Adaptive immune response, survival, and somatic cell score between postpartum Holstein and Norwegian Red × Holstein first-calf heifers.

The objectives of this study were to evaluate antibody (AMIR) and cell-mediated immune responses (CMIR), survival, and somatic cell score (SCS) between purebred Holstein (HO) and crossbred Norwegian Red × Holstein (NRHO) first-calf heifers postpartum. Additionally, immune response traits observed as calves in a previous study were correlated with their immune response traits as first-calf heifers. Heifers, previously immunized as calves, were bled and reimmunized 6 to 9 d postcalving with known type 1 and type 2 antigens and human serum albumin (HSA). Seven days later, heifers were rebled, and background skinfold measurements of the tail fold were taken. Intradermal injections of PBS and type 1 antigen were administered on either side of the tail fold. On d 9 final skinfold measurements were taken and used to assess delayed-type hypersensitivity (DTH) as an indicator of CMIR. Blood samples were also collected for a final time on d 14 from heifers that received the antigen HSA. Serum was obtained from blood collected on d 0, 7, and 14 and analyzed by ELISA to assess AMIR. Data on survival and somatic cell count, which was converted to SCS, were obtained from CanWest Dairy Herd Improvement (DHI). All SCS, survival, and immune response data were analyzed using general linear models to determine significance between HO and NRHO first-calf heifers. To determine residual correlations between immune response traits observed in calves to their responses as first-calf heifers, residuals were obtained from models, and correlations between traits were determined using PROC CORR in SAS. Results showed NRHO had a greater primary IgG antibody response to HSA and greater tertiary IgG antibody response to the type 2 antigen compared with HO. Crossbreds (NRHO)also had significantly greater DTH response (P < 0.05) and, in general, greater survival from calving to 100 d in milk (dim), 100 to 305 dim, calving to 305 dim, and age at immune response testing as calf to 305 dim. No difference was observed between breeds for SCS. Results also showed most correlations between calf and first-calf heifer immune response traits were found to be positive and significant (P < 0.05). In conclusion, NRHO heifers have greater survival, which likely relates at least in part to increases in aspects of both AMIR and CMIR and could indicate that crossbred heifers have enhanced disease resistance.

Antibody and cell-mediated immune responses and survival between Holstein and Norwegian Red × Holstein Canadian calves.

As an extension of a former study, the objectives of this study were to evaluate purebred Holstein (HO; n=140) and crossbred Norwegian Red × Holstein (NRFX; n=142) calves for antibody (AMIR) and cell-mediated immune responses (CMIR) as well as survival. Blood was collected on d 0, 14, and 21, and calves were immunized on d 0 and 14 with type 1 (Candida albicans) and type 2 (hen egg white lysozyme) antigens, which have been shown to induce CMIR and AMIR, respectively. Day 21 background skin-fold measurements of either side of the tail-fold were taken and intradermal injections of test (type 1 antigen) and control (phosphate saline buffer) were administered. Day 23 final skin-fold measurements were taken to assess delayed type hypersensitivity as an indicator of CMIR. Survival data were obtained from CanWest Dairy Herd Improvement. Statistical Analysis System general linear models were used to analyze all immune response and survival data and to determine statistical significance between breeds. Results showed that NRFX had greater primary IgM, IgG, IgG1, and secondary IgG1 antibody response, as well as greater primary IgG1:IgG2 ratio to the type 2 antigen compared with HO. The NRFX also had greater primary IgG1 and IgG2, and secondary IgG2 antibody response as well as greater primary IgG1:IgG2 ratio to the type 1 antigen. The NRFX calves had a tendency toward greater survival from age at immune response testing to calving. No difference was observed between breeds for other secondary antibody response traits or delayed type hypersensitivity. Results indicate NRFX have greater AMIR and therefore may have enhanced defense against extracellular pathogens. This may contribute to increased survival compared with HO. Both breeds, however, likely have similar defense against intracellular pathogens, because no differences in CMIR were observed. In general, these results may suggest that crossbreeding could improve resistance to certain diseases in dairy calves, resulting in decreased input costs to producers for crossbred calves compared with purebred calves. However, more research with larger sample sizes and different breeds should be conducted to confirm these results and obtain a complete picture of the benefits of crossbreeding on immune response traits in calves.

