Polled Genetics: Benefits, Detriments and Identification of Polled Dairy Cattle

Abstract Text: The polled trait demonstrates autosomal complete dominance that results in horn growth suppression. Selection for polled cattle has become increasingly popular and can be identified phenotypically by observation and/or genotypically through genomic testing. Dairy cattle are classified with 3 identifiers: observed polled (PO), heterozygous polled (P), and homozygous polled (PP). Observed polled cattle are visually identified by the producer, whereas; genomic testing requires analysis of the DNA. Animals identified through genotyping can be determined with a high-density SNP (single nucleotide polymorphism) chip. A genome-wide association analysis in beef and dairy cattle revealed a 1Mb region within chromosome 1 associated (P ≤ 0.002) with P and PP. Further analyses determined a SNP (AC000158:G1390292G>A) located within intron 3 of Interferon gamma receptor 2 gene (IFNGR₂), an immune gene was co-segregated with polledness in Holsteins. The SNP, AC000158:G1390292G>A, can be used as a genetic marker when testing for polledness in dairy cattle.  The benefits of polled cattle include: increased docility, decreased labor requirements, improved public perception, and eliminating the necessity of dehorning the animal. Polled genetics allows the producer to realize a profit of $7.50 per animal. Conversely, the disadvantages of selecting for polled genetics include: decreased genomic total production index (GTPI), a reduced net merit value (NM$), and an increased risk of inbreeding due to a smaller available gene pool. One possible solution to incorporate polled genetics into the herd is to breed for heterozygous polled cattle by crossing genetically superior cows with polled bulls or breeding polled cows with superior bulls.

Keywords: Polled, Dairy Cattle, Single Nucleotide Polymorphism