| Three experiments were conducted to investigate the effects of commercially available feed additives on production variables and metabolic markers when supplemented during the periparturient period. The hypothesis was that the supplementation of feed additives throughout the periparturient period would improve production variables and metabolic markers. For all experiments, the variables of interest included daily dry matter intake, milk yield, and feed efficiency as well as weekly body condition score, body weight, milk composition, 3.5% fat-corrected milk, energy-corrected milk, and colostrum immunoglobulin concentrations as measures of production performance. Plasma glucose, nonesterified fatty acids (NEFA), and beta-hydroxybutyrate (BHBA) were examined in all experiments as markers of metabolic health.;In the first experiment, the effects of feeding a B-vitamin and yeast supplement as a top dressing were examined. Cows received either 56 g/d of OmniGen-AF (OG; n = 9) or control (56 g/d soyhulls; n = 13) as a top dressing from -46 prepartum until 30 d postpartum. No overall treatment effects were observed for dry matter intake, milk yield, plasma metabolites, or colostrum immunoglobulin concentration; however treatment by time interactions were detected. Supplementation of OG increased milk protein percent in week one of lactation. Additionally, a trend indicated that OG cows had lower milk fat yield in week one but higher in week four of lactation compared to control treated cows. Energy-corrected milk, 3.5% fat-corrected milk, and fat-corrected milk efficiency were significantly affected over time by OG supplementation and followed the same pattern as milk fat yield. A trend in feed to milk conversion efficiency was observed with control cows more efficient on day 3 and OG supplemented cows more efficient on days 17 and 19 of lactation.;In the second experiment, the effects of trace mineral supplementation from inorganic or organic sources were examined. Cows were randomly assigned to either a control group (CTL, n = 13) without Mn, Co, Cu, and Zn supplementation, an inorganic trace mineral group (ITM, n = 11) supplemented with 200 mg Mn, 25 mg Co, 125 mg Cu and 360 mg Zn from sulfate and carbonate sources, or an organic trace mineral group (OTM, n = 11) supplemented with the same level of these trace minerals from a combination of inorganic and organic trace minerals chelated to amino acids or glucoheptonate. Mineral supplementation or control was administered daily via an oral gelcap bolus from -57.1 +/- 1 prepartum through 8 d postpartum. In addition to the variables of interest listed above, plasma thiol and thiobarbituric acid reactive substances (TBARS) were examined at days -58 +/- 1, -27 +/- 1, -14 +/- 1, -7 +/- 1, 1, and six relative to parturition as markers of oxidative stress. The OTM cows had the greatest intake and BCS throughout the study while ITM treated cows had the lowest. A treatment by time effect was observed when DMI was analyzed for the far-off and whole dry periods. The CTL cows had higher DMI than OTM or ITM treated cows from -58 to -55 d and -51 to -42 d relative to calving; respectively. The OTM treated cows had higher intakes than CTL cows during the last 17 d of the dry period and higher intakes than ITM treated cows from -52 to -2 d.;In the third experiment, the effects of feeding yeast culture were examined. Cows were randomly assigned to one of four treatments. Control (CTL, n = 39) without yeast culture, yeast culture supplemented at a rate of 56 g/d (1X, n = 40) or 112 g/d (2X, n = 37; Diamond V XP), or a new yeast product at the rate of 14g/d (LAC, n = 42). Treatment was mixed into total mixed ration diet daily from approximately -28 d prepartum through 86 d postpartum. Plasma glucose, NEFA, and beta-BHBA were measured at days -28 +/- 1, -7 +/- 1, 1 +/- 1, 7 +/- 1, 21 +/- 1, 42 +/- 1 and 84 +/- 1 relative to calving. Milk fat and protein yield were increased with 1X but not 2X; 2X supplementation decreased colostrum IgG and IgM concentrations and both 1X and 2X yeast culture supplementation decreased the net energy balance of cattle on study when compared to control cows. Dry mater intake decreased linearly while energy-corrected milk efficiency (ECM efficiency), somatic cell score, milk fat, protein, and solids-not-fat yield increased with 1X but not with 2X supplementation. The LAC treatment was also examined and found to be similar to control in nearly all variables of interest. (Abstract shortened by ProQuest.). |
