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Titolo: STATISTICALANALYSIS OF LENGTH OF PRODUCTIVE LIFE FOR DAIRYCOWS OF THE NORMANDE BREED
Autore: DUCROCQ V;
 Indirizzi:
 INRA,GENET QUANTITAT & APPL STN F78352 JOUY EN JOSAS FRANCE
 Titolo Testata:
 Journal of dairy science
fascicolo: 3,
volume: 77,
anno: 1994,
pagine: 855  866
 SICI:
 00220302(1994)77:3<855:SOLOPL>2.0.ZU;2X
 Fonte:
 ISI
 Lingua:
 ENG
 Soggetto:
 LINEAR TYPE TRAITS; GENETIC ANALYSES; HERD LIFE; PEDIGREE;
 Keywords:
 LONGEVITY; GENETIC EVALUATION; NONLINEAR MODEL; SURVIVAL ANALYSIS;
 Tipo documento:
 Article
 Natura:
 Periodico
 Settore Disciplinare:
 Science Citation Index Expanded
 Science Citation Index Expanded
 Citazioni:
 18
 Recensione:
 Indirizzi per estratti:



 Citazione:
 V. Ducrocq, "STATISTICALANALYSIS OF LENGTH OF PRODUCTIVE LIFE FOR DAIRYCOWS OF THE NORMANDE BREED", Journal of dairy science, 77(3), 1994, pp. 855866
Abstract
The length of productive life of 103,214 Normande cows milked from 1979 to 1989 in purebred herds was analyzed using a mixed Weibull model:their probability of being culled, or hazard function, was supposed to be the product of a baseline Weibull hazard function and explanatoryvariables that were loglinear and timedependent. Fixed effects thatmay have an impact on culling rate were successively added to the model. Two random effects, a herdyear and a sire effect, were also included. The dispersion parameter of the loggamma prior distributions assumed for these effects was estimated maximizing a marginal posterior density obtained after algebraic integration of the corresponding random effect. The other effects and the Weibull parameter could not be integrated out easily. The probability of being culled was not changed byage at first calving but increased with stage of lactation. It also increased for low producing cows and for herds of decreasing size, especially during the 3 mo preceding the end of the period on which yearlymilk production is calculated for the European Community quota system. This last phenomenon seems to be crucial for proper statistical and genetic analysis of length of productive life. The estimated variancesof the herdyear and sire effects indicated a large influence of these effects on culling rate. Under certain assumptions, the standard deviation of sire effects can be assessed at >.5 expected complete lactations. This value is not reduced by consideration of differences in milk production of the cows.
ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 04/12/20 alle ore 22:31:33