Some abstracts do not have video files because ASAS was denied recording rights.
393
Analysis of genetic residual feed intake in Danish Holstein cows by covariance functions using random regression models
Feed efficiency is of major concern due to economic reasons, environmental impacts but also because of limited feed resources. So far feed efficiency cannot be defined unambiguously. One trait to select for can be residual feed intake (RFI), which is primarily determined by dry matter intake (DMI), production traits and body weight. The aim of this study was to derive variance-covariance components of RFI over the first 44 lactation weeks in primiparous Danish Holstein cows by a covariance function from a tri-variate random regression analysis to describe genetic and permanent environmental effects of average DMI, average metabolic body weight (mBW) and average kg milk (Mkg) over the whole lactation. Commonly, RFI is derived from phenotypic regression and subsequently genetically analyzed. In total, 22,375 records of 648 primiparous Holstein cows from the Danish Cattle Research Centre were used. Phenotypic information was collected between 2003 and 2015 over the entire standard-lactations. The random regressions were fitted using DMU 6.5.2. The pedigree was traced back as far as possible resulting in 16,339 animals. After estimating variance-covariance components of DMI, mBW and Mkg, the covariance function was applied to directly derive RFI due to the assumption that RFI is defined as a depended genetic variance of DMI, body weight and milk yield. The approach gave reliable results for RFI. Heritabilities for RFI ranged from 0.05 to 0.15. The highest heritability for RFI was observed in the 1st week of lactation, the lowest in lactation week 22. Heritabilities for the traits DMI, mBW and Mkg ranged from 0.30 to 0.46, 0.53 to 0.61 and 0.25 to 0.55, respectively. The genetic variance of RFI was on average 9.5 % (ranging from 4.3 % in lactation week 23 to 28.7 % in lactation week 1) of the genetic variance of DMI. Heritabilities of RFI, DMI, mBW and Mkg were in accordance with previous studies. The genetic variance of RFI in DMI has to be considered as low to moderate. Results imply that a genetic improvement of DMI, independent of production, is limited, except for the first 4 weeks of lactation where the genetic variance of RFI was > 20 % of the genetic variance of DMI.
Keywords: DAIRY COW, RANDOM REGRESSION MODEL and RESIDUAL FEED INTAKE