Respiratory burst activity of blood and milk neutrophils in dairy cows during different stages of lactation.

The non-stimulated and phorbol 12-myristate 13-acetate (PMA)-stimulated luminol-augmented cellular chemiluminescence (CL) response and viability of milk and blood polymorphonuclear leukocytes (PMN) were determined in lactating dairy cows during different stages of lactation. In the first study, ten healthy cows each in early, mid and late lactation were compared. In a second study, the same measurements as in the first study were evaluated longitudinally in 12 cows during 1 month following parturition. The CL activity and myeloperoxidase (MPO) content of milk PMN and macrophages (M) were also compared. Milk M did not possess MPO activity and were devoid of any luminol-enhanced CL. The CL activity of milk and blood PMN was significantly lower in early lactation than in mid and late lactation (P < 0.001). Whereas little changes were observed in viability of blood PMN, the viability of milk PMN was lower in early lactation than in mid and late lactation (P < 0.001). The percentage of PMN in isolated milk cells was also lower during early lactation than during mid and late lactation (P < 0.001). The CL activity in response to PMA during early, mid and late lactation increased 13, 59 and 42-fold in blood PMN and 1.7, 2.6 and 2.4-fold in milk PMN, respectively, in comparison with non-stimulated PMN. The CL activity, both in milk and blood PMN. the milk PMN viability and the percentage of milk PMN were lowest between 3 d and 11 d post partum. These observed changes immediately after calving could contribute to a higher susceptibility to mastitis in that period.     

T lymphocyte proliferative capacity and CD4+/CD8+ ratio in primiparous and pluriparous lactating cows

T cells play a central role in specific immunity; their populations and phenotypes could be affected by number of lactation in high-yielding dairy cows. To investigate the effects of parity on the dynamics of T lymphocytes, lymphoproliferative capacity, T lymphocyte subsets and CD4+/CD8+ ratio were studied in peripheral blood of primiparous and pluriparous dairy cows during mid-late lactation. A non-radioactive technique was also adapted for a detailed lymphoproliferation assay. Compared with the primiparous cows, the pluriparous cows exhibited weaker lymphoproliferative activity, larger number of CD4+ cells and substantially greater CD4+/CD8+ ratio in their blood circulation. The increase of the CD4+/CD8+ ratio in the blood of pluriparous dairy cows was mainly due to the rise in the proportion of CD4+ cells and decline in the proportion of CD8+ cells. This increase of the CD4+/CD8+ ratio coincided with the decrease of mitogen-induced proliferation capacity of T lymphocytes. Of four lymphocyte divisions or generations during the lymphoproliferation assay, maximal lymphocyte proliferation capacity at generation 3 in primiparous cows was markedly greater than in pluriparous cows. With an alternatively safer, faster and more reproducible assay (compared with 3H-thymidine scintillation assay) we showed for the first time that aging in dairy cows leads to a decreased mitogen-induced lymphoproliferation and disturbed proportion between CD4+ and CD8+ T cells. This CD4+-CD8+ imbalance together with diminished lymphoproliferative capacity may lead to a weaker T cytotoxic-mediated immunity and increased susceptibility to infectious diseases in pluriparous lactating cows. Our study also emphasizes further application of the methods in farm animals.     

Viability of milk neutrophils and severity of bovine coliform mastitis

To study the host-pathogen interactions during Escherichia coli mastitis, we first determined whether E. coli infection would change blood and milk polymorphonuclear neutrophil (PMN) chemiluminescence (CL) and viability. We then hypothesized that when E. coli invade the mammary gland, the viable PMN in milk would efficiently phagocytose and destroy E. coli before establishment of infection. We observed that the phagocytosis-dependent and independent CL were closely linked to PMN viability and were crucial to the outcome of mastitis. Maximal PMN influx and colony-forming units in infected quarters appeared at postinfection hours (PIH) 6 to 24. This further boosted PMN recruitment through bone marrow-blood barrier as well as blood-milk barrier. The survival of recruited PMN in the E. coli-infected quarters was much higher than that of noninfected quarters. Chemiluminescence activity of PMN from the infected quarters significantly increased following E. coli infection, even exceeding that of blood at PIH 6, 12, and 18 to 24; no such increase was observed in noninfected quarters, suggesting that the various responses of milk PMN to stimuli resulted largely from PMN viability. The highest CL intensity and durability was observed in milk PMN from infected quarters at PIH 12. Whereas an increased viability of PMN in the noninfected quarters was only significant at PIH 6, the viability of PMN in infected quarters was long lasting and significantly higher at PIH 6 to 72. Importantly, higher preinfection milk PMN viability correlated with bacterial clearance, which was accompanied by faster recovery. Our study strongly supports the hypothesis that boosting milk PMN viability could be a strategy with which to prevent or reduce the severity of coliform mastitis in dairy cows. This strategy might be achieved through strengthening bone marrow functionality.     

