Modulation of the inflammatory reaction and neutrophil defense of the bovine lactating mammary gland by growth hormone

Tracing recombinant bovine somatotropin ab(use) through transcriptomics: the potential of bovine somatic cells in a multi-dose longitudinal study

In the European Union, the use of recombinant bovine somatotropin (rbST) in dairy cattle is forbidden. Monitoring rbST (ab)use by its direct detection in animal matrices still remains a challenging task. New monitoring methods based on indirect detection of the substance are necessary. A new transcriptomic system based on the use of high-throughput real-time PCR in combination with somatic cells was developed to control rbST administration in dairy animals. A total of nine cows, separated into control and rbST-treated groups, were included in the study. A subcutaneous injection containing 500 mg of rbST was administered to the treated group every 14 days, up to a total of 12 doses. Milk somatic cells (MSCs) were sampled from each animal at different time points throughout 8 months of study. It was possible to obtain the transcriptomic profile of 18 genes in MSCs of rbST-treated and control groups, and using univariate and multivariate statistical analysis control and treated animals were discriminated. The transcription of CCND1, IGF-1R, TNF and IL-1β genes resulted strongly influenced by rbST treatment. The combination of MSCs, transcriptomic tools and statistical analysis has allowed the selection of four genes as potential biomarkers that could be used in a transcriptomic panel for monitoring rbST administration in cows.

Butyric acid stimulates bovine neutrophil functions and potentiates the effect of platelet activating factor

Increased short-chain fatty acid (SCFA) production is associated with subacute ruminal acidosis (SARA) and activation of inflammatory processes. In humans and rodents, SCFAs modulate inflammatory responses in the gut via free fatty acid receptor 2 (FFA2). In bovines, butyric acid is one of the most potent FFA2 agonists. Its expression in bovine neutrophils has recently been demonstrated, suggesting a role in innate immune response in cattle. This study aimed to evaluate if butyric acid modulates oxidative and non-oxidative functions or if it can potentiate other inflammatory mediators in bovine neutrophils. Our results showed that butyric acid can activate bovine neutrophils, inducing calcium (Ca(2+)) influx and mitogen-activated protein kinase (MAPK) phosphorylation, two second messengers involved in FFA2 activation. Ca(2+) influx induced by butyric acid was dependent on the extracellular and intracellular Ca(2+) source and phospholipase C (PLC) activation. Butyric acid alone had no significant effect on reactive oxygen species (ROS) production and chemotaxis; however, a priming effect on platelet-activating factor (PAF), a potent inflammatory mediator, was observed. Butyric acid increased CD63 expression and induced the release of neutrophil granule markers matrix metalloproteinase-9 (MMP-9) and lactoferrin. Finally, we observed that butyric acid induced neutrophil extracellular trap (NET) formation without affecting cellular viability. These findings suggest that butyric acid, a component of the ruminal fermentative process, can modulate the innate immune response of ruminants.

Staphylococcus aureus inhibits nuclear factor kappa B activation mediated by prolactin in bovine mammary epithelial cells

The hormone prolactin (PRL) regulates differentiation and lactation in the bovine mammary epithelium. This tissue is especially prone to contracting mastitis, a disease characterized by an inflammatory response in the mammary gland. Staphylococcus aureus is the infectious agent primarily responsible for mastitis. In a previous study, we have shown that bovine PRL (bPRL) stimulates S. aureus internalization in bovine mammary epithelial cells (bMECs) by regulating several host innate immune elements, which are often modulated by nuclear factor kappa B (NF-κB). However, it is unknown whether the activation of the NF-κB transcription factor is regulated by bPRL during S. aureus internalization. The objective of this study was to determine the role of NF-κB in bPRL-stimulated bMECs during S. aureus internalization. Our results showed that bPRL (5 ng/ml) induced NF-κB activation in bMECs; however, it was inhibited by S. aureus in presence of the hormone. When we blocked NF-κB activation with acetylsalicylic acid, we detected an inhibition in S. aureus internalization (48%) in bPRL-stimulated bMECs. The infection-induced inhibition of NF-κB activation in the presence of bPRL correlates with the downregulation in bPRL-mediated tumor necrosis factor (TNF)-α (27%) and tracheal antimicrobial peptide (TAP, 70%) mRNA expression and nitric oxide (NO) production in bMECs. We also detected an inhibition in the expression of the bPRL target gene κ-casein (50%) under these conditions. Interestingly, these effects are not achieved through increased PRL receptor expression (PRLR), as it was inhibited (48%) compared to control cells. In conclusion, NF-κB activation in bMECs is inhibited by S. aureus in the presence of bPRL, suggesting a mechanism by which the host innate immune response may be compromised during subclinical mastitis.

