Abstract:
Thyrotropin Releasing Hormone (TRH) and related synthetic peptides extend the rapid growth phase of poultry thereby decreasing the time required to produce fowl of marketable size.

Description:
BACKGROUND OF THE INVENTION 
     This invention is concerned with the use of thyrotropin releasing hormone (TRH) or a related tripeptide as a growth promotant for poultry. 
     The United States broiler chicken industry has been quite successful in providing high protein meat at relatively low cost to the consumer. Nonetheless it is always striving to improve the efficiency of its operations to make the industry more profitable and/or decrease the market cost of the product. There are several factors that can be explored toward this end such as improving feed efficiency, and one very important factor, the length of time required to produce a marketable bird from a chick. Clearly the shorter the time the better. 
     At present, broiler chickens in the United States grow at their maximum exponential rate until they are about 4 weeks of age and their growth rate progressively decreases thereafter. Since chickens are usually slaughtered at 6 to 8 weeks of age their rate of growth during the final weeks is less than maximum. Thus one way of promoting the growth of broiler chickens would be to manipulate their endocrine system so that the period of most rapid growth is prolonged. Such a growth promotant would increase the growth rate of chickens older than approximately four weeks and would thereby decrease the time required to produce a bird of marketable weight. 
     Other growth promotants have been used in efforts to reduce the time of maturation of poultry such as certain antibiotics including bacitracin and tylosin with the usual onus that attaches to the use of antibiotics for such purposes. However, the industry has never had access to an endocrine mediated growth promotant and especially one devoid of safety problems. 
     Other commercial fowl production, although not on the same scale as the broiler industry would also benefit from the same improvements in efficiency. 
     Now, with the present invention, there is provided a method of promoting the growth of poultry. This method comprises the administration of TRH or a related tripeptide to poultry starting at about the time when their initial rapid growth rate begins to decrease and continuing until the desired final weight is attained. In the case of broiler chickens administration would normally begin at about 4 weeks of age and would continue until 6-8 weeks of age. 
     DETAILED DESCRIPTION OF THE INVENTION 
     This invention is concerned with the use of TRH and related tripeptides as endocrine mediated growth promotants for poultry such as chickens, and even more especially broiler chickens. 
     The tripeptides useful in the novel method of treatment and novel formulations of this invention are of formula: 
     
         M.sub.1 --M.sub.2 --M.sub.3 
    
     or a pharmaceutically acceptable salt thereof, 
     wherein: 
     M 1  is L-pyroglutamyl (Glp), L-cycloserinyl (CSer), L-cyclothreoninyl, (CThr), N-formyl-L-proline (HCO-Pro), L-Glutamic acid-5-methyl ester (Glu(OMe)), L-Proline (Pro), L-2-Ketopiperidine-6-carbonyl (Kpc), D-2-ketopiperidine-6-carbonyl (D-Kpc), or L-2-ketoimidazolidine-4-carbonyl (Kic) 
     M 2  is L-histidyl (His), D-histidyl (D-His), L-leucine (Leu), L-α-methylhistidine (MeHis), L-phenylalanine (Phe), L-β-(pyrazolyl-1)alanine (Pyr(1)ala), L-β-(thienyl-2)alanine (Thi), L-im-N-methylhistidine (His(N Me)). L-β-(pyrazolyl-3)alanine (Pyr(3)ala), L-methionine (Met), or L-im-N (CH 2  COOH)histidine (His(N CH 2  COOH), and, 
     M 3  is L-prolinamide (Pro-NH 2 ), N-(6-aminohexyl)-L-prolinamide (Pro-NH(CH 2 ) 6  NH 2 ), 2-methyl-L-alaninamide (MeAla-NH 2 ), N-methyl-L-prolinamide (Pro-NHMe), N-ethyl-L-prolinamide (Pro-NHEt), L-prolylglycinamide (Pro-Gly-NH 2 ), L-azetedinecarboxylic acid amide (Azet), L-prolyl-L-alaninamide (Pro-Ala NH 2 ), N-hexyl-L-prolylamide (Pr-NH(CH 2 ) 6  Me), N-cyclohexyl-L-prolinamide (Pro-NH-cyclohexyl), L-thiazolidine-4-carboxamide (Tca-NH 2 ), L-piperidine-2-carboxamide (Pc-NH 2 , or Methyl L-piperidine-2-carboxylate (Pc-OMe), 
     A preferred group of compounds includes the following: 
     (1) Glp--His--Pro--NH 2  (TRH) 
     (2) Glp--His(N Me)--Pro--NH 2   
     (3) Glp--MeHis--Pro--NH 2   
     (4) Glp--Pyr(1)ala--Pro--NH 2   
     (5) Glp--His--Pro--Gly--NH 2   
     (6) Glp--Thi--Pro--NH 2   
     (7) Kpc--His--Tca--NH 2   
     (8) Kpc--His--Pro--NH 2   
     (9) Glp--His--Pc--NH 2   
     Of particular importance in the novel method of treatment is TRH with the systematic name as given above and the following chemical structure: ##STR1## 
     The novel method of treatment of this invention comprises the administration of an effective amount of one or more of the active tripeptides, previously defined, to poultry such as chickens, turkeys, geese or ducks, preferably chickens, starting at about the time when the initial exponential growth rate begins to decline and continuing until the desired body weight is attained. In the case of broiler chickens administration of active tripeptide would generally start at about 4 weeks of age and would continue until 6 to 8 weeks of age. 
    
