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ISSN : 2287-5824(Print)
ISSN : 2287-5832(Online)
Journal of The Korean Society of Grassland and Forage Science Vol.45 No.3 pp.170-178
DOI : https://doi.org/10.5333/KGFS.2025.45.3.170

Effects of Dietary Protein Levels on Growth and Morphological Traits in Crossbred Goats (Capra hircus )

Kwan-Woo Kim, Eun-Do Lee, Dong-Kyo Kim, Hee Chung Ji, Bong-Hwan Choi, Ga-Eun Kim, Byamungu Mayange Tomple*
Animal Genetics Resources Research Center, National Institute of Animal Science, RDA, Hamyang 50000, Republic of Korea
* Corresponding author: Byamungu Mayange Tomple, Animal Genetics Resources Research Center, National Institute of Animal Science, RDA, Hamyang 50000, Republic of Korea. Tel: +82-55-960-3546, E-mail: tomplemayange07@korea.kr
June 18, 2025 September 11, 2025 September 18, 2025

Abstract


This study investigated the effects of different protein levels on growth performance, feed efficiency, and morphological traits in female and male Boer × Korean native crossbred goats (Capra hircus) raised in Korea. A total of twenty-four goats (12 per sex) with an average age of seven months were included in the experiment. The initial body weights (BW) were 31.0 ± 0.6 kg for females and 27.4 ± 1.5 kg for males. A randomized block design was used with three dietary crude protein (CP) treatments: 15% (T1), 18% (T2), and 21% (T3). The results demonstrated that, in female goats, no significant differences (p>0.05) were observed in most growth parameters, except for dry matter intake (DMI), which was significantly higher in T2 and T3 (p<0.05). The total weight gain (TWG) was 2.2 kg in both T1 and T2, and 2.8 kg in T3. The average daily gain (ADG) in females reached 82 g/d in T3, significantly higher than the other. In male goats, DMI was also greater in T2 and T3 compared to T1, with the highest TWG (4.4 kg) and ADG (126.9 g/d) recorded in T3, surpassing the other treatments. Regarding morphological traits, female goats in T3 exhibited significantly greater body length (66.9 cm), withers height (62.8 cm), and chest girth (19.3 cm) compared with T1 and T2 (p<0.05). In contrast, male goats in T2 showed superior body length (65.6 cm), chest width (20.1 cm), and chest girth (78.5 cm) (p<0.05). In conclusion, the study indicates that higher protein levels (21% CP) enhance growth performance and morphological development in female goats, whereas a moderate level (18% CP) appears to be more effective for male goats. These findings suggest that protein requirements differ by sex, and sex-specific feeding strategies should be considered to optimize growth and body conformation in crossbred goats.


Dietary Protein Levels , Growth Performance , Morphological Traits , Sex Differences , Crossbred Goats

초록

    Ⅰ. INTRODUCTION

    Goats play an essential role in global livestock production, contributing substantially to food security, income generation, and rural livelihoods (Liang et al., 2014). Their adaptability to diverse environments, high reproductive efficiency, and ability to utilize low-quality forage position them as a cornerstone of sustainable agricultural systems (Nazan, 2023). In Korea, goat consumption has traditionally been associated with health benefits, and in recent years the demand for goat products has increased markedly due to growing consumer interest in livestock-derived foods (Kim et al., 2014). This rising demand highlights the need to optimize goat productivity, particularly through improved nutrition and feed efficiency.

    Crossbreeding has become a key strategy for improving growth performance, disease resistance, and overall productivity in goats (Sousa et al., 2011;Mohammed et al., 2013;Mbuku et al., 2015;Tesema and Kebede, 2022). Crossbred goats, in particular, exhibit superior growth rates compared with native breeds such as the Korean native black goat (Lee et al., 2019). Nevertheless, the nutritional requirements of crossbred goats— especially regarding the effects of concentrate supplementation with different protein levels—remain insufficiently characterized. Addressing this gap is critical to fully exploiting the potential of crossbred goats in meeting the increasing demand for goat products.

