Sep 16, 1991 - test scores was observed. California ... testing and measurement of enzyme concentra- ..... 1 Beale, E.M.L., M. G. Kendall, and D. W. Mann.
Relationship of In Vitro Immune Function with Health and Production in Holstein Cattle1 K. A. WEIGEL,2 A. E. FREEMAN, M. E. KEHRLI, JR.,3 J. R. THURSTON,3 and D. H. KELLEY Department of Animal Science Iowa State University Ames 50011
ABSTRACT
vitro immune function assays may serve as indicators of susceptibility to health problems in dairy cattle, particularly for traits associated with udder health. (Key words: immune function, health, production)
Eighty-seven lactating Holstein cows from the Iowa State University Breeding Research Herd were evaluated for 20 in vitro measures of immune function. Principal component analysis was used to discard redundant assay variables such that the 11 remaining variables were more nearly independent than the original variables. Multiple linear regression in an animal model was used to determine the effects of these 11 variables on lifetime production and on general, udder, and reproductive health traits. A significant joint effect of the 11 inunune function variables on California mastitis test scores was observed. California mastitis test scores were positively correlated with antibody-dependent neutrophil cytotoxicity and negatively correlated with antibody-independent neutrophil cytotoxicity. Wisconsin mastitis test scores were also positively associated with antibody-dependent neutrophil cytotoxicity. Cytochrome c reduction was negatively associated with mammary and total health costs. A positive relationship between clinical mastitis and discarded milk and IgG2 was observed, and IgGI was associated with increased quarter California mastitis test scores and increased production. Thus, certain in
Abbreviation key: ADNC = antibodydependent neutrophil cytotoxicity, AINC = antibody-independent neutrophil cytotoxicity, CMT = California mastitis test, WMT = Wisconsin mastitis test. INTRODUCTION
Received September 16, 1991. Accepted February 10, 1992. IJoumal Paper Number J-14505 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Pro~t Number 1053. Present Address: Department of Dairy Science, University of Wisconsin, Madison 53706. 3Agricultural Research Service, USDA, National Animal Disease Center, Ames, IA 50010.
1992 J Dairy Sci 75:1672-1679
Extensive research in recent years has demonstrated the potential for genetic improvement of resistance to health problems in domestic livestock species (16, 17, 21, 23, 32, 36, 38, 39). To implement such a genetic improvement scheme, a particular trait or set of traits on which to base genetic selection needs to be defined. The most likely objective would be reduction of total health costs, although one may consider categorizing health costs and attempting to reduce a particular component, such as reproductive or mammary system costs (2, 28). Obvious problems exist with selection based on cost data. because treatment costs depend on nongenetic factors, such as proper and timely detection of the problem, the decision of whether to treat the problem, and the choice of treatment. Each of these factors may depend on the individual producer, the attending veterinarian, or the value of the animal (30). In this respect, actual health incidence data appear to be more suitable criteria. The major drawback, however, of both incidence and cost data is that adequate data for an individual animal may not be available until late in life, and, even then, data may be insufficient or inaccurately recorded (21). Numerous alternative criteria have been
1672
IMMUNE FUNCTION AND HBALm
suggested for measurement of mastitis, which is the most economically important disease in dairy cattle. Indirect measures, such as California mastitis test (CMT) (27) and Wisconsin mastitis test (WMT) (33) scores and somatic cell counts (5, 8, 30), share the advantage of detecting both clinical and subclinical mastitis while being objective, simple, and economical (5,30). Other methods, such as bacteriological testing and measurement of enzyme concentrations, lactose, certain milk proteins, and ionic composition of milk. also exist (23). However, the primary disadvantage of those and all other previously discussed methods is that they involve sex-limited traits, which are not measurable until the cow is of lactating age. In this sense, direct measures of immune system functions would be most desirable in that early (e.g., calfhood) detection in both sexes would be possible. A distinction must be made between specific and general measures of immunity. Specific immunity, such as antibody titer relative to a specific pathogen, could be imparted by vaccination. Such immunity, however, may be of limited value with regard to a disease such as mastitis, which is caused by a multiplicity of pathogens (3). Increases in general immune competence could allow enhanced resistance to all pathogens and would, thus, be a much more desirable selection criterion. Although methods for assessing general immune competence are not yet sufficiently simple and economical for widespread use, increasingly accurate and efficient methods are rapidly being developed. Various in vitro assays have been applied to serve as correlates of in vivo neutrophil function; lymphocyte proliferation; and serum Ig, complement, and conglutinin concentrations (16). The purpose of this study was to examine the association of 20 in vitro measures of general immune competence with 12 health and production traits to determine the potential of these assays as criteria for genetic selection for improved health in dairy cattle. MATERIALS AND METHODS
Experimental Animals
Eighty-seven lactating Holstein cows of high or average genetic merit for milk production from the Iowa State milk selection experi-
1673
ment (2, 29) were used in the study as described by Weigel et a1 (39). This sample included 36, 20, 14, 8, 5, 3, and 1 cows of first, second, third, fourth, fIfth, sixth, and seventh parities, respectively. Immune FuncUon Data
Five peripheral blood samples per cow were taken over a 2-mo period in June and July 1988. The in vitro immune function assays have been described in detail (16) and are summarized briefly herein. Neutrophil Function Assays. Neutrophil extracellular killing was measured by antibodydependent neutrophil cytotoxicity (ADNC) and antibody-independent neutrophil cytotoxicity (AINC). These assays evaluate the ability of the neutrophil to lyse radiolabeled target cells in the presence and absence of specific antibody against the target cells as measured by the percentage of release of 51er (20, 25). Neutrophil phagocytic ability was evaluated by ingestion, chemiluminescence, cytochrome c reduction, and iodination assays. The ingestion assay measures the rate of engulfment (percentage of 60 bacteria ingested per neutrophil) of 12SI-labeled Staphylococcus aureus into neutrophil phagosomes (26). Native chemiluminescence detects light emitted (loglO total counts) during the metabolic burst associated with phagocytosis (e.g., from superoxide anion production, oxidation of bacterial proteins, and peroxidation of lipids) (14). The cytochrome c reduction assay specifically measures superoxide anion production (nanomoles reduced per 107 neutrophilsJh) by neutrophils (4). Iodination measures the release and activity of myeloperoxidase to evaluate degranulation of primary granules (26). Random and directed migration assays evaluate movement of neutrophils either randomly or toward a chemotactic factor, respectively, as correlates of the ability of the neutrophils to move through tissue to an infection site (24). Lymphocyte Blastogenesis Assays. Lymphocyte blastogenesis assays measure in vitro DNA synthesis by peripheral T and B lymphocytes as a correlate of the ability of these cells to undergo clonal expansion in response to infection. Blastogenesis was measured (log10 counts per minute) when lymphocytes were both unstimulated and stimulated by T