DNA sequence polymorphisms in a panel of eight candidate bovine imprinted genes and their association with performance traits in Irish Holstein-Friesian cattle

Background

Studies in mice and humans have shown that imprinted genes, whereby expression from one of the two parentally inherited alleles is attenuated or completely silenced, have a major effect on mammalian growth, metabolism and physiology. More recently, investigations in livestock species indicate that genes subject to this type of epigenetic regulation contribute to, or are associated with, several performance traits, most notably muscle mass and fat deposition. In the present study, a candidate gene approach was adopted to assess 17 validated single nucleotide polymorphisms (SNPs) and their association with a range of performance traits in 848 progeny-tested Irish Holstein-Friesian artificial insemination sires. These SNPs are located proximal to, or within, the bovine orthologs of eight genes (CALCR, GRB10, PEG3, PHLDA2, RASGRF1, TSPAN32, ZIM2 and ZNF215) that have been shown to be imprinted in cattle or in at least one other mammalian species (i.e. human/mouse/pig/sheep).

Results

Heterozygosities for all SNPs analysed ranged from 0.09 to 0.46 and significant deviations from Hardy-Weinberg proportions (P ≤ 0.01) were observed at four loci. Phenotypic associations (P ≤ 0.05) were observed between nine SNPs proximal to, or within, six of the eight analysed genes and a number of performance traits evaluated, including milk protein percentage, somatic cell count, culled cow and progeny carcass weight, angularity, body conditioning score, progeny carcass conformation, body depth, rump angle, rump width, animal stature, calving difficulty, gestation length and calf perinatal mortality. Notably, SNPs within the imprinted paternally expressed gene 3 (PEG3) gene cluster were associated (P ≤ 0.05) with calving, calf performance and fertility traits, while a single SNP in the zinc finger protein 215 gene (ZNF215) was associated with milk protein percentage (P ≤ 0.05), progeny carcass weight (P ≤ 0.05), culled cow carcass weight (P ≤ 0.01), angularity (P ≤ 0.01), body depth (P ≤ 0.01), rump width (P ≤ 0.01) and animal stature (P ≤ 0.01).

Conclusions

Of the eight candidate bovine imprinted genes assessed, DNA sequence polymorphisms in six of these genes (CALCR, GRB10, PEG3, RASGRF1, ZIM2 and ZNF215) displayed associations with several of the phenotypes included for analyses. The genotype-phenotype associations detected here are further supported by the biological function of these six genes, each of which plays important roles in mammalian growth, development and physiology. The associations between SNPs within the imprinted PEG3 gene cluster and traits related to calving, calf performance and gestation length suggest that this domain on chromosome 18 may play a role regulating pre-natal growth and development and fertility. SNPs within the bovine ZNF215 gene were associated with bovine growth and body conformation traits and studies in humans have revealed that the human ZNF215 ortholog belongs to the imprinted gene cluster associated with Beckwith-Wiedemann syndrome--a genetic disorder characterised by growth abnormalities. Similarly, the data presented here suggest that the ZNF215 gene may have an important role in regulating bovine growth. Collectively, our results support previous work showing that (candidate) imprinted genes/loci contribute to heritable variation in bovine performance traits and suggest that DNA sequence polymorphisms within these genes/loci represents an important reservoir of genomic markers for future genetic improvement of dairy and beef cattle populations.

