Bernadette O’Brien

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.

The effect of storage temperature and duration on the microbial quality of bulk tank milk

The dairy industry in Ireland is currently undergoing a period of expansion and, as a result, it is anticipated that milk may be stored in bulk tanks on-farm for periods greater than 48 h. The objective of this study was to investigate the effects of storage temperature and duration on microbial quality of bulk tank milk when fresh milk is added to the bulk tank twice daily. Bulk tank milk stored at 3 temperatures was sampled at 24-h intervals during storage periods of 0 to 96 h. Bulk tank milk samples were analyzed for total bacterial count (TBC), psychrotrophic bacterial count (PBC), laboratory pasteurization count (LPC), psychrotrophic-thermoduric bacterial count (PBC-LPC), proteolytic bacterial count, lipolytic bacterial count, presumptive Bacillus cereus, sulfite-reducing Clostridia (SRC), and SCC. The bulk tank milk temperature was set at each of 3 temperatures (2°C, 4°C, and 6°C) in each of 3 tanks on 2 occasions during two 6-wk periods. Period 1 was undertaken in August and September, when all cows were in mid lactation, and period 2 was undertaken in October and November, when all cows were in late lactation. None of the bulk tank bacterial counts except the proteolytic count were affected by lactation period. The proteolytic bacterial count was greater in period 2 than in period 1. The TBC and PBC of milk stored at 6°C increased as storage duration increased. The TBC did not increase with increasing storage duration when milk was stored at 2°C or 4°C but the PBC of milk stored at 4°C increased significantly between 0 and 96 h. The numbers of proteolytic and lipolytic bacteria, LPC, or PBC-LPC in bulk tank milk were not affected by temperature or duration of storage. Presumptive B. cereus were detected in 10% of all bulk tank milk samples taken over the two 6-wk periods, with similar proportions observed in both. In bulk tank milk samples, a greater incidence of SRC was observed in period 2 (20%) compared with period 1 (3%). Milk produced on-farm with minimal bacterial contamination can be successfully stored at 2°C and 4°C for up to 96h with little effect on its microbial quality.

A reduction in milking frequency and feed allowance improves dairy cow immune status

Twice-daily milking is the most common milking regimen used globally. A reduction in milking frequency to once daily, combined with a reduced feed allowance (FA), could reduce the physiological stress associated with the transition to peak milk production, and hence improve immune function. This study investigated how milking frequency and FA affect dairy cow immune status. Cows (n = 48) were milked once a day (OAD) or twice a day (TAD) on 1 of 2 FA: high (HFA) or low (LFA), in a 2 × 2 factorial arrangement of treatments. After the mean calving date of March 11, HFA cows were offered ad libitum grass silage and 7 kg of concentrates/cow per day until March 22, then 4 kg of concentrates/cow per day until April 17, and thereafter allocated 31.3 kg of dry matter (DM) grass/cow per day. The LFA cows were offered 4 kg of concentrates/cow per day, 1 kg of concentrates/cow per day, and allocated 19 kg of DM grass/cow per day for the same respective periods. Milk yield was recorded daily and body condition score weekly, and somatic cell count was performed at approximately 2-wk intervals. Blood samples were collected prepartum (d -7 to -1) and at d 1 to 7, d 14 to 21, and d 42 to 49 postpartum. Total and differential leukocyte percentage, IFN-γ production in response to concanavalin A and phytohemagglutinin, and cortisol, haptoglobin (Hp), and serum amyloid A (SAA) concentrations were evaluated. Cows milked OAD had reduced milk yield and body reserve mobilization, but higher somatic cell counts. Milking frequency and diet had no effect on total leukocyte counts. Cows milked OAD had a higher lymphocyte percentage and lower monocyte percentage, and tended to have a lower neutrophil percentage than cows milked TAD. In addition, the LFA cows had a higher eosinophil percentage than cows fed the HFA. Milking frequency and diet had no effect on IFN-γ, Hp, SAA, or cortisol production. Utilization of strategies to reduce milk yield at the beginning of the lactation could not only reduce body reserve mobilization, but also help to maintain a functioning immune system, and thus improve cow welfare.

