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Periods of elevated heat load can negatively affect productivity and animal welfare in beef cattle systems (Edwards-Calloway, 2021). In extreme instances, elevated temperatures paired with high relative humidity and solar radiation can result in mortality losses in livestock systems (NPR, 2022). St. Pierre et al. (2003) quantified economic losses to the beef industry as a result of heat stress to be approximately $369 million/year due to mortality, reproduction loss, and performance loss. With abnormal heat stress events continuing to occur, it is evident mitigation strategies must be implemented to improve livestock efficiency and animal comfort. Heat stress mitigation strategies (e.g., shade) can be used to improve performance, animal comfort, and reduce water consumption in beef cattle (Morrison, 1983; Beede and Collier, 1986; Edwards-Calloway et al., 2021). Recent research has demonstrated high-energy limit-fed diets can improve feed efficiency without detrimental effects on performance characteristics (i.e., body weight gain, average daily gain; Spore et al., 2019). By replacing traditional high-roughage diets fed for ad libitum intake with limit-fed high-energy diets, producers can achieve similar gains with less total feed input. In addition, reducing dry matter (DM) intake may modulate heat production, which could potentially improve animal welfare and performance (Mader and Davis, 2004). To our knowledge, no work has been conducted evaluating limit-fed high-energy diets in conjunction with shade in growing cattle. The objectives of this study were to evaluate the use of shade and limit feeding a high-energy diet on performance, animal comfort, water usage, diet digestibility, and ruminal characteristics during periods of heat stress.
A group of 852 predominately black-hided heifers (553 ± 62 lb) were received at the Kansas State Beef Stocker Unit during May and June of 2021 and 2022. Heifers were blocked by truckload (8), stratified by individual arrival weight within block, and assigned to pens containing nine to twelve heifers. Within block, pens were assigned to 1 of 4 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 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’ 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 ft. × 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 ft2 of shade per animal (Strobel Manufacturing Inc. Clarks, NE). Diets included a high-energy diet formulated to provide 60 Mcal of net energy for gain (NEg) per 100 lb of dry matter fed at 2.2% of body weight daily (60) and a high-roughage diet formulated to provide 45 Mcal of NEg per 100 lb of dry matter fed for ad libitum intake (45). Animals were fed once daily beginning at 7:00 am 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 dry matter fed the previous day. Using a pen scale (Rice Lake Weighing Systems, Rice Lake, WI) pen body weights 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 body weight daily (dry matter basis) formulated to contain 53 Mcal of NEg per 100 lb of dry matter (53) to all treatment groups. Feed ingredient samples were collected weekly. A portion of the sample was used to determine diet dry matter and the remaining feed sample was immediately frozen. Diet dry matters were used weekly to adjust feed offerings. To determine the effects of shade on animal comfort, animals were evaluated at 9:30 am, 1:30 pm, and 5:30 pm 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) 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 averaged 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.
Effect of Diet:
On day 0 body weights did not differ (P = 0.90) between the dietary treatments; however, on day 90 body weights 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) body weights compared with calves previously fed for ad libitum intake. This demonstrates how the diet affects gut fill and subsequently body weight; it is important to equalize gut fill to obtain the best possible estimates of true body weight gain. Average daily gains 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) was observed through day 97 where calves fed for ad libitum intake had greater dry matter intake compared with limit-fed calves. Dry matter intake did not differ (P = 0.69) between treatments during 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 compared with limit-fed calves. This better efficiency is associated with a lower dry matter intake of limit-fed calves compared with calves fed for ad libitum intake while average daily gains 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), and the greater time spent ruminating was associated with greater dry matter 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 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 dry matter intake.
Effect of Shade:
On day 0 body weights did not differ (P = 0.22) between shaded and non-shaded calves. Heifers provided shade had heavier (P < 0.01) day 90 and day 97 body weights 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) dry matter 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 dry matter 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) mean panting scores than calves in shaded pens. We attribute this difference to an increase in animal comfort due to reduced solar radiation exposure to calves in shaded pens, which led to a lower heat load during the summer. Water usage was 11% less (P < 0.01) 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.
These data demonstrate 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.