Methods of Selection | Animal Husbandry & Veterinary Science Optional for UPSC PDF Download

Introduction

The Tandem Method involves selecting one characteristic at a time until the desired improvement is achieved, then moving on to the next. However, this approach has drawbacks, as the time required to reach the desired quality for one trait might result in the loss of progress made in previous selections. The method's efficiency depends on the genetic correlation between traits, and negative correlations can hinder overall progress.

Method of Independent Culling Levels

The Method of Independent Culling Levels establishes culling thresholds for each characteristic, below which all individuals are culled, regardless of their performance in other traits. While this method simplifies the selection process, only a fraction of animals may possess all desired qualities simultaneously. Practical challenges may arise in culling animals that do not meet established standards, and the approach might penalize animals with high performance in one trait but minor deficiencies in others.

Example of Culling Levels:

• Age at maturity: 18 months
• Lactation length: 305 days
• 306-day milk yield: 1500 kg
• Fat percentage: 5%

Selection Index Method

The Selection Index Method, inspired by the work of Salt and Hazel, utilizes scores or index values for each individual to closely correlate with their composite breeding value. This method is essential for efficiently selecting traits of varying economic importance, accounting for differences in heritability among traits, and considering phenotypic and genetic interrelationships. The approach allows for differential weighting of traits based on their economic impact and acknowledges the influence of interrelationships on the selection process.

In the development of a selection index for an animal enterprise, the following information methods:

• The relative net comic importance of a change in each of the traits. This information effectively defines the goal of the selection program. A competition for the several traits weighted by their relative net economic importance is the goal of Improvement rather than a trait.
• The veritably or the magnitude of the genetic variance for each of the traits and the phenotype variances for each trait.
• The phenotypic and genetic covariances among each trait in the index.
• The computation of the action index involves the technique of multiple regression

The index is in the form of
where x's represent the phenotypic values for different traits and the bis are the weights given to each of the trails. The Selection Index approach has provided a more precise focus on parameters, particularly in situations where selection involves numerous traits, each carrying significant additive genetic importance.

Advantages of the Selection Index Approach

Clarity in Trait Emphasis: The Selection Index approach allows for a clearer focus on parameters, particularly when dealing with multiple traits, each possessing considerable additive genetic significance.

Limitations and Challenges:

Despite its benefits, the Selection Index approach encounters certain limitations:

• Undefined Selection Goals: Breeders may face challenges in qualitatively defining the goals of selection, leading to ambiguity in the decision-making process.
• Varied Economic Importance: The relative economic importance of traits can vary across different enterprises, making it challenging to establish universally applicable selection indices.
• Population-Specific Considerations: Heritability values and genetic/phenotypic interrelationships differ among various populations, making it difficult to recommend generalized selection indices applicable across diverse breeding contexts.

Total Score Method:

• Similar to the Selection Index method, the Total Score Method is a kind of selection index. It involves listing all characteristics related to net phenotypic efficiency or profitability in order of preference. 
• Maximum scores are assigned to each trait based on their relative importance, heritability, and genetic correlations between traits.

Quantitative Example of Relative Importance:

• To illustrate the concept of relative importance, consider a quantitative example where 1 kg of wool is deemed equivalent to 3.4 kg of lamb. The weightage assigned to each trait is determined by factors such as their economic importance, heritability, and genetic correlations. For instance, a highly heritable trait would be given greater importance than a trait with lower heritability.
• As an example of the index, let us asume that wo have a pig, one of a litter of eight all ch were hard to live months and that this pig weghe 175 lb at five months Seering. The Selection Index proves to be a practical method for assessing the overall performance of animals by assigning scores to specific traits. Using the example of a pig from a litter of eight, we can illustrate how the index is calculated based on various criteria.

• By adding the score for each trait, a single figure total acore is obtained which is an index of the total performance of the animal. It is now said to at the animals in order of merit and this makes selection comparatively easy.
• Selective feds and Total Seeve methods are by far the beat methods of selection, the main disadvantage being that the traits very important from time to time, and the index built at one time will not be applicable for all times. It has to be modified from to time.