Fatty acids (FAs) of milk fat are considered to be important nutritional components of the diets of a significant portion of the human population and substantially affect human health. With regard to dairy farming, the FA profile is also seen as an important factor in the technological quality of raw milk. In this sense, making targeted modifications to the FA profile has the potential to significantly contribute to the production of dairy products with higher added value. Thus, FAs also have economic importance. Current developments in analytical methods and their increasing efficiency enable the study of FA profiles not only for scientific purposes but also in terms of practical technological applications. It is important to study the sources of variability of FAs in milk, which include population genetics, type of farming, and targeted animal nutrition. It is equally important to study the health and technological impacts of FAs. This review summarizes current knowledge in the field regarding sources of FA variability, including the impact of factors such as: animal nutrition, seasonal feed changes, type of animal farming (conventional and organic), genetic parameters (influence of breed), animal individuality, lactation, and milk yield. Potential practical applications (to improve food technology and consumer health) of FA profile information are also reviewed.

The concentration (<I>c</I>) of free fatty acids (FFAs) in milk is an indicator of dairy cow nutrition, milk straining, its bacterial contamination and storage quality. High FFA concentrations (<I>cs</I>) caused by lipolysis can damage the quality properties of milk products. Therefore the FFA content is introduced thanks to an increase in the efficiency of modern analytical methods as a milk quality indicator and as an indicator for its price as well. The goal of this paper was to analyse the FFA relations to the other milk quality indicators. The data set (<I>n</I> = 11 586) was evaluated by regression methods. In November and December the respective FFA means were 0.614 ± 0.458 and 0.835 ± 0.491 mmol/100 g with a relatively high variability of 74.6 and 58.8%. The frequency of unsatisfactory FFA values (> 1.3) was 7.51 and 13.93%. Casein content (<I>r</I> = –0.17; <I>P</I> < 0.01) and crude protein content (<I>r</I> = –0.12; <I>P</I> < 0.01) were related more closely with FFA <I>c</I>. The FFAs can increase by 0.066 mmol/100 g with casein decrease by 0.10%. The FFAs in milk fat can slightly increase by the supply of energy to dairy cows (protein and casein decrease) and rise with the deteriorating health state of mammary gland (lactose, <I>r</I> = –0.14; <I>P</I> < 0.01) as well. The somatic cell count correlated with FFAs more weakly (<I>r</I> = 0.07; <I>P</I> < 0.05), similarly like the total mesophilic bacteria count (<I>r</I> = 0.11; <I>P</I> < 0.01), relatively more closely the psychrotrophic bacteria count (<I>r</I> = 0.27; <I>P</I> < 0.05). The deterioration of almost all hygienic indicators signified an FFA c increase. The urea content correlated with FFAs weakly (<I>r</I> = –0.08; <I>P</I> < 0.05) and the fat content imperceptibly as a component of similar substance like FFAs. The mechanical milk stress led to FFA liberation from fat esters proportionally to the intervention intensity (<I>P</I> < 0.001). Even a relatively small mechanical stress caused by mixing comparable to the current milking technology, milk transport and storage increased the FFA c of milk fat from 1.11 ± 0.19 to 1.80 ± 0.40 mmol/100 g (<I>P</I> < 0.05). The highest experimental stress up to 6.88 ± 0.55 mmol/100 g (<I>P</I> < 0.001).

ABSTRACT:The fatty acid (FA) composition of bulk milk fat was examined on three mountain dairy farms in the Czech Republic. Milk samples were collected in the period of indoor grass silage feeding (November-April) and in the grazing period (May-October). In total fifty FAs were identified in the milk fat. The two-way ANOVA with factors of the farm and of the period of milk sample collection was used for the evaluation of variation in FA concentrations. Significant differences between the farms (P < 0.01) were found in the concentration of five FAs, which accounted for 30.40 g/100 g total FAs. Significant differences between the indoor and the grazing period (P < 0.01) were found in the concentration of sixteen FAs, which accounted for 63.86 g/100 g total FAs. The content of long-chain (> C16), mono-and polyunsaturated FAs in the milk fat was higher in the grazing period (49.22, 31.69 and 4.69 g/100 g total FAs) than in the indoor period (42.25, 27.55 and 4.15 g/100 g total FAs, respectively; P < 0.01). The proportion of conjugated linoleic acid (CLA) was also higher in the grazing period (1.09 g/100 g total FAs) than in the indoor period (0.74 g/100 g total FAs; P < 0.01). The medium-chain (C12-C16) and the saturated FAs were more abundant in the milk fat in the indoor period (48.91 and 67.16 g/100 g total FAs) than in the grazing period (41.31 and 62.16 g/100 g total FAs; P < 0.001 and P < 0.01; respectively). These results indicated a positive influence of seasonal grazing on the FA profile of cow milk fat as regards its potential health effects in consumers.

