Effect of dietary phosphorus on intestinal phosphorus absorption in growing Holstein steers

Abstract

The effect of dietary P intake on intestinal P absorption was evaluated in growing Holstein steers. Diets varying in P content (0.15, 0.27, 0.36, and 0.45%, DM basis) were fed to 8 steers (174±10kg of BW) fitted with permanent duodenal and ileal cannulas in a replicated 4×4 Latin square with 14-d periods. Ytterbium-labeled corn silage and cobalt-EDTA were used as particulate and liquid phase markers, respectively, to measure digesta flow. Duodenal and ileal samples and spot urine samples were collected every 9 h from d 11 to 14. Total fecal collection was conducted on d 11 to 14 with fecal bags. Blood samples were collected from the coccygeal vessel on d 14. Feed, digesta, and fecal samples were analyzed for total P and inorganic P. Data were analyzed using PROC GLIMMIX in SAS with a model including treatment, square, period, and interaction of treatment and square. Preplanned contrasts were used to evaluate linear and quadratic treatment effects. Results were reported as least squares means. Dry matter intake (mean=4.90kg/d, 2.8% of BW) and apparent DM digestibility (mean=78.1%) were unaffected by treatment. Duodenal and ileal flow of total P increased linearly with increasing P intake (13.4, 18.5, 23.0, and 27.4g/d; 6.80, 7.87, 8.42, and 10.4g/d). Increasing P intake increased the quantity of P absorbed from the small intestine linearly (6.96, 11.1, 14.6, and 17.2g/d), but absorption efficiency was unchanged (mean=59.6%). Phosphorus was absorbed on a net basis from the large intestine, but this was not affected by treatment and was a small proportion of total P absorption. Blood inorganic P increased linearly with increased dietary P (4.36, 6.31, 7.68, and 8.5mg/dL) and salivary P secretion was unchanged (mean=5.79g/d), suggesting that rumen function was prioritized during short-term P deficiency. These data showing an absence of change in absorption efficiency and salivary P secretion in the face of short-term P deficiency may be used to improve published models of P digestion, absorption, and metabolism.

Parameterization of a ruminant model of phosphorus digestion and metabolism

“…Willing, and K. F. Knowlton, 2011, personal communication), XF2 (Feng et al, 2013), XF3 (Feng et al, 2015), PR1 (Ray et al, 2012), PR2 (Ray et al, 2013), and JJ1 (Jarrett et al, 2014). The data are summarized in Table 2.…”

“…Initial fits included parameter estimates for Pp and Po degradation in the SI (f PpSI,DegSI , f PoSI,DegSI ), but these were found to be essentially 0 and thus were fixed to values of 0 and removed from the parameter estimation list. The exponents controlling Pp degradation in the rumen (equation [1]) and Pi absorption from the SI (equation [8]) were not uniquely identifiable from the data, but range testing indicated they should be set to values of approximately 2.0 and 2.5, respectively, and Ray et al (2012Ray et al ( , 2013, Feng et al (2011, personal communication), Feng et al (2013Feng et al ( , 2015, and Jarrett et al (2014 …”

“…Absorption of Pi from the LI (F PiLI,PiBld ) has been observed (Ray et al, 2013;Feng et al, 2015) and was represented as…”

“…Since this time, our group has conducted several experiments (X. Feng, J. P. Jarrett, P. P. Ray, L. Karpinski, B. Willing, and K. F. Knowlton, 2011, personal communication;Feng et al, 2013Feng et al, , 2015Ray et al, 2012Ray et al, , 2013Jarrett et al, 2014) that should provide the data required for parameterization of the digestive elements. It was hypothesized that sufficient data were available to parameterize the digestion and metabolism coefficients within the model, and the behavior simulated from the resultant model could be used to derive P bioavailabilities for various feed ingredients.…”

“…An interference Table 3. Model inputs for Ray et al (2012Ray et al ( , 2013, Feng et al (2011, personal communication), Feng et al (2013Feng et al ( , 2015, and Jarrett et al (2014) factor of 4 and 4 resamplings was used. Analyses were performed using the FAST algorithm with the default frequency step.…”