Effects of feed restriction and supplementary folic acid and vitamin B12 on immune cell functions and blood cell populations in dairy cows.

Cows undergoing a negative energy balance (NEB) often experience a state of immunosuppression and are at greater risk of infectious diseases. The present study aimed to evaluate the impact of a folic acid and vitamin B12 supplement and feed restriction on several immune parameters. Sixteen cows at 45 ± 3 days in milk were assigned to 8 blocks of 2 cows each according to each cow's milk production in the previous week, and within each block, the cows randomly received weekly intramuscular injections of either saline or 320 mg of folic acid and 10 mg of vitamin B12 for 5 weeks. During week 5, the cows were fed 75% of their ad libitum intake for 4 days. Blood samples were taken before the beginning of the experiment, just before feed restriction and after 3 days of feed restriction, in order to evaluate blood cell populations, the phagocytosis capacity and oxidative burst of polymorphonuclear leukocytes (PMNs), the proliferation of peripheral blood mononuclear cells (PBMCs) and concentrations of non-esterified fatty acids (NEFAs) and ß-hydroxybutyrate. The vitamin supplement did not affect any of the tested variables except milk fat and lactose content. Feed restriction reduced milk production and increased the concentration of NEFAs. Feed restriction did not affect blood cell populations but did reduce the percentage of PMN positive for oxidative burst after stimulation with phorbol 12-myristate 13-acetate. The proliferation of PBMCs was reduced when the cell culture medium was supplemented with sera collected during the feed restriction. In conclusion, feed restriction affected the functions of PMN and PBMC and this effect was not prevented by the folic acid and vitamin B12 supplement. These results support the hypothesis that the greater risk of infectious diseases in cows experiencing a NEB is related to impaired immune cell functions by high circulating concentration of NEFAs.

Review: Inhibition of prolactin as a management tool in dairy husbandry.

Accumulating evidence supports that the hormone prolactin (PRL) is galactopoietic in dairy ruminants. Accordingly, the inhibition of PRL secretion by the dopamine agonists quinagolide and cabergoline causes a sharp decline in milk production and could be useful in several critical periods. First, PRL inhibition may reduce the incidence during the periparturient period of metabolic disorders caused by the abrupt increase in energy demand for milk production. Metabolic disturbances can be lessened by reducing milk output by milking once a day or incompletely in the first few days of lactation. The injection of cows with quinagolide for the first 4 days of lactation reduced milk production during the first week of lactation without any residual effects. Blood glucose and calcium concentrations were higher and ß-hydroxybutyric acid concentration was lower in the quinagolide-treated cows. Second, PRL inhibition may help sick or injured lactating cows, considering that they can fall into severe negative energy balance when they are unable to consume enough feed to support their milk production. This leads to a weakened immune system and increased susceptibility to diseases. When cows were subjected to feed restriction and were treated with quinagolide, the decrease in milk production was accelerated without any residual effects. The quinagolide-treated cows had higher glucose and lower ß-hydroxybutyric acid and non-esterified fatty acid concentrations than the control cows did. Third, PRL inhibition may facilitate drying-off in high-yielding cows, because they are often dried off while still producing significant quantities of milk, which delays mammary involution and increases risk of mastitis. Therefore, strategies that reduce milk production before drying-off and accelerate mammary gland involution could be an important management tool. In this context, inhibition of PRL was utilised to accelerate mammary gland dry-off. Quinagolide decreased milk production within the first day of treatment, and both quinagolide and cabergoline induced more rapid changes in several markers of mammary gland involution after drying-off. In addition, quinagolide improved the animals' resistance to intramammary infection. These results suggest that the inhibition of PRL could be a strategy for facilitating drying-off, reducing metabolic stress during the postpartum period, and alleviating acute nutritional stress during illness without compromising the overall productivity of dairy ruminants.

Glucose and insulin responses to an intravenous glucose tolerance test administered to feed-restricted dairy cows receiving folic acid and vitamin B12 supplements.

