June 2015
Characteristics of Browse Plants for Goats and Sheep
Ken Turner, Ph.D.,
USDA-Agricultural Research Service,
Grazinglands Research Laboratory,
El Reno, Oklahoma
Background. Goats, sheep, and cattle are ruminants meaning that they have a four-compartmented stomach (rumen, reticulum, omasum, and abomasum), each with a specialized purpose to allow utilization of grasses, forbs (herbs and broadleaf plants, including legumes), and browse (leaf and twigs from woody plants, shrubs, vines, brambles, and trees) via microbial fermentation in the rumen. For clarity on definitions, please see Turner and Belesky (2010; Available at: http://www.joe.org/joe/2010april/a5.php; Ctrl+Click to follow link).
Goats, sheep and cattle graze differently by selecting plants and plant parts to satisfy nutrient demands. Goats are classified as browsing animals, whereas, cattle are classified as grazing animals; sheep are somewhat intermediate. When allowed to choose freely, goats select about 30% grasses and legumes, 10% weedy plants, and 60% browse while sheep diets typically include 50% grasses and legumes, 30% weeds, and 20% browse; grazing cattle select diets that contain 70% grasses and legumes, 20% weedy plants, and 10% browse.
Because diet preferences differ by ruminant species, producers can take advantage of this selectivity through grazing management practices (mixed grazing of livestock species) to help improve management of pastures, improve the nutritive value (especially protein) of forages in pastures, improve the overall forage utilization from pastures, and aid in gastrointestinal (GI) parasite control.
A wide range in crude protein and fiber concentrations among browse plants has been reported. Turner and Foster (2000) reported that while crude protein concentration and overall digestibility of the growing points (which included the new leaves and immature stems) of autumn olive (Elaeagnus umbellata Thunb.), Morrow’s honeysuckle (Lonicera morowii Gray), and multiflora rose (Rosa multiflora Thunb.) were variable over the growing season, these plants were considered of high nutritive value for goats. When averaged across the growing season, crude protein (%) was 26.5 (autumn olive), 16.7 (honeysuckle) , and 14.5 (multiflora rose), and while estimated organic matter digestibility (%) was 63.2 (autumn olive), 68.5 (honeysuckle), and 67.0 (multiflora rose) (see Table 1 below).
Concentrations of several minerals in autumn olive, honeysuckle, and multiflora rose were also determined (Table 1). The calcium to phosphorus (Ca:P) ratio was highest in multiflora rose (5.9:1) and honeysuckle (4.1:1) and lowest in autumn olive (1.7:1). The Ca:P ratio in autumn olive was close to 2:1. It is recommended that the Ca:P ratio in sheep and goat diets be maintained in a range from 1:1 to 2:1. A lengthy period of time with an imbalance of Ca:P in the diet often results in urolithiasis (urinary calculi formation in the urinary tract, especially of male animals). Goats and sheep with access to autumn olive along with other forages in a pasture or supplemental hays probably would not need additional phosphorus. However, goats consuming multiflora rose or honeysuckle as the sole component of the diets for extended periods of time may need supplemental phosphorus. Supplementation with corn grain or cereal grains (high in P in relation to Ca) can be used to help correct the Ca:P ratio imbalance.
Generally, legumes and some browse plants have higher levels of several minerals (calcium, copper, magnesium, phosphorus and zinc) in comparison to grasses. The minerals copper, iron, manganese, selenium and zinc can help support a healthy immune system in animals for improved tolerance to GI parasites.
Grasses, legumes, forbs, and browse also can contain plant secondary compounds, which in the past have been categorized and referred to as anti-quality or anti-nutritional components. Plant secondary compounds are being re-evaluated to better understand how these constituents influence animal health and performance by improving feed intake, digestion, and nutrient-use efficiency. In addition, secondary compounds (such as condensed tannins) in plants have anthelmintic (deworming) properties that can help control GI parasites in ruminants.
Condensed Tannins (CT)
Condensed tannins are water-soluble, polyphenolic compounds that occur in many browse and forage plants. Condensed tannin levels in autumn olive, honeysuckle, and multiflora rose were determined (Foster, 2005; Table 1) and varied throughout the growing season. Two forage legumes with high concentrations of CT are birdsfoot trefoil (Lotus
Birdsfoot trefoil (flowering)
Sericea lespedeza
Goats browsing Black Locust (Robinia pseudoacacia)
corniculatus L.) and sericea lespedeza [Lespedeza cuneata (Dum. Cours.) G. Don]. Condensed tannins in browse and forage plants can have positive or negative effects on livestock health and performance, depending on the type and concentration of CT present in the diet.
