other effects were fixed. Sires were assumed to be unrelated. Variance components were computed separately for first and second parity by Henderson's method 3. First parity heritabilities were .035 for conception status [1/number of inseminations to conception], .048 for days from calving to first breeding, and .135 for milk production. Corresponding second parity heritabilities were .022, .031, and .125. First parity genetic correlations were -.02 between conception status and milk, .27 between days to first breeding and milk, and -.03 between the two fertility traits. All environmental correlations, and all second parity genetic correlations among these traits, were between -.2 and .2. Genetic trends, estimated as twice the regression of the evaluation of the cow's sire on calving date, were 1% for conception status, .1 for days to first breeding, and 154 kg milk/yr. Thus, there was no indication of an adverse genetic relationship between fertility and milk production in this population.

Animals↗

PubMed1988

Inclusion of partial lactations in the genetic analysis of yield traits by differential weighting of records.

Mixed model equations are constructed using the convention of regression on dummy variables that are given values of either unity (presence of the effect) or zero (absence of the effect). In the proposed method, incomplete records were included by computing regression coefficients of sire effects as the regression of the effect on the partial record on the same effect on the complete record. Partial and complete records were treated equally for other effects. Regression and the error components of variance were estimated as simple functions of the length of the partial records. The only additional computation required in sire evaluation was the differential weighting of records in the construction of the mixed model equations. This method was tested on field data and was slightly more accurate than evaluations including partial records without differential weighting and significantly more accurate than evaluations obtained with partial records deleted.

Animals↗

PubMed1988

Genetic analysis of dystocia and calf mortality in Israeli-Holsteins by threshold and linear models.

Calvings of 106,751 Israeli Holstein heifers were analyzed for dystocia and calf mortality, scored dichotomously, and a composite trait, scored trichotomously. Dystocia was also studied with 146,973 second and third parity records. Models fitted included herd-year-season, sex of calf, calving age, calving month, sire of cow, sire of calf, and groups of sire of cow and of calf. Herd-year-season, sire of cow and calf, and residuals were random with diagonal variance-covariance matrices. Herd-year-season variance was assume to be 10% of the residual component. Other variance components were estimated by REML for linear models and by the counterpart of REML for threshold models. Heritability estimates were two to five times greater in threshold than in linear models, but correlations between corresponding sire evaluations were all greater than .9. Linear model sire evaluations were skewed positively, whereas threshold model evaluations had symmetrical distributions. Heritability for dystocia was greater in first than in later parities. Correlations between first and later parity sire evaluations were less than .5. Thus, the genetic control of dystocia seems to be different for heifers and cows. Correlations between sire of cow and calf evaluations were less than .3. Correlations between dystocia and calf mortality evaluations were about .7.

Animals↗

PubMed1987

Effects of persistency and production on the genetic parameters of milk and fat yield in Israeli-Holsteins.

Herd-years of Israeli-Holsteins were stratified into three groups by two criteria: mean annualized milk yield [365 (total lactations yield/calving interval)] and mean persistency, estimated as the ratio of daily milk production at the 5th mo postpartum to daily production during the postpartum peak period. The latter was taken as an indication of the relative environmental stress on the cow. Primi- and multiparous cows were analyzed separately. Genetic parameters were estimated for annualized milk and fat production at each production and persistency group. Heritabilities increased with a rise in production for both primiparous and multiparous cows, but the effect was greater for multiparous cows. Even though persistency and production were correlated, no clear trends were evident for stratification by persistency; thus, a relationship between stress and heritability was not established. Genetic correlations among stratification groups were between .7 and .9 for persistency and between .6 and .86 for production; thus, sire x environmental interaction was greater for production than for persistency stratification. Production in a given year can be used as a criterion for selecting herds to test progeny of young sires in the following year.

Animals↗

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↗

PubMed1986

Sire and maternal grandsire effects on calving difficulty and calf mortality in Israeli Holsteins.

Associations among sire and maternal grandsire evaluations for calving difficulty and calf mortality were investigated in the Israeli Holstein population. Primiparous and multiparous calvings were analysed separately. Genetic correlations between calving difficulty and calf mortality were close to unity for primiparous calvings but lower for multiparous calvings. Genetic correlations between primiparous and multiparous sire evaluations were .94 and .72 for calving difficulty and calf mortality. Genetic correlations between sire and maternal grandsire evaluations were .6 for primiparous calvings and not-significant for multiparous calvings for both traits. These results correspond to findings that the direct genetic effect is larger than the maternal effect but that there is a slight negative correlation between them. We suggest that sire evaluations for calving difficulty of multiparous cows be used as a preliminary prediction of heifer calving difficulty and calf mortality and that the separate calving trait evaluations be combined into an overall calving selection index.

