Vitamin E analogs limit in vitro oxidant damage to bovine mammary endothelial cells.

Diseases that occur during the transition period are exacerbated when cows are unable to cope with an increased pro-oxidant load that results in oxidative stress. Dairy cattle are routinely supplemented with the vitamin E analog α-tocopherol to mitigate the severity of oxidative stress. Nonetheless, oxidative stress remains a disease predisposing condition for many dairy cattle. A better method of optimizing the antioxidant functions of vitamin E is needed. α-Tocopherol is only 1 of 8 analogs of vitamin E, all of which have varying antioxidant properties in other mammals, albeit a shorter physiological half-life compared with α-tocopherol. A primary bovine mammary endothelial cell oxidant challenge model was used to determine functions of certain vitamin E analogs. The aim of this study was to determine if other analogs, namely γ-tocopherol or γ-tocotrienol, have antioxidative functions in bovine cells and if these functions may protect cellular viability and endothelial function from oxidant damage. Physiological (10 µM) and supraphysiological (50 µM) concentrations of γ-tocopherol and γ-tocotrienol had a greater capacity to reduce accumulated reactive oxygen species derived from a nitric oxide donating pro-oxidant antagonist, when compared with α-tocopherol, after 30 min to 6 h of treatment. Further, γ-tocotrienol (10 µM) decreased cell cytotoxicity to a greater amount than other analogs at like concentrations, whereas γ-tocopherol (10 µM) reduced lipid peroxidation and apoptosis more effectively than other analogs. Last, α-tocopherol (5 and 10 µM) and γ-tocopherol (5 and 10 µM) significantly slowed pro-oxidant induced loss of endothelial cell barrier integrity over a 48-h period using an electrical cell-substrate impedance sensing system. Concerningly, γ-tocotrienol drastically reduced the endothelial barrier integrity at only 5 µM despite no apparent effect on cellular viability at like concentrations. γ-Tocotrienol, however, was also the only analog to show significant cytotoxicity and reductions in viability at supraphysiological doses (25 and 50 µM). Our results suggest that γ-tocopherol has antioxidant activities that reduces cellular damage and loss of function due to oxidant challenge as effectively as α-tocopherol. These data set the foundation for further investigation into the antioxidant properties of vitamin E analogs in other bovine cells types or whole animal models.

Evaluation of natural plant extracts as antioxidants in a bovine in vitro model of oxidative stress.

Oxidative stress contributes to many inflammatory-based diseases of dairy cattle especially during periods of increased metabolic activity such as around calving. Endothelial cells play a key role in maintaining normal inflammatory responses, but they are especially susceptible to macromolecule damage during times of oxidative stress. Therefore, bovine aortic endothelial cells (BAEC) were used to study the effect of natural tannin-based extracts on oxidative stress that may improve health and well-being of cattle. Tannins are secondary metabolites in plants with potent antioxidant activity that have been used as natural feed additives for food-producing animals. However, there is little information on how tannin-rich plant extracts may affect oxidative stress in dairy cattle. The objective of this study was to evaluate the antioxidant effect of pomegranate (Punica granatum; PMG), tara (Caesalpinia spinosa; TA), chestnut (Castanea sativa; CH), and gambier (Uncaria gambir; GM) natural extracts using an in vitro BAEC model of oxidative stress. Natural extracts were tested at a concentration of 80 µg/mL. Viability, apoptosis, intracellular reactive oxygen species, and isoprostanes were determined on cultured BAEC treated with different plant natural extracts. No changes in cell viability was detected following PMG and GM treatments. In contrast, there was a 30% reduction of BAEC viability following treatment with CH or TA extracts. Intracellular reactive oxygen species production was significantly less abundant in cells treated with natural extracts than with the lipopolysaccharide control. Moreover, antioxidant activity varied according to the tested extract, showing a reduction of 63, 45, 51, and 27% in PMG, GM, CH, and TA, respectively. The formation of isoprostanes as a consequence of lipid peroxidation after induction of oxidative stress also were significantly decreased in PMG-treated cells when compared with the untreated cells. Theses findings suggest that PMG extract has the potential to mitigate oxidative stress without detrimental effects on cell viability. Further in vitro and in vivo research is warranted to explore the antioxidant potential of PMG extract as a dietary supplement to control oxidative stress in dairy cattle.

