# Validation of the Residual Feed Intake Model in Brangus Heifers: Determination of the Optimal Days on Feed Interval to Estimate Dry Matter Intake and Average Daily Gain

## TL;DR

This study finds that a 56-day test period is enough to accurately measure feed efficiency in Brangus heifers, helping improve breeding programs and reduce costs.

## Contribution

The study identifies the optimal 56-day testing interval for estimating feed intake in Brangus heifers, a hybrid breed not previously well studied for residual feed intake.

## Key findings

- A 56-day test period provides accurate dry matter intake measurements with high correlation to 70-day results.
- Ultrasound backfat measures should be included in the RFI model for heifers that calved to account for maturity differences.
- Shortening the test period reduces costs and increases the number of animals that can be genetically evaluated annually.

## Abstract

With the threat of climate change, a growing world population, and the demand for agricultural products rising, it’s crucial to enhance feed efficiency for the sustainability of beef production. Utilizing crossbred animals such as Brangus cattle to combine the heat tolerance of Brahman with the carcass merit of Angus is one potential strategy to meet these challenges, especially in warm humid climate regions. Incorporating selection for low residual feed intake (RFI) into breeding programs is another method that can speed genetic improvement of feed efficiency and reduce feed costs. However, accurately identifying such low RFI, feed efficient cattle is a timely and costly process, and little is known concerning the appropriate test conditions for Brangus cattle. We aimed to optimize the duration of RFI testing for daily feed intake in Brangus heifers. Our findings indicate that a 56-day test period is sufficient for accurate measurements of feed intake, with minimal loss in accuracy compared to a 70-day test. This reduces upfront costs for genetic evaluation and enhances the rationale for adopting RFI in Brangus breeding programs. Our research contributes to the long-term sustainability of beef production, aligning with the growing global demand for agricultural products and the need for increased efficiency in beef production.

Brangus cattle are gaining popularity in the Southeast U.S. due to the desirable heat tolerance from their Brahman influence combined with the superior carcass merit aspects of Angus genetics. However, little is known about the optimal evaluation conditions for this hybrid breed when placed on test for Residual Feed Intake (RFI), a heritable measure of feed efficiency that allows improvement in performance without altering carcass traits. To address this, dry matter intake (DMI) was measured on Brangus heifers for 70-d to determine the optimal days on feed required to estimate feed intake and ADG and assess if inclusion of ultrasound measures of carcass merit into the model impact RFI rankings for this breed. The 56-d test period had a regression coefficient of 0.96 (p < 0.0001), R2 = 0.94, rp = 0.97 (p < 0.0001), and rs = 0.97 (p < 0.0001), indicating little change in rank of cattle for DMI compared to a 70-d test. ADG was the limiting factor in determining test duration. Based upon examining only heifers that calved, ultrasound backfat measures should be included in the RFI model to normalize for differences in heifer maturity. Results from this study indicate that a test duration of 56-d is sufficient to accurately estimate DMI in this population. This data indicates on-test duration can be shortened, enhancing the rate of genetic change by reducing cost and increasing the number of animals that can be tested annually.