[Transport of nitrates and nitrites into the milk of dairy cows through the digestive system].

Increased nitrate concentrations in milk are not only dangerous to human health as the milk is the material for production of baby and infant food, but they cause also many problems in technological milk processing. The study was aimed at the transfer of nitrates and nitrites into milk of dairy cows following nitrate loading. An experiment included 6 dairy cows of the Slovakian Spotted breed at the Experimental Veterinary Centre at Zemplínska Teplica. Prior to start of the experiment samples of feedstuffs and feed water, milk were taken and examined for the presence of nitrates and nitrites. KNO3 in water solution was applied to selected dairy cows in two-week intervals in single peroral doses of 150; 75; 37.5; 18.75 and 9.5 g two hours before evening milking. Nitrate and nitrite residue contents were studied in individual milk samples obtained from manual milking 2, 14, 26, 38 and 50 hours after application of appropriate KNO3 amount. Following the peroral application of KNO3 to dairy cows, a marked increase in nitrate content in milk appeared in dependence on applied KNO3 (Tab. I). Average value of residual nitrate in milk two hours after administration of 150 g of KNO3 was 34.60 mg of NO3-/l. Increased levels of residual nitrate in milk were found also 38 hours after KNO3 application. Nitrate content in milk after 50 hours was almost identical with that that was determined in milk of experimental cows from morning milking on the day of administration of 150 g of KNO3, considered as the control samples. The values of residual nitrate exceeded 0.05 mg neither in single sample of NaNO2/l.(ABSTRACT TRUNCATED AT 250 WORDS)