Nitrogen balance of goat kids fed diets containing peach palm meal

The use of agribusiness residues could help to improve the efficiency of livestock production systems by supplying nutrients to animals during periods of feed shortages, reducing costs associated with feeding, and improving the sustainability of the sector by reducing environmental impacts (Santos Filho et al., 2015). Peach palm (Bactris gasipaes Kunth) has become an agricultural species in the humid tropical region of Brazil (Conceição et al., 2018). In addition to providing the heart-of-palm, which has an excellent international market value, its fruit can be used for the extraction of seeds. The heartof-palm industry directs part of the cultivation area to the production of fruit for the extraction of seeds (Pereira et al., 2019a). Hence, this process generates large amounts of fruit pulp waste, which does not yet have a suitable destination.

The pulp is a waste that could be used for the production of peach palm meal (PP) as an alternative feedstuff for ruminants (Santos et al., 2016), but for that, it is necessary to know inclusion levels that guarantee animal productivity. This waste contains oil contents ranging from 20 to 620 g kg −1 of DM (Pereira et al., 2019b;Gomez et al., 1998;Murillo et al., 1991Murillo et al., , 1983, depending on the amount added to the diet can promote rumen fermentation modification and thus to affect microbial efficiency (Palmquist and Mattos, 2011). In this regard, modifications in the microbial utilization of protein and energy can occur, promoting an increase in urinary urea excretion and negative nitrogen retention.
One of the major challenges in ruminant nutrition is to improve understanding of nitrogen metabolism to formulate the most efficient diets and improve the nutritional management of animals (Silva et al., 2019). Thus, the evaluation of these parameters is necessary to establish limits of applications of sustainable technologies, without causing damage to animal production. This study was conducted to examine the nitrogen balance and the plasma urea concentration in goat kids fed diets containing peach palm meal substituting corn (0, 10, 40, 60, and 85% of the dry matter).

MATERIAL AND METHODS
All the animal care and handling procedures were approved by the Ethics Committee on Animal Use of the State University of Southwest Bahia -UESB, Itapetinga Campus, with protocol number 11/2012. The experiment was conducted in the sheep farming sector of UESB, State of Bahia, Brazil. Thirty Boer crossbred kids, approximately 90 days old and initial body weight of 16.7 ± 3.5kg, were distributed in a completely randomized design with five treatments (0, 10, 40, 60, and 85% peach palm meal (PP) to replace corn in the concentrate) and six replicates. The experimental period was 84 days, with 14 days for adaptation to experimental diets and three 28-day periods for data collection.
The pulp of the pitted fruit (pericarp and mesocarp) was supplied by Indústria de Alimentos no Mercado de Palmitos -INACERES, located in Uruçuca municipality, Bahia State, Brazil. The PP was produced in a flour mill at Instituto Federal Baiano -IFBAIANO, Uruçuca Campus. The obtained pulp was dried in the sun for three consecutive days, with the material being turned over three times a day until its moisture content was reduced by half. Subsequently, it was disintegrated in a cassava grinder, and then the ground mass was roasted in a mechanized flour roaster. This roasting procedure lasted 30 to 40 min, with the mass being turned over using wooden squeegees until its final drying, at approximately 13 g kg -1 moisture.
Diets were isonitrogenous (crude protein at 152 g kg -1 DM) and formulated to allow a body weight (BW) gain rate of 200 g day -1 as recommended by the NRC (Nutrient…, 2007) for goat kids in the growing. The proximate and chemical compositions of the diets are listed in Table 1. Diets were supplied daily as complete mixing, at 0700 h and 1600 h, ad libitum, so as to allow for 10 to 20 g kg -1 leftover. The daily voluntary intake was calculated as the difference between the total feed supplied and the leftovers, which were collected and weighed in the morning and afternoon, during the 84 experimental days. Similarly, nitrogen (N) intake in (g day -1 ). The feces were collected at 0600 h and 1800 h for five consecutive days in each experimental subperiod. The 24-h feces from each animal were weighed, and 10% aliquots from each day were sampled, mixed, and stored in a freezer at −20°C for later analyses.  Detmann et al. (2012). For the sequential analyses of neutral (NDF) and acid (ADF) detergent fiber, samples were treated with thermostable alpha-amylase, without sodium sulfate, and corrected for residual ash (Mertens et al., 2002). The NDF correction for nitrogen compounds and estimate of the neutral (NDIN) and acid (ADIN) detergent insoluble nitrogen compounds were carried out according to Licitra et al. (1996). Lignin (method INCT-CA F -005/1) was obtained based on the methodology described by Detmann et al. (2012), with the ADF residue treated with 72% sulfuric acid. Non-fiber carbohydrates (NFC) content was calculated according to Hall et al. (1999) with modifications, utilizing NDFap. Total digestible nutrients (TDN) were calculated according to Weiss (1999).
The lipid fraction of the experimental diets was determined at the Center for Chromatographic Analyses of UESB, according to the method of Bligh and Dyer (1959). Peak areas were determined by the normalization method using ChromQuest 4.1 software. Peaks were identified by comparison of the retention times of fatty acid methyl esters (Sigma, USA), and after determining the equivalent chain length (Table 1).
On the 28th day of each experimental period, after the intermediate weighting session, the urine was collected as spot samples during the animal's spontaneous urination, approximately 4 h after the morning feeding was supplied.
These samples were intended for the quantification of the urinary concentrations of urea and creatinine, using commercial kits (Bioclin). Blood was collected from the jugular vein approximately 4 h after the morning feeding, using Vacutainer ® tubes containing EDTA. The nitrogen balance (N-retained, g day -1 ) was calculated as follows: N-retained = N intake (g) -N in feces (g) -N in urine (g). The statistical analysis of the data was achieved by the MIXED procedure of the SAS statistical computer program (Statistical…, 2006), considering a mixed model. Polynomial contrasts were performed for the comparison between the means of the diet that contained only corn (0% peach palm meal) and the diets in which the corn was substituted for the PP (10, 40, 60, and 85%). The following statistical model was adopted: Yijk = (β0 + β1T + β2T 2 ) + εijk; NID (0; σ 2 ), where Y = the estimated value according to the diets; β0 = intercept; β1 and β2 defined the variation of Y according to the level of substitution; and T = level of substitution (0, 10, 40, 60, and 85% PP). For all statistical procedures, the critical level of probability for type 1 error was fixed at 0.05.

