Int J Pharm Pharm Sci, Vol 7, Issue 3, 91-94Original Article


AN ORAL FEED STRATEGY IN SHEEP FOR IMPROVED DIGESTIBILITY, NUTRIENT UTILIZATION AND METHANE MITIGATION

P. K. PANKAJ1, D. B. V. RAMANA1, CH. SRINIVASA RAO1, K. RAVIKANTH2, RITA RANI1, M. NIKHILA1, ADARSH2*

1Livestock Production Management, Central Research Institute for Dryland Agriculture, Santoshnagar, Saidabad, Hyderabad 500059 (Telangana), India, 2Clinical Research, Ayurvet Limited, Baddi, 173205, Himachal Pradesh, India.
Email: clinical@ayurvet.in

Received: 19 Nov 2014 Revised and Accepted: 10 Dec 2014

ABSTRACT

Objective: A trial was conducted to study the efficacy of herbal formulation Ruchamax (M/S Ayurvet Limited, India) on digestibility and nutrient utilization in Deccani sheep.

Methods: 12 growing healthy Deccani sheep (5-6 months) were randomly divided into 2 groups. Control Group I (T0) was not given any treatment. Group II (T­1) supplemented with Ruchamax (appetite stimulant and digestive tonic). The test herbal formulation was mixed in the concentrate feed as per the recommendations. Parameters like body weight, plasma cortisol level, blood enzyme estimation, feed analysis, nitrogen balance, methane estimation and carcass quality traits were studied.

Results: Statistically (P<0.05) Ruchamax supplemented group had significantly superior average daily gain (g) than that of control. DMI, Dry matter digestibility and FCR of Ruchamax supplemented group were significantly (P<0.05) improved. The maximum nitrogen balance was obtained in Ruchamax supplemented group T1. Significantly (P<0.05) lower level of cortisol in Ruchamax supplemented animals confirmed the increased resilience of animal towards stress. The Ruchamax supplemented group T1 emitted significantly less methane as compared to control group T0. Animals belonging to Ruchamax supplemented group T1 had significantly higher dressing % as compared to control group T0. The enzymatic values in both groups were under normal physiological level.

Conclusion: The herbal appetite stimulant and digestive tonic Ruchamax was found to be safe for usage and efficient to improve digestibility, nutrient utility, performance traits in sheep alongwith added benefit of its methane mitigating potential.

Keywords: Plasma cortisol, Methane estimation, Carcass quality traits, Herbal formulation.

INTRODUCTION

Small ruminants occupy an important economic and ecological niche in agricultural systems throughout the developing countries [1]. Sheep provided milk, meat and clothing to mesopotamian and northern Indian civilizations and had a significant role in the economies of the cold north [2]. According to the 1972 census, the country had 40 m sheep, which contributed approximately $175 m (Rs 1400 m) per year to the national economy, based on a rough estimate of production of 34.3 m kg of wool, 101 m kg of mutton, and 14.6 m skins [3]. The total sheep population in India was 65.06 million in 2012, declined by about 9.07% over census 2007 [4].

Health status of the animal is very important from the economics point of view. Inadequate nutrition in ruminant animals has often been associated with heavy economic losses because of animal weight and condition losses, reduced reproductive capacity and increased mortality rates [5]. The digestion process is carried out by fibrolytic bacteria such as Ruminococcus albus, R. flavefaciens and Fibrobacter succinogenes, fungi, some protozoa [6] and by enzymes [7]. During the dry season, the natural pastures and crop residues available for animals after crop harvest are usually fibrous and devoid of most essential nutrients including proteins, energy, minerals and vitamins which are required for increased microbial fermentation and improved performance of the host animal [8]. Enzymes and antibiotics in feed served as aids to nutrition and are widely used in intensive livestock production systems in developed societies to improve the digestibility of feeds and utilization of nutrients, are not available to many resource poor farmers in developing countries [9].

These synthetic supplements are often beyond the purchasing capacity of many resource-poor farmers. Polyherbal economic therapies are synergistic, potentiative and agonistic / antagonistic pharmacological agents within themselves that work together in a dynamic way to produce therapeutic efficacy with minimum side effects [10]. They are naturally safe with pharmacologically active principles [11]. Current study was designed to evaluate the efficacy of herbal formulation Ruchamax (m/s Ayurvet Limited, Baddi, India) on rumen ecology. Ruchamax is a unique blend of scientifically processed herbs for appetite stimulation and better utilization of feed through improved digestive functions.

