Abstract
ABSTRACTSeveral functions (Ali-Schaeffer curve, Legendre polynomials, and the combination of Legendre polynomial and the Wilmink function) were used to adjust the lactation curve of somatic cell score (SCS) of primiparous Holstein cows in Iran. Data included 204,374 test-day records collected on 29,215 animals over 10 freshening years, from 2002 to 2011. The model included herd-year of calving (HY), additive genetic (AG), permanent environmental (PE) and residual effects as random and age-season of calving (A-S) as fixed regression effects. In addition, contemporary group effect (herd-year-month of test-day) was included as fixed effect. Residual variances were modelled considering 1, 4, 7, 10 or 20 classes of days in milk (DIM). Estimates of residual variance were quite similar, rating from 1.30 to 1.56. Estimates of daily heritability were practically constant until DIM 250 of lactation (around 0.03) and increased toward the end of lactation (0.07), thereby indicating the presence of low AG variation for SCS in this population of Holstein cattle. Regarding low heritabilities, a relatively low genetic progress will be expected following selection. The chosen model (according to the deviance- and Bayesian-information criterion) had Legendre polynomials with six coefficients for A-S effect, four coefficients for HY effect, five coefficients for additive effect, and six coefficients for PE effect with a homogeneous error structure.
Highlights
Mastitis is an important infectious disease that affects primarily cattle
According to Ødegard et al (2003), the results of the present study show that Legendre polynomials well suited for genetic analysis of somatic cell score (SCS) compared with other RR functions
RR models using Legendre polynomials seem well suited for the genetic analysis of SCS compared with other RR functions
Summary
Mastitis is an important infectious disease that affects primarily cattle. Average annual economic losses to dairymen in the Iran attributable to mastitis have been estimated at $80 per Holstein cow (Sadeghi-Sefidmazgi et al 2011). With a current cow population of approximately 8 million (Sadeghi-Sefidmazgi et al 2012), the annual cost of this disease to the dairy industry approaches $0.6 billion. The Norwegian prevention programm, partly described by Østerås et al (2007), has been successful at decreasing the prevalence of mastitis. The authors described three principal reasons for this decrease: effect of preventive management programs, effect of changed attitudes of the farmers toward treatment, and genetic improvement. In contrast to the first two reasons, the effect of genetic change is permanent to the dairy population (Sørensen et al 2010). It is of interest to increase the genetic gain of resistance to mastitis
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