The present experiment was conducted to determine whether, during periods of negative energy balance, the increase in glucose availability, despite similar DMI and greater milk production, induced by a combined supplement of folic acid and vitamin B12 was related to effects of insulin on metabolism. Sixteen multiparous Holstein cows averaging 45 days in milk (standard deviation: 3) were assigned to 8 blocks of 2 animals each according to their milk production (45 kg/d; standard deviation: 6) during the week preceding the beginning of the experiment. Within each block, they received weekly intramuscular injections of either saline (CON) or folic acid and vitamin B12 (VIT) during 5 consecutive weeks. During the last week, the cows were fed 75% of their ad libitum intake during 4 d. Blood samples were taken the morning before starting the feed restriction and on the third day of feed restriction. On the fourth day of feed restriction, the daily meal was not served and an intravenous glucose tolerance test was performed. During the 4 wk preceding the feed restriction, milk production and DMI were not affected by treatments. During the feed restriction, the vitamin supplement tended to decrease milk fat concentration and increase milk concentration of lactose. Plasma concentrations of homocysteine, Ile, Leu, Val, and branched-chain AA increased in VIT cows during the restriction but not in CON cows. During the glucose tolerance test, insulin peak height was lower and insulin incremental positive area under the curve tended to be lower for VIT than for CON [83 (95% confidence interval, CI: 64-108) vs. 123 (95% CI: 84-180) µg·180 min/L, respectively]. Free fatty acid nadir was reached earlier for VIT than for CON [34 (95% CI: 26-43) vs. 46 (95% CI: 31-57) min, respectively]. Glucose area under the curve, clearance rate and peak height, insulin time to reach the peak and clearance rate, and free fatty acid nadir did not differ between VIT and CON. The reduction in insulin release during a glucose tolerance test without changes in glucose clearance rate or area under the curve suggests that the vitamin supplement improved insulin sensitivity in feed-restricted lactating dairy cows.

Innovative dairy cow management to improve resistance to metabolic and infectious diseases during the transition period.

The incidence of metabolic and infectious diseases varies greatly during the lactation cycle. Most new cases of clinical mastitis appear at the beginning of lactation, and the incidence increases with the level of milk production. In addition to mastitis, many other infectious diseases become clinically apparent during the first 2weeks of lactation. During this time, cows are in a negative energy balance and must mobilize body reserves to balance the deficit between food energy intake and energy required for milk production. The relationships between energy deficit and metabolic diseases, such as ketosis and hepatic lipidosis, are well known. Furthermore, cows in energy deficit have a weakened immune system and are therefore more susceptible to infections. There is now good evidence that the increase in circulating non-esterified fatty acids impairs immune cell functions. Therefore, management approaches that reduce the negative energy balance and the increase in non-esterified fatty acids at the beginning of lactation are likely to improve resistance to infection. Improving the nutrient supply through periparturient nutritional management has been the subject of considerable research. However, another way to reduce the imbalance between nutrient supply and demand is to temporarily decrease the latter. In this review, we examine how management strategies such as conjugated linoleic acid feeding, prepartum milking, or limiting postpartum milk production could be used to reduce metabolic perturbations and immunosuppression during the transition period. At this stage, it appears that reducing the amount of milk harvested postpartum by means of partial milking in the first days after calving is the most promising approach to reduce metabolic stress and immunosuppression without compromising the productivity of high-yielding dairy cows.

Effect of inhibiting the lactogenic signal at calving on milk production and metabolic and immune perturbations in dairy cows.

