Influence factors of bamboo intake in captive giant pandas (Ailuropoda melanoleuca)

doi:10.21203/rs.3.rs-2000980/v1

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Influence factors of bamboo intake in captive giant pandas (Ailuropoda melanoleuca)

https://doi.org/10.21203/rs.3.rs-2000980/v1

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published 17 Apr, 2023

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Bamboo is the main food source of the giant panda. To increase bamboo intake in captive giant pandas, we studied factors affecting the bamboo intake. Fourteen healthy captive giant pandas in Dujiangyan Base of China Conservation and Research Center for The Giant Panda (" Dujiangyan Base "for short) were selected as research objects. Bamboo feeding experiment was conducted to study the effects of seasons, bamboo age, slope orientation and felling-feeding time on bamboo intake of the giant panda. We found that the type of bamboo that captive giant pandas feed on was rich in spring and summer, but relatively simple in winter. With the increase of bamboo age, the intake of bamboo leaves decreased, while bamboo culms increased. The feed intake of 1-year-old bamboo leaves and 5-year bamboo culms reached the highest respectively. The slope orientation of bamboo growth also affected the panda's bamboo intake. Moreover, the bamboo intake reached the highest when the felling-feeding time was less than 24h. In short, we confirmed that seasons, bamboo age, slope orientations and felling-feeding time were factors affecting bamboo intake for captive giant pandas. This study was expected to provide scientific guidance improving the feeding behavior management of captive giant pandas.

The giant panda is not only a rare wild animal unique to China, but also a flagship species of biodiversity conservation in the world^1–3. It has been receiving high attention for many years. The giant panda belongs to carnivorous animals, but it takes bamboo plants as staple food, and it is the only carnivorous species with this special feeding nature⁴. Bamboo is the main source of nutrients for giant pandas. Compared with wild giant pandas who freely choose bamboo as staple food, captive giant pandas are limited by geographical location and environment and can only passively accept bamboo provided by captive units. Therefore, it is extremely important to choose bamboo for captive giant pandas scientifically.

At present, researches on bamboo selection for captive giant pandas have been reported. Fu⁵ and He⁶ found that captive giant pandas in the Qinling Mountains have a wide range of bamboo species selection, and the bamboo selection follows the law of energy economics, that is, they prefer to eat bamboo that can quickly obtain the maximum energy, such as bamboo with large leaves and thick mesophyll, or bamboo with tender stems, low lignification and easy to chew. It was investigated that the bamboo species preference of captive giant pandas by Li⁷ and found that captive giant pandas do not like bamboo species with high fiber content. Yang⁸ analyzed the relationship between nutrient content and bamboo intake of captive giant pandas in the Qinling Mountains, and the result indicated that the crude fat, crude protein and ash content of bamboo leaves had a great influence on the selection of staple bamboo species. Meanwhile, the quality of single leaves was also an important factor. Zhao⁹ demonstrated that captive giant pandas tend to choose bamboo with high nutritional value and good palatability in winter. Qu¹⁰ and Yuan¹¹ also confirmed that the bamboo selection of captive giant pandas follows the rule of energy and nutrition, with a bamboo preference for palatability and nutritional value. These researches focused on analyzing the selection preference of captive giant pandas from the perspective of bamboo nutritional composition, but there are few reports on the influence factors of bamboo intake from environment or others.

In this study, fourteen healthy captive giant pandas in Dujiangyan Base were selected as research objects to analyze the effects of seasons, bamboo age, slope orientation and felling-feeding time on bamboo intake. These results were expected to provide scientific guidance and reference for enhancing the bamboo intake and improving the feeding behavior management of captive giant pandas.

Composition and feed intake of staple food bamboo for captive giant pandas in seasonal variation

To understand the feed intake of staple food bamboo for captive giant pandas in seasonal variation, we first analyzed the bamboo type in different months, and the result showed that the type of bamboo that captive giant pandas feed on varied in different seasons. (Figure 1A). The type of bamboo in spring and summer (Apr. to Aug.) was rich, including Chimonobambusa quadrangularis, Chimonobambusa neopurpurea, Chimonobambusa szechuanensis and Phyllostachys nidularia, while relatively simple in winter (Nov. to Mar. of the next year), including C. quadrangularis and Pleioblastus maculate. The bamboo type in autumn (Sep. to Oct.) was in transition between summer and winter. In Sep., the main bamboo species eaten by captive giant pandas were C. neopurpurea, C. szechuanensis and P. maculate, while in Oct., the main bamboo species were C. quadrangularis and P. maculate (Figure 1A).

