Apparent and standardised ileal digestibilities and growth performance of finishing pigs fed diets formulated with new corn hybrids

Abstract

Two experiments were conducted to evaluate the nutritive value of four new corn hybrids (H515, P7573, P30F94 and P3086). In Experiment 1, five crossbred (Yorkshire×Duroc) finishing barrows (52 kg initial body weight [BW]), were fitted with a simple T-cannula at the terminal ileum, to determine the apparent (AID) and standardised (SID) ileal digestibilities of amino acids (AA) and other nutrients. Pigs were individually penned in metabolism crates and had free access to water; feed was offered at 2.5 times the metabolisable energy (ME) requirement for maintenance. A 5×5 latin square design was used, with five periods of seven days each; the collection of samples was at days sixth and seventh, every two h. In Experiment 2, 15 finishing (63±2.4 kg initial BW) barrows were randomly allotted into three diets to determine growth performance and backfat thickness. The experiment lasted 49 days. In Experiment 1, the AID and SID of all AA were similar between diets (hybrids). Only the P3086 corn diet had the highest AID and SID for cystine, ash and crude protein (CP). In Experiment 2, the average daily gain, average daily feed intake and feed efficiency of pigs were not affected by the formulation system. The backfat thickness was higher in pigs fed T3. These results show that the new corn hybrids had similar nutritive value for finishing pigs as in regular corn.

Keywords:

• amino acids digestibility
• growth performance
• pigs
• corn hybrids

Introduction

Corn is the main ingredient for pigs in the world, because its amino acids (AA) pattern combines with the one of soybean meal. In addition, corn is the main grain produced in Mexico and that is the reason why new hybrids are frequently produced, especially for the weather conditions and soil characteristics of each region. These new hybrids need to be evaluated as dietary ingredients for pigs. The apparent ileal digestibility of CP and AA is affected by their dietary composition (Pedersen and Boisen 2002). The nutritive value of protein in feedstuffs for pigs is determined by the composition and availability of AA, especially the limiting AA (Sauer et al. 2000) and energy. The determination of this availability is expensive and time consuming. The apparent ileal digestibility of AA is often determined in ingredients and used as reasonable estimate of the availability of AA for pigs, compared to faecal digestibilities (Moughan 1995).

The objectives of this study were to determine the apparent and standardised ileal digestibilities of AA and other nutrients in four new corn hybrids, and the performance of finishing pigs fed conventional diets formulated with new corn hybrids.

Materials and methods

This research was conducted at the Swine Unit of the Centro de Estudios Profesionales del Colegio Superior Agropecuario del Estado de Guerrero, México. The animals used in this research were cared for in accordance with the guidelines of the ‘International Guiding Principles for Biomedical Research Involving Animals’, as well as the ‘Mexican Official Standards for the Production, Protection and Use of Lab Animals’ (Diario Oficial de la Federación 2001).

Experiment 1

Five diets (treatments; T) were formulated containing 16% CP and 3.265 Mcal ME kg⁻¹ (NRC, 1998), with corn starch and regular soybean meal for T1; soybean meal and hybrid (H) 515 corn for T2; soybean meal and pioneer corn (P) 7573 for T3; soybean meal and P30F94 for T4; and soybean meal and P3086 for T5. Each diet contained 0.3% chromic oxide as an indigestible marker. Control diets were T1 (semipurified diet) and T2 (HC515, regular corn hybrid).

Five crossbred (Yorkshire×Duroc) finishing (52 kg) barrows were individually penned in metabolism crates. Each barrow was fitted with a simple T-cannula at the terminal ileum. After surgery, a 15-day period was allowed for full recovery, during which time pigs were fed twice a day (08:00 and 17:00 h) increasing the amount of diet until pigs reached the previous feed intake level. After recovery, pigs were randomly assigned to one of five diets, in a 5×5 latin square design (Steel et al. 1997). The experiment lasted 35 days; five periods of seven days: five days for adaptation to diets, and the two last days for sample collection (every two hours; 48 h). Pigs had free access to water, and feed was offered at 2.5 times maintenance requirement of ME (i.e. 100 kcal/kg body weight [BW] 0.75), which was estimated at the beginning of each experimental period.

