Introduction
Goat and sheep farming are present on all continents due to the adaptation of these animals to adverse soil and climate conditions (Silva et al., Reference Silva, Santos, Duarte, Turco, Cruz Neto, Jardim and dos Santos2019). Semi-arid regions are characterized by prolonged periods of drought, resulting in the unavailability of water and food for animals, which has a negative impact on production systems (Fernandes et al., Reference Fernandes, Ramalho, Rosa, Souza and Mello2020).
Among the possible strategies used for animal feed, we highlight the use of alternative foods that have the potential to meet the nutritional needs of animals at a low production cost. One of the feedstuffs used in the northeast region to maintain livestock farming is spineless cactus (Galvão Júnior et al., Reference Galvão Júnior, Silva, Morais and Lima2014). The spineless cactus is able to grow well in semi-arid regions and maintain a productive profile even in dry periods. In addition to its productivity, it is known for being a source of food and water for animals. However, in order to use palm, it is necessary to add a good source of fibre, since this fodder has a low content of fibre and a low concentration of protein (Cordova-Torres et al., Reference Cordova-Torres, Guerra, Araújo Filho, Medeiros, Costa, Ribeiro and Bezerra2022).
The water crisis is a factor that has affected livestock worldwide. Water is responsible for maintaining the body of animals, as it participates in chemical, enzymatic and metabolic reactions, temperature regulation, among other diverse functions (Silva et al., Reference Silva, Araújo, Santos, Oliveira, Godoi, Gois, Perazzo, Ribeiro, Turco and Campos2023). Foods such as spineless cactus have little dependence on water and are still able to meet part of the animals' requirements, as they are made up of around 90% water (Tegegne et al., Reference Tegegne, Kijora and Peters2007).
Therefore, when animals are fed with palm, lower consumption of water has been reported in research carried out with lactating goats and sheep (Bispo et al., Reference Bispo, Ferreira, Véras, Batista, Pessoa and Bleuel2007; Costa et al., Reference Costa, Beltrão Filho, Medeiros, Givisiez, Queiroga and Melo2009). Spineless cactus is an excellent food source, but there are some restrictions on its prolonged use, as it can cause changes in the animals' digestive tract.
Goats and sheep that receive fodder palm in their diet have osmotic diarrhoea, characterized by increased moisture in the faeces, but without indicating a pathological condition. In scientific studies, this effect has been associated with the high content of soluble carbohydrates and magnesium in fodder palm (Pordeus Neto et al., Reference Pordeus Neto, Soares, Batista, Andrade, Andrade, Lucena and Guim2016).
Realizing the importance of palm as an alternative to meet water needs in semi-arid regions that experience annual water shortages, the aim of this research was to evaluate the productive performance and the occurrence of histological and morphometric changes in the digestive, hepatic and renal systems of goats fed with a diet containing different contents of spineless cactus (Nopalea cochenillifera (L.)) and with partial or total restriction of water for drinking.
Materials and methods
Characterization of the experimental site
The experiment was conducted in the Small Ruminant Experimental Shed at the Zootechnics Demonstration and Experimental Center of the Federal University of Alagoas (UFAL), Arapiraca Campus, which is located in the city of Arapiraca, in the mesoregion of Agreste Alagoano (latitude 9°45′09″ and longitude 36°39′40″). The climate is tropical semi-humid, according to the Köppen-Geiger climate classification. The average temperature is 23.7°C and the average rainfall is 752 mm.
Animals, diets and experiment
The experiment used 35 castrated male goats with no defined breed pattern (SPRD), with an average initial body weight of 19 + 1.4 kg and an average age of 8 months. The animals underwent a 15-day adaptation period and a 75-day experimental period, totalling 90 days of confinement. Before the start of the experimental period, the animals were treated for ecto- and endoparasites.
