The effect of replacing soybean meal by field pea (Pisum sativum) seed meal in diets on growth performance, carcass traits and meat quality of finishing pigs in the tropical climate conditions of Viet Nam

Nguyen Vu Thuy Hong Loan, La Van Kinh, William Riley¹, La Thi Thanh Huyen² and Le Duc Ngoan³

HUTECH University, Faculty of Veterinary and Animal Science, P25, Binh Thanh, Ho Chi Minh City 717.000, Viet Nam
bakinh4@gmail.com
¹ Jinan University, International School, Guangzhou 510632, China
² Center for Tropical Animal Science, 224/9 Phan Van Han, P17, Binh Thanh, Ho Chi Minh City 717.000, Viet Nam
³ University of Agriculture and Forestry, Hue University; 102 Phung Hung, Hue City, Thua Thien Hue 530000, Viet Nam

Abstract

In this study, the effect of field peas as a partial or total replacement for soybean meal (SBM) in finisher pig diets on growth performance and carcass characteristics was evaluated. Twelve-hundred (1,200) crossbred F1 (Yorkshire × Landrace) pigs (60.71± 0.16 kg live weight) were allocated to five dietary treatments replicated six times, in a complete block (sex) design, with sex as the block. The five treatments represented 0, 25, 50, 75, and 100 percent replacement of SBM by pea meal (PM) and were labeled as CTL, S75-P25, S50-P50, S25-P75, and S0-P100, respectively. Growth performance indices and carcass traits were measured. Replacement of 100 percent SBM or inclusion of up to 32 percent pea meal in the diet did not adversely affect average daily gain, daily feed intake, the feed conversion ratio, blood urea nitrogen, carcass dressing, loin eye area, backfat thickness at P2, muscle percentage or meat pH values at 45 minutes, 24- and 48-hours post-slaughter. In conclusion, peas can totally replace SBM or include at up to 32 percent DM in the diet of finisher pigs with no adverse effects on growth performance or carcass traits.

Keywords: average daily gain, BUN, feed conversion ratio, feed cost, pH

Introduction

Field peas ( Pisum sativum L.), although legumes in the same family as lupin and soybeans, differ considerably in their chemical composition. Compared to soybean meal (SBM), field pea meal (PM) has lower crude protein (21-25 percent), very low crude fat (< 1 percent), a high level of carbohydrate, minimal fiber, and 86-87 percent total digestible nutrients (Endres and Kandel 2021). The availability of essential amino acids in peas is quite high, especially lysine and arginine, and peas contain low levels of anti-nutritional factors (e.g., tannins, trypsin inhibitors), but the fiber in peas is poorly digested by monogastric species (Hawthorne 2006). Pea protein is limiting in the sulfur amino acids methionine and cysteine, and in tryptophan (Smith et al 2013).

Peas can partially or completely replace SBM in the diet of growing and finishing pigs without negatively affecting performance, carcass composition, or carcass quality (Stein et al, 2006). However, Castell et al (1996) recommended a maximum inclusion level of 15 percent peas for pigs up to 20 kg live weight in diets adequate in the sulfur amino acids. Gatel et al (1989) and Prandini et al (2005) observed similar growth performance in weaned pigs (8-25 kg) fed diets with 20-40 percent peas, while Landblom and Poland (1997) reported a reduction in growth rate and feed efficiency in 7-25 kg pigs fed diets containing 30-40 percent peas. In contrast, Hungman et al (2020) concluded that weaned pigs fed 40 percent peas as a replacement for SBM could maintain growth performance.

In Viet Nam, swine production plays an important role in the nation’s economy, accounting for 60 percent of the total value of the livestock industry (Ngoan et al 2019). During the ten-year period from 2010 to 2020, annual swine production in Viet Nam increased by 3.3 percent (GSO 2020). In the most recent year, the swine population numbered 28.8 million head, and pork production totaled 5.1 million tonnes (GSO, 2021). An increase in swine production results in increased demand for compound feed, of which protein ingredients represent 20-25 percent of the formulation. SBM and fish meal (FM) are the main sources of protein used in animal and aquatic feeds in Viet Nam, and 80-85 percent of these two ingredients are imported, at increasingly higher prices over the last several years (VFA 2017).

