Electrical conductivity of milk as related to daily milk yield of udder quarters in automatically milked cows

The aim of the study was to determine the frequency of udders with specific levels of milk electrical conductivity and milk yield in primiparous and multiparous cows. Relationships between the health and milk yield of individual udder quarters in the primiparous and multiparous cows were also analysed. The left and right front quarters constituted, respectively, 67.39 and 67.90% of the quarters from which milk with electrical conductivity ≤5.50 mS/ cm was drawn. In the conductivity class >7.00 mS/cm, the right and left rear quarters showed the highest proportions (9.59 and 7.13%, respectively). Individual udder quarters from the cows most often produced either less than 7.00 kg or more than 10.00 kg milk per day. These differences concerned the front and rear udders. In the first two classes of milk electrical conductivity, the frequency of individual udder quarters in the primiparous and multiparous cows was similar. For milk with the lowest electrical conductivity, the values ranged from 50.38% (front left) to 52.62% (rear left) in primiparous cows, and from 47.38% (rear left) to 49.62% (front left) in multiparous cows. As the health of the mammary gland deteriorated, daily milk production of all its quarters was observed to decrease. A more marked reaction to this condition was observed in the front quarters, the yield of which decreased by 3.40 kg (left) and 3.02 kg (right). The rear left quarters decreased their yield by 2.85 kg/day, and the rear right ones by 2.18 kg/day. Higher production levels in all mammary quarters and in every milk electrical conductivity class were noted in the multiparous cows. The increasing milk electrical conductivity was paralleled by a lower daily milk yield of the udder quarters in both primiparous and multiparous cows. For the front left and right quarters, this decrease was 2.77 and 2.41 kg in the youngest cows, and 4.27 and 4.26 kg in the older cows. The decrease in milk production from the rear left quarters was 2.67 kg/day in primiparous and 3.76 kg/day in multiparous cows; the respective values for the rear right quarters were 2.01 and 3.86 kg milk/day.

Quarter vs. composite colostrum composition assessed by Brix refractometry, specific gravity and visual color appearance in primiparous and multiparous dairy cows

The control of colostrum quality is essential for successful calf rearing. Instruments for on-farm colostrum quality determination are mostly utilized for testing composite colostrum samples, but do not take potential variation between quarters into account. In cases of low composite colostrum quality, feeding of better quality colostrum from individual quarters might be beneficial. The objective of the present study was to identify relationships between colostrum color, colostrum quality and composition. Besides laboratory methods, a colostrometer and a Brix refractometer were used to assess colostrum quality at quarter levels. Quarter and composite colostrum samples from 17 primiparous and 11 multiparous Holstein cows were analyzed for total IgG, fat, protein and lactose content; color was measured by a spectrophotometer. In the present study, an IgG concentration below 50 g/L as determined by ELISA was found in 14.3% of the analyzed quarter samples. Concentration and mass of IgG in composite colostrum samples were greater in multiparous compared with primiparous cows. Specific gravity (SG) of colostrum of individual and composite samples was lower in primiparous compared with multiparous cows. Milk fat content was greater in quarter and composite colostrum samples of primiparous compared with multiparous dairy cows. No clear relationships between IgG content and SG, Brix, and the color space coordinates L*, a*, and b* were detected. Interestingly, results indicate that despite a similar range of the variables investigated, correlations between those parameters can differ at quarter compared to composite level. Not only for SG and Brix determination, but also for the color space coordinates measured, correlation coefficients with IgG concentration of the respective samples were greater at a composite compared with the individual quarter level. In conclusion, accuracy and limitations of on-farm instruments estimating colostrum quality apply to both quarter colostrum samples and composite evaluations. Identification of quarters with superior colostrum quality would possibly be a way to improve the immunization of newborn calves. However, the potential on-farm methods validated in the present study to estimate quarter colostrum quality are not sufficiently sensitive to distinguish between quarters. This is due to the variation of gross colostrum composition between individual quarters of a cow.

Bovine milk proteome: quantitative changes in normal milk exosomes, milk fat globule membranes and whey proteomes resulting from Staphylococcus aureus mastitis

Milk protein expression in healthy cows and cows with mastitis will provide information important for the dairy food industry and immune function in the mammary gland. To facilitate protein discovery, milk was fractioned into whey, milk fat globule membranes (MFGM) and exosomes from healthy and Staphylococcus aureus infected cows. Amine-reactive isobaric tags (iTRAQ) were used to quantify protein changes between milk fractions isolated from healthy and S. aureus infected cows. 2971 milk proteins were identified with a false discovery rate of 0.1%. Greater than 300 milk proteins associated with host defense were identified and 94 were significantly differentially regulated in S. aureus infected milk compared to their uninfected controls. These differentially regulated host defense proteins were selectively segregated in the 3 milk compartments examined. An example of this segregation of host defense proteins was the partitioning and high concentration of proteins indicative of neutrophil extracellular traps (NETs) formation in the MFGM preparations from S. aureus infected milk as compared to exosomes or whey. Protein composition changes found in milk exosomes, MFGM and whey during an infection provides new and comprehensive information on milk protein composition in general as well as changes occurring during an infection.

BIOLOGICAL SIGNIFICANCE

The significance of this study is the identification and quantification of the individual components of the neutrophil extracellular traps (NET) functional proteome in an apparent stable complex with MFGM and/or milk fat globules during an intra-mammary infection. NETs could be functionally relevant in intra-mammary infection, as it is known that during an infection neutrophils ingest large amounts of milk fat that down regulates many of their traditional immune functions. Thus the presence of NETs in milk fat provides new insights to mammary immune function and suggests a role for NETs in clinical mastitis. These in vivo NETs can now be tested to determine if they retain functional antimicrobial activity when primarily associated with milk fat. Then we can estimate their real world functional relevance during an intra-mammary infection, which is one key to understanding clinical mastitis in dairy cows.