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Animal Science Departmental Report 2004-2005 Return to Beef Cattle articles
Afternoon Harvest Increases Intake and Digestibility of Forages for
Goats and Cattle G. B. Huntington, J. C. Burns, and A. K. Sauve Introduction Like other plants, grasses vary in their concentration of nonstructural carbohydrates during the daily cycle of sunshine and nighttime. Nonstructural carbohydrates include simple sugars, disaccharides, polysaccharides, and starch that are synthesized with the energy captured by the photosynthetic machinery of the plant. During the nighttime, plants move these carbohydrates to support synthesis of more complex structural components, like cellulose, and to the roots for their growth and development. Therefore, in the late afternoon, forages have a higher concentration of nonstructural carbohydrates than they do in the morning (Table 1). Recent work at North Carolina State University with collaborators in Idaho has shown clear intake preferences and a slight improvement in apparent dry matter (DM) digestibility of cattle, sheep, and goats fed alfalfa or fescue hays harvested in the late afternoon compared with hays harvested in the morning (Fisher et al., 1999,2002; Burns et al., 2004). Hays harvested in the afternoon have higher content of soluble sugars than hays harvested in the morning. We designed two experiment to determine if the advantage of PM harvest applied to warm-season grasses conserved as hay or ensiled in large, round bales. Materials and Methods Experiment 1. The objective of Experiment 1 was to evaluate the differences in total nonstructural carbohydrates (TNC) of Iuka gamagrass (Tripsacum dactyloides L.) harvested at 0530 (AM) or 1730 (PM), and to measure how TNC concentration and a protein supplement interact to affect the voluntary dry matter (DM) intake and digestible DM intake of gamagrass field-cured and stored in square bales. Boer X Spanish wethers (53 ± 7 lb) were randomly assigned to a pelleted supplement fed at 11% of DM offered (14 goats) or no supplement (14 goats). Ingredients were chosen to create a supplement with ruminal degradation properties similar to that previously reported for gamagrass hay (Table 2). Within supplement or no supplement, goats were randomly assigned to a crossover design of AM gamagrass (7 goats) or PM gamagrass (7 goats). Goats were individually housed in metabolism crates with free access to water and mineral blocks. They were fed amounts twice daily, with supplement being offered once a day 30 min before morning feedings. After a 7-day adaptation, voluntary intake (goats were fed 110% of previous day’s intake) was measured for 14 days, followed by a 4-day adjustment of feed offered (to equalize DM offered between periods) and a 5-day digestion trial to measure DM digestibility. After Period 1 the goats were switched to their new diets, and the protocol was repeated. Water and trace-mineralized salt were available free choice. Experiment 2. The objective was to determine if AM (0600) vs PM (1800) harvest affects CHO composition and voluntary intake of gamagrass or switchgrass stored as baleage. Iuka gamagrass (Tripsacum dactyloides L.) and Alamo SG (Panicum virgatum L.) were direct-cut and stored as baleage in round bales wrapped in plastic (Figures 1, 2 and 3). Black steers ( 573 ± 35 lb) were assigned (5 steers per treatment) to gamagrass/AM harvest, gamagrass/PM harvest, switchgrass/AM harvest, or switchgrass/PM harvest. Steers were group-housed in covered, outdoor pens with individual feeding gates. After adaptation to the facility and 14 d standardization, ad libitum intake was measured for 21d (7 d adjustment and 14 d intake estimate) followed by a 5-d digestion trial in indoor digestion crates. Water and trace-mineralized salt were available free choice. Results Experiment 1. Compared to AM harvest, PM harvest had higher (P < 0.05) concentrations of TNC and sugars than PM harvest (Table 1). Time of harvest did not affect the concentration (% of DM) of CP (7.91), NDF (70.5) or ADF (36.0) in the gamagrass hay. Voluntary DM intake of gamagrass (552 vs. 