Commercial Concentrate Supplementation in Phan Rang Sheep Diets: Effects on Digestibility Traits, Growth and Carcass Performance

Vietnam has a small ruminant animal group called Phan Rang sheep whose tail is short and thin (Chon, 2000). The sheep originally came from Mongolia and China (Nguyen et al., 2005) and has been widely raised and adapted well with the hot and dry weather in Ninh Thuan province, which accounts for the highest sheep population (94%) in Vietnam with an estimation of more than 107 thousand heads in 2022 (General Statistic Office, 2022). Hence, Phan Rang sheep has gradually become a local and famous animal of Ninh Thuan farmers.

In Ninh Thuan, sheep flocks are raised mostly under severe environments where the feed shortage is the major constraint to their production development. Sheep are freely raised in crop fields where rice and other cultivars have been harvested and left crop residues. Hence, these feed resources are normally low in nutrition, energy and digestible proteins. Moreover, the continuous and rapid increase of human demand for small ruminant meat, especially lambs and goat meat, while the decreasing tendency of rangelands for grazing brought about an increasing pressure on sheep husbandry systems. Thus, concentrate supplementation is highly needed for stall-fed and free grazing animals to meet their nutrient demands and improve their production performance.

Concentrate supplementation has been widely used on ruminant animals to improve animal performance and production, including goat and sheep fattening (Salim et al., 2002; Szumacher-Strabel et al., 2002; Tripathi et al., 2007; Cantalapiedra-Hijar et al., 2009; Majdoub-Mathlouthi et al., 2013); however, there is no report on concentrate supplement for Phan Rang sheep in the aspects of itself-animal effects and economy impacts for local farmers. Therefore, this research was conducted to examine the effects of different concentrate levels in the diets on nutrient digestibility; rumen pH, ammonia, and volatile fatty acid profile; growth performance and meat production of the Phan Rang sheep.

The experiment was conducted at the Goat and Sheep Breeding Research Station in Ninh Thuan located at 11°45’34.7”N latitude and 109°04’28.3”E longitude. The climate is hot and semi-arid. The study was initiated in July and ended in September, 2022. During the experiment, the average ambient temperature ranged from 29-31oC and relative humidity varied from 50-55%.

The research was carried out on 25 Phan Rang male sheep weighed 15.4 ± 1.3kg (3-4 months). The sheep was individually housed in pens (1.4×1.8×1.3 m) with separate feeding trough and freely accessed to fresh tap water.

The animals were allowed to have 2-weeks adaption period before starting the experiment. All the animals were weighed again before randomly allocated to five experimental treatments. The experiment was designed as completely randomized design with 5 treatments on 25 Phan Rang intact male sheep and 5 replications (5×5= 25). The five treatments were: control (C) (ad libitum access to grass feeding); 0.75% (control plus 0.75% of commercial concentrate); 1.5% (control plus 1.5% of commercial concentrate); 2.25% (control plus 2.25% of commercial concentrate) and 3.0% C (control plus 3.0% of commercial concentrate) as a percentage of live weight on dry matter basis. The animals were fed concentrate for a period of 90 days. The body live weight of the animals was measured every 14 days to calculate gained weight and adjust the concentrate supplementation levels for each animal.

Fresh Guinea grass (Panicum maximum Jacq.) was harvested twice daily in the morning and in the afternoon. Animals were fed concentrate 30 minutes before feeding ad libitum Guinea grass at 4 times per day (at 7h30; 10h30; 13h30 and 16h30). Chemical composition of the grass and commercial concentrate were shown at Table 1. Feed intake of the animals was daily recorded by measuring individual daily feeding supply and refusal. It was then calculated for average feeding intake by dry matter. Deworming was applied at the beginning of the experiment using “Albendazole” at 3ml/head of sheep.

Table 1: Chemical composition of the grass and commercial concentrate.

Digestibility trial was conducted for a week since 45th day of the experiment period. Feed sub-samples, feed refusals and feces were collected daily and analyzed to calculate nutrition digestibility.

On the last day of the digestibility trial, rumen fluid of each sheep was taken using esophageal-rumen tube at 0 and 4 hours after feeding concentrate. The rumen fluid was then filtered through a muslin cloth to remove coarse particles. Thereafter, pH values were directly measured by pH machine (HANNA HI8314, Romania). The rumen fluid tubes were then stored at -20oC for further analysis of ammonia concentration and volatile fatty acids.

