Biomedical subjects

B G Cassell

Publications and source records attributed to B G Cassell.

At least 19 recordsLinked to original sources

PubMed2006

Relationships among lipid peroxidation, glutathione peroxidase, superoxide dismutase, sperm parameters, and competitive index in dairy bulls.

Sperm membranes contain high concentrations of polyunsaturated fatty acids that are highly susceptible to oxidative damage that interferes with fertilization ability. The objective of this study was to determine associations among lipid peroxidation (thiobarbituric-acid-reactive substance concentration), antioxidant enzymatic activities in frozen spermatozoa, and competitive indices. Semen from multiple ejaculates collected in succession from each bull (four Holstein and four Jersey) was pooled. Heterospermic doses (20x10(6)sperm/0.5mL straw) were made to obtain 16 Holstein/Jersey combinations (equal number of sperm from each bull). Cows were inseminated on observed or synchronized estrus. The sire of calves (N=460) was determined; based on the number of calves sired, a competitive index was obtained for each bull. Prior to preparation of the heterospermic doses, a sub-sample of semen from each bull was taken, processed, frozen, and stored concurrent with heterospermic samples. After thawing, these homospermic samples were assessed for lipid peroxidation, superoxide dismutase (SOD) activity, glutathione peroxidase (GPx) activity, DNA fragmentation index (DFI), plasma membrane integrity (PMI), and total progressive motility (assessed by CASA). Sperm lipid peroxidation and the competitive index were negatively correlated (r=-0.78; P<0.05), the DFI and sperm lipid peroxidation were positively correlated (r=0.86; P<0.001), and there were negative correlations (P<0.05) for sperm lipid peroxidation and both PMI and total progressive motility (r=-0.78 and -0.83, respectively). There was neither significant association between SOD activity and competitive index, nor between GPx activity and competitive index. In conclusion, bulls with lower sperm lipid peroxidation had higher chances of siring calves; this was attributed to the deleterious effects of lipid peroxidation on sperm plasma membrane integrity and sperm DNA, which may reduce sperm fertilizing potential.

Animals↗

PubMed2006

Breed differences in competitive indices of Holstein and Jersey bulls and their association with sperm DNA fragmentation index and plasma membrane integrity.

The objective was to evaluate the relationship of a competitive index (CI) determined by heterospermic performance and post-thaw semen quality of the same stored ejaculates. Semen from multiple ejaculates collected in succession from each bull (four Holstein and four Jersey) was pooled. Heterospermic doses (20x10(6)/straw) were made to obtain all possible Holstein-Jersey combinations (16 two-bull combinations) and contained 20x10(6) sperm/mL/bull. Cows at two University dairy farms were inseminated on observed or synchronized estrus. The sire of calves (N=460) were determined and a CI was determined for each bull (based on the number of calves sired). Prior to preparation of the heterospermic doses, a sub-sample of semen from each bull was taken, processed, frozen, and stored concurrently with heterospermic samples. Post-thaw semen samples (homospermic) from each bull were assessed for: sperm morphology, acrosome integrity, sperm motility parameters assessed by computer assisted sperm analysis (CASA), flow cytometry analysis of DNA Fragmentation Index (DFI), and Plasma Membrane Integrity (PMI). Heterospermic performance of Holstein bulls was superior to that of Jersey bulls. The DFI was negatively correlated to CI (r=-0.87; P<0.001), whereas the PMI (r=0.87; P<0.001) and total progressive motility (r=0.74; P<0.05) assessed by CASA were positively correlated to CI. In multivariate regression models, the DFI and PMI accounted for 87% variance in competitive index. In conclusion, bulls with less DFI and higher PMI had higher probabilities of siring calves.

Acrosome↗

PubMed2006

Effects of inbreeding in the dam on dystocia and stillbirths in US Holsteins.

Dystocia scores were recorded by producers on 120,434 Holsteins (218,213 records) from 1985 through 1996; dystocia scores 3 to 5 were coded as difficult births. Stillbirths were recorded for deaths within the first 48 h after birth. Data were restricted to registered cows for pedigree completeness, and inbreeding coefficients were calculated using 5-generation pedigrees. Computational restrictions required that subsets of the data be created by choosing herds at random but using all records from selected herds. Effects of inbreeding in the dam were estimated in a sire-maternal grandsire (of the calf) threshold model using Gibbs sampling. The model included fixed effects of calf sex and inbreeding of the dam and random effects of herd-year-season of birth, additive genetic, and residual effects. First, second, and third parities were analyzed separately. Solutions for sex of calf and inbreeding from different parities were converted to expected change in probability of dystocia or stillbirth per 1% increase in inbreeding. Inbreeding effects were largest for first-parity cows giving birth to male calves at a 0.42% increase in probability of dystocia/1% increase in inbreeding. Effects of inbreeding for first-parity dams giving birth to female calves were smaller, 0.30%/1% increase in inbreeding. Incidence of stillbirths increased 0.25 and 0.20% for male and female calves/1% increase in inbreeding for first parity births. Effects of inbreeding on dystocia and stillbirths declined with parity. Effects of inbreeding were small, especially in later parities, but were consistently unfavorable.