Representative samples of ingredients and diets were taken. Ileal digesta samples were collected into plastic (10×4 cm) bags for 48 h, added with HCl 0.2 N to minimise bacterial activity. Digesta samples were frozen at −20 °C immediately after collection, until laboratory analysis. All samples for each pig during the experimental period were mixed, lyophilised and grounded in a 1-mm Wiley mill. The analysis included crude protein (N×6.25) by Kjeldahl, ash, dry matter, ether extract and gross energy (bomb calorimeter; Parr Instruments-1266; AOAC 1990). AA concentration was determined using ion exchange chromatography after a 24 h acid hydrolysis with HCl 6 N. Methionine and cysteine were oxidised to methionine sulphone and cisteic acid by a performic oxidation procedure (AOAC 1990). Tryptophan was not determined. In addition, neutral (NDF) and acid detergent fibre (ADF; Van Soest et al. 1991) and chromic oxide (Fenton and Fenton 1979) were also determined. The apparent ileal digestibility of AA was determined using the following equation (Nyachoti et al. 1997):

where, AID is the apparent ileal digestibility of nutrients in the experimental diets (%); I_D is the marker concentration in the diet; N_D is the nutrient concentration in ileal digesta; I_F is the marker concentration in ileal digesta; and N_F is the nutrient concentration in the diet.

The standardised ileal digestibility and the endogenous losses of AA were determined using the following equation (Otto et al. 2003):

where, AID% is the apparent ileal digestibility; EAL is the endogenous AA losses; and SID% is the standardised ileal digestibility of AA; where AA_f is the AA concentration in the feed; AA_d is the AA concentration in the digesta; Cr_f is the chromic oxide in the feed; and Cr_d is the chromic oxide in the digesta.

The data of digestibility and endogenous losses were analysed using PROC GLM of SAS (SAS Inst. Inc., Cary, NC), and treatment means were analysed with the multiple comparison test of Tukey. For ash, crude protein, NDF, ADF, gross energy and dry matter, feed intake was used as a covariate for their statistical analysis.

Experiment 2

After the first experiment, the H515 hybrid corn was selected because of its higher availability and its production in the state, to conduct a growth performance trial to evaluate three diets equal in CP (16%) and isocaloric (3.265 Mcal kg⁻¹ dry matter [DM]), formulated for total protein, total AA concentrations and true ileal digestibility of AA; the last obtained in Experiment 1.

Fifteen crossbred (Yorkshire×Duroc) finishing (63 kg BW) barrows were individually allotted in concrete floor pens, with a feeder and a waterer. After five days of adaptation to pens, pigs were randomly assigned to one of three diets, according to a completely randomised design (Steel et al. 1997) with five replicates per treatment. The experiment lasted 49 days. Pigs had free access to feed and water.

Feed intake was determined daily; average daily gain and gain:feed ratio were estimated weekly. Backfat thickness was measured at the first, tenth and last ribs directly in the carcass with a vernier rule, immediately after pigs were slaughtered at 100 kg of BW. Growth performance data were analysed by ANOVA using PROC GLM of SAS (SAS Inst. Inc., Cary, NC), and means were compared with the Tukey test.

Results and discussion

Experiment 1

There was no difference in the AID and SID of most AA, both essential and non-essential (Table 1), except for sulfur AA. These results were not affected by the different AA balance, CP or gross energy (GE) dietary concentration. The values are very close to other research with 15% (Otto et al. 2003) CP diets. However, the AID and SID of methionine was lower in the control diet, but it was higher than the reports of Otto et al. (2003). The AID and SID of cystine was higher in the P3086 hybrid, and the lowest values were found in H515 and P30F94 hybrids. These values are higher than other studies (Otto et al. 2003) where corn and soybean meal were the main ingredients. The AID of ash and CP were higher in P3086 corn; the values are similar to the reports where high-oil corn was used (O'Quinn et al. 2000). Similar results for DM and GE were found in pigs fed corn-soybean meal diets (Moeser et al. 2002); but lower in other reports where high-oil corn was used for growing pigs (O'Quinn et al. 2000). The endogenous loss of most essential and nonessential AA was similar in all diets. These values are slightly higher to other report where corn-soybean meal was fed to pigs (Otto et al. 2003). However, the endogenous losses of methionine and cystine were higher in P7573 and P30F94 diets, maybe due to their lower CP concentration. On the other hand, a high endogenous loss of proline was observed in H515 and P30F94 diets in spite of the higher proline concentration. Similar findings were reported previously (Otto et al. 2003).