Animals↗

PubMed1986

Prediction of annualized lactation yield from partial lactations.

Extension factors for annualized lactation yields [365 (total lactation yield)/-days between calvings] were computed by generating 747,904 partial lactations from complete lactation records of 105,379 Israeli-Holstein cows with one to three lactations. Factors included in the model were last test yield, days pregnant, days in milk, farm type, calving season, and days remaining in the lactation. Both linear and quadratic effects were assumed for the first three factors. Primiparous and multiparous cows were analyzed separately for milk, fat, and economically fat-corrected milk [.67 (milk) + 10 (fat)] yields. Adjusted coefficients of determination computed for this model were .04 higher for fat and .01 higher for milk and economically fat-corrected milk than for an alternate model in which remaining yield was predicted as a linear function of last test yield and remaining days in milk. Correlations between actual and predicted lactations for partial lactations of less than 4 mo in milk computed by the first model were .03 higher for fat but were nearly identical to those computed by the second model for milk. Although last test yields was the most important factor in predicting annualized yields, inclusion of other factors increased accuracy of annualized fat yield prediction.

Animals↗

PubMed1986

Maximum likelihood techniques for the mapping and analysis of quantitative trait loci with the aid of genetic markers.

A method is presented to estimate the biometric parameters of a quantitative trait locus linked to a genetic marker when both loci are segregating in the F-2 generation of a cross between two inbred lines. The method, which assumes underlying normal distributions, is a combination of maximum likelihood and moments methods and uses the statistics of the genetic marker genotype samples for the quantitative trait to estimate the recombination frequency between the two loci and the means and variances of the genotypes of the quantitative trait locus. With this method, the genetic parameters of a locus affecting plant height linked to an electrophoretic marker for esterase were accurately estimated from a sample of 1596 F-2 progeny of a cross between two species of Lycopersicon (tomato). Linkage distance between the two loci was 38 map units and the effect of the quantitative trait locus was 1.6 phenotypic standard deviation units. Accurate estimates of the genetic parameters and linkage distance for populations of 2000 individuals simulated with a segregating codominant locus with an effect of 1.63 standard deviations linked to a genetic marker with .2 recombination were also derived by this method. The method is not effective in distinguishing between complete and partial linkage in samples of only 500 individuals or for quantitative loci with effects less than a phenotypic standard deviation. The method is more effective for codominant than for dominant loci.

Algorithms↗

PubMed1985

Effects of days open on annualized milk yields in current and following lactations.

Length of open period affected annualized yield [(total lactation yield/calving interval) 365]. Yield was maximum with more days open for low, as opposed to high, peak production and for primiparous, as opposed to multiparous, cows. Interactions with days open were not found for mean herd production or cow production relative to the herd mean. Number of days open for maximum yield was similar for milk, fat, and economically fat-corrected milk [.67 kg milk + 10 kg fat]. Correction factors were derived by smoothed least square means of days open classes. Additive adjustment factors were more appropriate than multiplicative adjustment factors. Records adjusted for days open were not able to predict the following lactation yield significantly better than unadjusted records. Cumulative yield of current and following annualized lactations, including the contribution of the calf expressed in units of milk production, was greatest at 117 and 98 days open for primiparous and multiparous cows. For cows with high peak production maximum yield was with 12 to 14 fewer days open than for cows with moderate peak. Conception prior to 2 mo postpartum had an adverse effect on cumulative yield.

Animals↗

PubMed1984

Genetic evaluation of dairy goat bucks for daughter milk and fat.

Genetic evaluations were computed for milk and fat for 3,181 Alpine, 1,039 LaMancha, 4,455 Nubian, 1,449 Saanen, and 1,546 Toggenburg bucks. These evaluations were based on 58,562 lactations of 43,913 does that kidded from 1976 through 1982. Best linear unbiased predictions were computed with relationships among multiherd bucks and information from all lactations included. An interaction between herd and sire was included in the model. Evaluations were computed across breed, which allowed does of different breeds to be herdmates. Bucks were grouped by breed and herd usage (single herd versus multiherd). Correlations between evaluations computed with and without relationships were only .84 to .88, which indicates that relationships had a significant effect. Evaluations of 2,491 bucks with Repeatability 15% or more were released to the industry.

Animals↗