The animals were confined in individual stalls with access to a feeding and drinking trough, all duly identified to improve control of the experiment. During the experiment, the goats were weighed at the beginning of the experimental period and at the end before slaughter, to obtain the initial and final weight of the animals, respectively. The data were used to calculate average daily gain and dry matter intake (DMI).
Once the goats had been weighed, they were divided into five treatments (Table 1) according to the NRC (2007) for goats at maintenance, the water requirement is 1.1 kg water/kg dry matter (DM) intake, and the contents of spineless cactus were calculated to meet this demand.
Table 1. Proportion of water, hay and forage palm in the treatments
The diet was formulated based on the NRC (2007) to achieve a daily weight gain of 100 g. All treatments had a volume:concentrate ratio of 80:20, and the spineless cactus offerings studied (0.25 or 0.55) were complemented with Tifton-85 hay (0.55 or 0.25, respectively). The concentrate fraction was made up of corn, soy, urea and mineral supplement (Caprinofos).
Feed was offered ad libitum, twice a day (08.00 and 15.00 h). The amount of feed offered and leftovers were recorded to estimate feed intake. Tifton-85 hay and spineless cactus were chopped daily and mixed with the concentrate before being fed to the animals. The goats were fed at will, allowing around 0.20 of the feed to be left over to encourage voluntary consumption. Water intake was measured individually every 3 days during the experimental period, as well as evaporation from two water buckets strategically distributed in the shed, with the aim of correcting water loss through evaporation.
Slaughter and sample collection
At the end of the experiment, the animals were slaughtered in accordance with animal welfare standards and were fasted on solids for 16 h. The entire slaughter process was carried out in accordance with the rules, and the method used was cerebral concussion (Brasil, 2020). The animals were then skinned and eviscerated. The pelvic, thoracic and abdominal cavities were removed. Samples were then taken from the rumen (dorsal sac wall), small intestine (middle portion of the duodenum), liver (left lateral lobe) and kidney (cortical area). The samples were immersed in 10% formaldehyde in labelled plastic jars. Before fixation, the samples were washed in 0.9% saline solution to remove excess food content (Table 2).
Table 2. Chemical composition of diet ingredients on a DM basis (g/kg DM)
a Fresh weight of spineless cactus.
b Neutral detergent fibre corrected for ash and protein.
c Calculated according to Hall (Reference Hall2000).
Histological, morphometric and histopathological analyses and production performance
The analyses took place at the Animal Histology Laboratory at the Agricultural Sciences Center of the Federal University of Paraíba. Initially, the identified material was dehydrated, clarified and embedded in paraffin. For the dehydration stage, the material was immersed in an increasing solution of 70, 90, 100% I and 100% II ethyl alcohol for 1 h each. It was then immersed in xylene I and II for 1 h each. It was then immersed in paraffin (I and II) for 1 h each.
For microtomy of the blocks, the sections were cut on a LEICA® Minot rotary microtome at 5 μm, placed on slides and taken to an oven at 36°C for 2 h. The sections were stained with haematoxylin and eosin. Photomicrographs of each animal's tissue were digitized using an Olympus BX-51 microscope (Olympus) coupled to a digital camera (Olympus DP73) with cellSens Dimension® software, in order to measure the structures in the images.
For the rumen and small intestine, four photomicrographs were taken of each tissue per animal, 7 animals × 4 photomicrographs × 7 measurements, with a total of 196 samples per treatment. The objective used was 10×, but for the thickness of the muscle layer and keratinized portion it was 40×.
The following measurements were evaluated for the rumen: width (middle region of the papillae), length of the rumen papilla (from the base to the apex of the papillae), absorption area, thickness of the muscle layer, thickness of the epithelium and keratinized portion. For the duodenum, submucosal thickness, mucosal thickness and goblet cells were assessed. For the goblet cells of the duodenum, periodic acid Schiff (PAS) staining was used, where cells in 2000 μm of linear intestinal epithelium were counted for each animal (Table 3).