MATERIALS AND METHODS

Present study was undertaken on Deccani sheep at Livestock Farm, Hayathnagar Research Farm (HRF), Central Research Institute for Dry land Agriculture (CRIDA), Hyderabad, India and was situated at 17°27’N latitude and 78°35’E longitude and about 515 m above sea level. The climate is semi-arid with hot summers and mild winters. The mean maximum air temperature during summer (March, April and May) ranges from 35.6 to 38.6°C, whereas, in winter (December, January and February) ranges from 13.5 to 16.8°C.

Experiment design

12 growing healthy Deccani sheep of nearly same age (5-6 months) and body weight 16.35 to 16.48 were selected for the study. These animals were randomly divided into two groups, so that each group was having similar and uniform age and body weight. The animals were kept in two pens to acclimatize to the conditions for a period of 7 days prior to commencement of animal experimentation. Group T0 (n=6) was not given any treatment to serve as control. Group T1 (n=6) was supplemented with Ruchamax, 500g/tonne of feed for 3 months along with concentrate mixture. Concentrate mixture was made from maize, groundnut cake, wheat bran, rice polish, mineral mixture and salt and offered to each animal 250 Gms daily. Green fodder of Hybrid Napier (Co-4 variety) was offered fresh in the pen after thorough chaff cutting 4 Kg per day. Hygiene conditions were maintained each day, the floor of the experimental shed was cleaned with potassium permanganate, a sanitizer. During the trial parameters like body weight gain/week, analysis of food/faeces samples, plasma cortisol level, blood enzyme estimation, phenolic compound estimation, methane production estimation and carcass quality traits were studied.

Statistical analysis

Statistical analysis of the scientific data collected during the experiment was done with method described by Snedecor and Cochran [12]. Results obtained from the present investigation are presented herewith in the form of Mean ± SE and significant level at 5%.

RESULTS

Average daily weight gain

The results of average daily weight gain (gms/d) are presented in table 1. Group T1 animals supplemented with Ruchamax started showing significantly (p<0.05) superiority weight gain over control at 15th day of the treatment. After three months of treatment the average daily weight gain (gms/d) in Ruchamax supplemented group T1 (55.09±16.15b) was significantly (p<0.05) maximum in comparison to control group T0 (42.07±5.69a). The results are in accordance with the findings of Pradhan et al [13] and Hadiya et al [14].

DMI and FCR

Dry matter intake (g/d) (table 2) of Ruchamax supplemented group T1 (765.63±19.12b) was significantly (p<0.05) more than that of in control (698.71±12.12a) which suggests that the product supplementation has improved the palatability of the feed. Similar findings of improvement in DMI by polyherbal supplementation were reported by Ramana et al [15]. Feed conversion ratio of Ruchamax supplemented T1 group was significantly (p<0.05) superior (13.89±1.19b) than control T0 group (16.64±1.21a), which suggests supplementation of Ruchamax to be efficient in converting feed to meat. The results of FCR valve are in accordance with Handekar et al [16].

Table 1: Effect of feed supplements in terms of body weight and Average Daily Gain (ADG) (Mean ± SE) at fortnightly intervals in Deccani sheep

Particulars T0 T1
0 Days 16.45±0.83 16.35±0.82
15 Days 16.63±0.76a 17.89±1.05b
30 Days 16.67±0.98a 17.64±1.19b
45 Days 17.36±0.82a 18.31±1.39b
60 Days 18.18±0.91a 19.20±1.38b
75 Days 19.21±0.82a 19.70±1.56b
90 Days 20.23±0.83a 21.31±1.68b
ADG (gms/d) 42.07±5.69a 55.09±16.15b

abMeans with different superscripts in the same row differ at 5% level of significance

Table 2: Dry matter intake and feed conversion efficiency in Deccani sheep

Groups Initial B. wt. (kg) Final B. wt. (kg) DMI (g/day) DMI (kg/100kg b. wt.) FCR (kg/kg wt. gain)
T0 16.45±0.83 20.23±0.83a 698.71±12.12a 4.25a 16.64±1.2a
T1 16.35±0.82 21.31±1.68b 765.63±19.12b 4.68b 13.89±1.19b

abMeans with different superscripts in a column differ at 5% level of significance

