Table 7.

Least square means for growth performance, carcass characteristics, and bone mineralization of growing-finishing pigs fed increasing analyzed calcium to analyzed phosphorus (Ca:P) ratio from 26- to 127-kg body weight (BW) in Exp. 2¹

Item4	Analyzed Ca:P ratio2,3:	0.75:1	1.00:1	1.25:1	1.50:1	2.00:1	SEM	P-value
	STTD Ca:STTD P5:	0.95:1	1.18:1	1.40:1	1.62:1	2.07:1		Linear	Quadratic
Grower period (day 0 to 58)
ADG, g		820	838	830	852	830	12.3	0.390	0.061
ADFI, g		1,695	1,701	1,694	1,742	1,706	37.7	0.349	0.289
G:F, g/kg		485	494	491	489	487	5.7	0.908	0.179
Finisher period (day 59 to 114)
ADG, g		895	952	980	982	994	11.7	<0.001	0.001
ADFI, g		2,685	2,769	2,814	2,825	2,816	41.8	0.011	0.044
G:F, g/kg		334	344	345	348	354	5.7	0.002	0.229
Overall (day 0 to 114)
ADG, g		861	898	905	918	913	8.6	<0.001	0.001
ADFI, g		2,173	2,220	2,228	2,269	2,245	37.1	0.025	0.090
G:F, g/kg		397	405	407	405	407	4.7	0.018	0.116
BW, kg
Day 0		25.3	25.3	25.4	25.3	25.3	0.93	0.924	0.766
Day 58		73.6	74.5	74.3	75.4	74.2	1.55	0.427	0.096
Day 114		121.8	127.3	127.8	128.7	127.3	1.80	0.001	<0.001
Carcass characteristics6
HCW, kg		90.4	92.9	93.6	94.6	94.0	1.33	0.002	0.014
Yield, %		74.4	73.1	73.2	73.5	73.6	0.42	0.550	0.090
Backfat, mm7		16.1	16.0	16.5	16.2	16.2	– 8	0.855	0.604
Fat-free lean, %7		57.4	57.5	57.2	57.2	57.3	– 8	0.650	0.615
Loin depth, mm7		69.5	70.2	69.8	68.7	69.2	– 8	0.406	0.984
Bone characteristics9
Ash, %7,10		60.5	61.1	61.9	61.8	61.8	0.19	<0.001	0.001

¹A total of 1,214 pigs (PIC 337 × 1050, initial pen average BW of 25.3 kg) were used in a 114-d growth trial with 27 pigs per pen and 9 pens per treatment.

²Treatments were formulated to be adequate in STTD P within phases, which corresponded to 0.38, 0.32, 0.29, and 0.26% STTD P for phases 1, 2, 3, and 4, respectively.

³Phytase (Ronozyme HiPhos, DSM Nutritional Products, Parsippany, NJ) was added to the diets at 1,000 FYT/kg feed with assumed release values of 0.15% avP, 0.132% STTD P, 0.144% total Ca, and 0.096% STTD Ca.

⁴ADG = average daily gain; ADFI = average daily feed intake; G:F = gain-to-feed ratio; HWC = hot carcass weight.

⁵Coefficients for standardized total tract digestibility (STTD) of P were obtained from NRC (2012), while values for STTD Ca in feed ingredients were obtained from Stein et al. (2016). These represent a weighted average of the ratio between STTD Ca:STTD P across treatments for the 4 dietary phases.

⁶Nine hundred and seven pigs were transported to a commercial packing plant for processing and data collection (Swift and Company, Worthington, MN).

⁷Adjusted for HCW.

⁸SEM for backfat were 0.38, 036, 0.37, and 0.38; SEM for fat-free lean were 0.25, 0.24, 0.25, 0.25, and 0.25; SEM for loin depth were 0.71, 0.68, 0.68, 0.68, and 0.70 for the 0.75:1, 1.00:1, 1.25:1, 1.50:1, and 2.00:1 analyzed Ca:P ratio treatments, respectively.

⁹Ninety pigs (2 pigs per pen, 1 barrow/1 gilt) visually assumed to represent the mean live weight of the pen were subsampled and shipped to a separate processing facility for bone collection (Natural Foods Holdings, Inc., Sioux Center, IA). A total of 90 third metacarpals were autoclaved for 1 h. After cleaning, bones were placed in Soxhlets containing petroleum ether for 7 d as a means of removing water and fat. They were then dried at 105 °C for 7 d, and then ashed at 600 °C for 24 h.

¹⁰The 2-way interaction was tested and no evidence for significant interaction was observed. There was a marginal significant gender effect (P < 0.10) on percentage bone ash, with barrows having greater bone mineralization than gilts (61.6% and 61.3% for barrows and gilts, respectively).