Table 3. Proportion of ingredients and chemical composition (DM) of the experimental diets
a Fresh weight of spineless cactus.
b Neutral detergent fibre corrected for ash and protein.
c Calculated according to Hall (Reference Hall2000).
PAS stain was used to analyse the hepatic glycogen reserve index, which stains glycoproteins, including hepatic glycogen. The photomicrographs – six for each animal, yielding a sample size of 42 per treatment (6 photomicrographs × 7 animals) – were analysed under light microscopy by the same histologist, without his prior knowledge of the group each goat belonged to. The photomicrographs were classified according to the degree of glycogen deposition based on their positivity to PAS staining: degree +: little hepatic glycogen deposition; degree ++: moderate hepatic glycogen deposition and degree +++: high hepatic glycogen deposition. To analyse the hepatic glycogen reserve index, the crosses were transformed into corresponding numbers (+ = 1, ++ = 2, +++ = 3) for statistical analysis according to the modified Ishak semi-quantitative score (Ishak et al., Reference Ishak, Baptista, Bianchi, Callea, De Groote, Gudat, Denk, Desmet, Korb and MacSween1995).
A 40× objective was used to photomicrograph the kidney samples, with a sample number of 28 per treatment (7 animals × 4 photomicrographs). In the kidney, the same histologist assessed the existence of histopathological alterations in the nephron (renal corpuscle, proximal convoluted tubules, distal convoluted tubules and loop of Henle) and whether there were any possible kidney lesions caused by the anti-nutritional factors of fodder palm in the diet and the restriction of drinking water.
Feed consumption, DM consumption, water intake and weight gain were collected throughout the experimental period to analyse the animals' productive performance.
Statistical analysis
The experiment used a double factorial design with a control as an additional treatment, of the type (2 × 2) + 1, totalling five treatments. Each treatment had seven replicates. The means were compared by contrast (treatments: control v. diet I; control v. diet II; control v. diet III; control v. diet IV and control v. diet V) using Dunnett's test at 5% probability, using PROC GLM from the SAS statistical package (SAS Institute, 2001).
Results
The performance variables were not influenced (P > 0.05) by the interaction between the content of spineless cactus in the diet and the water supply (S × W), nor were they influenced by the effect of the content of spineless cactus (S) in the diet (Table 4). The water intake variable was influenced by the water supply factor (P = 0.019), with significant differences between the amount ingested by the animals depending on the treatment.
Table 4. Initial weight (IW), final weight (FW), total weight gain (TWG), average daily weight gain (ADG), DMI and water intake (WI) of goats fed with forage cactus as an exclusive or partial source of water
C × F, control v. factorial; S, effect of spineless cactus content; W, effect of water supply; S × W, effect of interaction between spineless cactus content and water supply; s.e.m., standard error of the mean; different letters in the row differ from each other by the test of Dunnett's (P < 0.05).
The average initial weight of the five treatments was 19.1 ± 0.32 kg and the average final weight was 18.8 + 0.72 kg, with a loss of weight. This low performance is explained by the 80:20 roughage:concentrate ratio, in which the low proportion of concentrate contributed to this low performance, with insignificant gains and weight loss in some treatments, because the feed was not very palatable and this behaviour was seen in all the treatments. As for the animals' water intake, in the treatments that had palm added to the diet, the animals ingested less water compared to the control.
DMI (P = 0.004) and water intake (P ≤ 0.001) were influenced by the control v. the factorial. In the treatment with 0.25 forage palm and 0.55 Tifton-85 hay, the DMI increased by 26% compared to the control treatment with 0.80 Tifton-85 hay. This higher DMI reflected in a higher final weight for the animals (19.70 kg) and a higher total weight gain (0.77 kg) for this treatment.
