| Livestock Research for Rural Development 30 (12) 2018 | Guide for preparation of papers | LRRD Newsletter | Citation of this paper |
The objective of this study was to evaluate the inclusion of up to 30% crude glycerin (CG) in feedlot Nellore cattle diets and its effects on in situ ruminal degradability of dry matter, organic matter, crude protein, neutral detergent fiber, and acid detergent fiber from the feed ingredients maize, sunflower meal, soybean hulls, and maize silage. Five permanently rumen-cannulated Nellore steers (approximately 400 kg BW and 24 months old) were used for ruminal incubations. Animals were randomly assigned to one of the five treatments: G0 – (control), no CG inclusion in the diet; G7.5 – 75 g CG/kg dietary dry matter (DM); G15 – 150 g CGL/kg dietary DM; G22 – 220 g CG/kg dietary DM; and G30 – 300 g CG/kg dietary DM. Data were analyzed as a Latin square design 5 × 5. Contrasts were performed observing the significance of linear and quadratic models and significance of control treatment × glycerin treatments. Crude glycerin did not affect most of degradation parameters of DM and OM of tested ingredients, with exception of effective degradation of DM of maize silage, which was linearly decreased with the inclusion of CG (P = 0.02). The CG quadratically affected fermentation rate of CP of sunflower meal, with the greatest values 8.36 and 9.05, respectively for treatments G15 and G22.5. The degradation parameters of NDF of all the ingredients tested were linearly decreased with the inclusion of CG (P < 0.01). The inclusion of up to 30% crude glycerin in Nellore cattle diets changes “in situ” ruminal degradation kinetics of feed ingredients, highly impairing fiber fraction use.
Keywords: biodiesel, by-product, glycerin, ruminal degradation
The research on the quality of feed ingredients provided to livestock has evolved considerably in recent years, since it directly influences the productivity and profitability of the business. The introduction of novel and alternative ingredients, such as the by-products from the biodiesel industry has brought to the fore the classical feed evaluation methods, such as in situ ruminal degradability trials. Due to the variation in the chemical composition and the diversification of methods of analysis of the feed fractions and ruminal parameters, a more accurate evaluation of the nutritive value of the forages and concentrates is necessary. The knowledge of the rates of degradation and passage of these feed ingredients may provide data to improve feed balance (Carvalho et al 2006), improving diet utilization.
The technique of in situ degradability, despite several criticisms, such as the use of cannulated animals, and the microbial contamination of nylon bags (Nocek and Grant 1987), is still considered the best and the most widely used method for the evaluation of degradability (Broderick 1995), mainly because of its simplicity and reliability (Mohamed and Chaudhry 2008). The effective degradability and degradation rate allow the calculation of a more adequate diet, providing a more efficient production and it is an important tool in the estimation of voluntary feed intake (Evangelista et al 2002).
Crude glycerin, the main by-product of biodiesel industry, is increasingly being considered an attractive source of energy to replace conventional ingredients, such as maize in diets for ruminants. The economic and humanitarian gains of such strategy may be auspicious as it could increase the availability of this crop for the needs of human nutrition (van Cleef et al 2015). However, preliminary studies indicate that the inclusion of crude glycerin in ruminant diets causes losses in the utilization of the fibrous fraction by the animals, and this mechanism is still unknown (Parsons and Drouillard 2010, van Cleef at al 2018).
In this sense, the objective of this study was to evaluate the inclusion of crude glycerin in diets for finishing Nellore cattle and its effect on in situ ruminal degradability of dry matter, organic matter, crude protein, neutral detergent fiber and detergent fiber of maize, sunflower meal, soybean hulls and maize silage.
The experiment was conducted at Animal Unit of Digestive and Metabolic Studies and at the Laboratory of Ingredients and Pollutant Gases from the Animal Science Department of São Paulo State University, Jaboticabal Campus. The Institutional Animal Care and Use Committee of São Paulo State University previously approved all the procedures adopted in this trial, under the protocol 010707.
Five ruminally-cannulated Nellore steers (approximately 24 months and 400 kg BW) were used in this trial. Animals were housed in individual, and semi-covered concrete pens, equipped with individual feed bunks and waterers, and were randomly distributed in a Latin square (5 × 5) design and received one of the 5 treatments in each 30-d period.
