Oats are a valuable feed for ruminants used to feed beef cattle, dairy cattle and sheep. In the USA, 18% of the dairy farmers reported using oats (Dann, 2010). Oats are a popular creep feed in the Great Plains of the USA and are considered to be a good feed for growing cattle. For beef cattle, oats may constitute 50-70% of the grain mix while cattle are becoming accustomed to a full feed. The level of oats should be reduced over time to 20-30% of the diet. In finishing cattle, good quality oats can be used at levels up to 1/3 of the concentrate intake without affecting growth and feed efficiency (Boyles et al., 2006). In Australia, oats are a traditional feed for sheep and are used as supplementary feed for grazing animals, whether growing, fattening or at lambing time (Cuddeford, 1995).
Digestibility and nutritive value
The high gross energy content of oats is offset by their high fibre content, resulting in a lower OM digestibility (77% vs. 88, 83 and 89% for maize, barley and maize respectively) and lower ME content (12.2 MJ/kg DM vs. 13.1, 12.4 and 13.6 MJ/kg DM for maize, barley and maize). The protein value of oats is lower due to a lower protein content and high N degradability (81%, Sauvant et al., 2004; Herrera-Saldana et al., 1990). The nutritive value of naked oats is higher by 20-30% compared to hulled oats (Sauvant et al., 2004). This favours their inclusion in diets when voluntary intake is limiting, such as with dairy cows. However, high inclusion rates of naked oats are not recommended, as their high lipid content may have an adverse effect on fibre digestion (Martin et al., 1988b).
Oats in ruminant production
Despite their lower ME and metabolizable protein supply (Gozho et al., 2008), oats can be a competitive cereal source relative to barley for dairy cows, in terms of milk and fat yield (Moran, 1983; Lampila et al., 1986; Antila, 1986; Antila, 1990, all cited by Cuddeford, 1995). Oats provide less saturated milk fatty acids (Moran, 1986; Martin et al., 1987).
The utilization of wheat distillers grains with solubles by beef cattle was optimized by blending with 25% oats (Damiran et al., 2013). The replacement of maize grain by up to 30-40% oat grain in high concentrate diets did not affect digestion in crossbred cattle (Dutta et al., 1992), or growth performance of feedlot lambs (Borges et al., 2011). However, oats gave a lower performance when they replaced barley in starter feeds for calves (Bush, 1989), and in fattening diets for bulls (Latrille et al., 1983), or when they replaced sorghum in diets for finishing steers (Faturi et al., 2003). Oats appeared less efficient than good quality lucerne as supplement for ewes at lambing (Holst, 1987), or for growing sheep (Round, 1988).
Effects of processing
Processing oats may in some cases have positive effects on cattle and sheep performance. However, such effects are often limited, and processing costs may cancel much of these advantages (Boyles et al., 2006; Cuddeford, 1995).
Physical processes such as grinding, rolling and cracking have variable and often debatable effects on the nutritive value of oats (Cuddeford, 1995).
Calves chew oats sufficiently well until approximately 10 months old and little or no benefit is gained from processing them prior to this time. Grinding oats is usually not required for young calves, unless the grain fed with the oats is also ground (Boyles et al., 2006). In dairy cattle, dry rolling had a strong positive effect on OM digestibility (Nordin et al., 1976) but a negligible one in steers (Toland, 1976). In grazing dairy cows, crushing did not improve milk yield, and it depressed milk fat production (Hodge et al., 1984). Compared to whole grains, hammermilling oats did not affect production of dairy cows at pasture (Valentine et al., 1989). In beef cattle, feeding rolled or ground oats to yearlings resulted in a 1% improvement in feed efficiency compared to feeding oats whole. Some studies found that beef cattle fed whole oats consumed more grain per day but gained at the same rate compared to cattle fed rolled or ground oats. Fine grinding oats, coupled with pelleting, improved performance of growing cattle over either whole or ground oats. Studies have shown that gains can be improved by 11% and feed efficiency by 13% with grinding and pelleting, compared to feeding oats whole (Boyles et al., 2006).
In sheep, no positive effect of processing on OM digestibility has been recorded (Orskov et al., 1974a; Orskov et al., 1974b). Several authors have concluded that, in most situations, oats should be given whole to ewes, whereas rolling is required with wheat and barley (Vipond et al., 1985; Chestnutt, 1992).
Dry heat processes (extruding, micronizing, roasting, popping) and hydrothermal processes (steam rolling, steam flaking, pressure cooking, exploding) do reduce the rumen degradation rate of starch, but have only limited impact on the protein and energy value of oats (Owens et al., 1997; Sauvant et al., 2004).
In the 1980s, alkali treatments were shown to be promising, since they increased the digestibility of the fibrous layers, making the starchy endosperm more available. Treating oats with 4.5-5% NaOH (Orskov et al., 1980) resulted in non-significant increases in DM intake and fat-corrected milk yield in dairy cows (Moran, 1986), and in better feed conversion, digestibility and growth rate in lambs (Orskov et al., 1981). Treatment with ammonia (up to 30 g NH3/kg oats) increased OM digestibility in adult weathers (Brand et al., 1985). The addition of 1.5% urea to low-protein oats increased intake in ewes and growth in Merinos sheep (Hodge et al., 1981). In dairy cows, treatment with formaldehyde was shown to increase milk yield and reduce milk fat content, with no effect on fatty acid composition (Martin et al., 1988a). However, in spite of these favourable results, such treatments have not been implemented in practice, probably for reasons of cost and feasibility.