Urea enriched finger millet (Elensine coracana) straw: Effect of feeding on yak

R.N. Pal, S. Pattanaik and T.K. Mohanty

National Research Centre on Yak, Dirang-790 101, West Kameng District, Arunachal, Pradesh, India

Summary

The experiment was designed to find the suitability of using urea-enriched straw in yak. Three yak were subjected to feeding trial with three rations: millet straw (phase I), 200 g urea/30 kg straw (phase II), and 400 g urea/30 kg straw (phase III). Urea treatment did not increase dry matter intake in yak. Dry matter digestibilities of the three treatments (58.6, 58.6 and 61.2%, respectively) were not different. Crude protein digestibility, digestible crude protein and nitrogen balances were significantly different between the three rations. Digestible crude protein contents of the three diets were 2.09, 5.36 and 8.74%, respectively. The results of biochemical characterisation of strained rumen liquor and serum also revealed differences among animals. The treatment of straw with urea affected total nitrogen and total volatile fatty acids in strained rumen liquor and urea in serum. Ammonia nitrogen in strained rumen liquor and serum glucose remained unaffected.

Keywords: Biochemical composition, digestibility, finger millet straw, urea, yak

Introduction

It is well known that simple nitrogenous compounds are broken down in the rumen by the microbial population and utilised to build up microbial protein, which ultimately finds its way into the true stomach, get digested and absorbed in the lumen of the intestine as amino acids (Maynard and Loosle 1951). However, opinions differ on the extent of utilisation of such simple nitrogenous compounds by the host bovid. Urea feeding to animals were attempted on large scale during the second world war because of serious shortage of protein supplements viz. oil cakes.

Urea, a very simple nitrogenous compound (Co: NH₂-NH₂), contains 46% of nitrogen. Various studies carried out to date have shown that urea treatment increases the feeding value of straw by increasing the digestibility and intake (Schiere et al. 1988). The conversion is not efficient when the ratio is low in available carbohydrate or other sources of energy for the bacteria, or when urea is added to a ration that is already fairly rich in protein (Rai et al. 1989).

In developing countries, substantial emphasis is put in crop cultivation to feed a large and growing number of human populations from limited available arable lands. Urea treatment of low quality straw has been used mainly on experimental basis in developing countries. However, it is widely recognised that this technology offers very good prospects in these regions where large numbers of ruminant populations depend, to large extent, on crop residues. Urea is comparatively cheap, easily available and readily hydrolysed to NH₄ under the warm tropical climate. By and large, the use of urea to enrich the straws has remained confined to research and other government farms and has not yet made an impact on the farmers field. Large-scale application of this technology is likely to ultimately benefit the farmers. However, to date the work on urea application has been limited principally to nutrition trails involving cattle. Specifically, the potential application of urea in the yak has not been reported. The present study was, thus, conducted to investigate the suitability of the use of urea feeding in the yak.

Materials and methods

The basic straw used in this study was finger millet (Elensine coracana). Three male yak weighing 208, 236 and 280 kg were utilised in the feeding trials. Three feeding trials were conducted on consecutive months, each trial spanning 30 days. Faecal and urine samples were collected on the last seven days of each trial period. The first trial was conducted on chaffed finger millet straw (FMS) without any supplementation (Phase I). The second trial was conducted by supplementing the FMS with urea at the rate of 200 g urea/30 kg FMS (Phase II). The third trial was conducted on FMS treated with 400 g urea for every 30 kg FMS (Phase III). Earlier reports (Pal et al. 1999a; Pal et al. 1999b; Pal et al. 1999c) revealed that the dry matter intake in yak is approximately 1.5% of live weights of animals consuming 7–8 kg of FMS per day. In the present study, the 7–8 kg of the treated FMS provided approximately 50 g urea/day per animal in Phase II and about 105 g urea/day per animal in Phase III. This amount is small in comparison to the recommendation for cattle of 4 kg/100 kg of air-dried straw (ICAR 1985). As urea use in yak feeding had not been tried, treatment with high amount of urea was avoided in the present study. This paper presents results comparing phases I and II with those of phase III. The effect on digestibility, on strained rumen liquor (SRL) and blood serum was also studied. Total N_2, concentration of NH₄N₂ and total volatile fatty acids (TVFA) in SRL and urea, total NH₄N₂ (Conway Micro Diffusion Method) and glucose in blood serum were estimated using methods described by Briggs et al. (1957), AOAC (1984) and Chaudhury (1989), respectively. Statistical analysis was carried out according to the methods of Snedecor and Cochran (1967).