RESULTS AND DISCUSSION
The N intake (g day -1 ) decreased linearly (p = 0.000) with the elevation in the levels of peach palm meal (PP) in the concentrate ( Table 2). The animals fed the diet 0% (control) ingested 35.11% more N (g day -1 ) than the goat kids fed on the diet with 85%. Similarly, it is possible that the decrease of N intake caused a reduction in the digested N (Table 2). According to Van Soest (1994), the rates of excretion of nitrogen compounds in the urine and feces of ruminants are associated with the amount of nitrogen ingested, which may explain the linear reduction (p = 0.0022) in the excretion of N in the feces (Table 2).
For the urinary N, there was greater excretion for the diet without PP and a linear change (p = 0.0453) with an increase of 0.064 g day -1 to each percentage unit of PP. Consistently, the average N retention (g day -1 ) presented a quadratic effect, in which the goat kids presented greater N utilization (7.0 g day -1 ) at a 28.9% level of replacement. Hence, the corn substitution with PP at this level in the diet may be recommended for better use of N and upper levels increase the urinary N excretion as described above. When the protein degradation rate exceeds the carbohydrate fermentation, a large amount of N compounds can be lost in the urine (Nocek and Russell, 1988;Meijer et al., 1990;Reynolds, 1992).
The diets with PP present an increase in the unsaturated fatty acids content and lignin/NDF ratio, especially in the diets containing 85% of PP replacing corn (Table 1), which is related to the negative implication that lipids and bioactive secondary compounds have on ruminal fermentation and feed digestibility by inhibiting microbial growth (Silva et al., 2019;Amira et al., 2014;Martinele et al., 2008;Clement et al., 2004;Nutrient…, 2001). These characteristics of the peach palm meal composition could explain reduced energy use in the rumen with increased urinary N excretion.
Also, it can be inferred that, from the replacement level (around 45%) reported above, the rumen fermentation was modified by PP because of lipid content (Santos et al., 2016). The main mechanisms involved in this process include the physical coating of the fiber, the filling effects on the microbial membranes, and a decrease in the availability of cations by the formation of soaps, which can influence rumen pH, limiting microbial growth, and the toxicity of the excess of polyunsaturated fatty acids to the ruminal microorganisms (Palmiquist and Mattos, 2011). There are several implications of fat for ruminant nutrition, it interferes with rumen fermentation, influences dietary energy utilization, and also affects the intermediate metabolism (Medeiros and Alberitni, 2012).
The concentration of plasma urea-N showed a quadratic response with maximum concentration (15.6 mg dL -1 ) at a 38% replacement by the PP (Table 3). The excretions of urea and urea-N in the urine (g day -1 ) were lower at 39% of corn substitution, when expressed as mg kg -1 BW, the minimum excretion was observed at a 36% level. In addition, the group of animals fed diet containing only corn with those that received PP levels showed greater excretion of urea and Nurea in the urine (g day -1 and mg kg -1 BW) (Table  3). Lower excretion of urinary N-urea is a consequence of reduced N intake provided by PP.
Ruminants have the ability to change the rates of excretion of N compounds in urine and feces as a function of the amount of ingested N (Van Soest, 1994). This metabolic characteristic is possibly related to the activity of urea transporters in the kidneys that regulate the rate of urinary excretion and urea transporters in the gastrointestinal tract that regulate the N excretion in feces (Reynolds and Kristensen, 2008). Although the concentration of plasma N-urea represents only the circulating pool, the renal tubular reabsorption of urea can occur, depending on the requirement for nitrogen by rumen microorganisms.
It may have occurred in this study when the animals consumed diets with an average level of 35% of PP, whose above levels can impair the microbial activity. Consistently, with increased urea excretion when higher levels of PP were used. The concentration of plasma N-urea varies according to dietary protein/energy ratio, animal species, or category, and studies are needed to establish an optimal range for each situation. A high concentration of N-urea can indicate excess dietary N and/or an energy metabolic cost from gluconeogenesis and ureagenesis (Stefanello et al., 2018).
Replacing corn with PP reduces the N intake in goat kids. However, the PP has the potential to replace corn in the concentrated, because maximum N retention was verified when it replaces corn at 28.9%. Also, from the environmental point of view, the use of the residues of fruit pulp waste (peach palm) contributes to the sustainability of livestock productions, as it supports a reduction of environmental impacts.