Effect of genetic merit on the estimated partitioning of energy
towards milk production or liveweight gain by Jersey cows grazing on
pasture
J.R. BRYANT, N. LOPEZ-VILLALOBOS, C.W. HOLMES, G.D. PITMAN AND
I.M. BROOKES
Massey University, Private Bag 11-222, Palmerston North.
E-Mail:
NZSAP 2003 Abstract No. 18
Proceedings of the New Zealand Society of Animal Production
63: 69-72
Data from the 1999/2000 season of the Stratford demonstration
farm stocking rate trial was used to estimate metabolisable energy
intakes (MEI) and the amount of metabolisable energy (ME) partitioned
into milk, maintenance and liveweight (Lwt) changes of Jersey cows of
either high genetic merit (HGM) (average milksolids breeding value of 28
kg) or low genetic merit (LGM) (average milksolids breeding value of
11kg). Least-square mean yields for HGM and LGM cows were 327 and 289 kg
of milksolids per cow respectively. HGM cows partitioned a significantly
higher proportion of MEI into milk than LGM cows in early (0.67 vs 0.63;
P<0.01), peak (0.59 vs 0.57; P<0.05), mid (0.58 vs 0.56;
P<0.01) and late lactation (0.54 vs 0.51; P<0.01) (HGM vs LGM
respectively). In early lactation, HGM cows utilised more body reserves
for milk production (-0.05 vs -0.01, for HGM and LGM respectively).
These results confirm that HGM cows partition more ME to milk throughout
lactation than LGM animals for a range of feeding levels on grazed
pasture. The greatest difference occurred in early lactation, resulting
in increased body tissue loss and a greater negative energy balance in
HGM cows.
Keywords: NZSAPAB;
partitioning; genetic merit; energy; pasture-based; energy
balance; dairy cows
Last Updated 8/07/2004