Short communication: Serum osteoprotegerin concentrations in periparturient dairy cows

Dairy cows experience hypocalcemia at the onset of lactation; however, the contribution of bone metabolism to circulating Ca concentrations during the periparturient period is not well understood. Osteoprotegerin (OPG) protects against loss of skeletal mass by regulating osteoclastogenesis. We previously reported that the bone resorption increased around parturition in dairy cows from the perspective of bone markers in blood. The aim of this study was to explore osteoclastic bone resorption in periparturient dairy cows by measuring changes in serum OPG concentrations around calving. The OPG concentrations were evaluated in primiparous (n = 9) and multiparous (n = 9) cows at 21 d precalving and over 5 d after calving. Based on mixed model analyses, the multiparous cows had a higher serum OPG concentration than primiparous cows at precalving and exhibited a significant decline in serum OPG and Ca concentrations after calving. In contrast to multiparous cows, primiparous cows did not exhibit these changes. Therefore, we hypothesized that multiparous cows preserve their bone mineral content during late pregnancy and activate the osteoclastic bone resorption after calving. Based on our serum OPG data, we identified the different periparturient osteoclastic bone resorption patterns in healthy primiparous and multiparous 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), β-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 β-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.     

Decreased number and bactericidal activity against Staphylococcus aureus of the resident cells in milk of dairy cows during early lactation

Phagocytic and bactericidal activity of polymorphonuclear neutrophil leukocytes (PMN) isolated from blood and milk, against Staphylococcus aureus, was compared between groups of six healthy dairy cows in early, mid- and late lactation using a bacteriological assay. PMN were isolated from blood with a high degree of purity, but the cells isolated from milk contained variable amounts of macrophages (Mphi) and lymphocytes (L). The results were therefore calculated using the percentage PMN in order to evaluate phagocytosis and killing by PMN only. Blood PMN phagocytosed 82% Staph. aureus and milk PMN 43% on average and there was no significant difference between the different stages of lactation. The bactericidal activity of blood PMN against Staph. aureus was 36+/-8% in early lactation (significantly different from mid lactation, P < 0.05), 64+/-10% in mid lactation and 53+/-6% in late lactation. Milk PMN killed only 6+/-3% Staph. aureus in early lactation (significantly different from mid lactation, P < 0.01), 27+/-3% in mid lactation and 20+/-9% Staph. aureus in late lactation. The ratio of the bactericidal activity of milk to blood PMN was 0.08, 0.43 and 0.22 in early, mid- and late lactation, respectively. In addition to the decreased function. the number of cells in milk (somatic cell count, SCC) was also 60% lower in early lactation than in mid lactation cows (P < 0.01). Our results suggest an impairment of blood and milk-resident PMN bactericidal activity against Staph. aureus and a decreased number of milk-resident PMN in dairy cows at the onset of lactation.     

Effects of an exogenous enzyme preparation extracted from a mixed culture of Aspergillus spp. on lactational performance,metabolism, and digestibility in primiparous and multiparous cows

The objective of this study was to investigate the effects of an exogenous enzyme preparation from Aspergillus oryzae and Aspergillus niger on lactational performance of dairy cows. Forty-eight Holstein cows (32 primiparous and 16 multiparous) averaging (± SD) 36.3 ± 8.7 kg/d milk yield and 141 ± 52 d in milk were enrolled in a 10-wk randomized complete block design experiment (total of 24 blocks) and assigned to 1 of 2 treatments: basal diet, no enzyme supplementation (CON) or the basal diet supplemented with 4.2 g/kg dry matter intake (DMI) of an exogenous enzyme preparation containing amylolytic and fibrolytic activities (ENZ). After a 2-wk covariate period, premixes with the enzyme preparation or control were top-dressed daily by mixing with approximately 500 g of total mixed ration. Production data were collected daily and averaged by week. Milk samples were collected every other week, and milk composition was averaged by week. Blood, fecal, and urine samples were collected over 2 consecutive days at 0, 4, 8, 12, and 36 h after feeding during the last week of the experiment. Compared with CON, cows fed ENZ tended to increase DMI and had increased milk concentrations of true protein, lactose, and other solids. Milk fat content tended to be higher in CON cows. A treatment × parity interaction was found for some of the production variables. Primiparous cows receiving ENZ had greater yields of milk, energy-corrected milk, milk true protein, and lactose compared with CON primiparous cows; these production variables did not differ between treatments for multiparous cows. Intake and total-tract digestibility of nutrients did not differ between treatments. Concentrations of blood glucose and total fatty acids were not affected by ENZ supplementation, but β-hydroxybutyrate concentration tended to be greater in ENZ cows. Overall, the exogenous enzyme preparation used in this study increased milk protein and lactose concentrations in all cows, and milk production in primiparous but not multiparous cows. The differential production response between primiparous and multiparous cows was likely a result of a greater increase in DMI with ENZ supplementation in the younger animals.     

