August 08, 2019

Interpretive Summary: Carcass and meat quality effects for polymorphisms

Interpretive Summary:  Enhanced estimates of carcass and meat quality effects for polymorphisms in myostatin and u-calpain genes

By: Jackie Walling

An article published in the February 2019 Issue of the Journal of Animal Science investigated enhanced estimates of polymorphism effects on carcass and meat quality. Researchers looked at polymorphisms (more than one allele at a locus causing different forms of the gene) in myostatin (MSTN) and µ-calpain (CAPN1) genes. Some variants in MSTN can cause muscle hypertrophy while CAPN1 is associated with proteolysis (breakdown of proteins) and meat tenderness. Additive, dominant, and epistatic (dependency of genes on one another) effects were evaluated based on genetic markers. 

Steers (after three years selection) were chosen from the composite herd, MARC I, originating in 1978. The single nucleotide polymorphism (SNP) for MSTN studied was F94L, a substation of leucine (L) for phenylalanine (F) at position 94. SNP for CAPN1 was CAPN1_316 (segregates C and G alleles) and CAPN_4751 (segregates C and T) which produced the common haplotypes: CC, GT, and GC (denoted CAPN1hXX). 

Three phases composed the experiment: base, selection, and evaluation. Base established frequencies in four populations finding allele L more frequently than allele F in the Limousin breed and nearly absent in others. Selection aimed to increase frequencies of allele L, CAPN1hCC, and CAPN1hGT to 0.5 while eliminating CAPN1hGC. Evaluation bred bulls heterozygous for F94L and CAPN1 and harvested steers at 487 days to evaluate carcass and meat traits. During the evaluation, individual frequencies of allele L and CAPN1hCC neared 0.5. Combined frequencies of CAPN1hCC and CAPN1hGT were .75. 

For MSTN, two variants are known to decrease functional activity causing hypertrophy greatly. F94L is minor in comparison but is thought to affect protein folding and stability with significant additive effects. Genotype LL is associated with reduced fat thickness, larger ribeye area, better yield grade, lower marbling scores, more tender meat, and lighter color. LF (L partially recessive to F) results were more similar to FF, but differences were not significant except in ribeye area.     

For CAPN1, no additive or dominant associations were significant, including meat tenderness. CAPN1hCC was most frequent and therefore used in conjunction with all other haplotypes (CAPN1hNN) to measure traits except slice shear force. Slice shear force described tenderness which directly correlated with CAPN1. To avoid bias, animals with diplotypes (two haplotypes either CAPN1hCC or CAPN1hGT) were used to assess slice shear force for a better understanding of each haplotype’s effect.

A significant epistatic effect of CAPN1 additive with F94L additive was seen for slice shear force with the L allele interfering with the usual effects CAPN1 has on meat tenderness. For the full article, visit the Journal of Animal Science.