| Livestock Research for Rural Development 36 (5) 2024 | LRRD Search | LRRD Misssion | Guide for preparation of papers | LRRD Newsletter | Citation of this paper |
This study aims to evaluate the effect of feed with different level CP (crude protein) and TDN (total digestible nutrient) on animal performance and environmental cost by studying emissions per unit of product in lambs. A total of 24 male Thin-tailed lamb aged 3–4 months with a body weight of 13.69 ± 2.43 kg (CV=5.89%) were used in this study. This study used a Completely Randomized Design with a 3x2 factorial pattern. Factor 1st was the CP level consisting 14% C, 16% CP and 18% CP while factor 2nd was the TDN level consisting of 2 levels, 60% TDN and 70% TDN. Increasing the CP level resulted in increased protein intake and digestibility. Increasing the TDN level decreased intake and increased digestibility of DM and OM. Lambs fed with 60% TDN produced higher non-carcass and bone weight compared to 70% TDN. The N excreted through urine was greater in lamb fed with 16% and 18% CP compared to 14% CP. The amount of N (g) excreted through feces and urine decreased with increasing TDN levels. The amount of N2O emission was greater in lamb fed 60% TDN compared to 70% TDN. The CH4 emissions were higher in lamb fed 60% TDN compared to 70% TDN. The N, N2O and CH4 emissions per ADG and meat production were lower in lamb fed with 70% TDN compared to 60% TDN. The feed 70% TDN was more environmentally friendly than 60% TDN.
Keywords: carcass, feed, methane, nitrogen, performance
In the ever-evolving landscape of sustainable agriculture, the intricate relationship between feeding management for reducing methane and nitrogen emissions and improving productivity and meat quality in ruminant production stands as a unique set of challenges, particularly in tropical countries (Giamouri et al 2023). The diverse climate change conditions in tropical areas such as increasing temperatures, and the long dry season will impact feed availability and quality and pose significant hurdles for farmers striving to ensure optimal nutrition and growth for their lambs (Costa et al 2013). Moreover, low-quality feed also can increase the emissions of methane and nitrogen (Broucek 2015). The negative combo is not only detrimental economically but also environmentally. In light of these obstacles, employing feeding management strategic approaches becomes imperative for farmers seeking to enhance lamb nutrition and reduce emissions.
The kind of feeding management to reduce methane emissions without negative impact on livestock namely, the first was dietary manipulation by adjusting the diet composition by incorporating feed additives such as lipids, tannins, and certain oils or supplements like nitrate can alter the rumen microbial population (Palangi and Lackner, 2022). The second was improved forage management by implementing rotational grazing systems, selecting pasture species with better digestibility, and optimizing forage quality through proper harvesting techniques can aid in reducing methane emissions (Badgery et al 2023). However, those ways were hard to apply on a small-scale farm that was dominantly in tropical areas. Optimizing the utilization of local feedstuff and following up with balancing energy-protein in the diet were the possible ways to apply on a small-scale farm in facing that obstacle (Purbowati et al 2021). Balancing energy-protein in the diet by precision nutritional needs of animals can minimize excessive nutrient intake, subsequently decreasing nitrogen excretion and methane emissions (de Azevedo 2021).
Even though the study of the effect level of energy-protein in lambs has been widely reported the information dominantly discusses related to productivity, while the information related to environmental cost from the emissions was still scarce. Therefore, this study aims to evaluate from the side of environmental cost by studying emissions per unit of product (meat) in lambs fed different levels of protein and energy. Understanding this nexus not only holds promise for environmental conservation but also revolutionizes the way we perceive and optimize livestock nutrition for a more sustainable future.
A total of 24 male Thin-tailed sheep aged 3–4 months with a body weight of 13.69 ± 2.43 kg (CV=5.89%) were used in this study. The lamb was kept in individual pens equipped with feed and drink containers. The feed given was pelleted complete feed. The lamb received feed and water ad libitum. The feed was given to them at six o'clock in the morning, and the refusal was collected and weighed in the morning before the new feed was given. Both feed offered and refusal were measured on a daily basis, and the difference between the two measurements was used to determine the feed intake. To measure growth performance, lambs were weighed once a week in the morning before feeding. This study used a Completely Randomized Design with a 3x2 factorial pattern. Factor 1 was the crude protein (CP) level consisting of CP14 (14% CP), CP16 (16% CP) and CP18 (18% CP) while factor 2 was the total digestible nutrient (TDN) level consisting of 2 levels, namely E60 (60% TDN) and E70 (70% TDN) so that there are 6 types of treatment combinations with 4 replications. The composition and nutrient content of the treatment feed are shown in Table 1.
