The optimal concentration of nutrients required by growing pigs generally decreases over the growing-finishing period with a phase feeding program used as an attempt to meet the needs of the pigs over the changing requirements. Thus, in commercial production, phase feeding is thought to improve economics and reduce nitrogen excretion by more closely meeting the pig’s nutrient requirements compared to feeding fewer phases. However, in practice, it is challenging to accurately estimate feed intake and consequently deliver the optimal concentration of nutrients required for growth at each stage of the finishing period. Therefore, it is important to understand the biological and economic implications of feeding below, at, or above the nutritional requirements.
Establishing the dietary lysine requirement is the core component of developing feeding strategies for growing-finishing pigs. Lysine is the first limiting amino acid in typical swine diets and is therefore involved in optimal growth and lean deposition.4 Approaches to estimate the lysine requirement with prediction equations have been focused on either maximizing growth rate and feed efficiency, or optimizing income over feed cost. The objective of this study was to compare phase feeding strategies for grow-finish pigs and determine their effects on growth performance, carcass characteristics, and economics.
The Kansas State University Institutional Animal Care and Use Committee approved the protocol used in this experiment. The study was conducted at a commercial research facility in southwestern Minnesota. The barn was naturally ventilated and double curtain-sided. Each pen was equipped with a 4-hole stainless steel dry self-feeder and a cup waterer for ad libitum access to feed and water. Feed additions to each individual pen were made and recorded by a robotic feeding system (FeedPro, Feedlogic Corp., Wilmar, MN).
A total of 1,188 pigs (PIC 359 × 1050; initially 61.5 lb BW) were used in a 117-d growth trial with 27 pigs per pen and 11 pens per treatment. Pigs were allotted to treatments based on initial BW in a randomized complete block design.
The treatments consisted of different phase feeding programs based on the estimated lysine requirements for maximal growth rate and feed efficiency or for optimal income over feed cost (IOFC) adapted from Tokach et al. The equations used to estimate SID lysine requirement of finishing gilts in g/Mcal NE were: 0.00006 × BW, lb - 0.0291 × BW, lb + 6.6894 for maximum growth and -0.00000015 × BW, lb + 0.00010 × BW, lb - 0.0304 × BW, lb + 6.0435 for optimal IOFC (adapted from Tokach et al., 2012).
The treatments were arranged in a 1-way treatment structure: MAX, a 4-phase feeding program with lysine levels for maximum growth (1.13, 0.96, 0.82, and 0.77% SID Lys in Phases 1 to 4, respectively); STD, a standard 4-phase feeding program to optimize IOFC (1.02, 0.87, 0.76, and 0.67% SID Lys in Phases 1 to 4, respectively); STD/MAX, a 4-phase feeding program based on standard lysine levels in early finishing and lysine levels for maximum growth in late finishing (1.02, 0.87, 0.82, and 0.77% SID Lys in Phases 1 to 4, respectively); and 2-PHASE, a 2-phase feeding program based on the average estimated lysine requirements for maximum growth during the first three phases with 0.96% SID lysine fed during Phases 1, 2, and 3 (d 0 to 81) and 0.77% SID lysine fed during Phase 4 (d 81 to 117). Phases 1 to 4 were fed from d 0 to 25, 25 to 53, 53 to 81, and 81 to 117, respectively, which corresponded to body weights of approximately 60 to 110, 110 to 160, 160 to 220, and 220 to 280 lb, respectively (Table 1).
The diets were based on corn, distillers dried grains with solubles, and soybean meal (Table 2). Lysine levels in experimental diets were achieved by manipulating the ratio of corn to soybean meal while keeping the amount of L-Lys HCl constant within phases. Diet samples from each phase were taken from 6 feeders per dietary treatment 3 d after the beginning and 3 d before the end of each phase and stored at -4°F. Composite samples were homogenized, subsampled, and analyzed for DM, CP, ADF, NDF, ether extract, Ca, and P (Ward Laboratories Inc., Kearney, NE). Composite samples were additionally analyzed for CP, Ca, and P by Midwest Laboratories (Omaha, NE) and the average estimates between the laboratories were reported.
Pens of pigs were weighed and feed disappearance measured on d 0, 12, 25, 40, 53, 68, 81, 95, and 117 to determine ADG, ADFI, and F/G. On d 95, the 3 heaviest pigs in each pen were weighed and marketed according to the farm marketing strategy. On d 117, final pen weights were taken and pigs were tattooed with a pen identification number and transported to a USDA-inspected packing plant (JBS Swift and Co., Worthington, MN) for processing and carcass data collection. Carcass measurements included HCW, backfat, loin depth, and lean percentage. Percentage lean was calculated from plant proprietary equation. Carcass yield was calculated by dividing the pen average HCW by the pen average final live weight obtained at the farm.
For the economic analysis, feed cost per pig, feed cost per lb of gain, revenue per pig, and IOFC were calculated on a pen basis. Corn was valued at $3.30/bu ($118/ton), soybean meal at $290/ton, distillers dried grains with solubles at $94/ton, L-lysine at $0.75/lb, DL-methionine at $1.30/lb, L-threonine at $1.10/lb, and L-tryptophan at $4.75/lb. Feed cost per pig was calculated by multiplying the feed cost per lb by ADFI and by the number of days in each phase, then adding up the values of each phase. Feed cost per lb of gain was calculated by dividing the feed cost per pig by the overall weight gain.
