Intake, rumen fermentation and apparent digestibility of Aerbasi cashmere goats fed corn stover, caragana and their mixture on the Mongolian plateau

Background To effectively use local available feed resources to address the problem of animal feed shortage in winter, the intake, rumen fermentation and apparent digestibility of Aerbasi cashmere goats fed corn stover (CS), caragana (CA) and their mixture were studied on Mongolian plateau. Results Sixty healthy Aerbasi cashmere goats (BW 30 ± 2.35 kg) were used in this experiment and the diet were assigned randomly to one of 5 groups (12 sheep/group) in a completely randomized design. The basal diets contain same ratio of concentrate and premix, but different mixing ratio of dry CS and CA. The treatments were designed as CS, CA, CS 80% + CA 20% (MT1), CS 50% + CA 50% (MT2), and CS 20% + CA 80% (MT3). Statistical analyses of chemical composition, intake, apparent digestibility, particle size distribution and fermentation were performed by one-way ANOVA using the general linear model (GLM) procedure of SAS version 9.1. With an increased mixing ratio of CA, intake of DM, NDF, and half cellulose was decreased ( P <0.05). Meanwhile intake of CP, ADF, and acid detergent lignin (ADL) was increased ( P <0.05). The apparent digestibility of DM, organic matter (OM), and NDF in the CS treatment was higher ( P <0.05) than in the other treatments. Compared to the CS treatment, the proportion of particles ≤ 0.1 mm in size was significantly ( P <0.05) higher in the CA treatment, but this was not the case for particles > 5.0 mm. With an increased mixing ratio of CA, the proportions of 0.5–1.0 and 1.0–5.0 mm particles decreased ( P <0.05), but the proportion of > 5.0 mm particles did not. Meanwhile, the proportions of ≤ 0.1 and 0.1–0.5 mm particles increased ( P <0.05). Conclusion The results confirm that caragana and corn stover can be used as animal


Background
The Inner Mongolian plateau, located in North China, has an average altitude of > 1,000 m [1], and is as one of the highest areas in China with a low winter temperature [2]. The dry continental climate is characterised by an annual rainfall of approximately 8 inches (200 mm) and the mean temperatures during the warmest and coldest months vary over an enormous range [3]. Traditionally, the people living in the Inner Mongolian plateau region were nomadic and principally engaged in raising sheep and goats; however, extensive livestock farms were developed in the 20th century [4]. Although the harsh climate restricts the agricultural and animal industry, in irrigated areas, corn and other crops can be grown on the plateau.
The major constraint on raising dairy on the plateau is poor livestock feed quality and quantity, especially during the winter season. The main feed resources for goats are hay, made from native grasses, and by-products from agriculture. Animals fed on low-quality roughage show low production; this is a problem for both the livestock industry and the local economy. In general, cashmere goats feed extensively during the summer, showing relative fatness and thinness during the autumn and winter, respectively, and physical weakness during the spring [5]. To improve the livestock production system, to cover the animal feed shortage during the winter season, technologies exploiting locally available resources have been developed. These include determining the adaptability of crop residues and legume shrubs to various conditions, and exploring their nutritional value and potential productivity [6].
Corn (Zea mays L.) stover (CS) is a locally available crop by-product that is widely used for cattle, sheep, and goat feed, at a lower cost than traditional animal feed [7]. When corn is harvested for grain, 40-50% of the dry matter (DM) of the corn plant remains in the field, including the leaves, stalks, husks, and cobs. After field exposure, the dry stover are collected and preserved for use as roughage for livestock. The use of CS as an animal feed has proven to be economically viable, not only as a way of disposing of CS residues but also as an alternative for feeding livestock in regions where corn is the main crop [8]. At present, CS is the major forage crop in goat dietary regimes in China [9], and it has the potential to provide more support to animal production systems than conventional forage crops in areas with high corn production [10].
Caragana (Caragana arborescens Lam.; CA) is a common shrub located in arid and semiarid areas of North China, and widely distributed in Inner Mongolia [11]. Most previous studies on CA were concerned with its biological taxonomy, genetic diversity, and ecological value; very few studies have assessed its potential applications [12]. In recently years, large quantities of CA were planted as forage crops in Inner Mongolia, due to its high DM yield and CP content [13]. Generally, local farms collect and store CA in the autumn, and mix it with CS for livestock feed during the winter. The nutritional value of CA can compensate for any shortage of CS, and their mixture can be used as a uniquely valuable feed.
CS and CA are believed to be important locally available feed sources, which can be preserved to help farmers feed their livestock throughout the winter. In general, fresh CS and silage can be used for animal feed, since they contain appropriate quantities of nutrients. However, due to a scarcity of winter feed, large amounts of dry CS or CA are currently being fed to sheep and goats in local farms on the Inner Mongolian plateau. When the CS is exposed in the field for a long period, it results in low-quality yields with decreased CP content and poor digestibility. In pastoral areas of grassland, there is a shortage of pasture resources [12,14]. Therefore, it is particularly important to feed cashmere goats at this location. The energy value of the feed directly affects the digestion of nutrients by the animals [15]. In particular, protein energy is a measure of diet quality [16]. Caragana is abundant on the Inner Mongolian plateau and has a high CP content, which is an important indicator of its nutritional status. Local cashmere goats are not productive during the winter, a season in which local farmers can only use dry CS to meet the basic energy requirements of cashmere goats. To improve the nutrient content of CS, local farmers collect CA in the late autumn, and then mix it with CS as a feed supply for livestock during the winter. In general, the feed mixing ratios used by farms are as follows: CS 80% + CA 20%, CS 50% + CA 50%, and CS 20% + CA 80%. As such, the same ratios were used in this study.
However, to our knowledge, limited information is available on the optimal ratio of CA to CS for promoting growth of goats during the winter. Therefore, the objective of this research is to determine the optimum CS:CA ratio for promoting sheep and goat production in the Inner Mongolian plateau, by adding CA to CS in varying proportions. Further objectives were to determine the effects of the feed on the intake amounts, rumen fermentation, and apparent digestibility of Aerbasi cashmere goats.