Table 3: Digestibility coefficients of nutrients in both groups of Deccani sheep

Groups Dry matter Organic matter Crude fibre Crude protein Ether extract NFE NDF ADF
T0 58.33a 68.80a 73.73a 55.86a 53.14a 62.26a 67.68a 72.19a
T1 60.86b 71.66b 75.95b 57.51b 56.08b 65.08b 70.42b 74.77b

abValues with different superscripts in a column differ at 5% level of significance

When energy and protein intake as per dry matter intake (DMI) was extrapolated, it was observed that in supplemented group consumed significantly (p<0.05) more TDN, DCP, DE and ME which along with added advantage of superior digestibility resulted into attainment of better body weight as compared to control (Table 4). Group T1 supplemented with Ruchamax consumed the significantly (p<0.05) more TDN, DCP, DE and ME.

Table 4: Plane of nutrition of Deccani sheep as treated with both treatments

Particulars T0 T1
TDN Intake (g/d) 422.51a 480.44b
DCP Intake (g/d) 56.55a 67.06b
DE Intake (MJ/d) 7.80a 8.87b
ME Intake (MJ/d) 6.39a 7.27b

abValues with different superscripts in a rows differ at 5% level of significance

Digestibility coefficients and plane of nutrition of Deccani sheep

One week of digestibility trial suggested that DM, OM, CF, CP, EE, NDF and ADF digestibility was significantly (p<0.05) better in Ruchamax supplemented group T1 as compared to control group T0 (table 3). This improvement in nutrient digestibility leads to better availability of nutrients which explains the superior average daily gain and achieving greater body weight of Ruchamax supplemented group as compared to control.

This was because the polyherbal supplement Ruchamax feeding stimulate the appetite and digestive function with increased salivary function, increased ruminal bacteria and protozoa [17] that help in better feed assimilation and metabolism.

Nitrogen balance

When nitrogen balance through the metabolic trial results were estimated, It was observed that significantly (p<0.05) higher nitrogen was retained by Ruchamax supplemented group T1 and which attained the maximum body weight during the experiment (table 5). The high level of nitrogen balance represents a great interest for decreasing the nitrogen secretions in the environment.

Table 5: Nitrogen balance of deccani sheep on the experimental diets

Particulars T0 T1
Nitrogen intake (g/day) 9.05±0.76a 10.73±0.89b
Faecal nitrogen (g/day) 1.77±0.01 1.72±0.05
Digested nitrogen (g/day) 7.28±0.56a 9.01±0.75b
Urinary nitrogen (g/day) 3.95±0.02a 3.30±0.06b
Nitrogen balance (g/day) 3.33±0.12a 5.71±0.23b

abValues with different superscripts in a rows differ at 5% level of significance

Table 6: Blood cortisol (ng/mL) level in both groups of Deccani sheep at different time intervals

Days T0 T1
0 day 40.01±1.69a 43.23±1.43b
45 day 37.08±3.20a 27.31±1.58b
90 day 22.56±1.43a 8.94±1.9b
Overall 33.12±2.02a 26.49±1.79b

abValues with different superscripts in a rows differ at 5% level of significance

Blood cortisol level

Cortisol is released in response tostress. Anxiety-related behavior of cattle can be correlated with cortisol levels [18]. Blood cortisol level was estimated in the both groups at different time intervals. Initially cortisol level was significantly less (p<0.05) in control group T0 animals than supplemented animals (Table 6). But the trend was totally reversed after supplementation where Ruchamax supplemented group T1 animals had less cortisol value (26.49±1.79b) than control (33.12±2.02a), which suggests that herbal formulation used in the experiment has increased the tolerance capacity of animals against heat stress.

Blood enzymes levels

The overall alkaline phosphatase levels (U/L) in control group T0 (176 U/L) and in ruchamax supplemented group T1 (186 U/L) were found to be in normal range. The reason for high numerical value of ALP (U/L) in ruchamax supplemented group may be that one of the biological roles of ALP is detoxification of endotoxin, so high level within physiological limit is making animals more endurable against toxins and a sign of superior physiological adaptation. The serum SGOT level was found to be 92 U/L in Ruchamax supplemented group T1, the values were significantly less than 124 U/L i. e of control group T0. The plasma SGPT level was significantly less in Ruchamax supplemented group T1 i. e 20 U/L in comparison to untreated control group T0, 27 U/L. The low level of SGOT and SGPT within physiological limits is a favourable adaptive status against stress.

