Tomato by-products are usually fed to ruminants due to their high fibre content. They are not excellent feed ingredients, being less digestible than most major oil meal and protein sources. They can be bitter and should then be used together with more palatable feeds. However, they can be a valuable source of protein, energy and fibre and cost-effective (Göhl, 1982; Caluya et al., 2003). In the Phillipines, Caluya et al., 2003 recommend to include tomato pomace at up to 50 % of the daily roughage requirement irrespective of whether it is fresh, dry or ensiled. The pomace should be given before the roughage or mixed (particularly when dry) thoroughly with the chopped roughage.
Digestibility and energy values
In vivo OM digestibility of dried tomato pomace was estimated at 56 % in sheep, using a balanced diet containing 34 % of pomace. In sacco rumen DM degradability was 48% (Abbeddou et al., 2011). A close value of 62 % for OM digestibility was obtained using the gas test method. Extremely wide estimates of ME have been obtained: depending on the method (in vitro, in sacco) and equation used, ME values of 4.9 (Chumpawadee et al., 2007), 7 to 9 (Gasa et al., 1991; Abbeddou et al., 2011) and 11.8 MJ/kg DM (Aghajanzadeh-Golshani et al., 2010) have been proposed.
In sacco protein degradability of dried tomato pomace in the rumen is quite high, from 65-70 % (Chumpawadee, 2009; Abbeddou et al., 2011) to 76-78 % (Ben Salem et al., 2008; Valizadeh et al., 2009). However, most of the protein is not digestible in the rumen but in the intestine (Gasa et al., 1988; Gasa et al., 1991, Ventura et al., 2009) probably because an important fraction this crude protein is acid-detergent insoluble (Weiss et al., 1997; Ventura et al., 2009).
Fresh or ensiled tomato pomace
Tomato pomace ensiled with whole maize plant up to 12 % (DM basis) showed good preservation characteristics. Dairy cows fed with this silage had the same DM intake (3.74 % BW) than cows fed with maize silage alone and had the same milk yield (35 kg/d) and milk composition (Weiss et al., 1997).
In lambs, fresh tomato pomace could replace more than 75 % of poor quality hay (6 % protein and 43 % OM digestibility), resulting in higher OM intake and OM digestibility (Ojeda et al., 2001).
Fresh tomato pomace ensiled with 10 % straw (Denek et al., 2006) or 15 % straw (Barroso et al., 2008) on DM basis, is well preserved. When offered as sole forage to 43 kg Awassi rams (Denek et al., 2006) or 47 kg Segureña ewes (Barroso et al., 2008) at maintenance level, DM intake was 0.95 kg/d (Denek et al., 2006) and 1.7 kg/d (Barroso et al., 2008) with a little daily weight gain of 50 g/d (Barroso et al., 2008). It can be concluded fresh tomato pomace ensiled with straw can be good quality roughage for sheep, particularly during periods of forage scarcity (Denek et al., 2006).
Ensiled tomato pomace (20 % DM) can be included in castrated lambs (43.5 kg) diets up to 45 % (diet DM) and replace maize silage without modifying total DM intake (91.7 g/kg0.75). However, OM digestibility of the diet significantly increased up to 30 % replacement but not beyond (Campos et al., 2007).
Dried tomato pomace
In dairy cows in early lactation (41 kg milk/d) dried tomato pomace included at 10 % (diet DM) did not change DM intake, milk yield and milk composition (Safari et al., 2007). In multiparous dairy cows (26 kg milk/d) dried tomato pomace could be included up to 32.5 % (concentrate diet DM), replacing part of barley grain and whole cottonseed meal without any adverse effect on health, milk yield and DM intake (Belibasakis, 1990).
Beef cattle and growing cattle
In beef heifers, dried tomato pomace could replace completely urea-treated straw, improving rumen digestion and feed efficiency. Diet DM intake increased from 66 (straw only) to 121 g DM/kg BW0.75 (70 % pomace) and decreased slightly (97 g DM/kg BW0.75) when pomace was fed alone (Yuangklang et al., 2006).
In Brahman-Thai steers (188 kg), dried tomato pomace could be included at 50 % (diet DM) in a total mixed ration without any problem. Diet DM intake (103 g/kg BW0.75) was comparable to that obtained with other by-products (brewers grains, palm kernel meal and soybean meal) included at the same amount in the diet (Chumpawadee et al., 2009).
In adult steers (370 kg) fed 21 days a total mixed ration where dried tomato pomace replaced cassava chips (up to 11 % of diet DM), there were no significant changes in DM intake and nutrient digestibilities (OM, protein and fibre) (Yuangklang et al., 2010a). In 2-year Brahman steers (258 kg) for 120 days, the replacement of cassava by tomato pomace tended to reduce daily weight gain (from 1037 to 881 g/d) but differences were not significant (Yuangklang et al., 2010b).
In adult rams, a diet containing dried tomato pomace and alfalfa hay in 1:1 ratio resulted in DM, OM and crude protein digestibilities of 57, 59 and 57 % respectively. Yeast addition (4 g/d) significantly increased digestibility up to 68, 67 and 66 % respectively (Paryad et al., 2009).
In growing lambs (18 kg), an experiment compared ad libitum straw-based diets supplemented with 500 g concentrate or with 250 or 125 g concentrate and a feed block containing wheat bran, salt, minerals and 48 % (DM) of dried tomato pulp. DM intake of the feed block + 125 g concentrate was higher. The DM intake of MNB increased (37.5 to 48.7 g/kg W0.75) when the DM intake of offered concentrate decreased (23.1 to 11.9 g/kg W0.75). Growth with the feed block was not significantly different from that of lambs fed straw and concentrate. Growth tended to decrease (57 to 48.7 g/d) when the concentrate offered decreased (Ben Salem et al., 2008).
In fattening lambs fed an alfalfa hay-based diet, dried tomato pomace included at up to 75 % decreased OM digestibility from 66 % to 57 % respectively. Daily weight gain was highest (132 g/d) at a 50 % inclusion rate, which was therefore the maximum recommended rate (Ibrahem et al., 1983). Young growing lambs (15.6 kg) fed for 6 weeks a barley-based diet with 200 g/kg DM of dried tomato pomace had similar N retention and growth performance (304 vs 337 g/d) than lambs fed a diet containing the same level of protein from soybean meal (Fondevila et al., 1994). In growing sheep (6-7 months, 32.6 kg), dried tomato pomace replacing 50 or 75 % of sunflower meal protein significantly decreased DM, crude protein and crude fibre digestibility and it was concluded that 12.5 % was the maximum replacement rate of dietary protein (Mohamed et al., 1997).
In goats goat fed 21 days with Napier grass ad libitum, dried tomato pomace could replace 25 to 100 % of soybean meal offered at 1.5 % BW without changing forage intake (0.535 kg DM/d), concentrate intake and N utilization (Yuangklang et al., 2007).