Peas are an annual cool season legume or pulse crop that are relatively easy to cultivate, but their growing period is limited (Endres and Kandel 2021). This means that peas do not grow well in hot climates, such as in Viet Nam and other southeast Asian countries. However, peas can be an alternative ingredient use to replace SBM in some countries. To our knowledge, no study on the use of field peas in food animals, including swine, in Viet Nam has been published. This study, therefore, was conducted to determine the effect of pea replacement of SBM in the diet of finisher pigs on growth performance, carcass traits, and meat quality.

Materials and methods

The experimental protocol was approved by the Hue University Animal Ethics Committee, No. HUVN0021 dated 10 November 2022. The experiment was carried out at Cu Chi Pig Farm, Ho Chi Minh City, Viet Nam.

Animals and housing

Twelve-hundred (1,200) finishing F1 (Yorkshire × Landrace) pigs, equally male and female, at an average weight of 60.71± 0.16 kg, were used for the 8-week feeding trial. The animals were vaccinated against the most common infectious diseases one week before the start of the experiment and kept in closed houses with concrete floors at 26-29⁰C and a relative humidity of 80-85 percent. The pigs were allocated to thirty pens measuring 6.5 m x 8 m equipped with two feeders and two nipple drinkers to access feed and water ad libitum. Each pen housed forty pigs grouped by sex, and there were six replicates per treatment, with three replicates of castrated male pigs and three replicates of female pigs.

Experimental design

The experiment was a complete block design, with sex designated as the block, and it lasted for 8 weeks. All animals were randomly allocated to one of five dietary treatments. The control diet (CTL) contained SBM as the main protein source, and S75-P25, S50-P50, S25-P75, and S0-P100 represented 25, 50, 75, and 100 percent pea meal replacement of SBM and 0, 8, 16, 24, and 32 percent actual pea inclusion in the diet on a dry matter (DM) basis (Table 1).

Diets and feeding

Iso-caloric and iso-nitrogenous diets were formulated using broken rice, rice bran, SBM, peas (PM) and FM, and their nutrient levels were determined based on the recommendations of the NRC (2012). All diets were formulated to equivalent levels of Standard Ileal Digestible (SID) lysine, methionine + cystine, threonine, and tryptophan, and synthetic amino acids were used to adjust the diets to the desired amino acid levels. Pigs were fed ad libitum. Diet ingredient and nutritive values are presented in Table 1. The diet cost was calculated based on individual ingredient prices and their inclusion levels at the start of the experiment (Table 1).

Measurement

Growth performance and economic benefit

In each pen, five pigs were randomly selected according to an average live weight of the animals in the treatment, and these animals were numbered by ear ring. Live weights of the five numbered pigs per pen were recorded at the beginning and at the end of the study, and average daily gains (ADG) were calculated. The quantity of feed offered was weighed and recorded daily, feed waste was recorded, and daily feed intake (DFI) was calculated for each pen. Feed conversion ratios (FCR) were calculated as DFI/ADG. To estimate the economic benefit of dietary pea inclusion, feed expenditure per kg live weight gain was calculated according to the treatment diet price and its FCR at the termination of the trial.

Carcass characteristics and meat quality

Upon trial termination, twenty pigs (two castrates and two females per treatment) were slaughtered to measure carcass traits and meat pH. Animals were moved to a slaughter-house, circa80 km from the experimental farm. At the slaughter-house, pigs were stunned (225–380 V, 0.5 A, 5–6 s) in the post-absorptive state (17 hr), allowing for the provision of water. A medial split was made in the animal carcass following removal of the head. Live weight at slaughter and hot carcass weight were recorded to calculate the dressing percentage. At 45 min postmortem, backfat thickness at P2 was measured on the partitioned carcass 10 cm from the midline behind the 10 ^th rib and on the left side of each carcass, using a Palmer caliper. Loin eye area samples were taken between the 10^th and 11^th ribs, and these were then minced and stored for subsequent pH measurement. After 45 minutes, pH⁴⁵ at the M. semimembranosus muscle was measured using a pH meter (CRISON 507, Crison Instruments S.A., Barcelona, Spain) fitted with a glass electrode. Similarly, pH²⁴ and pH⁴⁸ were measured at 24 hr and 48 hr post-slaughter.