A seven-day digestion study was carried out utilizing total collection techniques. Every day, the amounts of food that each animal offered, rejected, feces, and urine were weighed and recorded. 100 g of samples of each feed that was offered and rejected were taken from each lamb during the whole collection process. Throughout the course of the collection, 500 g of excrement and 500 cc of urine were sampled and kept at 18°C daily. The urine's ultimate pH was kept below 3. Each animal's daily urine and feces were taken at a rate of around 10% and kept in a deep freezer at -20°C for chemical analysis.
After being fed trial for 84 days, the lambs were slaughtered. The lambs were slain after a 6-hour fast. The halal procedure was used in the slaughter process. The visceral organs of lambs were removed and weighed after they had been skinned. After skinning the lambs, the internal organs were removed to get the carcass, and each component was weighed. After eight hours of refrigeration at 18 °C in a cold chamber, the carcass—including the kidneys and internal fat—was weighed. Every carcass was divided into two halves along the vertebrae. Meat, fat, and bone from the carcass were separated, and weighed, and the results were given as a percentage of the cold carcass weight (CCW). The average of the proportion of meat protein in the longissimus dorsi and bicep femoris muscles multiplied by the kilogram of carcass meat (kg) was used to calculate the amount of meat protein (kg).
The dry matter (DM), CP, ether extract (EE), and ash in feed and feces were analyzed following the AOAC (2005). In this study used the Kjeldahl technique according AOAC (2005) to evaluate the nitrogen (N) content of feed, feces, and urine. The Van Soest technique (1991) was used to determine the neutral detergent fiber (NDF) and acid detergent fiber (ADF). Nitrous oxide (N2O) g/day) excreted in feces and urine was calculated according to the guidelines of Prima et al (2019). The methane emission was measured according to the procedure reported by Restitrisnani et al (2022).
By dividing the quantity of nitrogen excretion (g/day) by the amount of ADG (g/day), carcass (kg), meat (kg), and kg meat protein, and similarly for N2O and methane (CH4) emissions (g/day), the efficiency of production to the emissions was calculated.
The data were analyzed using analysis of variance and for significant treatment continued with Duncan's multiple area test at the 5% level. The Linear model of a completely randomized design with a factorial pattern of 3 x 2 (Gomez and Gomez, 1995). The tools for analysis was used SPSS 26 Version.
Yijk = μ + αi + βj + (αβ)ij + eijk
where : Yijk: the dependent variable, μ: the overall mean, αi: effect of CP level, βj: effect of TDN level, (αβ)ij: effect of interaction level of CP and TDN, eijk: the random error
|
Table 1. Feeding treatments and nutrients composition |
||||||||
|
Item |
Feeding treatments |