6
The chemical compositions of CS, CA, and their mixture were assessed in The volatile fatty acid (VFA) contents in the rumen of Aerbasi cashmere goats fed CS, CA, and a mixture were analysed in Table 4. The ruminal pH of goats fed CS was significantly (P<0.05) lower than that of those fed CA. The ammonia content in CA was the highest, and the ammonia content of MT1 was significantly higher(P<0.05) than that in CS. Total VFA content in MT1 was significantly increased (P<0.05) compared to MT2 and MT3. With increased mixing ratio of CA, the acetic acid (AA), propionic acid (PA), butyric acid, and total VFA contents, and AA/PA ratio, significantly (P<0.05) decreased, and the content of AA,PA,BA in MT1 was higher than MT2 and MT3 (P<0.05); however, the ammonia content was significantly (P<0.05) reduced initially, and then increased.
The particle size distribution of rumen in Aerbasi cashmere goats fed CS, CA, and a mixture were analysed in Table 5. The 0.5 mm-sized particles had the highest relative abundance among all particle sizes in all treatments, at > 32%; the 5.0 mm-sized particles had the lowest relative abundance, of ≤ 1%. Compared to the CS treatment, the ≤ 0.1 mm-sized particles were significantly (P<0.05) more abundant in CA, but the abundance of the > 5.0 mm-sized particles did not differ. With