Condensed Tannins Reduce Bloat
Historically, bloating in ruminants was reduced or eliminated when grazing legumes that contained CT (e.g. birdsfoot trefoil). Bloat is caused by rapid fermentation of highly soluble forage proteins and carbohydrates by rumen microbes leading to a stable foam or froth in the rumen that traps gas (e.g. carbon dioxide). This most often occurs in the spring, especially when grazing pasture with a high proportion of non-tannin containing legumes, such as alfalfa and clovers, with limited stemmy material; stems help to stimulate eructation (belching). Condensed tannin can block bloat by combining with protein to prevent foam formation and gas entrapment in the rumen. The minimum CT concentration to prevent bloat in cattle is about 0.5% of the dry matter in plant tissue.
Condensed Tannins Help Improve Nutrient-use Efficiency.
Condensed tannins have the ability to combine with proteins, carbohydrates, minerals, and vitamins. Typically, CT are not a problem (beneficial) in lamb and sheep diets when the concentration is less than about 4% of the total dry matter intake. Condensed tannins in this case can help improve the protein-use efficiency of herbage by protecting plant proteins against excessive degradation in the rumen, thus increasing rumen-escape protein levels. By increasing the quantity of proteins reaching the small intestine, the amount of essential amino acids absorbed is increased (improving protein available at the intestine) and this extra protein can help support the immune system to combat GI parasites infection. In addition, overall protein-use efficiency and performance in these animals is often improved.
However, high CT concentrations (typically 5% and higher of the total dry matter intake of forages and browse) detrimentally inhibit protein and cellulose degradation in the rumen, reduce rumen microbial function, and thereby reduce (slow) the rate of passage of ingested nutrients, lower intake, reduce protein-use efficiency, and lower overall performance (weight gain, milk production) in livestock.
Condensed Tannins Aid in GI Parasite Control.
Addition of forages containing CT to diets of goats and sheep often results in a reduction of parasite larval development, GI parasite numbers, adult worm burden, and fecal egg count in these animals. Condensed tannins in sericea lespedeza (Terrill, 2014; Available at http://www.wormx.info/#!wisemans/c1pkl ; Ctrl+Click to follow link); panicled tick-clover [Desmodium paniculatum (L) DC.] (Muir et al., 2008); many tropical forages (Muir et al., 2012); and even CT in pine tree bark (Pinus taeda L.) (Min, 2014; Available at http://www.wormx.info/#!pinebark/coo1 ; Ctrl+Click to follow link) can help manage/reduce GI parasite problems.
Implications.
Using a mixed sward of grasses and legumes or legume (high protein) swards; using forage plants containing condensed tannins; and/or allowing access to browse plants can help in control of GI parasites in grazing goats and sheep. Additional benefits can include improved protein availability (and probably minerals) for support of the immune system and improved nutrient-use efficiency (especially protein) in livestock.
Table 1. Seasonal average of crude protein (CP), organic matter (OM) digestibility, neutral detergent fiber (NDF), acid detergent fiber (ADF), some minerals, total condensed tannin (total CT), and free condensed tannins (free CT) in autumn olive, honeysuckle, and multiflora rose during the 1999 growing season in West Virginia.
*Percentage and ppm concentrations are reported on a dry matter basis.
** quarbracho tannin equivalent per unit dry matter, ppt (Foster, 2005)
Literature cited
Foster, J.G. 2005. Condensed tannins in leaves of woody plants in Appalachian pastures. Proceedings of the American Forage and Grassland Council. 14:215-219.
Muir, J.P., J.R. Bow, W. Rodriguez, and J.M. Patterson. 2008. Defoliation of penciled tick-clover, Tweedy’s tick-clover, and tall brush-clover: II. Herbage nutritive value and condensed tannin concentrations. Agronomy Journal. 100:1635-1639.
Muir, J.P., T.H. Terrill, E. Valencia, S. Weiss, K. Littlefield, P.D. Jones, J. Mosjidis, and R.M. Wolfe. 2012. A wide range in forage condensed tannin in the southeastern USA shows promise in ruminant protein and parasite management. Proceedings of the American Forage and Grassland Council, June 21-24, Grand Rapids MI. CD Rom.
Turner, K.E. and D.P. Belesky. 2010. Terminology revisited: Effective communications for the agricultural community. Journal of Extension 48 (number 2):2FEA5. Available at: http://www.joe.org/joe/2010april/a5.php (Ctrl+Click to follow link)
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