4-5 generations. Selection of sires without
considering body size may result in free stalls
being too small for later generation cows.
Local research on the liveweight of dairy cows
Using LW records from the Elsenburg Holstein
herd, heritability estimates of LW together
with correlations with milk yield traits were
published. High heritability estimates (h 2 =0.65)
for LW were found. While the LW of cows
increased over time in this study, only the
genetic correlation between fat and protein
yield and LW reached statistical significance.
Earlier overseas studies showed selection for
higher milk yields resulted in heavier cows,
with an increased maintenance cost. Variable
genetic correlations between LW and milk
yield were also found mainly on depending on
when LW was recorded. As expected, negative
correlations were found in early lactation
when milk yield increases, and body condition
decreases because of high energy demand for
milk.
No research has been conducted locally to give
farmers any scientific support with regards to
the effect of LW on the milk yield and lifetime
performance of cows. For this reason, a study
to determine the effect of sire selection on the
production performance of Holstein cows was
initiated at Elsenburg. The aim of the study is
to compare the effect of sires selected for (i)
production (3 x protein EBV + 1 x fat EBV) and
(ii) sires selected from the production group
towards reducing the LW of cows using body
composite traits. The production performance,
live weight, body size, feed efficiency,
reproductive performance and longevity of
the progeny of the two sire groups will be
compared in a TMR-feeding system.
AgriKultuur |AgriCulture
In Table 1 the average genetic merit of two
groups of bulls currently being used in the
study, is presented. Better genetic merit values
for specific traits within sire groups are shown
in bold. As expected, EBVs for milk yield traits
are higher in the production sire group. Sire
selected for stature had lower EBVs for milk
yield traits although at higher fat and protein
percentages. Stature and body composite
traits are also lower for the stature group
while the EBV for productive life is higher.
Table 1. The average genetic merit of
Holstein bulls selected for fat and protein
yield (production group) and for smaller
(stature group) cows (EBV: Estimated
breeding value)
Traits
EBV milk (kg)
EBV protein (kg)
EBV fat (kg)
Protein (%)
Fat (%)
Productive life (months)
Stature
Body composite
Production
1504
44
47
-0.007
-0.035
0.78
0.69
0.71
Stature
1022
32
31
0.003
-0.027
4.07
-0.27
-0.31
In closing
Sire selection has a long-term effect on the
genetic merit of a dairy herd. A simulation
study showed that selection should be based
on an increased potential for milk yield
combined with a lower LW. This strategy is
now being applied in a structured breeding
programme towards finding scientific
information on the effect of LW on the
efficiency of production.
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