Malt whisky by-products
Fresh malt distillers, pot ale syrup and dried dark grains are traditionally fed to ruminants in Scotland and Ireland, though the dried grains have become more common (Crawshaw, 2004).
Draff has a moderate OM digestibility of about 50-54% due to its large concentration of fibre. Its energy value is disputed, with reported ME values in the 9-12 MJ/kg DM range (Crawshaw, 2004).
Draff is fed fresh to ruminants, or ensiled for later use. Because it contains only small amounts of available carbohydrates, draff has little effect on rumen acidity and can been fed ad libitum to cattle and sheep, though higher performance can be expected when draff is fed with an energy source such as cereals. A maximum inclusion rate of 30% in the diet DM is recommended (Crawshaw, 2004). The addition of minerals is generally beneficial for livestock consuming draff-based diets. They increased intake in sheep fed a draff-only diet at maintenance level (Crawshaw, 2004). Mineral supplementation with calcium or magnesium salts was found to increase diet digestibility, possibly due to interactions between the minerals and the relatively high fat content of the draff (El Hag et al., 1969; El Hag et al., 1972).
In Scotland, mixtures of draff and molassed beet pulp have given good results in dairy cows, beef cattle and lambs (Crawshaw, 2004). In dairy cows giving moderate yields, ensiled mixtures of draff and molassed sugar beet pulp replaced up to 5 kg/d (DM basis) of a cereal-based concentrate without affecting performance. This ensiled draff and molassed sugar beet pulp mixed with straw replaced grass silage in the diet of mid-lactation cows (McKendrick et al., 2003). Draff (supplemented with minerals) replaced barley/soybean meal in silage-based complete diets up to 30% of the DM (25 kg/d fresh basis) without any adverse effects on either intake or milk production (Hyslop et al., 1989). In beef cattle, weight gains higher than 1 kg/d have been reported in animals fed only draff supplemented with minerals. Beef cows have also been fed a diet consisting of 15 kg draff and 8 kg straw (plus vitamin and minerals) (Crawshaw, 2004).
In Scotland, a trial with lambs and sheep resulted in mixed results. Feeding pregnant ewes with mineralised draff as a sole feed resulted in cases of vaginal prolapse. Unrestricted access to draff caused dietary problems, and over-fat ewes that required increased assistance at lambing. The recommended maximum was 1 kg/d of draff per 25 kg live weight together with barley in the last 4 weeks of pregnancy, with regular attention to ewe condition and good management at lambing. In finishing lambs, mineralised draff used as the sole feed resulted in poor growth. The optimum use of draff for finishing lamb was offering it at a rate of 1 kg/d per 10 kg live weight, supplemented with 0.3 kg cereals per day plus minerals. Where draff was used in place of concentrates as a supplement to silage, the high NDF content led to reduced silage intake and live weight gain, resulting in a feed efficient but slow finishing system (Vipond et al., 1995).
Pot ale syrup
Pot ale syrup is very palatable and highly digestible to ruminants, with an in vivo OM digestibility between 89 and 93%. Estimated ME values for ruminants range from 14.2 to 15.6 MJ/kg DM. Pot ale syrup is used to feed ruminants in a variety of ways. It is poured on hay or straw, distributed in lick feeders or incorporated in complete diets. Pot ale syrup has been reported to contain a factor, possibly linked to yeast, that stimulates cellulolytic bacteria and thus the digestibility of roughages (Crawshaw, 2004). In Scotland, experiments with growing steers (200 kg) and heifers (350 kg) showed that moderate amounts (up to 2 kg/day) of pot ale syrup maintained or enhanced performance (Topps et al., 1979).
Malt distillers dark grains
Malt distillers dark grains have an OM digestibility of 65-69% and an ME value of 12-13 MJ/kg DM (Gizzi et al., 2001). The protein value for ruminants of malt distillers dark grains is disputed, since the draff contains insoluble protein while pot ale syrup contains soluble protein. A maximum inclusion rate of 35% in the diet DM is recommended (Crawshaw, 2004). In dairy cows fed silage and a conventional compound feed, malt distillers dark grains replaced 7 kg of the compound feed, resulting in an increase in milk yield and milk protein, and in a slight decrease in milk fat content (McKendrick et al., 1992).
The in situ DM degradability of distillers grains containing 70% barley was lower than that of wheat distillers grains (44 vs. 52%). In situ protein digestibility was only slightly lower (62 vs. 65%) but the soluble fraction was much lower for barley distillers, due to a higher acid detergent insoluble protein content, which may reduce the quality of the undegraded fraction (Mustafa et al., 2000a). A comparison between laboratory-made wet barley, wheat and maize distillers grains concluded that barley distillers were of lower nutritional value for ruminants than distillers from other grains, as they had lower in situ degradability values for DM, crude protein and NDF (Mustafa et al., 2000b).
In the USA, dried barley distillers grain produced from a mix of 65% barley and 35% maize were fed to dairy cows as a protein supplement (12.5% or 4.5% of diet DM). There was no effect on milk production, milk fat or DM intake, but milk protein decreased. Dried distillers grains were then judged an acceptable protein source for dairy cows (Weiss et al., 1989). In Finland, in dairy cows fed grass silage and a cereal-based concentrate, the replacement of part of the concentrate by 1.5 kg/d of dried barley distillers had no effect on dairy performance but milk and milk protein yield increased when the distillers grain was treated with formaldehyde. Treated distillers grains gave results similar to those obtained using rapeseed meal as a protein supplement (Huhtanen et al., 1991).
In the USA, a comparison of barley distillers grains and soybean meal in isonitrogenous backgrounding and finishing rations showed no difference in backgrounding calf performance in either steers or heifers. However, steer calves fed soybean meal gained weight more rapidly and it was concluded that soybean meal should be preferred when gains greater than 1.4 kg/d were required. In backgrounding heifer calves, soybean meal and barley distillers were found to be interchangeable on a protein basis, with a slight advantage for barley distillers in terms of feed efficiency (Landblom et al., 1988).