Supplementary Readings | Animal Husbandry & Veterinary Science Optional for UPSC PDF Download

Standardization of Production Records

Lactation production in dairy cows is influenced by a complex interplay of genetic and environmental factors. Accurate selection for improved milk yield necessitates precise reflection of a cow's genetic potential. However, numerous environmental influences impact lactation records, making it crucial to consider various factors for accuracy.

Factors Affecting Lactation Records

Lactation Length

• Adoption of 305-day lactation records in the USDA-DHIA sire proving program and 300-day records in India.
• Aiming for a 12 to 13-month calving interval to maximize predictability in production.

Correction Factors for Incomplete Records

• Use of correction factors for converting incomplete records to a 305-day basis.
• Reduction of variation resulting from influences like pregnancy after calving.

Frequency of Milking

• Conversion of records from three milkings per day to the standard twice-a-day milking basis.
• Application of correction factors to ensure uniformity in comparing milk yields.

Age and Month of Calving:

• Gradual decline in lactation milk yields with advancing age, necessitating age correction factors.
• Factors for standardizing 305-day lactation records for age.

Days Dry and Days Open

• Limited impact of days dry prior to calving on lactation yields.
• Days open as a crucial factor influencing milk yield, emphasizing the need for conception timing after calving.

Fat Correction and Milk Composition

Testing for Fat Percentage:

• Common practice of testing for fat percentage in milk to meet market requirements.
• Correlation of fat percentage with other milk constituents, influencing overall milk quality.

Standardizing Milk Composition:

• Conversion to a standard fat-corrected milk (FCM) for fair comparisons.
• Formula for converting any milk test to a given standard (4% FCM).

Optimizing lactation production records involves considering a multitude of factors, from lactation length to milk composition. Accurate selection in dairy cattle breeding programs requires a comprehensive understanding and correction for various environmental influences on production records.

Nicking

Definition of "Nick" or "Nicking" in breeding terminology. Description of individual matings or family matings resulting in progeny with unexpected qualities. Exploration of favorable and unfavorable Nicks. Genetic and chance-related explanations for favorable Nicks in individual matings or between different families.

Importance of Nicks in Breeding:

• Limited demonstration of the significance of Nicks in outbred animals within pure breeds.
• Discussion on breeders' perceptions and the need for evidence-based emphasis on favorable Nicks.
• Consideration of increased relevance in highly inbred lines, often referred to as specific combining ability.

Chromosomal Aberrations in Farm Animals

Introduction to chromosomal aberrations in farm animals and their low frequency in populations. Impact of sterility or low reproductive rates on the prevalence of chromosomal aberrations. Examples of chromosomal abnormalities such as trisomies and polyploidy in pig embryos.

Robertsonian Translocations:

• Definition and explanation of Robertsonian translocations involving centromere fusion.
• Discussion on heterozygous and homozygous states and their effects on chromosome number.
• Identification of Robertsonian translocations in various farm animal breeds, including cattle, sheep, and goats.

Persistence of Chromosomal Aberrations:

• Overview of the general rule where most chromosomal aberrations lead to lower viability or reduced reproductive rates.
• The exception to the rule: Robertsonian translocations and their unexpected persistence in populations.

Factors Influencing Chromosomal Aberrations:

• Limited understanding of the reasons behind the occurrence of chromosomal aberrations in non-experimental populations.
• Experimental factors contribute to increased chromosomal aberrations, such as chemicals, radiation, aging, and specific environmental conditions.

Choice of effective breeding plans

Laboratory studies have indicated that selection based on quantitative traits can be effective for several generations, but eventually, plateaus are reached. While laboratory results are valuable, they may not fully align with outcomes observed in larger livestock populations. The challenge lies in reaching genetic limits in farm livestock breeding, as rates of genetic improvement diminish over time.

Heterosis and Hybrid Vigor

Increasing recognition of the value of heterosis or hybrid vigor has led to inbreeding becoming the primary breeding system in swine, sheep, and cattle. The exploitation of hybrid vigor is expected to be a major focus in future breeding programs.

Challenges of Inbreeding

Inbreeding does not seem poised to make significant contributions to farm animal breeding in the next two decades. Reproductive fitness becomes a limiting factor, especially in large animal populations like cattle, and inbreeding significantly narrows the base of selection.

Utilization of Heterosis through Crossbreeding

Heterosis will be predominantly utilized through crossbreeding systems, relying on the development of specialized seed stock. The availability of heterosis depends on the establishment of specialized seed stock.

Technological Advances in Breeding

As physiological techniques, such as embryo culture, improve, the utilization of outstanding genetic traits can be maximized. The use of stored semen and fertilized ova enables the establishment of large elite families of breeding stock. Genetic engineering may play a more significant role in the future, but the current emphasis remains on research and development.

Future Prospects and the Role of Computers

With more intensive research in the future, computers are expected to play an increasing role in planning breeding programs. Genetic changes at the chromosome and gene level may become more direct, and continued investigation is needed to guide breeding programs effectively.

Main Breeding Plans Applicable to All Breeders:

Define Breeding Objectives:

• Breeders should first determine the ideal type of animal and production level based on their circumstances and traditions.

