1. Introduction
The use of intensive systems (feedlots) for the production of dairy animals is considered an important strategy to control the proper management of animals, especially the nutritional management, which can greatly affect the productive performance of the animals [
1]. This type of system ensures the continuity of protein products of animal origin to satisfy the demand for human food, both in quantity and quality.
However, intensive production systems are usually associated with higher costs. Animal feed represents the highest proportion of production costs, accounting for nearly 70% of the total cost [
2]. The use of alternative feed ingredients, which can replace conventional and more expensive ones (such as corn ground and soybean meal), is an important strategy to reduce production costs and, consequently, improve the economic performance of the activity.
Several agro-industrial by-products have been suggested in the literature as alternative feeds for animal nutrition that can contribute to cost reductions. The licury tree (
Syagrus coronata) is a palm species highly resistant to drought in semi-arid regions. The fruit is composed of a fibrous pericarp and an oil-rich endosperm (almonds). In Brazil, licury oil is the suitable for the manufacture of detergents, powdered soap, and bar soap. Furthermore, licury products are successfully used in human nutrition in the form of
in natura, cereal bars, yogurt, and licury flour, among others [
3]. From the process of extracting the oil from the almonds by the pressing method, between 30 and 40% of licury cake (LC) is obtained [
4]. Ferreira et al. [
5] reported that the inclusion of LC in the feed of lactating cows reduced the cost of concentrates to 38.5%, which shows its potential in animal feed and a considerable reduction in production costs.
In addition to having lower commercial value compared to ingredients that are traditionally used in animal feed, LC has an additional favorable composition: an average of 221.8 g of crude protein (CP) kg
−1 dry matter (DM), 60.7 g of ether extract (EE) kg
−1 DM, and 486.0 g of neutral detergent fiber (NDF) kg
−1 DM [
6].
Various studies have already evaluated the use of by-products in animal feed but studies with licury cake in lactating goat feeding are scarce. The results obtained with the inclusion of LC in the feeding of ruminants are different among the species and the categories, resulting in controversial conclusions about the adequate amount of LC addition in the diets of ruminants. In feedlot systems for beef cattle, the use of LC in the diet at a level of 85.0 g kg
−1 DM is recommended [
7]. For feedlot meat goats, in highly concentrated diets, the inclusion of LC of up to 100 g kg
−1 DM is accepted [
5]. In grazing lambs supplemented with LC, the inclusion of 174 g kg
−1 DM of the total diet was found to be the ideal level of inclusion [
8]. In grazing lactating cows, the ideal LC inclusion level was observed to be up to 70 g kg
−1 DM based on the total diet [
9].
Given the results obtained from studies that have analyzed the inclusion of LC in the ruminant diet, we can assume that this by-product can be included in diets and promote higher productive performance in feedlot dairy goats without affecting animal metabolism and product quality. In this context, the objective of the current study was to evaluate the inclusion of increasing levels of LC (0, 66.7, 133.3, and 200 g kg−1 DM) in the diets of feedlot lactating goats on the intake and digestibility of nutritional components, feeding behavior, productive performance, milk composition, blood metabolites, and nitrogen balance.
2. Materials and Methods
2.1. Ethics Committee and Experiment Location
The use of goats in this study was approved by the Ethics Committee for the Use of Animals (CEUA) of the Federal University of Bahia (UFBA) under registration number 73/2018.
The experiment was conducted from October to December 2018, in the goat sector of the UFBA Experimental Farm, located in the Entre Rios municipality, Bahia, Brazil (11°56′31″ S, 38°05′04″ W, altitude 162 m). The region has an average minimum temperature of 22 °C, an average maximum temperature of 29 °C, average annual rainfall of 1000 to 1251 mm, and a warm semi-humid climate.
2.2. Animals, Experimental Design, and Management
Eight Saanen and four Anglo-Nubian goats, multiparous, with an average body weight of 37.93 ± 9.22 kg (mean ± standard deviation), an average of 30 days of lactation, and an average production of 0.7 kg of milk day−1 were used. Goats were distributed in a Latin square design (4 × 4) in triplicate, considering four periods and four animals by square. One square was created with Anglo-Nubian goats, and Saanen goats were randomly distributed in the other two squares.