Immune responses of Holstein and Norwegian Red x Holstein calves on Canadian dairy farms.

The objective of this study was to compare the immune response of Holstein and Norwegian Red x Holstein calves on 13 commercial Canadian dairy farms. Data were collected on 135 calves, 68 Holstein and 67 Norwegian Red x Holstein calves aged between 2 and 6 mo. The calves were immunized with hen egg white lysozyme to induce antibody-mediated immune response. Candida albicans was used as an in vivo indicator of cell-mediated immune response, with delayed-type hypersensitivity used as the indicator. Antibody response to hen egg white lysozyme (IgG, IgG1, and IgG2) was measured by ELISA. Calves of both breed groups produced a significant primary and secondary antibody-mediated immune response, as well as a delayed-type hypersensitivity reaction. The Norwegian Red x Holstein produced a greater primary IgG antibody-mediated immune response (d 14, and d 14 minus d 0) when compared with the Holstein. No differences were observed between the breeds for secondary response or antihen egg white lysozyme isotype (IgG1 or IgG2) production or the ratio of IgG1:IgG2. There was no effect of breed on delayed-type hypersensitivity. Nonetheless, high and low immune responders could be identified in both breed groups, but with no difference in the proportion of high and low responders observed for either antibody-mediated immune response or cell-mediated immune response between breed groups.

Genetic evaluation for herd life in Canada.

Methods were developed for the national genetic evaluation of herd life for Canadian Holstein sires. The genetic evaluations incorporate information from survival (direct herd life) and information from conformation traits that are related to herd life (indirect herd life) after adjustment for production in first lactation to remove the effect of culling for production. Direct genetic evaluations for herd life were based on survival in each of the first three lactations, which was analyzed using a multiple-trait animal model. Sire evaluations thus obtained for survival in each of the first three lactations were combined based on their economic weights into an overall sire evaluation for direct herd life. Sire evaluations for indirect herd life were based on an index of sire evaluations for mammary system, feet and legs, rump, and capacity. A multiple-trait sire model based on multiple-trait across country evaluation methodology was used to combine direct and indirect genetic evaluations for herd life into an overall genetic evaluation for herd life. Sire evaluations for herd life were expressed in estimated transmitting ability as the number of lactations and represent expected differences among daughters in functional herd life (number of lactations); the average functional herd life was set equal to three lactations. Estimated transmitting abilities were normally distributed and ranged from 2.31 to 3.43 lactations.

Optimal size of progeny groups for progeny-testing programs by artificial insemination firms.

A semi-stochastic model for the simulation of genetic improvement in a dairy cattle population was used to evaluate and optimize progeny-testing programs for AI firms that operate in a competitive market for semen from progeny-tested bulls with regard to number of bulls sampled and size of progeny groups. The population was serviced by four firms. The competition for market share and semen sales was determined by the relative rank of progeny-tested bulls from a firm based on EBV for a trait with a heritability of 25%. For a fixed total number of daughters from young bulls for an AI program (test capacity), optimal size of the progeny groups was highly dependent on the objective to be maximized. The rate of genetic gain was maximized with a progeny group of 57 to 61 daughters per bull, but was relatively robust to changes in size of progeny groups. The number of marketable bulls was maximized with progeny groups between 20 and 40 daughters, depending on the test capacity. However, when a relationship between price per dose of semen and EBV of marketable bulls was considered, returns from semen sales were maximized at 49 and 82 daughters per bull, respectively, for linear and quadratic functions for semen price. The critical objective, net returns from semen sales, subtracting costs of sampling bulls, was maximized for progeny groups of between 95 and 105 daughters. Optimal size of progeny groups was robust to changes in economic parameters and the breeding programs of competitors. For economic parameters that were typical for Canadian AI firms, net returns per annual cohort of young bulls were 40% higher for the optimal size of the progeny groups than for sampling with 60 daughters per bull.

Nonadditive genetic effects and inbreeding depression for somatic cell counts of Holstein cattle.