|||||||
|
LPLE |
MPLE |
HPLE |
LPHE |
MPHE |
HPHE |
|||
|
Feedstuffs |
||||||||
|
Molasses |
6.0 |
6.0 |
6.0 |
8.0 |
8.0 |
8.0 |
||
|
Cassava flour |
11.5 |
9.5 |
7.0 |
38.5 |
36.4 |
34.3 |
||
|
Sugarcane leave |
30.2 |
29.0 |
28.5 |
10.4 |
8.9 |
7.0 |
||
|
Rice bran |
18.0 |
16.0 |
14.0 |
19.6 |
18.0 |
17.3 |
||
|
Cassava peel |
15.0 |
15.0 |
15.0 |
3.0 |
3.0 |
3.0 |
||
|
Soybean meal |
13.5 |
17.5 |
21.5 |
14.5 |
18.5 |
22.2 |
||
|
Fish meal |
3.8 |
5.0 |
6.0 |
4.0 |
5.2 |
6.2 |
||
|
Mineral Mix |
2.0 |
2.0 |
2.0 |
2.0 |
2.0 |
2.0 |
||
|
Total |
100,0 |
100.0 |
100.0 |
100.0 |
100.0 |
100.0 |
||
|
Chemical compositions |
(%) |
|||||||
|
Dry matter |
79.4 |
81.7 |
81.1 |
87.2 |
84.8 |
81.8 |
||
|
Crude protein |
13.4 |
15.6 |
17.6 |
13.4 |
15.6 |
17.7 |
||
|
Ether extract |
3.9 |
3.7 |
3.5 |
3.9 |
3.7 |
3.7 |
||
|
Crude fiber |
14.3 |
13.6 |
13.0 |
9.4 |
8.7 |
8.1 |
||
|
Neutral detergent fiber |
54.6 |
52.8 |
51.3 |
42.5 |
40.6 |
38.7 |
||
|
Acid detergent fiber |
34.5 |
33.3 |
32.6 |
17.8 |
16.6 |
15.3 |
||
|
Ash |
28.3 |
28.3 |
27.8 |
28.4 |
28.3 |
23.8 |
||
|
Nitrogen free extract |
40.0 |
38.7 |
37.9 |
44.9 |
43.5 |
46.6 |
||
|
Total digestible nutrients |
60.4 |
61.1 |
61.6 |
69.0 |
69.6 |
70.1 |
||
|
ME (MJ kg) |
10.6 |
10.6 |
10.7 |
10.8 |
10.8 |
10.9 |
||
|
LPLE, low protein low energy (crude protein 14%, total digestible nutrients 60%); MPLE, medium protein low energy (crude protein 16%, total digestible nutrients 60%); HPLE, high protein low energy (crude protein 18%, total digestible nutrients 60%); LPHE, low protein high energy (crude protein 14%, total digestible nutrients 70%); MPHE, medium protein high energy (crude protein 16%, total digestible nutrients 70%); HEPE, high protein high energy (crude protein 18%, total digestible nutrients 70%) |
||||||||
The results of the study on the feed intake and digestibility of lamb feed nutrients fed with different levels of crude protein (CP) and total digestible nutrients (TDN) are shown in Table 2. In this study, there was no interaction (p>0.05) between CP and TDN levels on nutrient intake and digestibility. Different CP levels did not affect (p>0.05) on the intake and digestibility of dry matter (DM) and organic matter (OM), but increasing the CP level resulted in increased protein intake and digestibility (p<0.05). On the other hand, increasing the TDN level decreased (p<0.05) the intake of DM, OM and CP, but increased (P<0.05) the digestibility of DM and OM although it had no effect (p>0.05) on CP digestibility.
|
Table 2. Nutrient intake and digestibility |
||||||||
|
Parameters |
Treatment |
Treatment |
Average |
|||||
|
CP14 |
CP16 |
CP18 |
||||||
|
DM intake (g) |
E60 |
1,274 |
1,291 |
1,265 |
1,276.0y |
|||
|
E70 |
815.8 |
918.8 |
853.8 |
862.8x |
||||
|
Average |
1.045 |
1.105 |
1.050 |
|||||
|
OM intake (g) |
E60 |
911.0 |
928.5 |
911.7 |
917,1y |
|||
|
E70 |
689.0 |
779.5 |
728.0 |
732,2x |
||||
|
Average |
800.0 |
