Phosphorus concentrations in blood, milk, feces, bone and selected fluids and tissues of growing heifers as affected by dietary phosphorus

Phosphorus concentrations in blood, milk, feces, bone and selected fluids and tissues of growing heifers as affected by dietary phosphorus

*University of Florida, Gainesville, FL 32611-0691, USA
**Roche Vitamins and Fine Chemicals 340 Kingsland St, Nutley, NJ 07110-1199, USA

Effects of dietary P on concentrations of P in blood, milk, 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 d depending on slaughter date of individual animals. Initially, 14 weaned Angus heifers were fed "ad libitum" a low-P diet (0.10% P, dry basis) for 270 d. Heifers were subse- quently allotted randomly into two groups (seven animals/group) and received either 0.12% P (low P) or 0.20% P (adequate P) (dry basis). The experimental period was 245 d of the treatment phase for non-pregnant and until 3 week postpartum for pregnant heifers.

Serum, plasma and whole blood P concentrations varied throughout the experiment but, generally, tended to reflect dietary P addition. 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. Dietary P level had no effect on P or Ca content of milk. Saliva P concentration was related to treatment groups for both sampling periods. Rib bone P expressed as percent ash or milligram P/cm³ was greater (P<0.05) for animals receiving higher dietary P. Of the parameters studied, bone P concentration best reflected dietary P intake.

The importance and essentiality of P in ruminant diets worldwide is well established and probably is the nutrient, other than common salt (NaCl), most frequently given as a supplement to grazing ruminants (McDowell 1985). 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 (Underwood 1981). Whole blood or blood serum or plasma is widely used for studies in mineral nutrition (McDowell 1985), and since it is easily obtained from live animals, it is an ideal tissue for study. Phosphorus concentrations in saliva (Clark et al 1973), bone (Williams et al 1990), rumen fluid (Cohen 1974), feces (Cohen 1980) and hair (Legel 1971) have been suggested as indicators of P status. However, a number of reports suggest limitations for P status evaluation from these types of samples (McDowell 1985; Williams 1987).

The purpose of the present study was to compare the influence of two dietary levels (0.12 and 0.20%, DM basis) of P in a long-term study on P concentrations in blood (serum, plasma and whole blood), milk, saliva, rumen fluid, hair and selected body tissues.

The experiment consisted of a P depletion phase (270 d), an adaptation period (10 d), and a P supplementation phase (ranging from 245 to 492 d in length; common experimental endpoint was day 245 of P supplementation phase for non-pregnant and 3 week postpartum for pregnant heifers).

Fourteen weaned Angus heifers, 7 to 8 months of age, weighing 160 ± 3 kg 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 d P depletion phase. Animals were bled by jugular vein puncture (Fick et al 1979) four times during the depletion phase.

Table 1: Composition of basal diets fed during P depletion and supplementation phases

	Amount (%) *
Ingredient			Depletion Phase		Supplementation Phase**

Citrus pulp		30.0		35.0
Cottonseed hulls		30.0		17.5
Soybean hulls				20.0
Coastal Bermuda Hay, ground, pelleted		15.5
Cardboard paper, ground		10.5		11.0
Cane molasses		10.0		10.0
Animal fat				2.5
Urea		2.0		2.0
Mineral premix		2.0		2.0
Vitamin A and D		+		+
Total		100.0		100.0

* Dry-matter basis (DMB)
** Monofos (International Mineral and Chemical Corporation, Mundelein, IL) added to the basal diet at expense of cane molasses to achieve 0.20% total P in supplemented diet.

In the P supplementation phase of the experiment, heifers (mean LW, 210±6 kg) were allotted randomly (7 animals/group) to one of two dietary levels of P: (1) continuation of low P (LP) basal diet containing 0.12% P (DM basis, DMB), or (2) adequate P (AP) diet consisting of basal diet supplemented to provide 0.20% total P (DMB) (Table 1). Basal diets fed during the course of the experiment were formulated to be low in P yet provide adequate energy, nitrogen, other minerals and vitamins to gain approximately 0.5 kg/d. Calcium-to-P ratios in the P supplementation phase ranged from 3.1:1 in the AP diet to 5.2:1 in the LP diet. Heifers were group fed ad libitum their respective treatment diets for the initial 210 d of the P supplementation phase. Feed intake then was restricted and animals were fed to maintain body condition.

