GENETIC INDICES EXPLAINED
Table 2: Examples of 95% confi dence intervals (+/-) at various reliability levels for a number of traits
35
Milk 50
Fat Prt 20.1 17.1
50 517 17.7 15.0 65 433 14.8 12.5 75 366 12.5 10.6 85 283 90 231 95 164 99
73
9.7 7.9 5.6 2.5
8.2 6.7 4.7 2.1
SCC 18 16 13 11 9 7 5 2
LS
0.5 0.4 0.3 0.3 0.2 0.2 0.1 0.1
* SCC = Somatic Cell Count; LS = Lifespan; FI = Fertility Index
FI
12.3 10.8 7.6 7.6 5.9 4.8 3.4 1.5
Legs Udder 1.9 1.6 1.2 1.2 0.9 0.7 0.5 0.2
1.7 1.5 1.1 1.1 0.8 0.7 0.5 0.2
Figure 2 gives a rough guide to the
recommended levels of usage of semen from individual bulls at different levels of reliability. For example – for a bull with a 35% reliability it is recommended to breed no more than about 7% of the herd to the bull, whereas at 95% reliability up to 50% of the herd can normally safely be bred to a single bull.
Figure 2: Guide to proportion of semen usage for single bull at several levels of reliability (35%, 45%, ... 95%).
proof can still change slightly as we are not able to assess the genetic merit at 100% accuracy - but any changes at that stage are expected to be very small.
Figure 1: Confidence interval (+/- 100%) at increasing reliability levels between 1 and 99% reliability.
Q: What about using a team of bulls? Most producers already use more than one bull in a breeding season to avoid the risk of disappointments. The level of reliability does not change this, but as a rule the lower the reliability of a bull’s PTA, the lower the confidence that the figures are a true reflection of the bulls potential, and therefore the fewer doses of semen you should use per bull. Therefore, when using low reliability bulls, it is advisable to use a variety of such bulls.
However, it is not true that team reliabilities are higher than the reliabilities of the individual bull in that team.
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THE JOURNAL DECEMBER 2010 31
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