Effects of replacing corn stover silage by Psophocarpus scandens-based forages on nutrient digestibility and productivity of growing sheep

Le Thanh Phuong¹, Nguyen Thanh Dat² and Nguyen Thiet²

¹ Emivest Feedmill Vietnam Company Limited, Binh Duong province, Vietnam
nthiet@ctu.edu.vn
² College of Rural Development, Can Tho University, Can Tho City, Vietnam

Abstract

This experiment aimed to evaluate the effects of replacing maize stover silage with Psophocarpusforages on the productivity and nutrient digestibility of growing sheep. Nine male sheep were selected and arranged into a completely randomized design, consisting of three dietary treatments with three replicates. The treatments were: PS0: 100% maize stover silage; PS20: 80% maize stover silage plus 20% Psophocarpus; PS40: 60% maize stover silage plus 40% Psophocarpus. All animals received 300 g of commercial concentrate daily (200 g for morning feeding and 100 g for afternoon feeding). The results showed that Psophocarpus had a low level of soluble protein, ranging from 12.4 to 13.5 (%/ of total CP). There were positive relationships (R ² =1) between the level of PS in the diet and live weight gain and feed conversion. It was concluded that replacing maize stover silage with Psophocarpus scandens up to 40% could be a viable strategy for sheep farms.

Keywords: nutrient intakes, sheep, tropical legumes, weight gain

Introduction

Forages are a critical component of ruminant diets, supplying essential fiber, energy, and nutrients necessary for optimal productivity and health. Among the most widely used forages, maize stover silage is a popular roughage choice at cattle, goat or sheep farm in Vietnam due to its high energy content, and palatability. However, maize stover silage has low protein and high cost for production. As such, there is growing interest in alternative forages that can improve nutrient utilization and reduce feed costs. Among legume forages, Psophocarpus scandens) is popular in Vietnam and has emerged as promising candidates for replacing corn stover silage in ruminant diets. Psophocarpus is known for high protein content compared to grasses (Kambashi et al. 2014), as well as their ability to fix atmospheric nitrogen, which can contribute to soil fertility and lower the need for synthetic fertilizers in forage production (Phillips, 1980). Previous studies have shown that Psophocarpus can replace concentrate up to 20% without negatively affecting performance in pigs (Kambashi et al 2016) and can improve rumen function, leading to increase in feed efficiency and nutrient utilization (Castro-Montoya and Dickhoefer, 2018). Despite the well-documented nutritional benefits of Psophocarpus, its effects on sheep productivity and nutrient digestibility when used as a replacement for corn stover silage are not fully understood. Therefore, it is important to evaluate whether these benefits can translate into improved productivity and nutrient digestibility in sheep. The objective of this study is to investigate the effects of replacing corn stover silage with Psophocarpus -based forages on the productivity and nutrient digestibility of sheep. We hypothesize that replacing corn stover silage with legume-based forages may improve nutrient digestibility and lead to enhanced growth performance in sheep.

Materials and methods

Experimental design

Nine male sheep with average body weight (BW) of 19.03 ± 0.58 kg was arranged into a completely randomized design, consisting of three dietary treatments with three replicates. Sheep were randomly assigned to one of three groups, corresponding to different levels of Psophocarpus scanden (Photo 1) inclusion in the diet.

Photo 1. Psophocarpus scanden develop in the experimental area

The treatments were as follows: (PS0): 100% maize stover silage (control);

(PS20): 80% maize stover silage + 20% Psophocarpus;

(PS40): 60% maize stover silage + 40% Psophocarpus.

All animals received 300 g/day of commercial concentrate daily (200 g for morning feeding and 100 g for afternoon feeding). The experiment lasted for 42 days, including a 07-day adaptation period followed by a 35-day data collection period. The chemical composition of experimental roughage diets and concentrate was presented in Table 1. The sheep were fed twice daily at 08:00 and 15:00 h.

Data collection and measurement

Feed intake was recorded daily throughout the experiment. Daily feed intake was measured by calculating the difference between the amount of feed offered and the refusals. Feed samples were collected weekly and stored at -20°C for later chemical analysis. At the end of the experiment, all feed samples were thawed and mixed thoroughly, and subsamples were dried at 65 °C approximately 24 hours to determine dry matter (DM). Crude protein (CP) and ash were analyzed according to AOAC (1990), while neutral detergent fiber (NDF) and acid detergent fiber (ADF) were determined using the procedure developed by Van Soest et al (1991). The body weight of the sheep was recorded at the beginning and the end of the experiment, with the sheep weighed before morning feeding.

Nutrient digestibility was assessed using a total collection method. During the final 7 days of the experiment, feces were collected from each animal for five consecutive days. Fecal samples were weighed and stored at -20°C. At the end of the collection period, samples were pooled for each sheep, dried, and ground for chemical analysis. Digestibility coefficients were calculated for the following nutrients: dry matter; crude protein; neutral detergent fiber and acid detergent fiber.

This study we also analyzed protein solubility of Psophocarpus scanden. The method for determination of protein solubility we applied from the recommendation of Hong and Trang (2022) and determined the nitrogen content of the filtrate according to (Whitelaw and Preston 1963). Briefly, three grams of samples were shacked into the 100 ml of 1M NaCl for 3 hours and then filtered throughout Whatman No 4 of filter paper and after that N content of filtrate was determined according to the recommendation of Whitelaw and Preston (1963).

