Genetic parameters for gaussian and categorical traits in organic and low input dairy cattle herds based on random regression methodology

Abstract

Organic and low input farming differ substantially from conventional farming, suggesting the need for separate breeding programs. This requires knowledge of (co)variance components of important traits in low input or organic production systems. Test-day data for production and data for reproduction traits from 1283 Brown Swiss cows kept in 54 small, low input farms across Switzerland were available. Production traits milk yield (MY), fat percentage (Fat%), protein percentage (Pro%), lactose percentage (Lac%), somatic cell score (SCS), and milk urea nitrogen (MUN), were analyzed with a multi-trait random regression animal model with days in milk (DIM) as a time covariate. Female fertility traits of number of inseminations (NI), stillbirth (SB), calving ease (CE), calving to first service (CTFS), days open (DO), and gestation length (GL) were analyzed with parity as a time covariate, with threshold methodology applied for the first three traits. A threshold-linear sire model was applied to estimate daily correlations between MY, Fat%, Pro%, SCS, MUN and the binary distributed fertility trait conception rate (CR). In general, daily heritabilities for production traits followed the pattern as found for high input production systems. Expected genetic antagonisms were found between MY and Pro%, and between MY and Fat% for all DIM. An antagonistic relationship between MY and SCS was only found directly after calving in parity 1. In parities 2 to 7, heritabilities for an interval trait describing the cows' ability to recover after calving, e.g. CTFS, were lower than estimates for traits associated with a successful insemination, e.g. NI and DO. Pronounced antagonistic relationships between MY and CR were in the range of −0.40 to −0.80 from DIM 20 to DIM 200. In this study, we showed the variety and flexibility of random regression methodology which can be applied to data from small herds, and for a limited number of repeated measurements of a categorical trait per cow. Estimated genetic parameters for reproduction traits were partly different from those estimated in high input production systems. In particular, these differences underline the necessity to implement an own organic breeding program using estimates from the current study which are based on data obtained only from cows in organic or low input herds.