Seasonal trends in milk quality in Ireland between 2007 and 2011

The objectives of this study were to evaluate annual and seasonal trends in bulk tank somatic cell count (SCC), total bacterial count (TBC), and laboratory pasteurization count (LPC) in Ireland between 2007 and 2011 (inclusive), and to compare trends based on herd type and herd size. The unadjusted median SCC and TBC of all records were 266,000 and 17,000 cfu/mL, respectively. Data were transformed to log values and analyzed using a mixed model. Fixed effects included milk processor, year, month, and total monthly milk volume; milk producer was fitted as a random variable. After analysis, means were back transformed for interpretation. Annual SCC increased slightly from 259,000 cells/mL in 2007 to a peak of 272,647 cells/mL in 2009 and then declined slightly thereafter. Although statistically significant changes in annual TBC are probably not biologically relevant, values ranged between 23,922 and 26,290 cfu/mL. Annual LPC peaked in 2008 (265 cfu/mL), declined in 2009, and increased thereafter. Monthly mean SCC of all records increased from April onward, with the greatest increases seen from October to December, when the majority of cows entered late lactation. Monthly mean TBC exhibited a seasonal trend, whereby TBC was greatest at the beginning and end of the year, coinciding with winter housing. Seasonal milk production herds (n=8,002 herds) calve all cows in spring (February to April), whereas split-calving herds (n=1,829 herds) calve cows in the spring and autumn. From February to September, monthly SCC was lower for seasonal herds than for split-calving herds, whereas SCC was lower for split-calving herds for the remaining months. During winter (October to March), split-calving herds had lower monthly TBC than seasonal herds, most likely because of stricter regulations imposed upon them. Herd size was approximated using total annual milk production figures. Across all months, larger herds had lower SCC and TBC compared with smaller herds. No obvious improvements in milk quality were seen between 2007 and 2011. Farmers have the opportunity to improve milk quality by reducing bulk tank SCC in late lactation and by imposing stricter hygiene practices at the beginning and end of the year to overcome the seasonal variation of bulk tank TBC.

Investigation of the persistence of rafoxanide residues in bovine milk and fate during processing

Rafoxanide is an effective treatment for the control of fluke infections in animals, but it is currently not permitted for treating animals whose milk is intended for human consumption. In this study, the persistence of rafoxanide residues in milk, and their migration to dairy products, was investigated following the treatment of six lactating dairy cows with Curafluke 10% oral drench. The highest concentration of rafoxanide residues detected in the individual cows milk ranged from 249 to 627 μg kg−1 and occurred at 2–3 days post-treatment. At 2 and 23 days post-treatment (representing high and low residue concentrations) the milk was pooled into two independent aliquots, each containing the full day’s milk produced by three cows. Milk products were made from pasteurised and unpasteurised milk. Pasteurisation appeared to have little impact on the stability of the residues. Rafoxanide concentrated sixfold in the cheese (week 0) compared to the starting milk (2070 vs. 349 μg kg−1) but was four times lower in whey (75 μg kg−1). Rafoxanide residues were up to 14 times higher in butter (week 0) than in the starting milk (5468 vs. 376 μg kg−1). Residues were found to further concentrate in butter and cheese at longer storage and ripening times, respectively. Skim-milk powder was manufactured from skim milk, and residues were 10-fold higher than in the starting skim milk (5468 vs. 376 μg kg−1) despite the 185°C temperature required for the process. Rafoxanide residues were stable in this skim-milk powder when stored at ambient temperature for at least 1 year. Results showed that detectable rafoxanide residues were excreted in milk for 47 days, and concentrated in the fat-based products. The analytical ranges of the UHPLC-MS/MS method used were 1.0–200 μg kg−1 (milk and whey) and 10–2000 μg kg−1 (other dairy products).