A total of 65,491 lactation means of log2-transformed SCC measures were analyzed from first lactation Holstein cows in Ontario. Effects of inbreeding on SCC were estimated by a nonadditive sire and dam model that included additive, dominance, and additive by additive genetic effects and regression of lactation somatic cell score on inbreeding coefficients of the cows. Variance components were estimated using the tildehat approximation to REML. Solutions were by iteration on data. Estimates of heritability for lactation somatic cell score in the narrow sense were .165 and in the broad sense were .203. The additive by additive component (2.5% of the total phenotypic variance) was almost twice as large as the dominance component (1.3%). The regression coefficient of lactation somatic cell score per 1% increase of inbreeding was .012. The average increase of the population mean of lactation somatic cell score caused by a 10% increase of inbreeding coefficient was estimated to be 10.5% of the original phenotypic standard deviation of 1.153. The inbreeding depression was thus relatively low, but, on average, inbred animals tended to have higher lactation somatic cell score. This study provides preliminary evidence that inbreeding is related to disease prevalence in large purebred dairy populations.

Production traits of Holstein cattle: estimation of nonadditive genetic variance components and inbreeding depression.

Additive, dominance, and additive by additive components of genetic variance and inbreeding depression were estimated for production traits from a group of daughters of young sires from the Canadian Holstein population. First lactations of 92,838 cows were analyzed. Three sire and dam models (additive, additive plus dominance, additive plus dominance plus additive by additive genetic effects), all including regression of the trait on inbreeding coefficient of the cow, were used to estimate the effect of inbreeding on production traits. For all production traits, heritability in the narrow sense was overestimated with the simplest model, in which only the additive effect was fitted. Estimates of dominance variance were low for all traits, .9 to 3%. Additive by additive components were low for milk, 2.8%, and fat yield, 2.8%, but higher for protein yield, 6.8%, and for fat, 9%, and protein percentages, 8.9%. Estimates of inbreeding depression for the five traits were similar across all models (-25, -.9, and -.8 kg; .05% and .05% per 1% increase in inbreeding for milk, fat, and protein production and fat and protein percentages, respectively). More accurate estimates of additive effects might be obtained with the inclusion of nonadditive effects for genetic evaluation. If the estimation of inbreeding depression is the only objective, simple models and small random samples of the population may be adequate.

Genetic response and inbreeding with different selection methods and mating designs for nucleus breeding programs of dairy cattle.

Stochastic simulation was used to study the effect of selection and mating strategy on rates of genetic response and inbreeding with a closed nucleus breeding program for juvenile and adult schemes with 8 males and 64 females selected to produce 1024 progeny (512 females). Selection strategies considered using all available information or only individual and sibling records. Selection of sires was either unrestricted or restricted to between full-sib families. The effect of avoidance of mating of relatives to limit inbreeding was also evaluated. Four mating designs were examined: each dam was mated to 1, 2, 4, or all sires. Mating designs involving one sire per dam and more than one dam per sire were referred to as hierarchical. Use of several mates per dam resulted in a factorial mating design. Selected parents were mated either randomly, best to best, or best to worst. An index based on relative inbreeding to response ratio was used to describe the effectiveness of strategies for reducing inbreeding relative to changes in rates of genetic response. Strategies that lower index values were preferred and include selection on BLUP or approximations of BLUP and factorial mating designs that involve the random mating of dams to several sires. Factorial mating designs were effective for a range of heritabilities. Avoidance of matings of full sibs and restriction of selection of sires to between full-sib families enabled appreciable reductions in the index. Nucleus breeding programs based entirely on the selection of juveniles were not indicated because they had higher index values than adult schemes.

Adjustment factors and genetic evaluation for somatic cell score and relationships with other traits of Canadian Holsteins.