Investigation of mammary blood flow changes by transrectal colour Doppler sonography in anEscherichia colimastitis model

The objectives of this preliminary investigation were to evaluate the feasibility of transrectal colour Doppler sonography (TCDS) for determining blood flow of the pudendoepigastric trunk in cows with experimentally inducedEscherichia coliMastitis. Five primiparous Holstein dairy cows, 4–6 months after calving, were examined in two trials. All monitored udder quarters were initially clinically healthy, somatic cell count (SCC) was <50 000 cells/ml and bacteriologically negative. The blood flow of the left and the right pudendoepigastric trunk was described by the blood flow volume (BFV). In the methodological part of the study, the intra-observer precision of the method was evaluated. The coefficients of variation of the BFV were 7·1% for the left and 9·4% for the right pudendoepigastric trunk. The intraclass correlation coefficients of the BFV were 0·99 (P<0·001) for the left and 0·75 (P=0·004) for the right vessel. BFV did not differ significantly between the left and the right side nor between pre- and post-milking nor between oestrus and dioestrus. In the experimental part of the study, significant differences of increasing BFV between 0 and 12 h p.i. (post infectionem) (P=0·043) and decreasing BFV between 12 and 24 h p.i. (P=0·043) were discovered for the pudendoepigastric trunk of the infected right side. In the left-right (control-infection) comparison a significant increase of the right BFV was observed at 12 h p.i. (P=0·043). The difference of an increasing SCC correlated positively with the difference of an increasing BFV between 0 and 12 h p.i. (Spearman's ρ=1·00;P=0·043) for the right infected side. It was shown that TCDS is a reproducible technique for investigating pathological mammary blood flow changes at an early stage of acute mastitis.

Supplementing Holstein cows with low doses of bovine somatotropin prepartum and postpartum reduces calving-related diseases

The objective of this study was to evaluate whether supplementing Holstein cows with bovine somatotropin (bST; 142.8 mg/14 d), beginning at 21 d (+/-3 d) before expected calving and continuing through 42 d in milk (+/-3 d), affected the incidence rates of retained fetal membranes (RFM), metritis (MET), clinical mastitis (MAS), digestive problems (DIG), ketosis (KET), milk fever (MF), displaced abomasum (DA, left or right), lameness (LAM), or number of sick cows during the first 60 d in milk. Data for multiparous Holstein cows from 3 separate trials were merged for analyses (n = 437). Cows in the bST-supplemented group (n = 162) received biweekly subcutaneous injections of Posilac, whereas control cows (n = 166) and a group of cohorts (n = 109) were not supplemented. Incidences of disease were collected from the herd health records. Across all treatment groups, the incidence rates (number of diseased cows divided by the total number of cows) for RFM, MET, MAS, DIG, KET, MF, DA, and LAM were 8.47, 18.31, 16.02, 4.35, 4.35, 3.66, 3.20, and 3.66%, respectively. The incidence rates of RFM, MET, MAS, DIG, KET, MF, DA, and LAM for cows in the bST-supplemented, control, and cohort groups were 6.79, 7.83, and 11.93%; 16.05, 7.47, and 22.94%; 10.49, 18.07, and 21.10%; 1.23, 5.42, and 7.34%; 1.23, 6.02, and 6.42%; 2.47, 4.22, and 4.59%; 2.47, 3.61, and 3.67%; and 3.70, 3.61, and 3.67%, respectively. The percentages of sick cows (number of cows having one or more cases of disease divided by the total number of cows) in the bST-supplemented, control, and cohort groups were 33.95, 43.37, and 49.54%, respectively. Significant chi-squared values were detected between the bST-supplemented and control groups for MAS, DIG, and KET, with a greater number of healthy cows in the bST-supplemented group. No differences in incidences of diseases or sick cows were detected between the control and cohort groups. Results indicated that a low dose of bST supplemented to Holstein cows for 3 wk prepartum through 60 d in milk reduced the incidences of some calving-related diseases compared with nonsupplemented controls or cohorts. Importantly, no negative effects of bST supplementation on postpartum calving diseases were detected compared with nonsupplemented cows.