Animals↗

PubMed2006

Effects of breed and region on longevity traits through five years of age in Brown Swiss, Holstein, and Jersey cows in the United States.

The objective of this study was to assess breed, and breed x region interactions for several longevity-related traits, measured up to 5 yr of age in Brown Swiss, Holstein, and Jersey cows in 7 regions of the United States. Data were analyzed using logistic, poisson, and linear models, and survival analyses. The traits were stayability (yes/no survived to 5 yr of age), number of completed lactations, days lived, herd-life, and days in milk (DIM) to 5 yr of age. Probable lifetime DIM were also estimated using data from the first 5 yr of age of the cows. Herd-life was defined as the days lived up to 5 yr of age minus the age at first calving. Days in milk consisted of herd-life up to 5 yr of age minus the dry periods. Three data files were analyzed: herds with one breed of cows, herds with Holstein and Brown Swiss, and herds with Holstein and Jersey cows. Breed x region interaction was usually significant, with larger effects for the southern regions. Jerseys obtained largest values for the ratio of DIM to days lived, and for the number of completed lactations to 5 yr of age. Brown Swiss had the largest probabilities of surviving to 5 yr of age (stayabilities) in all regions. For the other traits, the results for Brown Swiss were inconsistent, but usually the cows of this breed had shorter herd-life and DIM to 5 yr of age than Holsteins. Brown Swiss cows were expected to have more total DIM in their lifetime in the Southeast than Holsteins. Survival analysis gave the most readily interpretable information, although the linear, poisson, and logistic analyses answered slightly different questions. Adjustment for herd size did not modify the results.

Animals↗

PubMed2005

Comparisons of Holsteins with Brown Swiss and Jersey cows on the same farm for age at first calving and first calving interval.

Our objective was to evaluate breed differences for heat-stress resistance as reflected by age at first calving and first calving interval. We examined the effect of geographic location and birth season on age at first calving, and geographic location and first calving season on first calving interval on Holsteins and Jerseys, and Holsteins and Brown Swiss located on the same farm. We defined 7 regions within the United States: Northwest, Central north, Northeast, Central, Central south, Southwest, and Southeast, and analyzed 7 individual states: Ohio, Wisconsin, Oregon, California, Arizona, Texas, and Florida. Brown Swiss were older than Holsteins at first calving (833 +/- 2.4 vs. 806 +/- 2.0 d in regions, and 830 +/- 3.1 vs. 803 +/- 2.4 d in states), but Holsteins and Brown Swiss did not differ for first calving interval. Jerseys were younger than Holsteins at first calving and had shorter first calving intervals. In data from individual states, Holsteins housed with Brown Swiss were older at first calving than were Holsteins housed with Jerseys (800 +/- 2.7 vs. 780 +/- 2.5 d). Holsteins housed with one breed or the other were analyzed as a separate data set, and referred to as "type of Holstein." The interaction of "type of Holstein" with first calving season was highly significant for first calving interval. Geographic location and season effects were smaller for Jerseys than for Holsteins; thus, Jerseys showed evidence of heat-stress resistance with respect to Holsteins. Management modified age at first calving in Holsteins to more nearly match that of the other breed. Longer calving intervals might be partly due to voluntary waiting period to breed the cows.

Aging↗

PubMed2003

Effect of incomplete pedigrees on estimates of inbreeding and inbreeding depression for days to first service and summit milk yield in Holsteins and Jerseys.