Ex vivo phagocytic overall performance of neutrophilic granulocytes and the relation to plasma insulin-like growth factor-I concentrations in dairy cows during the transition period

Impaired function of polymorphonuclear neutrophilic leukocyte (PMNL) during the peripartal period is a major reason for increased susceptibility of dairy cows to infections in this critical interval. Factors dysregulating PMNL function are widely unknown. Insulin-like growth factor (IGF-I) enhanced PMNL functions in vitro. The objective of this study was to investigate the influence of IGF-I and, additionally, β-hydroxybutyrate and nonesterified fatty acid concentrations on phagocytic activity (PA, percentage of viable PMNL) and phagocytic capacity (PC, mean fluorescence intensity of phagocytic PMNL) assessed by flow cytometry. Antepartum (i.e., wk −3, −2, −1; before calving), plasma concentrations of IGF-I were high (80-110 ng/mL) without significant differences between primiparous and pluriparous cows (n = 18 and n = 41, respectively). Concentrations of IGF-I declined toward the week of calving (wk 1). Postpartum (i.e., wk 2, 3, and 4; after calving), IGF-I remained lower than before parturition, with concentrations higher in primiparous compared with those of pluriparous cows. The PA was constant in primiparous cows throughout the study period. Conversely, PMNL of pluriparous cows had a significantly increased and higher PA in wk 2 and 3 postpartum compared with that of primiparous cows. The PC decreased significantly only in primiparous cows the week of calving, whereas the number of PMNL in primiparous cows exceeded that of pluriparous cows significantly. The phagocytic power (PP, a product of PA by PC), but not the phagocytic overall performance (POP, a product of PA, PC, and PMNL number), differed between primiparous and pluriparous cows in wk 3 postpartum. No significant differences in POP were found, except in wk 4 after calving between the primi- and pluriparous cows. In both groups, POP increased in the week of calving (wk 1). In contrast to β-hydroxybutyrate, which was weakly positive correlated with PA and PP in pluriparous cows in the transition period (wk −3 antepartum to wk 4 postpartum), pluriparous animals had weak negative correlations of PMNL number, PA, PP, POP, and IGF-I concentration in this period. In primiparous animals, only PP and PC were weakly negatively correlated with IGF-I in the transition period. Increased plasma IGF-I concentrations were not associated with enhanced phagocytosis function of bovine blood PMNL ex vivo and, thus, can not be regarded as a suitable predictor for this function.     

Effects of milking frequency on phagocytosis and oxidative burst activity of phagocytes from primiparous and multiparous dairy cows during early lactation

The objective of this study was to investigate the effect of milking frequency on the phagocytosis and respiratory burst activity of polymorphonuclear neutrophils (PMN) and monocytes of primiparous and multiparous cows under 2 nutritional management regimens during early lactation. At calving, 12 primiparous and 12 multiparous cows were randomly assigned to 1 of 4 treatments, in which animals were milked once (OAD) or twice a day at a high or low nutritional level. Blood samples were taken 1 to 7 d before calving (prepartum) and 1 to 7, 14 to 21, and 42 to 49 d postpartum. Phagocytic and oxidative burst activity of PMN and monocytes were determined in whole blood and analyzed separately by flow cytometry. Once-a-day milking reduced significantly the percentage of phagocytic PMN and tended to decrease the number of bacteria ingested by these cells. The percentage of oxidative burst positive cells and overall respiratory burst activity of monocytes also tended to be reduced by OAD milking. The reduction of oxidative burst activity of monocytes was more pronounced 1 to 7 d postpartum compared with the prepartum sample and other postpartum samples. Oxidative burst activity of PMN and monocytes of multiparous cows was impaired compared with primiparous cows. The percentage of oxidative burst positive monocytes from multiparous cows was reduced prepartum and also 1 to 7 d postpartum. Once-a-day milking reduced the mean respiratory burst activity of PMN from primiparous cows to levels similar to that of multiparous cows. Therefore, an OAD milking regimen reduces phagocytic activity of PMN and monocytes and would be detrimental for the immune system in high-yielding dairy cows during early lactation.     

