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Brunanet Login
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Survey on Methods used for Genetic Evaluation
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Methods used for breeding value estimation
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Since May 2005, breeding values for milk, fat, protein and somatic cell count transformed to log(2) somatic cell scores (scs) are estimated jointly using a random regression-test day-BLUP-animal model. Test day records from all lactations are included in the evaluation. The procedure considers individual lactation curves from which an estimated breeding value (ebv) for persistency (published for bulls and cows) can be derived. Since July 2007, ebvs for scs are also published for cows (previously for bulls only).
Breeding values for conformation traits (linear description and classification) as well as for milking speed (judged by breeders on a scale from 1 (very slow) to 6 (very fast) recorded by classifiers at linear description of first lactation cows) are estimated using a BLUP-animal model. Multiple trait evaluations are applied to each of the five trait groups body format, feet & legs, udder, teats (including milking speed) and classification rankings. Conformation data of cows classified in first as well as later lactations are included in the evaluation.
For estimation of breeding values for longevity a survival analysis using a sire model is performed, which allows for the inclusion of censored data (cows still living). In order to increase reliability, breeding values for direct longevity are combined with breeding values for five indicator traits. This results in breeding values for combined longevity published for bulls only.
Breeding values for female fertility (daughters’ non return rate and interval from calving to first service) are estimated using a two-trait-BLUP-animal-model. Due to the low heritability, breeding values for female fertility are being published for bulls only.
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Interpretation of breeding values for milk, fat and protein
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Since May 2005 the Swiss Brown Cattle Breeders’ Federation has been using the following definition of the genetic base for estimated breeding values (EBV) of production traits: The average EBV of all cows born six to eight years ago equals to 0. This rolling base is adjusted yearly in april. As of april 2008 cows born 2000 to 2002 are used to define the genetic base (BV08). Interpretation of EBVs is more straight forward compared to the previously used fixed base, since the reference values (average breeding values of all living cows) need no longer be accounted for. Based on EBVs, the genetic potential of an animal can be directly compared to the adult cows of the population. For this purpose, the table "Interpretation of breeding values" can be useful. The indicated EBV-ranges are approximate values, which can be maintained over several years due to the yearly adjustment of the rolling base.
EBVs of Original Braunvieh (OB) animals are published on a separate base (OB08). In order to be comparable to EBVs on the Brown Swiss base, base differences given in table "Interpretation of breeding values" have to be considered (EBV OB = EBV BS + OB-base difference).
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Interpretation of estimated breeding values for production traits
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Valuation
(% aller ZW) |
average
(ca. 68 %) |
good
(ca. 14 %) |
very good
(ca. 2 %) |
OB-base
difference |
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Milk kg |
-400 bis +400 |
+401 bis +800 |
³ +801 |
+487 |
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Fat kg |
-17 bis +17 |
+18 bis +35 |
³ +36 |
+26 |
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Fat % |
-0.15 bis +0.15 |
+0.16 bis +0.30 |
³ +0.31 |
+0.1 |
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Protein kg |
-12 bis +12 |
+13 bis +25 |
³ +26 |
+16 |
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Protein % |
-0.10 bis +0.10 |
+0.11 bis +0.20 |
³ +0.21 |
-0.01 |
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Milk index |
90 bis 110 |
111 bis 120 |
³ 121 |
+13 |
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Persistency |
90 bis 110 |
111 bis 120 |
³ 121 |
-4 |
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SCC |
90 bis 110 |
111 bis 120 |
³ 121 |
-11 |
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Longevity |
90 bis 110 |
111 bis 120 |
³ 121 |
-6 |
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Milking speed |
90 bis 110 |
111 bis 120 |
³ 121 |
-6 |
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NRR daughters |
90 bis 110 |
111 bis 120 |
³ 121 |
0 |
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Days to first service |
90 bis 110 |
111 bis 120 |
³ 121 |
0 |
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Functional traits
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When the rolling base was introduced in May 2005, the scale for ebvs of functional traits somatic cell score, persistency, longevity, female fertility, calving ease and milking speed has been changed as well. Since then, we publish relative breeding values (RBV) standardised to a base mean of 100 and a genetic standard deviation of 12 for these traits. For traits where low phenotypic values are desired (SCS, days to first service) the scale is inversed, such that high RBVs are always better. This makes the interpretation of RBVs much easier: two thirds of all RBVs are between 90 and 110 index points. RBVs over 110 are good, RBVs over 120 very good. Extreme values over 130 or under 70 index points are rare.
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Interpretation of breeding values for conformation traits
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Since 1997 conformation traits of all first lactation cows on farms involved in the national progeny test program have been linearly described and classified. Estimated breeding values for conformation traits are published as standardised indices, where the average ebv of all cows born six to eight years ago equals to zero and one unit of the index corresponds to one genetic standard deviation for each trait. Please note that not for all conformation traits high positive values are most desirable.
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Contact
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For questions concerning genetic evaluation please contact
Dr. Madeleine Berweger or Beat Bapst
(see address below)
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