A method to measure completeness of pedigree information is applied to populations of Holstein (registered and grade) and Jersey (largely registered) cows. Inbreeding coefficients where missing ancestors make no contribution were compared to a method using average relationships for missing ancestors. Estimated inbreeding depression was from an animal model that simultaneously adjusted for breeding values. Inbreeding and its standard deviation increased with more information, from 0.04 +/- 0.84 to 1.65 +/- 2.05 and 2.06 +/- 2.22 for grade Holsteins with <31%, 31 to 70%, and 71 to 100% complete five-generation pedigrees. Inbreeding from the method of average relationships for missing ancestors was 2.75 +/- 1.06, 3.10 +/- 2.21, and 2.89 +/- 2.37 for the same groups. Pedigrees of registered Holsteins and Jerseys were over 97% and over 89% complete, respectively. Inbreeding depression in days to first service and summit milk yield was estimated from both methods. Inbreeding depression for days to first service was not consistently significant for grade Holsteins and ranged from -0.37 d/1% increase in inbreeding (grade Holstein pedigrees <31% complete) to 0.15 d for grade Holstein pedigrees >70% complete. Estimates were similar for both methods. Inbreeding depression for registered Holsteins and Jerseys were positive (undesirable) but not significant for days to first service. Inbreeding depressed summit milk yield significantly in all groups by both methods. Summit milk yield declined by -0.12 to -0.06 kg/d per 1% increase in inbreeding in Holsteins and by -0.08 kg/1% increase in inbreeding in Jerseys. Pedigrees of grade animals are frequently incomplete and can yield misleading estimates of inbreeding depression. This problem is not overcome by inserting average relationships for missing ancestors in calculation of inbreeding coefficients.

Animals↗

PubMed2003

Maternal and fetal inbreeding depression for 70-day nonreturn and calving rate in Holsteins and Jerseys.

Inbreeding depression for 70-d nonreturn rate was estimated in 50,613 Holstein and 47,673 Jersey cows with five-generation pedigrees using an animal model. Heritabilities of 70-d nonreturn rate were very low for both breeds (1 to 2%). Maternal inbreeding depression was small (3% reduction for 10% inbreeding) and significant only for Jerseys. Fetal and maternal inbreeding depression was not significant for individual parities in Holsteins, but maternal inbreeding depression was significant in first parity only in Jerseys. Maternal and fetal inbreeding depression of calving rate (verified by a subsequent calving) was estimated on separate datasets by parity from 13,229 to 26,876 Holstein and 7374 to 11,742 Jersey cows. First-parity estimates for heritability of calving rate were 1% or less, whereas estimates for later parities varied from 1 to 6%. Significant inbreeding depression in first-parity Holsteins reduced calving rate by 4% per 10% maternal or fetal inbreeding, but effects, while undesirable, were not consistently significant in other parities. In Jerseys, maternal inbreeding significantly reduced calving rate by 6% per 10% inbreeding in first parity, and was undesirable but not significant for second through fourth parities. Fetal inbreeding depression was not significant in Jerseys. Maternal inbreeding depression of 70-d nonreturn and calving rate was small, undesirable, but not consistently significant across breeds and parities. The cumulative economic impact of maternal or fetal inbreeding on lifetime reproductive performance of Holstein or Jersey cows would be more dramatic than results for a single breeding.

Animals↗

PubMed2002

Evaluating sire selection practices using lifetime net income functions.

Dairy farmers do not take full advantage of opportunities available for genetic improvement through use of artificial insemination, perhaps because economic advantages of good sire selection may not be fully recognized or understood. This study was undertaken to document differences between use of AI and non-AI bulls and to develop prediction equations to compare lifetime economic merit of future progeny from alternative sire selection policies. We describe the use of two methods of measuring lifetime economic merit, with and without adjustment for opportunity cost of a postponed replacement. Comparison of lifetime relative net income adjusted for opportunity cost on groups of cows sired by different kinds of bulls showed that daughters of proven AI bulls generated $148 and $120 more lifetime net income under fluid and manufactured milk market conditions than daughters of non-AI bulls. Daughters of proven AI bulls produced $60 more than daughters of AI young sires in progeny testing programs at the time of daughter conception. We developed prediction equations from combinations of genetic evaluations for production, productive life, SCS, and linear type traits on sires to predict lifetime relative net income of progeny produced from alternative sire selection strategies. Prediction equations explained 14 to 18% of variation in relative net income (not adjusted for opportunity cost), but herd and year of first freshening accounted for considerably more variation than did genetic evaluations on the sire of the cow. Finally, two independent data sets were used to develop and test predictions of lifetime relative net income adjusted for opportunity cost using genetic evaluations based on the eight traits included in the Merit indexes for the sire of each cow. Prediction equations from odd numbered herds were used to predict lifetime economic merit in even numbered herds and vice versa. Coefficients of determination ranged from 0.088 to 0.103 and averaged 0.004 higher than prediction equations with Net or Fluid Merit. Accuracy of predictions showed that Net and Fluid Merit were robust and useful indexes that accurately identified bulls whose daughters generated highest lifetime economic merit.