At the end of the experiment, 03 lambs with body weight closed to mean weight of their treatment were selected for carcass assessment. Carcass was weighed immediately to obtain hot carcass weight. Longissimus lumborum muscle was taken to evaluate chemical compositions of lamb meat.

Nitrogen concentration of feeds and animal feces was determined by using the Kjeltec 8200 following the Kjeldahl method (AOAC, 1990). Neutral Detergent Fiber was analysed following the protocol of Vogel et al. (1999) using the Ankom 2000 Fiber Analyser (Ankom®, Tech. Co., Fairport, NY, USA). Ether extract was determined using the Soxtec 2050 (Foss, Sweden) (AOAC, 1990). Ammonia concentration and volatile fatty acids (VFAs) in the rumen fluid were analysed at the laboratory of Animal Nutrition, Okayama University, Japan using the standard Gas Chromatography Method.

Experimental data were analysed using General Linear Model by SPSS version 20.0. The analysis fitted model was:

Yij = µ + Ci + Ɛij

Where; µ = The overall mean; Ci = The fixed effect of treatment (concentrate levels); i= Control; 0.75, 1.5, 2.25, 3.0; Ɛij = The random error; Tukey’s statistic was used to test differences (p<0.05) among means.

Concentrate level in the diet had significant effects (p<0.05) on average feed intake of sheep, where grass feed intake decreased with an increase of concentrate level (Table 2). Grass feed intake of animals in control and treatment 0.75% was significantly (p<0.05) higher than those in treatments 1.5%, 2.25% and 3%. As a result, there was a significant effect (p<0.05) in total dry matter intake of animals among different treatments (Table 2).

Concentrate supplemented in the diet had significant (p<0.05) effects on nutrient digestibility of DM, OM, CP and NDF (Table 3). However, the differences did not show clearly among treatments. The highest OM digestibility was recorded in treatment 0.75% (77.1%), which was significantly different from those in treatment 2.25% (71.2%). The greatest CP digestibility was in treatment 3.0% (65.9%) which was significantly higher than in control and treatment 0.75% (52.2% and 59.0%, respectively). In contrast, the digestibility of NDF in the control (65.4%), treatments 0.75% (65.1%) and 1.5% (59.3%) was significantly (p<0.001) higher than in treatments 2.25% (54.3%) and 3.0% (53.6%) (Table 3).

Table 2: Effects of concentrate supplementation on feed intake of animals (Means ± SD)

abc Means within the same row sharing the same letter are not significantly different; SD: Standard deviation; p: probability; DM: Dry matter; LW: Live weight

Table 3: Effects of concentrate supplementation on digestibility of the animals (Means ± SD).

abc Means within the same row sharing the same letter are not significantly different; SD: Standard deviation; p: probability; DM: Dry matter; OM: Organic matter; CP: Crude protein; NDF: Neutral detergent fiber

Table 4: Effects of concentrate supplementation on live weight and daily gain weight of the animals (Means±SD).

abc Means within the same row sharing the same letter are not significantly different; SD: Standard deviation; p: probability

Table 5: pH value and ammonia concentration of rumen fluid before and after 4 hours feeding (Means ± SD).

abc Means within the same row sharing the same letter are not significantly different; SD: Standard deviation; p: probability.

Concentrate supplement did not have significant effects on live weight (LW) of the animals between treatments on the first 15-days of the experiment, whereas the significant effects were obviously observed from day 30 onwards (Table 4). At the end of the experiment, LW of the animals in the control was significantly (p<0.001) lower than in the concentrate-supplemented groups. The highest LW of the animals was recorded in treatment 3.0% (30kg/head) which was significantly (p<0.001) higher than others treatment groups.

Daily gain weight (DGW) of the animals was significantly (p<0.001) affected by levels of concentrate (Table 4). Average DGW significantly increased when the proportion of concentrates in the diets increased. The highest DGW was significantly recorded in treatment 3.0% (161.3g/day), followed by treatment 2.25% (117.1g/day) and the lowest DGW was observed in control (25.6g/day). There was no significant difference in DGW of the animals between treatments 0.75% and 1.5% (Table 4).

pH values were significantly (p<0.05) different among treatments before feeding, especially there was a statistically significant difference in pH values between treatment 0.75% (6.43) and treatment 2.25% (6.57). However, these values did not show significant differences after 4h feeding (Table 5). In general, concentrate supplement caused a reduction in ammonia values, but there were no significant differences in ammonia values between treatments before (p=0.235) and after (p=0.961) feeding (Table 5).