Cumulative physiological events influence the inflammatory response of the bovine udder to Escherichia coli infections during the transition period

A high proportion of intramammary coliform infections present at parturition develop disease characterized by severe inflammatory signs and sepsis during the first 60 to 70 d of lactation. In the lactating bovine mammary gland, the innate immune system plays a critical role in determining the outcome of these infections. Since the beginning of the 1990s, research has increased significantly on bovine mammary innate defense mechanisms in connection with the pathogenesis of coliform mastitis. Neutrophils are key effector cells of the innate immune response to intramammary infection, and their function is influenced by many physiological events that occur during the transition period. Opportunistic infections occur when the integrity of the host immune system is compromised by physical and physiological conditions that make the host more susceptible. The innate immune system of many periparturient cows is immunocompromised. It is unlikely that periparturient immunosuppression is the result of a single physiological factor; more likely, several entities act in concert, with profound effects on the function of many organ systems of the periparturient dairy cow. Their defense system is unable to modulate the complex network of innate immune responses, leading to incomplete resolution of the pathogen and the inflammatory reaction. During the last 30 yr, most efforts have been focused on neutrophil diapedesis, phagocytosis, and bacterial killing. How these functions modulate the clinical outcome of coliform mastitis, and how they can be influenced by hormones and metabolism has been the subject of intensive research and is the focus of this review. The afferent (sensing) arm of innate immunity, which enables host recognition of a diverse array of pathogens, is the subject of intense research interest and may contribute to the variable inflammatory response to intramammary infections during different stages of lactation. The development of novel interventions that modulate the inflammatory response or contribute to the elimination of the pathogen or both may offer therapeutic promise in the treatment of mastitis in periparturient cows.

Physiology of the periparturient period and its relation to severity of clinical mastitis

Incidence of clinical mastitis is highest at drying off and during the periparturient period. Intramammary Escherichia coli infection in high-yielding cows can show a severe clinical response during the early post-partum period. Severe clinical mastitis is mainly determined by cow factors, in particular the functionality of the circulating polymorphonuclear leukocytes (PMN) which are recruited to the mammary gland during the inflammatory reaction. There is a co-incidence between the periods of highest incidence of clinical mastitis and specific structural changes in the mammary gland. During the periparturient period, marked changes in various systemic and local hormones are related to the secretory state of the mammary gland epithelium (lactogenesis). Estrogen and progesterone induce proliferation of the mammary epithelium throughout gestation and act as survival factors in different tissues, although conflicting data have been reported on their effect on PMN oxidative burst. Somatotropin (STH), responsible for maintenance of lactation in ruminants, has been shown to positively influence innate immunity and a more rapid recovery in milk production of severely affected animals. The concentration of STH, and as a result also IGF-I levels is, however, quite low during early lactation. IGF-I and its regulating binding proteins are associated with cell survival, modulation of apoptosis and functionality of PMN in humans. During early lactation, bio-availability of IGF-I is decreased, which might reduce its stimulating effects on PMN quality and functionality. PRL, concomitantly known as a lactogenic hormone and an immunoregulatory cytokine, has also been associated with modulation of the immune system. It is expected that in periparturient animals, hormone changes could interfere with the immune response and the clinical response of mastitis.