Investment appraisal of automatic milking and conventional milking technologies in a pasture-based dairy system

The successful integration of automatic milking (AM) systems and grazing has resulted in AM becoming a feasible alternative to conventional milking (CM) in pasture-based systems. The objective of this study was to identify the profitability of AM in a pasture-based system, relative to CM herringbone parlors with 2 different levels of automation, across 2 farm sizes, over a 10-yr period following initial investment. The scenarios which were evaluated were (1) a medium farm milking 70 cows twice daily, with 1 AM unit, a 12-unit CM medium-specification (MS) parlor and a 12-unit CM high-specification (HS) parlor, and (2) a large farm milking 140 cows twice daily with 2 AM units, a 20-unit CM MS parlor and a 20-unit CM HS parlor. A stochastic whole-farm budgetary simulation model combined capital investment costs and annual labor and maintenance costs for each investment scenario, with each scenario evaluated using multiple financial metrics, such as annual net profit, annual net cash flow, total discounted net profitability, total discounted net cash flow, and return on investment. The capital required for each investment was financed from borrowings at an interest rate of 5% and repaid over 10-yr, whereas milking equipment and building infrastructure were depreciated over 10 and 20 yr, respectively. A supporting labor audit (conducted on both AM and CM farms) showed a 36% reduction in labor demand associated with AM. However, despite this reduction in labor, MS CM technologies consistently achieved greater profitability, irrespective of farm size. The AM system achieved intermediate profitability at medium farm size; it was 0.5% less profitable than HS technology at the large farm size. The difference in profitability was greatest in the years after the initial investment. This study indicated that although milking with AM was less profitable than MS technologies, it was competitive when compared with a CM parlor of similar technology.

Investigation of the migration of triclabendazole residues to milk products manufactured from bovine milk, and stability therein, following lactating cow treatment

Triclabendazole (TCB) is a flukicide used in the treatment of liver fluke in cattle; however, its use is currently prohibited in lactating dairy cows. In this study, following administration of 10% Fasinex (triclabendazole, Novartis Animal Health UK Ltd., Camberley, UK) the milk of 6 animals was used to manufacture dairy products, to ascertain if TCB residues in milk migrate into dairy products. The detection limit of the ultra-high-performance liquid chromatography-tandem mass spectrometry method used was 0.67 μg/kg. The highest concentrations of TCB residue measured, within the individual cow milk yield, was 1,529 ± 244 µg/kg (n=6), on d 2 posttreatment. Days 2 and 23 posttreatment represented high and low residue concentrations, respectively. At each of these 2 time points, the milk was pooled into 2 independent aliquots and refrigerated. Milk products, including cheese, butter, and skim milk powder were manufactured using pasteurized and unpasteurized milk from each aliquot. The results for high residue milks demonstrated that TCB residues concentrated in the cheese by a factor of 5 (5,372 vs. 918 µg/kg for cheese vs. milk) compared with the starting milk. Residue concentrations are the sum of TCB and its metabolites, expressed as keto-TCB. Residues were concentrated in the butter by a factor of 9 (9,177 vs. 1,082 μg/kg for butter vs. milk) compared with the starting milk. For milk, which was separated to skim milk and cream fractions, the residues were concentrated in the cream. Once skim milk powder was manufactured from the skim milk fraction, the residue in powder was concentrated 15-fold compared with the starting skim milk (7,252 vs. 423 µg/kg for powder vs. skim milk), despite the high temperature (185 °C) required during powder manufacture. For products manufactured from milk with low residue concentrations at d 23 posttreatment, TCB residues were detected in butter, cheese, and skim milk powder, even though there was no detectable residue in the milk used to manufacture these products. Triclabendazole residues were concentrated in some milk products (despite manufacturing treatments), exceeding residue levels in the starting milk and, depending on the storage conditions, may be relatively stable over time.

Investigation of the Persistence of Closantel Residues in Bovine Milk Following Lactating-Cow and Dry-Cow Treatments and Its Migration into Dairy Products

Closantel is a veterinary drug used to treat liver fluke in cattle and sheep. A provisional maximum residue limit (MRL) of 45 μg/kg in milk has been set by the European Union. The purpose of this study was to investigate the persistence of closantel residues in milk and the migration of residues into milk products. Following dry-cow treatment, residues ranged from undetectable to 8.7 μg/kg at the first milking. Following lactating-cow treatment, residues detected ranged from 278 to 482 μg/kg at day 1 post-treatment and were detectable above the MRL for 52 days and detectable for 198 days. At day 2 and day 23 post-treatment, the milk was collected and dairy products manufactured. Closantel residues concentrated in the cheese, butter, and skim milk powder. The results indicate that closantel is best used as a dry-cow treatment.