    Feeding concentrates with varying protein levels is a widely adopted approach for meeting the nutrient requirements of goats, particularly during growth and lactation. Previous studies have demonstrated that concentrate feeding enhances dry matter intake, nutrient digestibility, and metabolic responses, thereby improving growth and feed efficiency (Fernández et al., 2021). Higher levels of crude protein (CP) have been reported to linearly increase growth, feed intake, and feed efficiency in growing goats, with dry matter intake and average daily gain also rising in proportion to dietary CP level (Mohsan et al., 2019). However, the optimal level of concentrate supplementation depends on factors such as breed, sex, and physiological stage. For example, a concentrate level equivalent to 2.1% of body weight was identified as optimal for growth performance in growing black goats (Kim et al., 2013). Similarly, moderate concentrate levels have been associated with greater daily gain, improved feed efficiency, and enhanced fattening performance (Salam et al., 2024). In addition, higher protein levels in concentrates have been shown to positively influence body condition score, wither height, and chest girth, with high-protein groups outperforming those fed low- and medium-protein diets (Mohsan et al., 2019).

    Despite these findings, little information is available on sex-specific responses to concentrate feeding in crossbred goats, highlighting the need for further research. Although concentrate supplementation is widely recognized as essential for improving goat productivity, the optimal protein levels for crossbred goats, particularly in relation to sex-specific growth patterns, remain poorly understood. Most previous studies have focused on single-sex populations or have not adequately addressed the differential nutrient requirements of female and male goats. For instance, feeding levels have been reported to affect growth and development differently in female dairy goats, with variations depending on body weight stage (Panzuti et al., 2019). Likewise, concentrate supplementation has been shown to enhance live weight gain, dry matter intake, and milk yield in female black goats (Isnaini et al., 2022). However, comprehensive studies directly comparing growth performance, feed efficiency, and morphological traits in both female and male crossbred goats fed concentrates with different protein levels are lacking. Morphological traits such as body length, withers height, and chest girth are critical indicators of growth and development, and morphological characterization has been emphasized as a valuable tool for breed identification and classification (Elieser et al., 2024).

    Therefore, the objective of this study was to determine the optimal crude protein level in concentrates for maximizing growth performance in crossbred goats, to evaluate the effects of concentrate supplementation on feed efficiency and nutrient utilization, and to investigate sex-specific responses in growth and morphological traits under varying protein levels.

    Ⅱ. MATERIALS AND METHODS

    1. Experimental design and feeding management

    The feeding trial was conducted over 151 days (approximately 22 weeks), from May 10 to October 8, using twenty-four Boer × Korean native crossbred goats (Capra hircus) consisting of 12 females and 12 males with an average age of seven months. Animals were stratified into blocks based on sex (female vs. male) and initial body weight, and then randomly allocated to one of three dietary treatments within each block to minimize variation due to these factors. The initial body weights were 31.0 ± 0.6 kg for females and 27.4 ± 1.5 kg for males. Each goat was housed individually in an iron pen (120 × 90 cm) to allow precise monitoring of feed intake, body weight changes, and health status throughout the experiment.

    All procedures were conducted in accordance with the guidelines of the Institutional Animal Care and Use Committee (IACUC) and were approved under protocol number 2023-597. Prior to the feeding trial, goats underwent a 7-day adaptation period to acclimate to housing conditions and dietary regimen, thereby minimizing stress and stabilizing physiological responses before data collection.

    After adaptation, goats were assigned to one of three concentrate diets containing 15% (T1), 18% (T2), or 21% (T3) crude protein (CP). The Korean Feeding Standards for Goats (NIAS, Korea, 2022) recommend approximately 14–16% CP for growing goats aged 6–9 months. Based on these guidelines, 15% CP was selected as the reference level, 18% CP as a moderate surplus to evaluate potential improvements in growth and feed efficiency, and 21% CP as a high-protein boundary to assess the physiological limits and possible effects of overfeeding.

    To ensure adequate fiber intake, Italian ryegrass (IRG) hay was offered daily at 1.8% of body weight (DM basis), which falls within the recommended range (≈1.8–2.0% BW) for maintaining rumen health and function in growing goats. The amounts of IRG hay and concentrate were adjusted weekly according to updated body weights to secure consistent nutrient intake across all treatment groups. Feeding was carried out twice daily at 09:00 and 16:00 h, with refusals recorded daily to determine individual dry matter intake (DMI). Clean, fresh water was available ad libitum throughout the experiment.

    Although the number of animals per treatment was limited (n = 4), the use of a randomized block design with stratification by sex and initial body weight, combined with the extended trial duration (151 days), reduced variability and enabled consistent detection of treatment effects.

