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.

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.