Animals↗

PubMed1999

Comparisons of cows and herds in two progeny testing programs and two corresponding states.

Data were USDA genetic evaluations of cows and DHI herd profiles from 4154 Holstein progeny-test herds from two artificial insemination organizations. 21st Century Genetics (Shawano, WI) and Genex (Ithaca, NY), and from 6361 additional herds from Minnesota and New York. We grouped herds into four categories: 21st Century Genetics herds, other Minnesota herds, Genex herds, and other New York herds. Herds were eliminated if they contributed fewer than 10 cows with genetic evaluations and birth dates from January 1989 to March 1995. Data included 83 and 74%, respectively, of first-crop daughters of 21st Century Genetics and Genex progeny-test bulls with genetic evaluations from January 1995 to February 1997. Herds were characterized by DHI profile and cow evaluation data. Daughters of progeny-test bulls with extreme production records (outside of 3 SD) relative to herd mean and variance did not appear in disproportionate numbers among the progeny of bulls likely culled or considered for further use. The two organizations appear to have selected larger, genetically superior, and better managed herds from within their respective regions for progeny-testing purposes. We were not able to predict whether a bull in the progeny-testing programs of these two organizations was going to exceed or fail to meet the pedigree prediction from characteristics of herds in which his daughters performed. Differences between parent average and daughter yield deviations for typical young sires appear to result from Mendelian segregation of genes.

Animals↗

PubMed1998

Influences of progeny test programs on genetic evaluations of young sires.

Our purpose was to examine differences among AI progeny test programs in their effectiveness in identifying elite young sires for milk and protein. Data were from 6238 Holstein sires in five animal model evaluations of the USDA from January 1995 to February 1997. Bulls were required to be < or = 8 yr of age and to have > or = 10 daughters in production at the time of the evaluation. Bulls in AI programs were placed in nine groups based on affiliation with major AI organizations; from these nine groups, bulls with daughters averaging < 150 DIM and bulls sampled in > 100 herds were placed in two separate groups. Bulls sampled in organizations with controller numbers > or = 30 and bulls that had no connection to a sampling organization formed two additional groups. We also classified bulls by sampling codes of the National Association of Animal Breeders. A model predicting daughter yield deviation included effects of organization or sampling code, parent average (free of progeny information), and the interaction of organization or sampling method and parent average. When all data were used, a common intercept for milk was appropriate for all sampling methods, but the slopes differed (R2 = 0.44). Neither a common intercept nor a common slope was appropriate for protein. When data were restricted to the nine major organizations, a common intercept and slope were appropriate for milk, and R2 decreased to 0.14. A common intercept and slope were found for protein, and R2 decreased to 0.15. We detected no important differences in response to pedigree selection among progeny-testing methods used by major organizations that provide semen, but a difference was detected among the sampling codes of the National Association of Animal Breeders.

Animals↗

PubMed1998

The effects of inbreeding on the lifetime performance of dairy cattle.

The effects of inbreeding on the lifetime performance of dairy cattle were examined using data for production, somatic cell score, and linear type for all Holstein cows that were scored between 1983 and 1993. The results of fixed and mixed animal models differed. Relative net income adjusted for opportunity cost for the 2,610,123 cows with an 84-mo opportunity for herdlife was depressed by $14.79 for fluid market pricing and by $12.40 for manufacturing pricing per 1% increase in inbreeding. Mixed model estimates of depression per 1% of increase in inbreeding were +0.55 d for age at first calving, -6 d for days of productive life, and -4.8 for days in milk. Inbreeding decreased the mature equivalent production of milk, fat, and protein during first lactation by 27, 0.9, and 0.8 kg and the lifetime production of milk, fat, and protein by 177, 6.0, and 5.5 kg, respectively, per 1% increase in inbreeding. Inbreeding had little effect on conformation traits. The effects of inbreeding were cumulative, and effects on lifetime profit functions were relatively larger than the effects on lactation traits. Registered cows had higher levels of inbreeding and larger standard deviations than did grade cows. Inbreeding in registered cows depressed relative net income adjusted for opportunity cost for fluid and manufacturing prices by $24.43 and $21.78, respectively; income was depressed $9.43 and $9.02, respectively, for grade cows. The difference between registered and grade cattle is likely due to the incomplete pedigree information in grade animals. Inbreeding among cows in this study was not high on average, but economic losses represented a significant cost to the producer.

