Research Geneticist USDA/ARS/LARRL Miles City, Montana, United States
Abstract: Extending longevity of cows is currently of major interest to beef producers but selection on this trait is difficult due to its delayed expression and low-to-moderate estimated heritabilities. In regions that experience harsh winters, some culling decisions may be directly or indirectly impacted by the ability of heifers and cows to maintain body condition over winter. Management practices such as winter supplementation may be implemented to help cows maintain favorable body condition score (BCS) and reduce involuntary culling due to poor BCS leading into spring. However, the appropriate supplementation for each individual may be conditional on their genetic basis and identifying such a trend could potentially reduce costs to producers by allowing development of tailored diets and increase herd longevity by reducing involuntary culling due to poor BCS.
The present study explored whether there evidence exists for a GxE interaction for pre-calving (PC_BCS) and pre-breeding (PB_BCS) BCS across three winter supplementation treatments in a composite breed (1/2 Red Angus, ¼ Charolais, ¼ Tarentaise) of beef cattle born in Montana at the Fort Keogh Livestock and Range Research Laboratory between 2012-2020. The data consisted of 1,100 and 1,010 cows and heifers with 3,143 and 2,988 records for PC_BCS and PB_BCS, respectively. Heifers and cows received one of three winter supplementation treatments throughout their lifetime. The treatments were: corn silage/ground hay while confined to a feedlot (T1), native range and 1.8 kg of an 18% CP supplement daily (T2), and native range and unrestricted access to 60% CP and mineral mix supplement (T3).
To investigate evidence for GxE interactions of PC_BCS and PB_BCS with the treatments, records were grouped into traits based on the individual’s treatment and genetic correlations were estimated in a multi-trait repeatability model. The model included a mean, cow birth year, year of measurement, and parity as fixed effects and animal and permanent environment as random effects. In a single-trait repeatability model, heritabilities (s.e.) were 0.17 (0.036) and 0.23 (0.041) and repeatabilities were 0.20 (0.022) and 0.25 (0.023) for PC_BCS and PB_BCS, respectively. These estimates suggest a moderate heritability for PCS_BCS and PB_BCS and are consistent with estimates reported previously in the literature for beef cattle. Under the multi-trait repeatability model, genetic correlations for PC_BCS were 0.93, 0.91, and 0.71 and for PB_BCS were 0.98, 0.93, and 0.96 between T1 and T2, T1 and T3, and T2 and T3, respectively. This suggests that a GxE interaction may exist for PC_BCS across T2 and T3 but not between T1 and T2 or T1 and T3. The genetic correlations for PB_BCS do not suggest a GxE interaction across the treatments.