Serum vitamin D concentrations at dry-off and close-up predict increased postpartum urine ketone concentrations in dairy cattle.

Vitamin D is commonly supplemented to dairy cows as vitamin D3 to support calcium homeostasis and in times of low sunlight exposure. Vitamin D has beneficial immunomodulatory and anti-inflammatory properties. Serum 25-hydroxyvitamin D [25(OH)D] concentrations fluctuated during lactation, with the lowest concentrations measured in healthy cows within 7 d of calving. However, it is unknown if serum 25(OH)D concentrations measured during the previous lactation are associated with transition diseases or health risk factors in dairy cattle. We collected serum samples from 279 dairy cattle from 5 commercial dairy herds in Michigan at dry-off, close-up, and 2-10 d in milk (DIM). Vitamin D concentrations were determined by measuring serum 25(OH)D by radioimmunoassay. Total serum calcium was measured by colorimetric methods. Body condition scores (BCS) were assigned at the time of blood collection. Clinical disease incidence was monitored until 30 d postparturition. Separate bivariable logistic regression analyses were used to determine if serum 25(OH)D at dry-off, close-up, and 2-10 DIM was associated with various clinical diseases including mastitis, lameness, and uterine disorders (classified as metritis, retained placenta, or both) and increased urine ketone concentrations at P < 0.05. Among all significant bivariable analyses, multivariable logistic regression analyses were built to adjust for potential confounding variables including parity, BCS, season, and calcium. Receiver operator characteristic (ROC) curve analyses were used to determine optimal concentrations of serum 25(OH)D. We found that higher serum 25(OH)D concentrations at dry-off and close-up predicted increased urine ketone concentrations in early lactation, even after adjustment for confounders. Alternatively, we found that lower serum 25(OH)D at 2-10 DIM was associated with uterine diseases. Optimal concentrations for serum 25(OH)D at dry-off and close-up for lower risk of increased urine ketone concentrations were below 103.4 and 91.1 ng/mL, respectively. The optimal concentration for serum 25(OH)D at 2-10 DIM for uterine diseases was above 71.4 ng/mL. These results indicate that serum 25(OH)D at dry-off and close-up may be a novel predictive biomarker for increased urine ketone concentrations during early lactation. Increased urine ketone concentrations are not necessarily harmful or diagnostic for ketosis but do indicate development of negative energy balance, metabolic stress, and increased risk of early lactation diseases. Predicting that dairy cattle are at increased risk of disease facilitates implementation of intervention strategies that may lower disease incidence. Future studies should confirm these findings and determine the utility of serum 25(OH)D concentrations as a predictive biomarker for clinical and subclinical ketosis.

Reduced serum vitamin D concentrations in healthy early-lactation dairy cattle.

Cattle obtain vitamin D by ingestion or cutaneous exposure to UV light. Dairy cattle diets are frequently supplemented with vitamin D to compensate for limited sun exposure or during times of increased metabolic demands, such as the periparturient period, to maintain calcium homeostasis. Whether housing and supplemental vitamin D practices supply adequate amounts of vitamin D to optimally support the transition from gestation to lactation in dairy cattle is unknown. Our objective was to determine how serum vitamin D concentrations of dairy cows change with season, age, parity, and stage of lactation. Clinically healthy cows (n = 183) from 5 commercial dairies were enrolled in the study. Serum samples were collected at dry off, within 7 d of entering the close-up group, and within 7 d after calving (calving+7). Vitamin D status was determined by measuring serum 25-hydroxyvitamin D [25(OH)D] by radioimmunoassay. We performed repeated-measures mixed-effects linear regression to determine the effects of season, age, parity, and lactation stage (dry off, close-up, and calving+7) on 25(OH)D concentrations in serum. Bivariable analysis indicated that parity, age, and season were not associated with serum 25(OH)D concentrations. Sample period affected 25(OH)D concentrations, with the highest 25(OH)D levels at dry off (99.7 ± 1.9 ng/mL) followed by close up (93.8 ± 2.1 ng/mL), with the lowest levels at calving+7 (82.6 ± 1.7 ng/mL). These data showed a large depletion of 25(OH)D in dairy cattle postpartum compared with late prepartum, although the biological significance of this change in these healthy cattle is unclear. Consumption of serum 25(OH)D by immune system functions and calcium homeostasis in early lactation likely caused the reduction in serum 25(OH)D concentrations after calving. These results suggest that determining whether serum 25(OH)D concentrations are associated with the incidence of transition period disease is an appropriate next step. Assessing the effects of enhanced vitamin D supplementation of cows in early lactation on postpartum diseases may be warranted.