Statistical analysis

The data are presented as the mean ± SEM. The data for protein solubility was analyzed by unpaired T-test. Other data were analyzed with one-way ANOVA. The significance of pairwise comparisons was determined by Tukey posttest. Significance was declared at p<0.05.

Results and discussion

Soluble protein of Psophocarpus scanden

A tendency of significant difference of soluble protein was found between fresh and sun-drying of Psophocarpus scanden (Table 2). Fresh status tended to be higherprotein solubility than sun-drying status (p=0.07). Similar finding was reported byHong and Trang (2022). Additionally, Psophocarpus scanden was low in protein solubility, ranging from 12.44 to 13.47 (%/CP). This result was similar to protein solubility of Mimosa leaves and much lower than protein solubility of water spinach as reported by Hong and Trang (2022).

Feed intake and nutrient digestibility

The study revealed significant differences in dry matter intake (DMI) among the treatment groups (p<0.05; Table 3). Sheep fed the 40% Psophocarpus diet (T3) had the highest DMI, while those in the 100% corn silage diet (PS0) consumed the least. The 20% Psophocarpus diet (PS20) group exhibited intermediate intake levels (Table 3). The higher DMI in T3 group could be attributed to the palatability of legumes, or higher nutrient digestibility and nutrient-dense than corn silage (p<0.05, Table 3). Some studies have shown that substituting grass silages by legume silages was generally associated with increased DMI (Dewhurst, 2013; Huhtanen et al 2007), which aligns with the findings of this study. But previous study suggested that there was a negative relationship between legume inclusion and DMI in ruminant (Castro-Montoya and Dickhoefer, 2018). Lower digestibility may result in a higher passage rate (Krizsan et al 2010) or the silage containing legumes has higher NDF content than sole maize silage (Castro-Montoya and Dickhoefer, 2017). Similarly, Longo et al. (2008) found that sheep fed with 40% Leucaena leucocephala showed increased DMI, but DMI decreased when the inclusion level of Leucaena leucocephala was increased to 60%. The intermediate DMI observed in the PS20 group (80% corn stover silage + 20% Psophocarpus) suggests that while a high level of Psophocarpus can increase intake, combining a lower level of Psophocarpus with corn silage may moderate this effect. The results from this study and previous research suggest that the optimal level of legumes in ruminant diets may be less than 40%.

Replacing corn silage with 40% Psophocarpus led to significant improvements in nutrient digestibility (p<0.05, Table 3). Sheep in the 40% Psophocarpus diet (PS40) showed the highest digestibility coefficients for DM, CP, NDF and ADF, while those in the control group (PS0) had the lowest values. The legume’s higher nitrogen content likely contributed to improved protein digestion, as legumes generally provide more degradable protein, which enhances microbial activity in the rumen. These findings are opposite with research suggesting that increasing levels of legumes decreased nitrogen utilization and fiber digestibility compared to grasses due to high level of tannin in legumes (Longo et al 2008). The better fiber digestibility observed in the 40% Psophocarpus diet in this study may also explain the increased DMI, as faster fiber breakdown allows for quicker passage through the rumen, promoting higher feed intake.

Growth performance

Liveweight gain and feed conversion ratio (FCR) did not differ among the treatments (Table 4, p > 0.05), but there was a trend to increase the FCR when sheep consumed high levels of Psophocarpus (Figure 1, R² = 1). However, sheep fed with 40% Psophocarpus (PS40) had significantly higher weight gain compared to those fed solely on maize stover silage (PS0 group) or a lower level of Psophocarpus (PS20 group) (p<0.05, Table 4) and had a linear increase of weight gain with increasing levels of Psophocarpus (Figure 2, R ² = 1). This suggests that legumes offer superior nutritional benefits for growth compared to maize stover silage. The improved performance in the PS40 group can be attributed to the higher crude protein (CP) intake or digestibility from Psophocarpus, which enhances rumen microbial protein synthesis and supports muscle development. This result is consistent with other studies, where weight gain was greater with legume inclusions of 10-40% compared to diets with higher inclusions or without legumes (Castro-Montoya and Dickhoefer, 2018). Similarly, Thu and Dong (2008) reported that replacing para grass with Psophocarpus scandens at a level of 30% improved rabbit performance.

Figure 1. Effects of replacing corn stover silage with Psophocarpus-based forages on FCR	Figure 2. Effects of replacing corn stover silage with Psophocarpus-based forages on weight gain of sheep

Conclusion

The results of this study indicate that replacing maize stover silage with Psophocarpus scanden increased the growth rate of sheep from 99 to 137 g/day and improved the feed conversion 40% in diet without any negative effects on sheep productivity and nutrient digestibility. This is particularly important in regions where Psophocarpus scanden is more available, offering a sustainable and nutritionally superior forage option for ruminants.

Acknowledgments

The author would like to thank the manager of the Experimental farm at College of Rural Development, Can Tho university for supplying all the experiment materials and sincere gratitude thanks to Mr. Van for taking care of the experiment.

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