Two heifers from both LP and AP groups were slaughtered on day 245 of the supplementation phase. The remaining pregnant heifers (5 per group; 10 total) were maintained until 3 week postpartum at which time they were slaughtered. Calving occurred between d 387 (birth of first calf) and 471 (birth of last calf) of the P supplementation phase. Blood samples were obtained from both heifers and calves at birth and 3 week postpartum. Colostrum samples were taken from heifers within the first 6 h after birth of calves. Milk samples also were collected 3 week postpartum. Two heifers that lost calves due to death were administered oxytocin and milked out by hand twice daily (0800 and 1700 h) until 3 week postpartum.

Heifers were sampled throughout the P supplementation phase for whole blood, serum and plasma. In addition to blood, samples included colostrum, milk, hair, rib bone, fecal grab samples, saliva, rumen fluid, liver, kidney, heart and longissimus muscle. Sample method preparation and analysis procedures have been reported (Fick et al 1979; Williams 1987), with inorganic P analyzed in serum, and plasma and total P for all other samples. Rib cortical bone biopsies were removed from the 12th rib of all animals (left side on d 120 and right side on d 294) using a 1.4 cm diameter trephine. Trephine depth was set to allow the sample collected to include both medial and lateral cortical bone of the intercostal appendage. The procedure for collection and treatment of bone biopsy samples has been described (Little and Shaw, 1979). Rumen and abomasal contents with fluid component were collected at slaughter by making a small incision through the respective compartments. Hair samples were obtained by clipping a 30 squared cm area of each heifer's left flank using electric shears. Rumen fluid was obtained with animals restrained in a squeeze chute via a stainless steel Frick speculum which was placed in the mouth through which a stomach tube was passed into the rumen. All samples, except hair, were stored frozen (-15 ?C) in plastic containers for subsequent chemical analysis. Hemoglobin (Hb) was determined colorimetrically and hematocrit (PCV) by a microhematocrit method.

Animal tissue, ruminal and abomasal contents and rumen fluid data were statistically analyzed using a completely randomized design. Data were analyzed by least squares ANOVA using the General Linear Model procedure (PROC GLM) of SAS (SAS 1982). Data collected from experimental animals on two or more occasions were analyzed using a split-plot design as is appropriate for repeated measures of animals, with nesting and cross-classification by least squares ANOVA using the GLM procedure (SAS 1982). Treatment effects were tested using animal-within-treatment mean square as an error term. Period and period x treatment effects were tested using the residual mean square as an error term.

Temporal trends were tested for blood data (linear, quadratic or cubic) as well as for hair and feces data (linear or quadratic). Time trends were not tested for data having only two collection periods (i.e., cow/calf, parturition/3 week postpartum, blood/milk parameters and saliva data); in these cases only comparisons between periods were made.

Average daily gain of heifers during the 270 d P depletion was 0.19 kg/d. Total gain (kg) and ADG (kg/d) were greater (P<0.01) for LP than AP heifers over the 210 d ad libitum feeding period of the P supplementation phase. The total gain and ADG values represent a 20% benefit to P supplemented heifers. The AP heifers consumed more feed (11%) and also tended to be more efficient (10%) than LP heifers.

Tables 2 and 3 contain mean values for blood serum, plasma, and whole blood P and Ca concentrations as well as hemoglobin (Hb) and packed-cell volume (PCV) values of heifers during the P depletion and supplementation phases, respectively. During the 270 d P depletion phase, blood serum inorganic P concentrations showed no temporal trend (P>0.10). Mean values ranged from 3.41 to 6.21 mg P/100ml (Table 2); however, the higher value was based on only four observations. Serum Ca concentration showed a cubic trend (P<0.05). Blood plasma P and Ca concentrations both exhibited cubic period effects (P<0.01) over the periods they were sampled during the P depletion phase. Calcium concentration showed a linear decrease (P<0.01) from day 180 to 222, while no significant period effect (P>0.10) was observed for whole blood P concentration.

Hemoglobin values were similar during all sampling periods of the P depletion phase and exhibited no time trends (P>0.10). Mean Hb values for periods ranged from 11.28 to 11.81 g/100ml (Table 2). Packed-cell volume (hematocrit) values fluctuated from 30.0 to 32.4 during the P depletion phase (cubic effect; P<0.10).

Blood inorganic P concentrations observed in heifers during the P depletion phase (Table 2) are lower than those reported by Little (1980) for cattle fed a similar dietary P level. Murray et al (1936) suggested that blood inorganic P levels, indicating P deficiency, are less than 3.8 mg/100ml serum in mature cattle and 5.3 mg P/100ml serum in young cattle.

