Straws are generally bulky and the feeding value of untreated straws for ruminants is rather low: the OM digestibility of straws is in the 42-54% range. Their ingestibility is low: it is higher for sorghum, faba bean, pea and grasses than for rice, wheat, barley and oat (INRA, 2007). The nutritive values of legume straws are intermediate between those of medium-quality hays and those of cereal straws (Lopez et al., 2005).
Large differences in degradation can be observed within the same species, as reported for barley straw (Capper et al., 1992) and rice straw (Vadiveloo, 1992; Abou-El-Enin et al., 1999; Agbagla-Dohnani et al., 2001). In ruminants, oat straw is more palatable than barley straw, while barley straw is more palatable than wheat straw (Hamilton, 2010). However, despite their poor feeding value, straws can be useful during dry periods when high quality forages are lacking. Straws must be harvested well dried, and stored in a dry place.
Straw digestibility is limited both by its lignification and by its low nitrogen content. The digestibility and the rate of rumen passage can be increased by supplementing the straw with protein concentrate or urea plus minerals. It may also be economical to increase the nutritive value of straws by physical or chemical treatments (Göhl, 1982).
Effect of treatments on intake and digestibility
The feeding value of straw can be improved by grinding or by treatment with alkalis such as NaOH and ammonia.
Physical treatment
Grinding improves the ingestibility of straws, but not its energy or nitrogen value. Grinding also deprives the animal of the opportunity to reject the fibrous parts, thus reducing the digestibility of the feed, although this disadvantage is usually counterbalanced by the higher voluntary feed intake. For example, grinding wheat straw, even rather coarsely, can result in a 20-30% increase in intake because of the faster rate of passage through the rumen (Göhl, 1982). The following table shows the effect of combining grinding and NaOH treatment on barley straw fed to sheep (Fernandez-Carmona et al., 1972):
| Chopped straw |
Untreated |
16% NaOH |
| OM digestibility (%) |
45 |
61 |
| DM intake (g/kg W0.75) |
27 |
48 |
| Digestible energy intake (MJ/kg W0.75) |
0.19 |
0.48 |
| Ground straw |
Untreated |
16% NaOH |
| OM digestibility (%) |
45 |
64 |
| DM intake (g/kg W0.75) |
36 |
54 |
| Digestible energy intake (MJ/kg W0.75) |
0.25 |
0.55 |
Such increases in digestible energy intake can result in much greater performance. For instance, there have been reports of a 50% increase in the daily gains of beef cattle fed on all-roughage diets. It should be noted that the increased intake of digestible energy raises the protein requirement as well. When ground forage is mixed with concentrates, grinding tends to eliminate the difference in forage quality (Göhl, 1982).
NaOH treatment
NaOH treatment can increase the organic matter digestibility of wheat straw from 46% to more than 70%. Chromatographically treated wheat straw has a crude fibre digestibility of about 90%. An additional benefit is that straw treated with NaOH becomes softer, so less energy is lost in chewing and digestion. NaOH-treated straw is palatable and can be consumed in large quantities by livestock. Beef cattle can be fed up to 20 kg of treated straw per day, dairy cows up to 15 kg, young heifers up to 10 kg and sheep up to 3 kg. However, as noted previously, NaOH treatment is expensive and dangerous and does not improve the nitrogen value of the straw (Göhl, 1982).
Ammonia or urea treatment
Ammonia treatment (by the addition of anhydrous NH3 or urea) is easier to do in practice than NaOH treatment, and more valuable since it improves ingestibility, digestibility and nitrogen content (Baumont, 2011).
In sheep, the increase in voluntary intake induced by NH3-treatment is on average + 5 g/kg BW in sheep. In cattle, data are scarce but are of the same order of magnitude (+ 1.8 kg/d for steers and heifers; Baumont, 2011). This is far from being negligible given the low ingestibility of untreated straws (e.g. 11-12 g/kg BW in sheep and heifers for a barley straw; Dulphy et al., 1994). The increase in OM digestibility is on average 10-12 percentage points for wheat, barley, sorghum and maize, but is lower for rice (on average 4 points), which is initially more digestible. The increase in digestibility of crude protein is on average 6.2-6.5%, and an extra 14-20 g/kg DM of PDIN (true protein absorbable in the small intestine when N is limiting in the rumen) for wheat, barley and rice straws. For sorghum, crude protein digestibility is increased by 9.6%, with an extra 38 g/kg DM of PDIE (true protein absorbable in the small intestine when energy is limiting in the rumen). Ammonia-treated straws have an energy value and ingestibility comparable to that of late cut grass hays, but their nitrogen value remains lower (INRA, 2007; Baumont, 2011).
Supplementation
Straw is generally combined with other forages such as hay or silage, but it can be used as sole forage with supplementation where more nutritive forages are scarce. The first objective of supplementation is to meet the requirements of the rumen microbes in order to improve straw digestibility. Soluble nitrogen and fermentable carbohydrates can be provided by liquid feeds (such as a molasses-urea mixture included at 5-10% by weight of straw), protein concentrate (100 g of soybean meal or 150 g rapeseed meal per kg straw), by-products (corn gluten feed, DDGS and other maize processing by-products, rice bran), or legume forages such as leucaena leaves (Leucaena leucocephala). Minerals, trace elements and vitamins must also be provided. The second objective is to meet the energy and nitrogen requirements of the animal without affecting the cellulolytic activity of rumen microbes. Cracking or coarsely grinding cereal grains must be preferred to fine grinding in order to avoid an excess of rapidly fermentable carbohydrates. When a high level of concentrates is required, fibrous concentrates such as beet pulp, bran or corn gluten feed can be used (Devun et al., 2011).
Straw can be the main forage for heifers older than 15 months, and for suckling cows before the 8th month of pregnancy, provided that their body condition score is sufficient. For younger heifers and for early calving suckling cows or animals with a low body condition score, other forages must be offered with the straw. For dairy cows and fattening steers, straw is mainly used to meet appetite and to ensure adequate rumen function as well as a fractioned distribution of concentrate among the day. Straw must be offered as long particles, ad libitum and several times per day (Devun et al., 2011). Urea-treated rice straw is sometimes used as roughage for milking cows in dairy farms (e.g. in Northern Thailand) but requires a true protein supplement (Sruamsiri, 2007).
In fattening lambs, straws can result in a performance similar to that obtained with hay. Ewes have a limited intake capacity and at least 500 g/d of good quality hay must be given with the straw (1-1.5 kg/d) from late pregnancy to early lactation (Devun et al., 2011).
Specific information on straws
For detailed information on the use of specific straws in ruminants, see the datasheets for those species in Related feeds on the "Description" tab.