In the rumen, the thickness of the epithelium, keratinized portion, papilla height, papilla area and thickness of the rumen muscle layer showed no significant effect (P > 0.05) for the interaction between the content of spineless cactus in the diet and access or restriction to drinking water. The thickness of the epithelium (P ≤ 0.001) and the papilla absorption area (P = 0.015) showed a significant effect depending on the content of forage palm in the diet. The thickness of the epithelium was greater at the 0.25 content of spineless cactus when compared to the 0.55 content (Fig. 1(a)). The papilla absorption area showed that the 0.55 content of spineless cactus provided a larger area (P < 0.05) compared to the 0.25 content and the control (Table 5) (Fig. 1(c)).
Figure 1. Photomicrographs of rumen and small intestine of goats fed with Opuntia ficus indica as the sole or partial source of water. (a) Rumen: observe the thickness of epithelium (e) and larger keratinized portion (k), respectively, as a function of the content of 25% of forage palm and water supply for dewatering. (b) Rumen, observe epithelium thickness (e) and smaller keratinized portion (k), respectively, due to the content of 55% of forage palm and no water supply for watering. (c) Rumen: larger absorption area for the content of 55% of forage palm. p, papilla. (d) Rumen: smaller absorption area for a content of 25% forage palm. p, papilla. (e) Intestine: mucosal thickness (m) and submucosal thickness (sm) greater for water-intensifying supply. (f) Intestine: mucosal thickness (m) and submucosal thickness (sm) smaller without supply of water for watering. Haematoxylin–eosin staining.
Table 5. Epithelial thickness (EE), keratinized portion (KQ), papilla height (PH), papilla width (PW), papilla absorption area (PAA) and muscle layer thickness (MLT) of the rumen of goats fed spineless cactus as an exclusive or partial source of water
C × F, control v. factorial; S, effect of spineless cactus content; W, effect of water supply; S × W, effect of interaction between spineless cactus content and water supply; s.e.m., standard error of the mean; different letters in the row differ from each other by the test of Dunnett's (P < 0.05).
The keratinized portion (P ≤ 0.001) showed a significant effect for access and restriction to drinking water, with the animals that had access to water showing a greater keratinized portion compared to the group restricted to drinking water (Figs 1(a) and (b)). The other variables showed no significant results for access or restriction to drinking water. The keratinized portion (P = 0.021) and the absorption area (P = 0.023) showed a significant effect for control v. factorial (Table 5).
In the intestine, the thickness of the submucosa (P = 0.027) showed a significant effect for the interaction between the content of palm in the diet and access and restriction to drinking water (Table 6). Mucosal thickness (P = 0.716) and submucosal thickness (P = 0.062) did not change as a result of palm contents. The variables mucosal thickness (P = 0.023) and submucosal thickness (P = 0.046) showed higher averages in goats that did not receive drinking water (Fig. 1(e)).
Table 6. Mucosal thickness (MS), submucosal thickness (SS) and goblet cell index in the epithelium (GCI) of the small intestine of goats fed spineless cactus as an exclusive or partial source of water
C × F, control v. factorial; S, effect of spineless cactus content; W, effect of water supply; S × W, effect of interaction between spineless cactus content and water supply; s.e.m., standard error of the mean; different letters in the row differ from each other by the test of Dunnett's (P < 0.05).
The epithelial goblet cell index changed according to the inclusion of palm (P ≤ 0.001), yielding the highest average at the 0.55 palm content, as well as showing significant results (P = 0.005) for whether or not water was given, with the highest average in the animals that received desiccation water. The goblet index also showed a control v. factorial effect (P = 0.002), showing that the control group differed from the other treatments, with the control being inferior to the others.
The hepatic glycogen stock index evaluated was significantly higher for the 0.55 of spineless cactus with access to water treatment compared to the 0.55 of spineless cactus without access to water treatment (Table 7).
