The effect of bermudagrass hybrid on forage characteristics, animal performance, and grazing behavior of beef steers1,2

Abstract

Bermudagrass (Cynodon dactylon [L.] Pers.) is a major feed source for ruminants across the southeastern United States. In 4 consecutive yr, 3 different bermudagrass hybrids, Alicia, Jiggs, and Tifton-85, were evaluated under a low stocking rate as forage and hay sources. The nutritive value, in situ DM digestibility, and performance and grazing behavior of beef steers under similar management were evaluated. Sampling day had an effect (P < 0.05) on all forage variables. Percentages of CP and TDN decreased while concentration of ADF, NDF, lignin, and nonfiber carbohydrates (NFC) increased as grazing season advanced. Alicia had lower nutritive value, showing greater lignin (5.3%) and indigestible fraction (44.9%) compared to Jiggs (4.9 and 35.6%, respectively) and Tifton-85 (4.5 and 40.1%, respectively). Tifton-85 contained the lowest concentration of NFC (11.8%). Steers grazing Jiggs and Tifton-85 had greater ADG (0.51 and 0.55 kg, respectively) and BW gain per hectare (258 and 279 kg, respectively) than those on Alicia (0.36 kg and 184 kg/ha, respectively); results that are probably explained by the lower nutritive value characteristics of the latter. Most grazing behavior variables were affected (P < 0.05) by time of the day (TOD) and grazing period. Two major grazing events were observed at dawn and dusk. Grazing time (32 min) was lowest (P = 0.003) while standing (140 min) and lying (98 min) time were greater (P = 0.001 and 0.04, respectively) from 1100 to 1559 h, probably as an effect of temperature and humidity at that time of the day. During summer, the temperature humidity index (THI) is above 72 (mild heat load) for the entire season and above 79 (severe heat load) during most of the daylight hours from June to August. Heat load likely affected animal performance and grazing behavior; however, some characteristics associated with these bermudagrass hybrids, especially with Alicia, such as its percentages of lignin and indigestible fraction may also partially explain the poor animal performance. In the conditions of the study, environmental variables (temperature and humidity), as well as the type of bermudagrass hybrid, affected animal performance and grazing behavior of recently weaned beef steers.

Effect of Summer Annual Forage and Type of Shade on Grazing Behavior of Beef Stocker Heifers

“…Scaglia and Boland (2014), under similar weather conditions to those in the present experiment, observed that between 0600 h and midnight for all four months of grazing season (June to September) THI was above that considered to provoke mild heat stress on cattle. Even more dramatic to observe was the fact that the THI for June, July, and August between 0600 and 2100 h would cause a severe heat load (Scaglia & Boland, 2014). Similar data were observed for the present experiment (Figure 4).…”

“…Even though it was reported in feedlot conditions, during heat stress, eating behavior decreased (7.1 vs. 9.1%), drinking behavior increased (3.1 vs. 1.7%), standing behavior increased (48.1 vs. 42.0%), lying behavior decreased (41.1 vs. 44.3%), and agonistic behavior decreased (2.6 vs. 0.2%) for heat stressed cattle vs. those in a thermoneutral zone, respectively (Brown-Brandl et al, 2006). Scaglia and Boland (2014) reported that steers spent less time grazing, walking and lying and more time standing (to dissipate heat) during the period of peak THI as well as during the first 3 months of the grazing period. In the present experiment a similar impact (except for walking time) was observed due to THI.…”

“…Alyceclover (Alysicarpus vaginalis L.; 12 kg per hectare) and pearl millet (Pennisetum glaucum; 22 kg per hectare) were used as a mean of increasing forage nutritive value (compared to bermudagrass) for young beef cattle as suggested by Scaglia & Boland (2014). Every year on early May, Glyphosate (N-(phosphonomethyl)glycine (Roundup ® ; Monsanto Co., St. Louis, MO, USA) was applied for weed control; however, small areas (less than 0.01 hectare) with crabgrass (Digitaria sanguinalis) and johnsongrass (Sorghum halepense (L.) Pers.)…”

“…As expected, nutritive value for alyceclover (a legume) was greater (p < 0.05) than pearl millet (Table 1); however, nutritive value parameters for the latter were adequate for yearling heifers as those used in the present experiment (NRC, 1996). Most forage systems in the Gulf Coast states are based on warm season perennial grasses, such as bermudagrass (Cynodon dactylon) and/or bahiagrass (Paspalum notatum), but these grasses do not meet the nutrient requirements of young growing animals (Scaglia & Boland, 2014). There was no shade type or forage type x shade type interaction effect on ADG or beef produced per hectare (Table 2); hence, the main effect of forage type (p = 0.03) is discussed.…”

“…Heifers with artificial shade (under which the temperature was 1.7 ºC greater than under the trees) spent more time standing and less time lying down than those with access to natural shade (Table 3). This behavior is used as a mean of dissipating heat as indicated for steers grazing bermudagrass under similar conditions (Scaglia & Boland, 2014).…”