854.0 |
819.9 |
|||||
|
CP intake (g) |
E60 |
170.4 |
201.1 |
223.7 |
198.4y |
|||
|
E70 |
109.7 |
143.9 |
151.3 |
135.0x |
||||
|
140.0a |
172.5b |
187.5c |
||||||
|
TDN intake (g) |
E60 |
769.7 |
789.6 |
780.1 |
779.8y |
|||
|
E70 |
562.3 |
639.7 |
599.1 |
600.4x |
||||
|
Average |
666.0 |
714.7 |
689.6 |
|||||
|
DM digestibility (%) |
E60 |
51.4 |
48.0 |
55.3 |
51.5x |
|||
|
E70 |
68.0 |
73.4 |
70.1 |
70.5y |
||||
|
Average |
59.7 |
60.7 |
62.8 |
|||||
|
OM digestibility (%) |
E60 |
50.8 |
49.1 |
55.5 |
51.8x |
|||
|
E70 |
72.7 |
77.7 |
75.0 |
75.1y |
||||
|
Average |
61.7 |
63.4 |
65.2 |
|||||
|
CP digestibility (%) |
E60 |
68.09 |
69.60 |
76.76 |
71.48 |
|||
|
E70 |
70.50 |
78.82 |
77.01 |
75.44 |
||||
|
Average |
69.29b |
74.21ab |
76.89a |
|||||
|
DM digestible (g) |
E60 |
661.4 |
632.2 |
697.2 |
663.6 |
|||
|
E70 |
558.0 |
679.4 |
597.0 |
611.5 |
||||
|
Average |
609.7 |
655.8 |
647.1 |
|||||
|
OM digestible (g) |
E60 |
655.2 |
645.8 |
700.0 |
667.0 |
|||
|
E70 |
595.7 |
718.1 |
639.5 |
651.1 |
||||
|
Average |
625.5 |
682.0 |
669.8 |
|||||
|
CP digestible (g) |
E60 |
116,6 |
141,0 |
114,4 |
143,0y |
|||
|
E70 |
77,8 |
114,4 |
116,6 |
102,9x |
||||
|
Average |
97,2b |
127,7a |
144,0a |
|||||
The results of the study on the performance of production and carcass quality of lambs fed with different levels of CP and TDN are shown in Tables 3 and Table 4. The results showed no interaction and significant affect (p>0.05) between CP and TDN levels on the performance of production and carcass quality of lamb. On the other hand, lambs treated with 60% TDN produced higher non-carcass weight (p<0.05) compared to lambs treated with 70% TDN. Increasing CP and TDN levels did not result in differences (p>0.05) in meat and fat weight, percentage of meat, fat and bone to slaughter weight and meat and bone balance, but bone weight in lambs fed with 60% TDN was higher (p<0.05) compared to 70% TDN.
|
Table 3. Animal performance and carcass quality |
||||||
|
Parameter |
Treatment |
Treatment |
Average |
|||
|
CP14 |
CP16 |
CP18 |
||||
|
Average daily gain (g) |
E60 |
138.00 |
151.00 |
134.00 |
141.00 |
|
|
E70 |
100.00 |
130.00 |
129.00 |
120.00 |
||
|
Average |
119.00 |
140.00 |
132.00 |
|||
|
Feed conversion ratio (g/g) |
E60 |
9.25 |
8.63 |
9.53 |
9.13 |
|
|
E70 |
8.41 |
7.43 |
7.31 |
7.71 |
||
|
Average |
8.82 |
8.03 |
8.42 |
|||
|
Slaughter weight (kg) |
E60 |
24.88 |
26.50 |
26.07 |
25.81 |
|
|
E70 |
20.86 |
23.82 |
24.73 |
23.14 |
||
|
Average |
22.87 |
25.16 |
25.40 |
|||
|
Hot carcass weight (kg) |
E60 |
12.02 |
12.56 |
12.83 |
12.63 |
|
|
E70 |
10.39 |
12.28 |
13.01 |
11.77 |
||
|
Average |
11.21 |
12.56 |
12.83 |
|||
|
Cold carcass weight (kg) |
E60 |
11.29 |
12.23 |
12.34 |
11.95 |
|
|
E70 |
9.34 |
11.92 |
12.00 |
11.09 |
||
|
Average |
10.31 |
12.07 |
12.17 |
|||
|
Non carcass weight (kg) |
E60 |
12.85 |
13.65 |
13.05 |
13.18y |
|
|
E70 |
10.46 |
11.54 |
12.08 |
11.36x |
||
|
Average |