Each experimental period lasted fourteen days, with the last four days dedicated to sample and data collection. The diets were formulated according to the NRC [
10] to meet the maintenance and milk production requirements of lactating goats. Treatments consisted of a diet without the inclusion of LC and three with the inclusion of LC at levels of 66.7, 133.3, and 200 g kg
−1 DM of the total diet (
Table 1). In order to keep the diets as isonitrogenous and isoenergetic as possible, we partially replaced ground corn and cottonseed meal as LC was included in the diet. The forage used was corn silage and the forage:concentrate ratio was 50:50.
The animals were managed in individual pens of 1.5 m2, with a suspended floor and wooden slats, equipped with feeders and drinkers with free access to water and feed.
Diets were provided as a total mixed ration, twice daily (08:00 and 15:00). The supplied diet and leftovers were weighed daily to control the daily intake of nutritional compounds of the animals, and to adjust the supplied feed to guarantee approximately 20% leftovers.
Animals were milked daily, manually, once a day (07:00), using 0.5% iodized glycerin for pre- and post-milking. The process was carried out in previously sanitized boxes, following the regulatory hygiene practices for milking. The first streams of milk were poured into a glass with a dark bottom to detect possible cases of mastitis.
2.3. Intake and Apparent Digestibility of Nutritional Components
The intake of nutritional compounds (g day−1) was calculated as the difference between the amount of the nutrient present in the diet and the amount of the nutrient contained in the leftovers. The diet and leftover sample collections were carried out in the last four days of each experimental period.
The apparent digestibility was determined by the indirect method using spot feces collection. Feces were collected directly from the rectal ampulla between days 12 and 14 of each experimental period, twice daily, as follows: day 12—8:00 and 14:00, day 13—10:00 and 16:00, and day 14—12:00 and 18:00. After collection, feces were weighed and placed in a forced ventilation oven at 55 °C. The samples were then weighed and stored for further analysis. After the digestibility trial, the diet, leftover, and feces samples were ground to 1 mm for the determination of DM, ash, EE, CP, NDF, and non-fibrous carbohydrates (NFC). Total fecal excretion was estimated using non-digestible neutral detergent fiber (NDFi) as an internal indicator [
11].
To estimate the apparent digestibility of the nutritional components, we used the values of the nutrient intake and the nutrient excretion in feces. The digestibility coefficients (
DC) of DM, CP, NDF, and EE were calculated according to Berchielli et al. [
12] as follows:
2.4. Feeding Behavior
The animals were subjected to visual observation (day 11 of each experimental period), during a 24-h period, with 5-min intervals, to assess feeding, rumination, and idling times [
13]. Feeding behavior data were recorded by eight trained raters, which were strategically positioned so that they did not interfere with the natural behavior of the animals. During nightly evaluations, the environment was maintained with artificial light, and the goats were adapted to these conditions three days before the evaluation. Feeding behavior data were obtained according to the methodology described by Bürger et al. [
14].
The time spent feeding, ruminating, and idling was obtained by multiplying the frequency of each activity by the time interval of the observations. Periods were obtained by observing the number of episodes in a 24-h interval. Feeding and rumination efficiencies of DM and NDF were calculated by dividing the intake of these nutrients by the time spent feeding and ruminating.
2.5. Milk Production and Composition
Daily milk production was recorded by weighing the milk throughout the experimental period; unusual days (decreased production due to stress or illness) were not observed in the analysis.
For the analysis of the chemical composition, we collected milk samples at the time of milking. The collected samples were stored in a plastic bottle with 2-bromo 2-nitropropane 1-3-diol (bromopol) preservative, for further analysis of protein, fat, lactose, urea, and total solids, using the Bentley-2000 Infrared Analyzer instrument (Bentley Instruments Inc., Curitiba, Paraná, Brazil). Between the collection time and the analysis of the samples, up to 48 h elapsed. The corrected milk fat (CMF) at 4% was obtained according to the following equation: CMF = 0.4 × milk production (g day
−1) + 15 × milk fat (g day
−1) [
15].
Somatic cell counting (SCC) was performed using a Bentley Somacount-500 device (Bentley Instruments Inc., Curitiba, Paraná, Brazil). The somatic cell score (SCS) was estimated using the following equation: SCS = log base 2 (SCC 100,000
−1) + 3 [
16]. These analyses were carried out in the laboratory of Clínica do Leite ESALQ/USP, in Piracicaba-SP, Brazil.