During the periparturient period, the abrupt increase in energy demand for milk production often induces metabolic and immunological disturbances in dairy cows. Our previous work has shown that reducing milk output by milking once a day or incompletely in the first few days of lactation reduces these disturbances. The aim of this study was to reduce metabolic and immunological disturbances by limiting milk production during the first week of lactation by inhibiting the lactogenic signal driven by prolactin. Twenty-two fresh cows received 8 i.m. injections of the prolactin-release inhibitor quinagolide (QUIN; 2 mg) or water as a control (CTL). The first injection was given just after calving, and the subsequent 7 injections were given every 12 h. Milk production was measured until d 28 after calving. Blood samples were taken from d 1 (calving) to d 5 and then on d 7, 10, 14, 21, and 28 to measure concentrations of urea, phosphorus, calcium, glucose, nonesterified fatty acids (NEFA), ß-hydroxybutyrate, and prolactin. Other blood samples were taken on d 2, 5, 10, and 28 to analyze oxidative burst, phagocytosis, and the effect of the serum on the lymphoproliferation of peripheral blood mononuclear cells from donor cows. Blood prolactin concentration was lower from d 2 to 5 but higher from d 10 to 28 in the QUIN cows than in the CTL cows. Milk production was lower from d 2 to 6 in the QUIN cows than in the CTL cows (24.3 ± 6.4 and 34.8 ± 4.1 kg/d on average, respectively). We observed no residual effect of quinagolide on milk production after d 6. During the first week of lactation, blood glucose and calcium concentrations were higher and ß-hydroxybutyrate concentration was lower in the QUIN cows than in the CTL cows. Blood NEFA, urea, and phosphorus concentrations were not affected by the treatment. At d 2 and 5, the phagocytosis ability of polymorphonuclear leukocytes was not affected by treatment; however, quinagolide injection enhanced the proportion of cells that entered oxidative burst, The mitogen-induced proliferation of peripheral blood mononuclear cells was greater when they were incubated with serum harvested from the CTL cows and was negatively correlated with the NEFA concentration in the serum. Reducing the prolactin peak at calving was effective in reducing milk production during the first week of lactation without compromising the dairy cow's overall productivity. Slowing the increase in milk production allowed a more gradual transition from pregnancy to lactation and led to a reduction in metabolic stress and an improvement in some immune system aspects during this period.

Effect of reducing milk production using a prolactin-release inhibitor or a glucocorticoid on metabolism and immune functions in cows subjected to acute nutritional stress.

When cows are unable to consume enough feed to support milk production, they often fall into severe negative energy balance. This leads to a weakened immune system and increases their susceptibility to infectious diseases. Reducing the milk production of cows subjected to acute nutritional stress decreases their energy deficit. The aim of this study was to compare the effects on metabolism and immune function of reducing milk production using quinagolide (a prolactin-release inhibitor) or dexamethasone in feed-restricted cows. A total of 23 cows in early/mid-lactation were fed for 5 d at 55.9% of their previous dry matter intake to subject them to acute nutritional stress. After 1 d of feed restriction and for 4 d afterward (d 2 to 5), cows received twice-daily i.m. injections of water (control group; n=8), 2mg of quinagolide (QN group; n=7), or water after a first injection of 20mg of dexamethasone (DEX group; n=8). Feed restriction decreased milk production, but the decrease was greater in the QN and DEX cows than in the control cows on d 2 and 3. As expected, feed restriction reduced the energy balance, but the reduction was lower in the QN cows than in the control cows. Feed restriction decreased plasma glucose concentration and increased plasma nonesterified fatty acid (NEFA) and ß-hydroxybutyrate (BHB) concentrations. The QN cows had higher glucose concentration and lower BHB concentration than the control cows. The NEFA concentration was also lower in the QN cows than in the control cows on d 2. Dexamethasone injection induced transient hyperglycemia concomitant with a reduction in milk lactose concentration; it also decreased BHB concentration and decreased NEFA initially but increased it later. Feed restriction and quinagolide injections did not affect the blood concentration or activity of polymorphonuclear leukocytes (PMN), whereas dexamethasone injection increased PMN blood concentration but decreased the proportion of PMN capable of inducing oxidative burst. Incubation of peripheral blood mononuclear cells in serum harvested on d 2 of the restriction period reduced their ability to react to mitogen-induced proliferation, and injection of quinagolide or dexamethasone could not alleviate this effect. This experiment shows that prolactin-release inhibition could be an alternative to dexamethasone for reducing milk production and energy deficit in cows under acute nutritional stress, without disturbing immune function.