Results and discussion

The chemical compositions of the FMS in the three phases viz. untreated FMS, treated by 200 g/30 kg straw and by 400 g/30 kg straw, respectively, are presented in Table 1 and those of faecal samples are summarised in Table 2.

The average body weight (BW) changes in the three phases of feeding were –2.33, –1.7 and –1.3 kg, respectively. The maximum loss of BW of one yak in Phase III was –13 kg. Only one yak gained weight in Phase III by 11 kg. The intake figures (in kg per 100 kg dry matter) are presented in Table 3. The CP percentages in the three phases were 6.19, 10.00 and 15.42, respectively. The rest of the chemical constituents showed some variations, which could be attributed to the fact that the lots of FMS used were procured from different sources. The average excretion of all the nutrients was very variable.

Table 1. Chemical composition of untreated and treated finger millet straw (FMS) (% on dry basis).

Table 2. Chemical composition of faeces in the three metabolic collections in three yak in each trial (% on dry basis.

Animals	CP	EE	CF	NFE	TA	IA	Ca	P
Untreated FMS
1	11.88	0.53	15.53	35.85	36.21	25.82	1.33	0.26
2	9.56	0.53	18.00	37.58	34.33	24.50	1.41	0.32
3	8.31	0.94	15.32	33.00	42.43	28.52	1.33	0.35
Average	9.92	0.67	16.28	35.48	37.66	26.28	1.36	0.31
Treated FMS (200 g/30 kg)
1	11.21	1.80	19.69	38.14	29.15	18.48	1.94	0.50
2	11.44	2.25	22.61	39.42	24.28	14.53	1.79	0.47
3	11.03	1.99	23.37	34.41	29.20	16.23	1.75	0.44
Average	11.23	2.01	21.89	37.32	27.54	16.41	1.83	0.47
Treated FMS (400 g/30 kg)
1	21.50	2.50	20.97	28.96	26.07	15.48	2.57	0.95
2	15.50	1.19	24.21	18.50	40.60	29.99	1.47	0.62
3	15.20	2.16	23.64	30.94	28.01	15.95	2.06	1.09
Average	17.40	1.95	22.94	26.13	31.56	20.47	2.03	0.88
CP= crude protein, EE= ether extract, CF= crude fibre, NFE=nitrogen free extract, TA= total ash, IA= insoluble ash, Ca=calcium, P= phosphorus.

The intakes of DM (kg/100 kg BW) were not significant but when compared on total intake basis, irrespective of the BW, there were significant differences among animals but not between the treated and untreated FMS. The average daily intakes of DM were 3.08, 4.16 and 3.68 kg, respectively, in the three phases (Table 3).

Table 3. Intake of dry matter, kg/100 kg body weight (BW), in the three phases of the trial.

Urea incorporation did not affect the DM, EE and NFE digestibility. The CP and CF digestibility were significantly different (P<0.05). The CP was digested at a significantly higher rate but there was no significant difference between the 200 and 400 g incorporation/30 kg FMS. The digestibility of CF was adversely affected by incorporation of urea. Untreated FMS recorded higher digestibility and there was no difference between the treated and untreated FMS (Tables 4 and 5).

Table 4. Digestibility coefficients of dry matter (DM), crude protein (CP), ether extract (EE), crude fibre (CF) and nitrogen free extract (NFE) in the three rations (%).

Table 5. The mean 'F' values of digestibility coefficients (%) of different nutrients in the three rations.

	Phase I	Phase II	Phase III	' F' (2, 4)
Dry matter (DM)	58.63	58.65	61.22	2.23ns
Crude protein (CP)	33.89a	53.62b	56.67b	10.6*
Ether extract (EE)	61.36	58.37	62.32	0.89ns
Crude fibre (CF)	75.49a	67.76b	67.23b	12.35*
Nitrogen free extract (NFE)	70.68	67.19	76.82	5.08ns
ns = not significant; * = significant at P<0.05; superscripts in the same row differ from each other.

