Effect of crossbreeding strategies on long-term rates of genetic
gain in New Zealand dairy cattle.
N. Lopez-Villalobos and D.J. Garrick
Department of Animal Science, Massey University Private Bag
11222, Palmerston North.
Proceedings of the New Zealand Society of Animal Production. 1997,
57: 22-25
Crossbred cows tend to be more profitable than straightbred cows
because they fit the present milk payment system and show favourable
heterosis for milk traits. This may encourage greater use of crossbred
cows eroding the number of potential bull mothers (active cows) thereby
reducing genetic progress. The objective of this research was to
evaluate the effects of crossbreeding on active cow numbers and genetic
gain over 25 years. A deterministic model was used to calculate the
number of cows and the breeding worth (BW) of Holstein-Friesian (F) and
Jersey (J) bulls each year. Three strategies were considered: upgrading
to F (UPGF); upgrading to J (UPGJ); and some two-breed rotational mating
plans. In 1996, sizes of F and J active populations were taken to be
250,000 and 76,400 cows and mean bull BWs were $72 (F) and $82 (J).
After 25 years of UPGF the number of active F and J cows were 1,520,000
and 13,000, the BWs of F and J bulls were $245 and $213 and genetic
gains of F and J bull teams were 8.5 and 4.25 $BW/year. UPGJ had the
opposite effect. Mating 10% of >/=2/3F cows to F bulls and 10% of </=1/3F
cows to J bulls (ROTATE10) for 25 years led to active F and J
populations of 70,200 and 75,800 cows, BWs of F and J bulls of $227 and
$230 and genetic gains for F and J bull teams equal to 7.0 $BW/year.
Results suggest that widespread adoption of a rotational crossbreeding
scheme could be achieved without penalising annual genetic gain in
bulls. However, annual recruitment of new active cows should be
routinely monitored to ensure long term gain will be maintained.
Keywords: NZSAPAB;
dairy cattle; upgrading; rotational crossbreeding; genetic
gain.
Last Updated 12-09-1998