Muscle percentage was calculated according to the USDA Pork Grade:

Muscle (%) = [8.588 + (0.465 x Carcass weight) + (3.005 x Loin eye area) – (21.896 x P2 backfat thickness)]/Carcass weight

In which the backfat thickness P2 is in Inches, the Loin eye area is in square inches, and the Carcass weight is in pounds.

Chemical analysis

Feed ingredient and loin muscle samples were retained and chemically analyzed as dry matter (DM), crude protein (CP), ether extract (EE), crude fiber (CF), total ash, total calcium, and total and available phosphorus according to the AOAC (1990). The blood urea nitrogen (BUN) concentration was measured at the beginning and end of the experiment using the Beckman Unicel DxC800 Synchron method. The BUN value was used as a criterion in the selection of the optimum dietary pea inclusion level. Blood samples were taken at the termination of the experiment from two pigs per pen before morning feeding via anterior vena cava puncture and placed into 10-ml heparin-free vacutainer tubes (Becton Dickinson Vacutainer Systems, Franklin Lakes, NJ, USA) to determine the BUN concentration. Blood samples were centrifuged at 1,200 x g for 15 min at room temperature, and the serum was then stored immediately using a BUN color test kit.

Data analysis

Data were analyzed by ANOVA using the General Linear Model (GLM) procedure of Minitab (2016) version 16.2. Pair wise comparisons with a confidence level of 95 were used to determine the effect of the pea dietary inclusion level. The results are presented as least square mean (M) and pooled standard error of the mean (SEM). Statistical model:

Y _ij = μ + T _i + S _i + + T_iS _i + e_ij;

In which: Y _ij = observed value; μ = population mean; T_i = treatment effect; S _i = effect of sex; T_iS_i = interaction effect of treatment and sex; e _ij = natural errors; i = tested factors; j = replicates.

Results and discussion

Growth performance

No diseases or mortalities were evident in any treatment group, so no veterinary services were required during the study. Growth performance data are displayed in Table 2. During the full length of the finishing period (60-100 kg), no differences in ADG, DFI, FCR or BUN levels were observed among dietary treatments (p>0.05). The final live weight ranges were 105.36-106.43 kg, ADG were 797.62-816.16 g, and DFI were 2.19-2.20 kg.

Figure 1. Relationship between pea in the diets with ADG	Figure 2. Relationship between pea in the diets with FCR

In addition, higher values for castrates than females for ADG, DFI, G:F and BUN, and lower values of FCR, were evident (p<0.05), but no interaction between dietary pea inclusion and sex was observed (Table 3).

In several recent studies, the partial or total replacement of SBM was accomplished by the addition of several different protein meals. Parrini et al (2023) recommended the use of alternative legumes (e.g, peas) as protein sources but emphasized the need for awareness of meal components that could create problems in palatability, digestion, and low nutritional value. Gatel and Grosjean (1990) reported that the use of peas and faba beans as alternative protein sources in pig diets at > 20 percent inclusion levels reduced performance due to limiting methionine and tryptophan levels. Therefore, the inclusion of peas in swine diets must be accompanied by the addition of other protein sources to balance total nutrients and especially, the essential amino acids. In the present study, synthetic essential amino acids were added to the diets containing peas to balance the amino acid profile of the diet (Table 1).

The results reported herein suggest that replacement of SBM with increasing levels of pea meal had no adverse effect on swine growth performance. These results are in agreement with those previously obtained by others (Gatel 1994; Stein 2002; Degola and Jokus 2018). Degola and Jokus (2018) studied the effect of the inclusion of peas Almara, faba beans, and lupins as replacements for SBM on growth performance, and they concluded that there were no differences in ADG, DFI, or G:F in grower-finisher swine between diets. Stein (2002) included up to 18 percent peas in grower swine diets and up to 36 percent peas in finisher swine feed as replacements for SBM and found no negative effects on final bodyweight, ADG, DFI, or G:F. Similarly, Gatel (1994) and Landblom and Poland (1997) reported no adverse effects on growth performance when 40 percent peas were included in grower-finisher swine diets, and Sonta et al (2021) also indicated positive results for ADG and FCR when different levels of peas replaced SBM in their experimental diets.

