Standardized Total Tract Digestible Phosphorus Requirement of 11- to 25-Kg Pigs

A total of 1,080 barrows and gilts (PIC; 337 × Camborough, initially 11.4 ± 0.29 kg BW) were used in a 21-d trial to determine the standardized total tract digestible (STTD) P requirement of nursery pigs from 11- to 25-kg. Pigs were allotted to pens at weaning according to BW and gender. There were 6 replicate pens/treatment and 23 to 27 pigs/pen. Pens of pigs were randomly allotted to experimental diets based on average BW 21 or 24-d postweaning, in a randomized complete block design. The 7 dietary treatments consisted of 0.26, 0.30, 0.33, 0.38, 0.43, 0.48, and 0.53% STTD P. The NRC (2012) estimates a 0.33% STTD P requirement for nursery pigs from 11- to 25-kg. Two corn-soybean-meal-based diets were formulated to contain 0.26 and 0.53% STTD P by increasing the inclusion of calcium carbonate and monocalcium phosphate at the expense of corn, maintaining a constant 1.17:1 total Ca:P ratio, with no phytase added to the diets. Diets were blended using a robotic feeding system to achieve the intermediate STTD P levels. Experimental data was analyzed using generalized linear and non-linear mixed models, fitting the data with heterogeneous residual variances when needed, and pen as the experimental unit. Competing models included linear (LM), quadratic polynomial (QP), broken-line linear (BLL), and broken-line quadratic (BLQ). Best-fitting models for each response were selected using Bayesian information criterion. Increasing STTD P improved ADG, ADFI, and G:F (linear, P<0.05). For ADG, the best-fitting models were LM and QP, estimating the maximum response at greater than 0.53% STTD P for both models. For G:F, best-fitting models were QP and BLL. The QP model estimated the maximum at 0.43% (95% CI: 0.36 to >0.53%), with 99% of maximum G:F achieved at 0.36%. The BLL plateau was estimated at 0.34% (95% CI: 0.29 to 0.38%). In conclusion, the estimated STTD P requirement for nursery pigs from 11- to 25-kg ranged from 0.34 to at least 0.53% depending on the response criteria and statistical model.

	STTD P, %							Probability, P<
Item1	0.26	0.30	0.33	0.38	0.43	0.48	0.53	Linear	Quadratic
ADG, g	513	510	533	532	566	563	573	0.001	0.718
ADFI, g	782	764	776	780	818	824	828	0.004	0.603
G:F, g/kg	656	667	687	682	692	684	693	0.001	0.067

¹SEM for ADG, ADFI, and G:F were 11.57, 19.44, and 7.36, respectively.