Effect of source of supplementary dietary protein and feed offer level (ad libitum or restricted) on feed intake, digestibility and N balance in local “Yellow” cattle fed rice straw treated with urea as basal diet

Sangkhom Inthapanya and T R Preston¹

Faculty of Agriculture and Forest Resources, Souphanouvong University,
Luang Prabang, Lao PDR
inthapanyasangkhom@gmail.com
¹ Investigador Emérito, Centro para la Investigación en Sistemas Sostenibles
de Producción Agropecuaria (CIPAV), Carrera 25 No 6-62 Cali, Colombia

Abstract

The aims of the present study were to determine effects of source of supplementary dietary protein and feed offer level on feed intake, digestibility and N balance in local “Yellow” cattle fed rice straw treated with urea as basal diet.  Four local (“Yellow”) male cattle were assigned to 4 treatments in a 4*4 Latin square arrangement: AL-CSF: ad lib urea-treated rice straw supplemented with cassava foliage, AL-WS: ad lib urea-treated rice straw supplemented with water spinach, R-CSF: same as AL-CSF but intake restricted to 75% of ad libitum; R-WS: same as AL-WS but intake restricted to 75% of ad libitum. Experimental periods were of 15 days: 9 days for adaptation, 5 days for collection of feces and urine and the last day to take rumen fluid by stomach tube.

Water spinach increased the intake and the digestibility of the basal diet of urea-treated rice straw but this was not reflected in increased N retention which was the same when cassava foliage was the supplement. It is concluded that the protein available for metabolism was the result of increased rumen microbial protein on the water spinach supplement  but for the cassava foliage supplement it was derived from the protein that escaped the rumen digestion.

Key words: bypass protein, soluble protein, rumen ammonia

Introduction

Lao PDR is a country with a population of close to 7 million people. Over 75% of the population in Lao PDR relies on agriculture as their primary source of income, mainly from production of crops, livestock and forestry. Most farmers raise livestock as their main source of income and draft power. Cattle and buffaloes are important on smallholder farms in most developing countries to provide meat, milk, traction power and manure in integrated crop and livestock farming systems (Preston and Leng 2009).

The negative aspect of the agriculture sector is its contribution to greenhouse gas emissions which cause global warming. World agriculture produces 14-22% of global anthropogenic greenhouse gas (GHG) emissions (Ecofys 2013). Ruminant livestock such as cattle, buffalo, sheep and goats are a substantial source of the methane (Lassey 2007; Chabra et al 2009; Hristov et al 2013). Reducing greenhouse gas (GHG) emissions from agriculture and especially from ruminant livestock should therefore be a top priority since it could curb global warming fairly rapidly (Sejian et al 2010).

The key to improving the use of crop residues for ruminants is to overcome the inherent barriers to rumen microbial fermentation, which in rice straw is the lignification of the cellulose and hemicellulose cell wall components, and to provide supplements of fermentable nitrogen, vitamins and minerals. Among the strategies to improve the straw fermentation, in practical on-farm application, urea has been the most widely accepted and safer than using anhydrous or aqueous ammonia and also provides a source of nitrogen (crude protein) in which straw is deficient for (Schiere and Ibrahim 1989). According to Vadiveloo (2003), rice varieties with a low degradability responded better to urea treatments than higher quality straw, increasing the in vitro dry matter degradability from 45 to 55-62%.

The protein in cassava (Manihotesculenta, Crant) leaves is considered to be a good source of bypass protein (Ffoulkes and Preston 1978; Wanapat et al 2001; Sath et al 2008). It is widely cultivated in all tropical counties and is thus a logicalforage to provide the additional protein required in diets high in non-protein nitrogen.