551 g/d, P < 0.89) and voluntary total (hay plus supplement) digestible DM intake. (331 vs. 318 g/d, P < 0.15) were similar for PM and AM hays; however, total digestible DM intake during the digestion trial was greater for PM vs. AM (325 vs. 304 g/d), because the adjustment in feed offered during the digestion trial decreased variation among goats and the made the statistical test more sensitive. Compared to no supplement, protein supplement increased total digestible DM intake (DM intake multiplied by the digestion coefficient from the digestion trial) during the voluntary intake phase (344 vs. 305 g/d) as well as during the digestion trial (337 vs. 292 g/d). Supplementation tended (P > 0.17) to decrease DM intake of gamagrass during the voluntary intake phase(531 vs. 571) and during digestion trial (522 vs. 554 g/d). There were no interactions between supplement and time of harvest. Experiment 2. ). Compared to AM harvest, PM harvest had more starch, TNC, and sugars (Table 1). Compared to AM harvest, PM harvest had less (P < 0.01) acetate (1.3 vs 1.8 % of DM) and propionate (0.03 vs 0.08 % of DM), and tended (P = 0.12) to have less lactate (0.29 vs 0.35 % of DM) and butyrate (0.39 vs 0.51 % of DM). Gamagrass baleage had more (P < 0.01) starch, sugars and TNC than switchgrass baleage (Table 1). Switchgrass baleage had higher (P < 0.02) pH (5.79 vs 5.32) and more ethanol (2.7 vs 1.9 % of DM, acetate (1.9 vs 1.2 % of DM), propionate (0.11 vs 0.00 % of DM), and butyrate (0.84 vs 0.06 % of DM) than gamagrass baleage, but switchgrass baleage had less (P < 0.02) DM (24.2 vs 32.4 %), and lower concentrations of CP (9.7 vs 11.4 % of DM) and lactate (0.16 vs 0.48 % of DM). Daily DM intake (2.16 vs 1.83 % of bodyweight) and digestible DM intake (1.15 vs 0.95 % of bodyweight) were greater (P < 0.05) for PM vs AM harvest. Discussion Our results indicate that the advantage in voluntary intake and apparent digestibility reported for PM vs AM harvests of alfalfa and fescue are evident in the warm-season grasses that we measured (switchgrass and gamagrass). Although the protein supplement increased total digestible DM intake for the goats in Experiment 1, most of the increase was due to the higher digestibility of the supplement relative the hay, and could not be attributed to an interaction between increased intake of ruminally degradable protein and increased intake of TNC with the PM harvest. Both gamagrass and switchgrass were conserved acceptably as baleage, indicating that both grasses can be harvested and stored in this manner, thereby decreasing the dependence of farmers on ideal hay-making weather. The ensiling process did not eliminate the PM advantage in TNC. We conclude that the PM harvest of gamagrass hay supported 7% greater digestible DM intake in the goats, and that PM harvest of gamagrass or switchgrass baleage supported 17% greater and digestible DM intake in the steers. The reason for the increased intake is the increased content of TNC in grasses harvested in PM over grasses harvested in the AM. References Fisher, D.S., H.F. Mayland, and J. C. Burns. 1999. Variation in ruminants’ preference for tall fescue hays cut either at sundown or at sunup. J. Anim. Sci. 77:762-768. Fisher, D.S., H.F. Mayland, and J. C. Burns. 2002. Variation in ruminant preference for alfalfa hays cut at sunup and sundown. Crop Sci. 42:231-237. Burns, J. C., H. F. Mayland, and D. S. Fisher. Dry matter intake and digestion of alfalfa harvested at sunset and sunrise. J. Anim. Sci. 83:262-270.
Table 1.. Starch, sugars and total nonstructural carbohydrate concentration in forages used in Experiment 1 and Experiment 2.
Table 2. Composition and concentration of crude protein (CP) and crude protein fractions in the supplement fed to goats.
1A and B1 are readily degradable in the rumen. B2, and B3 are less degradable in the rumen. C is undegradable and indigestible crude protein.
Figures 1-3. Forage is cut and conditioned (Figure 1), baled in large, round bales (Figure 2), wrapped in plastic (Figure 3) and stored for at least 60 days before being fed to steers. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