Next, we analyzed the monthly bamboo intake respectively, and the results showed that the intake of P. maculate in Mar. was significantly higher than that of C. quadrangularis (p<0.01), while the intake of P. maculate in Oct. and Nov. was significantly lower than that of C. quadrangularis (p<0.01) (Figure 1B). In Apr., there was no significant difference between feed intake for P. maculate, C. quadrangularis and C. szechuanensis (p>0.05) (Figure 1C), and in the same way, there was no significant difference in the intake of C. szechuanensis and C. neopurpurea in May (p<0.05) (Figure 1D). The intake of C. quadrangularis in June was significantly higher than that of P. nidularia (p<0.01), and the feed intake of P. nidularia was significantly higher than that of C. neopurpurea (p<0.01) (Figure 1E). In August, the feed intake of C. szechuanensis and C. neopurpurea was significantly lower than that of C. quadrangularis (p<0.01) (Figure 1F). Moreover, the intake of C. szechuanensis was higher than that of P. nidularia and C. neopurpurea (p<0.01) (Figure 1G). Therefore, the above results indicated that the composition of bamboo species varied in different months, and captive giant pandas had different preferences for bamboo in the same months.

Effects of bamboo age on bamboo intake

Fiber content and palatability of bamboo varied with different bamboo ages. To understand the effect of bamboo age on bamboo intake of captive giant pandas, we analyzed the feed intake of bamboo at different bamboo ages under the same conditions of other variables, such as the same bamboo slope orientation and felling-feeding time. Our results showed that the intake of 1-year-old bamboo leaves was the highest for captive giant pandas in the Base (Figure 2A). The leaves intake decreased with the increase of bamboo age, and the intake of 5-year-old and 6-year-old bamboo leaves was almost zero (Figure 2A). However, the intake of bamboo culms increased with the increase bamboo age, and the intake of 5-year-old bamboo culms reached the peak (Figure 2B).

Due to the feed intake of different bamboo species is different in captive giant pandas, we have carried out a detailed study on this. Our results showed that the intake of 1-2 years old bamboo leaves of P. maculate, C. szechuanensis, C. neopurpurea and C. quadrangularis was significantly higher than that of 4-6 years old bamboo leaves (p<0.01) (Figure 2C, 2E-G), but there was no significant difference in the intake of bamboo leaves of P. nidularia among 1-3 years old (p>0.05) (Figure 2D) (bamboo leaves of 4, 5 and 6 years old were not taken). With the increase of bamboo age, the culm intake of P. maculate, P. nidularia, C. szechuanensis, C. neopurpurea and C. quadrangularis was increased respectively, but there was no rise for the bamboo of 6-year-old (p<0.01) (Figure 2H-L). The above results revealed that bamboo intake was significantly affected by bamboo age.

Effects of slope orientation on bamboo intake

Previous studies have shown that there are complex and variable environmental factors such as light, soil moisture, soil temperature and soil mineral content in different slope orientations¹². To understand the effect of slope orientation on bamboo intake of captive giant pandas, we analyzed the feed intake of bamboo growing on four different slope orientations under the same conditions of other variables, such as the same bamboo age and felling-feeding time. Due to bamboo supply factors, only culms of P. nidularia and leaves of C. quadrangularis were fed to giant pandas. Our results showed that the order of leaves intake from high to low was semi-sunny slope, sunny slope, semi-shady slope and shady slope (Figure 3A), and that of culms intake was sunny slope, semi-sun slope, semi-shady slope and shady slope (except P. nidularia) (Figure 3B).

Then feed intake of bamboo leaves and culms in different bamboo species was analyzed respectively, and we found that bamboo intake of leaves of C. quadrangularis, C. szechuanensis, P. maculate, C. neopurpurea growing on the semi-sunny slope was significantly higher than that of leaves growing on other slopes, and culms of P. nidularia growing on the semi-sunny slope was also significantly higher than that of culms growing on other slopes (p<0.01) (Figure 3C-F, 3H). Culms intake of P. maculate growing on the sunny slope was significantly higher than that of culms growing on other slopes (p<0.01) (Figure 3G). There was no significant difference in the feed intake of C. szechuanensis culms and C. neopurpurea culms between sunny slope and semi-sunny slope (p>0.05) (Figure 3I, 3J), but there was a significant difference in the intake of culms between sunny slope and shady slope (Figure 3I, 3J) (p<0.01).