Table 1.  Apparent ileal digestibility (%) of AA and other nutrients (Experiment 1).

	1	2	3	4	5
	Control	HC 515 Control	PC 7573	PC 30F94	PC 3086	SEM*
Essential AA
Arginine	92.54	91.03	91.67	89.96	90.40	0.382
Histidine	90.78	89.20	90.26	87.51	88.47	0.550
Isoleucine	90.02	89.23	91.48	85.75	86.35	0.812
Leucine	90.70	89.93	90.83	88.94	89.15	0.465
Lysine	91.90	90.67	91.64	90.18	89.71	0.513
Methionine	87.82^b	88.62^ab	88.69^ab	88.99^ab	90.80^a	0.325
Phenylalanine	90.42	90.14	90.97	89.11	88.99	0.521
Threonine	89.29	88.93	89.48	87.43	87.61	0.650
Valine	88.16	88.60	90.81	85.10	85.86	0.862
Non-essential AA
Alanine	87.00	87.76	88.01	87.03	87.56	0.625
Aspartic acid	90.12	89.33	90.10	88.83	89.17	0.544
Glutamic acid	91.19	90.37	91.07	89.74	90.55	0.273
Glycine	87.39	87.45	88.11	86.79	87.44	0.658
Proline	89.40	89.40	89.58	88.49	89.51	0.379
Serine	90.27	89.35	89.76	88.83	88.90	0.493
Tyrosine	90.89	89.82	90.66	88.76	88.65	0.556
Cysteine	89.21^ab	88.31^b	90.12^ab	88.27^b	91.20^a	0.294
Other components
Ash	86.67^bc	87.71^b	88.29^b	85.42^c	90.83^a	0.253
CP	86.83^bc	86.94^b	88.11^b	83.70^c	90.97^a	0.315
NDF	88.18^a	82.70^c	81.21^c	82.95^c	86.37^b	0.280
ADF	75.84^bc	78.12^b	70.26^cd	64.10^d	81.86^a	0.731
GE	90.23^a	86.46^b	87.49^b	85.22^c	90.42^a	0.148
DM	89.78^a	86.46^b	87.25^b	84.70^a	90.38^a	0.155
Note: HC, hybrid corn; PC, pioneer corn.
^abcdSuperscripts indicate differences among diets within a row (P≤0.05).
*Standard error of the mean.

The SID of the essential AA (Table 2), as the AID, were similar between treatments, except for methionine. Pigs fed a control diet had the lowest SID of methionine (P≤0.05). For non-essential AA, the SID was similar (P >0.05) for all AA except cystine. Pigs fed P3086 diet showed the highest SID (P≤0.05) for cystine, and pigs fed H515 and P30F94 diets had the lowest values (P≤0.05) of this AA. The endogenous AA losses (Table 3) were similar (P >0.05) for all AA except sulfur AA and proline, independently of the dietary treatment. Methionine showed the highest losses in pigs fed P7573 and P30F94 diets (P≤0.05); and the lowest in pigs fed P3086 (P≤0.05). For cystine, pigs fed P30F94 diet had the highest endogenous losses (P≤0.05); the lowest values were observed in pigs fed P3086 diet(P≤0.05). The endogenous loss of proline was higher in pigs fed P30F94 diet (P≤0.05); the lowest value was observed with control diet (P≤0.05).

Table 2.  Standardised ileal digestibility (%) of AA (Experiment 1).

	1	2	3	4	5
AA	Control	HC515 control	PC7573	PC30F94	PC3086	SEM*
Essential
Arginine	92.57	91.06	91.69	89.99	90.65	0.384
Histidine	90.82	89.26	90.30	87.57	89.05	0.564
Isoleucine	90.07	89.28	91.51	85.83	86.78	0.815
Leucine	90.74	89.97	90.86	88.99	89.51	0.467
Lysine	91.93	90.71	91.66	90.22	89.97	0.516
Methionine	87.90^b	88.68^ab	88.74^ab	89.04^ab	91.28^a	0.316
Phenylalanine	90.46	90.18	91.00	89.16	89.56	0.542
Threonine	89.35	88.99	89.53	87.49	88.03	0.655
Valine	88.23	88.66	90.84	85.20	86.34	0.869
Non-essential
Alanine	87.09	87.82	88.07	87.10	88.04	0.637
Aspartic acid	90.17	89.38	90.14	88.87	89.20	0.537
Glutamic acid	91.23	90.41	91.10	89.78	90.88	0.276
Glycine	87.47	87.52	88.18	86.87	87.93	0.670
Proline	89.46	89.45	89.63	88.55	90.02	0.376
Serine	90.31	89.40	89.80	88.79	89.25	0.498
Tyrosine	90.94	89.86	90.69	88.81	89.01	0.559
Cysteine	89.27^ab	88.37^b	90.16^ab	88.32^b	91.64^a	0.283
Note: HC, hybrid corn; PC, pioneer corn.
^abSuperscripts indicate differences among diets within a row (P <0.05).
*Standard error of the mean.

