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Trabajos en Prensa
Estimation of genetic parameters for milk production traits and subclinical mastitis in Pampinta sheep
The goal of the present work was to estimate heritabilities, repeteabilities, and genetic and phenotypic correlations for production traits such as milk yield (MY; l/d), total fat (TF; g/d), total protein (TP; g/d), percentage of fat (F%; %), percentage of protein (P%; %), and subclinical mastitis (SCM, present or absent – based on Californian Mastitis Test) in lactations of 210 d long. To that purpose, test day records collected from 2009 to 2017 in an experimental farm (INTA EEA Anguil “Ing. Agr. Guillermo Covas”) were used. After editing, a total of 833 lactations were obtained from 425 Pampinta ewes, and, in turn, a genealogy with 1092 sheep was built. The following classificatory factors: age at first lambing (AFL); year and season of lambing (YSL); number of lambing (NL); lambing and weaning kind (LWK); days form lambing to first test day (DLFTD); and lactation length (LL) were tested for each response variable through univariate mixed models with repeated observations using the lme4 package in R. Among these, AFL was not selected for any model, while YSL was for all models. Besides, the model for MY did not include LWK; the one for TP did not include NL and LWK; for P% did not include LL; and for SCM did not include DLFTD and LL. For variance component estimations, bivariate animal mixed-models were used. These were estimated with a Bayesian approach using the TM program. Repeatability estimates for productive traits –MY, TF, TP, F%, P%– were intermediate, in the range from 0.41 to 0.51, showing that one observation could be a good predictor of individual productivity. On the other hand, for SCM the repeatability was 0.20; this is pointing the fact that environment plays such a great deal in the expression of that trait. In the case of heritabilities, the estimates were intermediate to low; for productive traits, they were between 0.21 and 0.33, in accordance with those in the bibliography. To the best of our knowledge, this is the first study to estimate heritability for SCM, which was 0.1. This value is slightly lower than that published for
somatic cell counts. However, it seems possible to select against mastitis using SCM. Phenotypic and genetic correlations between MY with TF and with TP, and TF with TP were high, from 0.92 to 0.98, and these are in line with the literature. Phenotypic correlations between SCM and each productive trait were negative, which is good from a productive point of view; and the genetic correlations were positive, although they had very wide credibility intervals. Based on these estimates, if a selection program was put in place, for example, to increase MY and TF, a correlated response to selection could increase the incidence of SCM. Consequently, this fact should be taken into account to avoid negative consequences from the selection program.
Keywords: sheeps, Pampinta ewes, subclinical mastitis, production traits.
1Instituto Nacional de Tecnología Agropecuaria (INTA), Centro Regional (CR) La Pampa San Luis, Estación Experimental Agropecuaria
(EEA) Anguil “Ing. Agr. Guillermo Covas”, Ruta Nac. N.o 5 km 580, Anguil (6326), La Pampa, Argentina.
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2Universidad Nacional La Pampa (UNLPam), Facultad de Agronomía, Ruta Nac. N.o 35 km 334, Santa Rosa (6300), La Pampa, Argentina.
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3Universidad Nacional La Plata (UNLP), Facultad de Ciencias Veterinarias (FCV), Instituto de Genética Veterinaria (IGEVET), CCT,
Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Calle 60, B1900AVW, CC 296, La Plata, Argentina.
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