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Relationships among First-Lactation and Lifetime Measurements in a Dairy Population

1969; Elsevier BV; Volume: 52; Issue: 5 Linguagem: Inglês

10.3168/jds.s0022-0302(69)86623-3

1529-9066

G.L. Hargrove, Jackeline Salazar, J.E. Legates,

Animal Behavior and Welfare Studies

Relationships between first-lactation and lifetime traits were investigated for 6,468 lactation records of 1,861 Holsteins in seven herds of the North Carolina Institutional Breeding Association.The phenotypic coi~relation between first-lactation milk yield and lifetime production on a within herd-year of first calving basis was 0.48 and the correlation between first-lactation milk yield and productive life was 0.43.For these data the optimum age at first calving for maximum lifetime production was 27 months.Cows calving first at 24 months of age produced 579 kg less milk in their lifetime than those calving first at 27 months; whereas, those calving first at 30 months produced 458 kg less milk during their productive life.Genetic parameters were estimated from 1,017 daughter-dam pairs.The heritability estimates of lifetime milk yield and length of productive life were 0.18 and 0.15, respectively.The genetic correlation between first-lactation milk yield and lifetime production was 0.85 and between first-lactation milk yield and length of productive life, 0.76.The genetic correlations between the measures of lifetime production; namely, lifetime milk yield, length of productive life, and number of lactations were 0.95 or above.Even though selection is directed toward high first-laetation production, this should not produce a decline in lifetime performance in these herds.Concern has been expressed about the possible deterioration of lifetime performance as a result of continued selection for high firstlactation performance.Most selection for eeo-