The adaptation period to the experimental diets was 14 d and the incubations were performed from d 16 to d 21. During each experimental period, animals received an average of 8.4 kg DM, in which feed bunk scores were kept between 0 and 1, according to Pritchard (1993). The experimental diets were delivered twice daily (0800 and 1700h) and were evaluated daily, as well as orts, for posterior calculation of DM intake.
Experimental diets were formulated according to NRC (1996) and were composed of maize silage (30%) and concentrate (70%), labeled: G0 – (control), no crude glycerin (CG) in the diet; G7.5 – 75 g CG/kg of dietary dry matter (DM); G15 – 150 g CGL/kg dietary DM; G22 – 220 g CG/kg dietary DM; and G30 – 300 g CG/kg dietary DM (Table 1). The CG tested contained 860 g glycerol/kg of DM, 950 g of DM/ kg, 1.1 g CP/kg of DM, 60 g salts/kg of DM, and less than 0.01% methanol.
|
Table 1. Feed ingredients and nutrient composition of experimental diets (DM basis) |
||||||
|
Item |
Treatments |
|||||
|
G01 |
G7.52 |
G153 |
G22.54 |
G305 |
||
|
Ingredients (g/kg of DM) |
||||||
|
Maize silage |
300.0 |
300.0 |
300.0 |
300.0 |
300.0 |
|
|
Maize grain |
350.0 |
255.0 |
180.0 |
125.0 |
50.0 |
|
|
Soybean hulls |
192.0 |
180.5 |
145.5 |
89.0 |
54.5 |
|
|
Sunflower meal |
146.0 |
178.0 |
213.0 |
249.0 |
284.0 |
|
|
Crude glycerin |
- |
75.0 |
150.0 |
225.0 |
300.0 |
|
|
Salt (NaCl) |
5.0 |
5.0 |
5.0 |
5.0 |
5.0 |
|
|
Limestone |
7.0 |
6.5 |
5.5 |
7.0 |
6.5 |
|
|
Dicalcium phosphate |
- |
1.0 |
1.0 |
- |
- |
|
|
Nutrients |
||||||
|
CP (% DM) |
122.0 |
122.1 |
122.2 |
122.0 |
122.1 |
|
|
ME (Mcal/kg DM) |
25.3 |
25.2 |
25.2 |
25.3 |
25.2 |
|
|
EE (%) |
29.0 |
25.8 |
23.1 |
20.9 |
18.1 |
|
|
NDF (%) |
408.3 |
400.7 |
381.1 |
350.1 |
330.8 |
|
|
ADF (%) |
254.1 |
255.6 |
247.1 |
228.9 |
220.6 |
|
|
HEM (%) |
154.2 |
145.1 |
134.1 |
121.2 |
110.2 |
|
|
Ca (%) |
5.6 |
5.6 |
5.5 |
5.7 |
5.5 |
|
|
P (%) |
3.2 |
3.2 |
3.5 |
3.4 |
3.4 |
|
|
1 G0 = without crude glycerin, 2 G7.5 = 75 g of crude glycerin/kg of DM, 3 G15 = 150 g of crude glycerin/kg of DM, 4 G22.5 = 225 g of crude glycerin/kg of DM, 5 G30 = 300 g of crude glycerin/kg of DM. |
||||||
The in situ ruminal degradation technique (Ørskov and McDonald 1979) was used, adopting nylon bags (100% polyamide) with 50 μm pores, available area of 14.0 × 7.0 cm, containing approximately 20 mg MS/cm2. The silage was ground to 5 mm diameter and the concentrate ingredients to 2 mm. Rumen incubation times used in this trial were: 6, 12, 24, 48, 72, 96, and 120 h (maize silage), 3, 6, 12, 24, 48, 72, 96 and 120 h (sunflower meal), 3, 6, 12, 24, 48, and 72 h (soybean hulls), and 3, 6, 12, 24, and 48 hours (maize), and the nylon bags (three per ingredient per h) were incubated into the rumen in reverse order of time, attached to a metal chain.
