Unique Dairy Applications of Eastern Gamagrass Forages in Central Wisconsin: II. Nutritive Value and Energy Density

Abstract

Recently, perennial warm‐season grasses have received considerable interest, largely through bioenergy initiatives, but their suitability for limiting caloric intake by fiber‐demanding livestock classes, such as dairy replacement heifers (Bos taurus) and/or dry cows has not been explored. Our objectives were to evaluate eastern gamagrass [Tripsacum dactyloides (L.) L.] forages harvested from nine single‐ or double‐harvest systems with four N fertilization regimes for macromineral, protein, and fiber composition, and then to estimate the energy densities for these forages by the summative approach. Across the 3‐yr trial, concentrations of neutral‐detergent fiber (NDF) from single‐harvest systems increased with mostly linear (P < 0.001) and quadratic (P = 0.010) effects of harvest date, reaching maximum concentrations ranging from 746 to 801 g kg−1 by early or mid‐August. Similarly, concentrations of lignin increased with delayed harvest dates across single‐harvest systems in predominantly linear (P < 0.001) patterns. Generally, concentrations of lignin were lower than reported for eastern gamagrass forages grown at more southerly latitudes, and ranged from 37.5 to 46.0 g kg−1 in mid‐August. As a result, estimates of total digestible nutrients (TDN) determined by the acid‐detergent lignin option for calculating truly digestible fiber remained relatively high through mid‐August (582 g kg−1). Adjusting truly digestible fiber on the basis of the alternate in vitro 48‐h neutral‐detergent fiber digestibility (NDFD) approach resulted in reduced TDN estimates for eastern gamagrass. In northern climates, eastern gamagrass forages have large concentrations of NDF, and could be used to dilute dietary energy for livestock species with low or moderate energy requirements.

Using eastern gamagrass to construct diets that limit intake and caloric density for dairy replacement heifers

“…Recently, research conducted in central Wisconsin has verified that this perennial warm-season grass can survive winter climatic conditions throughout the region, and will produce yields of DM ranging generally from 7,000 to 10,000 kg/ha by mid-August using a 1-cut harvest system (Coblentz et al, 2010b). Furthermore, concentrations of NDF in EGG forages harvested during this time period ranged from 74.6 to 80.1% (Coblentz et al, 2010a). However, estimation of TDN by the summative equation (NRC, 2001) for these forages was complicated by discrepancies in determining totally digestible fiber.…”

“…These estimates were based on the summative approach (NRC, 2001), in which the 48-h NDFD option was used to estimate truly digestible fiber. As noted previously, a serious bias has been noted between the lignin and 48-h NDFD options for estimating truly digestible fiber within EGG forages grown in central Wisconsin (Coblentz et al, 2010a). Obviously, this uncertainty complicated initial diet formulation, and it has been attributed to the relatively limited lignification of highly fibrous forage that was likely a consequence of the cool growing conditions existing throughout central Wisconsin relative to more southerly latitudes (Coblentz et al, 2010a).…”

“…However, estimation of TDN by the summative equation (NRC, 2001) for these forages was complicated by discrepancies in determining totally digestible fiber. In part, this was caused by the relatively limited lignification of cell walls occurring by mid-August (3.75 to 4.60%), likely in response to the cool growing conditions (Coblentz et al, 2010a). On this basis, the potential of EGG for diluting the energy density of heifer diets containing high-quality forages remains unclear.…”

Growth performance and sorting characteristics of corn silage-alfalfa haylage diets with or without forage dilution offered to replacement Holstein dairy heifers

“…Research conducted in central Wisconsin has verified that this perennial warm-season grass can survive winter climatic conditions throughout the region, and will produce yields of DM ranging generally from 7,000 to 10,000 kg/ha by mid-August using a 1-cut harvest system (Coblentz et al, 2010a), although more recent work (Coblentz et al, 2014) has shown that yields from 1-cut harvest systems are likely maximized during midto-late September. Furthermore, concentrations of NDF in eastern gamagrass forages harvested during this time period range generally from 75 to 80% (Coblentz et al, 2010b(Coblentz et al, , 2014). An intriguing observation made during the previous feeding trial with this forage was that heifers did not exhibit the undesirable sorting behaviors that typically are observed when chopped straw is used to dilute heifer diets (Coblentz et al, 2012).…”

Fall Harvest Management of Eastern Gamagrass in Central Wisconsin

“…§TDN‐LIG adjusted by the equation: TDN‐NDFD = (2.52 × TDN‐LIG) − 95.3 to reflect the slow digestion rate of EGG (Coblentz et al, 2010a). …”