Effect of stage of lactation and parity on mammary gland cell renewal

Milk production is a function of the number and activity of mammary epithelial cells, regardless of stage of lactation. Milk yield is generally higher in multiparous cows than in primiparous cows, but persistency is usually greater in the latter group. We compared several measures related to metabolic activity, apoptosis, and endocrine control of mammary cell growth in 8 primiparous and 9 multiparous cows throughout lactation. Mammary gland biopsies were taken in early [10 d in milk (DIM)], peak (50 DIM), and late (250 DIM) lactation to evaluate gene expression and determine DNA and fatty acid synthase (FAS) content. Milk samples taken the day before the biopsies were used to detect protease activities and to determine stanniocalcin-1 (STC) concentrations. Blood samples served to measure insulin-like growth factor-1, prolactin, and STC concentrations. Milk yield was higher in multiparous cows than in primiparous cows at the 10 DIM (32.8 ± 1.3 and 25.2 ± 0.8 kg/d) and 50 DIM (38.0 ± 1.2 and 29.8 ± 1.1 kg/d), but it was the same for both groups at 250 DIM (23.9 ± 1.5 and 23.8 ± 1.1 kg/d). Except for stearoyl-coenzyme A desaturase, expression of genes related to milk synthesis was not affected by stage of lactation. However, gene expression of acetyl-coenzyme A carboxylase, β-casein, and FAS was lower in early lactation in primiparous cows. Expression of both proapoptotic bax and antiapoptotic bcl-2 genes was higher in primiparous cows, whereas the bax-to-bcl-2 ratio was not changed. Mammary DNA concentration was higher in multiparous cows, as was the amount of FAS protein in early lactation. Two bands of protease activity were found in milk samples, and one of the bands had an apparent molecular weight similar to gelatinase A and was dependent on the stage of lactation. Serum insulin-like growth factor-1 increased with day of lactation and was higher in primiparous cows. Serum prolactin decreased in late lactation, but peak values were observed in early lactation for primiparous cows and peak lactation for multiparous cows. Milk STC content increased with advancing lactation. The results are consistent with a lower degree of differentiation and a greater capacity for cell renewal in the mammary gland of primiparous cows.     

Layouts for small freestall dairy barns: effect on milk yield for cows in different parities

Freestall housing for dairy cows has many different layouts and the space allocated for cows differs considerably. The objective of the present study was to investigate possible associations between barn layout and milk yield for different parities in small dairy freestall barns. Layouts of 204 Norwegian freestall barns constructed during the period from 1995 to 2005, and with a mean herd size of 42.7 ± 15.5 cows, were obtained and merged with milk yield data and calving interval, for each parity, from the Norwegian Milk Recording System (NDHRS). The milk yield data set contained 20,221 different lactations from these 204 herds. Both simple mixed models, including the different explanatory variables one by one together with parity, calving interval, and herd as random effect, and a final mixed model, including all significant explanatory variables, were created. According to variables tested in this study, the final mixed model estimates show that only primiparous cows benefit significantly from increased free space allocation. Milk yield was generally higher in automatic milking system barns compared with that in barns with milking parlors, but not for primiparous cows. Milk yield was higher for all parities for barns using separation pens in accordance with the recommendations. Barns with 2 or more dead-end alleys had lower milk yield compared with that from layouts without dead-end alleys. Primiparous cows benefited from water troughs located for easy access and responded with increased milk yield. In 10% of the barns, the water trough capacity was less than 47% of the recommendations, and all parities benefited from a water trough capacity higher than this level. Higher parities had increased milk yield when water trough capacity was more than 80%. Feed bunk space, number of freestall rows, and the location of freestalls had no significant effect on the milk yield. The present study showed that increased space and improved access to water is beneficial to primiparous cows, whereas layouts without dead-end alleys and improved water capacity is beneficial for all cows in freestall systems.     