Test day SCC records were obtained from the Ontario DHI and converted to somatic cell score using a logarithmic transformation. Adjustment factors for stage of lactation and calendar month were obtained for first and later lactations. Effects of stage of lactation were significant and followed a systematic pattern. Seasonal effects were small. Sire estimated breeding values for lactation mean adjusted test day somatic cell scores were obtained from an animal model based on first, later, and all lactations, assuming a heritability of .11 and repeatability of .27. Mean accuracy of estimated breeding values for sires with at least 30 daughters was .64 for first lactation, .76 for second to fifth, and .86 for all lactations. Genetic trends for somatic cell score were not significant. The correlation of breeding values estimated from first lactations with estimates based on later lactations was .62 for sires with at least 50 daughters, which resulted in an approximate genetic correlation of .72. Correlations of sire estimated breeding values for somatic cell score from first lactation with estimated breeding values for milk, fat, protein, fat percentage, protein percentage, and milking speed were .12, .05, .11, -.09, -.02, and .20. Correlations between sire estimated breeding values for somatic cell score and type traits were generally small, but favorable with mammary system, -.13, and fore udder, -.16, and unfavorable with dairy character, .24. Somatic cell score should be considered as an auxiliary trait in dairy cattle breeding programs.

Method and effect of adjustment for heterogeneous variance of Holstein conformation traits.

Type classification records of Canadian Holsteins were investigated for evidence of heterogeneous variance across herds. Data consisted of records for 1,139,104 cows from 20,226 herds with classifications on 26 conformation traits collected from 1982 through 1992 and 338,046 cows from 9600 herds with classifications on 2 additional traits from 1990 through 1992. Phenotypic standard deviations of herd-round-classifier were fitted to a mixed model that included round, classifier, and region as fixed effects, herd size as a covariant, and herd as a random effect. Estimates of the variance components, solutions of fixed effects, and BLUP estimates for herd were obtained by maximum likelihood procedures. Repeatability of within-herd standard deviation across rounds ranged from 1.4 to 10.3% for the 28 traits. Type classification data were subsequently standardized for phenotypic standard deviations of herd-round-classifier that were derived from estimates of the fixed effects and the BLUP estimate of the herd effect. Genetic evaluations for cows and bulls were produced from adjusted and unadjusted data. Correlations between 3754 sire and 1,142,782 cow estimated transmitting abilities obtained from unadjusted and adjusted data were essentially unity. Although some evidence of heterogeneous variance existed across herds for 28 conformation traits, standardization of the classification records had only a minor effect on genetic evaluations.

Analysis of levels of inbreeding and inbreeding depression in Jersey cattle.

A pedigree file of 157,015 male and female Jersey cattle (born after 1955) from the Canadian herdbooks was investigated for the occurrence of inbreeding. A large proportion of Jersey bulls and cows were inbred (32.4 and 36.3% for bulls and cows, respectively). However, average inbreeding coefficients of these inbred cows and of all cows were low. First lactation milk, fat, and fat percentage records for 53,592 Jersey cows were analyzed. Inbreeding was included in the animal model as a linear covariate. The regression coefficients of milk, fat, and fat percentage on inbreeding were -9.84 kg, -.55 kg, and -.0011% per 1% increase of inbreeding. Inbreeding depression was not enough to cause large reductions of milk and fat yield of a cow with average inbreeding. However, when the inbreeding coefficient was greater than 12.5%, the inbreeding depression was significantly higher than expected and such that intentional inbreeding is not justified unless the mating is to an animal with exceptionally high breeding value.

Threshold models applied to Holstein conformation traits.

Threshold animal models were applied to five conformation traits of Canadian Holsteins. The estimated breeding values for sires from the threshold model allowed the calculation of predicted percentages of daughters in the desirable categories. Results were compared with those from a linear animal model in terms of their ability to predict future percentages of daughters in the desirable categories using an independent set of data. There was no advantage in a threshold model compared with a conventional linear animal model in its ability to predict future daughter performance. This was likely due to the 18 categories used in the classification of major type traits in Canada and the nearly normal distribution of observations across categories.

Selection of sires to reduce sampling variance in the estimates of heritability by half-sib correlation.

Standard methods to estimate heritability by half-sib correlation are biased if selection has operated in the parental generation. In this paper a simple method to correct for selection of animals used as sires is described. By selection of both the top and the bottom ranking sires, the sampling variances of the corrected estimates of heritability are substantially reduced. Algebraic expressions to predict the sampling variance of the estimates of heritability using selected sires are derived. Theoretical predictions were checked by Monte-Carlo simulation. The results may have application in the design of experiments to estimate heritabilities.