Supplementation of linoleic acid (C18:2n-6) or α-linolenic acid (C18:3n-3) changes microbial agonist-induced oxylipid biosynthesis.

Oxylipids are derived from polyunsaturated fatty acids (PUFA) in cellular membranes and the relative abundance or balance may contribute to disease pathogenesis. Previous studies documented unique oxylipid profiles from cows with either coliform or Streptococcus uberis mastitis, suggesting that lipid mediator biosynthesis may be dependent on the type of microbial-derived agonist. Changing the fatty acid content of peripheral blood leukocytes also may be critical to the relative expression of oxylipid profiles and the outcome of bacterial infection. No information is available in dairy cows describing how changing cellular PUFA content will modify oxylipids in the context of a microbial agonist challenge. Therefore, the hypothesis for the current study was that PUFA supplementation would change bovine leukocyte fatty acid content and respective oxylipid profiles from ex vivo microbial agonist-challenged leukocytes. Fatty acid content of leukocytes and plasma was quantified in (1) samples from cows not supplemented with PUFA, (2) cows supplemented with linoleic acid (LnA), and (3) cows supplemented with α-linolenic acid (ALA). Plasma oxylipids were assessed after S. uberis or lipopolysaccharide exposure and was compared with unstimulated oxylipid profiles. Fatty acid supplementation with ALA significantly increased ALA content of blood leukocytes and plasma relative to LnA. Fatty acid supplementation affected several S. uberis-induced oxylipids, but only S. uberis-induced 15-oxoETE was greater with ALA supplementation compared with LnA. Notably, only LPS-induced 5,6 LXA4 was altered with fatty acid supplementation, but no significant effect of LnA vs. ALA treatment was identified. Future studies are needed to understand how leukocyte activation and membrane PUFA availability collectively contribute to differential oxylipid profiles.

Comparison of supplementation of n-3 fatty acids from fish and flax oil on cytokine gene expression and growth of milk-fed Holstein calves.

The ability to reduce incidence of disease in calves and improve early vaccination strategies is of particular interest for dairy producers. The n-3 fatty acids have been reported to reduce inflammatory diseases in humans but limited research has been done in calves. The objective of this study was to compare supplementation of n-3 fatty acids from fish and flax oil on gene expression of whole blood cells and growth of milk-fed Holstein calves. Forty-eight Holstein bull calves from a commercial dairy were randomly assigned to 1 of 3 diets beginning at 4d old: (1) control milk replacer (MR) with all pork fat, (2) MR with 2% flax oil, and (3) MR with 2% fish oil. All MR were 17% fat, 27% crude protein on a dry matter (DM) basis, with all protein from whey sources. Calves were each fed 654g DM of MR daily for the first 25d and then 327g/d for d26, 27, and 28. On d28, calves were challenged with a Pasteurella vaccine and the temperature response to the vaccine was recorded. Milk and feed intake and fecal scores were recorded daily, and body weight and hip width were recorded weekly. Blood was collected from all calves on d25. One tube of collected blood was incubated with endotoxin (lipopolysaccharide; LPS) for 2h and frozen with a second tube of control blood. Quantitative real-time PCR was used to assess the effects of LPS stimulation on cytokine gene expression. During the 28 d, calves supplemented with flax oil had a greater growth rate and feed efficiency than calves fed fish oil (0.52±0.02 vs. 0.48±0.02g of gain:g of feed). Fish oil tended to decrease LPS stimulation of tumor necrosis factor-α expression. Flax oil, but not fish oil, decreased the expression of IL-4 and tended to decrease expression of osteopontin and IL-8. Flax oil tended to reduce the increase in rectal temperature in response to a Pasteurella vaccine. In conclusion, our data support the idea that supplementation with n-3 fatty acids affects cytokine gene expression.