Table 6 reveals that the rations differ significantly (P<0.01) in terms of digestible CP (DCP) although the total digestible nutrient (TDN) values were not significantly different among the rations. Urea supplementation increased the N₂ utilisation only.

Table 6. Digestible crude protein (DCP) and total digestible nutrient (TDN) content, kg/100kg dry matter (DM), in the three rations.

Animals	Phase I	Phase II	Phase III	F (2, 4)
DCP
1	1.35	5.60	7.82
2	2.32	5.43	9.12
3	2.61	5.06	9.25
Average	2.09a	5.36b	8.74c	106.53**
TDN
1	59.07	62.32	63.26
2	58.48	59.62	65.64
3	60.00	58.20	60.41
Average	59.18	60.04	63.10	3.07ns
ns = not significant; ** = Significant at P<0.01; superscripts in the same row differ from each other.

The N₂ balance in the untreated FMS was marginally positive and was not significantly different from the mean value of +8.76 in the treated FMS (200 g/30 kg straw). The 400 g urea supplementation per 30 kg FMS gave a significantly (P<0.05) higher balance (+33.73) of N₂ than the two other feeding regimens. The calcium balance was positive but appeared to be very erratic. Untreated and treated (400 g/30 kg FMS) straws gave almost similar balances and differed significantly from 200 g supplementation ration. The phosphorus balance was positive and remained unaffected (Table 7).

Table 7. Nitrogen, calcium (Ca) and phosphorus (P) balances (g/day).

Animals	Phase I	Phase II	Phase III	F (2, 6)
N2 (g/day)
1	–3.17	+3.67	+17.91
2	+5.61	+15.33	+12.90
3	+4.86	+7.27	+40.39
Average	+2.43a	+8.76a	+33.73b	16.28*
Ca (g/day)
1	11.59	2.13	9.56
2	13.53	6.26	26.03
3	11.03	2.90	14.49
Average	12.05a	3.76b	16.69a	8.18*
P (g/day)
1	1.89	1.80	4.16
2	1.38	2.96	9.13
3	0.50	2.18	1.06
Average	1.26	2.31	4.78	2.08ns
ns = not significant; * = Significant at P<0.05; superscripts in the same row differ from each other.

Rumen liquor obtained by stomach tube from all the three animals in all the three feeding regimen viz. untreated FMS and treated FMS (200 g/30 kg and 400 g/30 kg) on three consecutive days were analysed for total N₂, ammonia N₂, and TVFA. The results are summarised in Table 8.

Table 8. Total N₂ (mg/100 mL strained rumen liquor (SRL)), ammonia N₂ (mg/100 mL SRL) and total volatile fatty acids (TVFA) (mmo L/100 mL SRL) in three rations.

		Phase I			Phase II			Phase III
		Animals
Days		1	2	3	1	2	3	1	2	3
Total N2	Day 1	29	48	46	39	69	51	70	73	79
	Day 2	35	46	50	47	60	70	55	52	72
	Day 3	32	49	52	48	56	67	58	50	77
	Mean	32	48	49	45	62	63	61	58	76
Ammonia N2	Day 1	3.5	4.1	15.4	2.8	3.6	9.5	1.9	3.0	8.4
	Day 2	2.8	6.0	10.0	3.1	4.5	2.8	3.1	5.2	8.4
	Day 3	5.1	6.5	11.2	4.3	7.2	9.6	2.7	6.3	7.0
	Mean	3.8	5.5	12.2	3.4	5.1	7.0	2.6	4.8	7.9
TVFA	Day 1	9.5	12.2	10.0	8.4	10.4	10.0	8.2	9.0	8.0
	Day 2	12.3	11.8	12.8	11.2	10.0	10.2	11.1	8.5	9.6
	Day 3	11.3	12.0	11.5	10.0	8.9	11.4	10.0	9.8	10.5
	Mean	11.0	12.0	11.4	9.9	9.8	10.5	9.8	9.1	9.4

From the serum of the experimental yak, ammonia N₂, urea and glucose were estimated for three days and data are presented in Table 9.