Revenue was obtained by multiplying carcass gain by an assumed value of $70 per cwt of carcass. The IOFC was calculated by subtracting the feed cost per pig from revenue per pig.
Data were analyzed using a linear mixed model with treatment as fixed effect, block as random effect, and pen as the experimental unit. Hot carcass weight was used as a covariate for analyses of backfat, loin depth, and lean percentage. Statistical models were fitted using the GLIMMIX procedure of SAS version 9.4 (SAS Institute Inc., Cary, NC). Results were considered significant at P ≤ 0.05 and marginally significant at 0.05 < P ≤ 0.10.
Results and Discussion
The analyzed DM, CP, ADF, NDF, ether extract, Ca, and P content of experimental diets (Table 3) were consistent with formulated estimates.
In Phase 1 (d 0 to 25), ADG increased (P = 0.001) in pigs fed the MAX or STD feeding programs compared to the 2-PHASE diet. This response was associated with the higher lysine levels in MAX and STD diets compared to the 2-PHASE diet (1.13% and 1.02% vs. 0.96% SID Lys, respectively). Although the STD/MAX pigs received the same lysine level as STD in this phase (1.02% SID Lys), ADG was intermediate. Average daily feed intake was lower (P = 0.001) in the 2-PHASE feeding program compared to all other treatments. Feed efficiency was marginally improved (P = 0.063) in MAXfed pigs compared to STD/MAX, with STD and 2-PHASE intermediate. At the end of Phase 1, BW was increased (P = 0.002) in pigs under MAX or STD regimens compared to the 2-PHASE diet, with pigs fed the STD/MAX regimen being intermediate.
In Phase 2 (d 25 to 53), ADG increased (P = 0.005) in pigs fed the 2-PHASE feeding program compared to STD and STD/MAX, with MAX intermediate. This response was due to the higher lysine levels in the 2-PHASE diet compared to STD and STD/ MAX diets (0.96% vs. 0.87% SID Lys, respectively) during this Phase. Although there was no evidence for difference in ADFI, F/G was improved (P < 0.001) in the 2-PHASE-fed pigs compared to all other treatments. The improvement in F/G associated with 2-PHASE diet, even compared to MAX diet that was formulated with the same lysine level (0.96%), can possibly be explained by a compensatory growth improvement following the poor performance of 2-PHASE pigs in Phase 1. There was no evidence for differences in BW at the end of Phase 2.
In Phase 3 (d 53 to 81), ADG and F/G were improved (P < 0.01) in pigs under the 2-PHASE feeding program compared to MAX and STD regimens due to the higher lysine levels in the 2-PHASE diet (0.96% vs. 0.82% and 0.76% SID Lys, respectively). Compensatory growth benefits were observed in pigs fed the STD/MAX regimen, with similar ADG and F/G as 2-PHASE regimen even though the lysine level was lower in STD/MAX diet compared to the 2-PHASE diet (0.82% vs. 0.96% SID Lys, respectively). There was no evidence for differences in ADFI in this phase. Body weight was increased (P = 0.029) in pigs under 2-PHASE regimen compared to STD, with MAX and STD/MAX regimens intermediate.
In Phase 4 (d 81 to 117), there was no evidence for differences in ADG and F/G across the treatments. Average daily feed intake was marginally increased (P = 0.051) in pigs fed 2-PHASE feeding program compared to STD, while MAX and STD/MAX were intermediate.
Overall (d 0 to 117), pigs fed the 2-PHASE feeding program had increased (P = 0.048) ADG compared to pigs fed the STD regimen. Feeding either the MAX or STD/MAX regimen, i.e. a 4-phase feeding program for maximum growth or a combination of STD lysine levels in early finishing and lysine levels for maximum growth in late finishing, resulted in intermediate ADG. There was no evidence for differences in ADFI, F/G, or final BW across the treatments in the overall period. Also, no evidence for differences was observed across the dietary treatments for the carcass traits HCW, yield, backfat, loin depth, or lean percentage.
For economics, the STD feeding program resulted in the lowest (P < 0.001) feed cost per pig and feed cost per lb of gain. Revenue and IOFC per pig were similar across the feeding programs.
The results of this study demonstrate that feeding lysine levels for maximum growth of finishing pigs in either a 2- or 4-phase feeding program (2-PHASE or MAX, respectively) results in the same overall growth performance and feed cost. These results allow for the possibility of using fewer feeding phases in the grow-finish phase, which may have practical advantages for feed manufacture, storage, and delivery. From the economic standpoint, lower feed cost per lb of gain was achieved by feeding the STD program. Feeding STD lysine levels in early finishing and MAX levels in late finishing (STD/ MAX) resulted in a similar feed cost as a full maximum-growth program (MAX). This result was not expected because, according to Main, pigs fed lysine-deficient diets in early finishing, and at the estimated lysine requirement in late finishing, have lower feed cost per lb of gain compared to pigs fed at the estimated lysine requirement in both early and late finishing. However, it is noteworthy that in the present study none of the diets were considerably below the estimated lysine requirement in early finishing.
In conclusion, feeding lysine levels for maximum growth and efficiency in either a 2- or 4-phase feeding program results in the same growth performance and feed cost. A broad range of lysine specifications within the levels tested herein can be utilized in grow-finish diets without compromising income over feed cost.
This article was originally published in Kansas Agricultural Experiment Station Research Reports: Vol. 3: Iss. 7. https://doi.org/10.4148/2378-5977.7487. This is an Open Access article licensed under a Creative Commons Attribution 4.0 License.