11.66 |
12.59 |
12.57 |
|||
|
Hot carcass percentage (%) |
E60 |
48.01 |
48.42 |
49.82 |
48.75 |
|
|
E70 |
49.84 |
51.33 |
50.67 |
50.61 |
||
|
Average |
48.92 |
49.87 |
50.24 |
|||
|
Cold carcass percentage (%) |
E60 |
45.06 |
46.10 |
47.26 |
46.14 |
|
|
E70 |
44.58 |
49.86 |
48.11 |
47.52 |
||
|
Average |
44.82 |
47.98 |
47.68 |
|||
|
Non carcass percentage (%) |
E60 |
51.99 |
51.58 |
50.18 |
51.25 |
|
|
E70 |
50.16 |
48.67 |
49.36 |
49.40 |
||
|
Average |
51.07 |
49.12 |
49.76 |
|||
|
Table 4. Meat, Bone and Fat of carcass |
||||||
|
Treatment |
Treatment |
Average
|
||||
|
CP14 |
CP16 |
CP18 |
||||
|
Meat weight (kg) |
E60 |
7.84 |
8.07 |
8.08 |
8.00 |
|
|
E70 |
7.45 |
7.58 |
8.06 |
7.70 |
||
|
Average |
7.65 |
7.82 |
8.07 |
|||
|
Bone weight (kg) |
E60 |
2.85 |
2.82 |
2.86 |
2.84y |
|
|
E70 |
2.61 |
2.70 |
2.76 |
2.69x |
||
|
Average |
2.73 |
2.76 |
2.81 |
|||
|
Fat weight (kg) |
E60 |
2.36 |
2.82 |
2.74 |
2.64 |
|
|
E70 |
1.98 |
3.28 |
2.74 |
2.67 |
||
|
Average |
2.17 |
3.05 |
2.74 |
|||
|
Meat (% of slaughter weight) |
E60 |
60.15 |
58.88 |
59.19 |
59.41 |
|
|
E70 |
61.95 |
56.42 |
60.10 |
59.50 |
||
|
Average |
61.05 |
57.65 |
59.65 |
|||
|
Bone (% of slaughter weight) |
E60 |
21.96 |
20.60 |
21.01 |
21.20 |
|
|
E70 |
21.76 |
19.99 |
20.81 |
20.85 |
||
|
Average |
21.86 |
20.30 |
20.91 |
|||
|
Fat (% of slaughter weight) |
E60 |
17.88 |
20.51 |
19.79 |
19.39 |
|
|
E70 |
16.28 |
23.58 |
19.08 |
19.65 |
||
|
Average |
17.08 |
22.04 |
19.44 |
|||
|
Meat (kg) / bone (kg) ratio |
E60 |
2.72 |
3.01 |
2.92 |
2.88 |
|
|
E70 |
3.01 |
2.99 |
3.19 |
3.06 |
||
|
Average |
2.86 |
3.00 |
3.05 |
|||
The N intake in lamb fed with 16% and 18% CP were higher (p<0.05) than lamb fed with 14% CP. On the other hand, N intake decreased (p<0.05) with increasing TDN levels. The amount of N excreted through urine was greater (p<0.05) in lamb fed with 16% and 18% CP compared to 14% CP. The amount of N (g) excreted through feces and urine decreased (p<0.05) with increasing TDN levels. Increasing CP levels caused the highest amount of retained N (P<0.05) in lamb fed with 18% CP and the lowest in 14% CP, while in 16% CP it was the same for both. On the other hand, retained N decreased (p<0.05) with increasing TDN levels. The amount of N2O in feces, urine and total was greater (p<0.05) in lamb fed 60% TDN compared to 70% TDN. The CP level only affected (p<0.05) N2O in urine, the amount of N2O in urine of lamb fed 18% and 16% CP was greater (p<0.05) than 14% CP. There was no interaction (p>0.05) between CP and TDN levels on intake, retention and output of N and N2O through feces and urine. There was no interaction (p>0.05) between CP levels and TDN levels on intake, retention and output of N and N2O through feces and urine (Table 5). There was no interaction (p>0.05) between CP levels and TDN levels on methane emission, however the methane emission of lamb fed 70% TDN was lower than those of 60% TDN (Table 6).