Enhanced n-3 phospholipid content reduces inflammatory responses in bovine endothelial cells.

Uncontrolled inflammation contributes to the increased incidence and severity of infectious diseases in periparturient dairy cattle. The objective of this study was to determine if increasing n-3 fatty acid (FA) content and altering the profile of vasoactive eicosanoids could attenuate endothelial cell inflammatory responses. Bovine aortic endothelial cells (BAEC) were cultured with free FA mixtures that mimic the plasma NEFA composition during the first week of lactation of dairy cows or with a free FA mixture supplemented with a higher proportion of n-3 FA, including eicosapentaenoic and docosahexaenoic acids. The effects of increasing the docosahexaenoic and eicosapentaenoic acid content of BAEC on the expression of proinflammatory mediators and eicosanoid biosynthesis was assessed. Culturing BAEC with enriched concentrations of n-3 FA decreased the expression of proinflammatory cytokines, adhesion molecules, and reactive oxygen species with a concomitant increase in the biosynthesis of proresolving eicosanoids, including resolvins, protectins, and lipoxins. This study showed for the first time that increasing the n-3 FA content of endothelial cell phospholipids could alter the expression of eicosanoids and control the magnitude of inflammatory responses. Future studies are necessary to elucidate the mechanisms by which resolvins, protectins, and lipoxins may modify endothelial inflammatory pathways necessary to reduce the severity and duration of disease in periparturient cows.

Fatty acid intake alters growth and immunity in milk-fed calves.

The aim of the present study was to determine the effect of supplementing milk replacer (MR) with NeoTec4 (Provimi North America, Brookville, OH), a commercially available blend of butyric acid, coconut oil, and flax oil, on calf growth, efficiency, and indices of immune function. In trial 1a, 48 male Holstein calves were fed either a control MR that contained only animal fat or the same MR with NeoTec4 (treatment) along with free-choice starter. The MR (28.7% crude protein, 15.6% fat) was fed at an average of 1 kg of dry matter (DM)/d. In trial 1b, weaned calves from trial 1a were all fed dry starter for 28 d without NeoTec4 (phase 1), and then half the calves were fed NeoTec4 for 28 d (phase 2). In trial 2, 40 male Holstein calves were fed a control MR with lard, coconut oil, and soy lecithin or the same MR supplemented with NeoTec4 (treatment). The MR (22.8% crude protein, 18.9% fat) was fed at an average of 1 kg of DM/d; no starter was fed. In trial 1a, NeoTec4 improved average daily gain, feed intake, and feed efficiency, reduced the number of days that calves experienced scours, and reduced the medical treatments for clostridium sickness. In trials 1a and 2, NeoTec4 altered the inflammatory response to vaccination with Pasteurella at 5 wk of age and to challenge with Salmonella toxin at less than 2 wk of age (fed NeoTec4 for 6 d), as observed by reduced hyperthermia and hypophagia, and altered the tumor necrosis factor-α response. In addition, NeoTec4 enhanced the response in IL-4 and globular protein estimates postchallenge and enhanced titers for bovine viral diarrhea and respiratory parainfluenza-3. Postchallenge serum concentrations of albumin were lower and urea nitrogen concentrations were greater in control calves than in calves fed NeoTec4. In trial 1b, performance did not differ during the first 28 d when no calves received NeoTec4, but calves receiving NeoTec4 in the second 28 d had greater average daily gain and feed efficiency. We conclude that supplementation of MR with NeoTec4 alters some immune and inflammatory responses, including increasing titers to bovine viral diarrhea and respiratory parainfluenza-3 vaccinations, reduces scours, reduces medical treatments for clostridium sickness, and improves growth rates and feed efficiency.

Oxidant stress enhances Lyso-PAF-AcT activity by modifying phospholipase D and phosphatidic acid in aortic endothelial cells.