Discussion
Compared to CS, the CP content of CA was higher by 6%, and its NDF was lower by 4%. Therefore, with increased mixing ratio of CA, the CP content of the mixtures increased and the NDF content decreased. Since woody plants have high lignin content [17], the ADF and ADL contents of CA were higher than those of CS or their mixture. The MT1 in this study was close to meeting the CP requirement of goats [18]; when 20% of CA was added to the CS, the CP content increased and the nutritional requirements were met to the goats.
Five diets were formulated to meet the animals' mineral and vitamin requirements based on the Cornell-Penn-Miner recommendations [9]. It showed the MT1 was 6.37% DM which can meet the CP requirements (5.1% DM) of cashmere goats during the winter, and we can assess its utility as feed. As shown in Table 2, these diets were formulated as a general winter feed, but the energy and protein contents were insufficient to meet the nutritional requirements of the Mongolian sheep [4].
General, woody plants contain large amounts of ADF and ADL, which results in decreased nutrient uptake and digestibility for livestock [19][20]. In the present study, the ADF and ADL contents of CA were higher than those of CS [6]. In addition, with increased mixing ratio of CA, the DM intake decreased. The major reason for this is that that CA has higher fibre and lignin content, which results in reduced dietary energy, feed uptake, and digestibility. If the ADF and ADL content in the diet was increased, and the goats had full rumens, continuous feed intake would be inhibited [21]. The high fibre content could influence digestibility and cause the goats to feel more full, and therefore reduce their intake [9]. The lignin content of CA, and its effect on the production performance of goats, is a major factor limiting its use in feed mixtures [22][23].
The apparent digestibility of DM in MT2 and MT3 was lower than that in MT1, showing that the MT1 was a good mixing ratio which has a higher apparent digestibility of DM. When the mixing ratio of CA was over 20%, the high lignin resulted in low apparent digestibility of DM. Regarding production, the apparent digestibility of CP increases with an increase of dietary CP. This could be due to reasonable dietary protein levels being conducive to the reproduction of rumen microbes, enhancing the ability to break down fibres, and thereby increasing their digestion and absorption [4,24]. Additionally, CA contains various vitamins, trace elements, fats, sugars, nucleic acids, and inorganic nutrients, such as potassium, calcium, and magnesium, all of which are conducive to the growth and reproduction of fibre-decomposing bacteria [25]. Generally, the activity of rumen microorganisms may be low when ruminant fed low CP feed. As a result, it is difficult to correctly evaluate the difference in digestibility and rumen fermentation. In the future, it is necessary to study the relationship between low CP content and rumen microorganism activity, digestibility or rumen fermentation.
The proportions of various sizes of pellets in sheep rumen and faeces were assessed. Small particles were most abundant, with those < 3 mm in size accounting for > 90% of all particles for both CA and CS. There was no significant difference in particle size distribution among the different types of roughage (P> 0.05). The proportion of > 1.0 mm-sized particles in MT1 (11.96%) was higher than those in MT2 and MT3. The small-sized particles (0.1-1 mm) were most abundant in MT3 relative to the other treatments, while the large particles (1-5 mm) were most abundant in CS. The reason for this may be related to the lignin in the diet, the lower ADL content in MT1 affects digestible particle activities and nutrient digestion [16,[26][27]. The ADL content in MT3 (22.82% of DM) was lower than that in CA (24.72% of DM), but higher than in the other treatments. Due to the difficulty in digesting ADL, it stayed in the rumen for a long period [28]. Particles are chewed by cashmere goats repeatedly, such that the number of particles and surface area of the cell walls are increased, in turn increasing the chance that bacteria can reach the fibre and colonise it [29]. There were no significant effects of particle size on the pH of the gastrointestinal tract at the time of slaughter. Previous studies reported no effect of corn particle size on rumen pH, and that starch content varying from 28% to 46% does not affect pH [30].
Similarly, in the present study, differences in particle size did not greatly influence pH [31]. A higher proportion of 1.0 mm-sized particles indicates that the indigestible and degradable content of feed is higher [22,32]. Here we found the MT1 contained a higher proportion of > 1.0 mm-sized particles, which explains why the goats were able to refine the feed pellets via multiple ruminations and chewing, to increase the availability of surface microorganisms [33]. Therefore, adding 20% CA was effective for improving feed digestibility.
Typically, grazing is prohibited from mid-March to mid-June, but it remains necessary to supply cashmere goats with proper nutrition at a low cost. Cashmere goats are most productive from the beginning of September to the end of December, and their productivity ceases in February. In this study, we were able to supply nutrients at, or slightly below, the level required to maintain the goats.
Cashmere goats have a greater ability to digest high-fibre materials than do sheep [10,34]. Our data showed that, even though the CA cannot meet the nutritional needs of cashmere goats, increasing the ratio of CA to CS is feasible for feeding cashmere goats. In the future, a longer-term experiment is needed to study changes in digestive metabolism, carcass health status, and production performance after long-term feeding of livestock with unconventional feed in the Inner Mongolian Plateau desert grassland.