Concentrate supplement did not cause significant differences in the concentration of acetate, propionate, butyrate and sum of VFA among treatments before and after feeding. However, the sum of VFA concentration tended to be increased after feeding. In general, the major proportion of VFA profile in rumen fluid was acetate, then followed by propionate and the lowest percentage was butyrate (Table 6).

Concentrate supplement had significant effects on percentage of carcass performance between 5 treatments. The highest carcass percentage was recorded in treatment 3.0% (51.8%) which was significantly (p<0.001) higher than treatments 1.5% (46.0%), 0.75% (44.7%), and control (43.9%). Concentrate supplement had significant effects on chemical composition of lamb meat. Dry matter, crude protein and intramuscular fate (%) increased linearly with increasing supplement level; and it was significantly (p<0.01) lower in control compared to supplemented treatments (Table 7).

Table 6: Volatile fatty acid (VFA) of rumen fluid before and 4h after feeding (Means ± SD).

abc Means within the same row sharing the same letter are not significantly different; SD: Standard deviation; p: probability

Table 7: Carcass performance and chemical composition of lamb meat (Means ± SD).

abc Means within the same row sharing the same letter are not significantly different; SD: Standard deviation; p: probability

Table 8: Economic efficiency calculation of different treatments.

Concentrate supplement had greatly increased benefits for farmers. The higher concentrate levels applied; the more benefit farmers gained. The highest benefit value was observed in treatment 3.0%, with 967,230 vnd/head compared to the lowest concentrate level treatment (512,820 vnd/head) and control (253,440 vnd/head) for a period of 90-day fattening (Table 8).

It is necessary to quantify dry matter intake (DMI) for an estimation of nutrient consumption by ruminants. Animals consume less roughage when concentrate diet increases (Tripathi et al., 2007; Papi et al., 2011; Quan et al., 2014). In this study, grass DMI was reduced when the level of concentrate diet increased. Experimental animals consumed 4.1% of grass DM without concentrate supplement. This value decreased to 3.4% and 2.2% when the animals were supplied with 0.75% and 3% of concentrate, respectively. The finding in this research is consistent with some other researchers (Holden et al., 1995; Reeves et al., 1996; Tripathi et al., 2007; Papi et al., 2011; Quan et al., 2014) who revealed that forage intake reduces with the increased intake of supplemental feed due to substitution of grain for forage. With the increase of concentrate level, total DM feed intake (including grass and concentrate) of animals in this study ranged from 4.1% to 5.1%. The quantity feed required for animals depends on size of the animal and their production stage (National Research Council, 2007). In this study, sheep are on the fast-growing stage, so perhaps they need higher energy diet to meet their growing demand. Earlier study conducted by Tripathi et al. (2007) also reported that DMI of sheep fed by 1.5% and 2.5% concentrate levels in the diets was 4.2% and 4.9%LW, respectively.

In this study, live body weight and average daily gain weight (DGW) of the animals significantly improved with the increase of concentrate levels. The highest DGW was recorded in treatment 3% with an average of 161g/day, followed by treatment 2.25% with 117g/day, treatment 1.5% was 85.3g/day and DGW of animal without concentrate added was only 25.6 g/day. These results are higher than those reported by Tripathi et al. (2007) who revealed that daily gain weight of sheep fed by ad libitum and 1.5%BW concentration were 150.7g/day and 77.2 g/day, respectively.