Influence of 17β-Estradiol, Progesterone, and Dexamethasone on Diapedesis and Viability of Bovine Blood Polymorphonuclear Leukocytes

The aim of the current study was to investigate whether polymorphonuclear leukocyte (PMN) diapedesis and viability are influenced by steroid hormones. Using an in vitro model with different types of cell layers (bovine mammary epithelial cells and fibroblasts), we investigate whether steroid hormone treatments (17beta-estradiol, progesterone, and dexamethasone) have an influence on the diapedesis capacity and viability of PMN. In addition, we studied apoptosis of PMN in the in vitro model and evaluated the influence of different types of cell layers and steroid hormone treatments on this process. A significant decrease in the number of viable PMN in the lower compartment of the in vitro model (i.e., number of migrated PMN x viability after migration) was found after 17beta-estradiol treatment, whereas no influence was detected after progesterone or dexamethasone treatment. The effect of 17beta-estradiol was not due to a lower viability before migration as none of the treatments caused a significant effect on the viability before diapedesis. This treatment effect was not influenced by endogenous 17beta-estradiol or progesterone levels before isolation because there was no correlation between these plasma levels and PMN diapedesis capacity or viability. Furthermore, migration through epithelial cells caused a significant decrease in viability of PMN due to increased apoptosis but not necrosis.

Low Doses of Bovine Somatotropin During the Transition Period and Early Lactation Improves Milk Yield, Efficiency of Production, and Other Physiological Responses of Holstein Cows

The objectives of this experiment were to determine whether low doses of bovine somatotropin (bST) during the transition period and early lactation period improved dry matter intake (DMI), body weight (BW), or body condition score (BCS); provoked positive changes in concentrations of somatotropin, insulin, insulin-like growth factor-I (IGF-I), glucose, nonesterified fatty acids, and Ca; or improved milk yield (MY) response without obvious adverse effects on health status. Eighty-four multiparous Holstein cows completed treatments arranged in a 2 x 3 x 2 factorial design that included prepartum and postpartum bST, dry period (30 d dry, 30 d dry + estradiol cypionate, and 60 d dry), and prepartum anionic or cationic diets. Biweekly injections of bST began at 21 +/- 3 d before expected calving date through 42 +/- 2 d postpartum (control = 0 vs. bST = 10.2 mg of bST/d; POSILAC). At 56 +/- 2 d in milk, all cows were injected with a full dose of bST (500 mg of bST/14 d; POSILAC). During the prepartum period and during the first 28 d postpartum, no differences in mean BW, BCS, or DMI were detected between the bST treatment group and the control group. During the first 10 wk of lactation, cows in the bST treatment group had greater mean MY and 3.5% fat-corrected milk yield and lower SCC than did cows in the control group. When cows received a full dose of bST, an increase in milk production through wk 21 was maintained better by cows in the bST group. Mean concentrations of somatotropin, IGF-I, and insulin differed during the overall prepartum period (d -21 to -1). During the postpartum period (d 1 to 28), cows in the bST group had greater mean concentrations of somatotropin and IGF-I in plasma. Concentrations of Ca around calving did not differ because of bST treatment. Results suggest that changes in concentrations of blood measures provoked by injections of bST during the transition period and early lactation period resulted in improved metabolic status and production of the cows without apparent positive or negative effects on calving or health.

Effect of Lipopolysaccharide on Indices of Peripheral and Hepatic Metabolism in Lactating Cows

Four multiparous lactating cows (175 to 220 d in milk [DIM]) were used in a 4 x 4 Latin square design to assess the effects of four doses (0.0, 0.5, 1.0, and 1.5 microg/kg of body weight) of lipopolysaccharide (LPS; Escherichia coli 0111:B4) on performance and plasma metabolite and hormone concentrations. In addition, effects of immune activation on in vitro hepatic metabolic capacity were evaluated in 12 multiparous lactating cows (150 to 220 DIM) infused with 0 (n = 6), 1.0 (n = 4) or 2.0 (n = 2) microg of LPS/kg. Milk production and DMI decreased linearly with LPS dose for 24 h after LPS infusion. Overall mean plasma tumor necrosis factor-alpha, insulin, glucagon, and cortisol concentrations increased linearly with LPS dose, and plasma beta-hydroxybutyrate decreased linearly by dose after LPS infusion. Infusion of LPS decreased the insulin:glucagon molar ratio, but did not affect plasma concentrations of growth hormone, insulin-like growth factor-1, leptin, or L-(+)-lactate. Plasma concentrations of glucose tended to increase initially and subsequently decrease, and there was a quadratic tendency for increased plasma nonesterified fatty acid concentrations after LPS administration. In vitro hepatic capacity for conversion of [1-(14)C]L-(+)-lactate and [1-(14)C]palmitate, but not [1-(14)C]propionate or [1-(14)C]L-alanine, to CO2 increased after LPS administration. Hepatic capacity to convert [1-(14)C]propionate to glucose tended to increase, but neither esterification nor the conversion of palmitate to acid soluble products was altered by LPS. The LPS infusion resulted in significant changes of endocrine mediators responsible for regulation of energy metabolism of lactating cows and tended to alter subsequent in vitro hepatic metabolic capacity.