|
Table 5. Nitrogen excretion, nitrogen oxide (N2O) excretion |
||||||
|
Parameter |
Treatment |
Treatment |
Average
|
|||
|
CP14 |
CP16 |
CP18 |
||||
|
N intake (g) |
E60 |
27.26 |
32.19 |
35.80 |
31,75y |
|
|
E70 |
17.55 |
23.03 |
24.20 |
21,60x |
||
|
Average |
22.41a |
27.61b |
30.00b |
|||
|
N feces (g) |
E60 |
8.60 |
9.63 |
8.37 |
8.87x |
|
|
E70 |
5.10 |
4.73 |
5.55 |
5.12y |
||
|
Average |
6.85 |
7.18 |
6.96 |
|||
|
N urine (g) |
E60 |
6.56 |
8.68 |
8.05 |
7.76x |
|
|
E70 |
3.39 |
5.97 |
5.88 |
5.08y |
||
|
Average |
4.98a |
7.32b |
6.97b |
|||
|
N retention (g) |
E60 |
12.09 |
13.88 |
19.37 |
15.11y |
|
|
E70 |
9.06 |
12.32 |
12.77 |
11.38x |
||
|
Average |
10.58a |
13.10ab |
16.07b |
|||
|
N2O feces (g) |
E60 |
0.17 |
0.19 |
0.17 |
0.18y |
|
|
E70 |
0.10 |
0.09 |
0.11 |
0.10x |
||
|
Average |
0.13 |
0.14 |
0.14 |
|||
|
N2O urine (g) |
E60 |
0.13 |
0.17 |
0.16 |
0.16y |
|
|
E70 |
0.07 |
0.12 |
0.12 |
0.10x |
||
|
Average |
0.10a |
0.14b |
0.14b |
|||
|
N2O total (g) |
E60 |
0.30 |
0.37 |
0.33 |
0.33y |
|
|
E70 |
0.17 |
0.21 |
0.23 |
0.20x |
||
|
Average |
0.23 |
0.28 |
0.28 |
|||
|
Table 6. Methane emission (CH4) |
||||||
|
Parameter |
Treatment |
Treatment |
Average |
|||
|
CP14 |
CP16 |
CP18 |
||||
|
CH 4 (g/day) |
E60 |
32.20 |
27.58 |
24.33 |
28.04y |
|
|
E70 |
21.91 |
21.28 |
18.16 |
20.45x |
||
|
Average |
27.05 |
24.43 |
21.24 |
|||
|
CH 4 (g/day)/ BK (kg/day) |
E60 |
25.87 |
21.03 |
19.46 |
22.12 |
|
|
E70 |
27.00 |
23.52 |
21.57 |
24.03 |
||
|
Average |
26.43 |
22.28 |
20.51 |
|||
|
CH 4 (g/day) / TDN (kg/day) |
E60 |
42,84 |
34.40 |
31.58 |
36.26 |
|
|
E70 |
39.17 |
33.78 |
30.74 |
34.56 |
||
|
Average |
41.00 |
34.09 |
31.15 |
|||
The CP level did not affect N, N2O and CH4emissions per ADG and meat production, but TDN level affected N, N2O and CH 4 emissions per ADG and meat production. The N, N2O and CH 4 emissions per ADG and meat production were lower (p<0.05) in lamb fed with 70% TDN compared to 60% TDN. There was no interaction between CP level and TDN level on N, N2O and CH4emissions per ADG and meat production (Table 7).