Investigation of the persistence of triclabendazole residues in bovine milk following lactating-cow and dry-cow treatments.

Triclabendazole is a flukicide used in the treatment of liver fluke in cattle. However, its use in the treatment of liver fluke is prohibited in dairy cows. In this work, two independent studies were designed to investigate the persistence of triclabendazole residues in milk following the administration of 10% Fasinex® as dry-cow and lactating-cow treatments. In the dry-cow study, 36 in-calf dairy cows were treated with a commercial product, 10% Fasinex®, at drying-off and three triclabendazole residues (triclabendazole, triclabendazole sulphoxide and triclabendazole sulphone) were monitored in the milk following calving, approximately 60 days post-treatment. No residues were measurable in the milk of the 36 cows tested – the LOQ of the method was 1.00 µg kg−1. In the lactating-cow study, the persistence of four triclabendazole residues was investigated in the milk of six dairy cows. The highest levels of triclabendazole, triclabendazole sulphoxide, triclabendazole sulphone and keto-triclabendazole residues measured in individual milk samples were 244, 525, 1710 and 16 μg kg−1, respectively. Residues of triclabendazole, triclabendazole sulphoxide, triclabendazole sulphone and keto-triclabendazole were detectable in milk for up to 5.5, 15.5, 20 and 5 days post-treatment, respectively. Triclabendazole sulphone was found to be the most important residue, accounting for >87% of marker residues at ≥3.5 days following drug administration. These results indicate that following treatment at drying-off, triclabendazole residues in milk post-calving are well below the current MRL. Therefore, triclabendazole is a suitable flukicide for use during the dry period.

Effect of pre-milking teat disinfection on new mastitis infection rates of dairy cows

BackgroundThe practise of teat disinfection prior to cluster attachment for milking is being adopted by farmers in Ireland, particularly where there are herd issues with new infection rates. Pre-milking teat disinfection has been shown to reduce bacterial numbers on teat skin and to be most effective against environmental bacteria such as Escherichia coli and Streptococcus uberis. A split udder design experiment was undertaken on two research herds (A = 96 cows: B = 168 cows) to test the benefit of pre-milking teat disinfection on new mastitis infection levels. The disinfectant was applied to the left front and right hind teats of all cows in each herd and the right front and left hind teats received no disinfectant treatment prior to milking over a complete lactation. Individual quarter foremilk samples were taken on 5 occasions during the lactation and all clinical cases were recorded. The presence and number of staphylococcus and streptococcus bacteria on teat skin of a random sample of experimental cows (n = 20) was measured on 3 occasions during lactation (April, June, and October).ResultsPre-milking teat disinfection had no significant impact on quarter SCC and new infection rates (P > 0.05). The median SCC was 169 (95% CI = 144–198) × 103 cells/mL and 170 (95% CI = 145–199) × 103 cells/mL for disinfected teats and non-disinfected teats, respectively. There were no differences in SCC observed between herds (A = 161 (95% CI = 127–205) × 103 cells/mL; B = 169 (95% CI = 144–198) × 103 cells/mL) over the complete lactation. Bacterial levels on teat skin were reduced significantly with pre-milking teat disinfection compared to teats receiving no disinfectant (P < 0.001). Total infections (clinical and sub-clinical) were similar for disinfected teats (n = 36) and not disinfected teats (n = 40), respectively. Staphylococcus aureus (n = 47) and Strep. uberis (n = 9) were identified as the predominant bacteria in quarter foremilk samples with both clinical and sub-clinical infections.ConclusionSCC and new infection rates were similar in non-disinfected teats and disinfected (pre-milking) teats. The routine application of pre-milking teat disinfectant in pasture-grazed herds is unlikely to be of benefit where herd SCC is below 200 × 103 cells/mL.