Identify Ideal Genes:

• Evaluate animals based on physical appearance, performance, and pedigree. Identify animals with genes that align with the breeder's ideal specifications.

Strategic Purchases:

• Acquire animals with ideal genes at reasonable prices and breed them in proportion to their hereditary closeness to the desired ideal.

Breeding Plans for Pure Breeders:

• Maintain Lineage: Keep the future herd closely related to the best animals from recent and past generations while allowing for the natural halving effect of inheritance.
• Limited Outcrossing: Outcross only when necessary to prevent serious defects from being fixed in the entire flock or herd.

Breeding Plans for Market Animal Breeders

Avoid Close Inbreeding:

• Minimize close inbreeding to maintain heterosis and individual merit without sacrificing uniformity.

Effective breeding plans vary for different types of breeders, but common principles include defining objectives, identifying ideal genes, and making strategic purchases. Pure breeders focus on maintaining lineage, while market animal breeders prioritize avoiding close inbreeding to preserve heterosis and individual merit. Continued research and technological advancements will shape the future of livestock breeding programs.

Strategic Breeding Plans for Livestock Improvement

Breeders are encouraged to carefully consider their physical and biological resources, market demands, and personal preferences when determining the characteristics of their ideal animals. Striking a balance between satisfying market needs and aligning with local preferences is crucial for successful breeding.

Ideal Animal Characteristics and Market Considerations

• Breeding decisions should factor in the breeder's inclinations, market demands, and local preferences.
• Market demands may vary, and the ideal animal may differ based on factors such as dressing percentage and meat quality.
• The commercial ideal is subject to changing economic conditions, requiring breeders to adapt but not necessarily follow every trend.

Meeting Market Demands with Economic Justification

• Breeders should align their breeding goals with market demands and consumer preferences, ensuring economic justification for any changes.
• Careful consideration is needed to avoid catering to a niche preference that might not be economically viable for the majority.

Selection Strategies for Breeding

• The search for perfect animals is challenging; breeders are advised to be content with animals above average.
• Individual selection is reliable, with pedigree or progeny tests required for traits not visible in daily observation.
• Inbreeding is valuable to identify animals with superior genes, and progeny tests can be conducted by leasing stock to other herds.

Line Breeding for Sustained Excellence

• Pure breeders should stay with the best individuals, employing line breeding to maintain excellence.
• Collaboration with other herds is recommended for large-scale line breeding efforts.
• Caution is advised not to carry line breeding too far to avoid the fixation of undesirable traits.

Breeding Strategies for Market Animals

• Market animal breeders should practice continuous outbreeding to maximize heterosis and individual merit.
• Using closely bred sires with good individuality, each unrelated to the breeding females, is recommended for achieving maximum heterosis.
• The principle of criss-crossing is suggested for swine breeding.

Breeding System for Whole Breed Improvement

• Division of each breed into small, distinct groups is proposed for uniformity and trait selection.
• Introducing limited breeding animals across groups facilitates genetic diversity and desirable trait expression.
• Rigorous inbreeding and selection processes eliminate undesirable traits and solidify desired traits in the overall population.

Inbreeding Depression in Domestic Animals

Inbreeding, a common breeding practice, can have detrimental effects on the genetic health of domestic animals. This article explores the concept of inbreeding depression, the consequences of reduced heterozygosity, and the impact on various traits in animal populations.

The Mechanism of Inbreeding Depression

• Inbreeding reduces the frequency of heterozygotes, exposing harmful recessive genes.
• The example of a recessive gene with a frequency of 0.05 illustrates the increase in homozygotes and the consequent rise in the recessive phenotype's frequency.

Consequences on Embryonic Health

• Many harmful recessive genes, often lethal, lead to an increase in embryonic death and stillbirths.
• Less severe recessive genes contribute to a decrease in overall productive and reproductive performance, termed inbreeding depression.

Factors Influencing Inbreeding Depression

• Inbreeding depression occurs when the performance of heterozygotes deviates from the midpoint between the two homozygotes.
• Genes with dominance at a locus are more prone to inbreeding depression.
• The extent of inbreeding depression is influenced by the departure of performance from the intermediate level and the gene frequencies at the locus.

Traits Most Affected by Inbreeding Depression

• Traits associated with natural stress, such as viability and reproductive ability, experience the greatest inbreeding depression.
• Reproductive and viability traits generally decrease at a rate of around 1 percent for every 1 percent increase in the inbreeding coefficient.

Documentation of Inbreeding Depression in Domestic Animals

• Extensive documentation of inbreeding depression exists in domestic animals.
• Reproductive traits and viability traits are particularly affected, showing a decrease of around 1 percent for every 1 percent increase in the inbreeding coefficient.

Challenges in Creating Highly Inbred Lines

• Attempts to create highly inbred lines of domestic animals have often failed due to the severe effects of inbreeding depression.
• In some instances, large-scale inbreeding in chickens has been possible, but with substantial wastage and limited success.

Inbreeding depression poses significant challenges to the genetic health and performance of domestic animals. Understanding its mechanisms and consequences is crucial for breeders to make informed decisions and mitigate the negative impacts on their livestock.