After the incubation period, all bags were removed and immersed in iced water for 30 min to cease the microbial activity and were washed thoroughly under running tap water. Following this step, the bags containing the incubation residues were dried in an oven with forced air circulation at 55° C for 72 h. To determine the soluble fraction “a”, the bags were washed with autoclaved rumen fluid, following the methodology proposed by Ezequiel et al (2002).
Samples of feed ingredients and residues were ground in a Willey type mill using a sieve with mesh size of 1 mm (AOAC 1998; method 934.01) and were submitted to analysis of DM (AOAC 1995; method 930.15), ash (AOAC 1990; method 942.05), nitrogen (AOAC 1998; method 988.05, and CP content was estimated multiplying N content by 6.25), NDF and ADF (Van Soest and Wine 1967, using a heat-stable α-amylase, without sodium sulfite, and expressed inclusive of residual ash).
The equation: PD = a + b (1 − e−ct), was used to calculate potential degradation, where “PD” = potential ruminal degradability at time “t”, “a” = the soluble fraction in water, “b” = the insoluble and potentially degradable fraction, “c” = the degradation rate of fraction “b” per hour, and “t” = the time of incubation. Degradation constants were estimated using the NLIN procedure of SAS (Version 9.4).
The effective degradation was estimated using the equation: ED = a + (bc/(c + k)), where “ED” = effect ruminal degradability, “k” = small particle outflow rate of nutritive fraction (2, 5, and 8%/h), and “a”, “b” and “c” as described previously.
Data were analyzed using the MIXED procedure of SAS (version 9.4). The model was:
Yijk = µ + Di + Pj + Ak + eijk
where µ represents the overall mean, D, P, and A, are the effects of diet, period and animal, respectively, and e ijk is the residual error. The linear and quadratic effects of crude glycerin were tested, as well as the contrast control treatment × crude glycerin treatments. Treatment means were computed with the LSMEANS option and significance was defined as P < 0.05 and trends as 0.05 ≤ P ≤ 0.10.
The inclusion of crude glycerin did not affect the degradation parameters of DM of soybean hulls, sunflower meal and maize (P > 0.05, Table 2). However, the effective degradation of DM of maize silage was linearly decreased with the inclusion of crude glycerin in the diets, specially evaluating the passage rate of 5%/h (P = 0.02, Table 3).
|
Table 2. In situ ruminal degradation parameters of dry matter of feed ingredients in Nellore cattle fed diets containing up to 30% crude glycerin |
||||||||
|
In situ ruminal degradation parameters of DM1 (S.E) 2 |
||||||||
|
a |
b |
c |
k |
PD |
ED2 |
ED5 |
ED8 |
|
|
Soybean hulls |
16.58 |
50.62 |
32.79 |
4.54 |
67.20 |
51.73 |
40.62 |
34.87 |
|
(1.69) |
(3.48) |
(2.58) |
(0.45) |
(2.58) |
(1.95) |
(1.76) |
(1.66) |
|
|
Sunflower meal |
30.42 |
36.68 |
32.90 |
6.52 |
67.10 |
58.48 |
51.18 |
46.90 |
|
(3.57) |
(5.65) |
(2.86) |
(0.63) |
(2.85) |
(2.25) |
(1.86) |
(1.81) |
|
|
Maize |
23.97 |
50.92 |
25.11 |
4.40 |
74.89 |
58.27 |
47.56 |
42.03 |
|
(2.69) |
(2.80) |
(1.94) |
(0.33) |
(1.94) |
(4.50) |
(2.55) |
(1.98) |
|
|
1 a = Soluble, b = Insoluble but potentially degradable, c = Undegradable, k = Fermentation rate, PD = Potential degradability, ED2, 5, 8 = Effective degradability at 0.02, 2 Values in parentheses correspond to the error standard of the mean. |
||||||||
|
Table 3. In situ ruminal degradation parameters of dry matter of maize silage in Nellore cattle fed diets containing up to 30% crude glycerin |
|||||||||
|
Item1 |
Treatments (% crude glycerin) |
Contrast, P-value2 |
SEM |
||||||
|
G0 |
G7.5 |
G15 |
G22.5 |
G30 |
L |
Q |