The milk freezing point (MFP) is used for the control of milk food chain quality especially for possible adulteration with water. A crucial issue is the acceptance of the legislative discrimination limit (RLDL) of MFP for standard quality. The aim was to explain the relations between MFP and spectrum of milk indicators (MI) and possible impacts of MFP on technological milk properties. 76 bulk milk samples (BMS) from Holstein (1, <I>n</I> = 36) and Czech Fleckvieh (2, <I>n</I> = 40) cattle were analyzed for 48 MIs. The dairy cows were relatively healthy as for the occurrence of production disorders. BMSs were taken from February to June. Extraneous water was excluded. 44 MIs were correlated with the MFP. The relations were not regularly consistent between breeds. Milk yield was connected with MFP (<I>r</I> = 0.40; <I>P</I> < 0.05). It shows the necessity of modification of RLDL of MFP in dependence on dairy cow breeding. Further relations (<I>P</I> ≤ 0.05) were among MFP and: total milk solids (<I>r</I> = –0.50); solids-non-fat (–0.33); crude protein (–0.32); true protein (–0.43); whey protein (–0.47); milk fat (–0.46); electrical conductivity (–0.35); lactose (–0.35); somatic cell count (–0.36); fat/protein ratio (–0.36); milk citric acid (0.47); Na (–0.34). The poor relations (<I>P</I> > 0.05) were among MFP and casein, milk urea and acetone. The cheese-making indicators were not affected by MFP. The MFP was related to milk fermentation indicators (<I>r</I> = from –0.34 to –0.39, <I>P</I> < 0.05). It is important for the control of milk food chain quality by MFP and for the estimation of its RLDL.

The milk yield (MY) is an important economic and health factor closely connected with the health status of dairy cows, their reproduction performance, longevity and milk composition and properties (MIs). The differences within MIs between high yielding herd (Group 1; 10 282 kg per lactation) and three herds with average MY (Group 2; 7 926 kg) were tested. The files with 96 and 290 milk samples were collected in summer and winter feeding seasons and well balanced in lactation factors. Group 1 had higher genetical value, better nutrition and was milked three times per day and its MY was higher by 30% (P < 0.001). among 23 milk indicators (MIs) under study only a few MIs (30.4%) were influenced (P < 0.05): somatic cell count (SCC); urea (U); acetone (aC); pH acidity; alcohol stability; curd firmness; the ratio of urea nitrogen in non-protein nitrogen (URn). Except for U, these changes were less important. Protein spectrum was not affected (P > 0.05). The U was probably higher due to higher loading of the nitrogen nutrition (4.27 > 3.57 mmol·l Dairy cow, Holstein cattle, milk yield, milk composition, milk properties, health status indicatorsIn dairy cattle, genetic improvement and well balanced nutrition are the main factors improving the milk yield (MY). Furthermore, feeding technology may help to fully exploit the genetic potential as evidenced in current Holstein (H) population. In general, a better use of these factors in dairy herds may enhance the lactation physiology and also the composition and milk properties of high yielding cows. The resistance degree to health disorders (e. g. mastitis) or stress may increase as well. These facts are interesting for milk producers, veterinarians and dairy operations because of impacts on farmer milk price, processing efficiency and product quality. Relevant changes are observed due to routine performance of milk recording in dairy herds. However, it is only possible for a limited number of milk indicators such as MY, fat, protein, lactose and urea contents and somatic cell counts. These are usually included in milk recording and dairy herd improvement programmes. Of course, interesting changes could be found in other milk components and properties as well. The genetic and nutritional improvements are in accordance with the basic equation phenotype = genotype + environment the main factors of cow MY increase. However, high MY is often a reason for breeder fears from its possible negative consequences. It could cause production health disorders as a result of impaired immunity decrease of cows including a shorter production age of dairy cows. Poor reproduction