|
Table 7. Emissions per average daily gain and meat production |
||||||
|
Parameter |
Treatment |
Treatment |
Average
|
|||
|
CP14 |
CP16 |
CP18 |
||||
|
N (g) / ADG (g) |
E60 |
110.4 |
124.8 |
123.9 |
119.7y |
|
|
E70 |
88.0 |
89.1 |
95.4 |
90.8x |
||
|
Average |
99.2 |
106.9 |
109.6 |
|||
|
N (g) / meat (kg) |
E60 |
1.94 |
2.27 |
2.04 |
2.08y |
|
|
E70 |
1.13 |
1.42 |
1.42 |
1.33x |
||
|
Average |
1.54 |
1.85 |
1.73 |
|||
|
N2O (g) / ADG (g) |
E60 |
2.21 |
2.50 |
2.48 |
2.40y |
|
|
E70 |
1.76 |
1.78 |
1.91 |
1.82x |
||
|
Average |
1.98 |
2.13 |
2.19 |
|||
|
N2O (g) / meat (kg) |
E60 |
0.050 |
0.054 |
0.048 |
0.051y |
|
|
E70 |
0.023 |
0.029 |
0.029 |
0.027x |
||
|
Average |
0.036 |
0.041 |
0.038 |
|||
|
CH 4 (g)/ ADG (g) |
E60 |
232.4 |
181.7 |
184.3 |
199.5y |
|
|
E70 |
233.3 |
175.5 |
162.5 |
190.4x |
||
|
Average |
232.8 |
178.6 |
173.4 |
|||
|
CH 4 (g)/ meat (g) |
E60 |
4.17 |
3.40 |
2.99 |
3.52y |
|
|
E70 |
2.94 |
2.82 |
1.92 |
2.56x |
||
|
Average |
3.55 |
3.11 |
2.45 |
|||
The TDN value was a description of the energy content in feed, it’s explaining that the 60% TDN treatment contains lower feed energy than 70% TDN. Low feed energy causes DM and OM intake to increase. The increase in was an effort to meet energy requirement (Dutta et al 2009). This statement was in line with the results of this study that DM and OM consumption were higher in the 60% TDN treatment compared to 70% TDN. This study used lamb with the same age and body weight range, in theory these lambs were able to consume the same amount of TDN because physiologically their nutritional needs were similar, however the TDN intake were different. This difference was caused by acidosis in sheep treated with 70% TDN as indicated by rumen pH data before eating of 6.6 decreasing to 5.5 3 hours after eating (unpublished data). Low pH values cause rumen conditions to become acidic and lamb were uncomfortable, so they will respond by reducing the intake (Maktabi et al 2016). This acidosis was caused by low crude fiber content and high NFE in the 70% TDN treatment (Table 1). The high of NFE content causes high concentrations of Volatile Fatty Acid (VFA) in rumen fluid and results in a decrease in rumen pH. Pantaya et al. (2016) stated that acidosis occurs when carbohydrates (starch) in feed were too high, so it will cause an increase in the amount of VFA which results in a decrease in rumen pH. On the other hand, low CF content causes the chewing process to be suboptimal, so that the amount of saliva produced and entering the rumen was limited. Castillo-lopez et al (2021) stated that saliva has buffer properties that are very useful in maintaining rumen pH in the level of neutral condition.
The TDN content in feed describes the digestibility value of the feed, the higher the TDN content, the higher the digestibility of the feed (Santos et al 2015). The statement explains the results of this study, that the digestibility values of DM and OM in lamb fed 70% TDN were higher compared to 60% TDN. In addition to the influence of TDN content, the digestibility value is also influenced by feed intake. The higher the feed intake, the higher the pressure of the feed to leave the digestive tract which results in the length of stay of the feed in the digestive tract being shorter and the opportunity for the feed to be digested being less. This statement was supported by the results of research reported by Nugroho et al. (2017) that there is a large correlation between feed intake with feed flow rate and feed digestibility, the higher the intake, the higher the frequency of defecation and the lower the digestibility value.
Feeding with high protein aims to increase growth in lamb (Ma et al., 2017), but in this study, increasing the protein level was not able to increase ADG, slaughter weight and carcass weight. The difference in digested protein between CP and TDN level treatments was approximately 40 g/day (Table 4). Referring to the Table of feed requirements for lamb by Kearl (1982), this amount should be able to provide a difference in ADG of 100 g/day. However, in this study, it only provided a difference in ADG of 10-20 g and was not statistically significantly different. It was because the nutrients that play a major role in increasing ADG are not only protein but also influenced by carbohydrates and fats, which are reflected in the amount of digested OM (Table 2). The absence of the amount of digested OM was a strong reason for the absence of differences in the result of ADG.
