Table 2. Trial results Cncentratin f Captan,ppm liem 0 160 320 640 Dry matter digestibility (%) Ruminal 65.1 72.8 69.4 74.3 Ttal 82.1 81.9 82.4 82.0 Starch digestin (%) Ruminal 87.7 93.6 89.3 92.2 N digestibility 74.8 72.1 77.3 74.8 Nn-ammnia nitrgen Ruminalutflw, g/day 142.1b 132.8ab 126.7ab 110.6a Ruminal ammnia, mg/dl 3.4 3.6 4.3 2.5 Nitrgen retentin, g/day 45.2 47.8 50.4 49.2 Urine vlume, liter 25.2 27.7 26.8 27.4 Abmasal passage Liquids, liter/day 66.4 80.8 80.8 75.2 Organic matter, g/day 1316 968 1136 947 Starch, g/day 306 138 256 183 abmeans in a rw with different superscripts differ significantly (P<.05). Ruminal Availability f Phsphrus and Its Effect n Digestin K. E. Witt and F. N. Owens Stry in Brief The phsphrus cncentratin in ruminal fluid was determined fr steers limit-fed ratins with phsphrus cncentratins ranging frm.06 t.17 percent. Ruminal phsphrus cncentratin was increased with phsphrus intake at dietary cncentratins belw.12 percent fr steers. This relatinship was emplyed t estimate the ruminal availability f phsphrus frm fur phsphrus surces. Cmpared with sdium phsphate, assumed t have a ruminal phsphrus a\'ailability f I00 percent, a 21-percent phsphrus mn-dical, an 18.5-percent phsphrus mn-dical, and a deflurinated rck phsphate were fund t be 59, 42 and 28 percent as available in the rumen. Phsphrus slubility in slutins buttered at ph 5, 6 and 7 paralleled the apparent availability in the rumen. Lw ruminal dietary phsphrus did nt reduce ttal tract r ruminal digestibility greatly, hwe\'er, suggesting that ruminal cncentratins abve 210 mg per liter are adequate fr micrbial digestin in the rumen. Intrductin Phsphrus in the frm f sme inrganic phsphrus supplement is added t mst livestck ratins t help meet the requirement f animals. \\'ith noli-ruminant animals, the phsphrus requirement is ften assessed by feeding trials and grwth measurements. Ruminants require phsphrus bth fr grwth f tissue and bne, as well as multiplicatin f micrrganisms within the rumen. Phsphrus a\'ailability, 1981 Animal Science Research Reprt 151
thereby, becmes imprtant at tw sites fr the ruminant. Rate f grwth f bacteria and rate f digestin f feed cmpnents within the rumen may be limited by phsphrus supply. Thrugh reduced micrbial activity, a deficiency f phsphrus may precipitate deficiencies f energy r prtein. This cncept is supprted by the bservatin that lss f appetite is ne f the first clinical signs f a phsphrus deficiency in ruminants. Tw added factrs in phsphrus metablism are peculiar t ruminant animals. First, ruminal phytase liberates bund phytin phsphate. Phytin phsphate is f lw availability fr nn-ruminant animals. Secndly, pancreatic ribnuclease is secreted int the small intestine f ruminant animals in large amunts. Ribnuclease will liberate phsphrus frm nucleic acids fr recycling t the rumen via saliva. Ruminal micrbes btain needed phsphrus frm rumina I fluid and frm feedstuffs being digested. Phsphrus in ruminal fluid is derived frm slubilized r degraded feed ingredients as well as frm recycling t the rumen. Little infrmatin has been published n ruminal phsphrus cncentratins and ruminal availability f varius phsphrus surces. Therefre, these trials were designed I) t determine if ruminal phsphrus cncentratin was linearly related t phsphrus intake s that it might be used t evaluate ruminal availability f phsphrus frm \'arius phsphrus surces, 2) t estimate ruminal availability f \"arius phsphrus surces fr mature cattle, 3) t measure slubility f phsphrus surces in a buffer slutin as influenced by ph and time and 4) t determine if lw dietary phsphrus le\"els decrease digcstin in the rumen r the ttal digesti\'e tract. Standard curve Materials and Methds Six mature ruminally cannulated Herefrd steers (1122 Ib) were indi\"idually fed 7.1 Ib f a basal ratin (Table I) twice daily. Sdium phsphate was added as the standard phsphrus surce t prm"ide ratin phsphrus cncentratins f.068,.123 and.173 percent. After a fin-day adaptatin perid, a ruminal fluid sample was cllected via ruminal cannula fr analysis f inrganic phsphrus cncentratin. The line relating ruminal phsphrus cncentratin t ratin phsphrus cncentratin was used t determine the relative