Oxidant stress, as a consequence of selenium (Se) deficiency, alters production of vasoactive compounds including platelet-activating factor (PAF). Recent studies report that enhanced PAF production during Se deficiency is a consequence of increased lyso-PAF:acetyl-coenzyme A acetyltransferase (Lyso-PAF-AcT) activity. To elucidate the mechanism behind increased Lyso-PAF-AcT activity during oxidant stress, phospholipase D (PLD) activity and phosphatidic acid (PA) production were examined. Increased PLD activity and PA production were exhibited in bovine aortic endothelial cells using a Se-deficient model of oxidant stress. The direct effects of PLD and PA on Lyso-PAF-AcT activity were assessed using selective inhibitors and repletion experiments. Following the inhibition of PLD and addition of exogenous PA, Lyso-PAF-AcT activity significantly decreased and increased, respectively. Therefore, Se deficiency enhances Lyso-PAF-AcT activity in part by modifying PLD and PA. This suggests a novel link between Se status and PAF production, providing potential upstream therapeutic targets for PAF regulation under conditions of oxidant stress.

Increased 15-HPETE production decreases prostacyclin synthase activity during oxidant stress in aortic endothelial cells.

Selenium (Se) is an integral component of glutathione peroxidase and is able to detoxify peroxides that can affect arachidonic acid (AA) metabolism, thereby influencing eicosanoid biosynthesis. This study investigated the effects of oxidant stress, a consequence of Se deficiency, on eicosanoid formation and important key enzyme expression in bovine aortic endothelial cells (BAEC). Bovine aortic endothelial cells cultured in Se-deficient media and stimulated with tumor necrosis factor alpha or H2O2 produced significantly less prostacyclin (PGI(2)) and more 15-hydroxyeicosatetraenoic acid, 15-hydroperoxyeicosatetraenoic acid (15-HPETE), and thromboxane than Se-supplemented BAEC. Additionally, reverse transcription polymerase chain reaction and immunoblotting determined that the mRNA and protein levels of the eicosanoid forming enzymes cyclooxygenase-1 (COX1), cyclooxygenase-2 (COX2), and PGI synthase were not significantly changed. The addition of 15-HPETE to Se-supplemented BAEC inhibited the production of PGI(2) suggesting that the accumulation of lipid hydroperoxides during Se-deficiency may be the underlying factor in the altered eicosanoid production during Se deficiency. Furthermore, inhibition of COX and addition of PGH(2) to Se-deficient or Se-supplemented BAEC still resulted in lower PGI(2) formation by Se-deficient cells. Together, these results suggest that Se deficiency modifies eicosanoid production by affecting the activity of key enzymes, particularly PGI synthase, rather than their transcription or translation.

Selenium modulates 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine (PAF) biosynthesis in bovine aortic endothelial cells.

Selenium (Se) deficiency has been reported to increase platelet-activating factor (PAF) production in human endothelial cells; however, the mechanism is unclear. This study demonstrated that tumor necrosis factor-alpha (TNF-alpha) stimulated Se-deficient bovine aortic endothelial cells (BAEC) produced significantly more PAF than Se-supplemented cells. Moreover, the increase in the level of PAF was associated with enhanced activity of two anabolic enzymes in the remodeling pathway: phospholipase A2 and Lyso-PAF:acetyl-coenzyme A acetyltransferase (Lyso-PAF-AcT). In contrast, the activity of the PAF catabolic enzyme, PAF-acetylhydrolase, was not affected by Se status. Interestingly, prostacyclin, a potent vasodilator and inhibitor of platelet aggregation, inhibited the activity of Lyso-PAF-AcT and reduced the PAF production in TNF-alpha-stimulated BAEC. Therefore, we conclude that Se deficiency alters PAF production in TNF-alpha-stimulated BAEC by altering the activity of anabolic enzymes involved in the remodeling pathway partially through the inhibition of prostacyclin production.

Altered eicosanoid biosynthesis in selenium-deficient endothelial cells.