In this study, though apparent digestibility of DM, OM, CP and NDF was statistically significant effect between treatments, it did not obviously show significant difference between control and treatments, with the exceptions of CP and NDF. CP digestibility in this study increased when the proportion of concentrate in the diet increased, which is in agreement with findings by Haddad (2005) and Cantalapiedra-Hijar et al. (2009). High digestibility of CP in treatments 2.25% and 3% is probably due to high amount of CP intake through concentrate provided. In contrast, animals in treatments fed low concentrate level and in control consumed high NDF due to higher fiber intake through roughage source. The animals fed by higher concentrate levels (2.25% and 3%LW) had lower ruminal pH (6.31 and 6.26) than those given concentrate at 0.75% and 1.5%LW after 4h feeding, but the pH values remained in critical rumen pH range of 6.0-7.0 for optimum microbial growth and nutrient utilization (Erfle et al., 1982). Though high concentrate supplement induced the decline of pH value in rumen, it did not cause problem of acidosis. The rumen pH higher than 5.9 is considered as normal, while the pH values 5.6 to 5.8 induce a problem of ruminal acidosis (Olson, 1997). The greatest balance of fiber and starch digestion occurs at a rumen pH of around 6.0, with fiber-digesting bacteria surviving best at pH 6.0 to 6.8 and starch-digesting bacteria at pH 5.5 to 6.0. The decline of pH in ruminal fluid fed by high concentrate or grain diets has also been indicated by earlier research (Hristov et al., 2001; Tripathi et al., 2004, 2007).

Ammonia values in the treatments provided high concentrate levels were higher than control and treatment supplied 0.75% level of concentrate at both points of sample measurement. This could be explained that animals consumed a high amount of CP, which may lead to a faster rate of passage through animal rumen and a higher turn-over of ammonia. However, there was no significant difference in rumen ammonia concentration between treatments after 4 hours feeding.

Volatile fatty acid (VFA) ratios on rumen production are influenced by different factors, including composition of feed (Bergman, 1990; Dijkstra, 1994; Szumacher-Strabel et al., 2002). In this study, the results showed that increased concentrate level in the diet resulted in a decrease of acetate proportion while propionate increased. Similar findings have been reported in goat fed by high concentration level (Quan et al., 2014) and in cow fed by grass silage (Van Gastelen et al., 2015). Changing of VFA profile in rumen fluid has also been reported by some previous research using different types of feeding ingredients in the diet. Adding fish oil in the diet reduced level of acetic acid while it induced an increase of butyric acids (Chamberlain et al., 1983; Szumacher-Strabel et al., 2002); or increasing corn silage percentage in the diet led to an increase of butyrate proportion in rumen of cows (Van Gastelen et al., 2015). In general, concentrate supplement generally did not negatively affect VFA rumen profile of the animals in this study.

Concentrate supplement had significant effect on carcass performance of the animals. Hot carcass weight and dressing percentage increased when increasing level of concentrate in the diets. Those values were significantly higher in the treatments fed by 2.25% (12.7kg; 48.3%, respectively) and 3.0% (15.6kg; 51.8%, respectively). Carcass performance of sheep in this study was similar to other researchers (Archimède et al., 2008; Jacques et al., 2011; Papi et al., 2011; Majdoub-Mathlouthi et al., 2013) who studied the effects of varying concentrate levels in the diets on slaughtering traits of lambs and concluded that carcass performance of lambs increased with increasing level of concentrate.

Increasing level of concentrate supplement in the diets of Phan Rang sheep up to 2.25% or 3.0% of live weight increased daily gain weight, carcass performance and improved economical benifit for farmers without any adverse effects on nutrient digestibility and rumen fermentation of the animals. Those concentrate levels may be recommended for fattening the lambs by Ninh Thuan local farmers.

The authors would like to thank all members of Goat and Sheep Breeding Research Centre in Ninh Thuan for kindly supporting us the facility to conduct this experiment. We are also grateful to our students: Mr. Le Minh Can, Mr. Tran Van Hoai Phuoc and Mr. Vo Viet Trieu for their immense technical assistance in taking care of the animals and collecting data during experimental period. This work was supported by the Ministry of Education and Training under the project CT-2021-01-DHH-03.

This study is the first to evaluate levels of commercial concentrate supplementation for Phan Rang sheep in the aspects of itself-animal effects and economy impacts.

Idea and research design: NHV, DVD, NXB, NTM; Sample collection: NTM, VNP, TNL, LTH, LDT, NMD, BVL; Methodology, chemical analysis and data curation: NHV, NTM, VNMT, TNMT, NN; Statistical analysis: NTM; Writing the original draft and revising the final version: NHV, NTM; Review and editing: All authors. All authors read and approved the final manuscript.

The authors have declared no conflict of interest.