EFFECT OF TRACE MINERAL AMOUNT AND SOURCE ON IMMUNE FUNCTION AND OXIDATIVE STRESS IN DAIRY COWS
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Forty-eight multiparous Holstein cows during early to midlactation were utilized to assess effect of trace mineral amount and source on immune function and oxidative status in dairy cows. Cows were fed a diet formulated to meet or exceed NRC (2001) nutrient requirements for all nutrients except for trace minerals of interest (Zn, Cu, and Mn), which were supplied from basal ration ingredients only. In addition, all cows were fed a preliminary diet for four weeks (week ?3 to week 0), containing 0.37% sulfur (dry matter basis, ration addition), 5 ppm of molybdenum from sodium molybdate (topdress), and 250 ppm of iron from iron sulfate (topdress) to decrease trace mineral absorption and status. After this four-week preliminary period, the sulfur content of the basal diet was reduced to 0.30%, the topdress of the Mo and Fe ceased, and cows were assigned to one of four dietary treatments for six weeks (week 1 to week 6) in a randomized complete block design: 1) NRC inorganic (NRC 2001 levels using inorganic trace mineral supplements only); 2) NRC organic (NRC 2001 levels using organic trace mineral supplements only); 3) Commercial inorganic (commercial levels (approximately 2X NRC requirement) using inorganic trace mineral supplements only; 4) Commercial organic (commercial levels using organic trace mineral supplements only). Supplemental inorganic Zn, Cu, and Mn were supplied using zinc sulfate monohydrate, cupric sulfate pentahydrate, and manganese sulfate monohydrate, respectively. Organic trace minerals were supplied as Zn, Cu, and Mn chelated to 2-hydroxy-4-(methythio)-butanoic acid (HMTBA). All oxidative status parameters from weekly blood samples were not affected by treatments when assessed across the entire treatment period. However, there were tendencies at week 1 of treatment period for decreased glutathione peroxidase activity for cows fed trace minerals at commercial levels, decreased total antioxidant capacity (TAC) in plasma for cows fed inorganic sources of trace minerals at NRC levels, and decreased concentrations of thiobarbituric acid reactive substances (TBARS) for cows fed organic trace mineral sources. At week 6 of treatment (one week following LPS challenge), cows fed commercial levels of trace minerals tended to have increased TAC and cows fed organic trace minerals had decreased TBARS in plasma. Plasma IgG level was higher in cows supplemented with organic trace minerals over the entire treatment period; responses assessed as differences of before and after E. coli J5 vaccination at the end of week 2 of treatment period were not significant. After LPS intramammary challenge at the end of week 5, plasma cortisol concentrations and clinical indices (rectal temperature and heart rate) increased and then decreased to pre-challenge level by 48 h after the challenge. However, the extent and pattern of response of these variables to LPS challenge were not affected by trace mineral level and source. Dry matter intake, milk composition, and milk component yield were not affected by trace mineral level and source, except for a trend for increased milk true protein content for cows fed the commercial level of trace minerals. Body condition score and body weight were not affected by treatment. Overall, varying level and source of trace minerals in the diet resulted in modest effects on parameters related to oxidative stress but did not appear to markedly affect responses of cows to intramammary LPS challenge.
TRACE MINERALS IMMUNE FUNCTION OXIDATIVE STRESS DAIRY COWS
dissertation or thesis