Conclusion
The intake, rumen fermentation, and apparent digestibility of Aerbasi cashmere goats fed CS, CA, and a mixture of the two were studied in the Inner Mongolia plateau. With increased CA mixing ratio, the CP dietary content, intake amounts, and apparent digestibility of CP increased. The intake and apparent digestibility of DM, rumen ammonia, and VFA, and the proportion of > 1.0 mm-sized particles, were higher in MT1 than in MT2 and MT3, indicating that MT1 was a good option as goat feed.

Animal care
The  Table 1.  Growth trial Sixty healthy Aerbasi cashmere goats (BW = 30 ± 2.35 kg; mean ± SD) were used in a randomly experiment. Groups were balanced for parity and production during each period. The diet were assigned randomly to one of 5 groups (12 sheep/group) in a completely randomized design. They were penned individually in a well-ventilated shed that was cleaned weekly. Before starting the trial, all goats were vaccinated against clostridial diseases and treated for internal parasites. The diet was provided with an allowable refusal level of 10% DM of the diet. The animals were fed the diets three times a day at 8:00, 13:00 and 19:00, and clean drinking water was available at all times. After a 10 days adaptation period, the 45 days growth trial was started. Feed offered and feed residues were weighed daily along the growth trial to calculate the net intake of feed. The refused feed was collected daily, weighed, and individually bulked for analysis. Samples of the daily refusals from each animal and feed offered were dried at 105°C for 24 hours to determine the DM intake.

Digestibility trial
When the growth trial experiment was completed, the apparent nutrient digestibility of the experimental diets was taken in animals in metabolic cages equipped with separate feeders, an automatic watering trough, and a system for the separate collection of feces and urine. Twelve goats (

Chemical analysis
The feedstuff was recorded every day and it was weighed for 3 consecutive days to determine the dry matter intake (DMI), organic matter intake (OMI), crude protein intake (CPI), neutral detergent fiber intake (NDFI), acid detergent fiber intake (ADFI), acid detergent lignin intake (ADLI), half cellulose intake (HCI) and cellulose intake (CELI). The particle size of feedstuff was sampled by utilizing the Penn State

Statistical analysis
Statistical analyses of chemical composition, intake, apparent digestibility, particle size distribution and fermentation were performed by one-way analysis of variance of SAS (SAS 9.0, SAS Inc. Chicago, USA) and the statistical model is: AA/PA, ratio of acetic acid to propionic acid.

Overview
All authors have read and agreed to the content of the paper, which meets the submission requirements for BMC Veterinary Research.

Ethics and consent
The experiments goats were allowed to the local animal protection law, and there was no IRB review committee (institutions) or IACUC (institutional animal care and use committee) at local area, but we gain the technical support from the professors from Inner Mongolia agricultural university college of animal science. In addition, the experimental sheep will be well placed in the animal placement center of the west campus of Inner Mongolia agricultural university (located at 306 zhaowuda road, saihan district, Hohhot, Inner Mongolia) after the end of the experiment.
During the later management period, sufficient feed will be ensured for the experimental sheep.

Research involving animals
The experiments goats were allowed to the local animal protection law, and there was no IRB review committee (institutions) or IACUC (institutional animal care and use committee) at local area, but we gain the technical support from the professors from Inner Mongolia agricultural university college of animal science. In addition, the experimental sheep will be well placed in the animal placement center of the west campus of Inner Mongolia agricultural university (located at 306 zhaowuda road, saihan district, Hohhot, Inner Mongolia) after the end of the experiment.
During the later management period, sufficient feed will be ensured for the experimental sheep.

Biosafety and Biosecurity
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Standards for research in complementary and alternative medicine
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Trial registration
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Availability of data and materials
All data generated or analyzed during this study are included in this published article and its supplementary information files.

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