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Application of a probabilistic model to the selection of a beef cattle subpopulation

Célia M. Torres Cordeiro^I; José B. de Freitas Trovo^I; Rosângela S. Afanasieff^II; Alexander G. Razook^III; Luiz M. Bonilha-Net^III

^ICentro Nacional de Recursos Genéticos e Biotecnologia, CENARGEN-EMBRAPA, Caixa Postal 102372, 70770 Brasilia, DF, Brasil
^IIDepartamento de Estudos e Pesquisa, EMBRAPA, Caixa Postal 04315, 70770 Brasilia, DF, Brasil
^IIIEstação Experimental de Zootecnia de Sertãozinho, IZ, Caixa Postal 63, 14180 Sertãozinho, SP. Send correspondence to A.G.R.

ABSTRACT

The objective of the present study was to determine the truncation point for weaning weight for selection of a specific beef cattle subpopulation consisting of 378-day old animals whose weight was greater than or equal to a given value. The probabilities of selecting animals whose weaning weights were greater than a given value for several subpopulations of interest were calculated from the bivariate normal distribution of weaning weight and weight at 378 days. Data from five years of feeding tests were used to check the normality of the distribution and to estimate the bivariate normal correlation coefficient. The results obtained using this theoretical model showed that recovery of more than 90% of the subpopulations of interest, consisting of 378-day old animals weighing more than 1.28, 1.64 and 2.05 standard deviation units (SDU) above the mean can be obtained by accepting truncation points ≥ 0.5, 0.8 and 1.1 SDU above the mean weaning weight, respectively. Estimates were checked for accuracy by simulation. For herd sizes larger than 250 animals, the simulation results showed good approximation to theoretical values at truncation points ≤ 0.8 SDU above mean weaning weight.

Keywords: selection; beef cattle.

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