0 × G |
||
|
a |
49.5 |
45.59 |
48.32 |
46.15 |
46.55 |
NS |
NS |
NS |
2.72 |
|
b |
24.37 |
30.98 |
28.09 |
28.87 |
26.36 |
NS |
NS |
NS |
5.46 |
|
c |
26.13 |
23.42 |
23.59 |
24.98 |
27.09 |
NS |
NS |
NS |
3.34 |
|
k |
2.79 |
2.95 |
2.85 |
2.59 |
3.09 |
NS |
NS |
NS |
0.26 |
|
PD |
73.87 |
76.58 |
76.41 |
75.02 |
72.91 |
NS |
NS |
NS |
3.34 |
|
ED2 |
63.68 |
64.04 |
64.84 |
62.39 |
62.46 |
NS |
NS |
NS |
1.52 |
|
ED5 |
58.22 |
57.08 |
58.54 |
55.97 |
56.54 |
* |
NS |
NS |
1.29 |
|
ED8 |
55.79 |
53.94 |
55.72 |
53.19 |
53.84 |
NS |
NS |
NS |
1.54 |
|
1 a = Soluble, b = insoluble but potentially degradable, c = Undegradable, k = Fermentation rate, PD = Potential degradability, ED2, 5, 8 = Effective degradability at 0.02, 0.05 and 0.08 h-1. 2 L = Linear, Q = Quadratic, 0 × G = Control treatment × Crude glycerin treatments, *P<0.05; **P<0.01. NS = Not significant. |
|||||||||
There was no effect of the inclusion of crude glycerin on the degradation parameters of the organic matter of soybean hulls, sunflower meal, maize and maize silage (P > 0.05, Table 4), and treatments did not affect protein degradation parameters of soybean hulls, maize and maize silage (P > 0.05, Table 5).
|
Table 4. In situ ruminal degradation parameters of organic matter of maize silage in Nellore cattle fed diets containing up to 30% crude glycerin |
|||||||||
|
Ingredient |
In situ ruminal degradation parameters of OM1 (S.E) 2 |
||||||||
|
a |
b |
c |
k |
PD |
ED2 |
ED5 |
ED8 |
||
|
Soybean hulls |
14.59 |
54.91 |
30.53 |
4.78 |
69.36 |
53.23 |
41.36 |
35.07 |
|
|
(0.93)2 |
(2.99) |
(2.35) |
(0.32) |
(2.35) |
(1.55) |
(1.19) |
(1.02) |
||
|
Sunflower meal |
29.16 |
40.69 |
30.14 |
6.61 |
69.85 |
60.29 |
52.21 |
47.47 |
|
|
(3.39) |
(3.63) |
(1.73) |
(1.10) |
(1.73) |
(1.60) |
(1.95) |
(2.18) |
||
|
Maize |
21.46 |
59.67 |
18.87 |
4.57 |
81.14 |
62.90 |
49.91 |
43.12 |
|
|
(1.98) |
(2.54) |
(1.36) |
(0.33) |
(1.36) |
(1.42) |
(1.57) |
(1.61) |
||
|
Maize silage |
45.00 |
33.65 |
21.37 |
3.29 |
78.63 |
65.49 |
58.33 |
54.79 |
|
|
(2.38) |
(3.36) |
(2.43) |
(0.33) |
(3.09) |
(2.03) |
(2.05) |
(2.09) |
||
|
1 a = Soluble, b = insoluble but potentially degradable, c = Undegradable, k = Fermentation rate, PD = Potential degradability, ED2, 5, 8 = Effective degradability at 0.02, 0.05 and 0.08 h-1. 2 Values in parentheses correspond to the error standard of the mean. |
|||||||||
|
Table 5. In situ ruminal degradation parameters of crude protein of feed ingredients in Nellore cattle fed diets containing up to 30% crude glycerin |
||||||||
|
Ingredient |
In situ ruminal degradation parameters of CP1 (S.E) 2 |
|||||||
|
a |
b |
c |
k |
PD |
ED2 |
ED5 |
ED8 |
|
|
Soybean hulls |
30.33 |
41.51 |
28.16 |
5.64 |
71.84 |
60.90 |
52.27 |
47.44 |
|
(2.41)2 |
(3.06) |
(2.05) |
(0.59) |
(2.05) |
(1.82) |
(1.90) |
(2.41) |
|
|
Maize |
23.48 |
48.53 |
27.99 |
4.26 |
72.01 |
56.63 |
45.97 |
40.50 |
|
(2.16) |
(2.93) |
(2.15) |
(0.38) |
(2.15) |
(1.75) |
(1.70) |
(1.71) |
|
|
Maize silage |
64.11 |
17.79 |
18.10 |
3.51 |
81.90 |
75.26 |
71.32 |
69.48 |
|
(3.04) |
(2.75) |
(1.54) |
(1.14) |
(1.64) |
(1.71) |
(2.03) |
(2.20) |
|
|
1 a = Soluble, b = insoluble but potentially degradable, c = Undegradable, k = Fermentation rate, PD = Potential degradability, ED2, 5, 8 = Effective degradability at 0.02, 0.05 and 0.08 h-1.2 Values in parentheses correspond to the error standard of the mean. |
||||||||
It was observed a quadratic effect of the inclusion of crude glycerin on the fermentation rate of the protein of sunflower meal (Table 6), in which the highest values were observed for treatments containing 15 and 22.5% glycerin, which presented values of 8.36 and 9.05, respectively.