Table 7. Hepatic glycogen stock index and frequency of scores by treatment of goats fed with spineless cactus as an exclusive or partial source of water
CON, control; 25ADW, 0.25 of spineless cactus with access to water; 25NDA, 0.25 of spineless cactus without access to water; 55ADW, 0.55 of spineless cactus with access to water; 55NDA, 0.55 of spineless cactus without access to water.
a 0 (absence of positivity), 1 (low positivity), 2 (moderate positivity) and 3 (high positivity), adapted from Ishak et al. (Reference Ishak, Baptista, Bianchi, Callea, De Groote, Gudat, Denk, Desmet, Korb and MacSween1995).
b Frequency of the score of each photomicrograph analysed by treatment.
P < 0.005 ANOVA, Dunnett's post-test.
Histopathological changes were not found in the kidney structures in the control treatment. The presence of granular cylinders was observed in all treatments with palm oil, with these changes being more evident in treatment 0.55 of spineless cactus without access to water. Intratubular birefringent radiated crystals were observed with moderate alterations in the 0.25 of spineless cactus without access to water treatment and with mild alterations in the 0.55 of spineless cactus with access to water and 0.55 of spineless cactus without access to water treatments (Table 8).
Table 8. Histopathological changes in the kidneys of goats fed with forage cactus as an exclusive or partial source of water
–, absent; +, mild; ++, moderate; +++, acute.
CON, control; 25ADW, 25% of spineless cactus with access to water; 25NDA, 25% of spineless cactus without access to water; 55ADW, 55% of spineless cactus with access to water; 55NDA, 55% of spineless cactus without access to water.
Mild urinary space dilation was observed in the 0.25 of spineless cactus without access to water treatment and moderate in the 0.55 of spineless cactus without access to water and of spineless cactus without access to water treatments, and tubular cell necrosis was observed in the of spineless cactus without access to water treatment.
Discussion
Studies that used lower contents of forage palm silage (0.21 and 0.42) in sheep feed also observed an increase in DMI, which may be due to the high rate of degradability of DM as a result of the high concentration of non-fibrous carbohydrates in spineless cactus, when compared to diets that include Tifton hay (Nobre et al., Reference Nobre, Araújo, Santos, Carvalho, Albuquerque, Oliveira, Ribeiro, Turco, Gois, Silva, Perazzo, Zanine, Ferreira, Santos and Campos2023).
Akinmoladun et al. (Reference Akinmoladun, Fon, Mpendulo and Okoh2020) evaluated indigenous Xhosa goats from the Eastern Cape region of South Africa subjected to an 89-day experimental period under water restriction of 50 and 70% based on the ad libitum water intake of the control group. It was observed that the goats under water restriction significantly reduced their DMI during the experimental period in an adaptive response to water stress, which did not occur in the present study, since the palm provided enough water for adequate metabolism, as they were not under water restriction.
The reduction in the consumption of desiccation water is explained by the fact that spineless cactus has a high water content in its composition, supplying a large part of the animals' water needs (Silva et al., Reference Silva, Araújo, Santos, Oliveira, Godoi, Gois, Perazzo, Ribeiro, Turco and Campos2023).
The inclusion of spineless cactus in the goats' diet did not affect weight gain, and it could be an alternative source of water and nutrients for semi-arid regions such as northeastern Brazil. Studies carried out with sheep using contents of 0.20 (Moura et al., Reference Moura, Guim, Batista, Maciel, Cardoso, Lima Júnior and Carvalho2020), 0.30 (Cordova-Torres et al., Reference Cordova-Torres, Guerra, Araújo Filho, Medeiros, Costa, Ribeiro and Bezerra2022) and 0.42 (Nobre et al., Reference Nobre, Araújo, Santos, Carvalho, Albuquerque, Oliveira, Ribeiro, Turco, Gois, Silva, Perazzo, Zanine, Ferreira, Santos and Campos2023) of spineless cactus inclusion in the diet showed daily weight gains of 263, 170 and 208 g, respectively.
