Influences of dietary phosphorus variation on nutrient digestion, fecal endogenous phosphorus output and plasma parameters of goats

The effects of dietary phosphorus (P) variation on nutrient digestion, endogenous loss and plasma parameters were investigated in sixteen Liuyang black wether goats (8 months of age and average BW of 15 ± 0.25 kg) using a completely randomized design. The factors were phosphorus deficient in diet (1.41 g/kg DM, PDD) and phosphorus adequate in diet (PAD1.59, 1.77 and 1.92 g/kg DM, PAD1, PAD2 and PAD3). The results showed that increasing dietary P content increased the duodenal flow of dry matter (DM) (P < 0.05) and organic matter (OM) (P < 0.01) and intestinal digestibility of OM (P < 0.05). Dietary P deficiency had no effect (P > 0.05) on apparent digestibility of DM, OM and nitrogen (N) digestion. Intestinal P digestibility linearly decreased (P < 0.05) with increasing dietary P level and as dietary P content meets requirement. No difference (P > 0.05) was noted in fecal endogenous P loss, which ranged from 0.767 to 0.884 g/kg DMI or 0.372 to 0.473 g/d, and true dietary P digestibility, which ranged from 42.9 to 51.2%, for PDD and PAD, but the proportion of endogenous P in feces tended (P < 0.10) to be higher for PDD than PAD, and more than 45% of fecal P was contributed by endogenous P. Plasma P was higher (P < 0.001), and plasma insulin was lower (P < 0.05) in goats fed PDD, but there were no differences (P > 0.05) in plasma Calcitonin (CT), fibroblast growth factor 2,3 (FGF2,3), Parathormone (PTH), Thyroxine (T4), Ca and 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) concentrations. These results indicated that slight deficiency of dietary P had no significant effects on nutrient digestion. Insulin may be a regulator in phosphate absorption or re-absorption by ruminants.