Abstract

MULLER, C.J.C.  and  BOTHA, J.A.. The response to selection during first lactation on the phenotypic and genetic trends in the Elsenburg Holstein-Friesland herd. S. Afr. j. anim. sci. [online]. 2003, vol.33, n.2, pp.111-116. ISSN 2221-4062.

A breeding policy to improve milk production in the Elsenburg Holstein-Friesland herd was adopted in 1984. Cow selection was based on partial (90 days) and completed (300 days) lactation records of 4% fat corrected milk and protein yields during first lactation. Dutch type AI proven bulls as well as young unproven bulls from the herd were used initially. Holstein type bulls with the highest breeding value predictions (BV's) for milk and component yields were used since 1987. The phenotypic and genetic trends in milk yield for first lactation cows of the herd were derived from an animal model analysis conducted by the ARC-Animal Improvement Institute. The phenotypic trend for milk yield in the Elsenburg Holstein-Friesland herd was positive, amounting to 212 kg per year (R² = 0.88). Regression of average BV's on production year prior to 1984 suggested no change in genetic merit of first lactation cows over that period (R² = 0.35). Average BV's of first lactation cows in the Elsenburg Holstein-Friesland herd subsequently improved by 92.3 kg/year (R² = 0.96). This improvement was higher than corresponding genetic change in the national herd over the same period (76.4 kg/year; R² = 0.98). Ri gorous culling of inferior milk producing cows on first lactation records and using bulls with high breeding values for milk and component yields had a marked improvement on the genetic merit of first lactation cows in the herd. This improvement on the genetic merit of first lactation cows in the herd amounted to 1 200 kg milk per cow over the 13-year period it was practiced.

Keywords : Phenotypic change; genetic change; selection response; first lactation cows; milk yield; HolsteinFriesland.

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