Water spinach (Ipomoea aquatica) plays an important role for farmers in rural areas, it is easy to plant and has a very high yield of biomass with a short growth period; it can be harvested in dry or flood period (Sophea and Preston 2001). The crude protein content in the leaves and stems can be as high as 32 and 18 % in dry basis, respectively (Ly ThiLuyen 2003). Water spinach is widely used for human food, but at the same time this vegetable can be given to animals such as rabbits, pigs, poultry and small ruminants. Kongmanila et al (2011) reported positive responses in feed intake and N retention when foliage from the Mango tree which is rich in tannins and of low digestibility (Kongmanila et al 2007), was supplemented with water spinach (Ipomoea aquatica), the protein in which is considered to be highly degradable by rumen microbes (Kongmanila et al (2007). 

In vitro rumen fermentation studies have shown that methane production increases linearly over 48 hours independently of the substrate (Inthapanya et al 2011, Binh Phuong et al 2011, Thanh et al 2011). Leng (2014) has suggested that when the fermentation in an in vitro incubation exceeds 24h it will more resemble what occurs in a biodigester than in the rumen.  In ruminants fed well balanced diets, the rumen fermentation rarely exceeds 24h. However, if the diet is of low quality or is fed in restricted amounts, the rumen retention will be extended. It is hypothesized that reducing the feed level in cattle to 75% of the ad libitum intake will therefore lead to increased production of methane as occurs in the extended in vitro rumen fermentation.

The aims of the present study were to determine effects on feed intake, digestibility, N balance and methane production in local cattle fed a basal diet of straw treated with urea of: (i) supplements rich in soluble or bypass protein; and (ii) restricting the feed intake to 75% of ad libitum.

Materials and methods

Location and duration

The experiment was conducted in the farm of the Department of Animal Science, Faculty of Agriculture and Forest Resource, Souphanouvong University, LuangPrabang province, Lao PDR, from September to November, 2014.

Treatments and experimental design 

Local “Yellow” cattle were allocated to the following treatments arranged as a 4*4 Latin square:

• AL-CSF: ad lib urea-treated rice straw supplemented with bypass protein (cassava foliage)

• AL-WS: ad lib urea-treated rice straw supplemented with soluble protein (water spinach)

• R-CSF: Restricted 75% of AL-CSF Urea-treated rice straw supplemented with bypass protein (cassava foliage)

• R-WS: Restricted 75% of AL-WS Urea-treated rice straw supplemented with soluble protein (water spinach)

Experimental periods (Table 1) were of 15 days: 9 for adaptation, 5 for sample collection of feces and urine and the last day to take rumen fluid by stomach tube.

The basal diet is rice straw treated with urea at 3% of straw DM

Animals and housing

Four local “Yellow” male cattle were used with initial live weight of about 60 kg. All animals were confined in metabolism cage (made from wood and bamboo with the floor area 100*150 cm) with an arrangement to separate feces and urine. Vaccination was done against epidemic diseases and drenching against internal parasites before the commencement of the experiment.

Feeding and management

Animals were adapted gradually to the cages and to the basal diet of urea-treated straw for two weeks. The straw was bought from farmers in the area. The straw was treated with urea (3% of straw DM) by dissolving the urea in water (same weight of water as straw) and mixing it with the straw. The treated rice straw was stored in sealed plastic bags for 14 days before feeding.

Cassava foliage and water spinach (Photos 1 and 2) were collected from the farm of Souphanouvong University.

The treated straw was offered at 120% of recorded intake (AL) or 75% of recorded intake (R) the previous week. The protein supplements were offered at levels equivalent to 30% of DM intake. Feeds were offered two times a day, at 7.00 am and 4.30 pm.  Water was supplied during the whole period.

Data collection and measurements

The cattle were weighed in the morning before feeding at the beginning of the trial and after finishing each experiment period of 14 days. Feeds offered and refused were weighed and samples collected daily to determine feed intake. Feces and urine were collected daily during the last 5 days of each period. 100 ml of a solution of 10% H₂SO₄ were added daily to the urine collector to maintain the pH below 4.0.