    2. Data collection and measurements

    Data were collected systematically to evaluate growth performance, feed efficiency, and morphological traits. Initial and final body weights (BW) were recorded at the beginning and end of the feeding trial to calculate total weight gain (TWG) as the difference between final and initial BW. Dry matter intake (DMI) was monitored daily by measuring feed offered and refusals, allowing precise quantification of forage and concentrate consumption. Average daily gain (ADG) was calculated as TWG divided by the number of feeding days, while feed conversion ratio (FCR) was determined as total feed intake divided by TWG, providing an index of feed utilization efficiency. To minimize variability, BW measurements were taken weekly before the morning feeding using a calibrated digital scale.

    Morphological traits were measured to assess structural development under each dietary treatment (Fig. 1). Body length was defined as the distance from the point of the shoulder to the base of the tail; withers height as the vertical distance to the highest point of the withers; chest width as the distance between the outermost points of the chest; and chest girth as the thoracic circumference measured immediately behind the forelegs.

    3. Chemical composition analysis

    Feed samples were oven-dried at 65 °C for 48 h using a forced-air drying oven (OF-22GW, JEIO TECH, Daejeon, Korea) and subsequently ground through a 0.9-mm screen using a laboratory mill (Cyclotec™ 1093 Sample Mill, Foss Tecator, Höganäs, Sweden). Nutrient composition, including dry matter (DM), crude protein (CP), crude ash, and ether extract (EE), was determined in duplicate according to the standard procedures of the AOAC (2003). Organic matter (OM) was calculated as DM minus ash. Fiber fractions, including neutral detergent fiber (NDF) and acid detergent fiber (ADF), were analyzed using the ANKOM fiber analyzer (A2000i, ANKOM Technology, Macedon, NY, USA) following the method of Van Soest et al. (1991). Non-fiber carbohydrates (NFC) were estimated using the following equation: NFC (%) = 100 - (ash + CP + EE + NDF)

    This analytical approach verified that the formulated concentrate diets (15%, 18%, and 21% CP) corresponded to the intended protein levels, established relative to the Korean Feeding Standards for Goats (NIAS, 2022). The 15% CP diet represented the recommended requirement (14–16% CP), the 18% CP diet reflected a moderate surplus, and the 21% CP diet was set as a high-protein boundary to assess responses under potential overfeeding conditions.

    4. Statistical analysis

    All data were analyzed using SAS software (version 9.1, SAS Institute Inc., Cary, NC, USA). Growth performance and morphological traits were evaluated using the General Linear Model (GLM) procedure according to a randomized block design, with dietary protein level as the main effect and block (sex and initial BW) as a blocking factor.

    When significant differences were observed (p<0.05), Duncan’s multiple range test was applied for mean separation. Results are presented as means ± standard error (SE).

    Ⅲ. RESULTS AND DISCUSSION

    1. Effect of dietary protein levels on growth performance in female goats

    Table 2 summarizes the effects of dietary protein levels on growth performance in female goats. Goats fed the highest protein diet (T3; 21% CP) had the greatest final BW (34.9 kg) and total weight gain (2.8 kg), compared with 32.1 kg and 2.2 kg in T1 (15% CP) and 33.2 kg and 2.2 kg in T2 (18% CP), respectively. Although differences in total weight gain and ADG were not statistically significant (p>0.05), the numerical improvement in T3 suggests a potential growth-promoting effect of higher protein levels. The highest ADG was observed in T3 (82.0 g/day), which is consistent with the notion that increasing dietary CP enhances nutrient utilization efficiency. Dry matter intake (DMI) increased with dietary protein levels, with T2 (1,029 g) and T3 (1,031 g) showing significantly higher values than T1 (949 g; p<0.001). These results corroborate earlier reports by Mohsan et al. (2019), who demonstrated a linear increase in DMI and ADG with higher dietary CP in goats. The higher intake in T2 and T3 indicates that protein supplementation stimulates feed consumption, likely due to improved palatability and digestibility. Feed efficiency, expressed as the DMI/ADG ratio and FCR, varied among treatments. Although T3 goats consumed amounts similar to T2, they achieved superior growth, reflected in the lowest DMI/ADG ratio (20.3) and the most favorable FCR (0.09). In contrast, T2 showed the least efficient conversion despite higher intake, suggesting less effective nutrient utilization at moderate protein levels. This trend aligns with Andell et al. (2021), who reported improved FCR in animals receiving higher-protein concentrate diets compared with those on moderate or low-protein diets.

