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      Effects of stage of lactation and time of year on plasmin-derived proteolytic activity in bovine milk in New Zealand

      Nicholas, Gina D.; Auldist, Martin J.; Molan, Peter C.; Stelwagen, Kerst; Prosser, Colin G.
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      DOI
       10.1017/S0022029902005745
      Link
       journals.cambridge.org
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      Nicholas, G. D., Auldist, M. J., Molan, P. C., Stelwagen, K., & Prosser, C. G. (2002). Effects of stage of lactation and time of year on plasmin-derived proteolytic activity in bovine milk in New Zealand. Journal of Dairy Research, 69(04), 533-540.
      Permanent Research Commons link: https://hdl.handle.net/10289/956
      Abstract
      The objective of this study was to determine the effects of stage of lactation (SOL) and time of year on plasmin-derived proteolytic activity in the milk of pasture-fed dairy cows in New Zealand. Four herds of 20 Friesian cows were used, one herd calving in each of January, April, July and October. Cows grazed ryegrass/white clover pasture only, except during June (winter) when all cows received supplementary pasture silage. Milk samples were collected on four occasions during the year (spring, summer, autumn and winter) from each cow in milk, to give a total of three samples per cow (early, mid and late lactation; c. 30, 120 and 220 days after calving, respectively). Milk samples were analysed for plasmin-derived proteolytic activity. There was no effect of either SOL or time of year on plasmin activity and therefore yields of plasmin followed patterns in milk yield (highest in early lactation and in summer). There were effects of both SOL and time of year on plasminogen-derived and total plasmin plus plasminogen-derived activity, both of which were highest in late lactation and in spring. Changes in plasminogen-derived activity and total plasmin plus plasminogen-derived activity due to SOL were not only due to the decrease in milk yield associated with advancing lactation, because enzyme yields were also increased with advancing lactation. Similarly, effects of time of year on plasminogen-derived activity and total plasmin plus plasminogen-derived activity could not be attributed solely to concomitant changes in milk yield, and may be influenced by the variation in the quality and quantity of feed during the year inherent in a pasture-based dairy system. Effects of SOL on proteolytic activity were greater than, and independent of, effects of time of year.
      Date
      2002
      Type
      Journal Article
      Publisher
      Cambridge University Press
      Rights
      This article is published in the Journal of Dairy Research. Copyright © Proprietors of Journal of Dairy Research 2002.
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