Metabolic and lactational responses during recombinant bovine tumor necrosis factor-alpha treatment in lactating cows

This study examined the effects of recombinant bovine tumor necrosis factor-alpha (rbTNF) administration on metabolic and hormonal responses and lactational performance in dairy cows. Twelve lactating Holstein cows were injected subcutaneously with rbTNF (2.5 microg per kg per d) or saline (3 ml per head per d) at 1200 h daily for 7 d (d 0-6) and used in a crossover design. The rbTNF treatment induced increases in plasma haptoglobin, nonesterified fatty acid, cortisol, and growth hormone levels compared with the control levels. The rbTNF-treated cows had lower triiodothyronine and insulin-like growth factor-1 concentrations than control cows. In a somatoliberin challenge on d 6, the somatotropin response to somatoliberin (0.25 microg/kg) was smaller in the rbTNF group than in the control. The rbTNF treatment also produced increases of the nitrite plus nitrate concentration in plasma and milk during the period between d 1 and 7. Milk yield was reduced by rbTNF administration from d 1 to 8. The percentage of milk fat was increased on d 1-7 by rbTNF treatment, but milk protein content in the rbTNF group was decreased on d 5 and 7 as compared with that in the control group. These results support the possibility that tumor necrosis factor-alpha is responsible for the changes in hormone secretion, milk production and composition, and inflammatory parameters observed during coliform mastitis.

Growth hormone and milking frequency act differently on goat mammary gland in late lactation

In ruminants, milk yield can be affected by treatment with growth hormone (rbGH) and/or changes in frequency of milking. Frequent milkings encourage the maintenance of lactation, whereas infrequent milkings result in mammary involution. Our objective was to evaluate the influence of rbGH treatment and milking frequency on mammary gland morphology and milk composition. After adaptation to twice-daily milkings, six Saanen goats in late lactation were milked once daily from one udder-half and thrice-daily from the other udder-half. Concurrently, three of the six goats received daily injections of rbGH. After 23 d of treatment, milking frequency significantly affected milk yield (+8% vs. -26% for thrice- vs. once-daily milking). Additionally, treatments of rbGH increased milk yield from thrice-daily milked udder-halves (+19%), but failed to abate the reduction in milk yield from once-daily milked udder-halves (-31%). Mammary glands were heavier in the frequently milked udder-halves and in GH-treated goats. Based on histological and DNA analysis of mammary tissues, it was determined that milking frequency clearly affected epithelial cell numbers and alveolar diameter, whereas rbGH induced a potential cell hypertrophy and only a tendency to increase and/or maintain the mammary cell number. RNA concentration and kappa casein gene expression were not affected by treatments. In udder-halves milked once-daily, low casein:whey protein ratios, high Na+:K+ ratios, and high somatic cell counts (SCC) were indicative of changes in epithelial permeability, which rbGH treatment facilitated. The present data suggest that milking frequency and exogenous treatments of rbGH use different cellular mechanisms to influence mammary gland morphology and milk production.