Animals↗

PubMed1997

Prediction of transmitting abilities for productive life and lifetime profitability from production, somatic cell count, and type traits in milk markets for fluid milk and cheese.

Two net income functions were constructed to reflect differences in value of carrier, protein, and somatic cell score (SCS) between milk markets for fluid milk and those for cheese. Individual costs were for production of carrier (water, lactose, and minerals), fat, and protein. Totals for net income from a lactation were adjusted for the opportunity cost of postponed replacement using all herdmates on test. Heritabilities and correlations were estimated with a multiple-trait sire model using 52,688 registered and grade (24%) cows that were classified daughters of 844 bulls included in the Sire Evaluation for Type program of the Holstein Association of America. Although the genetic correlation between the net income traits was high (0.92), the resulting economic weights were quite different. Indexes to select for net income for a fluid milk market weighted milk production much more than it weighted fat or SCS and selected against protein yield. Indexes for a cheese market gave more weight to milk components, SCS, and traits related to productive life. The removal of some type traits had little effect on the evaluation of either net income trait. In contrast, weights for prediction of productive life from SCS and the production and type traits became more stable when strength, fore udder, and rear udder heights were removed. Removal of some of the type traits that were used for prediction reduced multicollinearity and the variance of weights without sacrificing accuracy.

Animals↗

PubMed1995

Multiple-trait prediction of transmitting abilities for herd life and estimation of economic weights using relative net income adjusted for opportunity cost.

Genetic and phenotypic (co)variances among linear type traits, final score, first lactation milk and fat yield, and 84-mo totals for longevity, relative net income, and relative net income adjusted for opportunity cost of postponed replacement were estimated with a multiple-trait sire model. Data were from 433,116 cows in herds participating in the classification program for conformation traits of the Holstein Association of America. Yield information from all cows in classified herds indicated that classified cows are not a random sample. Heritability of net income adjusted for opportunity cost was higher, .17, than unadjusted net income, .12, but the genetic correlation between the estimates of net income was high, .97. Adjusted net income also had high genetic correlations with first lactation milk yield, .80; fat yield, .60; and dairy form, .48. Heritability of longevity (months in milk to 84 mo) was .06. Adjustment of net income for opportunity cost lowered the genetic correlation with longevity from .84 to .70. Evaluation of lifetime merit using traits measured during first lactation with economic weights developed using adjusted net income was more accurate than indirect prediction of longevity; the approximate reliability of a first-crop AI sire for lifetime merit was .65 compared with .42 for longevity.

Animals↗

PubMed1994

Using somatic cell score evaluations for management decisions.

Genetic evaluations for mean somatic cell scores for lactation enable producers to reduce increases in SCC that accompany genetic improvement for milk yield. Current progeny test designs will produce lower reliabilities for somatic cell score evaluations than for milk yield because of lower heritability. Genetic correlations of somatic cell scores between first and second lactation are lower than for milk yield. Thus, changes in evaluations of sires over time should be greater for somatic cell score than for milk yield. Absence of interaction of genotype and environment for somatic cell score indicates that the same bulls would be selected for use in herds with high and low somatic cell scores. Most evaluations will be between -.25 and .25, averaging .01 for Holsteins, which represents an increase of approximately 50% in geometric mean SCC and an 11% higher incidence of clinical mastitis for daughters of bulls with highest evaluations compared with daughters of bulls with lowest evaluations. Selection to reduce somatic cell score does not appear to be justified economically. Properly constructed indexes would reduce the projected increases in mastitis incidence by 20 to 25% with a 2% decline in genetic progress for milk yield. The greatest impact of genetic evaluations for somatic cell score would likely result from choice of sires of bulls to progeny test.

Animals↗

PubMed1988

Phenotypic and genetic relationship between linear functional type traits and milk yield for five breeds.

