PHOSPHORUS CONCENTRATIONS IN BLOOD FECES, BONE AND SELECTED FLUIDS AND TISSUES OF GROWING HEIFERS AS AFFECTED BY DIETARY PHOSPHORUS

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1 PHOSPHORUS CONCENTRATIONS IN BLOOD FECES, BONE AND SELECTED FLUIDS AND TISSUES OF GROWING HEIFERS AS AFFECTED BY DIETARY PHOSPHORUS S.N. Williams, L.R. MeDowelt A.C. Warwick, N.S. Wilkinson and L A. Lawrence SUMMARY Effects of dietary P on concentrations of P in blood, feces, bone, saliva, rumen fluid, various tissues and hair of growing Angus heifers were evaluated. The duration of the experiment ranged from 525 to 772 days depending on slaughter date of individual animals. Initially, 14 weaned Angus heifers were fed ad libitum a low-p diet (.10% P. dry basis) for 270 days. Heifers were subsequently allotted randomly into two groups (seven animals/group) and received either.12% P (low P) or.20% P (high P) (dry basis). The experimental period was 245 days of the treatment phase for non-pregnant and the end point 3 weeks postpartum for pregnant heifers. Serum, plasma and whole blood P concentrations varied throughout the experiment but, generally, tended to reflect dietary P treatment groups. For the majority of the sampling periods, both treatment groups were able to maintain accepted normal serum and plasma P concentrations. Liver, kidney, heart, muscle, rumen fluid, feces and hair P levels proved insensitive for distinguishing between treatment groups. Saliva P concentrationwas related to treatment groups for both sampling periods. Rib bone P expressed as percent ash or milligram P/cm3 was greater (P <.05) for animals receiving higher dietary P. Of the parameters studied, bone P concentration best reflected dietary P intake. INTRODUCTION The importance and essentiality of P in ruminant diets worldwide is well established and is probably the nutrient, other than common salt, most frequently given as a supplement to grazing ruminants. Various criteria have been used as diagnostic aids in assessing the P status of grazing ruminants. The first known response to a dietary deficiency of P is a fall in the inorganic P fraction of blood plasma. Whole blood serum or plasma is widely used for studies in mineral nutrition, and since it is easily obtained from live animals, it is an ideal tissue for study. Phosphorus concentrations in saliva, bone, rumen fluid, feces and hair have been suggested as indicators of P status. However, a number of reports suggest limitations for P status evaluation from these types of samples. The purpose of the present study was to compare the influence of two dietary levels (.12 and.20%, DMB) of P in a long-term study on P concentrations in blood (serum, plasma and whole), bone, milk, saliva, rumen fluid, hair and selected body tissues. MATERIALS AND METHODS The experiment consisted of a P depletion phase (270 days), an adaptation period (10 days), and a P supplementation phase (ranging from 245 to 492 days in length; common

2 experimental endpoint was day 245 of P supplementation phase for nonpregnant and 3 weeks postpartum for pregnant heifers). Fourteen weaned Angus heifers, 7 to 8 months of age, 352 ± 66 lbs initially were housed under dry-lot conditions on concrete floors in a covered barn and allowed ad libitum intake of a low P diet (Table 1) during the 270 day P depletion phase. Animals were bled by jugular vein puncture four times during the depletion phase. In the supplementation phase of the experiment, heifers (averaging 462 ± 13.2 lb) were allotted randomly (7 animals/group) to one of two dietary levels of P; (1) continuation of low P (LP) basal diet containing.12% P (dry-matter basis, DMB), or (2) high P (HP) diet consisting of basal diet supplemented to provide.20% total P (DMB) (Table 1). Two heifers from both LP and HP groups were slaughtered on day 245 of the supplementation phase. The remaining pregnant heifers (5 per group; 10 total) were maintained until 3 weeks postpartum at which time they were slaughtered. Calving occurred between days 387 (birth of first calf) and 471 (birth of last calf) of the P supplementation phase. Heifers were sampled throughout the P supplementation phase. Samples collected included whole blood, serum and plasma for all collections. In addition to blood, samples included hair, rib bone, fecal grab samples, saliva, rumen fluid, liver, kidney, heart and longissimus muscle. RESULTS AND DISCUSSION Mean serum inorganic P concentration displayed a treatment by period interaction (P <.05) during the P supplementation phase (Table 2). Mean serum P concentrations were similar after 79 days for both levels of dietary P (i.e., 5.79 as 6.18 ma P/100 ml for LP and HP heifers, respectively); however, after 120 days of treatment, LP heifers blood serum inorganic P concentrations decreased to 2.33 vs 6.24 mg P/100 ml for the HP heifers. Blood serum inorganic P (as well as plasma inorganic P and whole blood P) levels during this sampling period agreed with rib bone biopsy P concentrations in ranking treatment groups by level of dietary P. However, by the final collection prior to parturition (day 294 of the P supplementation phase), both groups again exhibited similar serum, plasma and whole blood P concentrations (Table 2). Blood plasma inorganic P concentration followed a similar pattern as observed for serum inorganic P concentrations, except that values tended to be slightly lower than for serum (Table 2). Mean serum Ca concentration was different (P <.01) between treatment groups. However, all mean serum and plasma Ca values were within the normal range of 9 to 11 mg/100 ml for mature ruminants. Mean whole blood P hemoglobin and PCV concentrations were not affected by dietary P level (P>.10). Dietary P level had no effect (P >.10) on liver, kidney, heart or muscle P concentration at slaughter time (Table 3). P concentrations in ruminal and abomasal contents showed no treatment effect (P>.10); however, HP heifers had numerically greater P concentrations for both samples than LP heifers (.61 vs.49% and.49 vs 35% for ruminal and abomasal contents, respectively; Table 3). Mean rib bone, fecal, hair and saliva P concentrations are shown in Table 4. Rib P content (percent of ash) was greater (P <.05) in HP heifers, but no period effects were observed for this parameter (P >.10). When expressed as mg P/cm 3, HP heifers had