Sows intramammarily inoculated with Escherichia coli at parturition: I. Functional capacity of granulocytes in sows affected or non-affected by clinical mastitis

The objective of this study was to investigate if occurrence of clinical disease was related to granulocyte traits in sows. Functional capacity of granulocytes and plasma steroid hormone concentrations were assessed before inoculation with Escherichia coli in the mammary glands in sows at parturition. Blood samples were taken for 3 days approximately 1 week before parturition, and granulocyte migration, phagocytic capacity and expression of CD 18 adhesion molecules were determined. Inoculation was done within 36 h before partus. Thereafter, daily thorough clinical examinations were performed including udder health, habitus, appetite and rectal temperature, to assess the severity of disease. Based on the clinical findings four sows were classified as affected and eight as non-affected by clinical mastitis within 48 h after parturition.No difference (p>0.10) in pre-inoculation chemotaxis, phagocytosis or CD 18 expression was found between granulocytes from the sows resisting and developing clinical mastitis, respectively. However, there was an effect by the individual sow (p=0.001) on the numbers of granulocytes and white blood cells, and on plasma concentrations of estradiol-17beta and progesterone. In conclusion, these data does not suggest that impaired chemotaxis or phagocytosis by blood granulocytes contribute to the development of clinical coliform mastitis in the periparturient sow.

Clinical responses to intramammary endotoxin infusion in dairy cows subjected to feed restriction

Nonpregnant, midlactation primiparous Holstein cows were fed ad libitum (n = 12) or at 80% of maintenance energy requirements (n = 12) to determine whether feed restriction influences clinical response to endotoxin-induced mastitis. After 2 wk of ad libitum or restricted feeding, one mammary quarter per cow was infused with 100 microg of endotoxin. Within 3 to 6 h of intramammary infusion, endotoxin increased mean rectal temperature, heart rate, and milk somatic cell count and immunoglobulin (IgG) concentration; and decreased blood leukocyte count and rumen motility in both restricted and ad libitum-fed cows. Mean serum and milk tumor necrosis factor-alpha (TNF-alpha) concentrations showed only modest increases following endotoxin infusion. Restricted fed cows had slightly different acute fever responses and significantly increased heart and respiration rates than ad libitum fed cows. However, feed restriction did not influence mean total leukocyte count, rumen motility, serum TNF-a concentrations or milk IgG and TNF-alpha concentrations. Thus, results of this study suggest that energy balance does not significantly alter clinical symptoms following acute endotoxin-induced mastitis, at least in midlactation cows. As such, negative energy balance may not underlie the increases in severe coliform mastitis commonly observed in periparturient dairy cows.

Defense of the bovine mammary gland by polymorphonuclear neutrophil leukocytes

The primary phagocytic cells of the bovine mammary gland, polymorphonuclear neutrophil leukocytes (PMN), and macrophages, comprise the first line of defense against invading pathogens. In the normal healthy mammary gland, macrophages predominate and act as sentinels to invading mastitis-causing pathogens. Once invaders are detected, macrophages, and possibly mammary epithelial cells, release chemoattractants that direct migration of PMN into the area. In the mammary gland, protection is only effective if rapid influx of PMN from the circulation and subsequent phagocytosis and killing of bacteria occur. The second line of defense against infection consists of a network of memory cells and immunoglobulins that interact with the first line of defense. To minimize mammary tissue damage caused by bacterial toxins and oxidative products released by PMN, elimination of invading bacteria must proceed quickly. Therefore, the inflammatory response needs to be regulated. Hormones, metabolites, and acute phase proteins act to influence the outcome of mastitis, especially around parturition. The number of circulating PMN in cows during early lactation is highly heritable and closely related to susceptibility to clinical mastitis at this time. Advances in molecular biology are making available the tools, techniques, and products to study and modulate host-pathogen interactions. For example, the cloning and expression of proteins such as recombinant bovine soluble (rbos) CD (cluster of differentiation) 14 antigens, may provide ways of minimizing damaging effects of endotoxin during acute coliform mastitis. Soluble CD14 binds and neutralizes lipopolysacharide (LPS) and causes local recruitment of PMN after binding of CD14-LPS complexes to mammary epithelial cells. Development of transgenic animals that express rbosCD14 in their milk could prevent infection by Gram-negative pathogens.

