Limit-Fed, High-Energy Diets Can Achieve Improved Feed Conversion Rates Without Compromising Rate of Gain When Compared to Conventional High Roughage Diets

Objective: Compare and determine the effects on animal performance between a conventional high roughage diet and a limit-fed, high energy diet during the receiving and growing phase. Study Description: Crossbred heifer calves (n = 418) originating from Texas and New Mexico were used to determine performance when limit-fed a high energy diet initially offered at 85% of feed intakes from cattle fed a conventional high roughage diet ad libitum at the Kansas State University Beef Stocker Unit. The Bottom Line: Limit-feeding a high energy diet consisting primarily of dry-rolled corn and Sweet Bran (Cargill Animal Nutrition, Blair, NE) can improve rate of gain while significantly decreasing dry matter consumption over conventional high roughage diets fed ad libitum, and cattle exhibit greater muscling and fat deposition.


Introduction
Previous research conducted at the Kansas State Beef Stocker Unit has demonstrated the possible benefits of limit feeding high-energy diets based on dry-rolled corn and corn co-products for newly received growing cattle. This study was conducted to further explore subsequent feedlot performance and carcass merit implications. During the receiving and growing phase of production, roughage-based diets are commonplace in the industry. However, in times of drought, or when forage prices are high, producers often seek alternative, yet readily available feedstuffs such as corn, distiller's grains, or wet corn gluten feed. Coupled with limit feeding, the use of high-energy feeds is a powerful means to achieve comparable, or even improved performance in young growing cattle prior to feedlot entry.

Experimental Procedures
A total of 418 weaned, crossbred heifers (body weight = 615 ± 53 lb) were purchased at auction markets in Texas and New Mexico, assembled at two different farms approximately 90 miles southwest of Amarillo, TX, then shipped 570 miles to the Kansas State University Beef Stocker Unit, Manhattan, KS, on May 28, 2019. The heifers were used in a completely randomized block design, 84-day receiving and growing study to evaluate the impact of a high-energy, limit-fed diet containing dry-rolled corn and Sweet Bran (Cargill Animal Nutrition, Blair, NE) to a high roughage diet fed ad libitum on animal performance. Cattle were randomized by arrival weight and assigned to pens, each containing 13 or 14 heifers. Additionally, each pen was randomly assigned to one of two treatments in a "treatment pair" (one high-energy, limit-fed pen, and one high roughage, ad libitum pen). There was a total of 32 pens. The high roughage and high-energy diets were formulated to provide either 45 or 60 Mcal of net energy for gain/100 lb of dry matter, respectively. Feed intakes of the high-energy, limit-fed groups were initially set at 85% of the feed intakes of the high roughage, ad libitum groups. However, this percentage was reduced when it became apparent that 85% of the high roughage, ad libitum intakes resulting in ad libitum intakes for the high-energy, limitfed treatment. Both diets were formulated to contain 40% Sweet Bran on a dry matter basis (Table 1).
At the time of arrival, all calves were evaluated for disease and lameness. Each animal was individually weighed, given a visual identification ear tag, and was vaccinated for typical respiratory diseases. Cattle were fed once daily, and each pen was weighed once per week. A 24-hour shrunk weight was measured at the end of the study to calculate pen performance statistics. Pen was the experimental unit. On day 84, ultrasound was performed on all cattle to determine muscling and fat differences by a technician from the Cattle Performance Enhancement Company, and preliminary carcass data were obtained.

Results and Discussion
Performance and growth results are provided in Table 2 for each treatment group. Ultrasound data are shown in Table 3. Overall, the high-energy, limit-fed cattle outgained the high roughage, ad libitum cattle (P < 0.01). Inherently, dry matter intakes were considerably lower for the high-energy, limit-fed cattle; their efficiency was also markedly better, with gain-to-feed and feed-to-gain ratios better than the high roughage, ad libitum treatment (P < 0.01). Body weight was not different between treatments (P = 0.22) on day 84. Initially, the high-energy, limit-fed feed intake was set at 85% of the feed intakes of the high roughage, ad libitum treatment. However, the high roughage, ad libitum cattle consumed more dry matter than expected. Consequently, over subsequent weeks, each high-energy, limit-fed pen's intake was decreased to maintain limit-fed conditions according to each adjacent high roughage, ad libitum contemporary pen. Although 85% may work for some groups of cattle, this percentage is highly variable and depends on several factors such as breed type, age, weight, weather conditions, and eating experience. In practical producer settings, it would be more economical and convenient to base limit-fed cattle intakes on a fixed percentage of body weight to achieve a targeted rate of gain. In ultrasound scans, high-energy, limit-fed cattle showed greater muscle depth (P < 0.01) and marbling in the ribeye (P = 0.02). Furthermore, this treatment group also deposited more backfat (P < 0.01). These outcomes may allow for shorter times on feed to achieve desired carcass indices.

Implications
Limit feeding a high-energy diet, as compared to feeding a traditional high roughage diet ad libitum in growing cattle can result in comparable, or even improved, feed conversion without negatively affecting rate of gain. Moreover, limit feeding the higher energy diet also increases muscling depth and fat deposition.