3 greater (P <.01) P content in rib cortical bone than LP heifers. Also, P content (mg/cm 3 ) increased (P<.01) from the first to the second collection. Fecal P levels were related to dietary P; however, no differences (P>.10) were observed over the three sampling periods. Problems associated with the use of fecal P concentrations to assess P status in ruminants include selective grazing behavior and plant species varying in P digestibility and availability. Also, large differences in feed intake may result in different total fecal output between P supplemented and unsupplemented groups, resulting in a difference in total mass of P excreted but with no apparent difference in % P in the sample. Dietary P level had no effect (P >.10) on hair P concentrations (Table 5). Saliva P levels were greater (P<.05) in HP than LP heifers (Table 4). Values reported herein are considerably higher than those reported by other researchers. This research was supported, in part, by the US Department of Agriculture under CSRS special grant Number 86-CRSR managed by the Caribbean Advisory Group (CBAG). TABLE 1. COMPOSITION OF BASAL DIETS FED DURING P DEPLETION AND SUPPLEMENTATION PHASE Amount a Ingredient Depletion phase Supplementation phase b Citrus pulp, % Cottonseed hulls, % Soybean hulls,% Coastal Bermuda hay, ground, and pelleted, % Cardboard paper, ground, % Cane molasses, % Animal fat, % Urea, % Mineral premix, % Vitamin A and D, % + + Total a Dry matter basis (DMB). b Monofos TM (International Mineral and Chemical Corp., Mundddn, IL) added to the basal diet at expense of cane molasses to achieve 20%total P in supplemented diet. Average P content of basal diet P content varied from.11 to.13% during course of supplementation phase, dry-matter basis.

4 TABLE 2. INFLUENCE OF DIETARY P LEVEL AND SAMPLING PERIOD ON BLOOD SERUM, PLASMA AND WHOLE BLOOD P AND CA CONCENTRATIONS,HEMOGLOBIN AND PACKED- CELLVOLUME-P SUPPLEMENTATION PHASE 5/10/84(249) Sampling period a 10/8/83(79) b 11/18/83(120) 1/22/84(186) 3/15/84(238) Item LP c HP c LP HP LP HP LP HP LP HP SEM d Blood serum P g,i,k Ca j Blood plasma P g,j,l Ca h Whole blood P h Ca i HB e (g/100 ml) i PCV f (%) i,l a Least square means are based on the following number of samples: serum, plasma, hemoglobin and packed-cell volume and 7 for LP and HP groups, respectively, for all periods except May 10,1984, which was based on 5 and 5 samples for LP and HP groups, respectively; whole blood and 7, 6 and 7, 7 and 7, 7 and 6, and 5 and 5 for LP and HP groups, respectively, for the five periods chronologically. b Day of P supplementaion phase. c LP (low P;.12% of P. dry matter basis); HP (high P; 20% P. dry matter basis). d Standard error of least square mean. e Hemoglobin. f Packed-cell volume. g Treatment effect (P<.01). h Quadratic period effect (P<.01). i Cubic period effect (P ~.01). j Cubic period effect (P<.05). k Treatment x period interaction (P<.05). l Treatment x period interact/on (P <.10).

5 TABLE 3. INFLUENCE OF DIETARY P LEVEL ON P CONCENTRATION IN SELECTED TISSUES, RUMINAL CONTENTS, ABOMASAL CONTENTS AND RUMEN FLUID Dietary P level a Item b,c,d LP HP SEM e Liver, % Kidney, % Heart, % Muscle, % Rumen contents, % Abomaml contents, % Rumen fluid. mg P/ml a LP (low P;.12% P. DMB); HP (high P;.20% P. DMB). b Ail values on a dry-matter basis, except rumen fluid tug P/ml). c Least square means are based on seven animals per treatment for all items, except for liver biopsy (7 and 6 for LP and HP groups, respectively), and ruminal and abomasal contents (5 and 5 for LP and HP groups, respectively). d Rumen fluid was obtained on day 294 of the P supplementation phase; all other items obtained at slaughter. e Standard error of least square means. TABLE 4. INFLUENCE OF DIETARY P LEVEL AND SAMPLING PERIOD ON RIB BONE, FECAL, HAIR AND SALIVA P CONCENTRATION Sampling period a 11/18/83 (120) b 3/15/84 (238) 5/10/84 (294) Item c LP d HP d LP HP LP HP SEM e Rib bone (% P in ash) f Rib bone (ma P/cm 3, fresh) g Feces (%P) Hair (mgp/g) Saliva f (mg P/100 ml) a Least square means are based on the following number of samples: feces- -7 and 5, 6 and 7, 5 and 5 for the LP and HP groups, respectively, for the three collections chronologically, respetively; hair - -6 and 7, 7 and 7, 5 and 5 for the LP and HP groups, respectively, for the three collections chronologically, respectively; saliva - -7 and 7, 5 and 5 for the LP and HP groups, respectively, for the two collections chronologically, respectively. b Day of P supplementation phase. c Feces and hair P concentrations are on dry-matter basis. d LP (low P;.12% P, DMB); HP (high P, 20% P, DMB). e Standard error of least square mean. f Treatment effect (P<.05). g Treatment and period effect (P<.01).