    
     It is preferred that the active agent be administered daily, preferably but not necessarily in a single dose, during the treatment period. An effective amount of growth promotant is about 1 to 10 μg/day. The route of administration is by injection. 
     EXAMPLE 1 
     The Effect of Thyrotropin Releasing Hormone on Growth in 4-Week-Old Male Chicks 
     Materials and Methods 
     Four-week-old Hubbard x Hubbard cockerels were used in this experiment, and average initial weights were 841.75 g. Synthetic TRH (Beckman Co., Calif.) was dissolved in saline and given daily by intravenous injection via the brachial vein at 0.1 μg/bird, 1.0 μg/bird, and 10.0 μg/bird. Birds were weighed and feed consumption was measured at 2 times a week for 21/2 weeks. Data were analyzed by least squares analyses of variance, using initial weight as a covariant. 
     Results 
     Fourteen and 17 days after the start of treatment, TRH given at 1.0 μg/bird/day and 10 μg/bird/day increased body weight significantly compared with birds receiving saline injections, . . . and birds that were receiving TRH injections at 0.1 μg/bird/day showed slight increase in the body weight (Table I). In terms of body weight gain, birds that are receiving 1.0 μg/bird/day and 10 μg/bird/day also showed a significant increase (P 0.01) as compared with control 14 and 17 days after the start of treatment. At the end of the experiment (17 days after treatment), TRH given at 1.0 μg/bird/day and 10 μg/bird/day showed a 12.0% and 12.4% increase in body weight gain as compared with the control birds (Table II). 
     
                                           TABLE I__________________________________________________________________________EFFECTS OF THYROTROPIN RELEASING HORMONE (TRH) ON BODY WEIGHT IN4-WEEK-OLD COCKERELS.        Days After Start of TreatmentTreatment N  0  3.sup.a                  7.sup.a                         10.sup.a                                14.sup.a                                        17.sup.a__________________________________________________________________________Control   9  845.0           1008.3 ± 9.1                  1211.9 ± 13.8                         1377.1 ± 18.5                                1597.8 ± 23.2                                        1761.5 ± 26.0TRH (0.1 μg/bird)     8  837.0           1009.3 ± 9.7                  1230.6 ± 14.7                         1406.9 ± 19.7                                1662.1 ± 24.8                                        1837.1 ± 27.8           (+0.1) (+1.5) (+2.2) (+4.0)  (+3.9)TRH (1.0 μg/bird)     8  840.0           1011.8 ± 9.7                  1246.7 ± 14.6                         1420.5 ± 19.6                                1693.7 ± 24.6*                                        1878.8 ± 27.6*           (+0.3) (+2.9) (+3.2) (+6.0)  (+6.3)TRH (10 μg/bird)     10 845.0           1019.2 ± 8.7                  1236.9 ± 13.1                         1421.6 ± 17.6                                1690.8 ± 22.0*                                        1882.5 ± 24.7*           (+1.1) (+2.1) (+3.2) (+5.8)  (+6.5)__________________________________________________________________________ .sup.a Least squares mean ± Standard error of the mean corrected by initial weight. () Percent increased as compared with control. *P &lt; 0.01 
    
     
                                           TABLE II__________________________________________________________________________EFFECTS OF TRH ON BODY WEIGHT GAIN IN 4-WEEK-OLD COCKERELS.     Days After Start of TreatmentTreatment N  3     7      10     14     17__________________________________________________________________________Control   9  170.7 ± 9.1              374.3 ± 13.8                     539.5 ± 18.5                            757.0 ± 23.4                                   929.9 ± 26.0TRH (0.1 μg/bird)     8  171.7 ± 9.8              393.1 ± 14.7                     569.4 ± 19.7                            824.3 ± 24.9                                   999.5 ± 27.8        (+0.6)              (+5.0) (+5.5) (+8.9) (+7.5)TRH (1.0 μg/bird)     8  174.2 ± 9.7              409.2 ± 14.6                     582.9 ± 19.6                            856.2 ± 24.8*                                   1041.2 ± 27.6*                                   -  (+2.1) (+9.3) (+8.0) (+13.1) (+                                   12.0)TRH (10 μg/bird)     10 181.6 ± 8.7              399.3 ± 13.1                     584.0 ± 7.6                            853.3 ± 22.2*                                   1044.9 ± 24.7*        (+6.4)              (+6.7) (+8.2) (+12.7)                                   (+12.4)__________________________________________________________________________ () Percent increased as compared with control. *P &lt; 0.01 
    
