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Health data collected from 1996 to 1999 from 177 herds in Minnesota and Wisconsin were analyzed to establish genetic basis for infectious and noninfectious diseases. Three types of health traits were targeted. First, available infectious conditions were used to identify animals that are superior in their general immunity (including innate immunity) for infectious diseases. Generalized immunity may be thought of as a combination of immune responses to a variety of immune system challenges. Second, single infectious and noninfectious diseases were analyzed separately. Third, infectious reproductive diseases as one category of related conditions, and cystic ovary disease as one category of 3 related noninfectious ovary disorders were studied. Data were analyzed using a threshold model that included herd, calving year, season of calving, and parity as cross-classified fixed factors; and sire and cow within sires as random effects. Days at risk and days in milk at the beginning of a record were included by fitting the days as continuous covariates in the model. A heritability value of 0.202 +/- 0.083 was estimated for generalized immunity. Heritability values of 0.141 and 0.161 were estimated for uterine infection and mastitis, respectively. Heritability of single noninfectious disorders ranged from 0.087 to 0.349. The amount of additive genetic variance recovered in the underlying scale of noninfectious disorders tended to zero when combining multiple conditions. The study supports combining infectious diseases into categories of interest but we do not recommend the same approach for noninfectious disorders.

A great deal of evidence points to substantial genetic control over at least some of the immune responses, although genetic parameters for clinical disease have been less favorable. The past two decades have illustrated that single genes with a large impact on food animal health do exist and can be used to improve the health of domestic populations. The current focus on molecular genetics within food animal species will likely unveil numerous other examples of single genes with large effects, although the use of animals possessing favorable genotypes for disease resistance may represent a compromise in selection for increased production of raw product. Moreover, it is also clear that genetic control over the immune system is not limited to a few genes but is more likely influenced by many genes, each with small effects. The use of this information in animal improvement programs is not straightforward because of factors complicating the identification of superior individuals within the population. The scarcity of information dealing with phenotypic and genetic relationships between measures of disease resistance and aspects of immune response complicates the situation even further. Despite these potential hurdles, the potential for permanent improvement of disease resistance within food animal species in the future is tantalizing and merits intensified future study.

Environmental and genetic factors affecting prevalences of antibodies to bovine leukosis virus and bovine immunodeficiency-like virus were studied on 137 periparturient Holstein cows selected for milk production. Environmental effects were obtained by logistic regression, and genetic parameters were determined using threshold animal models. Cows selected for high predicted transmitting ability for kilograms of milk fat plus protein had the highest prevalence of antibodies to bovine immunodeficiency-like virus and the lowest prevalence of antibodies to bovine leukosis virus. Heritability estimates for susceptibility to retroviral infections were close to zero.

Data from twenty assays of traits associated with innate and adaptive immunity were evaluated from 137 periparturient Holstein cows. These cows had been selected through planned matings for four different levels of milk production (high and average pounds of milk, and high and average pounds of milk fat plus protein). For up to seven generations, the genetic lines were produced by mating females of each line to sires of corresponding merit. With the exceptions of neutrophil ingestion of Staphylococcus aureus and directed migration, all assays measuring neutrophil functions were depressed beginning 2 to 3 weeks before calving through 3 weeks after calving. Serum concentrations of immunoglobulin G1 decreased while those of immunoglobulin G2 increased around calving time. Serum complement and conglutinin concentrations decreased before calving and reached a minimum around calving time. Cows selected for high milk production (pounds of milk and pounds of milk fat plus proteins) had significantly higher (P < 0.10) numbers of circulating neutrophils and mononuclear cells, had higher (P < 0.10) neutrophil resting chemiluminescence and higher (P < 0.10) neutrophil directed migration than cows with average production potentials. There were significant (P < 0.001) sire progeny group differences for most traits associated with the immune system that we tested. These results can be considered encouraging, in that selection for high milk yield did not produce unfavorable correlated responses in the functional capacity of immune function traits, and that there is sufficient genetic variation in these immunological traits among sires of high genetic merit for milk production to potentially improve the immunocompetence of periparturient cows through planned mating experiments.