Studies using silages based on forage palm (N. cochenillifera) also observed an increase in the daily weight gain of sheep, with values of 293 g/d for spineless cactus silage and 303 g/d for spineless cactus + gliricidia silage (Silva et al., Reference Silva, Araújo, Santos, Oliveira, Godoi, Gois, Perazzo, Ribeiro, Turco and Campos2023), values higher than those established by the NRC (2007).
At the rumen level, the greater thickness of the epithelium for the 0.25 spineless cactus content must be linked to the supply of a greater amount of Tifton-85 hay (0.55) in the feed, which favours the production of volatile fatty acids, including acetate and butyrate, resulting from the greater amount of roughage in the diet, causing this layer to thicken due to its ability to influence the morphophysiology of the rumen depending on the diet (Górka et al., Reference Górka, Sliwinski, Flaga, Olszewski, Wojciechowski, Krupa, Godlewski, Zabielski and Kowalski2018). Specifically, butyrate and propionate increase the proliferation of rumen epithelial cells (Górka et al., Reference Górka, Sliwinski, Flaga, Olszewski, Wojciechowski, Krupa, Godlewski, Zabielski and Kowalski2018; Barboza et al., Reference Barboza, Oliveira, Souza, Lima Júnior, Lima and Guerra2019).
On the other hand, the keratinized portion of the rumen epithelium, which has a protective and mechanical function for the rumen papillae, did not become thicker with the inclusion of palm, thus ruling out, at the rumen level, the action of oxalic acid, an anti-nutritional factor in palm (Silva et al., Reference Silva, Araújo, Santos, Oliveira, Godoi, Gois, Perazzo, Ribeiro, Turco and Campos2023). High values of this anti-nutritional factor, as well as other foods such as cassava and castor bean, increase keratinized portion (Barboza et al., Reference Barboza, Oliveira, Souza, Lima Júnior, Lima and Guerra2019; Dantas Júnior et al., Reference Dantas Júnior, Oliveira, Ribeiro, Rola, Silva, Oliveira, Almeida, Lima Júnior and Guerra2021). The study showed the opposite, a reduction in thickness with the use of spineless cactus, due to less mechanical abrasion in the palm's keratinized portion when compared to diets containing the roughage Tifton-85 (Garcia et al., Reference Garcia, Ribeiro, Oliveira, Lima Júnior, Almeida, Silva, Costa and Guerra2022), which is a higher percentage in the control treatment.
The increase in absorption area increases the absorption surface for volatile fatty acids, making the absorption process more efficient and improving performance. This result demonstrates that the higher proportion of palm in the diet provides more degradation in volatile fatty acids, which are also important for the development of rumen papillae (Górka et al., Reference Górka, Sliwinski, Flaga, Olszewski, Wojciechowski, Krupa, Godlewski, Zabielski and Kowalski2018; Porto Filho et al., Reference Porto Filho, Costa, Ribeiro, Guerra, Oliveira and Beltrão2020).
The ruminal muscle layer showed no changes between treatments, despite the differences between treatments in terms of the amount of roughage. This layer is responsible for peristaltic movements and undergoes hyperplasia and hypertrophy when there is an increase in intake volume or an increase in dietary fibre (Lima et al., Reference Lima, Costa, Medeiros, Medeiros, Ribeiro, Oliveira, Guerra and Carvalho2019; Silva et al., Reference Silva, Oliveira, Santos, Cartaxo, Guerra, Souza, Muniz and Cruz2020; Cordova-Torres et al., Reference Cordova-Torres, Guerra, Araújo Filho, Medeiros, Costa, Ribeiro and Bezerra2022), which was not found in this study.
At an intestinal level, it is known that the digestion and absorption capacity of the intestine is related to the changes that occur in the intestinal mucosa. The thicker the mucosa, the greater the villus height and the greater the nutrient absorption area, consequently improving production (Lima et al., Reference Lima, Costa, Medeiros, Medeiros, Ribeiro, Oliveira, Guerra and Carvalho2019). The inclusion of palm had no influence on this intestinal variable, but the supply of water did.