     EXAMPLE 2 
     The Effect of Thyrotropin Releasing Hormone On Growth In 4-Week-Old Male Chicks 
     Materials &amp; Methods 
     Four-week-old Hubbard×Hubbard cockerels were used in this experiment, and average weight was 831.38 g. Synthetic TRH (Beckman Co., CA) was dissolved in saline and given daily by intravenous injection via the brachial vein at 0.1 μg/bird, 1.0 μg/bird, and 10 μg/ bird. Birds were weighed twice a week for 4 weeks. Data were analyzed by least squares of variance, using initial weight as a covariant. 
     Results 
     TRH given at 1.0 μg/bird/day showed a significant increase in body weight as compared with birds that were receiving saline injections on 22 (p 0.05) and 25 (p 0.025) days after the start of treatment, and birds that were receiving TRH injections at 0.1 μg/bird/day and 10 μg/bird/day showed slight increase in body weight (Table III). In terms of body weight gain, similar data were also obtained. Birds that were receiving TRH injections at 1.0 μg/bird/day showed a significant increase as compared with control birds on 22 (p 0.05) and 25 (p 0.025) days after the start of treatment. At the end of the experiment, TRH given at 0.1 μg/bird/day and 1.0 μg/bird/day showed a 5.6% and 7.5% increase in body weight gain as compared with the control birds. Birds that were given 10 μg/bird/day showed slight increase in body weight gain throughout the whole experiment (Table IV). 
     
                                           TABLE III__________________________________________________________________________EFFECTS OF THYROTROPIN RELEASING HORMONE (TRH) ON BODY WEIGHT IN4-WEEK-OLD COCKERELS  No.     Days After Start of TreatmentTreatment  Birds0      4      8      11     15     18      22      25__________________________________________________________________________Control  8822.5       990.6 ± 8.3             1219.5 ± 15.1                    1387.1 ± 20.3                           1620.7 ± 20.4                                  1796.9 ± 24.3                                          2010.3 ± 26.4                                                  2194.0 ± 28.7TRH (low)  8831.7      1012.2 ± 8.3             1248 ± 15.0                    1426.4 ± 20.3                           1664.2 ± 20.4                                  1856.9 ± 24.2.sup.a                                          2084.7 ± 26.3.sup.a                                                  2269.3 ±                                                  28.7.sup.a0.1 μg/bird      (+2.2) (+2.4) (+2.8) (+2.7) (+3.3)  (3.7)   (3.4)TRH (med.)  9835.6      1010.3 ± 7.8             1254.1 ± 14.2                    1415.4 ± 19.1                           1664.4 ± 19.2                                  1860.1 ± 22.8.sup.a                                          2091.7 ± 24.8.sup.b                                                  2294.4 ±                                                  27.0.sup.c1.0 μg/bird      (+2.0) (+2.8) (+2.0) (+2.7) (+3.5)  (4.1)   (4.6)TRH (high)  8831.7       997.7 ± 8.3             1219.1 ±  15.0                    1381.7 ± 20.3                           1627.6 ± 20.4                                  1821.6 ± 24.2                                          2034.4 ± 26.3                                                  2232.1 ± 28.710 μg/bird      (0.7)  (0)    (0)    (0.4)  (1.4)   (1.2)   (1.7)__________________________________________________________________________ Least squares mean ± standard error of the mean corrected by initial weight. (Δ) = Percent increased as compared with .sup.a = p &lt; 0.1 .sup.b = p &lt; 0.05 .sup.c = p &lt; 0.025 
    
     
                                           TABLE IV__________________________________________________________________________EFFECTS OF TRH ON BODY WEIGHT GAIN IN 4-WEEK-OLD COCKERELS   No.      Days After Start of TreatmentTreatment   Birds      4      8      11     15     18      22      25__________________________________________________________________________Control 8  149.4 ± 8.4             378.2 ± 15.1                    546.1 ± 20.5                           779.5 ± 20.5                                  955.6 ± 24.4                                          1169.0 ± 26.4                                                  1351.8 ± 28.7TRH (low)   8  167.1 ± 8.4             407.6 ± 15.1                    585.1 ± 20.5                           822.9 ± 20.4                                  1015.8 ± 24.3.sup.a                                          1243.5 ± 26.3.sup.a                                                  1428.1 ±                                                  28.7.sup.a0.1 μg/ (11.8) (7.8)  (7.0)  (5.6)  (6.3)   (6.4)   (5.6)TRH (med.)   9  170.1 ± 7.9             413.4 ± 14.2                    573.1 ± 19.3                           823.2 ± 19.2                                  1018.9 ± 22.9.sup.a                                          1250.5 ± 24.8.sup.b                                                  1453.2 ±                                                  27.0.sup.c1.0 μg/ (13.9) (9.3)  (4.5)  (5.7)  (6.6)   (7.0)   (7.5)TRH (high)   8  156.3 ± 8.4             377.9 ± 15.1                    542.9 ± 20.5                           786.4 ± 20.4                                  981.5 ± 24.3                                          1193.2 ± 26.3                                                  1390.9 ± 28.710 μg/bird      (4.6)  (0)    (0)    (0.9)  (2.7)   (2.1)   (2.9)__________________________________________________________________________ (Δ) = Percent increase as compared with .sup.a = p &lt; 0.1 .sup.b = p &lt; 0.05 .sup.c = p&lt;0.025