As explained above, increasing the CP level from 14–18% and TDN from 60–70% was not able to increase ADG, so that the resulting slaughter weight and carcass weight were the same. The same slaughter weight will produce the same carcass weight, as reported by Chay-canul et al. (2014) that slaughter weight affects carcass weight by 88–90%. Meat production, the ratio of meat to bone that was not different due to the same growth rate confirmed by the same ADG. On the other hand, although ADG was similar, non-carcass weight and bone weight were higher in lamb with 60% TDN treatment compared to 70% TDN. It was due to higher TDN intake in lamb fed with 60% TDN compared to 70% TDN. The higher the TDN intake, the more nutrients can be digested, so that the feed nutrients needed to support growth can be met (Santos et al., 2015).The lamb was experiencing rapid growth in bones and digestive organs so that the excess nutrients would be used to accelerate the growth of bones and viscera. This reason was supported by the statement of Owens et al. (1993) that the growth of bones and digestive organs and muscles occurs faster before the livestock reaches sexual maturity.
Increasing CP intake will increase N intake. The amount of N lost through feces did not differ, but N lost through urine was higher in lamb fed 16% and 18% CP compared to 14% CP. This is due to high N intake at CP 16% and 18% compared to CP 14% causing more N to be degraded in the rumen. Marini et al. (2004) reported that when feed is given ad libitum and more N was consumed, more N was degraded in the rumen and excreted through urine compared to N lost through feces. This explanation was also the reason why the amount of N lost in the urine of lamb with 60% TDN treatment was also greater than that of 70% TDN treatment. The amount of N lost through feces was greater in the 60% TDN compared to the 70% TDN treatment. It was due to the higher crude fiber content of the feed in the 60% TDN treatment compared to the 70% TDN treatment. It was in accordance with the statement of Seok et al (2016) that feed with high crude fiber makes the feed difficult to digest and some of the protein binds to lignin which was difficult to digest, causing a lot of N to be lost through feces. The results of this study were the same as those reported by Danso et al (2018) that the increase in protein levels was linear with N intake, N output in urine and N retention, but does not affect N output in feces. The higher the N excreted through feces and urine, the greater the N2O in feces and urine. The amount of N2O formed was estimated to be 2% of the N in feces and urine (IPCC, 2006). The amount of N2O in lamb that fed of CP 16% and 18% was greater than CP 14%. Likewise, the amount of N2O in urine and feces in lamb fed with 60% TDN was also greater than 70% TDN. The results of the study were the same as those reported by Menezes et al. (2016) reported that in Nellore cattle high N intake was linear with N and N2O waste in feces and urine.
The high CH4 output in lamb treated with 60% TDN compared to 70% TDN was due to the high DM intake in lamb treated with 60% TDN compared to 70% TDN. Methane output was linear with DM intake (Chaokaur et al 2015). High of DM intake causes the substrate available in the rumen for fermentation to increase and as a result the methane produced from the fermentation process also increases (Menezes et al 2016).
The increasing need for food from livestock will certainly also increase emissions, so the challenge going forward to reduce methane and nitrogen emissions without disrupting livestock productivity (Grainger and Bauchemin, 2011). Based on this statement, it was important to calculate emissions per unit of product produced by livestock, as an effort to determine the efficiency of feed utilization on production and the environmental impacts caused.
The results of the study showed that 70% TDN feed was more environmentally friendly than 60% TDN. It was because the ADG and meat produced were the same between lamb in the 60% TDN and 70% TDN treatments, but the 70% TDN feed produced lower emissions compared to the 60% TDN feed. This causes the ADG and meat per N, N2O and CH4 emissions produced to be lower in the 70% TDN treatment. This was because feed with high TDN will be easily digest in the rumen, thereby reducing the fermentation process that produces CH4, feed that was easily digested will also produce less N waste compared to feed that was difficult to digest. This statement was supported by the Zhao et al (2016) who reported that feed with high organic content and easy to digest was one of the feeds that can be given to livestock as an effort to mitigate methane and nitrogen emissions, the N and methane emissions were lower in lamb consuming ryegrass silage with a TDN content of 74% compared to lamb consuming ryegrass pellets with a TDN content of 64%.
The authors would like to thank Riset dan Inovasi Untuk Indonesia Maju RIIM 13/IV/KS/05/2023 dan 01/PKS/Bumi.Yasa.Svarga/V/2023 and Faculty of Animal and Agricultural Sciences, Universitas Diponegoro for financing this study.
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