|
Table 6. In situ ruminal degradation parameters of crude protein of sunflower meal in Nellore cattle fed diets containing up to 30% crude glycerin |
|||||||||
|
Item1 |
Treatments (% crude glycerin) |
Contrast, P-value2 |
SEM |
||||||
|
G0 |
G7.5 |
G15 |
G22.5 |
G30 |
L |
Q |
0 × G |
||
|
a |
50.54 |
51.87 |
51.48 |
50.73 |
52.56 |
NS |
NS |
NS |
1.86 |
|
b |
43.77 |
41.50 |
42.23 |
43.29 |
41.39 |
NS |
NS |
NS |
1.82 |
|
c |
5.68 |
6.63 |
6.24 |
5.97 |
6.05 |
NS |
NS |
NS |
1.09 |
|
k |
7.61 |
8.24 |
8.36 |
9.05 |
8.25 |
** |
* |
NS |
0.46 |
|
PD |
94.31 |
93.36 |
93.71 |
94.03 |
93.95 |
NS |
NS |
NS |
1.09 |
|
ED2 |
85.21 |
85.26 |
85.57 |
86.18 |
85.86 |
NS |
NS |
NS |
1.30 |
|
ED5 |
76.97 |
77.69 |
77.93 |
78.61 |
78.62 |
NS |
NS |
NS |
1.50 |
|
ED8 |
71.90 |
72.93 |
73.09 |
73.70 |
73.57 |
NS |
NS |
NS |
1.59 |
|
1 a = Soluble, b = insoluble but potentially degradable, c = Undegradable, k = Fermentation rate, PD = Potential degradability, ED2, 5, 8 = Effective degradability at 0.02, 0.05 and 0.08 h-1.2 L = Linear, Q = Quadratic, 0 × G = Control treatment × Crude glycerin treatments, *P<0.05; **P<0.01. NS = Not significant. |
|||||||||
The degradation parameters of NDF of all the ingredients tested were highly affected by experimental treatments. In sunflower meal, the effect of the addition of crude glycerin on the degradability of NDF was similar to that observed in soybean hulls. There was an increasing linear effect (P <0.01) on the fraction “c” and a decreasing linear effect (P < 0.01) on the fraction “b” and on the potential and effective degradability (regardless of the rate of passage considered).
Regarding maize silage, a linear increasing effect (P < 0.01) was observed in the fraction “c” of the NDF, concomitantly to the decreasing linear effect (P < 0.01) in fraction “b”, making the control treatment different from the treatments containing glycerin, evidenced by the significance of control × glycerin contrast (Table 7).
