An immunomodulatory feed additive enhances in vitro viral vaccine recall antigen responses in dairy heifers.

Enhancing immunological responses to vaccination is an important goal in many herd health management systems. OmniGen-AF®(OG) is an immunomodulatory feed additive that has been shown to enhance innate immune function in ruminants and its effects on adaptive immunity require additional study. The objective of this study was to evaluate post-vaccine antibody titers and circulating cellular memory development in heifers fed OG and administered a commercially available modified-live bovine respiratory disease (BRD) vaccine. Twenty-four Holstein heifers were assigned to one of two diets for 170 days: Control TMR (CON; n = 11), or TMR plus OG (TRT; 9 g/100 kg BW/day; n = 13). Samples for hematology, serology, and cellular assays were collected on D-110, 0, 21, 42, and 60 of the trial. Heifers were administered two priming doses of a modified-live BRD vaccine, with a third dose given on D0. There were no significant differences in total WBC and absolute number or the percentage of circulating lymphocytes, monocytes, neutrophils, RBC, or platelets on D-110 through D21. On D42 and D60, CON had significantly higher numbers of lymphocytes. On D0, mean serum neutralizing (SN) titer to BHV-1 was significantly higher for CON compared to TRT. SN titers were not significantly different between CON and TRT at any other time point for BHV-1, BVDV type 1, or BVDV type 2. TRT mounted a significantly stronger recall proliferative response to 0.5 multiplicity of infection (MOI) of BHV-1, BVDV type 1 and BVDV type 2 on D42 and D60; 0.25 MOI of BVDV type 1 on D21 and D42; and 0.25 MOI BVDV type 2 on D42 compared to CON. IL-4 production induced by 0.5 and 1.0 MOI BHV-1 (D42 and D60); 0.25 MOI of BVDV type 1 (D21); and 0.25 and 0.5 MOI of BVDV type 2 (D60) were significantly higher for TRT than CON. IL-17 production induced by 0.25 MOI of BVDV type 1 was significantly higher on D60 for TRT compared to CON. IFN-gamma and IL-10 were not significantly different between treatments. These data indicate feeding OG has a beneficial effect on responses to vaccine antigens in Holstein dairy heifers.

Effects of an immunomodulatory feed additive on intramammary infection prevalence and somatic cell counts in a dairy herd experiencing major health issues.

A trial was conducted to determine if feeding OmniGen-AF® (OG) to 22 late lactation cows 60 days prior to and during the early dry period, a time of increased susceptibility to mastitis, could reduce disease incidence in a dairy herd experiencing major health issues. Treated cows (n = 11) consumed a ration containing OG [9 g/100 kg of body weight/day] beginning 60 days before dry-off, during the dry period, and through 30 days in milk (DIM). Control cows received the same ration during the dry period through 30 DIM only. Body weights, body condition scores (BCS), intramammary infection (IMI) prevalence, new IMI rates, somatic cell counts (SCC), milk yield, and adverse health events were measured. No differences were found between treatments for body weight or BCS. Adverse health event data at calving showed no differences between treatments except for percentage of cows with hyperketonemia, which was lower among treated cows (63.6% vs 100%). Prevalence of IMI from calving through 30 DIM for treated cows (6.1%) was lower than controls (11.05%); likewise, new IMI rate during this time for treated cows (0.61%) was lower than controls (5.81%). The SCC from calving through 30 DIM for treated cows (215,000/ml) was lower than controls (493,000/ml). Average production/day at the first DHIA test (~33 DIM) showed that treated cows produced more milk (39.9 kg) than controls (35.34 kg). In conclusion, feeding OG 60 days prior to dry-off reduced hyperketonemia and mastitis, lowered SCC, and numerically increased milk yield in a dairy herd experiencing major health issues.

Effect of dietary supplementation on the antimicrobial activity of blood leukocytes isolated from Holstein heifers.

The purpose of this investigation was to evaluate the effect of an immunostimulating feed supplement (OmniGen-AF®) on the antimicrobial properties of blood leukocytes in dairy heifers in an attempt to prevent mastitis. Blood leukocytes from supplemented and unsupplemented controls were used. Phagocytic activity and reactive oxygen species (ROS) production were studied on d 0 (prior to feed supplementation) and on days 30 and 60 after supplementation. L-selectin and IL-8R mRNA expressions on blood leukocytes were evaluated on d 0 (prior to feed supplementation) and monthly thereafter for 15 mo. On d 30 after supplementation, neutrophils from treated heifers exhibited greater binding and internalization of Escherichia coli and greater ROS production compared with unsupplemented controls. L-selectin mRNA expression was increased in supplemented heifers vs. controls; however, IL-8R mRNA expression was not different. Results support the continued study of dietary supplementation as an additional management tool to enhance udder health in dairy heifers.

Nitrogen metabolism and hormonal responses of steers fed wheat silage and infused with amino acids or casein.

Four Holstein steers (159 kg) surgically fitted with abomasal-infusion cannulas were used in a 4 x 4 Latin square study to test amino acid (AA) and casein (CAS) infusions on nitrogen balance and hormonal status of steers consuming vegetative wheat (Triticum aestivum L.) silage (12.3% CP). Treatments were 5-d infusions of 1) water (CONT), 2) arginine (ARG; 13.69 g/d), 3) limiting amino acids (LAA, 13.69 g/d arginine + 10.92 g/d histidine + 28.97 g/d lysine + 10.88 g/d methionine + 16.96 g/d threonine, and 4) Na-CAS (300 g/d). Whole blood was collected for plasma AA, growth hormone (GH), insulin, and IGF-I concentrations. Data were analyzed by ANOVA, and the following orthogonal contrasts were used to separate treatment means: CONT vs ARG; ARG vs LAA; and LAA vs CAS. Urinary N increased (P < .02) for CAS vs LAA. Arginine increased N retention, as did CAS, compared to LAA. Total plasma essential AA were decreased by arginine. Mean plasma insulin concentrations were increased by CAS (P < .034). Arginine increased mean plasma GH levels, but not IGF-I. The CAS treatment increased (P < .015) IGF-I levels, but not GH. These data suggest that performance of steers fed wheat silage was limited by duodenal AA flow and that arginine was the first-limiting AA. Casein infusion increased plasma insulin and IGF-I, which would explain the improved growth noted in calves and lambs fed forages supplemented with ruminally undegraded protein.