Dynamics of amino acid profile in milk of BIV- And BLV-BIV-infected cows during storage

Abstract

Leukemia and viral immunodeficiency of cattle rank to the number of difficult diagnosed infections of farm animals which increases the probability of virus carrying. At present time there are no legislative approved standards for bovine immunodeficiency diagnosis so the milk from sick cows can infect bulk milk obtained from healthy animals. Frequently bovine immunodeficiency virus (BIV) is detected in animals infected by bovine leukemia virus (BLV). The present work reveals that milk of cows infected by retroviruses has an altered amino acid balance of the casein fraction, as well as lower protein stability when stored in a refrigerator. The aim of our research was to assay the amino acid composition and evaluate its stability in milk of BIV-infected and BLV-BIV-co-infected cows, as compared to milk of healthy animals. A total of 6 samples of pure cow milk obtained from 2.8-6.7-year old black-and-white dairy cows infected by bovine immunodeficiency virus (n = 3) and cows with BLV-BIV coinfection (n = 3) were tested. BIV and BLV-BIV infection was approved by PCR tests. Analysis of amino acid composition of the protein fraction was performed using a capillary electrophoresis system Capel 105M (LLC “Lumex-Marketing”, Russia). Milk was tested on day 1, day 3 and day 6 of storage at 4 С. The standard data on the amino acid balance of the casein fraction of healthy cows’ milk was used for the comparative analysis. Our results indicate that milk from BIV and BLV-BIV infected cows differs significantly in amino acid composition from healthy cows’ milk. We consider the milk casein fraction to be more illustrative because casein is the main milk protein and its amino acid profile in not changed even under hydrolysis. The weight percentage of the essential and conditionally essential amino acids such as methionine, glutamine, histidine and glycine in infected milk reduces 3-4-fold. The content of arginine, lysine, proline and asparagine are similar to normal, tyrosine is passed into the limiting position under a deficient phenylalanine which content is 6 times lower than normal. There was a comparative excess amount of threonine and serine. The weight percentage of lysine, valine, leucine-isoleucine and glutamine is 9, 13, 17.5 and 22 times lower that in healthy cows’ milk. The leucine-isoleucine and valine ratio of infected milk is approximately 1:1 whereas it amounts to 2.5:1 in healthy cows’ milk. It was observed that milk of BIV and BLV-BIV infected cows is characterized by expressed dynamic of amino acid profiles during storage in a refrigerator. The essential amino acids arginine, histidine and methionine were not detected in the milk of infected cows on the sixth day of the storage in the refrigerator. The weight percentage of tyrosine increased on day 3 and decreased on day 6 of storage. Moreover, these parameters were significantly changed in BIV infected milk. The weight percentage of phenylalanine, leucine-isoleucine, valine, serine and glycine in BIV and BLV-BIV infected milk increased on day 6 of storage by 27.1 and 2.4 %; 22.3 and 8.9 %; 43.9 and 37.2 %; 25.0 and 27.3 %, and 0 and 60 %. The weight percentage of proline and threonine reduced on day 6 of storage by 10.6 and 13.7 %; 5.3 and 0 %. The weight percentage of alanine on day 6 in BIV infected milk increased by 37.5 % but in BLV-BIV infected milk reduced by 17.8 %. The imbalance and instability of amino acid profile of BLV and BLV-BIV infected milk prove are indicative of development of uncontrolled processes.