Feed Efficiency is Better and Activity is Greater in Growing Cattle Feed Efficiency is Better and Activity is Greater in Growing Cattle Limit-Fed a High-Energy Diet During the Growing Phase Compared Limit-Fed a High-Energy Diet During the Growing Phase Compared to a Traditional Roughage-Based Diet Fed for Ad Libitum Intake to a Traditional Roughage-Based Diet Fed for Ad Libitum Intake

Abstract The objective of this experiment was to compare performance impacts of a high-energy diet limit-fed at 2.2% of body weight (BW) daily on a dry matter (DM) basis to a traditional roughage-based diet fed for ad libitum intake during the growing phase. Study Description: Study Description: Three hundred seventy crossbred heifers (initial BW = 496 ± 44 lb) were used in a receiving and growing study at the Kansas State University Beef Stocker Unit in the spring of 2020. Animals were fed once daily at 7:00 a.m. Bunks were visually observed, and feed refused was estimated. Ad libitum feed refusal was targeted at 20 lb. A pen scale was used to measure weekly pen BW, adjust feed offerings, and to calculate pen performance. The Bottom Line: The Bottom Line: Growing heifers limit-fed a high-energy diet at 2.2% of BW daily on a DM basis had 35% better feed efficiency and were more active by 23 minutes per day, on average, than heifers full-fed a traditional roughage-based diet. Abstract Three hundred seventy crossbred heifers [initial body weight (BW) = 496 ± 44 lb] were used in a complete randomized block design receiving and growing study at the Kansas State University Beef Stocker Unit. Two dietary treatments included: (1) 45 Mcal of net energy for gain (NE g ) per 100 lb of dry matter (DM) fed for ad libitum intake (45AL), or (2) 60 Mcal NE g per 100 lb of DM limit-fed at 2.2% of BW daily on a DM basis (60LF2.2). Both diets contained 40% of DM as Sweet Bran (Cargill Animal Nutrition, Blair, NE). Feed efficiency in the growing phase was greater ( P < 0.01) by 35% for 60LF2.2 heifers compared to 45AL heifers. Average daily gain was lower for 60LF2.2 heifers than 45AL heifers ( P < 0.01). Rumination time was greater ( P < 0.01) for 45AL heifers compared to 60LF2.2 heifers, whereas activity was greater ( P < 0.01) for 60LF2.2 heifers than 45AL heifers. These results suggest growing cattle fed a high-energy diet at a restricted intake level of 2.2% of BW daily on a DM basis have better feed efficiency and greater activity levels compared to growing cattle full-fed traditional roughage-based diets.


Introduction
Recent research suggests limit feeding a high-energy diet to growing cattle improves feed efficiency and reduces time spent ruminating during the growing phase prior to feedlot entry compared to roughage-based diets fed for ad libitum intakes on a dry matter (DM) basis. Intake restrictions were often applied based on a percentage of full-fed (ad libitum) intake. The objective of this experiment was to compare performance impacts of a high-energy diet limit-fed at 2.2% of body weight to a traditional roughage-based diet fed ad libitum during the growing phase.

Experimental Procedures
Three hundred seventy crossbred heifers [initial body weight (BW) = 496 ± 44 lb] were received at the Kansas State University Beef Stocker Unit on four separate days Kansas State University Agricultural Experiment Station and Cooperative Extension Service in mid-March 2020. The experimental design was a randomized complete block, and the experimental unit was pen. Heifers were blocked by truckload and were assigned to pens based on day-1 BW. There were 16 soil-surfaced pens, with four pens per block. Twenty to twenty-five heifers were allocated to each experimental pen. Experimental diets were formulated to contain 40% of DM as Sweet Bran (Cargill Animal Nutrition, Blair, NE), and heifers were assigned to one of two dietary treatments: 45 Mcal of net energy for gain (NE g ) per 100 lb of DM fed for ad libitum intake (45AL) or 60 Mcal of NE g per 100 lb of DM limit-fed at 2.2% of BW daily on a DM basis (60LF2.2). Animals were fed once daily at 7:00 a.m. using a Roto-Mix feed wagon (Model 414-14B, Dodge City, KS). Bunks were visually observed, and feed refused was estimated at 6:30 a.m. the following morning. Treatment 45AL feed refusal was targeted at 20 lb. A scale (Rice Lake Weighing Systems, Rice Lake, WI) was used to record weekly pen BW, adjust feed offerings, and to calculate pen performance. During the final 14 days of the study, all cattle were offered a gastrointestinal tract fill equilibration diet, which was formulated to contain 53 Mcal NE g per 100 lb of DM, limit-fed at 2.5% of BW daily on a DM basis. Individual BW were measured on arrival, at revaccination (day 14), and at the conclusion of the study. Feed samples were collected weekly and frozen at -4°F. At the conclusion of the study, feed samples were thawed, mixed, subsampled, refrozen, and taken to a commercial laboratory for nutrient analysis (SDK Labs, Hutchinson, KS).
On arrival (day -1) cattle were individually weighed, received a visual number ear tag, and any pre-assigned ear tags or markings were recorded. Additionally, all cattle were ear-notched to mark cattle persistently infected with bovine respiratory disease. Cattle had ad libitum access to long-stem prairie hay and water via automatic waterers (Lil' Spring 3000; Miraco Livestock Water Systems, Grinnell, IA) prior to allocation to experimental pens on day 0. Twenty-four hours after arrival (day 0), cattle were individually weighed and were assigned an electronic identification ear tag. Each heifer was also outfitted with a 3-axial accelerometer ear tag (Allflex Livestock Intelligence, Madison, WI) to measure rumination and activity in 2-hour increments throughout the day, summarized in minutes per day. Cattle received a 7-way clostridial vaccine (Caliber 7, Boehringer Ingelheim Animal Health, Duluth, GA); and Titanium 5 (Elanco Animal Health, Greenfield, IN), a modified-live vaccine for protecting against infectious bovine rhinotracheitis, bovine viral diarrhea types 1 and 2, and parainfluenza. Additionally, cattle received Nuplura PH (Elanco Animal Health, Greenfield, IN) for protection against Mannheimia haemolytica; and tulathromycin (Draxxin; Zoetis, Parsippany, NJ), a macrolide antibiotic. Cattle were revaccinated on day 14 using Titanium 5.

