The negative energy balance that accompanies a reduction in feed intake around parturition is an important contributor to immunosuppression. Thus, dry period feeding strategies that result in improved energy balance early post-partum may be effective tools for producers to minimize periparturient immunosuppression, which should in turn reduce morbidity and economic losses from culling of cows due to mastitis and other immune-related diseases. The objectives of the current proposal are to examine blood neutrophil and mammary gene expression profiles, using a newly developed 13,000-sequence oligonucleotide array and qPCR, as affected by negative energy balance and post-partum intrammamary challenge with S. uberis. Gene expression data will be combined with immune parameters (e.g., blood neutrophil phagocytosis and chemotaxis, blood inflammatory mediators, milk SCC) and production data that will allow creation of models demonstrating a link between prepartum nutrition, negative energy balance, and the immune system. Results will lead to feeding recommendations to minimize periparturient immunosuppresion, thus improving profitability of dairy production and animal well-being.
We will compare gene expression in mammary tissue and blood neutrophils in cows fed to energy requirements (95-105% of energy requirements; control cows) during the dry period with gene expression in cows fed excessive energy (160-185% of energy requirements), and cows with restricted energy (80% of energy requirements) intake during the dry period. We expect to enroll 14 cows per treatment, of which half will be challenged with S. uberis at 5 to 8 days postpartum. Mammary tissue will be obtained at 24 hours post-challenge, and blood at different time points before, during, and after the challenge. We will subject RNA isolated from blood neutrophils (24 hours post-challenge) and mammary tissue to microarray analysis using a 13,000 gene oligonucleotide array developed at the University of Illinois. We will obtain blood samples at -21, -15, daily from -10 through +10 days, +15, and +21 days relative to parturition. Plasma or serum isolated from the above samples will be assayed for concentrations of NEFA, BHBA, glucose, insulin, and cortisol using established methods. Neutrophil phagocytosis and chemotaxis will be assayed in blood collected prior to S. uberis challenge, 4 hours post-challenge (i.e., acute stress response), 12 hours post-challenge, just prior to mammary biopsy at 24 hours post-challenge, and at 36 hours post-challenge. Another aliquot of blood collected for neutrophil assays will be used to determine concentrations of TNF-alpha, IL-8, IL-1Beta, and SAA1. All of these blood parameters will be related to gene expression in neutrophils and mammary tissue.
Mastitis is the most costly disease to U.S. animal agriculture (close to $2 billion annually), due to losses in milk production, costs of drugs, costs of discarded milk, and high culling rates. The consequences of mastitis go far beyond economics, severely affecting animal well-being and thus represent a primary reason for culling or death of dairy cows. Mastitis caused by environmental pathogens such as S. uberis occurs with the highest frequency around parturition (periparturient period). Dairy cows undergo a period of reduced immunological capacity affecting numerous tissues during the transition from pregnancy to lactation, which renders them more sensitive to invading pathogens and highly susceptible to infectious diseases such as mastitis. Management practices, such as feeding strategies, during the dry period can have profound effects on animal metabolism and the immune system. Thus, feeding strategies that result in improved energy balance soon after calving might be effective tools for producers to minimize the extent of periparturient immunosuppression, which in the long run should reduce morbidity and economic losses due to mastitis or other infectious disorders.