The effects of methionine supply upon milk composition and
production of dairy cows in mid-lactation.
D. Pacheco-Rios, W.C. McNabb, J.P. Hill, T.N. Barry and D.D.S.
Mackenzie
Department of Animal Science, Massey University, Private Bag
11222, Palmerston North.
Proceedings of the New Zealand Society of Animal Production. 1997,
57: 147-150
A trial assessing the production response of dairy cows to
supplementation with methionine (Met) was conducted indoors over a
21-day period with 26 Friesian cows in mid-lactation and individually
fed fresh perennial ryegrass/white clover pasture. Group 1 (n=9)
received twice daily oral methionine (15 g/d) that was protected from
rumen degradation (RPM; Lactet); Group 2 (n=9) was given a continuous
intravenous infusion of free Met (15 g/d; MET-i.v.); and Group 3 (n=8)
was given no methionine supplement (Control). Supplementary methionine
tended to slightly depress feed intake but milk yield tended to be
higher (P=0.08) for the MET-i.v. group compared with the Control and RPM
groups (18.5 ± 0.48 vs 17.1 ± 0.45 and 17.2 ± 0.38 kg/d
± SE). Compared with the control group, there was a trend for Met
(both MET-i.v. and RPM) to reduce milkfat concentration and to increase
the concentration of casein. Neither lactose or whey nitrogen (N)
concentrations were affected by the treatments. Methionine
supplementation did not affect yields of total protein nor protein
components; however, when protein and casein yields were adjusted to
equal crude protein intake, Met supplemented cows produced significantly
(P=0.05) more total protein and casein per unit of N ingested. These
results suggest that post-ruminal Met supplementation improved the
efficiency with which dietary protein was converted to casein in the
pasture-fed dairy cow. More research is required to investigate which
AA, individually or in combination, are likely to limit milk protein
synthesis in the mammary gland of the pasture-fed dairy cow.
Keywords: NZSAPAB;
methionine; lactating cow; milk protein; casein.
Last Updated 12-09-1998
