Introduction

Grasses have low nutritional quality, and influenced by high temperature and radiation, would quickly cause their maturation and lignification, on the other hand, forage varieties with better nutritional profile, such as alfalfa, which had negative effects on productivity in response to climatic anomalies and periods of drought¹. The behaviour of Erythrina species, such as Erythrina americana foliage, the age of regrowth (60, 90 and 120 days) affected crude protein (CP), neutral detergent fibre (NDF) and acid detergent fibre (ADF)² contents, climatic conditions in the dry season in the foliage caused an increase in dry matter (DM 32.3 %) and a decrease in NDF (45.6 %), compared to the rainy season (25.9 and 50.6 % respectively), in addition, a stable production of 14.0 % in CP was maintained³ and in the rainy season E. poeppigiana, without considering the age of regrowth, showed that the CP content is between 16.8 to 20.9 %, in addition, its NDF content is 47.0 %^4,5.

In Apurímac 2012, with respect to the national population of guinea pigs, they represented approximately 8.0 % and their guinea pig production was carried out through family and commercial family farming systems⁶, currently it is reported that the national population of guinea pigs increased to 17.38 million, 45.6 % are raised by small and medium producers and 25.1 %, on a large scale⁷. In this process, their feeding has played an important role, one of the feeding systems is based on balanced feed, plus fresh fodder ad libitum⁸, the latter would provide vitamin C⁹, another is to supply fodder and vegetable residues from agriculture, with the aim of producing animal protein at low cost¹⁰. In addition, we have the use of non-conventional feeds for guinea pig feeding, such as fresh fodder from the foliage of E. poeppigiana¹¹ and the processing of E. edulis leaves into meal, which was included as a protein input¹².

The use of forage tree legumes is an available resource that contributes to the sustainability and efficiency of the production system, improves the quantity and quality of the diet, which will be beneficial for animal feed, and stands out for its protein content (15.7-18.3 %) and digestible energy (3.1 Mcal kg^-1)¹³, nutritional levels that could cover the requirements for guinea pigs. Guinea pigs have a functional caecum where fermentation occurs and according to the nutritional quality of the forage, it was observed that the grass Phleum pratense, both fresh and dry, denoted a convenient digestibility of NDF (76 and 71 %) and FDF (72 and 67 %)¹⁴ and E. poeppigiana harvested from the forage (72 and 67 %). E. poeppigiana harvested at 55 days in the rainy season, due to its notable protein content (17 %) would have a DM digestibility (47.2 %) and structural components (NDF 43.6 and FDA 26.2 %), this behaviour would indicate that it could be a feasible option for animal feed¹⁵.

In order to improve and achieve advantages in guinea pig productivity, the search for alternative feeds continues, including non-conventional feeds. The pisonay (E. edulis) as fresh forage at different ages of regrowth, 4 and 12 months, it was observed that the DM content tended to increase to 28.1 % and CP decreased to 20.1 %, at older ages there was a stability in the NDF content close to 58.0 %¹⁶ and the digestible energy was estimated at 2.6 Mcal kg^-1 DM¹⁷. These variations prompted us to evaluate the nutritional composition, apparent digestibility coefficient (DC) and estimate the digestible energy of E. edulis leaf meal at different regrowth ages (4, 8 and 12 months).

Materials and methods

The edible biomass of pisonay trees (E. edulis) of different regrowth ages (4, 8 and 12 months) from the last cut, from trees located in live fences and used for animal feed in Mosoccpampa, Abancay, was pruned.

The edible biomass consisted of leaves and petioles of the trees, which were subjected to a natural drying process under shade. After approximately 30 days, they were milled in a hammer mill with a 2 mm sieve.

In the maize and pisonay meal, as well as in the faeces, the nutritional composition was determined according to AOAC¹⁸. NDF and FDA were determined by Van Soest et al.¹⁹. Non-fibre carbohydrates (NFC), by arithmetic difference of the 4 components determined²⁰, NFC = 100 - [CP + (ether extract) EE + (total ash) CT + NDF] and crude energy (GE) by the formula of Nehring & Haenlein²¹, GE = 5.72 x CP + 9.50 x EE + 4.79 x crude fibre (CF) + 4.03 x extract free of nitrogen (ELN).

The nutritional evaluation of feed and faeces was carried out at the Laboratory of Nutrition and Animal Feeding, Professional Programme of Veterinary Medicine and Zootechnics of the Catholic University of Santa Maria (UCSM), Arequipa, Peru.