|
Table 7. In situ ruminal degradation parameters of neutral detergent fiber of feed ingredients in Nellore cattle fed diets containing up to 30% crude glycerin |
||||||||||
|
Item1 |
Treatments (% crude glycerin) |
Contrast, P-value2 |
SEM |
|||||||
|
G0 |
G7.5 |
G15 |
G22.5 |
G30 |
L |
Q |
0 × G |
|||
|
Soybean hulls |
||||||||||
|
a |
12.47 |
14.06 |
13.12 |
12.48 |
13.30 |
NS |
NS |
NS |
0.21 |
|
|
b |
51.25 |
49.62 |
49.43 |
42.24 |
42.64 |
** |
NS |
** |
3.19 |
|
|
c |
36.27 |
36.32 |
37.45 |
45.29 |
44.05 |
** |
NS |
* |
3.42 |
|
|
k |
4.95 |
4.89 |
4.77 |
4.51 |
4.86 |
NS |
NS |
NS |
0.51 |
|
|
PD |
63.72 |
63.68 |
62.55 |
54.72 |
55.95 |
** |
NS |
* |
3.41 |
|
|
ED2 |
50.52 |
50.03 |
47.80 |
43.50 |
46.42 |
** |
NS |
** |
1.96 |
|
|
ED5 |
39.05 |
39.15 |
37.11 |
33.69 |
36.36 |
** |
NS |
** |
1.43 |
|
|
ED8 |
31.99 |
32.88 |
31.46 |
27.63 |
29.39 |
** |
NS |
NS |
1.64 |
|
|
Sunflower meal |
||||||||||
|
a |
6.40 |
5.98 |
6.45 |
6.65 |
6.29 |
NS |
NS |
NS |
0.7 |
|
|
b |
42.36 |
41.78 |
37.09 |
32.22 |
31.22 |
** |
NS |
** |
3.14 |
|
|
c |
51.23 |
52.23 |
56.45 |
61.12 |
62.47 |
** |
NS |
** |
3.1 |
|
|
k |
6.23 |
6.77 |
6.78 |
6.84 |
6.36 |
NS |
NS |
NS |
0.61 |
|
|
PD |
48.77 |
47.77 |
43.55 |
38.87 |
37.52 |
** |
NS |
** |
3.11 |
|
|
ED2 |
40.48 |
39.19 |
35.66 |
32.08 |
30.35 |
** |
NS |
** |
2.77 |
|
|
ED5 |
31.46 |
30.72 |
28.24 |
25.67 |
23.97 |
** |
NS |
** |
2.16 |
|
|
ED8 |
24.96 |
25.05 |
23.44 |
21.52 |
20.04 |
** |
NS |
* |
1.69 |
|
|
Maize silage |
||||||||||
|
a |
14.21 |
13.84 |
14.53 |
14.03 |
15.03 |
NS |
NS |
NS |
1.29 |
|
|
b |
42.72 |
42.37 |
41.98 |
39.11 |
35.93 |
** |
NS |
* |
2.6 |
|
|
c |
43.06 |
43.58 |
43.47 |
46.85 |
49.03 |
** |
NS |
NS |
2.85 |
|
|
k |
3.19 |
3.13 |
3.35 |
2.99 |
3.18 |
NS |
NS |
NS |
0.31 |
|
|
PD |
56.94 |
56.41 |
56.52 |
53.15 |
50.97 |
** |
NS |
NS |
2.86 |
|
|
ED2 |
42.96 |
40.67 |
40.8 |
40.03 |
40.26 |
NS |
NS |
NS |
2.41 |
|
|
ED5 |
32.36 |
30.80 |
31.36 |
30.24 |
30.94 |
NS |
NS |
NS |
1.69 |
|
|
ED8 |
26.38 |
25.79 |
26.92 |
24.66 |
25.26 |
NS |
NS |
NS |
1.41 |
|
|
1 a = Soluble, b = insoluble but potentially degradable, c = Undegradable, k = Fermentation rate, PD = Potential degradability, ED2, 5, 8 = Effective degradability at 0.02, 0.05 and 0.08 h-1. 2 L = Linear, Q = Quadratic, 0 × G = Control treatment × Crude glycerin treatments, *P<0.05; **P<0.01. NS = Not significant. |
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Moreover, no effects (P < 0.05) were observed in the degradation parameters of ADF, for soybean meal or sunflower meal (Table 8), but when maize silage was evaluated, the fraction “c” of the control treatment was significantly greater than those observed in the treatments containing glycerin, which were not different among each other (Table 9). On the other hand, glycerin caused a beneficial effect on the potential degradability of maize silage, and the glycerin treatments taken together had higher mean values of PD (P < 0.05) than that observed in the control treatment (Table 9).