    The current findings also support Abdelrahman et al. (2014), who observed that lower dietary protein levels negatively affected weight gain and feed efficiency, and Huang et al. (2024), who highlighted the stage-dependent effects of protein nutrition on growth. Although Yusuf et al. (2020) suggested that 14% CP was sufficient for maintenance and growth in goats, the present study indicates that higher levels (≥18% CP) may further optimize performance in crossbred goats. Taken together, the results demonstrate that increasing dietary protein to 21% enhances growth efficiency in female goats by improving feed intake and nutrient utilization, even though some performance variables did not reach statistical significance. This suggests that protein requirements in crossbred female goats may be higher than those indicated in conventional feeding standards, warranting further investigation with larger sample sizes to confirm these trends.

    2. Effect of dietary protein levels on growth performance in male goats

    Table 3 summarizes the effects of dietary protein levels on growth performance in male goats. Animals fed the T2 diet (18% CP) achieved the highest final BW (32.5 kg) and total weight gain (4.4 kg), outperforming those in T1 (15% CP) and T3 (21% CP) (Fig. 2). These findings indicate that a moderate protein level (18% CP) provides a more balanced nutrient supply that promotes optimal growth in male goats.

    The superior performance in T2 is likely due to improved nutrient digestibility and utilization, as moderate dietary CP levels have been reported to support efficient protein metabolism (Binbin et al., 2010;Rukboon et al., 2018). Atti et al. (2004) similarly demonstrated that male goats receiving medium CP diets exhibited greater growth rates compared with those fed either low or excessive protein. In contrast, goats in T1 exhibited the lowest final BW and total gain (3.5 kg), confirming that diets with insufficient protein fail to meet the nutritional requirements of growing males.

    In terms of ADG, goats fed the T2 diet again outperformed the other groups, recording 126.9 g/day, followed by T3 (119.1 g/day) and T1 (102.9 g/day). These results agree with Wang et al. (2013), who reported that crude protein levels significantly influence ADG, feed intake, and weight gain in growing goats. Although T2 and T3 goats had similar initial BW, T2 showed the greatest feed efficiency, as indicated by the lowest DMI/ ADG ratio, suggesting superior nutrient utilization. T3 also supported relatively high growth, but its less efficient feed conversion indicates that excessively high protein levels may not further improve nutrient utilization. By contrast, T1 exhibited the least efficient feed conversion, with the highest FCR (0.13), consistent with its reduced growth performance. The ADG value observed in males under the T2 diet (126.9 g/day) slightly exceeded the upper range reported in the Korean Feeding Standards for Goats (NIAS, 2022). However, this finding is consistent with previous reports on Boer and Boer-cross goats under intensive feeding conditions, where growth rates above 120 g/day are commonly achieved (Lu et al., 1990;Bezerra et al., 2019;Brand et al., 2024). This supports the interpretation that the higher ADG in males reflects the enhanced genetic potential of Boer × Korean native crossbreds rather than overfeeding. Interestingly, in the present study, female goats had higher average BW than males, which contrasts with reports that male goats generally achieve superior growth and body weight in crossbreeding programs (Mohammed et al., 2018). However, Nwachukwu et al. (2021) observed that female crossbred kids had higher birth weights than males, emphasizing that sex-related growth differences may be breed-specific and influenced by management conditions. Although significant differences in DMI were observed among dietary treatments (p<0.05), no statistically significant differences were detected for total weight gain, ADG, DMI/ADG ratio, or FCR (p>0.05).

    3. Effect of dietary protein levels on morphological traits of female goats

    The effects of dietary protein levels on morphological traits of female goats are presented in Table 4. Goats fed the T3 diet (21% CP) exhibited the most pronounced structural development, with significantly greater body length (66.9 cm), withers height (62.8 cm), and chest width (19.3 cm) compared with T1 (15% CP) and T2 (18% CP) (p<0.05). This indicates that high-protein diets promote enhanced skeletal growth in female goats. In contrast, T1 goats showed the shortest body length (65.0 cm) and narrowest chest width (18.7 cm), reflecting less favorable structural development.