Effect of rumen-protected choline on performance, blood metabolites, and hepatic triacylglycerols of periparturient dairy cattle

The effects of a dietary supplement of rumen-protected choline on feed intake, milk yield, milk composition, blood metabolites, and hepatic triacylglycerol were evaluated in periparturient dairy cows. Thirty-eight multiparous cows were blocked into 19 pairs and then randomly allocated to either one of 2 treatments. The treatments were supplementation either with or without (control) rumen-protected choline. Treatments were applied from 3 wk before until 6 wk after calving. Both groups received the same basal diet, being a mixed feed of grass silage, corn silage, straw, and soybean meal, and a concentrate mixture delivered through transponder-controlled feed dispensers. For all cows, the concentrate mixture was gradually increased from 0 kg/day (wk −3) to 0.9 kg of dry matter (DM)/d (day of calving) and up to 8.1 kg of DM/d on d 17 postcalving until the end of the experiment. Additionally, a mixture of 60 g of a rumen-protected choline supplement (providing 14.4 g of choline) and of 540 g of soybean meal or a (isoenergetic) mixture of 18 g of palm oil and 582 g of soybean meal (control) was offered individually in feed dispensers. Individual feed intake, milk yield, and body weight were recorded daily. Milk samples were analyzed weekly for fat, protein, and lactose content. Blood was sampled at wk −3, d 1, d 4, d 7, d 10, wk 2, wk 3, and wk 6 and analyzed for glucose, nonesterified fatty acids, and β-hydroxybutyric acid. Liver biopsies were taken from 8 randomly selected pairs of cows at wk −3, wk 1, wk 4, and wk 6 and analyzed for triacylglycerol concentration. We found that choline supplementation increased DM intake from 14.4 to 16.0 kg/d and, hence, net energy intake from 98.2 to 109.1 MJ/d at the intercept of the lactation curve at 1 day in milk (DIM), but the effect of choline on milk protein yield gradually decreased during the course of the study. Choline supplementation had no effect on milk yield, milk fat yield, or lactose yield. Milk protein yield was increased from 1.13 to 1.26 kg/d at the intercept of the lactation curve at 1 DIM, but the effect of choline on milk protein yield gradually decreased during the course of the study. Choline supplementation was associated with decreased milk fat concentration at the intercept of the lactation curve at 1 DIM, but the effect of choline on milk fat concentration gradually decreased as lactation progressed. Choline supplementation had no effect on energy-corrected milk yield, energy balance, body weight, body condition score, and measured blood parameters. Choline supplementation decreased the concentration of liver triacylglycerol during the first 4 wk after parturition. Results from this study suggest that hepatic fat export in periparturient dairy cows is improved by choline supplementation during the transition period and this may potentially decrease the risk for metabolic disorders in the periparturient dairy cow.     

Reducing milking frequency from twice to once daily as an adjunct treatment for ketosis in lactating dairy cows—A randomized controlled trial

This randomized controlled trial investigated the effects of temporarily reducing milking frequency (MF) on the resolution of ketosis and milk production in dairy cows in early lactation. To detect ketosis [blood β-hydroxybutyrate (BHB) ≥1.2 mmol/L], Holstein cows were screened daily from 3 to 16 d in milk using a cow-side meter. Cows diagnosed with ketosis (n = 104) were randomly assigned to twice-daily milking (TDM) or reduced to once-daily milking (ODM) for 2 wk, then returned to twice-daily milking. Both treatment groups received a 5-d treatment of an oral propylene glycol drench (PG; 300 g) beginning on the afternoon of the diagnosis; cows received additional 5-d PG treatments if they had a ketotic test result (blood BHB ≥1.2 mmol/L) at least 4 d after finishing the first PG treatment. Blood BHB tests were conducted for the first 3 d after ketosis diagnosis, and then once every 3 d for 21 d of trial (DOT). Milk and milk component data were collected weekly for 15 wk following trial enrollment. The ODM group showed rapidly and markedly decreased blood BHB concentrations (primiparous cows: 1 DOT, 0.92 ODM vs. 1.22 TDM, 15 DOT, 0.55 vs. 0.81 mmol/L; multiparous cows: 1 DOT, 1.01 vs. 1.40, 15 DOT, 0.78 vs. 1.65 mmol/L). In addition, a logistic regression model indicated that ODM cows were less likely to have blood BHB concentrations ≥1.2 mmol/L [primiparous cows: 3 DOT: ODM 1% (95% confidence interval: 0–10%) vs. TDM 43% (30–58%), 15 DOT ODM 0% (0–0.2%) vs. TDM 22% (13–36%); multiparous cows: 3 DOT: ODM 33% (24–44%) vs. TDM 59% (48–69%), 15 DOT ODM 20.9% (13–31%) vs. TDM 64% (53–74%)]. The proportion of ODM cows that required additional treatments of PG were substantially lower than the TDM group (ODM: 39%; TDM: 64%) than the TDM cows during the initial 21-d period. However, during the 2-wk treatment period, cows in the ODM group produced 26% less milk and 25% less energy-corrected milk than the TDM cows. During wk 3 to 15, when all cows were milked twice daily, ODM cows produced less milk (?14%) and energy-corrected milk (?12%) compared with the TDM group. Milk protein percentage was greater, and milk fat percentage and linear score tended to be greater in the ODM group over 15 wk. In conclusion, a 2-wk reduction of MF in ketotic cows from twice to once daily with treatment with PG resolved ketosis and decreased blood BHB concentrations more effectively than treating TDM cows with PG alone. However, the 2-wk MF reduction had immediate and long-term (up to 13 wk after cessation of MF reduction) negative effects on milk production.     