The mucosa of water-supplied animals was less thick than that of restricted animals. Therefore, it is believed that in order to maximize the absorption of water from the palm in restricted animals, the intestinal mucosa adapted by increasing its thickness, which, however, leads to an increase in energy expenditure. This increase in energy expenditure occurs in an area that already consumes around 0.20 of the individual's nutrients (Mcbride and Kelly, Reference Mcbride and Kelly1990; Pluske et al., Reference Pluske, Hampson and Williams1997). The intestinal epithelium, for example, has a high cell turnover rate, renewing itself every 14 days (Bueno et al., Reference Bueno, Albuquerque, Murarolli, Aya, Raposo and Bordin2012).
Similar results were found in the submucosal layer, which was not affected by the introduction of palm in the diet. However, the literature mentions that diets composed of foods with a high digestible fibre content, such as palm, in sheep have the ability to reduce intestinal motility and decrease the thickness of the submucosa. This layer would decrease in thickness because it contains mucus-producing glands that help with peristalsis and prevent constipation, but with a decrease in the speed of motility, their volumes may decrease (Jin et al., Reference Jin, Jiang, Zhang, Shi and Wang2018).
In the intestine, an important variable usually used as a parameter for intestinal health is the index of goblet cells in the intestinal epithelium (ICC). For this variable, the higher the goblet cell index, the better the intestinal health (Dantas Júnior et al., Reference Dantas Júnior, Oliveira, Ribeiro, Rola, Silva, Oliveira, Almeida, Lima Júnior and Guerra2021). Goblet cells produce mucin, an important mucus for peristalsis, the prevention of constipation, protection of the mucosal surface against parasite attacks and digestion by the gastric and pancreatic ducts, as well as aiding digestion and absorption at the level of the intestinal microvilli (Bueno et al., Reference Bueno, Albuquerque, Murarolli, Aya, Raposo and Bordin2012).
In the present study, an important result was found: the greater inclusion of cactus (0.55) provided a significantly higher goblet cell index, being 25% higher than the control, indicating that cactus stimulates a greater development of intestinal goblet cells, which ends up helping in peristalsis and improving the protection of the intestine against infections, including a decrease in the occurrence of diarrhoea (Dantas Júnior et al., Reference Dantas Júnior, Oliveira, Ribeiro, Rola, Silva, Oliveira, Almeida, Lima Júnior and Guerra2021). Access to drinking water also provided a higher goblet cell index compared to restriction, which can be explained by the need for water for the production of mucins. In this sense, 0.55 cactus also made more water available for the production of mucins than the treatment with 0.25 cactus.
The treatment with 0.55 inclusion of palm with water also provided a liver with a greater store of hepatic glycogen when compared to the other treatments, which generates greater availability of glucose (energy) for the tissues, essential for carrying out the vital functions of maintenance and production of animals (Berne and Levy, Reference Berne and Levy2009). In this treatment, there was a decrease in the percentage of bulky Tifton-85, increasing the proportion of palm. This food provides greater production of propionate, volatile fatty acids used in hepatic gluconeogenesis (Jin et al., Reference Jin, Su, Wang, Liang, Lei, Bai, Liang, Li, Cao and Yao2023), which is converted into glycogen (Barboza et al., Reference Barboza, Oliveira, Souza, Lima Júnior, Lima and Guerra2019), which explains the greater storage in the treatment with 0.55 palm. However, this same content of palm without access to water for quenching leads to a decrease in the store of hepatic glycogen, perhaps even due to kidney problems, as will be discussed later.