Table 3.  Endogenous losses (g kg⁻¹ DM) of AA (Experiment 1).

	1	2	3	4	5
AA	Control	HC 515 control	PC 7573	PC 30F94	PC 3086	SEM*
Essential
Arginine	0.31	0.40	0.35	0.48	0.43	0.051
Histidine	0.22	0.32	0.26	0.34	0.29	0.033
Isoleucine	0.33	0.36	0.23	0.37	0.37	0.042
Leucine	0.63	1.02	0.72	1.00	0.93	0.097
Lysine	0.36	0.34	0.29	0.36	0.40	0.053
Methionine	0.12^ab	0.13^ab	0.15^a	0.14^a	0.07^b	0.007
Phenylalanine	0.43	0.46	0.35	0.49	0.45	0.056
Threonine	0.56	0.63	0.54	0.73	0.65	0.072
Valine	0.49	0.49	0.33	0.51	0.50	0.057
Non-essential
Alanine	0.69	0.90	0.76	0.93	0.77	0.081
Aspartic acid	1.13	1.03	0.93	1.17	1.07	0.122
Glutamic acid	1.44	1.78	1.38	1.83	1.38	0.123
Glycine	0.63	0.60	0.55	0.67	0.54	0.060
Proline	0.33^c	0.64^a	0.49^b	0.63^a	0.44^ab	0.040
Serine	0.51	0.60	0.53	0.67	0.59	0.062
Tyrosine	0.28	0.37	0.29	0.41	0.39	0.044
Cysteine	0.25^ab	0.27^ab	0.27^ab	0.37^a	0.14^b	0.016
Note: HC, hybrid corn; PC, pioneer corn.
^abcSuperscripts indicate differences among diets within a row (P <0.05).
*Standard error of the mean.

Experiment 2

The formulation system had no effect on the analysed variables (P >0.05), except for backfat thickness, that was higher (P≤0.05) in pigs fed a diet formulated with digestible AA values (Table 4). When corn soybean meal were used for finishing pigs, a lower backfat thickness was found (Spencer et al. 2000), compared to the results in this experiment. A standard 14% CP diet reduced the backfat thickness (Tuitoek et al. 1997). These results indicate that sorghum grain can be replaced by the H515 corn hybrid in diets for finishing pigs without affecting growth performance; the ADG was similar to the one obtained with regular corn-soybean meal standard diets (Spencer et al. 2000) fed to growing-finishing pigs, although ADFI was lower and feed:gain ratio was higher compared to the results of this experiment. In standard corn-soybean meal diets fed to finishing pigs, similar ADG and ADFI were found (Tuitoek et al. 1997), but higher gain:feed ratio was reported (Tuitoek et al. 1997).

Table 4.  Effect of three feed formulation systems on growth performance and backfat thickness of finishing pigs (Experiment 2).

	Treatment
Item	1	2	3	SEM*
Feed intake, kg d^−1	3.04	2.94	3.23	0.095
Weight gain, kg d^−1	0.94	0.85	0.95	0.020
Feed efficiency, kg kg^−1	0.31	0.29	0.30	0.003
Backfat thickness, mm	27.60^ab	18.10^b	29.40^a	0.118
Note: Treatments 1, 2 and 3, formulated on a total protein, total AA concentration, or true ileal digestibility of H515 hybrid corn basis, respectively. ^abSuperscripts indicate differences among diets within a row (P≤0.05).
*Standard error of the mean.

Acknowledgements

This study was supported by Fundación Produce de Guerrero, A. C., México.

Additional information

Notes on contributors

L. Reyna

Present address: Colegio Superior Agropecuario del Estado de Guerrero, Iguala, Guerrero 40000, México