Methane emission estimation

Enteric emissions from the animals were measured using closed respiratory chamber method. Air samples from the chamber were collected from various heights at regular interval of 60 min in 24h duration. After sampling, gas samples were analyzed on same day for methane concentration using a gas chromatograph (450-GC, BRUKER Daltonics, Bremen, Germany) with three detectors Thermal Conductivity Detector (TCD), Electron Capture Detector (ECD) and Flame Ionization Detector (FID) with a 1041 PWOC Packed/Wide bore On-Column [19]. In the present investigation, Ruchamax supplemented T1 group was found to be significant (p<0.05) efficient in reducing methane emission from the Deccani sheep. Further, Ruchamax supplemented T1 group emitted significantly less (p<0.05) methane (Methane weight emitted gms/kg of DDMI, 39.112b) as compared to control T0 group (47.322a) (table 7).

Table 7: Methane emission in different groups of Deccani sheep

Particulars T0 T1
Recovered CH4volume (L) 46.290a 41.923b
Recovered CH4weight (g) 33.064a 29.945b
Methane emission (L)/kg of DDMI 66.251a 54.756b
Methane weight emitted (gms)/kg of DDMI 47.322a 39.112b
Methane emission (L)/kg of DMI 113.579a 89.971b
Methane weight emitted (gms)/kg of DMI 81.128a 64.265b

abValues with different superscripts in a rows differ at 5% level of significance

Methane (CH4) promotes stratospheric ozone depletion [20]. Methane is the second major contributor to global warming with a 100-year global warming potential (GWP), 23 times that of CO2 [21]. Low emission of CH4 in the rumen with Ruchamax supplementation has implications not only for global environmental protection but also for efficient animal production.

Plant secondary metabolites such as saponins and tannins have a role in reducing CH4 emissions [22]. Saponins have been shown to possess strong defaunating properties both in vitro [23] and in vivo, which could reduce CH4 emissions. Recently, a number of studies have reported that feeding tannin-containing forages to ruminants may reduce methane emissions [24, 25, 26]. In the present experiment also, significantly (p<0.05) maximum pure tannin and CT content was found Ruchamax supplemented T1 group (Table 8) which explains the maximum reduction in methane emission by this group of animals.

Table 8: Phenolic content of the supplemented concentrate ration

Particulars T0 T1
Total phenolics (%) 5.23a 6.58b
Non-tannin phenolics (%) 2.23a 1.96b
Pure tannin phenolics (%) 3.00a 4.62b
Condensed tannins (CT) (%) 5.34a 7.26b

abValues with different superscripts in a rows differ at 5% level of significance

Carcass quality traits

At the end of the 90-day feeding trial, all animals were slaughtered for carcass characteristics evaluation. When animals were slaughtered for carcass characteristics, it was found that animals belonging to Ruchamax supplemented T1 group (52±3.34b) had significantly (p<0.05) higher dressing % (Table 9) as compared to control group T0 (44.1±1.02a), which suggests superior utilization of feed resources for production of edible parts in supplemented groups with Ruchamax.

Table 9: Carcass quality traits (Mean±SE) of Deccani sheep

Body parts T0 T1
All 4 feet (kg) 0.50±0.04a 0.54±0.06b
Head weight (kg) 1.46±0.24a 1.53±0.21b
Intestine with content (kg) 1.30±0.36a 1.03±0.23b
Stomach with content (kg) 3.44±0.86a 3.45±0.85b
Pluck (kg) 0.71±0.04a 0.59±0.01b
Separable fat weight (kg) 0.11±0.01a 0.15±0.02b
Skin (kg) 2.70±0.78a 2.31±0.19b
Blood weight (kg) 0.57±0.05a 0.64±0.04b
Live weight (Kg) 19.10±3.90a 20.44±2.64b
Dressed carcass weight (kg) 8.46±1.96a 10.50±0.66b
Dressing (%) 44.1±1.02a 52±3.34b

abValues with different superscripts in a rows differ at 5% level of significance