Histopathologically, no liver lesions caused by the inclusion of palm or water restriction were found, demonstrating once again the absence or irrelevant amount of oxalic acid in the liver, which could lead to liver lesions. Such liver lesions in goats have been described when other palm genotypes, such as Miúda and Orelha de Elefante Mexicana, were introduced into the diet. In the aforementioned experiment, inflammatory processes and necrosis of the liver parenchyma were described, however, without affecting weight gain (Silva et al., Reference Silva, Munhame, Lopes, Souza, Guim, Carvalho, Soares, Barros, Arandas and Batista2021). In addition to the different genotype, in the present study, the confinement time was shorter.
Although the inclusion of cactus in the diet did not promote adverse changes in the rumen, intestine and liver, histopathological changes were identified in the kidney in all treatments, except in the control. In studies using sheep and different species of cactus, changes in the kidney such as congestion, calcification, glomerular atrophy, nephrosis, vacuolization, intratubular protein and necrosis were also identified, regardless of the genotype of cactus used (Barboza et al., Reference Barboza, Oliveira, Souza, Lima Júnior, Lima and Guerra2019; Usman et al., Reference Usman, de Moraes, da Silva, Batista, Soares, de Araújo, de Carvalho and da Silva Júnior2022).
Oxalate, an antinutritional factor in palm, which is also found in other vegetables (Carvalho et al., Reference Carvalho, Villalobos, Castilho, Loureiro, Mello and Silva2011), is capable of forming elements such as calcium oxalate crystals, reducing the ability to absorb minerals at the renal level, and may also trigger urolithiasis and renal failure (Barboza et al., Reference Barboza, Oliveira, Souza, Lima Júnior, Lima and Guerra2019).
The presence of granular casts in the treatments with cactus pear offering indicates that there was a loss of tubular cells, especially in the proximal tubules, with these changes being more evident in the 55% of spineless cactus without access to water (55NDW) treatment. Intratubular birefringent radiated crystals were observed with moderate changes in the 25% of spineless cactus without access to water (25NDW) treatment and with mild changes in the 55% of spineless cactus with access to water (55ADW) and 55NDW treatments, indicating a possible consequence of the deposition of oxalates present in the cactus pear. The mild dilation of the urinary space in the 25NDW treatment and moderate in the 55ADW and 55NDW treatments indicate greater urine production and/or difficulty in passing urine through the altered tubules. Necrosis of tubular cells observed in the 55NDW treatment demonstrates that there was a serious injury to the renal structures that could result in chronic renal failure if confinement was carried out for a longer period of time. In any case, these alterations were not enough to cause losses in the animals' performance, as they had a short confinement period (60–90 days), so it is not a period that causes damage and leads to a loss of productivity.
Future projects need to look at the long-term effects of oxalates on animal health, as no research has been found on this topic with goats and the research that does exist is very superficial, and the long-term response is unknown
Conclusion
It is concluded that forage cactus (N. cochenillifera (L.)) can be used in the diet of goats at a concentration of up to 0.55, associated with Tifton-85, with or without access to water for quenching, without causing losses in animal performance or at the ruminal, intestinal and hepatic levels. The use of 0.55 cactus as the sole source of water in the diet of goats increases kidney lesions and decreases hepatic glycogen stores, but without altering animal performance, for the confinement period of the present study.
Acknowledgements
The study was funded by the Universidade Federal de Campina Grande and the Brazilian National Council for Scientific and Technological Development (CNPq).
Author contributions
T. M. C., G. M. B. M., R. R. G., O. B. N. and D. M. L. J. conceived and designed the study. T. M. C., G. M. B. M., R. R. G., O. B. N., V. V. S. A., E. G. S. and D. M. L. J. conducted data gathering. T. M. C., N. L. R. and R. R. G. performed statistical analyses and prepared graphics. T. M. C., G. M. B. M., R. R. G. and N. L. R. wrote the article. R. R. G., G. M. B. M. and N. L. R. supervised the work.
Competing interests
None.
Ethical standards
The study was approved by the Ethics Committee for the Use of Animals of the Federal University of Alagoas (UFAL), Brazil, certificate protocol no. 02/2018.