Lactation records of cows first calving between 18 and 35 mo were combined with linear type ratings assigned during the same lactation if before 43 mo. Phenotypic relationships were examined between final score and 13 type appraisal traits and first lactation milk yield from 2935 Ayrshire, 3154 Brown Swiss, 13,110 Guernsey, 50,422 Jersey, and 924 Milking Shorthorn records. Most phenotypic correlations between type and milk yield were low. Linear correlations of final score with first lactation milk yield were .18 to .38. Of the linear functional type traits, correlations with first lactation yield had greatest absolute values for dairy character (.19 to .53), udder depth (-.26 to -.30), and rear udder width (.20 to .31). Multiple correlations of all type appraisal traits with first lactation milk yield ranged from .41 to .59. Herd-year-season components of variance averaged 25% for type traits. Herd-year-season with sire interaction averaged 4%. Heritability estimates for final score from paternal half-sib analysis were from .11 to .21. Heritability estimates for linear traits ranged from .01 to .37. Genetic correlation between milk and final score was positive for Guernseys (.25) and Jerseys (.21). Genetic correlations between yield and most linear type traits were low to moderate except for dairy character (.53 to .77).

Animals↗

PubMed1987

Comparison of on-farm laboratory milk progesterone assays for identifying errors in detection of estrus and diagnosis of pregnancy.

A field study was conducted in 10 commercial dairy herds to test the efficacy of a rapid enzyme-linked immunosorbent assay to identify errors in detection of estrus and diagnosis of pregnancy. Milk samples were collected at the milking following detection of estrus and on d 21 postinsemination. Progesterone was measured on-farm by an enzyme-linked immunosorbent assay and in the laboratory by radioimmunoassay. Agreement between the two methods of progesterone analysis (n = 820) was 89.8%. There were 93 cows (18.7%) by laboratory analysis and 126 cows (25.4%) by on-farm analysis for which concentration of progesterone in the sample collected at suspected estrus (n = 497) was higher than normal estrual values. Exclusion of these cases increased the overall accuracy of pregnancy diagnosis by 6.8 and 6.4% for laboratory and on-farm methods. Overall agreement between pregnancy diagnosis by milk progesterone at d 21 postinsemination and diagnosis by return to estrus or palpation of reproductive organs was 80.5 and 75.8% for laboratory and on-farm methods (75.0% and 69.7% for pregnant cows and 94.5 and 93.9% for nonpregnant cows). These results indicate that an enzyme-linked immunosorbent assay for milk progesterone performed on-farm was equal in accuracy to a laboratory radioimmunoassay for identifying errors in detection of estrus and diagnosis of pregnancy.

Animals↗

PubMed1985

Differences in modified contemporary comparison sire evaluations from first and later lactations by breed.

Sire evaluations from three sets of daughter records, first records only (first), later records after firsts (later), and all records (all) by Modified Contemporary Comparison procedures were used to examine differences in first and later lactation evaluations by breed. January 1984 evaluations for milk for 767 Ayrshires, 3,175 Guernsey, 29,498 Holstein, 3,530 Jersey, and 984 Brown Swiss bulls with 10 or more daughters in each set were used. Average differences between evaluations (later minus first) were 36, 0, 6, 35, and 35 kg milk for Ayrshire, Guernsey, Holstein, Jersey, and Brown Swiss bulls. Standard deviations of the difference were 114, 94, 142, 91, and 134 kg, showing considerable sire-to-sire variation in difference. Correlations between evaluations based on first and later records were .84 to .86 for all breeds except .92 for Jerseys. Percent of first lactations culled was correlated .20, .18, .16, .16, and .19 with difference for Ayrshire, Guernsey, Holstein, Jersey, and Brown Swiss, indicating that culling produced larger differences between evaluations for first and later lactations in favor of later evaluations. Prediction of sire evaluation from later records was enhanced by knowledge of sire's age in addition to first evaluation for Guernsey, Holstein and Jersey sires. In these breeds, for a constant first evaluation, and percent culled in first lactation, younger bulls had higher evaluations from later records. This study showed important differences between evaluations from first and later records for all breeds.

Animals↗

PubMed1983

Use of later records in dairy sire evaluation: a review.

Performance in first lactation has been the standard of evaluation for most genetic studies with dairy cattle. First records are available sooner on more cows and are less susceptible to error from selection, injury, previous days dry, and mastitis than are later records. However, first records have been considerably less than perfect in predicting traits of lifetime performance, which should be the primary selection objective in dairy cattle. Later records provide additional information for more accurate sire evaluations and should be a better index of health and resistance to mastitis than first lactations. The economic importance of later records relative to first is that there are more and actual yields are higher. Herds with more older cows can reduce commitment of resources to heifer rearing, and heifers can be selected more intensely prior to first calving than herds with more cows of younger ages. Some sire evaluation systems ignore later records because of computational expense, potential selection bias, and difficulty of age adjustment. Later records may contain useful information relative to lifetime profitability of sire progeny groups. Development of proper methodology for utilizing information available in later records appears fruitful for research.

Animals↗