It examines how the genetic potential of the heifer varies
so much the growth has to be mapped against a model mapped to its genetic
mature live weight. The data showed that puberty does occur at a target
percentage of the live weight and therefore proves that hitting live weights is
critical to ensure successful mating in the spring. Knowing the mature weight
and therefore being able to extrapolate the critical weight to hit at certain
periods during the growth period is invaluable to ensure the heifer is able to
enter the herd successfully.
There is some feedback at meetings I have attended that the
linear LWT gain is not as applicable to the pastoral system. That the speed of
heifer growth will be directly proportionate to the quality and availability of
the pasture. Any period of limitation which slows growth is then followed by a
period of high quality feed which ensures the heifer has accelerated growth and
this averages out to an average daily gain that achieves the overall goal.
J. R. BRYANT, C.W.
HOLMES, N. LOPEZ-VILLALOBOS, L.R. MCNAUGHTON, I. M. BROOKES, G.A. VERKERK, and
J. E. PRYCE (2004) Use of breeding values for live weight to calculate
individual live weight targets for dairy heifers, Proceedings of the New
Zealand Society of Animal Production, 64, 118-121
Replacement heifers need to reach specific target live
weights (LW) to ensure they calve as two year olds, and subsequently achieve
high milk yields and good fertility. Currently, different LW targets are
recommended for heifers based on their expected mature LW according to
appearance or breed. However, the mature LW is difficult to estimate without
knowledge of the animals’ genetic potential for LW. The objective of this paper
is to develop and validate a growth model which uses estimated breeding values
for LW (EBV LW) of individual heifers of any breed to calculate target LW from
birth to maturity. Predicted live weights are presented for a range of four EBV
LW, from –40 to 100 kg. These values were very similar to other published
target values. Data from the Dexcel Holstein Friesian Strain Trial was used to
validate the model with respect to LW and age at puberty. For LW at puberty the
predicted values were significantly correlated (P<0.05), but were marginally
higher (3-5%) than the actual values. A report can be formulated to enable
farmers to identify individual heifers which are below (or above) their target
LW at any date.
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