Table 9. Serum ammonia N₂, urea and glucose concentrations (mg/100 mL) in three treatments.

Days		Phase I			Phase II			Phase III
		Animals
		1	2	3	1	2	3	1	2	3
Ammonia N2	Day 1	1.88	0.42	1.12	3.29	0.49	0.74	3.08	0.56	1.12
	Day 2	2.10	4.06	0.49	2.70	3.57	0.70	2.60	3.01	1.40
	Day 3	1.35	2.38	0.35	0.68	0.70	0.35	1.05	1.40	1.82
	Mean	1.78	2.29	0.65	2.22	1.59	0.60	2.24	1.66	1.45
Urea	Day 1	15.0	17.8	30.0	6.8	12.7	25.5	15.0	14.2	30.0
	Day 2	12.8	18.7	34.5	9.0	9.5	25.5	14.5	16.3	30.0
	Day 3	20.0	30.0	39.5	10.0	19.2	24.8	20.0	27.5	32.3
	Mean	15.9	22.2	34.7	8.6	13.8	25.3	16.5	19.3	30.8
Glucose	Day 1	50	49	77	57	49	77	71	37	67
	Day 2	45	51	72	59	54	69	45	49	50
	Day 3	50	38	77	52	48	72	46	42	61
	Mean	48	46	75	56	50	73	54	43	59

The differences among the animals were highly significant (P<0.01) in all the parameters except in the case of ammonia N_2. As would be expected, the total N₂ concentration in SRL increased with urea incorporation. This was not the case for ammonia concentrations. TVFA decreased significantly with the incorporation of urea in FMS. Ammonia N₂ and glucose in serum were not affected, but urea increased significantly in serum. The result that untreated straw had a higher concentration of urea was unusual and could not be explained (Table 10).

Table 10. The means with 'F' values in the three rations for total N₂, ammonia N₂ and total volatile fatty acids (TVFA) in strained rumen liquor (SRL), and ammonia N₂, urea and glucose in serum.

	Phase I	Phase II	Phase III	F (2, 22)
Total N2 in SRL (mg/100 mL)	43.0a	56.3b	65.1c	35.62**
Ammonia N2 in SRL (mg/100 mL)	7.18	5.16	5.11	1.78ns
TVFA in SRL (mmoL/100 mL)	11.49a	10.06b	9.41b	8.78**
Ammonia N2 in serum (mg/100 mL)	1.57	1.47	1.78	0.20ns
Urea in serum (mg/100 mL)	24.26a	15.89b	22.2c	10.44**
Serum glucose (mg/100 mL)	56.6	59.7	52.0	2.41ns
ns = not significant; ** = Significant at P<0.01; superscripts in the same row differ from each other.

It is concluded that urea treated of FMS at the rate of 200 and 400 g per 30 kg FMS did not increase the DM intake perceptibly. The average intake of 1.54 kg/100 kg BW of the untreated FMS came down to 1.50 kg/100 kg BW when treated with 200 g/30 kg and increased to 1.57 kg when treated with 400 g/30 kg FMS. The DM digestibility of the rations (58.6, 58.6 and 61.2%, respectively) was almost similar. CP digestibility (%), DCP (kg/100 kg DM) and N₂ balances were significantly affected by treatment. The CP digestibility progressively increased from 33.9 to 53.6% and then to 56.7%. Likewise the DCP (kg/100 DM) increased from 2.09 to 5.36% and then to 8.74%. N₂ balance of 8.76 g in 200 g treated ration was not significantly different from untreated value of 4.55, while N₂ balance in 400 g treated ration greatly increased the value to 33.7 g/day. The responses of the individual animals were high and in many cases were not uniform. The results of the biochemical characterisation of the SRL and serum also revealed the differences among the animals. The treatment of FMS with urea affected total N₂ and TVFA in SRL and urea in serum. Ammonia N₂ in SRL and serum glucose remained unaffected. Comparison of the results obtained could not be compared with literature values, as probably this is the first study of urea feeding in yak in India. Only one reference could be obtained from work in China but due to language barrier it could not be examined in sufficient detail.

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