A comparison of different measures of persistency with special respect to variation of test-day milk yields

Abstract

Six measures of persistency of milk yield were compared by estimation of heritabilities, genetic correlations and the amount of concentrates required by cows with high and low persistency. Persistency was expressed as ratio between different parts of the lactation (P2:1 and P3:1), as a ratio between maximum test-day milk yield and mean test-day milk yield and as the standard deviation of the test-day milk yields of a lactation. The investigation was based on 39 349 first, 23 910 second and 13 651 third lactation records of Simmental cows from the region of Lower Austria. The heritability estimates ranged from 0.12 to 0.18 for measurements including the first 200 days of lactation and from 0.17 to 0.22 when the whole 305-day lactation was included. The largest values were found for the standard deviation of test-day milk yields (305 days); 0.21, 0.22 and 0.22 for the first, second and third lactation, respectively. Genetic correlations between lactations were high for all measures of persistency, ranging from 0.79 to 0.95. Highly persistent cows required between 69 and 161 kg less concentrate than cows with a poor persistency to produce 5500 kg of milk. The difference was generally larger when the grouping was performed on measures including 305 days of lactation vs. measures including only earlier parts of the lactation; 161 kg was found for P3:1. © 1987.