|
Table 8. In situ ruminal degradation parameters of acid detergent fiber of feed ingredients in Nellore cattle fed diets containing up to 30% crude glycerin |
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|
Ingredient |
In situ ruminal degradation parameters of ADF1 (S.E) 2 |
|||||||
|
a |
b |
c |
k |
PD |
ED2 |
ED5 |
ED8 |
|
|
Soybean hulls |
10.83 |
43.36 |
45.80 |
4.16 |
54.19 |
40.02 |
30.44 |
25.59 |
|
(0.99)2 |
(3.29) |
(3.05) |
(0.27) |
(3.05) |
(2.20) |
(1.73) |
(1.50) |
|
|
Sunflower meal |
5.82 |
30.33 |
63.84 |
5.99 |
36.15 |
28.55 |
22.35 |
18.81 |
|
(0.56) |
(1.58) |
(2.97) |
(0.36) |
(1.90) |
(2.85) |
(1.38) |
(1.23) |
|
|
1 a = Soluble, b = Insoluble but potentially degradable, c = Undegradable, k = Fermentation rate, PD = Potential degradability, ED2, 5, 8 = Effective degradability at 0.02, 0.05 and 0.08 h-1. 2 Values in parentheses correspond to the error standard of the mean. |
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|
Table 9. In situ ruminal degradation parameters of acid detergent fiber of maize silage in Nellore cattle fed diets containing up to 30% crude glycerin |
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|
Item1 |
Treatments (% crude glycerin) |
Contrast, P-value2 |
SEM |
|||||||
|
G0 |
G7.5 |
G15 |
G22.5 |
G30 |
L |
Q |
0 × G |
|||
|
a |
10.87 |
11.42 |
12.07 |
10.89 |
11.53 |
NS |
NS |
NS |
1.26 |
|
|
b |
36.15 |
38.49 |
36.92 |
37.78 |
37.93 |
NS |
NS |
NS |
1.74 |
|
|
c |
52.98 |
50.09 |
51.01 |
51.32 |
50.53 |
NS |
NS |
* |
1.62 |
|
|
k |
2.81 |
2.8 |
2.76 |
2.55 |
2.75 |
NS |
NS |
NS |
0.23 |
|
|
PD |
47.01 |
49.91 |
48.99 |
48.67 |
49.46 |
NS |
NS |
* |
1.62 |
|
|
ED2 |
31.99 |
33.91 |
33.46 |
31.99 |
33.45 |
NS |
NS |
NS |
1.07 |
|
|
ED5 |
23.88 |
25.28 |
25.21 |
23.60 |
24.96 |
NS |
NS |
NS |
0.98 |
|
|
ED8 |
20.27 |
21.43 |
25.55 |
19.99 |
21.21 |
NS |
NS |
NS |
0.99 |
|
|
1 a = Soluble, b = insoluble but potentially degradable, c = Undegradable, k = Fermentation rate, PD = Potential degradability, ED2, 5, 8 = Effective degradability at 0.02, 0.05 and 0.08 h-1. 2 L = Linear, Q = Quadratic, 0 × G = Control treatment × Crude glycerin treatments, *P<0.05; **P<0.01. NS = Not significant. |
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The mean value of the soluble fraction “a” of the DM of the soybean hull observed in this study (16.8%) was lower than that found by Muniz (2003), who worked with sheep and reported a value of 20.2%, and lower than the value reported by Silva et al (1999), working with dairy cattle, who observed a value of 21.6%. Such differences may be due to the methodology applied in determining solubility, since in this study autoclaved rumen liquid was used instead of using fresh tap water. As the rumen fluid is more viscous than water, the feed particles have a slower transit.
Regarding the potentially degradable “b” and undegradable fractions “c” of soybean hulls, the mean values observed were, respectively, 50.6 and 32.8%, evidencing that, despite the high NDF content of this ingredient (68%), it can be effectively used by the animal. These results suggest that the soybean hull has the potential to partially replace both fibrous ingredients and energy concentrates.
