# Evaluation of the Beef Cattle Systems Model to Replicate a Beef Cow Genotype × Nutritional Environment Interaction

## TL;DR

This study evaluates if a computer model can replicate how different beef cow genotypes interact with nutritional environments to affect efficiency.

## Contribution

The study demonstrates that current simulation models fail to replicate observed genotype-nutritional environment interactions in beef cattle.

## Key findings

- The simulation model predicted similar responses across genotypes regardless of nutritional environment.
- Empirical research shows genotype-nutritional interactions, but the model did not capture these interactions.
- Lower dry matter intake reduced cow efficiency metrics like body condition and pregnancy rates in simulations.

## Abstract

The United States beef cow-calf sector consumes 70% of the feed resources and contributes approximately 70% of the carbon footprint to produce one kilogram of beef. Identifying beef cow genotypes that are more efficient at converting feed resources to weaned calves is vitally important to enhancing the sustainability of beef production. Previous research indicates that cow genotype interacts with the nutritional environment, indicating that large-scale research studies would be required to identify the most efficient genotype in the diverse nutritional environments across the U.S. The objective of this analysis was to determine whether a computer simulation model could replicate previous research demonstrating the genotype–nutritional environment interaction. Results indicate that the computer simulation model predicted a similar response of all genotypes across nutritional environments, indicating the absence of an interaction. In conclusion, current mathematical models estimate the performance of the average cow and are not substitutes for empirical research to identify the most efficient genotypes in diverse nutritional environments.

Cow efficiency is vitally important to beef sustainability, and computer simulation models may be useful tools to identify characteristics of the most efficient cow genotypes for a given production environment. The objective of this analysis was to determine whether the Beef Cattle Systems Model could replicate empirical research demonstrating a genotype–nutritional environment interaction for efficiency of feed conversion to calves weaned. Combinations of cow genotypes for lactation potential (8, 10, and 12 kg/d at peak milk) and growth potential (450, 505, and 650 kg mature weight) were simulated across four dry matter intake levels (58, 76, 93, and 111 g/kg BW0.75). At lower dry matter intakes, cows had lesser body condition scores and weight and longer postpartum intervals, but dry matter intake had minimal influence on pregnancy percentage or calf-weaning weight. These trends match empirical research except for pregnancy percentage, where decreasing dry matter intake had a dramatic effect on pregnancy percentage in high-milking, high-growth-potential genotypes. Efficiency of feed conversion was greatest at low dry matter intake for the model simulation with no evidence of a genotype–dry matter intake interaction, which is in contrast to empirical research demonstrating a genotype–dry matter intake interaction. In conclusion, standard nutrition equations do not replicate the genotype–nutritional environment interaction observed in empirical research studies.