Treatment of dairy cows with recombinant bovine somatotropin: genetic and phenotypic aspects.

Thirty-four multiparous and primiparous Holstein cows were utilized to examine the association between the response to long-term administration of recombinant bovine somatotropin and the cow's phenotypic and genetic production potential. Cows representing a range of phenotypic and genetic production potentials were assigned to one of four treatment groups: 0, 12.5, 25.0, or 50.0 mg recombinant bovine somatotropin daily. They were injected daily for 266 d beginning on d 24 to 35 postpartum. Pretreatment milk and fat yields were used to predict daily yields over the lactation and allowed treatment groups to serve as their own controls. Actual minus predicted yield estimated the response to treatment for milk, fat, and FCM for each cow. Milk composition (fat, protein, and lactose percentage) was not significantly affected by treatment. Response in yield for milk, fat, and FCM was significant during the treatment period (266 d). Milk yield increased by 18.5, 19.9, and 21.4%; fat yield increased by 13.4, 20.3, and 18.1%; and FCM increased by 16.3%, 19.7%, and 21.1% after receipt of 12.5, 25.0 and 50.0 mg recombinant bovine somatotropin, respectively. Differences in response were not significant. The dramatic effect recombinant bovine somatotropin has on production requires that alternative approaches be adopted in the future for accurate genetic evaluation of sires and dams if somatotropin is discriminantly used in the national herd.

The effect of repeated cycles of selection on genetic variance, heritability, and response.

The genetic variance of a quantitative trait decreases under directional selection due to generation of linkage disequilibrium. After a few cycles of selection on individual phenotype, a limit is reached where there is no further reduction in the genetic variance. Bulmer's model is extended to an animal breeding situation where selection is on information on relatives rather than on the individual's own performance. Algebraic expressions are derived to predict the decrease in genetic variance and associated reductions in heritability and response in the limit. Consequences of the results are discussed in the context of breeding strategies.

Heifer fertility and its relationship with cow fertility and production traits in Holstein dairy cattle.

Breeding receipts from three AI units were merged with Ontario Dairy Herd Improvement Corporation and Record of Performance production records. Data comprised 53,705 heifer, 41,253 lactation 1, 14,688 lactation 2, and 3054 lactation 3 records by daughters of 2150 sires represented in 15,877 herd-year-seasons of birth. Three measures of heifer fertility, three measures of cow fertility, and three measures of production were investigated. Measures of heifer fertility were ages at first and last breeding and number of inseminations per conception. Cow fertility traits were days from calving to first breeding, days open, and number of inseminations per conception. Production traits were breed class average milk, breed class average fat, and fat percentage. Relationships among these nine traits for the first three lactations were estimated using a maximum likelihood multiple-trait procedure. The linear mixed model for each trait included fixed effects of herd-year-season of birth and genetic groups of sire and the random effect of sire. Transformations of the data for nonnormality had no influence on the estimates of genetic and phenotypic parameters. The heritability of .12 for age at first insemination, which was higher than other heifer fertility traits, indicated that selection would result in genetic response. Genetic and phenotypic correlations between heifer fertility and cow fertility and production traits in all three lactations were not different from zero. There was no genetic antagonism between fertility and subsequent production traits.

Relationships between fertility and production in Holstein dairy cattle in different lactations.

Record of Performance and Dairy Herd Improvement Corporation production records of Ontario Holstein cows were merged with breeding receipts of three Ontario AI units from September 1981 through December 1985. Relationships between fertility and production in the first three lactations were investigated for 97,368 daughters of 3806 sires in 22,768 herd-hear-seasons of calving. Fertility traits were days from calving to first insemination, number of inseminations per conception, and days open. Production traits were age and month of calving adjusted 305-d milk and fat yields and fat percentage. Multiple-trait maximum likelihood was used to estimate variances and covariances. Heritabilities for the first three lactations were .18, .18, and .19 for milk yield; .20, .19, and .19 for fat yield; and .58, .52, and .48 for fat percentage. Heritabilities of fertility traits ranged from .03 to .06. Genetic and phenotypic correlations between fertility and production traits in all three lactations were essentially 0. Genetic correlations between different lactation production traits ranged from .2 to .65. Repeatabilities of fertility traits ranged from .05 to .16 in different lactations. Repeatabilities for production traits in different lactations ranged from .51 to .77. Genetic and phenotypic correlations between fertility and production in the subsequent lactation and between production and subsequent lactation fertility were also very low or zero.