The value found for the effective degradation of DM of maize silage in the treatment containing 30% of crude glycerin was 56%, which, despite being the lowest value found in this study, it is greater than that reported by previous studies. Katsuki et al (2006), who worked with Holstein cows, found the value of 44.5%. Therefore, even if there was a decrease in ED when high concentrations of crude glycerin were used, the value estimated for this parameter is still satisfactory for a good use of the ingredient by the animals.
The values observed for the soluble fraction of the dry matter of maize silage (47.2%) were similar to those found by Fontes (2005), who reported a value of 46.5%, and by Ezequiel et al (2002), who observed a value of 52.6%, both working with beef cattle.
Wang et al (2009) fed Simental cattle and studied the degradability of maize stover and the concentrate mix added with 0, 100, 200 or 300 g glycerin (99% purity) per animal per day. These authors observed that for maize stover, the fractions “a” and “b” of the DM were quadratically altered, while there was a linear increase in the effective degradation with the increased dose of glycerin administered. For the concentrated mix (maize, wheat meal, soybean meal, cottonseed cake and rapeseed cake), a linear increase of the soluble fraction and the effective degradability, and a decrease of the potential degradability was observed.
In general, the observed values of organic matter degradation parameters followed the same behavior as those observed in the dry matter degradation ones. The effective (41.4%) and potential (69.4%) degradability of the organic matter of the soybean hull observed in this study were lower than those found by Silva et al (1999), who reported values of 51.1% and 88.1%, respectively.
Despite the low protein content of maize silage (about 7% in this study), the degradability of the crude protein of this ingredient was extremely interesting, presenting mean values of 75.3, 71.1 and 69.5%, for the passage rates 2, 5 and 8%/h. The crude protein of sunflower meal (Table 8) presented a high solubility value (52.97%). Protein solubility may be advantageous, since the amino acid profile of the soluble fraction may be different from that presented in the degradable portion (Galati 2004).
The values observed for degradation rate of protein from sunflower meal, although high, are lower than those found by Fontes (2005), who observed an average value of 10.8%, working with diets without glycerin. The potential degradability of crude protein from sunflower meal was high (93.8%), regardless of the treatment, showing that this nutrient can be extensively degraded in the rumen.
In this experiment, regardless the treatment, the average values found for the degradability parameters of NDF of soybean hulls are below those found by Silva et al (2004). The values observed by these authors for a, b, k, DE 2, DE 5 and DE 8 were, respectively, 18.7, 69.9, 6.2, 71.6, 57.4, and 49.3, while those found in this study were, respectively, 13.1, 47.0, 4.8, 47.7, 37.1 and 30.7.
The increase of the fraction “c”, the decrease on the fraction “b” and consequent decrease on the potential and effective degradability of NDF of sunflower meal observed in this study is of fundamental importance since the contribution of sunflower meal to the NDF contents of the diets was increased when the crude glycerin was added, and maize grain was removed.
Although crude glycerin caused a decrease in the availability and utilization of the fibrous fraction of sunflower meal, it provided values for fraction “b”, PD, ED 5 and ED 8, similar to those found by Fontes (2005), which were on average 33.3, 39.0, 24.8 and 21.2, respectively.
An effect of glycerol on degradation parameters of NDF was previously reported by Wang et al (2009). These authors reported a linear increase of the soluble fraction of maize stover NDF in Simmental cattle fed up to 300 g of glycerin per day, however, the fraction “b” and the effective degradability of the NDF presented a quadratic effect resulting in an improvement when the intermediate values of glycerin were used and a decrease, when the highest dose was administered, disagreeing with the present study.
Pires et al (2010) evaluated the in situ degradability of maize silage in Nellore cattle and observed a mean value for the maize silage fraction “c” of 38.5%, which is much lower than that found in the present study (51.1%). This discrepancy is probably due to the different maize varieties used in these studies.
The authors thank the Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP, grant number 09/51857-3), for funding the present study and providing a scholarship to the first author (FAPESP, grant number 08/53712-0), to Prof. Dr. José Wanderley Cattelan for the cannulation surgery, and Caramuru Alimentos S.A. for supplying some of the ingredients used in the study.
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Received 10 October 2018; Accepted 22 November 2018; Published 2 December 2018