Heat stress abatement during the dry period influences metabolic gene expression and improves immune status in the transition period of dairy cows

Heat stress (HT) and photoperiod affect milk production and immune status of dairy cows. The objective was to evaluate the effects of HT abatement prepartum under controlled photoperiod on hepatic metabolic gene expression and cellular immune function of periparturient Holstein cows (n = 21). Cows were dried off 46 d before expected calving date and assigned to treatments by mature equivalent milk production. The treatments were 1) HT and 2) cooling (CL), both imposed during a photoperiod of 14L:10D. Rectal temperature was measured twice daily, whereas respiration rate was measured 3 times/wk at 1500 h during the entire dry period. After calving, cows were housed in a freestall barn with cooling, and milk yield was recorded daily up to 140 d in milk. Liver samples were taken at dry off, −20, 2, and 20 d relative to calving by biopsy. Under a similar schedule, neutrophil function was determined in blood of cows on HT (n = 12) and CL (n = 9). Blood samples were taken on −46, −32, −18, 0, 14, 28, and 42 d relative to calving for measurement of metabolites and were collected twice daily from −7 to 2 d relative to calving for prolactin (PRL) analysis. The HT cows had greater concentrations of PRL at 0 d relative to calving (150 vs. 93; SEM = 11 ng/mL) and had higher afternoon rectal temperatures (39.4 vs. 39.0; SEM = 0.04°C) and elevated respiration rates (78 vs. 56; SEM = 2 breaths/min) during the prepartum period compared with CL cows. Relative to HT cows, CL cows had greater hepatic expression of PRL-R, SOCS-3, and CAV-1 mRNA. Neutrophil oxidative burst was greater in CL cows relative to HT cows at 2 d (61 vs. 42; SEM = 6%) and at 20 d (62 vs. 49; SEM = 5%) relative to calving, and phagocytosis was greater in CL cows at 20 d (47 vs. 33; SEM = 4%) relative to calving compared with HT cows. Humoral response, as measured by IgG secretion against ovalbumin challenge, was greater for CL cows at −32 d (0.44 vs. 0.33; SEM = 0.05 OD) and −21 d (0.60 vs. 0.50 ± 0.04 OD) relative to calving compared with HT cows. These results suggest that HT abatement during the dry period improved innate and acquired immune status as measured by neutrophil function and immunoglobulin secretion against ovalbumin challenge, and altered hepatic gene expression related to PRL signaling in the periparturient period or subsequent lactation.     

Relationships between body condition,body condition loss,and serum metabolites during the transition period in primiparous and multiparous cows

In the transition period from late gestation to early lactation, dairy cows undergo tremendous metabolic changes. Insulin is a relevant antilipolytic factor. Decreasing serum concentrations of insulin and glucose, increasing serum concentrations of nonesterified fatty acids (NEFA) and β-hydroxybutyrate (BHB), and changes in body condition score (BCS) reflect the negative energy balance around calving. This study investigated peripartum metabolic adaptation in 359 primiparous and 235 multiparous German Holstein cows from a commercial dairy herd under field conditions. Body condition score was recorded and blood samples were taken 10 to 1 d prepartum, 2 to 4 d postpartum, and 12 to 20 d postpartum. Generalized mixed models and generalized estimation equations were applied to assess associations between prepartum BCS; BCS changes during the transition period; insulin, glucose, NEFA, and BHB serum concentrations; and milk yield, which was taken from an electronic milk meter from d 6 of lactation. Serum insulin concentrations of multiparous postpartum cows were lower compared with prepartum, and compared with primiparous cows. In general, primiparous cows had lower postpartum NEFA and BHB concentrations than multiparous cows. In primiparous cows, we identified a positive association between prepartum BCS and prepartum serum insulin concentration. Prepartum obese multiparous cows, but not primiparous cows, were characterized by higher postpartum serum NEFA and BHB concentrations and lower milk yield than other cows in the same parity class. Primiparous cows with a smaller degree of BCS loss during the transition period had higher postpartum insulin and lower NEFA concentrations and lower milk yield than other primiparous cows. In conclusion, primiparous cows had less lipolysis and lower milk yield than multiparous cows, associated with higher insulin concentrations. Avoiding high body condition loss during the transition period is a main factor in preventing peripartal metabolic imbalances of glucose and fat metabolism.     