At the end of each period, the samples of rumen fluid were taken 3 hours after feeding in the morning using a stomach tube (Photo 3). The pH was measured on the fresh sample; and 10 ml were preserved with H₂SO₄for determination of ammonia. And at the end of trial was measured the ratio of methane and carbon dioxide in eructed gas from each animal using the Gasmet equipment (GASMET 4030 (Gasmet Technologies Oy, Pulttitie 8A, FI-00880 Helsinki, Finland) (Photo 4).

Chemical analysis

Standard methods (AOAC 1990) were used to determine: DM, OM and N in feed offered and refused and in feces; N in urine; and pH and ammonia in rumen fluid.

Statistical analysis

The data wereanalyzed by the general linear model (GLM) option of the ANOVA program in the Minitab software (Minitab 2000). Sources of variation were animals, periods, treatments and error.

Results and discussion

Chemical composition of feeds

The concentrations of crude protein in cassava foliage and water spinach were similar but N solubility was more than doubled in water spinach compared with cassava foliage (Table 2).

Feed intake

When the basal diet was offered ad libitum the intakes of urea-treated straw and of the total diet DM were higher when the protein supplement was water spinach rather than cassava foliage (Table 3; Figure 1). The level of 11% crude protein in DM would appear to be adequate to maximize the feed intake on a basal diet of urea-treated straw.

Apparent digestibility, N balance and rumen ammonia

DM and OM digestibility were higher for water spinach than for cassava foliage; crude protein digestibility also tended (p=0.14) to be higher for water spinach (Table 4). By contrast, there were no differences in N retention (Figures 3-5). Thus it appears that on a basal diet of urea-treated rice straw a protein supplement providing rumen-fermentable protein was equally effective as a protein supplement providing bypass protein (ie: the cassava foliage).

Restricting the DM intake to 75% of the ad libitum intake led to decreases in apparent digestibility of DM, OM and crude protein and to reduced retention of nitrogen, as percent of nitrogen intake and of nitrogen digested.

The CH₄:CO₂ ratios in eructed gas from the cattle at the end of the last period of the experiment are presented to show the use of the “Gasmet” technique for determining methane emissions from animals (Madsen et al 2008).  No interpretation can be applied to these data as the measurements were made on only one animal on each treatment.

Discussion

The contradictory nature of the results are that the source of readily fermentable protein (water spinach) increased voluntary intake and the digestibility of the basal diet of urea-treated rice straw, but that these increases were not reflected in increased N retention which was similar on the cassava foliage treatment despite the fact that intake and digestibility were lower for this treatment. The implication is that the protein arriving at the intestine for enzymic digestion was similar for both supplements, but that the intestinal protein arising from water spinach resulted from increased synthesis of microbial protein (due to the higher voluntary intake and higher digestibility). By contrast, on the cassava foliage diet the protein arriving at the intestine was mainly a result of the “bypass” of theprotein present in the cassava foliage.

There is no obvious explanation for the lower apparent digestibility of the diet DM and crude protein, and the reduced retention of nitrogen as percent of nitrogen intake and nitrogen digested, when feed intake was restricted to 75% of the ad libitum level.

The hypothesis that methane emissions from the cattle would be higher on the restricted feeding regime could not be tested due to problems in storage of samples of eructed gases.  The plastic bags used for this purpose proved to be porous to the eructed gas which escaped during the period of storage and before the samples could be analyzed, as the Gasmet measuring equipment was not available until the end of the experiment.

Conclusions

• Water spinach and cassava foliage had similar concentrations of crude protein (19.6 and 19.4% in DM) but the solubility was three times higher in the former (66% versus 27%).  

  
  

• Water spinach stimulated the intake and the digestibility of the basal diet of urea-treated rice straw but this was not reflected in increased N retention which was the same when cassava foliage was the supplement.

  
  

• It is concluded that the protein available for metabolism was the result of increased rumen microbial protein on the water spinach supplement  but for the cassava foliage supplement it was derived from the protein that escaped the rumen digestion

Acknowledgement

This research is part of the requirement for the PhD of the senior author. The authors acknowledge support for this research from the MEKARN II project financed by Sida.

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Received 7 February 2015; Accepted 23 February 2015; Published 3 March 2015

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