Impact of simplified methods of monthly and twice monthly milk recording on genetic parameter estimates and genetic evaluation in dairy ewes under a low input production system

Abstract

ABSRACT:Sicilo-Sarde dairy flock test-day data were analyzed: 1) to check predicting ability of four alternate methods (AT) of milk recording, based on information from a single milking, two of them adjusted for the weight of the recorded milking in daily milk production (ATa) and two other usual methods without adjustment (ATu), and 2) to study their impact on the genetic estimates. Number of bimonthly test-day observations was 8219 (4323 monthly test-days), carried out between 1999 and 2009 from 303 ewes. Suitability of the simplified methods were evaluated by comparing their associated genetic estimates with those observed both in a reference plan, where the 2 daily milkings were recorded at two-weekly intervals (A2), and in the official A4 milk recording (monthly recording of the 2 daily milkings). Estimated milk yields were similar to those observed with the reference methods. They showed similar evolutions through the milking period. Phenotypic correlations between estimated and observed traits were high and positive, and their genetic correlations were equal to unity. Heritability and repeatability estimates associated to simplified methods were close to those obtained with reference methods, with the values from the adjusted methods being slightly higher than those from the usual methods. The Ranking of animals based on their genetic values was not affected by using the simplified recording plans. For practical and economical reasons, the simplified designs alternating a.m. and p.m. milkings are suggested for ovine milk recording. In such a case, the adjusted alternate methods (ATa) should be used rather than the usual alternate methods (ATu) without adjustment.Keywords: dairy ewes, genetic parameters, genetic evaluation, simplified milk recording.Abbreviation Key: A2 = twice-a-day twice monthly recording design, A4 = standard twice-a-day monthly recording, AT = alternate milk recording.