Hauke Hüttmann, 2007 - Institut für Tierzucht und Tierhaltung ...

6 Summary
6 Summary
As a further development of the bull dams performance test at the dairy research farm
Karkendamm the individual roughage intake has been measured since September 1, 2005
utilizing a computerized scale system to estimate daily energy balances as the difference
between energy intake and calculated energy requirements for lactation and maintenance.
Data of 289 heifers with observations between the 11 th and 180 th day of lactation over a
period of 487 days have been analyzed. Average energy corrected milk yield, feed intake, live
weight and energy balance were 31.8 kg, 20.6 kg, 584 kg and 13.6 MJ NEL, respectively, per
day. Fixed and random regression models have been used to find the model with the best fit
under consideration of (co)variance structures. The results of the likelihood-ratio-test show
that the best model-fitting is achieved with the random regression model including the
(co)variance structure Töplitz(4) for all traits. The consequences of a consideration of the
(co)variance structure have been determined by a comparison of the significance of the fixed
effects and the rank correlation between cow effects. As the significance levels changed for
some fixed effects, they should be analyzed under consideration of (co)variance structures,
whereas the very high rank correlations between cow effects allow the estimation of genetic
parameters without consideration of the (co)variance structures.
The resulting genetic correlations between observations made on different lactation stages
demonstrate that feed intake and energy balance at the beginning and the middle of lactation
are genetically different traits. Heritability of feed intake is low with h 2 = 0.06 during the first
days after parturition and increasing towards the middle of lactation, whereas the energy
balance shows the highest heritability with h 2 = 0.34 until the 30 th day of lactation. Genetic
correlations between energy balance and feed intake and milk yield, respectively, illustrate
that energy balance depends more on the feed intake than the milk yield. Genetic correlation
between body condition and energy balance decreases rapidly within the first 100 days of
lactation. Since the number of animals is rather small for a genetic analysis, the genetic
parameters have to be evaluated on a larger dataset.
Several criteria of energy balance have been defined over different lactation stages: mean
daily energy balance during the first 50 and 100 days of lactation, duration of negative energy
balance, total energy deficit and minimum daily energy balance in the early stage of lactation.
Residual correlations between the energy balance traits are predominantly high. Therefore, it
does not seem to be necessary to define different energy balance traits.
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