Kansas

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Introduction
Limit feeding high-energy diets can improve feed efficiency in growing calves compared with traditional high-roughage diets fed for ad libitum intake. Due to incidence of heat stress across the Central Plains region, the use of shade has been evaluated as a mitigation strategy to improve animal comfort and growth performance of finishing beef cattle. To our knowledge, limited information is available about effects of limit-fed high-energy diets in conjunction with shade on growth performance of growing beef cattle. The objective of this experiment was to evaluate the impacts of limit feeding and shade access as possible strategies to improve cattle efficiency, reduce water usage, and improve animal comfort in growing cattle.

Experimental Procedures
A group of 852 predominately black-hided heifers (553 ± 62 lb) were received at the Kansas State University Beef Stocker Unit during May and June of 2021 and 2022. Heifers were blocked by truckload (eight), stratified by individual arrival weight within block, and assigned to pens containing nine to twelve heifers. Within block, pens were assigned to one of four treatments for a total of 40 pens and 10 replications per treatment per year. The experimental design was a randomized block design with pen serving as the experimental unit.
On arrival, cattle were individually weighed, assigned a visual identification ear tag and an electronic identification ear tag, then provided 5 lb of prairie hay per animal [dry matter (DM) basis] and ad libitum access to water. On day 0 in 2021 (year 1), heifers were administered a 3-axial accelerometer ear tag (Allflex Livestock Intelligence Madison, WI) to measure rumination and activity. For both years, the heifers received a 7-way clostridial vaccine (Vision 7 with SPUR, Merck Animal Health, Madison, NJ), a modified-live vaccine to protect against infectious bovine rhinotracheitis, parainfluenza, and bovine viral diarrhea (Vista Once SQ, Merck, Madison, NJ), and an anti-parasitic drench (Valbazen, Zoetis Animal Health).
Prior to arrival, two shade structures (40 × 40 ft) per block were randomly assigned to cover two pens per structure; for the two pens under a common shade structure, one pen was fed each of the two dietary treatments. Shade structures provided 77 ± 6.3 ft 2 of shade per animal (Strobel Manufacturing Inc., Clarks, NE). Diets (Table 1) included a high-energy diet formulated to provide 60 Mcal of net energy for gain (NE g ) per 100 lb of DM fed at 2.2% of body weight (BW) daily and a high-roughage diet formulated to provide 45 Mcal of NE g per 100 lb of DM fed for ad libitum intake. Animals were fed once daily beginning at 7:00 a.m. using a Roto-Mix feed wagon (Model 414-14B, Dodge City, KS). Bunks were observed prior to feeding to estimate ad libitum intake. Refusals for ad libitum diets were targeted at 5% of DM fed the previous day. Using a pen scale (Rice Lake Weighing Systems, Rice Lake, WI) pen BW were measured weekly from day 14 to 84 as well as on days 0, 90, and 97. Pen weights were used to adjust feed delivery and calculate animal performance. A gut-fill equilibration period was used to account for gastrointestinal tract fill differences between treatments by providing a diet at 2.5% of BW daily (DM basis) formulated to contain 53 Mcal of NE g per 100 lb of DM to all treatment groups.
Feed ingredient samples were collected weekly. A portion of the sample was used to determine diet DM and the remaining feed sample was immediately frozen. Diet DM weights were used weekly to adjust feed offerings.
To determine the effects of shade on animal comfort, animals were evaluated at 9:30 a.m., 1:30 p.m., and 5:30 p.m. on days when the temperature humidity index (THI) was estimated to be greater than 74 (US MARC Animal Comfort Index). Using a method adapted from Guaghan et al. (2008; Table 2), individual panting score was determined using respiration rate and breathing conditions. Three animals per pen were selected randomly at each time point to represent each pen. The three values were aver-aged to obtain a mean panting score for each pen. Water usage was measured via iPERL water meters (SENSUS, Morrisville, NC) connected to individual automatic waterers (Lil' Spring 3000; Miraco Livestock Water Systems, Grinnell, IA) for each pen. The presented water usage and panting scores are only from year one.

Effects of diet
On day 0, BW did not differ (P = 0.90; Table 3) between dietary treatments; however, on day 90 BW were greater (P < 0.01) for calves fed for ad libitum intake compared with limit-fed calves. After the gut-fill equilibration period, limit-fed calves had greater (P < 0.01) BW compared with calves previously fed for ad libitum intake. This demonstrates how the diet affects gut fill and subsequently BW; it is important to equalize gut fill to obtain the best possible estimates of true BW gain. Average daily gains (ADG) from day 0 to 97 were greater (P < 0.01) for limit-fed heifers compared with heifers fed for ad libitum intake. A diet effect (P < 0.01; Table 3) was observed through day 97 where calves fed for ad libitum intake had greater DM intake compared with limit-fed calves. Dry matter intake did not differ (P = 0.69) between treatments during the gut-fill equilibration period, which was expected because all cattle were limit fed during this time. A diet effect was observed through day 97 for gain-to-feed where calves fed for ad libitum intake had worse feed efficiency than limit-fed calves; this is associated with a lower DM intake of limit-fed calves compared with calves fed for ad libitum intake, while ADG were greater (P < 0.01) for limit-fed calves compared with calves fed for ad libitum intake.
Heifers fed for ad libitum intake spent more time ruminating than limit-fed heifers (P < 0.01; Table 3), and the greater time spent ruminating was associated with greater DM intake and greater dietary forage concentration of the diets fed for ad libitum intake. Limit-fed heifers were more active (P < 0.01) compared with heifers fed for ad libitum intake.
Dietary treatments did not affect the mean panting scores. Limit-fed calves used 9% less (P < 0.01) water when compared with calves fed for ad libitum intake. Differences in water usage between diets may be attributed to differences in DM intake.

Effects of shade
On day 0, BW did not differ (P = 0.22; Table 3) between shaded and non-shaded calves. Heifers provided with shade had heavier (P < 0.01) day 90 and day 97 BW compared to heifers without access to shade. Average daily gains from day 0 to 97 were greater (P < 0.01) for shaded heifers compared with non-shaded heifers. Calves fed for ad libitum intake in shaded pens had greater (P < 0.01) DM intake compared with calves in non-shaded pens fed for ad libitum intake, whereas limit-fed calves in non-shaded pens and shaded pens did not differ in DM intake. Gain-to-feed was better (P < 0.01) for calves in shaded pens compared with calves in non-shaded pens.
Limit-fed heifers in shaded pens spent less time ruminating (P < 0.01) compared with limit-fed heifers in non-shaded pens; however, rumination time of calves fed for ad libitum intake was not affected by provision of shade. Heifers in shaded pens tended to be more active (P = 0.10) compared with heifers in non-shaded pens.
Calves in non-shaded pens had greater (P < 0.01; Figure 1) mean panting scores than calves in shaded pens. We attribute this difference to an increase in animal comfort due to reduced solar radiation exposure in shaded pens leading to lower heat load during the summer.
Water usage was 11% less (P < 0.01; Table 3) for shaded calves compared with non-shaded calves. This can be attributed to a decrease in heat load of calves in shaded pens compared with calves in non-shaded pens. Implications These data demonstrate that limit feeding a high-energy diet during the receiving period can improve feed efficiency and reduce water usage when compared to a higher forage diet fed for ad libitum intake. During periods of heat stress, shade can improve animal performance, reduce water usage, and improve animal comfort.   Analysis of year one data only: non-shaded 45 = 105 animals; shaded 45 = 106 animals; non-shaded 60 = 100 animals; shaded 60 = 102 animals. Treatments in year one comprised 10 pens each.