In contrast, Zmudzinska et al (2020) fed a diet containing peas, lupins, and rapeseed meal (RSM) to grower-finisher pigs, and the final body weight and ADG of the animals of their test animals was lower than the same parameters in their control SBM-fed pigs. Newman et al (2011) reported that there were no differences in final body weight, DFI and G:F of swine fed diets containing pea chips in place of SBM, but that there was a quadratic difference in ADG.

The differences in ADG, DFI, and FCR between castrate and female pigs in the present study were comparable to those obtained by Thacker and Qiao (2002), who reported that castrates gained faster and consumed more feed than did female pigs when both were fed either 10 percent peas or 6 percent canola meal, however, the FCR for castrates were lower than were those of the female animals. No interaction effect was evident for ADG, DFI, FCR, or G:F between diet and sex in the present study, which is consistent with the results of Zmudzinska et al (2020), who reported that the final body weights and ADG of grower-finisher pigs fed legume seeds, including pea cv. Tarchalska as replacement for SBM, were not affected by the type of mixed legume seeds or gender.

Carcass traits and pH of loin muscle

Data on carcass traits and pork pH are presented in Table 4. There were no significant differences in carcass dressing, loin muscle area, lean percentage, P2 backfat thickness and pH values at 45 minutes or at 24- and 48-hours post-slaughter. The carcass dressing percentage for the pigs that were slaughtered at ~100-kg bodyweight ranged from 77.10 to 77.93, and the muscle percentage ranged from 53.72 to 54.20, basis USDA average carcass. The pH values declined from slaughter to 48-hours post-slaughter (6.63-6.70 and 5.33-5.35, respectively). There were no differences between treatments in the chemical composition of the loin muscle.

Partial or total replacement of SBM by PM did not adversely affect carcass traits or the pork pH in post-slaughter pigs. These results are consistent with previous observations. Sonta et al (2022) replaced SBM with PM and found similar pig carcass characteristics. Cebulska et al (2021) concluded that replacing SBM protein with legume protein (peas and yellow lupins) did not adversely affect pork quality, including its pH, water holding capacity, water content, CP, or color, marbling, and firmness. Zmudzinska et al (2020) concluded that feeding grower-finisher pigs with diets containing mixed legume seeds (peas and lupins) and extracted RSM did not adversely affect carcass length, backfat thickness, pH⁴⁵ and pH⁴⁸, color, water holding capacity, or drip loss. Degola and Jonkus (2018) replaced 15 percent and 28 percent of dietary SBM with peas and found no differences in carcass dressing percent, muscle eye area, water content, CP content, ether extract (EE), pH, or cholesterol. Izquierdo et al (2017), replacing 100 percent of SBM with various varieties of peas, did not observe any differences in carcass lean and fat components, while Hanczakowska and Swiatkiewicz (2014), using a diet with peas replacing 50 percent of SBM during the grower stage and 100 percent during the finisher stage, showed no differences in backfat thickness, dressing yield, or loin eye area. However, Degola and Jonkus (2018) pointed out that pigs fed the diets with 28 percent peas and 25 percent faba beans had a lower lean meat percentage, greater backfat thickness at P2, and less internal fat.

In the present study, an interaction effect for the carcass characteristics between diet and sex was not determined, as Zmudzinska et al (2020), when replacing SBM with mixed legume seeds in grower-finisher swine diets, had concluded that pork meat quality parameters were not affected by sex.

Conclusions

• The results of this study demonstrate that PM can totally replace SBM and be included in finisher pig diets at up to 31 percent with no adverse effect on growth performance, carcass characteristics, or meat pH.

Acknowledgement

This study was funded in part by Pulse Canada, Winnipeg, Manitoba, Canada.

Conflict of interest

The authors declare no conflicts of interest.

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