    Chest girth did not differ significantly among treatments (p>0.05), although a slight increase was observed in T2 (79.5 cm), suggesting a marginal improvement in overall body condition. These findings are consistent with Mohsan et al. (2019), who reported that goats receiving high-protein, highconcentrate diets exhibited significantly greater body condition scores, withers height, and heart girth compared with those fed low- or medium-protein diets. Similarly, Patel et al. (2009) demonstrated that high dietary protein concentrations positively influenced most body measurements in growing calves, supporting the observed improvements in skeletal development in goats.

    The significant differences in body length, withers height, and chest width (p<0.05) confirm that concentrate supplementation at varying protein levels affects morphological traits. Specifically, T3 supported superior skeletal growth, whereas T2 contributed to slightly greater chest girth and body condition. These results are in agreement with Ryan et al. (2007), who observed increased body weight, body wall width, and leg circumference in goats fed concentrate-based diets compared with range-fed goats (p<0.05). Byamungu et al. (2025) further emphasized that higher protein intake enhanced body length, depth, chest width, and chest girth across sexes, corroborating the present findings.

    4. Effect of dietary protein levels on morphological traits of male goats

    The effects of dietary protein levels on morphological traits of male goats are presented in Table 5. Goats fed the T2 diet (18% CP) exhibited the greatest structural development, with the highest body length (66.1 cm), chest width (20.1 cm), and chest girth (78.5 cm) compared with the other treatments (p<0.05). This suggests that a moderate protein level promotes superior skeletal growth and contributes to a more robust body frame in male goats. Isnaini et al. (2022) similarly reported that concentrate supplementation significantly increased chest girth in goats, indicating improved growth relative to forage-based diets. In contrast, goats fed the T1 diet (15% CP) showed the smallest body length (63.6 cm), chest width (18.8 cm), and chest girth (71.6 cm), reflecting insufficient skeletal development. Goats fed T3 (21% CP) had intermediate values (body length 65.6 cm, chest width 19.0 cm, chest girth 75.1 cm), suggesting improved development compared with T1 but inferior to T2.

    These results indicate that the T2 diet promotes superior structural development of male goats, especially with respect to body size and skeletal frame. Interestingly, these findings differ from Mohsan et al. (2019), who reported that dietary protein and concentrate levels did not significantly affect body length in male goats but influenced body condition score, withers height, and heart girth. The discrepancies may reflect differences in breed, diet formulation, or experimental conditions.

    Ⅳ. CONCLUSIONS

    The present study demonstrates that dietary protein requirements differ between female and male crossbred goats. Higher protein levels (21% CP) enhanced growth performance and skeletal development in females, whereas moderate levels (18% CP) optimized growth and feed efficiency in males. These findings emphasize the importance of adopting sex-specific concentrate feeding strategies to improve productivity, feed utilization, and body development in goat production systems.

    Ⅴ. ACKNOWLEDGEMENTS

    This study was supported by the 2025 RDA Fellowship Program (Project No. PJ01739504) of National Institute of Animal Science, Rural Development Administration, Republic of Korea.

    Figure

    KGFS-45-3-170_F1.jpg

    Schematic representation of body measurements in goats: body length (1), chest girth (2), withers height (3) and chest width (4).

    KGFS-45-3-170_F2.jpg

    Effects of dietary protein levels on total weight gain in female and male crossbred goats.

    Table

    Ingredients and chemical composition of the experimental diets

    T1, T2, and T3 represent concentrate diets formulated to contain 15%, 18%, and 21% crude protein, respectively; IRG, Italian ryegrass; NFC (%) = 100 - (ash + CP + EE + NDF).

    Effect of dietary protein levels on growth performance and feed intake in female goats

    ab Superscripts within a row indicate significant differences (p<0.05). T1, 15% CP; T2, 18% CP; T3, 21% CP; SEM, standard error of the mean (n = 12).

    Effect of dietary protein levels on growth performance and feed intake in male goats

    ab Superscripts within a row indicate significant differences (p<0.05). T1, 15% CP; T2, 18% CP; T3, 21% CP; SEM, standard error of the mean (n = 12).

    Effect of dietary protein levels on morphological traits of female goats

    ab Superscripts within a row indicate significant differences (p<0.05). T1, 15% CP; T2, 18% CP; T3, 21% CP; SEM, standard error of the mean (n = 12).

    Effect of dietary protein levels on morphological traits of male goats

    abc Superscripts within a row indicate significant differences (p<0.05). T1, 15% CP; T2, 18% CP; T3, 21% CP; SEM, standard error of the mean (n = 12).

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