Changing dietary electrolyte balance for dairy cows in cool and hot environments

Two Latin square studies, each containing eight primiparous cows (four Holstein, four Jersey), were conducted to determine the effect of changing dietary electrolyte balance during cool and hot environmental conditions on performance of lactating dairy cows. Electrolyte balance, expressed as Na + K - Cl in milliequivalents per kilogram of diet, was altered by changing K and Cl content in the diet using potassium bicarbonate or calcium chloride. Maximum and minimum temperatures averaged 26.7 and 15.0 degrees C during the cool phase and 32.3 and 22.5 degrees C during the hot phase of the study. Milk yield improved linearly with increasing electrolyte balance with nonsignificant treatment by phase interaction, whereas DMI of cows improved quadratically with increasing dietary electrolyte balance. A treatment by phase interaction for DMI was detected, although intake of DM reached a plateau at a similar dietary electrolyte balance during the cool and hot phases. Body (milk) temperature of cows appeared to be related to the level of feed consumed and varied by treatment within phase. Body (milk) temperature was higher during the hot phase of the experiment. Blood bicarbonate and pH were lowest in cows offered the low electrolyte balance (high Cl) diet, and blood and urinary Na + K-Cl increased linearly with increasing dietary electrolyte balance. The response to dietary electrolyte balance appeared to be mediated through blood buffering and the impact on physiologic systems of the cow.     

Lactose in blood plasma and the ability of dairy cows to tolerate once-daily milking in terms of milk loss and milk recovery

This experiment described the variability among cows with the aim of studying the ability of dairy cows to tolerate once-daily milking (ODM) in terms of milk losses and milk recoveries observed when cows are switched from twice- to once-daily milking and then back to twice-daily milking (TDM). It also aimed to investigate whether or not lactose in blood plasma, which indicates the mammary epithelium permeability, is correlated with milk losses and recoveries and, consequently, a potential candidate assessor of dairy cow tolerance to ODM. The study used 86 crossbred dairy cows (Holstein × Normande) split into 5 groups over 2 yr. The trial consisted of 3 successive periods: a 1-wk control period of TDM, then 3 wk of ODM, followed by 2 wk of TDM. Blood samples were collected 1 to 1.5 h before the morning milking and 5 to 6 h after milking on d −3, 0, 1, 3, 7, 21, 23, and 28, where d 0 is the last d of the control period. Milk losses measured as kilograms per day were higher in cows with highest control-period milk yields (r = −0.66). When expressed in relative terms (%), milk losses were weakly correlated with the control-period milk yield (r = −0.22). When switched back to TDM, cows recovered only 47% of the milk lost. Milk recovery (kg/d) was weakly correlated with control milk yield (r = 0.34) and not correlated with ODM milk yield. Milk recovery was correlated with milk yield losses: the higher the milk yield losses (kg/d or %), the higher the milk recovery (kg/d; r = −0.59 and −0.52, respectively). Rate of milk recovery expressed as the quantity of milk recovered per kilogram of milk lost, was not correlated with milk loss expressed as a percentage. This means that to be considered well-adapted to ODM scheduling, a cow must be well adapted to milk loss, and be well adapted to milk recovery. Blood plasma lactose concentration (log₁₀-transformed data) was not correlated with milk production levels in either control, ODM, or back-to-TDM periods. It was poorly correlated with milk loss but was positively correlated with milk recovery (kg/d) and rate of milk recovery. We conclude that blood plasma lactose needs to be coupled with other indicators for evaluating dairy cow tolerance to ODM.     

