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Lifespan Score and the effect on Jersey cow productive life expectancy

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Lifespan Score and the effect on Jersey cow productive life expectancy in the UK and Jersey Island – June 08

Prepared for: Deputy P Ryan, Chairman, Bovine Semen Importation Scrutiny Panel Date: 23/06/08

Introduction

There has been some debate as to the productive life expectancy of Jersey cattle both on Jersey and in the UK and some have stated that the actual life expectancy on Jersey Island is considerably higher, due in part to the genetic tendencies of Island cows.

Due to environmental and management differences in other countries it is less reliable to directly compare Jersey Island with any Jersey population other than the UK, especially given the limited influence the Island animal has in these other populations in recent years. It would be possible to reasonably estimate productive life for international Jersey bulls within Jersey Island from their Interbull converted UK Jersey proofs.

Jersey Island compared to the UK Jersey

The current genetic evaluations for both Jersey populations, carried out by SAC and published by Dairy Co, indicate that a Jersey cow in the UK population averages 4.0 years actual from the commencement of milk production, whilst the Island cow lasts for 4.2 actual.

If each 0.1 of a year equates to 5.2 weeks the differential between the two populations is just 10.4 weeks in favour of the Island cow. In reality this is a skewed differential, needing further consideration of factors specific to the management of the local herd.

Factors specific to Jersey Island

There are known to be a number of factors peculiar to Jersey Island which do have a bearing on the local population calculation; these are:

  1. For a large number of years, during the BSE restrictions when older animals could not enter the human food chain, Jersey Island was unable to slaughter cull cows at an optimum time for the farmer. This had a definite effect on the ability of a farm to remove these animals from the milking herd and added weeks, months and occasionally even a further lactation, or year to the life expectancy of a less productive milking cow.
  2. Few milking cows move between herds within Jersey and no animal in Jersey transfers to another milk recording service provider. In the UK far more cows move herd or are lost from the milk recording process, triggering on occasions a presumed death.
  3. In recent years Jersey Island, in line with international policy, has decoupled subsidy payments from production. However, payments made under a welfare code to the local dairy industry and paid on the number of milking' cows in the herds of producers can encourage inefficient production through the retention of cows within the herd that would otherwise have been slaughtered. This is a seasonal phenomenon and in years of good autumn grass growth can add weeks onto the life expectancy of an otherwise unproductive cow. In the UK the size of the cull cow market and the low value attached to these animals within the meat trade means that such animals depart milk producing herds with little thought to any factors other than lack of economic milk production.
  4. The very small herds, still to be found in Jersey Island but considerably less so in the UK, tend to retain old cows longer due to the limited replacement options kept and the less stressful environment in which they are kept.

Summary

Whilst the difference in productive life is already minimal there is scope for the variance to be reduced even further, possibly to the extent that it is negated.