Influence of milking frequency and feeding level on plasmin activity
and casein degradation in milk
C.G. Prosser, G. Nicholas, K. Stelwagen, S.J. Lacy-Hulbert, M.W.
Woolford, T.B. McFadden
AgResearch, Ruakura Research Centre, Private Bag 3123, Hamilton,
New Zealand
Proceedings of the New Zealand Society of Animal Production. 1995,
55: 9-11
A total of 14 identical twinsets of cows were used and fed on
pasture (85%) and silage (15%). One group of 7 twinsets were milked
once a day, whilst the other were milked twice a day as normal. Within
each group, one twin received a daily intake of 15kgDM while the other
was restricted to 8 kgDM/day. Treatments began around 30-35 weeks of
lactation and continued for 4 weeks. The degree of casein degradation
induced by plasmin was assessed by the ratio of gamma-casein to Beta-
casein in
the milk after separation by anion exchange chromatography. Prior to
treatment commencing there were no significant differences between
animals in milk yield, plasmin activity or gamma/Beta-casein ratio in milk.
After 3 weeks of treatment, milk yield had decreased 24% relative to
pre-treatment yield for cows milked once daily, 38% on lower feed level
and 44% for cows milked once daily. Plasmin activity in milk was not
significantly affected by once a day milking, but was significantly
greater (p,0.05) than pre-treatment level following 3 weeks of feed
restriction. This increase was associated with an increased gamma/Beta-
casein ratio in the milk (correlation co-efficient of 0.51, p=0.01) indicating
that degradation of casein occurs in milk whilst stored within the gland.
Keywords: NZSAPAB;
plasmin; once daily milking; casein; feeding level; cows
Download abstract in text format
Last Updated 25-01-1997