Selenium (Se) is an integral part of the Se-dependent glutathione peroxidase (Se-GSH-Px) catalytic domain. By modulating the cellular levels of fatty acid hydroperoxides, Se-GSH-Px can influence key enzymes of arachidonic acid cascade, in this case cyclooxygenase (COX) and lipoxygenase (LOX). To investigate this phenomenon, the effects of cellular Se status on the enzymatic oxidation of arachidonic acid were investigated in bovine mammary endothelial cells (BMEC), which were cultured in either Se-deficient (-Se) or Se-adequate (+Se) media. When stimulated with calcium ionophore A23187, BMEC produced eicosanoids of both COX and LOX pathways. Compared with the Se-adequate cells, the production of prostaglandin I(2) (PGI(2)), prostaglandin F(2) (PGF(2alpha)), and prostaglandin E(2) (PGE(2)) was significantly decreased in Se-deficient cells, whereas the production of thromboxane A(2) (TXA(2)) was markedly increased in the -Se BMEC cultures. Although the enzymatic oxidation of arachidonic acid by the LOX pathway was found to be relatively less than by the COX pathway, the BMEC cultured in -Se media produced significantly more 15-hydroperoxyeicosatetraenoic acid (15-HPETE) than the +Se cells produced. Based on these results, we postulate that cellular Se status plays an important regulatory role in the enzymatic oxidation of arachidonic acid by the COX and LOX pathways. The altered eicosanoid biosynthesis, especially the overproduction of 15-HPETE, in -Se BMEC may be one of the underlying biochemical phenomena responsible for vascular dysfunction during Se deficiency.

Increased neutrophil adherence and adhesion molecule mRNA expression in endothelial cells during selenium deficiency.

Leukocyte aggregation and activation on endothelial cells (EC) are important preliminary events in leukocyte migration into tissue and subsequent inflammation. Thus, an increase in leukocyte adherence has the potential to affect inflammatory disease outcome. Selenium (Se) is an integral part of the antioxidant enzyme glutathione peroxidase (GSH-Px) and plays an important role in the maintenance of the redox state of a cell. Se supplementation in the bovine has been shown to improve the outcome of acute mastitis caused by coliform bacteria, in part by enhancing the speed of neutrophil migration into the affected mammary gland. However, the mechanisms by which Se modulates neutrophil migration have not been elucidated. Therefore, an in vitro model of Se deficiency in primary bovine mammary artery EC was used to examine the impact of Se status on the adhesive properties of EC. The effect of Se on functional activities was examined by measuring neutrophil adherence to Se-deficient and Se-supplemented EC. Se-deficient EC showed significantly enhanced neutrophil adherence when stimulated with tumor necrosis factor alpha (TNF-alpha) for 4 or 24 h, interleukin-1 for 12 h, or H2O2 for 20 min (P < 0.05). To determine the mechanisms underlying these changes in neutrophil adherence, the expression of EC adhesion molecules, ICAM-1, E-selectin, and P-selectin were examined at the molecular level by a competitive reverse transcription-polymerase chain reaction. Results revealed higher mRNA expression for E-selectin and ICAM-1 in Se-deficient EC stimulated with TNF-alpha for 3 and 6 h, and greater expression of P-selectin mRNA in Se-supplemented EC with 3-h TNF-alpha stimulation. These studies provide new information to establish the role of Se nutrition in the initiation of leukocyte adherence to endothelium.

Selenium and vitamin E deficiency impair transferrin receptor internalization but not IL-2, IL-2 receptor, or transferrin receptor expression.

Vitamin E and Se deficiency increase the risk of disease by impairing the immune response. To aid in the understanding of how vitamin E and Se deficiency reduce immune competence, this study examined several mechanisms necessary for lymphocyte proliferation. Weanling rats were fed a vitamin E-deficient, selenium-deficient, or control diet for 8 weeks. At this time splenic mononuclear cells were isolated and stimulated with concanavalin A for 48 h. Although the percentage of lymphocytes and monocytes capable of proliferating were consistent among the dietary groups, lymphocyte proliferation was decreased significantly in vitamin E- and selenium-deficient rats. This decrease in proliferation was not associated with alterations in interleukin-2, interleukin-2 receptor, or transferrin receptor expression. However, stimulated cells from vitamin E- and Se-deficient rats internalized few if any transferrin receptors. Reduced transferrin receptor internalization may limit lymphocyte expansion by depleting the intracellular iron stores needed for cellular function and proliferation.