2.6. Chemical Analysis
We processed and analyzed the ingredients, diets, leftovers, feces, and urine at the Animal Nutrition Laboratory, UFBA School of Veterinary Medicine and Animal Production. We dried all samples in a forced ventilation oven at 55 °C for 72 h. After pre-drying and grinding, we ground samples in a Willey-type mill equipped with 1-mm diameter sieves for bromatological composition analysis and 2-mm diameter sieves for NDFi evaluation. The analyses performed in 1-mm samples were DM (method 934.01), ash (method 930.06), EE (method 920.39), and CP (method 981.10) [
17].
For the analysis of NDF and acid detergent fiber (ADF), we used the methodology proposed by Van Soest et al. [
18]. NDF was assayed with a heat-stable amylase. NDFap and ADFap were expressed exclusively of residual ash [
19] and protein [
20]. Lignin was determined according to the AOAC 973.18 [
17] method.
Non-digestible neutral detergent fiber (NDFi) was determined by incubating the 2-mm samples by the in situ method, using TNT bags (100 g m
2), following the methodology described by Valente et al. [
21]. Potentially digestible neutral detergent fiber (NDFpd) was obtained as the difference between NDFap and NDFi.
To estimate the value of non-fibrous carbohydrates, we used the equation suggested by Hall [
22]: NFC (%) = 100 − (%CP + %EE + %ash + %NDFap).
The total digestible nutrients (TDN) were estimated using the formulas suggested by Da Cruz et al. [
23] for small ruminants. The metabolizable energy was obtained from the NRC equation [
15].
2.7. Blood Metabolites
We collected blood samples on day 14 of each experimental period, four hours after morning feeding, by venipuncture of the jugular vein in native tubes (Vacutainer). We immediately centrifugated blood samples at 3500 rpm for 15 min to obtain blood serum. Serum samples were then stored in Eppendorf tubes and stored in a freezer at −20 °C for further analysis.
We used the colorimetric method to determine the serum concentrations of albumin, total protein, and urea; we used commercial kits in our analysis (Doles Re-agentes Ltd., Goiânia, Goiás, Brazil), and readings were carried out in a spectrophotometer (AJX- 1900, Micronal SA, São Paulo, Brazil).
2.8. Nitrogen Balance
We collected urine spot samples on day 13 of each experimental period, approximately 4 h after feeding, during spontaneous urination. Immediately, urine aliquots of 10 mL were collected, which were diluted in 40 mL of 0.036 N sulfuric acid, as described by Valadares et al. [
24]. To estimate the daily urinary excretion, the creatinine content of the samples was determined using a commercial kit (Labtest
®, Lagoa Santa, Minas Gerais, Brazil) and reading in a spectrophotometer (AJX-1900, Micronal SA, São Paulo, Brazil). We used the formula suggested by Fonseca et al. [
25], which considers average creatinine excretion of 26.05 mg kg
−1 of body weight (BW) for lactating goats. Daily urinary excretion (L day
−1) = (26.05 × BW, kg) (creatinine excretion, mg L
−1)
−1.
The nitrogen content of the urine and feces samples was determined by the Kjeldahl method [
17]. The balance of nitrogen compounds was obtained using the formulas suggested by Zeoula et al. [
26].
2.9. Statistical Analysis
We ran our statistics analysis using the statistical software SAS version 9.2 (Statistical Analysis System, 2009) [
27]. The variables of intake, digestibility, feeding behavior, milk production and composition, and nitrogen metabolism were assessed according to a triplicated 4 × 4 Latin square. The mathematical model below was applied:
where Ŷ
ijkl = dependent variable; μ = overall mean; LS
i = fixed effect of the Latin square (i = 1, 2 and 3); A(LS
i)
j = random effect of the animal into the Latin square (j = 1, 2, 3 and 4); P
k = random effect of the period (k = 1, 2, 3 and 4); LC
l = effect of the LC level (l = 0, 80, 160, and 240 g kg
−1); LS
i × LC
l = fixed effect of the interaction between Latin square and LC inclusion level; and Ɛ
ijkl = random experimental error associated with each observation, with NID ~ (0, σ2) assumption.
Furthermore, we evaluated the effect of the LC inclusion level using Orthogonal Polynomial Contrasts to determine the linear (−3, −1, +1, +3) and quadratic (+1, −1, −1, +1) effects. We considered the level of a 5% probability of type I error (p ≤ 0.05) in our study. No interaction between treatment and racial group was observed for any of the variables studied.