Effect of apoptosis on phagocytosis, respiratory burst and CD18 adhesion receptor expression of bovine neutrophils

Polymorphonuclear neutrophil leukocytes (PMN) play an important role in intramammary defense against infections by Escherichia coli. During mastitis, PMN are confronted with various inflammatory mediators that can modulate their function. In severely diseased cows, increased concentrations of lipopolysaccharide (LPS) and tumor necrosis factor (TNF)-alpha (TNF-alpha) are detected in plasma. Binding of LPS to membrane bound CD14 molecules on monocytes cause release of inflammatory mediators such as TNF-alpha. Because apoptosis of PMN promotes resolution of inflammation and because the LPS and TNF-alpha response in milk and blood is related to the severity of E. coli mastitis, the effect on apoptosis of bovine PMN of increased concentrations LPS and TNF-alpha was studied together with the functionality of apoptotic PMN. Bovine PMN apoptosis, as determined with annexin-V, was induced with high concentrations of either LPS (1000 and 10,000ng/mL) or TNF-alpha (10,000ng/mL) in whole blood following a 6h incubation at 37 degrees C. The apoptosis inducing effect of LPS on PMN was not inhibited following coculture with either anti-bovine TNF-alpha or anti-ovine CD14 monoclonal antibodies. When compared to controls, apoptotic PMN had a similar level of CD18 expression but lacked phagocytic and respiratory burst activity. This is the first study reporting the effects of apoptosis on bovine PMN function. These functional impairments in apoptotic PMN could be important in contributing to the establishment of intramammary infection. Well functioning PMN could finally determine the severity of mastitis following an invasion of bacteria in the mammary gland.

Effect of somatotropin on thyroid hormones and cytokines in lactating dairy cows during ad libitum and restricted feed intake

Twelve Holsteins in first lactation were used to investigate the relationship between energy balance and effects of bovine somatotropin (bST) on thyroid hormone metabolism and cytokine concentrations in serum. Six cows were fed for ad libitum intake and six cows were feed restricted to induce negative energy balance during two treatment periods of 6 d. During treatment periods, cows were administered vehicle or 40 mg of bST/d according to a crossover design. Between treatment periods was a 15-d recovery period, during which all cows were fed ad libitum. Cows that were fed ad libitum remained in positive energy balance during control and bST treatments, whereas cows that were fed for restricted intake were in negative energy balance during control and bST treatment periods. In both dietary groups, bST decreased energy balance. Milk production and the fat percentage of milk increased during bST treatment in both dietary groups. Fat-corrected milk yield was increased 13% by bST treatment. Serum concentrations of IGF-I did not differ between dietary groups but were greater during bST than control periods. Serum thyroxine concentration was decreased by bST treatment. Serum triiodothyronine and reverse-triiodothyronine were not altered by hormone treatment, but circulating concentrations of thyroid hormones were apparently reduced by dietary restriction. Neither hepatic nor mammary thyroxine 5'-deiodinase was affected by bST treatment. Plasma concentration of tumor necrosis factor-alpha, a potential regulator of thyroxine 5'-deiodinase, was not affected by bST treatment. Short-term treatment with bST did not influence thyroid hormone metabolism in lactating cows in positive or negative energy balance.

Immunity in the mammary gland

The ruminant mammary gland is an extremely important economic organ in that it provides a major nutrition source for a significant portion of the world's human population. The ruminant mammary gland is also responsible for providing protective immunity to neonates and for defending itself from invading pathogens. A wide array of humoral and cellular immune mechanisms are present in the mammary gland and actively participate in providing immunity to newborns and the mammary gland per se. The acute inflammatory response is essential in determining the outcome of intramammary challenge, and factors affecting innate and adaptive immunity in the context of mammary health are reviewed in detail. The ruminant mammary gland is also unique in that lymphocyte trafficking, which is essential to adaptive immunity, is shared with the peripheral immune system rather than the common mucosal immune system.