The guinea pigs were sourced from the Del Corral farm (commercial breeding) located in Abancay, in good health and health assessment was carried out once a week throughout the experiment. Three male guinea pigs (replicates) with a live weight (BW) of 1004.3±92.0 g (coefficient of variability, CV = 9.1 %), with an approximate age of 3 months, were used for each age of regrowth of the feed mix, which were placed in individual metabolic cages of 0.16 m², with movable feeders and drinkers located on the outside of the cage. The cages were placed on a table covered with white formica to facilitate cleaning.

Figure 1 Temperature and humidity during the experiment, adapted according to SENAMHI 2022 

The guinea pigs received the feed mixture, in proportions of 64.0:36.0, 66.3:33.7 and 73.5:26.5 (Table 1), constituted by the different regrowth ages (4, 8 and 12 months)¹⁶ of pisonay meal (HP) plus maize meal, based on the nutritional composition of the inputs and according to the nutritional requirements, it was considered 18.0 % protein²² and coated vitamin C (Pro-Premix Nutrition SRL) was added in the amount of 0.5 g kg-1 of feed²³. This feed mixture was fed ad libitum once a day in the morning, in addition to clean, fresh water daily. The experiment was carried out in the facilities of the Biochemistry Laboratory of the Faculty of Veterinary Medicine and Animal Husbandry of the Universidad Nacional Micaela Bastidas de Apurímac (UNAMBA), Abancay, Peru. After 5 days of adaptation of the guinea pigs to the metabolic cages, a 7-day feed habituation phase and 7 days of faeces collection were started. The guinea pigs were subjected to natural light for approximately 12 h, the ambient temperature was between 21 and 24° C and the relative humidity was around 60 % (wall-mounted thermohydrometer).

In both stages, the feed offered and not consumed, consisting of residues and wastes, as well as the amount of faeces, all adjusted to DM, were recorded.

Apparent digestibility (AD) was performed by conventional in vivo digestion by total faecal collection and the formula was used:

The DM of the feed mixture and faeces of each guinea pig were previously determined, quantified, mixed, ground and analyzed.

For the digestible energy, first, the digestible energy content of the feed mixture (ED_A) was determined, using the following formula:

Subsequently, the ED of the different regrowth ages (4, 8 and 12 months) of the HP (ED_HP) was estimated according to the following formula:

The ED of maize (ED_M = 3.85 Mcal kg^-1 DM) proposed by Castro & Chirinos²⁴ and the percentage of substitution (% S) of 64.0, 66.3 and 73.5 % for each age of regrowth were used.

In the determination of the nutritional composition of feed and faeces, as well as digestibility, 2 replicates were carried out for each guinea pig.

For the composition of the HP of each regrowth age and apparent digestibility coefficient (DC) for each nutrient and digestible energy, the average was used and the confidence interval was calculated.

Results

Table 2 shows the nutritional composition of HP (E. edulis). DM ranged from 91.9 to 92.9 % at all 3 regrowth ages. The TP decreased 0.4 % between 4 and 8 months and 1.0 % between 8 and 12 months of regrowth age. At all 3 regrowth ages, EE and TC remained around 1.0 and 9.0 % respectively. NDF expressed a similarity of 46.0 % for 4 and 8 months and decreased to 44.8 % at the age of 12 months. FDF was similar (29.4 %) at ages 4 and 8 months and at 12 months decreased to 26.5 %. NFP remained close to 21.0 % at 4 and 8 months and increased by approximately 3.0 % at the age of 12 months. In the 3 ages of regrowth, the behaviour of BS was between 4.19 to 4.34 Mcal kg^-1 of DM.

Table 3 shows the percentage of digestibility of the nutrients evaluated by CD. The CDMS between the ages of 4 and 8 months decreased by 1.0 % and between the ages of 4 and 12 months it decreased by 4.4 % and in the CDPT the detriment was observed due to the effect of the maturity stage of 62.1, 58.2 up to 46.2 %.

At 8 months of regrowth age, EE and CT, had the highest digestibility percentage, at 12 months CDEE decreased to 11.0 % and CDCT at 4 months reached 30.0 %. The CDFDN at 4 months of regrowth age was around 25.0 %, it was observed that at 8 months it decreased by 3.9 % and at 12 months by 4.3 %.

CDCNF due to the effect of maturity stage tended to increase between the ages of 4 and 8 months by 1.4 % and between the ages of 4 and 12 months by 1.9 %. Digestible energy tends to decrease by 0.13 Mcal kg^-1 DM between the three regrowth ages.