ruminal a\'ailability f varius phsphrus surces fed in the a\"ailability trial. Rumina} availability f phsphrus surces Steers used in the standard cu[\"e trial were individually fed 13.9 Ib per day f a basal ratin (Table I) supplemented with phsphrus frm sdium phsphate (a Table 1. Basal ratin cmpsitin Trial Steer Steer Steer liem stdcurve avail. digestibility % f ratin ---------------- Cttnseed hulls ~~ ~O n.9 Supplement 3~ 3~ 22.1 ------------------------------------------------ Dehy cane mlasses 0 0 Urea 1.6 1.6 TM salt.5.5 CaC3.07.07 P surce + NaHC03.85.85 Vitamins A & D + + 20.1 1.1.5.44 + 152 Oklahma Agricultural Experiment Statin
standard surce), a mn-dicalcium phsphate with 21 percent phsphrus', a mndicalcium phsphate with 18.5 percent phsphrus2, r a deflurinated rck phsphate with 18 percent phsphrus3 (Table 2). Steers were fed twice daily fr a fh'e-day adaptatin perid. On day six, a ruminal fluid sample was cllected via ruminal cannula and analyzed fr inrganic phsphrus cncentratin. Relative ruminal availability f the varius surces f phsphrus was calculated by relating ruminal phsphrus cncentratins t the standard curve fr sdium phsphate generated in the previus trial. In vitr slubility f phsphrus surces Each f the fur phsphrus surces was incubated in Ohi buffer at a ph f5, 6 r 7. Samples were taken at 30 minutes, I, 2 and 3 hurs. Samples were analyzed fr inrganic phsphrus, and slubilities relative t the standard (sdium phsphate) were calculated. Phsphrus and ruminal digestin Fur Herefrd-Brwn Swiss and tw Herefrd-Angus steers (1527 Ib) hused in metablism stalls were individually fed at maintenance based n bdy weight, a basal ratin (Table I) cntaining.118 percent phsphrus r supplemented with sdium phsphate t achieve a phsphrus le\'el f.227 percent in the ratin. After a se\"cn-day ratin adaptatin perid, ttal feces were cllected fr five days. On the fifth day f the cllectin perid, ruminal fluid samples were btained, and nyln bags cntaining grund crn, cttnseed hulls r cttn duck strips were incubated in the rumen fr a 24 hur perid. Ruminal fluid and fecal samples were analyzed fr inrganic phsphrus. ~yln bags and cttn duck strips were thrughly washed, dried, and weighed t determine disappearance rate f dry matter. Standard curve Results and Discussin Cattle fed diets with sdium phsphate added t btain.068,.123 and.173 percent phsphrus had ruminal phsphrus cncentratins f 264, 406 and 434 mg phsphrus per liter f ruminal fluid (Figure I). The higher level f phsphrus additin increased ruminal phsphrus nly slightly, suggesting that cncentratin may have begun t plateau. Table 2. Supplement cmpsitin Phs.surce Steer std ----.-----.43.85 % f ratin.85 Trial ---steeravail.a ------------------- Na2HP04'7H20 Na2HP04 21%Pdical - - - -.47 18.5%P dical - - - - -.54 Deflur.P - - - - - -.55 NaHC03.85.42 0 0.38.31.30 0 Steerdlg.1i.44 aadded t urea, limestne, trace mineralized salt and vitamin mix t frm the ttal supplement. badded t dehydrated cane mlasses. urea. trace mineralized salt and vitamin mix t frm the ttal supplement. IOccid('ntaJ Chl'mical C.. HuslOn. Texas 21ntl"rnatin.tl ~lin('rals ;,wd Chemical Crp.. ~Iundclt"in. Illinis. JBrdt'n Ch«"mical,Brdl'n In('"..~rti)lk. \'ir~inia. 1981 Animal Science Research Reprt 153
Rumina} availability f phsphrus surces Sdium phsphate, 21 percent phsphrus mn-dical, 18.5 percent phsphrus mn-dical r deflurinated rck phsphate were added t a basal ratin (.067 percent phsphrus) t increase the phsphrus level t apprximately.17 percent. Ruminal fluid phsphrus cncentratins f the three cmmercial surces were cmpared with the sdium phsphate standard curve fr steers (Figure I). Estimates fr ruminal availability relative t sdium phsphate at 100 percent were 59.3 percent fr 21 percent phsphrus mn-dical, 42.2 percent fr 18.5 percent phsphrus mn-dical, and 28.4 percent fr deflurinated rck phsphate. Ratin and ruminal fluid phsphrus cncentratins fr the three phsphrus surces are presented in Table 3. 500 er::: LLJ f- -I I '- (.!:) T / I 400 -I LL -I «z :E er::: = 300 (/) er::: 0 = a... (/) 0= a... 200 Y = 89.8 + 2563X ~ L _.1.05.10.15 PHOSPHORUS,% RATION Figure 1. Ruminalfluid phsphrus cncentratins in steers vs. phsphrus intake 154 Oklahma Agricultural Experiment Statin
