Imitating modelling of different bulls selection scenarios by viability

From the biological point of view viability signs – are threshold. Their genetic characteristics in dairy cattle breeding are studied rather poorly. Thus, estimations of heritability coefficient for stillbirth in Israel Holstein population in 1970-ies were 1,3–3,6% (Bar-Anan et al., 1976), in 1980- ies - 3,1–7,1% (Weller et al., 1988). In the USA Holstein breed the coefficient estimations were 0,4–9% (Martinez et al., 1983a,b), in German population amounted 0,3% (Meijering, 1985), in the British one - 2-12% (McGuirk et al., 1995). In the USA Holstein breed the heritability coefficient estimation for perinatal survival were 0,3–2,2%, and a genetic trend for perinatal mortality within 10 year period were -0,01– -0,04% per year (Meyer et al., 2001).

Earlier we have estimated the heritability of viability traits (Kuznetsov V.M., Melkishev A.V., 2002, 2004), we also studied the possibility for selection (Kuznetsov V.M., Markova E.A., 2004), conducted BLUP-evaluation of bulls (Kuznetsov V.M., 2004, 2008), investigated the effectiveness of BLUP- selection (Kuznetsov V.M., 2009). This publication shows the results of different scenarios imitating modelling for bulls selection/culling by viability traits.

There have been used the data on registration of abortions, stillbirths and calves survival under one year (postnatal survival)
in 10 pedigree farms of «Vyatkaplem» company in Kirov region during the 3-year period (16452 records for 75 bulls
(еt least 50 registrations per bull) and BLUP- estimations of bulls from previous research. The frequency of abortions and stillbirths, as well as the relative BLUP- estimations of the bulls breeding value, were transformed into indicators of the pre - and perinatal survival. Frequency and genotype prognostic evaluation of bulls by the pre-, peri - and postnatal survival were used to calculate phenotypic, genetic and economic indexes of survival. The first two types of indexes included three indices: - additive, - multiplicative and - integrated ties coefficient (where P_ij, is the frequency for the j-th trait in the i-th bull; RP_ij is the rank of a bull). Calculation of genetic indexes differed only in that the BLUP- estimations (G_ij) were used instead of frequencies. The former was used and for construction of equivalent economic index.

There were simulated the following bulls selection/ culling scenarios: only by one trait (30 worse of 75 bulls), the step-by-step culling (10 worse bulls for each trait), culling by phenotypic, genetic and economic () indexes (30 worse of 75 bulls). The last scenario had factors of economic importance for pre-, peri - and postnatal survival (k_А:k_М:k_С):

Index:	IE1	IE2	IE3	IE4	IE5	IE6	IE7
(k_А:k_М:k_С):	1:1:1	1:1,5:2	1:1,5:3	1:2:3	1:2:4	1:2:5	1:2:6.

The studies show, that selection by one trait maximizes the genetic superiority of selected bulls on this trait, but minimises and even leads to negative correlated changes in other traits. The calves survival under one year is economically more important characteristic than the frequency of abortions and stillbirths. Thus the bull selection by only one vitality trait is needed, the preference should be given to postnatal calves survival. When breeding by three traits, best of simple indices is the «multiplicative» one. The step-by-step selection and «integrated ties coefficient» yields on economic efficiency by 11-17 %. Genetic and economic efficiency of «additive» index is close to that of «multiplicative» one. When using simple indexes on the BLUP-estimations basis it is possible to expect increase of bulls selection efficiency by 1,5-2 times. The «multiplicative» genetic index does not yield by efficiency to a «harmonious» economic index with a parity k_A:k_M:k_C=1:1,5:3 (or 1:2:4). As for the index with equal economic values, «harmonious» index yields by the genetic superiority of the bulls, selected by frequency of abortions or stillbirths by 56 and 32%, but exceeds the calves survival under one year by 44% and economic efficiency by 26%. The main advantage of the economic index is its flexibility. By manipulating the coefficients of the economic importance of traits, it is possible to harmonize (or optimize) the index for selection goals of any herd.

Key words: bulls, selection, viability traits, BLUP, economic index, modeling.

V. Kuznetsov

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Imitating modelling of different bulls selection scenarios by viability