Results and Discussion
Composition of study diets are presented in Table 1, and growing phase growth performance is presented in Table 2. Average daily gain for 60LF2.2 heifers was, on average, 15% lower (P < 0.01) than 45AL heifers, and feed to gain ratio was 35% greater (P < 0.01) for 60LF2.2 heifers than for heifers receiving 45AL. More DM was consumed by 45AL heifers than 60LF2.2 heifers (P < 0.01), except during gastrointestinal tract fill equilibration, by design (P = 0.23). The 45AL heifers lost BW during the first 7 days of the equilibration period. Concentration of NE g calculated based on animal performance was greater for 60LF2.2 heifers than 45AL heifers (P < 0.01), but calculated net energy (NE) was lower relative to diet formulation. Our results indicate cattle performed worse than would have been predicted by NE g , which may be due to environmental factors, including pen conditions, heat stress, or cold stress. Calculated 45AL NE concentration was 18.2% lower than diet formulation, whereas calculated 60LF2.2 NE concentration was only 3.8% lower than diet formulation.
The 60LF2.2 heifers spent, on average, 154 fewer minutes per day ruminating than 45AL heifers (P < 0.01; Table 2). An effect of diet was detected for rumination (P < 0.01, Figure 1), which was expected due to differences in DM intake between diets. A diet × day interaction was detected for rumination (P = 0.04; Figure 1), when the time 60LF2.2 heifers spent ruminating increased on day 56, increased between day 56 and day 75, and increased again on day 77. A diet × hour interaction was detected for rumination (P < 0.01; Figure 2); 45AL heifers spent more time ruminating overnight than 60LF2.2 cattle (8:00 p.m. to 6:00 a.m.; P < 0.05), but no differences (P > 0.10) were observed between treatments at 10:00 a.m. when rumination time for both groups reached a nadir. An effect of diet was detected for daily activity (P < 0.01; Figure 1), but no diet × day interaction for daily activity was detected (P = 0.93). A diet × hour interaction was detected for activity (P < 0.01; Figure 2), when 60LF2.2 heifers were more active 1 hour before feeding at 6:00 a.m., and again 3 to 7 hours after feeding between 10:00 a.m. and 2:00 p.m. (P < 0.01). The 60LF2.2 heifers were more active than 45AL heifers in this experiment, most likely due to increased appetite from meal-eating behavior and treatment design differences.

Implications
We interpret our results to suggest that growing cattle limit-fed a high-energy diet based on Sweet Bran and corn to have better feed to gain ratio, greater activity, and shorter rumination times compared to cattle fed traditional roughage-based diets ad libitum, which could enable more efficient observation of morbid cattle.   Figure 2. Effect of limit-fed high-energy or ad libitum roughage-based diets fed in the backgrounding phase on hourly rumination and activity. Top graph: 45AL (▲) = 45 Mcal of net energy for gain (NE g ) per 100 lb of dry matter (DM) offered for ad libitum intake, n = 186; 60LF2.2 (•) = 60 Mcal of NE g per 100 lb of DM limit-fed at 2.2% of body weight (BW) daily on a DM basis, n = 184. The arrow represents time of feeding (7:00 a.m.). Diet effect: P < 0.0001. Hour effect: P < 0.0001. Diet × hour effect: P < 0.0001. Standard error of the mean (SEM) = 1.18. Bottom graph: 45AL (▲) = 45 Mcal of NE g per 100 lb of DM offered for ad libitum DMI, n = 186; 60LF2.2 (•) = 60 Mcal of NE g per 100 lb of DM limit-fed at 2.2% of BW daily on a DM basis, n = 184. The arrow represents time of feeding (7:00 a.m.). Diet effect: P < 0.0001. Hour effect: P < 0.0001. Diet × hour effect: P < 0.0001. SEM = 0.65.