Discussion

The DM of HP was similar to the value reported for Moringa oleifera²⁵. The TP level was lower than that reported in E. americana (25.6 %)²⁶, with the foliage of Erythrina sp. harvested at 4 and 12 months of regrowth age, values that reached 26.0 % and 23.0 % respectively16,17 being at values (>20.0 %) reported in flours derived from shrub foliage²⁷.

Regarding NDF and FDF of HP, they presented values below 52.0 and 34.0 % respectively reported in the foliage of E. americana²⁶ and 58.0 % of NDF determined in Erythrina sp.¹⁵, with a similarity in the NDF of flours obtained from shrub foliage that had values of 30.0 to 50.0 %²⁷.

The ash content of HP was lower than that of E. variegata, which in the rainy period reached (19.0 %)²⁸. The EB of HP in the 3 ages of regrowth was below 4.68 Mcal kg^-1 DM reported in the leaves of E. glauca, it should be noted that this value was found by adiabatic calorimetric pump²⁹.

HP, due to its protein percentage and the fibre observed, could be considered an alternative as an input in the elaboration of food for guinea pigs, this behaviour would be corroborated by the values of PT 19.0 to 35.0 %, FDN 26.0 to 58.0 % and FDA 27.0 to 43. 0 % found in several species of Erythrina³⁰, in addition, it is mentioned that tree species with levels of CP 22.8 % (13.7 to 31.7 %), NDF 37.1 % (23.7 to 51.0 %) and FDA 20.3 % (11.9 to 29.4 %), suggest better digestibility and efficiency for use in livestock as a supplement⁵. On the other hand, the effect of the age of regrowth or state of maturity of the forage observed in E. variegata, caused a decrease of 28.0 to 17.0 % in protein quality²⁸, and could also be considered as a source of nutrients to be used in areas of forage scarcity³¹.

The NDF, FDA and hemicellulose (MEH >16.7 %) of the HP would have values like in other promising forage species (23.6 to 48.5 %, 15.4 to 32.1 % and 8.2 to 32.0 % respectively), which would indicate that their use would depend on the type of animal species³² and values higher than 14.0 % of EMH, such as Leucaena leaf meal (EMH 16.0 %) with a substitution level of 32.3 % in the guinea pig diet³³ , would guarantee benefits in feed consumption and productive parameters (earliness and profit weight), and therefore an improvement in productivity and guinea pig breeding³⁴.

The regrowth ages with HP had similar effects on CDPT, CDEE, CDCT and ED, moreover, these values reached an ideal digestibility with respect to the harvest carried out at 6 months in E. poeppigiana³⁵. On the other hand, the similarity in the behaviour of CDPT (62.1 %) observed at 4 months with respect to alfalfa (PT 62.8 %), suggests an optimal nutritional quality³⁶. Nutrient digestibility is associated with high CP (> 21.8 %), fat (> 6.1 %) and lower fibre (NDF 27.3 % and FDA 16.2 %)³⁷.

Fibre (> to 24.0 %) in HP would probably affect CD, as fibre would seem to increase the rate of passage and cause a decrease in nutrient digestibility³⁵. It would possibly not lead to the development of improved intestinal villus length and width and, therefore, there would be no production of the necessary fatty acids that would affect the luminal environment and its direct action on the intestinal epithelium³⁸.

Another factor would be the age of regrowth: the greater the maturity of the plant, the lower the digestibility of DM, CP and NDF of the HP, the slower the digestion, which would induce food stasis in guinea pigs³⁹, possibly due to the length of the small intestine and the volume of the colon, which represent 55.0 and 37.0 % respectively⁴⁰, furthermore, the greatest retention in the digestion process is observed in the caecum, which represents 60.0 % of the retention time⁴¹.

The DE in the HP would be positively correlated with the TP content, which is observed at 4 months of regrowth age and negatively correlated with the fibre content, which decreases in the other regrowth’s, which would indicate that energy would be available by increasing the protein content of the guinea pig diet⁴². The DA of BS would be around 40.75% and when compared to traditional guinea pig ingredients or inputs the DE is below 2.8 Mcal kg-1 DM⁴³.

HP could be considered as a protein ingredient for guinea pig feed, possibly due to the residence time that would increase digestion in the gastrointestinal tract, due to the contact with the intestinal villi⁴⁴. In addition, due to its remarkable level of fibre, which would be partially or fully fermented from the caecum to the mid-colon, this behaviour would improve nitrogen retention at the caecal level⁴⁵.

The use of non-conventional guinea pig feeds, such as fresh forage, pelleted or extruded, in different feeding systems, would probably improve productive characteristics, such as weight gain and feed conversion⁴⁶, would not significantly affect feed intake and would increase the proportion of fat in the carcasses⁴⁷.