No blood serum or plasma mineral concentrations were obtained in the period immediately prior to P supplementation. However, heifers could have been considered borderline P deficient during this time based on previously stated values in all but one sampling period (d 222); however, mean whole blood P concentration during this period (11.66 mg/100ml) was considerably lower than the 35 to 45 mg P/100ml whole blood reported by Rodgers (1975) as normal for cattle, yielding conflicting results to those obtained for blood serum and plasma inorganic P concentration.

Table 2: Blood parameters - P depletion phase*

	Day					SEM
Item	66**	124	180	222	264	***

	Serum, mg/100ml

P	4.13	4.02	3.41	6.21	3.99	0.223
Ca	10.27	10.03	12.15	11.14	12.59	0.195

	Plasma, mg/100ml

P	--	3.47	2.58	5.39	3.60	0.204
Ca	--	10.09	11.60	10.19	11.75	0.163

	Whole blood, mg/100ml

P	--	--	11.94	11.66	--	0.306
Ca	--	--	8.15	7.61	--	0.021

Hemoglobin, g/100ml	11.52	11.81	--	11.75	11.28	0.273

Packed-cell volume, %	31.7	30.0	--	32.4	31.5	0.69

* Least square means are based 7 to 14 samples per period.
** Day of P depletion phase.
*** Standard error of least square mean. Plasma Ca and P and serum Ca had cubic period effects (P<0.05), whole blood Ca had linear period effects (P<0.01).

Also complicating the use of blood inorganic P concentration in determining P status is the "adjustment" to low dietary P which leads to normal blood inorganic P concentration. Bone is mobilized to maintain a normal blood inorganic P level in P deficient animals; however, mobilization is not rapid (Duncan 1958); therefore, rapid changes in dietary P may be reflected in blood, whereas P deficiency, caused by prolonged low levels of dietary P, may be better detected by bone.

The usefulness of inorganic P in blood serum or plasma as an adequate criterion for assessing P status in ruminants is still in contention. Underwood (1981) concluded that serum inorganic P was a satisfactory criterion, whereas the NCMN (1973) does not recommend its use due to its great variation and the poor understanding of the factors that cause this variation. Some of these factors, which may increase blood inorganic P concentrations, include exercise or excitement (Eckles et al 1932; Gartner et al 1965) of cattle prior to bleeding, increased storage time or temperature post-sampling (Burdin and Howard 1963), water restriction (Rollinson and Bredon 1960) and time of sampling (Perge et al 1983).

Similar controversy over the use of whole blood P concentration as a P status indicator in ruminants also exists. Call et al (1978) have suggested that whole blood P concentration provides a more sensitive value for circulating levels of P on a high or low P diet, whereas Miller (1983) stated that total plasma P (i.e., inorganic P plus organically bound P) is not a very sensitive measure of P deficiency as the organically bound fraction is unavailable to the animal.

Table 3: Influence of dietary P on blood parameters*

								Packed
	mg/100ml						Hemo	cell
	Serum		Plasma		Whole Blood		globin	volume
	P***	Ca	P***	Ca	P	Ca	g/100ml	%

Day 79
LP**	5.8	9.9	3.7	11.2	10.5	8.6	15.6	36.4
AP**	6.2	10.3	3.9	11.8	11.1	8.3	15.5	33.6
Day 120
LP	2.3	11.1	2.0	11.1	10.6	7.1	14.1	39.8
AP	6.2	9.5	5.4	9.7	14.1	6.9	13.5	36.9
Day 186
LP	3.8	10.4	4.1	9.8	18.2	8.5	15.4	39.1
AP	4.8	8.8	5.1	8.3	15.3	6.9	15.6	40.1
Day 238
LP	5.0	8.7	4.8	8.3	10.3	6.8	14.9	37.9
AP	5.6	8.3	4.8	7.9	11.2	6.5	14.7	37.8
Day 294
LP	4.5	8.8	3.6	8.5	10.5	8.0	12.7	37.3
AP	4.7	8.6	4.2	8.0	9.9	7.3	14.1	39.1

SEM	0.29	0.21	0.21	0.21	0.93	0.23	0.35	0.70

* Least square means are based on five to seven samples.
** LP (low P; 0.12% P, DMB); AP (adequate P; 0.20% P, DMB).
*** Treatment effect (P<0.01), serum P had a treatment*period interaction (P<0.05).