Relationship of bull fertility with daughter fertility and production traits in Holstein dairy cattle.

The phenotypic and genetic correlations between fertility ratings of AI bulls for conception rate and their estimated breeding values for daughters' fertility and production traits were calculated. Genetic correlations between fertility ratings of bulls for conception and heifer fertility traits (age at first breeding, age at last breeding, and number of insemination per conception) were negative and ranged from -.04 to -.23, indicating daughters of bulls with high fertility ratings were younger at first breeding and required fewer services to conceive. In general, genetic correlations between fertility ratings of bulls for conception rate and cow fertility traits (days from calving to first breeding, days open, and number of inseminations per conception) and production traits (breed class average milk and fat and fat percentage) in the first two lactations were also moderate to high and in the favorable direction. Although heritability of both male and female fertility is low, these data indicate that heavy use of sires with high fertility ratings could have a mild positive effect on both male and female fertility. Evidence is also found to indicate that in this breed, selection for increased milk yield should not impair genetic ability of cows to reproduce.

Dinitrochlorobenzene contact hypersensitivity as a marker trait for selection to improve disease resistance in calves.

Measurements of double skin fold thickness (mm) were used to assess the feasibility of use of cutaneous delayed-type hypersensitivity response as a marker trait to select for genetically improved disease resistance. Data were from a sample of 149 7-wk-old Holstein calves, from 15 sires, that previously had been sensitized to the contact allergen dinitrochlorobenzene. Response was monitored 24 and 48 h postchallenge. Analysis was by least squares according to a model that included fixed managerial effects, disease prevalence, and severity categories and sire of calf. Double skin fold thickness increased about 50% by 24 h, followed by a 4% decrease between 24 and 48 h. Season of birth was the only consistently significant fixed effect. Calves born in fall showed larger skin changes at each stage of response than calves born in spring. Restricted maximum likelihood estimates of paternal half-sib heritability were moderate to high for all stages of response, and phenotypic and genetic correlations between stages were significant and positive. Although the prevalence and severity of naturally occurring pneumonia and diarrhea did not significantly affect quantity of response, there is need to study further this relationship for intracellular pathogens. Delayed-type hypersensitivity response to dinitrochlorobenzene can meet requirements for a successful marker on which to base sire selection for disease resistance, if it is related to economically important, intracellularly characterized, pathogenic bovine diseases.

Antibody responses to human erythrocytes and ovalbumin as marker traits of disease resistance in dairy calves.

Microhemagglutination procedures were used to quantify antibody titers against human erythrocytes and ovalbumin in calf sera. Calves were also monitored for the prevalence of pneumonia and diarrhea. Calves, 72 males and 82 females, were the progeny of 15 AI bulls. Blood was sampled weekly for 2 wk after primary and secondary immunizations. Antibody response peaks to both antigens occurred by 14 and 7 d postimmunization, respectively. There were significant effects of season and birth and location of rearing on antibody titers against both test antigens. Diarrhea prevalence was negatively associated with high primary response antibody titers against human erythrocytes, but no trends were observed for pneumonia prevalence and for antibody titers to ovalbumin. Paternal half-sib heritability estimates ranged from 0 to .40 +/- .32 for primary antibody responses and from 0 to .87 +/- .50 for secondary antibody responses, depending on antibody specificity, and those for average titer were higher for antiovalbumin antibody (h2 = .48 +/- .39) than for antihuman erythrocyte antibody (h2 = .31 +/- .21). Although the environmental component of the humoral immune response is substantial, heritabilities of the magnitude in this study suggest the feasibility for successful genetic manipulation of antibody response profiles of young calves, and these may contribute to enhanced disease resistance.