Ewe Selection
By Dr Mackie Hobson

Thursday, 3rd June 2021

EWE SELECTION

 

The Correlation between Reproduction, Bodyweight and Mohair Traits.

Gretha Snyman (Grootfontein Agricultural Development Institute) investigated the correlation between the various traits that Mohair Producers select for.

 

The more important selection criteria Producers concentrate on for Angora goats include:

  • body weight,
  • fleece weight,
  • fibre diameter
  • fleece quality traits,
  • reproduction (receives least attention)

 

For the producer to have an effective breeding plan, it is important that accurate genetic parameters for the traits involved be available.

Most producers select their maiden ewes at 16-18 months of age. Gretha Snyman estimated the genetic and phenotypic correlations between early and adult body weight, fleece traits and reproduction. The data was collected over 15 years.

Medium heritability:

  • body weight
  • fleece weight

High heritability:

  • fibre diameter

Low heritability:

  • Staple length
  • Reproductive performance of maiden ewes.

 

If used as selection criteria, care must be taken that maiden ewes reach an acceptable weight at first mating.

This implies that if any of these traits are included in the selection, genetic progress in the trait will result according to heritability.

 

EARLY SELECTION CORRELATIONS (maiden ewes):

Selection for early fleece weight will lead to a genetic INCREASE in:

  • in adult body weight,
  • fleece weight
  • staple length,
  • adult fibre diameter (economic impact)
  • Total weight of kid weaned

Selection for early fibre diameter (fineness) will lead to a genetic DECREASE in:

  • in adult body weight,
  • fleece weight,
  • staple length
  • Total weight of the weaned kid.

 

Selection of early staple length

  • The only trait that would be increased would be adult staple length

 

Selection for early bodyweight will be INCREASED:

  • adult body weight
  • reproduction,
  • an unfavourable effect on adult fibre diameter and should not influence adult fleece weight

 

Selection on maiden ewe reproductive performance will lead to an INCREASED:

  • Adult reproductive performance.

 

Genetic correlations estimated between maiden reproductive performance and adult body weight, fleece weight and fibre diameter were unreliable due to very high standard errors.

 

ADULT SELECTION CORRELATIONS:

Selection for adult fleece weight will DECREASE

  • reproduction,
  • in the fibre diameter profile traits.

The contradiction between the correlation of early and adult fleece weight with lifetime reproduction could possibly be explained through the fact that fleece production in Angora ewes decreases with age after peaking at three years of age (Snyman, 2018).

 

Selection for adult fleece weight will INCREASE:

  • The number of fibres in the fleece,
  • staple length

 

Selection for adult body weight will INCREASE

  • reproduction,
  • fibre diameter,

 

Unfortunately, the reproductive traits have the lowest heritability of all the economically important traits. Bodyweight indirectly contributes to reproduction through favourable genetic correlations with reproduction.

 

Selection of young ewes should therefore be focused on:

  • early body weight,
  • number of kids produced and
  • Weight of kids weaned at the first parity.

 

The negative relationship between reproduction and fleece production in the adult ewes emphasises the fact that positive selection pressure on early fleece weight should not be done at the cost of reproduction.

Only young ewes with unacceptably low fleece weights should be culled, while too much selection pressure on early fibre diameter in the young ewes should also be avoided. Selection for fleece production and fleece traits should rather be addressed through ram selection.

 

REFERENCE:

Extracted from: CORRELATIONS AMONG MOHAIR TRAITS, BODY WEIGHT AND REPRODUCTION IN SOUTH AFRICAN ANGORA GOATS. M.A. Snyman (Grootfontein Agricultural Development Institute)

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