Mean serum inorganic P concentration displayed a treatment-period interaction (P<0.05) during the P supplementation phase (Table 3). Mean serum P concentrations were similar after 79 d on treatment diets (i.e., 5.79 vs. 6.18 mg P/100ml for LP and AP heifers, respectively); however, after 120 d of treatment, LP heifer's blood serum inorganic P concentration decreased to 2.33 vs. 6.24 mg P/100ml for the AP heifers. Blood serum inorganic P (as well as plasma inorganic P and whole blood P) results during this sampling period agreed with rib bone biopsy P concentrations (Williams 1987) in ranking treatment groups as to level of dietary P. However, by the final collection prior to parturition (d 294 of the P supplementation phase), both groups again exhibited similar serum, plasma and whole blood P concentrations (Table 3).

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 3). Mean serum Ca concentration was different (P<0.01) between treatment groups and also showed a cubic period effect (P<0.01), whereas mean plasma Ca concentration exhibited no treatment effect (P>0.10) but did show a quadratic time response (P<0.01). All mean serum and plasma Ca values were within the normal range of 9 to 11 mg/100ml for mature ruminants (Underwood 1981).

Mean whole blood P concentration was not affected by dietary P level (P>0.10) but did show a quadratic time response (P<0.01). It is interesting to note that the mean whole blood P concentration of LP heifers was numerically greater than that of AP heifers on days 186 and 294 when both mean serum and plasma P concentrations of LP heifers were less than those of AP heifers (Table 3). Cubic time trends (P<0.01) were observed for whole blood Ca concentration during the P supplementation phase.

Hemoglobin displayed cubic time trends (P<0.01) but was not affected by dietary P level (P>0.10). Hemoglobin values of both LP and AP heifers during the P supplementation phase were numerically greater than those observed during the P depletion phase. Normal Hb values in adult cattle are reported to be approximately 12 to 13 g/100ml (Gutierrez et al 1971).

A treatment sampling period interaction (P<0.10) was observed for packed-cell volume. As with Hb, PCV values were numerically greater in the P supplement phase than in the P depletion phase. Gutierrez et al (1971) found PCV values around 37% to 40% in adult ruminants.

Even though great care was taken in obtaining all blood samples, considerable variation (tables 2 and 3) was observed with respect to P concentration in serum, plasma and whole blood. This would indicate that great care be taken when interpreting data as to P status in cattle when using any of these criteria as the sole indicator of P status.

Dietary P level had no affect (P>0.10) on liver, kidney, heart or muscle P concentration at slaughter time (Table 4). P concentrations in ruminal and abomasal contents showed no treatment effect (P>0.10); however, AP heifers had numerically greater P concentrations for both samples than LP heifers (0.61 vs. 0.49% and 0.49 vs. 0.35% for ruminal and abomasal contents, respectively; Table 4).

Table 4: Influence of dietary P level on P concentration of selected tissues, ruminal contents, abomasal contents and rumen fluid

	Dietary P level*
Item**	LP	AP	SEM***

Liver, % P	0.66	0.66	0.023
Kidney, % P	0.73	0.76	0.040
Heart, % P	0.80	0.73	0.030
Muscle, % P	0.50	0.44	0.041
Rumen contents, % P	0.49	0.61	0.064
Abomasal contents, % P	0.35	0.49	0.071
Rumen fluid, µg P/ml	272.6	274.9	57.10

* LP (low P; 0.12% P, DMB); AP (adequate P; 0.20% P, DMB).
** All values on a dry-matter basis, except rumen fluid (µg P/ml). Least square means are based on seven animals per treatment. Rumen fluid was obtained on day 294 of the P supplementation phase; all other items obtained at slaughter.
*** Standard error of least square means.

Dietary P level also had no effect (P>0.10) on rumen fluid P concentration (Table 4) in the present study. There was great variability between animals within treatment groups with respect to P concentration of rumen fluid. Values ranged in LP heifers from 61.6 to 413.4 g P/ml and from 104.5 to 525.9 g P/ml in AP heifers. Mean rumen fluid P concentrations reported herein are similar to those reported by Cohen (1980) of 150 and 183 mg P/l in heifers with low intakes of dietary P (5.0 and 15.3 g/d, respectively).

