Food consumption is changing along with more rapid global industrialization and urbanization as well as the increasing population. Global meat production is projected to rise from 233 (in 2000) to 300 million tons (in 2020), milk production will go from 568 to 700 million tons and egg production is projected to increase by 30% (
Speedy, 2016). Since arable land is limited, more attention has recently been focused on exploiting woody trees and shrubs that can grow in marginal land and be used as ruminant feeds
(Musco et al., 2016). Some studies have characterized the nutrient value of locally available woody-feed resources, such as
Leucaena leucocephala,
Moringa oleifera and
Prosopis juliflora (Kumar et al., 2015; Musco et al., 2016; Ramirez-Lozano et al., 2018). However, their feeding effects on meat quality remain, to a wide extent, unclear.
Toona sinensis (A. Juss.) Roem is a fast-growing tree in the family Meliaceae genus
Toona, which is widely distributed in southeastern Asia, including India, Indonesia, Bhutan, Laos, Malaysia, Myanmar, Nepal, Thailand and especially south China
(Peng et al., 2008). Traditionally, the nutritious young buds of
T. sinensis with their unique tangy flavor have been considered special “forest vegetables”. In addition to their distinctive taste, the buds of
T. sinensis are rich in polyphenols and possess many health benefits, such as antioxidative capacity and anti-inflammatory properties
(Peng et al., 2019). Mature leaves of
T. sinensis contain a higher proportion of polyphenols and possess better antioxidative capacity than young leaves (
Gong et al., 2012;
Liu et al., 2014). However, the millions of tons of mature leaves of
T. sinensis are wasted at present due to the lack of tangy flavor present in young leaves. Hence, the present study analyzed the feed value of the mature leaves of
T. sinensis and evaluated feeding effects on meat characteristics and nutritional status of sheep.
Plant materials
The mature leaves of
T. sinensis were hand harvested on July 20
th from the Golden Sun farm (Beijing, China). A small part were kept in a dry plastic foam box and taken to the lab for nutritional analysis; the remaining leaves were truncated, evenly mixed and vacuum-packed for subsequent feeding experiments.
Feeding of sheep
Twelve healthy male sheep (crossbred White Suffolk with local small-tailed Han-sheep), about 3 months old, were selected from Gold Sun Farm (Beijing, China). Equal numbers of sheep were randomly allotted into the
T. sinensis- fed group (TS) and the grass-fed group (CK). Sheep in TS were fed mature leaves of
T. sinensis and CK sheep were fed grass harvested from the farm to match normal grazing. All sheep were kept under confinement with uniform management conditions and offered 1.5 kg of their respective feed daily at 08:00 and 17:00 with free access to water. The feeding trial was conducted for 90 days. After being deprived of feed overnight (16 h), sheep were slaughtered according to the research of Werdi
Pratiwi et al., (2007). Meats of hind legs of 3 randomly selected sheep from TS and CK were respectively collected and kept under -80°C for the nutritional analysis.
Analytical measurements
The crude protein, crude fat and water content were analyzed according to
AOAC (2005). Neutral and acid detergent fiber contents were determined according to
Goering and Van Soest (1970). Amino acids and fatty acid profiles were evaluated according to the National Industry Standards of China
GB/T 5009.124 (2003) and
GB/T 22223 (2008). Mineral content was detected by 7700x inductively coupled plasma mass spectrometry (Agilent, USA). All chemicals used were analytical grade and obtained from Beijing Chemical Works (Beijing, China). All samples were analyzed in triplicate and the mean values were recorded.
WHO/FAO essential amino acid (EAA) pattern analysis (
Yan and Jin, 2016) was employed for comprehensive nutritional assessment. The ratio of amino acid (RAA), ratio coefficient of amino acid (RC) and score of the RC (SRC) of meat samples were calculated according to the ideal protein pattern provided by the WHO/FAO as below:
SRCs = (100 - variable coefficient of RCs × 100)
Descriptive statistical analysis and one-way ANOVA were conducted in IBM SPSS software package version 20.0.
Nutrient value of mature leaves of T. sinensis
Nutrient composition of young and mature leaves of
T. sinensis was comparable (Table 1). Both were rich in crude protein, minerals and amino acids. Mature leaves of
T. sinensis had higher crude protein than grains such as maize (9.51%), wheat (11.71%) and barley (10.18%) and agro-industrial by-products, such as wheat bran (14.46%), rice polish (12.80%) and wheat straw (3.39%)
(Kumar et al., 2015) and were comparable to the legumes
Clitoria ternate (18.38%),
Dolichos lablab (18.39%) and
Macroptilium bracteatum (18.89%)
(Hartutik et al., 2012).
The ratios of total essential amino acid content (TEAA) and total amino acids (TAA) and of TEAA and total non-essential amino acid content (TNEAA) of mature leaves of
T. sinensis were 37.19% and 59.21%, respectively. These values were respectively close to the WHO/FAO recommended 40% and 60% and were higher than those of young leaves (35.44% and 54.89%, respectively). High levels of delicious amino acids (DAA, including Glu and Asp) and sweet amino acids (SAA, including Ala, Gly, Ser, Pro, Thr and Trp) in food could contribute to the desirable flavor. The ratios of DAA/TAA and SAA/TAA were 34.43%, 32.37% and 38.64%, 29.98% in mature leaves and young leaves, respectively.
Ca, Mg, Fe and Mn of mature leaves of
T. sinensis were higher than in young leaves. Essential minerals for animals, such as Zn, Se, Mo and Co
(Sethy et al., 2018; Talukdar et al., 2016) were also detected in mature leaves. The contents of Cr, Pb, As and Cd of mature leaves of
T. sinensis were much lower than the allowances.
Effects of T. sinensis on meat characteristics of sheep
All sheep grew normally without any gastro-intestinal incidences or anorexia. As reported by
Goff and Klee (2006), taste, smell and related sensory perception of feedstuff are important for acceptance and palatability to livestock. During the feeding trial, sheep preferred
T. sinensis over grass and the unique flavor of
T. sinensis may be the reason.
Results of nutritional analysis of meats are shown in Table 2. General nutrient composition of meats from TS and CK were comparable. TAA (17.34%), TEAA (8.04%), DAA (4.60%), SAA (5.45%), DAA/TAA (26.51%) and SAA/TAA (31.43%), which may contribute to desirable flavor in the meat of TS group, were higher than control. Meats from TS and CK groups had comparable total fatty acids content, but the content of unsaturated fatty acids and essential fatty acid of meats from TS were slightly higher than CK. Moreover, the meats of the TS group had more Fe (14.30 mg/kg) and Zn (19.00 mg/kg) than CK.
Nutritional status assessment for meats of T. sinensis-fed sheep
In WHO/FAO essential amino acid pattern analysis, the closer RAAs were to 100 and RCs to 1, meant that the amino acids in food were much closer to the required protein pattern for adults. In addition, the closer SRCs were to 100, the higher nutritional value the food presents. As shown in Table 3, SRC for meats of the TS group was 81.01, which was 16% higher than CK (69.56). Thus, meats of the TS group were nutritionally superior over meats of CK.