DISCUSSION

Herbal remedies have been used for the treatment of live stock ailments [27]. Therefore the pharmacological activity in improving digestibility and improved nutrient utilization of Ruchamax, an herbal formulation was estimated. All the study parameters were compared with the unsupplemented control group. In previous experiments with different herbal dietary supplementation an average daily weight gain was reported in chickens [28], in cattle [29] and in pigs [30]. In the current study with supplementation of herbal formulations ruchamax a significant gain in body weight was observed in sheep. DMI, FCR, Digestibility coefficients were improved in ruchamax supplemented groups. This was because Ruchamax is a blend of 21 herbs and minerals, was highly effective in correcting and optimizing the digestion as an appetite stimulant and digestive tonic contains in bovines [31]. Approximately, 70-75% of the N consumed by animals is lost or excreted due to the inefficiencies associated with protein digestion and or absorption [32, 33]. Nitrous oxide is a potent greenhouse gas. Per gram, its atmospheric warming effect is approximately 296 times as strong as carbon dioxide. On Ruchamax supplementation the atmospheric emission of nitrogen due to enteric fermentation was significantly reduced and nitrogen absorption increased. Similarly the emission of methane form the sheep in ruchamax supplemented group was significantly reduced. Stress in animals leads to low productivity and health. Annual economic losses due to heat stress alone for the US dairy industry have been estimated at $900 million [34]. On Ruchamax supplementation stress hormone cortisol level was significantly reduced. Blood enzymes levels were in normal range after ruchamax supplementation, suggesting its safety as an appetite stimulant and digestive tonic. Carcass quality has a great economic importance. After supplementation with Ruchamax the significantly higher dressing % was recorded. This adds further economic benefit to the sheep rearers.

CONCLUSION

From the results of the present investigation it can be concluded that the herbal formulation Ruchamax feeding not only improved the digestibility, weight gain, health, carcass traits of the sheep but also maintained the nitrogen balance and reduced the emission of methane. It can be concluded that herbal formulation Ruchamax has both implications for efficient animal production and on global environmental protection.

ACKNOWLEDGEMENT

The author is thankful to Central Research Institute for Dry land Agriculture (CRIDA), Indian Council of Agricultural Research, Santosh Nagar, Hyderabad, A. P, India for providing research facilities and Ayurvet Limited, Baddi, H. P, India for providing necessary samples and guidance.

