RELATIONSHIP BETWEEN THE FERMENTATION OF BULK MILK SAMPLE, ITS COMPOSITION AND CONTENTS OF SOME METABOLITES

The fermentation is a significant technological property of milk and i ts determination enables to evaluate the suitability of the raw materi al for the production of fermented milk products. The relationship bet ween the composition of a bulk milk sample and the fermentation was ob served after excluding samples with a positive evidence of the presenc e of inhibitory substances, especially of an antibiotic character, by means of a microbiologic method (Bac. stearothermophilus, the IN-test) . The number of samples according to individual parameters observed wa s 124, 358 and 535 (Tab. I). The following parameters have been observ ed: milk fermentation (the yoghourt-test - JT) after milk pasteurizati on; the content of fat (T), proteins (B), lactose (L), non-fat solid ( TPS), dry matter (S), urea (M), acetone (A), and nitrates (D); titrabl e acidity (SH) and actual acidity (pH); somatic cell count (PSB); cond uctivity (gamma). Tab. I summarizes basic values and the variability o f parameters observed. The greatest variability was noted with paramet ers having a close relationship to the health and metabolic state of t he organism of milk cows: D, A, PSB, gamma, M, and JT. The lowest vari ability was found with TPS. Results of the correlation analysis are be ing summarized in Tab. II. Milk fermentation was in a significant rela tionship with decreased dependence on pH (r = -0.42, P < 0.0 1), PSB ( r = -0,23, P < 0.01), M (r = -0.23, P < 0.01), A (r = -0.21, P < 0.05) and further on SH, B, L, and TPS. The negative relationship to PSB me ntioned in literature as well documents a frequent occurrence of techn ological difficulties with processing of milk from cows with a deterio rated udder health state. Probably for the first time a negative relat ionship between JT and A was noted. With regard to the positive relati onship of fermentation to B and negative relationship to M and A, JT w ill be in a narrower negative dependence on the deficiency of energy i n the nutrition of cows, with decreasing content of milk proteins and increasing content of undesirable metabolites M and A. This also indic ates the method of evaluation used in Tab. III. JT values were divided into classes (I to 9) according to the content of B and M in milk wit h a premise of supply of feed nutrients in the feed ration. Significan t differences of the classes 2 and 7 compared with 1 (a balanced suppl y of energy and nitrogen substances in the nutrition with regard to ac tual milk yield is being presupposed) and the total trend of results i ndicate a decrease in JT values with a presupposed energy deficiency i n the nutrition. The relationship between JT and nitrate content was n on-significant (P > 0.05). The following correlation relationships (Ta b. II) are interesting as well: B x A (r = -0.22; P < 0.01), PSB x L ( r = -0.39; P < 0.01), SH x PSB (r = -0.25; P < 0.01), SH x A (r = -0. 17; P < 0.01) and the relationship of gamma to T, L, TPS and SH. The r elationship between L and M (r = -0.51; P < 0.01), when confirmed by a further research, could be used for a routine evaluation of the udder health state and supply of feed nutrients in cows according to the va lues of PSB and L or, as the case may be, for a specification of concl usions according to the values of PSB, B, M, and L in individual cows. It is generally known (H a n u s et al., 1992a, b) that the closeness of dependence between PSB and L decreases with an ameliorating udder health state. A confirmation of the hypothesis that, in opposite, the closeness of relationship between L and M increases with the ameliorat ing udder health state would mean an increased probability of the stat ement that - with a lower PSB (< 300 thous./ml) - the markedly decreas ed lactose content indicates a deficiency of energy in the feed ration (which could routinely be used in breeding). The results obtained giv e no answer to the question whether a deteriorated fermentation which accompanies increased levels of some undesirable metabolites could be the consequence of the effect of these very metabolites alone.