FIELD OF THE INVENTION 
     The present invention is concerned with a composition for improving the digestibility of feed intended for ruminants. In particular, this composition can be provided in the form of a concentrated mixture designed for incorporation as an additive into the usual feed for ruminants. 
     BACKGROUND OF THE INVENTION 
     In ruminants, it is important for the digestibility of the feed that the organic material (in particular, protein and starch) should not undergo too much degradation in the rumen, but that the nutrients be transferred into the small intestine in a less degraded form, so that they may undergo an enzymic digestion which has lesser energy requirements, since it allows an increased production of adenosine triphosphate (ATP). 
     SUMMARY OF THE INVENTION 
     The purpose of the present invention is to provide a composition. designed for incorporation into feed for ruminants and which makes it possible to improve substantially the digestibility thereof and, consequently also to improve the growth of ruminants receiving such a feed. 
     The composition according to the invention aimed at meeting the above objective includes as the active ingredient, an aromatic phenol derivative selected from cresols and benzenediols. 
     Actually, the present inventors have found unexpectedly that the desired active effect on digestion was obtained by using an aromatic phenol derivative, and more particularly a cresol or a benzenediol, and specially resorcinol (m-benzenediol), or a mixture thereof. 
     Furthermore, they have also found that the transfer of nutrients, which had undergone less degradation into the small intestine thanks to the composition according to the invention, had another advantage in milking cows, namely a reduction in nitrogenous toxins produced by microbial degradation, which toxins provoke an inflammation of the udder. This inflammation is countered by an immunological reaction with the effect of an important increase in the milk of leukocytes called &#34;somatic cells&#34;. Actually, these somatic cells cause problems in cheese making and for this reason, milks containing high levels of somatic cells are paid less to the farmer. 
    
    
     DETAILED DESCRIPTION 
     Preferably, the aromatic phenol derivatives are incorporated into the animal feed so that their intake be approximately of 1 to 100 mg per animal and per day, depending on the weight of said animal. 
     The compositions according to the invention intended for incorporation into standard animal feed can include an absorbing support and an aromatizing mixture, to which the active ingredient is added. For instance, the proportion may be as follows: 
     5 to 10% of the phenol derivative, 
     20 to 30% of an aromatizing mixture, 
     and from 60 to 75% of an absorbing support. 
     Concerning the phenol derivative, use is preferably made of eresol or resoreinol or of a mixture thereof, for example a mixture containing 60 to 90% cresol and 10 to 40% resoreinol. 
     For example, one can use the following mixtures of absorbing support and of aromatizing mixture. 
     
         ______________________________________(a) Absorbing support:Sterilized fir tree sawdust              40-50%Stearin             8-10%Curcuma powder     4-5%Rosemary powder    4-5%Limestone          22-28%Arabic gum         approx. 2%Water              approx. 10%(b) Aromatizing mixture:Thymol             25-35%Guaiacol           10-15%Eugenol             5-10%Vanillin           10-20%Salicylaldehyde     5-10%Limonene (solvent) 20-35%______________________________________ 
    
     In practice, the cresol and/or the resoreinol are added to the liquid aromatizing mixture, then this new mixture is incorporated into the absorbing support, for example in a flour mixer. 
     In principle, for the administration to the animals, the composition according to the invention must be diluted, such a dilution being generally carried out in two steps; in the first one, a concentrated mixture or premix is prepared in which the composition according to the invention is diluted to 0.5-5% and this premix is in the second step mixed into an animal feed of the usual type. 
     For example, the concentrated mixture or &#34;premix&#34; can have the following composition: 
     
         ______________________________________Composition according to the invention                       0.3-3%Vitamin mixture (A, B, D, E, niacin, etc)                       0.1-1%Mineral salts (CaHPO.sub.4, CaCO.sub.3, NaCl, CuO, MnO,                       25-75%FeSO.sub.4, ZnO, etc)Wheat middlings and brans   21-75%______________________________________ 
    
     Again and merely by way of example, the above-mentioned premix can be incorporated into a feed to yield the following preparation: 
     
         ______________________________________Premix according to the invention                0.3-3.5%Cereals and peas     approx. 50%Oilmeal (soya, rape, etc)                approx. 25%Wheat middlings and brans                21-25%______________________________________ 
    
