Resumen

MORA, María Gabriela; VARGAS, Bernardo; ROMERO, Juan José  y  CAMACHO, Jorge. Effect of genetic and environmental factors on somatic cell count of dairy cattle from Costa Rica. Agron. Costarricense [online]. 2016, vol.40, n.2, pp.7-18. ISSN 0377-9424.  http://dx.doi.org/10.15517/rac.v40i2.27346.

The study evaluated the effect of genetic and environmental factors on the Score of Somatic Cell Count [SCS = log2 (SCC/100 000)+3] in Costa Rica dairy cattle. A total of 198 685 daily records from 43 535 lactations, 23 749 cows, 237 herds and 3 breeds were analyzed. A mixed animal model was assessed with zone, herd within zone, breed, number of lactation, month/year or recording, lactation period and daily milk yield as fixed effects; and permanent environment, herd×sire and cow as random effects. Heritability (h2 ) and repeatability (r) indices for SCS were estimated. Breeding values and reliabilities were estimated for all individuals in the population. The average value of SCS was 3.30 (SD=1.87). All fixed effects were significant. SCS among zones ranged from 3.4 (bh-p) to 3.7 (bmh-p). For herds within zone, SCS ranged from 1.6 to 5.5. SCS increased from 2.7 in first lactation to 4.0 for lactation ≥6. SCS was higher in January (3.6) and lower in April (3.4). A consistent downward trend was observed in SCS from year 2004 (4.3) to 2015 (3.3). A nonlinear pattern was observed in SCS throughout lactation, starting at 3.7, with a marked decrease to a minimum of 3.1 around day 60 postpartum, and a progressive increase to a maximum of 3.9 around day 365 postpartum. A reduction of 0.051 in SCS was observed for each increase of 1 kg in daily milk production. Values of h2 and r for SCS were 0.08 (SD=0.008) and 0.33 (SD=0.004), respectively. Breeding values ranged from -1 to +1. Reliabilities of breeding values for cows and bulls were 0.40 (SD=0.16) and 0.44 (SD=0.20), respectively. These results can be used to improve SCS at the herd level, based on prevention in groups under higher risk, optimization of cow culling strategies and improved sire selection.

Palabras clave : Somatic cell count; heritability; udder health; dairy cows.

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