Incidences of 22 health related traits were analyzed for 11,008 lactation records provided by 21st Century Genetics. Traits were analyzed both individually and grouped into one of five health categories. Significant sources of variation included herd-year, lactation, cow, and sire effects. Genetic parameters were estimated with multiple-trait REML. Repeatability and heritability estimates were low to moderate. Estimates ranged from .09 to .57 for repeatability and from .02 to .21 for heritability when individual traits were pooled by health category. Reproductive and respiratory traits were the least heritable (less than .10); mammary and locomotive traits were slightly higher (less than .20); and digestive category was most heritable (.21). Genetic correlations of mature equivalent milk with number of inseminations and other reproductive problems were positive (antagonistic), but those with incidences of other health problems were negative. Phenotypic correlations among mature equivalent milk and fat with individual health traits and categories of health traits were small and mostly near zero. Genetic correlations among health traits were positive except for reproduction with mammary and respiratory traits. Phenotypic correlations among health traits were near zero. Results suggest that selection for reduction of health problems is possible. If selection is practiced for improved health, these health traits should be properly weighted relative to production and other traits by the appropriate economic value. Evaluation of animals for health problems should be done on a multiple-trait basis.

Genetic correlations between dystocia in first with later parities and between direct with maternal effects for dystocia were estimated. Dystocia in first and later parities represent similar traits because of a large genetic correlation of .84. This similarity should allow calving reports on older dams and heifers to be combined in predicting a bull's calving performance. Correlations for direct with maternal effects were -.38 for the heifer population and -.25 for the cow (second and greater parities) population. This correlation would reduce progress from selecting for reduced dystocia if only direct effects were considered. Breeding programs to reduce dystocia should consider both direct and maternal performance.

More than 17,000 events from 1,305 lactations of 551 cows in two herds were analyzed to quantify the distribution of costs and disorders of health during a lactation. Categories were mammary, reproduction, locomotion, digestion, respiration, other, insemination, and total. The largest costs and most disorders were associated with initiation of lactation rather than period of peak daily milk yield. Mammary and reproductive costs were 71% of total health cost in the first 30 days postpartum. Mammary and reproductive costs were 55% of the total health cost in an average 30-day interval. Insemination cost was 50% of the total health cost between 60 to 89 days postpartum. Parturition and extended days open were periods of large reproductive cost. Postpartum distributions of health cost and health disorders were similar implying that the prices assigned for severity added little information to counting disorders.

The effects of selection for the direct and maternal components of dystocia were estimated for first, second and later, and all parities. The effect of restricting maternal change to zero and the effect of selection for only the direct component were also examined. Gene flow procedure was used to compute economic weights as 1 and .347 for the direct and maternal effects, respectively. Genetic gain in aggregate genotype was the largest for first parity. For all parities all the gain in the aggregate genotype was accounted for by the direct effects. At the same time, a slight decrease in the genetic maternal effects was observed. For all cases, selection for both traits had almost no loss in aggregate genotype or accuracy compared with when maternal changes were restricted to zero. Total genetic gain and genetic gain for the direct effect of dystocia were greater and accuracy of selection was lower when selection was for the genetic direct effect only versus the index that included both direct and maternal effects. Selection for only the direct effects is not likely to produce any significant change in dystocia as a maternal trait.

Health costs by categories were summarized from 1,999 lactations of 863 cows in three dairy herds. These costs were projected to Dairy Herd Improvement data. Health categories were mammary, reproduction, locomotion, digestion, respiration, other, and total. The largest estimated total health cost of $67.63 was associated with postpartum length (days in milk and dry) greater than 420 days, an average 98 days dry, and milk production greater than 8,250 kg in fourth or later terminal lactations. The smallest estimated total health cost of $22.25 per lactation was associated with production between 5,750 and 6,999 kg in the nonterminal first lactation with postpartum length less than 300 days. For nonterminal first lactations of intermediate length, the estimated total health cost represented 3 to 6% of the value of milk production. First-calf heifers with milk production less than 5,750 kg and postpartum length 300 to 419 days had the least mammary cost. Cows in their fourth or later lactations with postpartum length greater than 420 days and milk production less than 5,750 kg had the highest reproductive cost. Mammary cost increased and reproductive cost decreased with increased days dry. Cows in terminal lactations had $11.38 more total health cost, $4.33 more mammary cost, and $6.31 more reproductive cost than cows in complete nonterminal lactations. Relatively more reproductive than mammary cost occurred in terminal lactations compared to nonterminal lactations. Mammary cost remained the largest component of total health cost. Multiparous cows had more total health, mammary, and reproductive costs than first parity cows. The repeatibility of total health cost was .12 +2- .03.

Multitrait procedure was used to investigate the genetic relationship between calf livability and calving difficulty of Holsteins. The genetic correlation between calf livability and calving difficulty was .66. Heritabilities were .9% for calf livability and 4.1% for calving difficulty. The product-moment correlation (.4) between sires' transmitting abilities estimated separately for livability and dystocia, with properties of Best Linear Unbiased Predicator, underestimated the genetic correlation (.66). The correlated response of calf livability is expected to be 41% greater when selection is for dystocia than is expected from direct selection on calf livability.