Dose-related effect of inhaled fluticasone on allergen-induced airway changes in rats.

To examine whether fluticasone propionate (FP) dose-dependently inhibits inflammatory as well as structural changes, Brown Norway rats were sensitised to ovalbumin (OA) on day 0 and 7. From day 14-28, rats were exposed to aerosolised OA (1%) or phosphate buffered saline every 2 days. Thirty minutes before each allergen exposure, animals were pre-treated with aerosolised placebo or FP (0.1, 1 or 10 mg) or prednisolone 3 mg x kg(-1) i.p. At day 29, 0.1 mg FP had no measurable effect, either on inflammatory or structural changes, such as goblet cell hyperplasia and airway wall thickening. The allergen-induced increase in eosinophilic inflammation in bronchoalveolar lavage fluid and in the airway mucosa, as well as increased fibronectin deposition, were inhibited by treatment with FP from a dose of 1 mg onwards. Inhibition of goblet cell hyperplasia and thickening of the airway wall required 10 mg inhaled FP. At this dose, systemic effects were observed. However, for a comparable degree of systemic activity, prednisolone was far less effective at preventing airway changes. The dose of inhaled fluticasone propionate required to inhibit allergen-induced structural alterations was higher than to prevent eosinophil influx, and caused systemic side-effects. However, for a similar systemic activity, prednisolone was ineffective in preventing airway remodelling.

Fluticasone inhibits the progression of allergen-induced structural airway changes.

BACKGROUND: Inhaled corticosteroids are widely used as first-line therapy in patients with asthma. The concept of early introduction is more and more accepted. OBJECTIVE: In our rat model of airway remodelling, we investigated whether treatment with inhaled fluticasone propionate can inhibit further progression of established structural airway changes. METHODS: Sensitized Brown Norway rats were exposed to aerosolized ovalbumin (1%) from day 14 to 42. From day 28 to 42, animals were treated with inhaled fluticasone or placebo 30 min before each allergen challenge. One control group was exposed to PBS from day 28 to 42, a second control group throughout the whole experiment. RESULTS: Exposure to ovalbumin during 2 weeks induced structural airway changes, including epithelial cell proliferation, increase in airway wall area and fibronectin deposition. Goblet cell number was increased, although not significantly compared with PBS. Continuing allergen exposure for 2 weeks further enhanced each of these features. In addition, the amount of collagen in the airway wall was enhanced by 4 weeks allergen exposure compared with PBS-exposed animals. These additional increases were inhibited by treatment with fluticasone during the last 2 weeks. CONCLUSION: The progression of established allergen-induced structural airway changes in sensitized rats can be inhibited by treatment with fluticasone.

Fluticasone inhibits but does not reverse allergen-induced structural airway changes.

Ethical and technical reasons limit the possibility of evaluating the effects of inhaled corticosteroids on structural changes in airways of humans with asthma. We therefore evaluated whether fluticasone propionate (FP) modifies airway remodeling, induced by repeated allergen exposure in rats. Sensitized BN rats were exposed to aerosolized ovalbumin (OA) for 2 wk. To assess the effect of FP on the development of or on established airway remodeling, animals were treated with aerosolized FP or placebo during allergen exposure or for 2 wk afterward. Compared with animals exposed to phosphate-buffered saline (PBS), OA-challenged animals developed an increase in total airway wall area, enhanced fibronectin deposition, epithelial cell proliferation, goblet cell hyperplasia, and airway hyperresponsiveness. Concomitant treatment with FP decreased all allergen-induced structural changes without being able to reverse them to normal. Initiating FP treatment after the allergen exposure had no effect on any of the OA-induced structural airway changes. The increase in total airway wall area, enhanced fibronectin deposition, and epithelial cell proliferation persisted. The goblet cell hyperplasia disappeared spontaneously. In conclusion, concomitant treatment with FP partly inhibits structural airway changes as well as hyperresponsiveness induced by OA exposure. Post hoc treatment fails to reverse established airway remodeling.