Application in Animal Breeding

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FAO anticipates that by 2050, the global demand for animal-based food products would increase by 70%. To be able to meet this demand and feed the growing population is a crucial challenge. The failure to meet this demand would imply the omission of animal-based protein from the diet leading to nutritional deficiencies and related disorders. The key approach to overcome this challenge is to adopt a path that minimally affects the environment, ensures that high animal welfare standards are met, and increases the production of animal-based foods.

Traditional livestock breeding approaches have inherent drawbacks of genetic linkage and limited genetic variations available within a breed. Technologies of genetic editing such as the CRISPR/Cas system easily helps to overcome these barriers and introduce desired genetic variations that might not be present within the breed. Being highly specific and efficient, CRISPR/Cas system offers the breeders the scope to manipulate the animal’s genome to suit their needs. Manipulations may involve deletion of genes related to undesired traits (e.g., susceptibility to disease, aggressive behaviour, etc.) or insertion of genes linked to desired phenotypic traits (e.g., disease resistance, absence of horns, heat tolerance, production of leaner meat, etc.).

Among the available genome editing technologies, the CRISPR/Cas system is preferred owing to its simple approach, high efficiency, and low cost. The use of CRISPR/Cas for animal breeding requires the efficient delivery of the CRISPR components into the zygotes using reproductive technologies such as somatic cell nuclear transfer (SCNT) and zygote microinjection, zygote electroporation, zygote transduction, and surrogate sire technology (SST).

Examples of genetic modification of farmed animals include mutation in the insulin-like growth factor 2 gene (IGF2) in animals that regulate muscle and body mass in pigs. Similarly, insertion of genes such as GH and IGF1 in pigs through zygote microinjection results in a faster gain in mass along with an 18% higher efficiency of feed conversion compared to the control group. This gene insertion in pigs lowers the accumulation of subcutaneous fat layer and increases bone, muscle, and skin development. Similarly, the AquaAdvantage™ salmon, an Atlantic salmon approved by USFDA for human consumption is based on the introduction of growth hormone gene from Chinook salmon (Oncorhynchus tshawytscha). Consequently, the AquaAdvantage™ salmon displayed 2 to 6 times higher growth rate and productivity compared to the wild type salmon.

Myostatin (MSTN) protein is known to negatively regulate muscle mass development. MSTN gene knock-out in pigs, goats, sheep, and rabbits using CRISPR technology has resulted in an increased muscle mass growth. Similarly, an increase in milk production can be achieved through CRISPR-mediated insertion of gene encoding bovine α-lactalbumin, while expression of IGF1 in skin or disruption of FGF5 can result in high wool production in sheep and cashmere goats. Similarly, CRISPR-based genetic manipulations in animals can help to increase the nutritional value of animal products and eliminate allergens from them.