Therefore, these results indicated that slope orientation was one of the factors affecting bamboo intake of captive giant pandas, and the bamboo growing on sunny or semi-sunny slopes was more favored by captive giant pandas.

Effects of felling-feeding time on bamboo intake

Felling-feeding time refers to the time spent from felling the bamboo to transporting it to the feeding enclosure. To obtain the best felling-feeding time, we set the felling-feeding time gradient (<24h, 24-48h, 48-72h and >72h) and analyzed the effect of felling-feeding time on the feed intake of bamboo under the same conditions of other variables, such as the same bamboo age and slope orientation. The results indicated that when felling-feeding time was less than 24h, the intake of bamboo leaves and bamboo culms was the highest respectively, and a decreased intake was observed with the extension of felling-feeding time. After 72h, the giant panda hardly ate bamboo leaves at all (Figure 4A, 4B).

Next, we analyzed the intake of bamboo leaves and culms in different bamboo species respectively, and found that with the increase of felling-feeding time, the leaves intake of C. szechuanensis, P. maculate, C. neopurpurea and C. quadrangularis decreased significantly (p<0.01) (Figure 4C-F). When felling-feeding time >72h, the leaves of C. neopurpurea were no longer taken (Figure 4E). Similarly, with the increase of felling-feeding time, the culms intake of P. maculate, P. nidularia, C. neopurpurea and C. quadrangularis also decreased significantly (p<0.01) (Figure 4G-J).

The above results indicated that with the increase of felling-feeding time, a significant decrease was found in bamboo intake, suggesting that we should shorten the felling-feeding time and try to maintain the freshness of bamboo.

Bamboo age is one of the factors affecting the feed intake of bamboo. Xie ¹³ studied the feeding time distribution of wild giant pandas during the transition period, and found that the feeding time of 1-year-old Fargesia robusta leaves was significantly higher than that of perennial bamboo leaves, which was consistent with our results. Although there were slight differences among different bamboo species, the overall trend of bamboo feeding was consistent. Specifically, the 1-year-old bamboo leaves were the most eaten by captive giant pandas, and with the increase of bamboo age, the feed intake decreased, and the 6-year-old bamboo leaves were almost no longer being fed.

Tannin is a kind of secondary compound produced by plants ¹⁴. The feeding taste of animals was reduced by the astringent sensation of tannin, which influenced the feeding behavior of herbivores¹⁵. Zhao¹⁶ studied the tannin content of leaves in Fargesia spathacea and Fargesia dracocephala, and found that the tannin content of leaves of 1-year-old and 2-year-old Fargesia spathacea was lower than that of perennial leaves, respectively. However, the tannin content of 1-year-old and 2-year-old Fargesia dracocephala leaves was higher than that of perennial leaves, respectively. Therefore, the above results indicate that tannin content of bamboo varies with age.

Previous studies have showed that the nutrient content of bamboo is also affected by bamboo age. Zhao¹⁶ studied the nutritional composition of bamboo and found that compared with perennial bamboo leaves, annual bamboo leaves had higher protein content. Tang¹⁷ found that crude protein content of 2-year-old Bashania spanostachya culms was higher than that of perennial bamboo culms. The nutrient composition analysis of leaves of Bashania fargesii by Wang¹⁸ showed that crude protein content of 1-year-old bamboo leaves was significantly higher than that of 2-year-old and perennial leaves respectively. Sun¹⁹ also indicated that crude protein content of Bashania fargesii leaves and culms decreased with the increase of bamboo age, and Wang²⁰ studied Bashania fargesii and found that amino acids content of young leaves was higher than that of old leaves. Therefore, we suspect that the differences in bamboo intake in this study may be related to tannin and nutrient content in different bamboo ages, but further studies are needed to prove this.

Studies have shown that the ecosystem is significantly affected by slope orientation, which is related to vegetation distribution and has a certain impact on soil carbon storage^21–24. Fan²⁵ found that the ecosystem carbon storage of Phyllostachys edulis on the sunny slope was significantly larger than that on the shady slope. Wei²⁶ suggested that the shoot rate of Bashania spanostachya decreased from the sunny slope to the shady slope. Wu²⁷ showed that slope orientation significantly affected the height of Bambusa pervariabilis × Dendrocalamopsis grandisi, in which bamboo on shady slope was 0.5 meters higher than bamboo on sunny slope on average. Yang's ²⁸ research on natural Phyllostachys heteroclada revealed that the bamboo density decreased gradually from the sunny slope to the shady slope. Yu²⁹ showed that the chlorophyll value of Phyllostachys prominens growing on the sunny side was generally higher than that of bamboo growing on the shady side. Our study demonstrated that feed intake of bamboo growing on the sunny slope was significantly higher than that of bamboo growing on the shady slope. Therefore, we speculate that the differences in bamboo intake may be related to chlorophyll or environmental factors in different slope orientations, but a further study is needed.

