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Characterization of host mechanisms associated with mastitis susceptibility and resistance. (i) Environment, Nutrition, and Management Related Host Factors Associated with IMI. Overall, there is a need to better understand how alterations in retinoid metabolism and retinol transport (i.e., RBP), due to a functional transition from a non-lactating to lactating status affects immune function relevant to incidence and severity of new IMI. Therefore, the central hypotheses to be tested are that 1) hyporetinemia associated with the intra-mammary infection (IMI) may be explained by a decrease in retinol-RBP complex, and 2) altered retinoid metabolism affects immune response to occurrence of an experimentally-induced mammary gland infection. <P>
Specific Aims: <OL> <LI> To determine the effect of dietary supplementation of vitamin A and protein, during the non-lactating period, on retinoid metabolism and circulating RBP in vivo during the periparturient period.<LI> To investigate whether dietary supplementation of vitamin A and protein, during the non-lactating period, modifies immune response to an experimentally (E. coli)-induced IMI during early lactation.
NON-TECHNICAL SUMMARY: The risk of mastitis is greatest during the transition period. The cost of mastitis is a significant loss for the dairy industry of greater than $1.7 billion each year. During the last 25 years, there has been improvement in mastitis prevention and control as well as a greater understanding of the effects of dietary nutrients on immune function. However, research on nutritional factors affecting immune function in particular, bovine retinoid metabolites and RBP, the carrier protein for retinol, are limited for dairy cows during the periparturient period and in response to intra-mammary infection. Our laboratory has been investigating the metabolic challenges during the transition period in dairy cows and their effects on specific immune measures and, in particular, on mastitis. This proposed project will create new knowledge of the effects of the retinoids (e.g., vitamin A) on immune system function in dairy cows. The results will lead to improved management practices and the potential to develop intervention strategies that can reduce the need for antibiotic use on dairy farms to treat infections.
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APPROACH: This study will be conducted using 60 high producing multiparous Holstein cows from ~ 4 weeks prepartum to 3 weeks postpartum, for which rations will be altered in CP and vitamin A contents. A complete randomized block design in a 2 x 2 factorial arrangement with 2 concentrations of ration CP and 2 concentrations of ration vitamin A will be used. Rations will be developed containing either 12.0% CP as recommended NRC (2001) or 16% CP. At each ration CP level, diets will be supplemented with vitamin A to provide either no supplemental or 110 IU/kg of BW (NRC, 2001). Fifteen cows will be randomly assigned to each dietary treatment. The cows will be blocked based on expected calving date, previous milk yield, current body condition score (BCS), and body weight (BW). The cows will be fed experimental total mixed rations twice a day, starting ~ 4 weeks prepartum (first week for adaptation) through parturition. A common lactation ration will be fed after parturition for all cows. Weekly BW, weekly BCS, and daily DMI will be measured. Using a subset of cows from Periparturient Study (n = 3/treatment), one quarter of each cow will be infused via the teat canal with E. coli. Quarter milk will be sampled at 0, 6, 12, 18 h after the intra-mammary E. coli infusion and at day +2,+ 3, +4, +7, +14 and +21, and used for bacteriological analysis. Quarter milk samples will be analyzed for beta-carotene, retinoids, fat, protein, total solid, lactose, and SCC. Quarter milk samples will be also used to isolate milk cells, and the population of neutrophils, B cells and T cells will be determined. Gene expression of pro-inflammatory cytokines including TNF-alpha, G/M-CSF, IL-1 beta, IL-6 and IL-8 will be measured in milk cells via quantitative real time reverse transcribed PCR. Blood samples will be collected at day -7 and 0 (relative to E. coli infusion), and at the same time point as milk samples . Concentrations of plasma albumin, haptoglobin, â-carotene, retinol, RBP, at-RA, 9-cis RA, 13-cis RA , total reactive oxygen species, thiobarbituric acid-reactive substances and leukocyte populations will be determined. The effects of increased dietary CP and retinol on measures of protein status, plasma RBP concentrations as well as retinoids and beta-carotene concentrations in milk and plasma/serum, and specific immune measures will be analyzed using the mixed model of SAS with cows as random effect and day as repeated measures. The interaction of effect of dietary treatments and effect of IM challenge on milk composition, leukocyte number, percentage of neutrophils, B cells and T cells, and the concentrations of IFN- gamma , and IL-10 as well as gene expression of pro-inflammatory cytokines will be analyzed using the mixed model of SAS (SAS, 2002). Significant differences will be declared when P is smaller than 0.05.