Almond hulls
Almond hulls can be used as an energy source in ruminants (Alibes et al., 1983). They have been described as a "cross-over" ingredient, which can be used both as a forage (due to its fibre) and a concentrate (due to its energy content) (Asmus, 2015). As they contain little protein, they cannot be fed alone and must be part of a diet containing better protein sources.
Palatability
Raw and ground almond hulls were reported to be relished by sheep (Miller, 1949).
Digestibility and degradability
In steers, DM digestibility of almond hulls was about 60-61% and the digestible energy (DE) was about 10 MJ/ kg (Aguilar et al., 1984). In sheep, the OM digestibility of coarse almond hulls was 63% and the digestible energy was 12 MJ/kg (Alibes et al., 1983).
The in vitro DM and OM degradability and gas production of dried almonds hulls measured with sheep rumen liquor were respectively 61%, 63% and 69.7 mL/200 g DM. Those values were higher than those observed on green almond hulls and on green and dry leaves of almond tree. Dried almond hulls had also the highest metabolizable energy value (10.1 MJ/kg DM) (Elahi et al., 2017).
Almond hulls were shown to have higher degradation parameters (a, b and c) and higher in situ DM degradability than alfalfa in sheep. The "a" parameter is favourable to good intake. These values advocate for almond hulls to be a potential fair value source of energy for sheep, though their lignin content could be a constraint (Yalchi et al., 2010).
Cattle
Steers
In Iran, almond hulls fed to steers had higher in situ total potentially degradable fraction (a+b) than alfalfa. The "a" value was also higher than for alfalfa which could be in favour of higher intake. However, the degradation rate was however lower in almond hulls than in alfalfa. Overall results showed that almond hulls could be used to feed steers and more broadly ruminants (Jafari et al., 2015).
In the USA, it was possible to use almond hulls as a roughage in fattening steer diets at 7.5 and 15% inclusion in order to replace alfalfa and oat hay. No significant difference could be found in weight gain, intake or feed efficiency. Meat quality parameters remained unaffected by the use of almond hulls as a roughage source (Beckett et al., 1992). It was possible to include up 40% almond hulls in a diet containing alfalfa hay, oat hay, barley, and urea and to maintain steers to maintenance + 10% (Aguilar et al., 1984). However, a later experiment was less positive: 8 month old Hereford steers recorded less intake and 42% lower weight gain when they were fed on 40% almond hulls. The feed efficiency was significantly hampered but the carcass quality remained unchanged. It was suggested to limit almond hulls inclusion to 30% for growing steers (Porte et al., 1991).
Dairy cows
Almond hulls were worth 60% of the energy provided by maize grain and 4.2% of the protein provided by soybean (Grasser et al., 1995). Based on their nutritive value, almond hulls were reported to enter the least-cost calculated rations for high producing cows in California at levels varying from 0.4 kg/day in Northern California to 1 kg in Central California and up to 2.45 kg in southern California out of (Grasser et al., 1995). It has been possible to feed lactating dairy cows on 25% almond hulls (dietary DM) without affecting weight gain and milk production performance (Aguilar et al., 1984).
Almond hulls and ensiled citrus pulp have been assessed on dairy cows for milk production and enteric methane emissions. Almonds hulls (4 kg representing 25% of the dietary DM) or citrus pulp (3 kg representing 18% dietary DM) replaced alfalfa in the cows diet. Almond hulls yielded lower milk (24.6 kg) than the control (27.4) or the ensiled citrus pulp (26.2 kg). Dietary treatment did not affect milk composition parameters like fat, protein, and lactose or fat yields or fatty acid profile (Williams et al., 2018). Formerly, the use of almond hulls or sugarbeet pulp in lactating dairy cows in Japan, resulted in similar milk yield and milk quality (Ueyama, 1979).
In a early report from 1949 in California, it was demonstrated that almond hulls should not be used as a sole feed for dairy cows because it resulted in poor condition and performance. This was likely caused by the poor protein content of the product. It could replace half of the alfalfa hay in dairy cows diet (Miller, 1949).
Concerns about methane emissions have raised awareness about the potentiel effect of some coproducts on the reduction of emissions. Almond hulls have been assessed for their possible effect on methane enteric emissions of cows but did not prove to be beneficial (Williams et al., 2018).
Sheep
Grinding almond hulls reduced diet digestibility while N supplementation of the diet increased intake (Alibes et al., 1983). In the USA, it was possible to prepare finishing diets containing increasing (0, 5%, 10%) levels of almond hulls as a replacer of alfalfa for Hampshire x Suffolk lambs. The almond hulls diet did not affect daily gain, feed intake, feed efficiency, carcass yield and carcass quality at slaughter (Phillips et al., 2015).
Trials in Italy showed that almond hulls could be included at up to 15% or even 30% dietary level (Vicenti et al., 1993; Vonghia et al., 1989). Farm fattening sheep could be fed during 56 days on isonitrogenous, isoenergetic diets supplemented with either 15% almond hulls or 10% safflower cake or 15% almond hulls+10% safflower cake. All the diets yielded similar weight gain, feed intake and feed conversion efficiency. However, the dressing percentage was higher in for animals fed on safflower cake than those fed on almond hulls. It was concluded that it was possible to feed lambs of both almond hulls and safflower either in combination or alone (Vicenti et al., 1993). It was possible to offer up to 30% almond hulls to finishing lambs provided they could receive enough protein through the diet (Vonghia et al., 1989).
In an early digestibility trial in California, a mixture of ground almond hulls (50% of the diet) and chopped alfalfa hay was readily eaten by finishing lambs. The total digestibility of nutrients was 65% which could compare to the digestibility of culled fruits and advocated for a good nutritive value of ground almond hulls for sheep (Miller, 1949).
Silage
In Palestine, feeding finishing lambs on maize-soybean based diet supplemented with ensiled almond hulls had no effect on daily weight gain and final weight gain but it improved feed efficiency and resulted in lower feed cost in the ration (Omar et al., 2018).
Urea treatment
In Iran, urea-treated almond hulls were fed to Shall male lambs at 20% or 40% dietary DM (iso energetic and iso protein) to replace alfalfa. Feeding urea-treated almond hulls had no effect on DM intake. In vivo digestibilities were respectively 82%, 73% and 24% for DM, OM and CP. The substitution of almond hulls for alfalfa had no effect on rumen parameters, protozoa population, and blood parameters. Up to 40% urea-treated almond hulls could be included in sheep diet (Rad et al., 2016).
Goats
In California, Alpine goats could be supplemented with almond hulls up to 35% (DM dietary level) as a replacer of alfalfa hay in isonitrogenous, isoenergetic rations mainly based on barley, cottonseed oilmeal, molasses and limestone. Though the digestibility of DM, organic matter, NDF and ash were decreased at the higher level of almond hulls, the DM intake and weight gain increased. No significant difference in milk yield (av. 3.6-3.7 kg/day) or fat content (2.7-2.8%), could be found but protein content was significantly highest with 25% almond hulls and lowest with 35% (3.0 vs. 2.9%). Results indicate that almond hulls can be given at these levels to goats without adversely affecting milk production (Reed et al., 1988).