CONFLICT OF INTERESTS

Declared None

REFERENCES

  1. Devendra C. Small Ruminants in Asia: Contribution to food security, poverty alleviation and opportunities for productivity enhancement. In: Ledin I Eds. Proceeding of international workshop on small ruminant production and development in South East Asia: Vietnam Mekarn, Nong Lam, HCMC; 2005. p. 19-32.
  2. Randhawa MS. A history of agriculture in India, Vol. I. Indian Council of Agricultural Research: New Delhi; 1980. p. 189.
  3. NCA. Report of the national commission on agriculture, Part VII: Animal Husbandry. Govt. of India, Ministry of Agriculture and Irrigation: New Delhi; 1976.
  4. NCSR. National council for scientific research, quantification and control of livestock production constraints in Zambia-a multidisciplinary approach project proposal for: LPRC, Chilanga, Zambia; 1985. p. 1-5.
  5. 19 livestock census-all India report. Government of India. Ministry of agriculture, department of animal husbandry, dairying and fisheries: New Delhi; 2012. p. 1-121.
  6. Joblin KN, Naylor GE. Ruminal fungi for increasing forage intake and animal productivity. In: Odongo NE, Garcia M, Viljoen GJ, Eds. Sustainable improvement nations, rome of animal production and health; 2010. p. 129-36.
  7. Selinger LB, Forsberg CW, Cheng KJ. The rumen: a unique source of enzymes for enhancing livestock production. Anaerobe 1996;1:263-84.
  8. Dixon RM, Egan AR. Strategies for utilizing fibrous crop residues as animal feeds, 7th AAFARR Workshop, Chiang Mai, Thailand; 1987.
  9. Ebiamadon AB, Umoren E, Umoren, Fraideh B, Pedro MM, Jorge FS, et al. Prior Nutritional characterisation and antioxidant capacity of different tissues of Artemisia annua L. Food Chem 2009;115:1240-6.
  10. Tiwari AK, Rao JM. Diabetic mellitus and multiple therapeutic approaches of phytochemicals: present status and future prospects. Curr Sci 2002;83:30-7.
  11. Mabeku LBK, Beng VP, Kouam J, Essame O, Etoa FX. Toxicological evaluation of ethyl acetate extract of Cylicodiscus gabunensis stem bark (Mimosaceae). J Ethnopharmacol 2007;111:598-606.
  12. Snedecor GW, Cochran WG. Statistical methods. Sixth Eds. Amos Lowa, USA, the lowa state University Press; 1991. p. 1-503.
  13. Pradhan NR, Biswas U. Studies on the efficacy of Ruchamax against indigestion in cattle. Indian Vet Med J 1994;18:268-72.
  14. Hadiya K, Maini S, Rekhe DS, Ravikanth K. Accelerated growth programme with polyherbal formulations for dairy calves. Vet World 2009;2:62-4.
  15. Ramana DBV, Vijay Kumara A, Sudheera D, Maini S. Improvement in nutrient utilization in Deccani rams fed with coarse cereal crop residue as basal diet by polyherbal supplements. J Vet Sci Photon 2014;115:338-43.
  16. Handekar PB, Kolte AY, Mendhe HC, Puri RM, Ravikanth K, Maini S, et al. Effect of polyherbal formulations on ruminal digestion in goat. Vet World 2010;3:230-3.
  17. Kolte AY, Ravikanth K, Rekhe DS, Maini S. Role of polyherbal formulation in modulating rumen biochemical and growth performance parameters in calves. Int J Vet Med 2009;6:1.
  18. Bristow DJ, Holmes DS. Cortisol levels and anxiety-related behaviors in cattle. Physiol Behav 2007;90:626-8.
  19. Sitaula BK, Luo J, Bakken LR. Rapid analysis of climate gases by wide bore capillary gas chromatography. J Environ Qual 1992;21:493-6.
  20. Blake DR, Rowland FS. Continuing worldwide increase in tropospheric methane 1978 to 1987. Sci 1988;239:1129-31.
  21. IPCC. Climate Change 2001. The Scientific Basis. In: Contribution of working group I to the third assessment report of the intergovernmental panel on climate change. New York: Cambridge University Press; 2001. p. 1-873.
  22. Wallace RJ. Antimicrobial properties of plant secondary metabolites. Proc Nutr Soc 2004;63:621-9.
  23. Wallace RJ, McPherson CA. Factors affecting the rate of breakdown of bacterial protein in rumen fluid. Br J Nutr 1987;58:313-23.
  24. Pinares-Patiño CS, Ulyatt MJ, Waghorn GC, Lassey KR, Barry TN, Holmes CW, et al. Methane emission by alpaca and sheep fed on lucerne hay or grazed on pastures of perennial ryegrass/white clover or birds foot trefoil. J Agric Sci 2003;140:215-26.
  25. Woodward SL, Waghorn GC, Laboyre P. Condensed tannins in birds foot trefoil (Lotus corniculatus) reduced methane emissions from dairy cow. Proc NZ Soc Anim Prod 2004;64:160-4.
  26. Puchala R, Min BR, Goetsch AL, Sahlu T. The effect of condensed tannin-containing forage on methane emission by goats. J Anim Sci 2005;83:182-6.
  27. Masikaa PJ, Van Averbekeb W, Sonandic A. Use of herbal remedies by small-scale farmers to treat livestock diseases in central Eastern Cape Province, South Africa. S Afr Vet Ass 2000;71:87-91.
  28. Pourali M, Mirghelenj SA, Kermanshahi. Effect of garlic powder on productive performance and immune response of broiler chicken challenged with new castle disease. Global Veterinarian 2010;4:616-821.
  29. Pimentel P, Filipe Vilela, Nguluve DW, James P Muir, Adolfo José. Supplementary feeding increases live weight gain of Angoni cattle during the dry season in Mozambique. Livestock Res Rural Dev 2011;23:1.
  30. Liu GM, Wei Y, Wang ZS, Wu D, Zhou AG, Liu GL. Effects of herbal extract supplementation on growth performance and insulin-like growth factor (IGF)-I system in finishing pigs. J Anim Feed Sci 2008;17:538–47.
  31. Pradhan NR, Biswas U. Studies on the efficacy of Ruchamax against indigestion in cattle. Indian Vet Med J 1994;18:268-72.
  32. Parsons CM. Nutrient utilization and methods of assessment. an environmental perspective, Deagussa Technical Symposium, Indianapolis, USA; 1995.
  33. Nahm KH. Feed formulation to reduce N excretion and ammonia emission from poultry manure. Bioresour Technol 2007;98:2282-300.
  34. Collier RJ, Dahl GE, VanBaale MJ. Major advances associated with environmental effects on dairy cattle. J Dairy Sci 2005;89:1244-53.