Increasing the value of raw bulk milk quality based on mammary glands as production units vs. the udder in dairy cows with mastitis

The current study measured the influence of milk of subclinically infected glands by different bacteria species on the cow’s milk and suggests different parameters for milk payment. The effects of bacterial infection or inflammation on gland milk yield were related to the bacteria species that caused the infection. The volume of milk of the inflamed gland from the cow’s milk yield was significantly lower (P<0.001) for the glands previously infected by Escherichia coli (PIEc) and those infected with Streptococcus dysgalactiae. Coagulation properties, rennet clotting time (RCT) and curd firmness (CF) also depended on the bacteria causing the infection. RCT values of all the inflamed glands were significantly longer (P<0.001) and CF values were significantly lower than that of the healthy ones. Moreover, in the whole milk, CF was also significantly lower and not proportional to the volume of the milk from the inflamed gland of the cow’s milk. Calculating the predicted 40% dry matter curd weight (PCW) on the cow level, including the healthy and inflamed glands or the healthy glands alone, found that for 9 of 13 PIEc cows, the presence of the affected gland’s milk in the whole cow milk resulted in a negative PCW value. Likewise, 5 of 20 cows infected by S. dysgalactiae had negative delta values. Unlike the latter bacteria, PCW from milk of glands infected with CNS increased, although in a lower magnitude than in the healthy glands. No correlation was found between logSCC in the whole cow milk (healthy and inflamed glands) and PCW.


Introduction
Mastitis in dairy cows remains one of the major issues of animal welfare in dairy farms [1]. 47 It is also a major cause of economic losses in dairy production, due to culling of cows and 48 increased replacement costs, treatment costs and discarding of abnormal milk [2,3]. Addition of 49 milk from inflamed (mastitic) mammary glands, with or without detected bacteria, to the bulk 50 milk tank, a routine practice in most cases of subclinically affected cows, reduces the whole 51 tank's milk quality [4,5]. Usually, emphasis is given to clinical mastitis, because it is notable and . Depending on country, the dairy industry pays for milk volume according to 76 certain formula, which include fat and protein levels, bacteria count and SCC [13]. In many 77 countries, bulk milk tank SCC (BMTSCC) < 2×10 5 cells/mL is considered high quality milk that 78 can be payed bonuses. However, BMSCC is the average of milk from all the individual cows 79 glands that were milked into the bulk tank, therefore, in each bulk tank the same SCC can be the 80 result of milk with different qualities and SCC levels of the individual cows, which is the 81 combination of all the glands. The various effects of SCC levels in raw milk on cheese yield and 82 quality are tabulated in [11] and in a recent study, that did not show differences in cheese yield 83 made from bulk milk if its SCC was 2×10 5 or 3×10 5 cells/mL [5].

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The aim of the current study was: To measure the influence of the milk of subclinically       The delta (difference) = expected CF -actual CF.
[2]     (Table 2). Moreover, RCT of the whole milk was also significantly longer and not 181 proportional to the volume of the milk from the inflamed gland of the cow's milk. The CF values 182 of all the inflamed glands were significantly lower than those of the healthy ones (Table 2). Only proportional to the volume of the milk from the inflamed gland of the cow's milk (Table 2). in the whole cow milk (healthy and inflamed glands) and PCW (Fig. 5).

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In the milk of all healthy glands log SCC was <5.2 (<2×10 5 cells/mL) whereas in the milk 203 of all the inflamed glands, regardless of bacteria species, log SCC was > 6.0 (>1×10 6 cells/mL)

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( Table 3). The percentage of total leucocytes (CD18 + ) and PMN were significantly higher 205 (P<0.001) in all the milk of the inflamed glands (~85% and ~70%, respectively) and had a direct 206 influence on the cow's milk and it was not proportional to milk volume ( Table 3). The  Thus, in dairies that produce only cheese and/or fermented products, segregation of the low 244 curd firmness milk from the inflamed glands will end in overall increased product yield as was 245 suggested in several publications on segregating milk for increased cheese yield [15,22].

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Moreover, in the eyes of the consumers, guarantee of using only milk that is milked from non-247 inflamed glands can increase the trust between the dairy and consumers. In order to generate a 248 mechanism where both the farmer and the dairy will benefit from increased product yield, milk 249 of inflamed cow/gland that negatively influence the cow/bulk should be detected. As shown in 250 the present study and others, not every infection and an increase in SCC has or is correlated with 251 negative impacts on product yield [11,23,24]. Because the larger negative impact is related to the 252 cheese industry, a coagulation parameter is probably the most important parameter to be tested 253 before accepting the milk for cheese production. In the Parmigiano Reggiano production routine,   Nevertheless, not every scientific finding and economical investment can or should be applied.

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In most of the intensive dairy operations, the production is oriented to two major lines: the farms,

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where the cow is a milk production unit and the dairy, where the bulk milk is the raw material for 282 the production system. Therefore, the decisions and control of each individual cow, if it to be 283 milked into the bulk tank or not regarding its health condition -inflamed and/or infected udder,  s milk quality for the cheese industry suggest different parameters for milk payment.

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As shown in the present study, not every infection and an increase in SCC has or is correlated 299 with negative impacts on product yield. In order to generate a mechanism where both the farmer 300 and the dairy will benefit from increased product yield, milk of inflamed cow/gland that