In vitr slubility f phsphrus surces Phsphrus surces differed (P<.OI) in slubility. Sdium phsphate was virtually all sluble in the buffer slutin, while the 21 percent phsphrus mn-dical was mre sluble (46.4 percent) than 18.5 percent phsphrus mn-dical (28.8 percent). Def10urinated rck phsphate was virtually insluble (2.5 percent, Figure 2). This rder f slubility fr the fur phsphrus surces is identical t the rder f ruminal availability (Figure 3). 500 400 cr: l.1.j f- -.J.. 300, (.I) => cr: c::> = a... (.I) c::> =a... 200r """'------ 21% P MONO-DICAL I 100 18.5% P MONO-DICAL DEFLUORI NATED 5.0 6,0 ph Figure 2. Effect f ph phsphrus slubility 7.0 ROCK PHOSPHATE 1981 Animal Science Research Reprt 155
60. 21% P MONO-OICAL ~- 40 0. 18.5% P MONO-OICAL ~...J a::i ~ < ><...J :2 z: ::I 0: W > I- <...J W 0: 0. LINEAR REGRESSION. 0 20 I-DEFLUORINATED CURVILINEAR REGRESSION '". ROCK PHOSPHATE 20 40 60 PHOSPHORUS SOLUBILITY IN BUFFER, % Figure 3. Ruminal availability vs. buffer slubility The standard sdium phsphate was mre sluble at ph 5 and 7 than at ph 6. Bth mn-dicalcium phsphates exhibited increased slubility at lwer ph values. Deflurinated rck phsphate was virtually insluble at all ph levels. O\'er 90 percent f the phsphrus ultimately fund in slutin was in slutin within tw minutes. Results indicate that phsphrus frm cmmercial inrganic phsphrus surces may be mre available in the rumen at lwer ruminal ph values. The limited slubility f rck phsphate may need t be cnsidered when using it as a supplemental surce f p~sphrus, if lw ruminal phsphrus levels reduce digestin. Phsphrus and ruminal digestin Sme wrkers have indicated that cellulse digestin and cell grwth by ruminal micrbes decrease when ruminal phsphrus is lw. Hwever, the ruminal requirement fr phsphrus has nt been quantitated. The dietary phsphrus requirement fr maintaining beef cattle is listed as.18 percent f the dry ratin (~RC Beef Cattle, 1976). In this study, ratins cntaining phsphrus at levels f.119 percent and.227 156 Oklahma Agricultural Experiment Statin
Table 3. Calculatin f ruminal availability f phsphrus surces Phsphrus Phsphrus Rumlnll Rumlnll Rumlnll surce BaSIlratin Added phsphrus 1 lliablll~ IVllllbUttyb % % mg/1 % % Na2HP04'7H20.067.0560 406 I 26 100 100 Na2HP04'7H20.067.1060 434 I 14 100 100 21% P dical.067.0885 397 I 16 59.3 57.1 18.5% P dical.067.1038 375 I 25 42.2 37.6 Deflur. P.067.1000 336 I 14 28.4 23.0 Nne.067.0000 264 I 15 "Calculated frm linear standard curve as fllws: Availability = 100 X Availability P Added P % 100 X (Ruminal P - 264)/142 X.056 Added P% bcalculated frm curvilinear standard curve. Table 4. Effect f phsphrus level n ruminal and ttal-tract digestibility Phsphrus In ratin liem.119%.227% Dry matter intake, g/day Phsphrus intake, g/day Fecal utput, g/day Fecal phsphrus, % Phsphrus retentin, g/day Dry matter digestibility, % Organic matter digestibility, % Ruminal phsphrus mg/liter Ruminal disappearance per day Cttnseed hulls, % Cttn duck, % Grund crn grain, % abmeans in a rw with different superscripts differ significantly (P<.01). 8025 8075 9.5a 18.3b 2857.0 2693.7.307.369 1.0a 8.3b 64.8 67.0 64.8 66.9 208.1a 398.1b 8.3 22.5 42.2 8.2 23.2 41.0 percent were fed t determine whether a phsphrus-deficient ratin and lw ruminal phsphrus wuld alter ruminal and ttal-tract digestibility. The lw-phsphrus ratin reduced daily phsphrus retentin and phsphrus cncentratin in ruminal fluid (Table 4). Hwe\'er, differences in dry matter digestibility r rganic matter digestibility fr the tw ratins were \'ery small. Ruminal digestin als appeared similar fr the cattle fed the tw ratins. Since n relatinship was detected, this implies that a ruminal phsphrus cncentratin f 210 mg per liter is adequate fr digestin, thugh inadequate fr maximum phsphrus retentin. This suggests that a\'ailability f phsphrus in the rumen is less imprtant than a\'ailability f phsphrus in the ttal digesti\'e tract. Cnsequently. phsphrus slubility at the acidic cnditins f the abmasum may be mre indicati\'e f the \"alue f phsphrus t ruminants than wuld be phsphrus slubility at the ruminal ph r ruminal phsphrus cncentratin. 1981 Animal Science Research Reprt 157