Experiments were carried out to study the effects of dietary P depletion on plasma concentrations of inorganic P (P|), calcium, l,25-(OH) 2 -Vit.D 3 and alkaline phosphatase, and to investigate the effects of P depletion, in comparison with P repletion, on intestinal flow and net disappearance of Ca and P in sheep. The animals were adapted to an experimental diet of pellets and chopped straw providing between 0-91 and 1-04 g P/day for depletion. They were repleted by single infusions of phosphate into the duodenum raising total P supply to about 4-1 g/day. During P depletion plasma P, concentrations decreased significantly whereas those of Ca increased. The development of hypercalcaemia is discussed with respect to intestinal absorption and bone accretion and resorption. Plasma l,25-(OH) 2 -Vit.D 3 and alkaline phosphatase were not affected by P depletion.In P depletion the flow through the gastrointestinal tract of total P contained in the digesta and faecal P excretion were significantly reduced and the P balance was slightly negative. Calcium net absorption from the gut was also reduced. Daily flow of total P and P, contained in the particle-free intestinal fluid was markedly lower in P depletion as compared with P repletion. The percentage of net disappearance from the small intestines of total P and P, in the particle-free fluid was 57 and 70 % in the depleted state and 79 and 93% in the repleted state.

The relationship between the concentration of phosphate in plasma and parotid saliva was studied in six conscious sheep and a goat, either intact or thyroparathyroidectomized (t.x.p.t.x.), under conditions designed to minimize marked fluctuations in flow rate of saliva. A linear relationship between acutely induced changes in plasma phosphate concentration and the phosphate level in saliva has been demonstrated in both intact and t.x.p.t.x. animals. Dietary phosphorus depletion caused adaptation of salivary phosphate concentration so that less was secreted at a given concentration of plasma phosphate. Attention is drawn to the similarity between this phenomenon and that already described for the proximal renal tubule. Parathyroid hormone (PTH) was shown to reduce the salivary phosphate concentration with little or no effect on phosphataemia. The administration of 1,25-dihydroxycholecalciferol (1,25(OH)2CC) also caused a reduction in salivary phosphate concentration despite hyperphosphataemia and hypercalcaemia. It is suggested that salivary phosphate concentration can be influenced directly by the concurrent level of plasma phosphate but that this relationship can be modified by the circulating concentration of 1,25(OH)2CC and indirectly by PTH via increased production of 1,25(OH)2CC.

Protein intake of first-calf beef heifers was restricted during the last 100 days of gestation, and the effects on passive transfer of colostral immunoglobins from the cow to the neonatal calf were examined. There were no significant correlations between concentration of immunoglobins (IgM, IgG1 and IgG2) in the sera or colostrum of the cow and prenatal crude protein consumption (.52 to .98 kg crude protein/day). Absorption of certain colostral immunoglobins (IgG1, and IgG2) by the calf were positively correlated (P less than .01) at 12, 18, 24 and 36 hr after birth to the maternal crude protein consumption. Colostrum was collected from the first milkings of pluriparous dairy cows, and then freeze-dried, mixed and reconstituted to be equivalent to 1 liter of colostrum. Mean IgG1 concentrations for the high and low protein groups were 6.02 +/- .90 and .78 +/- .15 mg . ml-1 (P less than .01), respectively. No relationship (P greater than .05) was found between the concentration of IgM in calf sera and daily crude protein intake of the dam. These data indicate that there was a selective decrease in absorption of IgG1 and IgG2 in calves from heifers fed low protein prenatal diets.

No abstract

Holstein heifers were treated with synthetic thyrotropin-releasing hormone (TRH) or saline twice daily from one week through 6 mo of age. Plasma concentrations of prolactin (PRL) and thyrotropin (TSH) were elevated (P less than .01) within 30 min after the first TRH injection (1 week of age). At 1 and 3 mo of treatment, PRL and TSH increased in response to TRH, although the TSH response was reduced (P less than .01) as compared to the first day of treatment. Although plasma growth hormone (GH) appeared to be elevated following the first TRH injection, this effect was not statistically significant (P less than .05), nor was it significantly influenced by treatment following subsequent TRH injections. None of the 3 hormones, PRL, TSH or GH, was elevated following the final TRH injection at 6 mo of age. In contrast, plasma concentrations of PRL and TSH were increased in a control heifer injected with TRH at 6 mo. These data indicate that hormonal responsiveness to TRH stimulation decreases with continued twice daily treatment at doses of TRH used in the present studies. Examination of weight gains indicated that chronic treatment with TRH was associated with increased growth rate through 6 mo of age (10.6% increased average daily gains P less than .10), which was exhibited in a steeper slope (P less than .05) of the growth curve in the TRH group. Feed intake was slightly greater in TRH heifers, although feed efficiency (kg feed/kg gain) was not different between the two groups. Plasma concentrations of PRL increased (P less than .01) with age (r = +0.938) in control heifers while plasma TSH and GH were not significantly related to age. This observation establishes a positive correlative relationship between PRL secretion and the approach of puberty in the dairly heirfer. It was also noted that elevation of PRL secretion by TRH treatment was associated with significant advancement of age at first observed estrus (9.4 vs. - 10.5 mo) suggesting that a functional relationship between PRL secretion and puberty may exist in dairy heifers.