Peripheral blood mononuclear cell mitochondrial enzyme activity is associated with parity and lactation performance in early lactation Holstein dairy cows

Mitochondria are central to metabolism and are the primary energy producers for all biosynthesis, including lactation. The objectives of this study were to determine if high- and low-producing dairy cows exhibit differences in peripheral blood mononuclear cell mitochondrial enzyme activities of citrate synthase, complex I, complex IV, and complex V during early lactation and, thus, to determine whether those differences were related to differences in lactation performance in the dairy cow. Fifty-six Holstein cows were assigned to 1 of 4 groups: (1) primiparous high, (2) primiparous low, (3) multiparous high, or (4) multiparous low. Primiparous and multiparous cows were analyzed separately. Then, cows were divided into high or low production groups for each production parameter [peak milk, average milk, energy-corrected milk (ECM), fat-corrected milk (FCM), milk lactose, milk fat, milk protein, total solids (TS), solids-not-fat, feed efficiency, and somatic cell count (SCC)]. For all data analysis, production parameters are expressed as yields (kg/d) and SCC (10³ cells/mL). High and low production groups were defined by their respective mean production parameters for the 56 cows, with below average cows defined as low and above average cows defined as high. Whole blood samples were collected at one time point, approximately 70 d in milk at 0800 h, and processed for crude mitochondrial extracts from peripheral blood mononuclear cells to determine the activity rates of mitochondrial enzymes. Milk samples were collected 9 times (3 d, 3 times per d) during the week of blood collection and analyzed for major components (fat, protein, lactose, TS, and SCC). Multiparous cows had lower citrate synthase activity than primiparous cows across all production parameters. High-producing cows had greater complex I activity for peak milk, milk yield, ECM, FCM, milk fat, TS, and feed efficiency, and greater complex V activity for ECM, FCM, milk lactose, milk fat, and TS across parities. These findings imply that the most influential respiratory chain enzymes on the level of milk production are those responsible for electron transport chain initialization and ATP production.     

A randomized study on the effect of extended voluntary waiting period in primiparous dairy cows on milk yield during first and second lactation

Extending the voluntary waiting period (VWP) for primiparous cows can have a positive impact on fertility without a negative impact on milk production per day in the calving interval (CInt). We investigated the effect of extended VWP during first lactation on milk yield (MY) during 2 consecutive lactations in primiparous cows. The study involved 16 commercial herds in southern Sweden. A total of 533 Holstein and Red dairy cattle (Swedish Red, Danish Red, Ayrshire) dairy cows were randomly assigned to a conventional 25 to 95 d VWP (n = 252) or extended 145 to 215 d VWP (n = 281). Data on calvings, inseminations, and test-day yields were retrieved from the Swedish Milk Recording System. Cows with VWP according to plan and completing 1 or 2 CInt with a second or third calving were included in the data analysis. Whole lactation and 305-d energy-corrected milk (ECM) yield were higher for the extended VWP group than the conventional VWP group in both the first lactation (12,307 vs. 9,587 and 9,653 vs. 9,127 kg ECM) and second lactation (12,817 vs. 11,986 and 11,957 vs. 11,304 kg ECM). We found no difference between the VWP groups in MY per day during the first CInt or during the first and second CInt combined, although MY per day during the second CInt was around 1.5 kg higher for cows with extended VWP than for cows with conventional VWP. Thus extended VWP for primiparous cows can be used as a management tool without compromising MY.     

Effects of intramuscular injections of vitamin B12 on lactation performance of dairy cows fed dietary supplements of folic acid and rumen-protected methionine

The experiment was undertaken to determine the effects of i.m. injections of vitamin B(12) on lactational performance of primiparous dairy cows fed dietary supplements of folic acid and rumen-protected methionine from 4 to 18 wk of lactation. Fourteen primiparous Holstein cows were assigned to 7 blocks of 2 cows each, according to milk production during the third week of lactation. All cows were fed a basal diet supplemented daily with rumen-protected methionine (18 g of supplement, to bring the estimated supply of methionine to 2.2% of metabolizable protein) plus folic acid (4 mg per kg of BW). Within each block, the cows received a weekly i.m. injection (2 mL) of saline or 10 mg of vitamin B(12). Milk production was recorded daily. Milk and blood were sampled every 2 wk. Supplementary vitamin B(12) increased energy-corrected milk from 25.8 to 29.0 (SE 1.6) kg/d, as well as milk yields of solids [3.52 to 3.90 (SE 0.22) kg/d], fat [0.87 to 1.01 (SE 0.06) kg/d], and lactose [1.48 to 1.64 (SE 0.11) kg/d]. Supplementation also increased concentrations and amounts of vitamin B(12) secreted in milk but had no significant effect on dry matter intake and concentrations and amounts of folates in milk. Packed cell volume, blood hemoglobin, and serum vitamin B(12) were increased by supplementary vitamin B(12), whereas serum methylmalonic acid was decreased. Serum concentrations of sulfur amino acids were unchanged by treatment. These findings support the hypothesis that, in early lactation, supply of vitamin B(12) was not optimal and limited the lactation performance of the cows.