Research Site Overview

The Dujiangyan Base of China Conservation and Research Center for The Giant Panda is located in Shiqiao Village (103° 33'E, 34° 57'N), Qingchengshan Town, Dujiangyan City, Sichuan Province, covering an area of about 51 hectares and 785 meters above sea level. The climate here is pleasant, with an average annual temperature is 15.2 degrees Celsius. The average minimum temperature is about 2 degrees Celsius, and the average maximum temperature is only about 28 degrees Celsius. It has abundant rainfall, with an average annual precipitation of about 1300-1800 mm, and a subtropical humid monsoon climate³⁰.

Basic information of captive giant pandas in Dujianyan Base

The healthy captive giant pandas in Dujianyan Base were selected as the research subjects. The basic information of giant pandas is shown in Table 1.

Sample collection

The experiment began on the 5th, 15th and 25th of each month. Bamboo samples were fed for three consecutive days (each sample weighed 5000g). Five kinds of bamboo leaves and culms were dispersed and placed side by side at 9:00 am, and the samples were recovered at 11:00 am. Then we observed the feeding situation of the giant panda and weighed the remaining unconsumed bamboo.

Statistical analysis

Bamboo intake refers to the input weight of bamboo minus the remaining unconsumed weight. To make the picture more concise and intuitive, only bamboos eaten by the giant pandas were shown in the results, bamboo species with zero intake were not shown. Excel 2019, GraphPad Prism 7.0 and AI software were used for data analysis and mapping respectively. All data were expressed as mean ± standard deviation (Mean ± SD), where p<0.05 indicates significant difference, p<0.01 means highly significant difference.

Author contributions

M.W., C.W., Y.Z., and W.L. conceived of the study, carried out the experiments, and drafted the manuscript. L.D., K.W., S.H. and W.Z., collected the samples and performed the research. S.S., and T. L. assisted with the data analysis. D.L., R.W. and Y.H. participated in the study's design and coordination. All authors reviewed the manuscript.

Funding

This work was supported by Giant Panda International Cooperation Fund Project (No. GH201708).

Ethics approval

All experimental protocols and procedures were reviewed and approved by the Conservation and Research Center for the Giant Panda Ethical Review Committee for Experimental Animals (CCRCGP2022002). All methods were performed in accordance with the relevant guidelines and regulations.

Competing interests

The authors declare no Competing interests.

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Table 1

Basic information about captive giant pandas in Dujiangyan Base.
Name	Stud#	Sex	Birth date	Birth origin	Location	Condition
Yingying	382	Female	1991.9.1	Wolong wild, China	Dujiangyan Base, China	Healthy
Ximeng	399	Male	1993.9.19	Wolong Base, China	Dujiangyan Base, China	Healthy
Yueyue	404	Female	1993.11.20	Wolong Base, China	Dujiangyan Base, China	Healthy
Shulan	407	Female	1994.8.31	Chengdu, China	Dujiangyan Base, China	Healthy
Didi	413	Male	1994.10.5	Wolong Base, China	Dujiangyan Base, China	Healthy
Qiaoyuan	416	Female	1993.9.1	Baoxing wild, China	Dujiangyan Base, China	Healthy
Daili	542	Male	1999.9.1	Baoxing wild, China	Dujiangyan Base, China	Healthy
Taishan	595	Male	2005.7.9	Nzp-wash, USA	Dujiangyan Base, China	Healthy
Hanhan	852	Male	2012.8.21	Yaan Base, China	Dujiangyan Base, China	Healthy
Fubao	887	Male	2013.8.14	Vienna, Austira	Dujiangyan Base, China	Healthy
Bingcheng	938	Male	2014.8.22	Yaan Base, China	Dujiangyan Base, China	Healthy
Jiamei	973	Female	2015.8.15	Yaan Base, China	Dujiangyan Base, China	Healthy
Qingqing	975	Male	2015.8.18	Yaan Base, China	Dujiangyan Base, China	Healthy
Nuannuan	977	Female	2015.8.18	Kualaium, Malaysia	Dujiangyan Base, China	Healthy

No competing interests reported.

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Influence factors of bamboo intake in captive giant pandas (Ailuropoda melanoleuca)

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