Mean rib bone, fecal, hair and saliva P concentrations are shown in Table 5. Rib P content (percent of ash) was greater (P<0.05) in AP heifers, but no period effects were observed for this variable (P>0.10). When expressed as mg P/ml, AP heifers had greater (P<0.01) P content in rib cortical bone than LP heifers. Also, P content [mg/ml] increased (P<0.01) from the first to the second collection. Little (1980) found that the expression of P content per unit volume of fresh bone, following determination of specific gravity, was more sensitive than the expression per unit weight of dry, fat-free bone. Little and Shaw (1979), in a study of rib bone P in grazing cattle, concluded that P levels around 120 mg/ml in the 12th rib indicate P deficiency while levels over 150 mg/ml indicate adequacy.

Fecal P levels were compared to dietary P; however, no differences (P>0.10) were observed over the three sampling periods. Clark et al (1973) indicated that since P homeostasis in ruminants is achieved to a great extent in the gastro-intestinal tract, by controlling secretion and reabsorption of salivary P, fecal losses should reflect intake or absorption. Cohen (1974) reported P intake of cattle may be estimated from regression equations of the intake of a specific feed source on total daily P excretion.

Problems associated with the use of fecal P concentrations to assess P status in ruminants include selective grazing behaviour and plant species varying in P digestibility and availability (Cohen 1974). Also, large differences in feed intake (Read et al 1986) 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. Fecal P concentrations in the present experiment are similar to those reported by others (Cohen 1974; Judkins et al 1985; Read et al 1986).

Table 5: Influence of dietary P level on various tissues*

	Rib bone
	% P in ash ***	fresh mg P/ml ****	Feces (% P)	Hair (µg P/g)	Saliva (mg P/100ml)

Day 120**
LP	16.5	123.0	0.39	152.3	--
AP	16.6	152.0	0.48	164.7	--
Day 238
LP	--	--	0.35	153.7	29.5
AP	--	--	0.52	154.0	35.3
Day 294
LP	16.8	157.0	0.39	170.5	25.4
AP	17.5	174.2	0.48	160.3	37.0
SEM	0.33	6.92	0.04	9.72	5.05

* Least square means are based on five to seven samples.
** Day of P supplementation phase. Feces and hair P concentrations are on dry-matter basis. LP (low P; 0.12% P, DMB); AP (adequate P, 0.20% P, DMB).
*** Treatment effect (P<0.05).
**** Treatment and period effect (P<0.01).

Dietary P level had no effect (P>0.10) on hair P concentrations (Table 5). The AP heifers showed a slight increase over the first two sampling periods; however, the reverse of this situation was observed during the third collection. The latter finding is inconsistent with blood serum and plasma P concentrations as well as P concentration of 12th rib bone biopsies (Williams 1987) obtained on the same sampling date. This apparently strengthens the conclusion of Cohen (1973) that hair P is not a satisfactory indicator of P status in cattle, in contrast to the findings of Legel (1971) who reported hair P concentration to be a suitable indicator of P status in ruminants.

Saliva P levels were greater (P<0.05) in AP than LP heifers (Table 5). Values reported here are considerably higher than those reported by Judkins et al (1985). Clark (1953) reported salivary P concentration of P-deficient animals to be approximately 50% that of animals supplemented with P. Judkins et al (1985) indicated that since P is cleared from blood in ruminants, primarily by the salivary glands, salivary P concentration may be indicative of blood levels and recycling. However, these authors suggested that salivary P concentration may not be a reliable indicator of P status due to variation in P concentration caused by varying amounts of saliva being secreted daily by cattle. Perge et al (1983) found wide variation in salivary P concentration as affected by dietary supply of Ca and P as well as time of sampling.

Tables 6 and 7 show cow and calf serum, plasma, and whole blood P and Ca concentrations as well as Hb and PCV values at day of birth and 3 week postpartum. Serum and plasma inorganic P concentrations were greater (P<0.01) in AP heifers at parturition and at 3 week postpartum (P<0.10) (Table 6). Serum and plasma concentrations were higher in the AP and LP groups 3 week postpartum than at parturition. Serum and plasma Ca concentrations were not affected by dietary P level (P>0.10); serum Ca decreased (P<0.10) 3 week postpartum, whereas plasma Ca was not affected by time of sampling (P>0.10). Both whole blood P and Ca showed treatment-sampling period interactions (P<0.10).