     Such a feed, containing the composition according to the invention and given in the amount of 2 to 10 kg per day per animal, provides daily doses of 5 to 100 mg of cresols and of i to 50 mg of benzenediols. 
     To demonstrate the efficacy of the composition according to the invention, three trials were carried out respectively to elucidate the effects in the rumen, on the occurrence of somatic cells in the milk and on the growth of the animals. 
     Trial 1: effects in the rumen 
     This trial was carried out according to the &#34;in vitro&#34; technique of Menke, using for the incubation: 
     (a) a feed containing 
     30% dried maize silage 
     25% dehydrated hay 
     15% barley 
     12.5 % maize 
     17.5% soya seed oilmeal 
     (b) the juices from the rumen of three animals with a fistula permanently inserted into the rumen; the animals receive feed (a) and the juices are sampled in the fasted state, 
     (c) Mac Dougall&#39;s buffer. 
     The incubation is continued during 48 hours at 39° C. and the different metabolites representative of the digestibility in the rumen are determined after 6 and 48 hours. 
     The test is repeated 12 times, on the one hand with the feed only (control) and on the other hand with a feed containing the composition according to the invention, more particularly a premix containing 10% of a cresol--resorcinol mixture (75%-25%), 20% of an aromatizing mixture of the type described previously by way of example and 70% of an absorbing support also corresponding to that described by way of example. 
     The results obtained are given in the following table: 
     
         ______________________________________Table of results:                       Feed with master           Control     batch of invention           6h      48h     6h    48h______________________________________(A) Precipitable protein           107.88  86.31   133.69                                 113.63(TCA) (mg/100 ml)(B) Ammonia, as nitrogen           24.19   40.32   4.83  6.75(mg/100 ml)(C) Total volatile acids           58.85   188.14  41.46 131.40(mg/100 ml)(D) Production of gas           72      122     56    85(mg/100 ml)(E) Dry substance, degrada-           --      --      54.12 41.28tion in % of the initial value______________________________________ 
    
     (A) The higher value for the feed with the premix according to the invention indicates that the protein of the feed is better protected. 
     (B) The important decrease in ammonia (as nitrogen) demonstrates that the protein is better protected and hence undergoes less degradation in the rumen. 
     (C) The decrease in the total volatile acids indicates that the starch is better protected. 
     (D) The decrease in the production of gas indicates also that the nutritive organic material undergoes less degradation and is hence better protected. 
     The results obtained in this test show therefore clearly that in the ease of the feed containing the premix according to the invention, the degradation in the rumen is decreased, which improves the digestibility of said feed. 
     Trial 2: effect on the somatic cells of milk 
     The test was carried firstly under farm conditions on a herd of 46 milking cows of initially excellent sanitary condition. Half the herd (control) received as feed a usual one, whereas the other half (trial) received a feed supplemented with the premix according to the invention, as it was described previously by way of example. After 6 weeks, the number of somatic cells of the control group was 113,000/ml of milk, whereas that of the control group fell to 99,900/ml of milk. 
     Another test was carried out on a herd of 50 milking cows of which the initial sanitary condition was average, and which had 395,000 somatic cells per ml of milk. After receiving a feed complemented with the premix according to the invention, this number decreased as follows: 
     
         ______________________________________After 1 week      305,000/ml of milkAfter 3 weeks     236,000/ml of milkAfter 5 weeks     219,000/ml of milkAfter 6 weeks     195,000/ml of milkAfter 7 weeks     128,000/ml of milk______________________________________ 
    
     The above results demonstrate clearly that the composition according to the invention makes it possible to reduce considerably the microbial catabolism. 
     Trial 3: effect on animal growth 
     This trial was carried out during 35 days under farm conditions on growing cattle. The trial was carried out on two groups of 20 animals, one of which (control group) received a standard feed and the other (trial group) received a feed complemented according to the invention as described by way of example above, in which the amount of active ingredient was approximately 100 mg per 3.3 kg of feed. 
     The results obtained are as follows: 
     
         ______________________________________            Control group                      Trial group______________________________________Average initial weight (kg)              185.7       185.1Average final weight (kg)              227.9       233.0Average daily weight increase (g)              1206        1369______________________________________ 
    
     The increase found in the growth (+13.5% on the average) can be explained by the improvement of the digestibility of the feed given, which is due to the incorporation of the composition according to the invention.
A composition designed for improving the digestibility of feed for ruminants contains as active ingredient an aromatic phenol derivative selected from cresols and benzenediols, as well as an absorbing support and an aromatizing mixture.