COMPOSITION AND TECHNOLOGICAL PROPERTIES OF MILK FROM DAIRY-COWS IN THE MIDDLE STAGE OF LACTATION AND THEIR INTERRELATIONSHIPS

The paper is focused on assessment of relations between milk compositi on and milk properties. Milk analyses involved the basic organic compo nents of milk, nitrogen fractions, contents of some undesirable metabo lites, health parameters and some physical and technological propertie s. Individual milk samples were taken every month from cans containing morning milk, from dairy cows of two herds of the Bohemian Pied breed and Black-Pied Lowland breed. The average milk yield was 13.23 kg mil k per cow/day for the herd of Bohemian Pied cows and 14.33 kg for the Black-Pied cows. A total of 288 samples was drawn throughout the year. The cows were in the 2nd and higher lactations and in the 3rd to the 5th month of lactation. Tab. I shows the basic statistical data for th e parameters concerned. Explanatory notes to abbreviations used are be low the table. The average values of most parameters correspond to mil k in the middle stage of lactation of dairy cows in the conditions of this country. Urea content can be considered as increased, acetone con tent is also higher indicating at higher variability the occurrence of states related to subclinical ketosis, probably most often in the 3rd month of lactation. Arithmetic and geometric means of somatic cell co unts (PSB) (230 and 141 thousand/ml) demonstrate the relatively good h ealth of the cows' udders. The highest values of variability were dete rmined for PSB, ACT, NBN and MOC, in technological properties it was f or OSY (volume of freely ejected whey at rennet coagulation), SYR (coa gulation time), KSY (subjectively determined curd quality, where class 1 = superior quality and class 3 = low quality) and for AC (alcohol c onsumption for coagulation of 5 mi milk). Table II summarizes the rela tionships between the parameters. The relations are not assessed by th e magnitude of the coefficient value, but by the actual function of th e relation. Apparent relations are not described, rather less close bu t less frequently mentioned relations are treated. An increase in BCE content was related to the higher content of NBN (0.21) and MOC (0.26) , and higher values of PSY (0.30) and KSY (-0.30). The same relation f or BCl applies to both cheese-making properties (0.28) and (-0.29), re spectively. Still higher closeness of the relation was confirmed for K AS content with respect to cheese-making properties (0.39 and -0.34, r esp.), that means that 15.2% variability in curd firmness and 11.6% va riability in curd quality can be ascribed to the variability of casein content. Further, it is possible to explain 4.4% variability in renne tability and 10.2% variability in curd firmness by means of casein num ber variability, since an increase in its value is associated with a s hortening of coagulation time and PSY increase (-0.21 and 0.32). Hence milk usability for renneting is linked up with the quality of milk pr otein fraction. A rising content of BSY resulted in the longer time of coagulation (0.20). BSY content exhibited a negative relationship to LAK content (-0.25), which documents a relationship with secretion dis orders. A relationship between NBN and MOC. was highly significant (0. 45). The contents of ACT and TUK in milk (0.21) showed an interesting positive relation, which may be due to degradation of body fat reserve s under negative energy balance during peak lactation, and also due to variations in the content of these components during lactation. A sim ilar relationship to ACT content was found in solids content. AC was n egatively influenced by NBN content (-0.13) and ACT content (-0.17), w hich indicates the effect of the lower plane of nutrition available to the cows. An increase in milk alkalinity was logically accompanied by an increase in AC (0.21). Alcohol stability (and/or thermostability a ccording to AC) was rising with the longer time of coagulation and wit h worse KSY, and it was decreasing at growing PSY and higher OSY (0.43 , 0.25, -0.21 and -0.19). Hence the better alcohol stability is relate d to worse cheese-making properties of milk, which is a paradoxical re lationship between two technologically important properties. TKM was i ncreasing with the growing KAC value (0.16), and also ACT content (0.1 8), when TKS was also rising (0.18). An increase in alcohol stability was observed at TKK drop (-0.17). An increase in TKM, TKS and TKK obvi ously improved the cheese-making properties of milk. Better cheese-mak ing properties could also be seen at an increase in TK-SB (PSY and OSY = 0.31 and 0.19). The correlation coefficients (shown in Tab. II) bet ween the parameters of secretion disorders and some cheese-making impo rtant parameters congruently indicate the worsening of cheese-making p roperties of milk with the higher degree of secretion disorder. The re lationships between the cheese-making properties were relatively close .