Table 6: Effect of dietary P on blood and milk parameters

	Parturition*		3 wk Postpartum*
Item	LP**	AP**	LP	AP	SEM

Blood serum (mg/100ml)
P***	2.91	4.74	4.05	5.05	.381
Ca	9.81	9.93	9.52	9.50	.170
Blood plasma (mg/100ml)
P***	2.28	4.18	3.55	4.61	.322
Ca	8.95	9.63	8.84	8.98	.280
Whole blood (mg/100ml)
P***	10.17	16.27	12.65	14.87	.983
Ca	6.73	8.05	7.86	7.31	.331
Hemoglobin (g/100ml)	12.9	11.4	12.1	12.1	.43
Milk (%, dry basis)
P	.88	1.01	.91	1.0	.060
Ca	.81	.92	1.08	1.10	.090

* Means based on five animals per treatment group.
** LP (low P; 0.12% P, DMB); AP (adequate P; .20% P, DMB).
*** Treatment effect (P<0.05). Period effect (P<0.05) was found for plasma P.

Whole blood P was more variable than serum or plasma inorganic P (Table 6), as standard errors of whole blood P are approximately threefold that of serum or plasma P assays. Hemoglobin was similar (P>0.05) in AP and LP heifers. Dietary P level had no effect on P or Ca content of colostrum or milk (DM basis) (P>0.10); however, AP heifers had a numerically greater P and Ca content in both fluids. Forar et al (1982) reported that milk inorganic P was not affected by dietary P or Ca but that it did decline as lactation proceeded and as milk yields decreased. Milk yield was not measured in the present experiment. When expressed on a DM basis, there also was no difference (P>0.10) between sampling periods in P content (i.e., similar content between colostrum and milk), whereas Ca content was greater (P<0.05) 3 week postpartum. Salih et al (1987) reported that P and Ca content of colostrum for Brahman cattle was greater (P<0.01) than that of milk samples collected 3 months postpartum.

Salih et al (1987), working with Brahman cattle, reported that serum Ca and P and PCV were higher at parturition than 3 months postpartum. This difference with respect to the present trial may be associated with the different time intervals involved in sample collection postpartum. Read et al (1986) reported results similar to those in the present trial.

Calf serum and plasma inorganic P concentrations were not affected by dietary P level of the dam (P>0.10; Table 7). Serum and plasma P concentrations increased (P<0.01) from day of birth to 3 week postpartum. Serum and plasma P concentrations at 3 week postpartum are typical of those reported as normal for young cattle (Underwood 1981).

Table 7: Influence of dietary P level on calf blood parameters*

	Day of Birth		3 wk Postpartum
Item	LP**	AP**	LP	AP	SEM

Blood Serum (mg/100ml)
P	4.92	5.18	7.39	8.14	.280
Ca	11.67	10.84	10.08	10.17	.461
Blood Plasma (mg/100ml)
P	4.25	3.85	6.78	6.98	.381
Ca***	10.60	9.55	9.67	9.72	.487
Whole Blood (mg/100ml)
P***	13.51	18.75	18.33	22.14	1.211
Ca	7.89	8.42	8.35	8.37	.219
Hemoglobin (g/100ml)	9.14	8.62	9.86	9.59	.458
Packed-cell volume, %	29.7	26.8	27.8	26.8	.97

* Least square means based on three to five samples.
** LP (low P; 0.12% P, DMB); AP (adequate P; 0.20% P, DMB).
*** Treatment effect (P<0.10). Period effects (P<0.10) were found for serum Ca, plasma P and whole blood P.

Serum and plasma Ca were affected conversely by diet and time. Serum Ca was not affected by dietary P level of the dam (P>0.10), but decreased (P<0.10) from day of birth to 3 week postpartum. Plasma Ca was not affected by sampling date (P>0.10) but was influenced by dietary P level of the dam (P<0.10; Table 7).

Calf whole blood P was affected by both dietary P level of the dam (P<0.01) and sampling period (P<0.05). There was no treatment- sampling date interaction for this variable (Table 7). The increasing P concentration patterns in the calf from day of birth to 3 week postpartum were similar for serum, plasma and whole blood. Calf whole blood Ca, hemoglobin and PCV were not affected by either dietary P level of dam (P>0.10) or sampling period (P>0.10).

Blood, saliva and rib bone P concentrations reflected dietary P additions, while liver, kidney, heart, muscle, rumen fluid, feces and hair proved insensitive for distinguishing between treatment groups. Of the variables studied, bone P concentration best reflected dietary P intake.

Florida Agricultural Experiment Station, Journal Series No. 9205. This research was supported in part by the U.S. Department of Agriculture under CSRC special grant No. 86-CRSR-2-2843 managed by the Caribbean Advisory Group (CBAG)

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