Arginine supplementation increases weight gain, depresses antibody production, and alters circulating leukocyte profiles in preruminant calves without affecting plasma growth hormone concentrations.

The hypothesis that dietary L-arginine (L-Arg) supplementation would increase growth hormone (GH) secretion and antibody production in preruminant calves was tested. Sixteen newborn calves were randomly assigned to either Arg+ or Arg- treatment groups. Both groups were fed a single dose of Colostrx within 6 h after birth followed by milk replacer twice daily until weaning. Beginning with the Colostrx feeding, calves in the Arg+ group were supplemented with L-arginine at 500 mg kg x BW(-1) x d(-1), and the Arg- group received equivalent, but unsupplemented, diets. All calves were immunized against keyhole limpet hemocyanin (KLH) on d 4 and received a booster vaccination on d 14. The Arg+ treatment increased (P < .05) plasma L-Arg and urea concentrations an average of 2.8-fold and 26%, respectively, during the 4-wk supplementation period. Average daily gain (ADG) of Arg+ calves was increased (P < .10) during wk 1, 3, and 5 of life. The Arg+ treatment depressed (P < .05) total and KLH-specific IgG concentrations in plasma and caused a decrease (P < .01) in circulating leukocyte numbers. Differential counts revealed that the decrease in circulating leukocyte numbers was due to decreases in absolute numbers of lymphocytes, monocytes, and neutrophils. The Arg+ diet did not affect mean plasma GH concentrations during the first 3 wk of life, but GH mean concentrations were decreased (P < .01) during wk 4 due to depressed (P < .10) pulse amplitudes. The decrease in GH mean concentrations during wk 4 was paralleled by lower (P < .10) plasma IGF binding protein-3 concentrations. These data show that supplementary L-Arg does not increase plasma GH concentrations, but it increases ADG, depresses KLH antibody production, and alters circulating leukocyte populations in preruminant calves.

alpha-Tocopherol concentrations in milk and plasma during clinical Escherichia coli mastitis.

Eighteen cows were challenged by intramammary infusion with Escherichia coli 727 to determine the effects of acute clinical mastitis on alpha-tocopherol concentrations in plasma and milk. Cows were fed diets supplemented with 1000 IU of vitamin E/d from calving through the experimental period. At challenge, geometric mean DIM was 33 d. Each mammary quarter was diagnosed with an IMI and clinical mastitis at 24 and 48 h after challenge. The alpha-tocopherol concentrations in milk from challenged quarters were approximately 60% greater by 24 and 48 h after challenge than concentrations at prechallenge and 168 h postchallenge. Plasma alpha-tocopherol concentrations did not change after intramammary challenge. The alpha-tocopherol in plasma and milk was correlated at 48 and 168 h postchallenge but not at prechallenge or 24 h postchallenge. Milk alpha-tocopherol and SCC were correlated positively across all sample periods. Milk fat and milk alpha-tocopherol concentrations were correlated at each sample period except 24 h postchallenge. Increases in milk alpha-tocopherol during clinical mastitis were not correlated to milk production, DMI, or BSA concentration in milk. Changes in milk alpha-tocopherol concentration during clinical mastitis were similar to the dynamics of milk SCC.

Effects of selenium status on bovine mononuclear cell function.

The effects of selenium (Se) status on the distribution and functional capabilities of bovine peripheral blood mononuclear cells (PBMC) were examined. No differences in proliferative responses to mitogens, interleukin (IL)-2 production, IL-2 receptor expression, or lymphocyte trafficking patterns were observed between PBMC from dairy cows maintained on Se adequate or Se deficient diets. In contrast, Se deficiency significantly reduced the numbers of circulating monocytes when compared to cows fed a Se adequate diet. Differences in the number of circulating monocytes had no apparent effect on the accessary functions of these cells with respect to antigen presentation and IL-2 production. These results suggest that the effect of Se-modified diets on bovine defense mechanisms is not mediated by the ability of peripheral blood lymphocytes to respond to antigen and mature into immunocompetent cells.