Functional longevity in dairy cattle is a trait that receives much attention in the durable performance sum (DPS), the Dutch total merit index (Vollema et al. 2000). In this index functional longevity is a measure of involuntary culling of lactating cows. Stillbirth, defined as a calf that dies just prior to, during or within 24 hours after parturation, is another trait for which a genetic evaluation is available (Harbers et al. 2000). Parameters for the period between birth and first lactation are not available in the Netherlands. The economic importance of this stage is substantial: the costs of raising replacement heifers represents 15 to 20% of the total milk production costs (Heinrichs 1993). The average costs of replacing a heifer during the first year are € 250 (PR 2000). Mortality is a stayability trait measuring whether or not an animal is alive at a certain age. It is therefore a binary trait and it does not contain complete information (Vollema 1998). Mortality of calves occurs mainly during the first month of life according to Olsson et al. (1993). They report an overall mortality of 2.1% during the first 3 months of which 1.3% occurs in the first month. Heinrichs (1993) reports mortality of calves from birth to 1 year of age to be from 6 to 20%. A mortality rate of 8.1% during the whole rearing period was found in a survey among 959 Dutch farmers (Mourits 2000). Mortality of replacement heifers can be used as a trait within the durable performance sum and thus become part of the breeding objective. Besides an economic importance breeding objectives must have a genetic component. The trait could also be used as a predictor of a breeding objective trait with a low reliability, when the genetic correlation between predictor and breeding objective is high and the predictor has a high reliability early in the life of the animal. A third option is to monitor the population. This gives the tools for a quick reaction if the genetic trend is undesirable. The objective of this study was to estimate phenotypic and genetic parameters for mortality of replacement heifers from 3 days to 1 year of age in the Netherlands and to evaluate the possible use of the trait in a breeding program.
Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume 2002. Session 1, , 1.26, 2002
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