Effect of supplementing urea treated rice straw and molasses with different forage species on the performance of lambs

 

Khuc Thi Hue, Do Thi Thanh Van^* and Inger Ledin ^**

Goat and Rabbit Research Center, Sontay, Hatay, Vietnam

^*National Institution of Animal Husbandry, Hanoi, Vietnam

^**Department  of Animal Nutrition and Management, Swedish University of Agricultural Sciences
P.O. Box 7024, 750 07 Uppsala, Sweden

 

Abstract

Forty weaned Phan Rang lambs with an initial weight of 14.9 kg and at around 3.5 months of age were used to study the effect of supplementing urea treated rice straw and molasses with different forage species, Stylosanthes (Stylosanthes guianensis), Cassava (Manihot esculenta Crantz) or Jackfruit (Artocarpus heterophyllus), as protein sources compared to a commercial concentrate with respect to digestibility, growth performance and number of gastro-intestinal parasite eggs. Eight males were used in a digestibility trial in a double 4*4 Latin square design. Thirty two lambs (12 males and 20 females) were used in a growth trial lasting 84 days.

 

The crude protein (CP) content in the concentrate, Stylosanthes forage, Cassava foliage and Jackfruit foliage was 171 g, 154 g, 202 g and 148 g/kg dry matter (DM), respectively. The treatments were four diets containing urea treated rice straw ad lib and molasses supplemented with concentrate (control), Stylosanthes forage (UTR-S), Cassava foliage (UTR-C) or Jackfruit foliage (UTR-J). The live weight gain (LWG) was 73.3 g, 70.0 g, 77.7 g and 70.2 g/day and the feed conversion ratio 9.3, 9.0, 7.5, 10.4 kg DM/kg LWG for control, UTR-S, UTR-C and UTR-J, respectively. The DM intake ranged from 33 g to 44 g DM/kg body weight. The DM digestibility was 633 g, 548 g, 604 g and 540 g/kg DM and the CP digestibility 636 g, 652 g, 669 g and 522 g/kg for control, UTR-S, UTR-C and UTR-J, respectively. The nitrogen retained was 10.4 g, 9.8 g, 10.9 g and 9.8 g/day for the diets control, UTR-S, UTR-C and UTR-J, respectively, and was not significantly different among treatments. The content of total tannins seemed to have a negative effect on the number of internal parasite eggs. In the diets, which contained total tannins, the number of eggs was reduced or slightly increased during the experiment.

 

Stylosanthes forage, Cassava and Jackfruit foliage could be used as protein sources in diets based on urea treated rice straw and replace a commercial concentrate without any effect on the live weight gain of the lambs.

 

Key words: Urea treated rice straw, molasses, Stylosanthes guianensis, Manihot esculenta Crantz, Artocarpus heterophyllus, lambs, growth, digestibility and parasites. 

 

Introduction

The major constraint for the development of sheep production in Vietnam is shortage of feed in the dry season. Rice straw is available all the year around in large quantities and can be used in the form of urea treated rice straw (UTR) as the main bulky feed for sheep (Hue, 2003). However, the low nutrient content (energy and crude protein (CP)) in the UTR compared to the requirement of sheep results in low growth rates and poor reproductive performance when using UTR as a feed. To solve this problem, farmers can use concentrate to meet the energy and protein requirements of the sheep. However, using concentrate in sheep production systems leads to high cost of the products and is difficult to apply by the farmers. One possibility to improve a diet based on UTR and reduce the cost of the products is to supplement with protein rich foliages or legumes such as Stylosanthes (Stylosanthes guianensis), Jackfruit (Artocarpus heterophyllus) or Cassava (Manihot esculenta Crantz).

 

Stylosanthes is a leguminous species, which occurs naturally in the tropical, subtropical and temperate regions of the Americas, Africa and Southeast Asia (‘t Mannetje, 1984; Tarawali, 2005). The natural habitats of Stylosanthes are usually areas of low soil fertility, especially where the soil has a low Phosphorus content and is of an acidic nature. Stylosanthes performs well under both drought and waterlogged conditions (Edye and Grof, 1984). The growing points of Stylosanthes are often close to the ground, which is advantageous under grazing. Another characteristic of Stylosanthes is its single seed, which helps to regulate germination and improve seed survival (Gardener, 1975). The CP concentration of Stylosanthes is around 170 g/kg DM but can range from 94 g to 188 g/kg DM depending on age at harvesting. According to Mani et al. (1988) and Ikwuegbu and Ofodile (1992), Bunaji cattle and West African Dwarf goats produced more milk, lost less weight and the survival rate of calves and kids improved when cattle and goats were allowed to graze on Stylosanthes pasture. Phengsavanh and Ledin (2003) indicated that the growth rate of goats was 64 g to 70 g/day when fed a diet consisting of grass and 30% to 40% of DM intake (DMI) as Stylosanthes. According to Mupangwa et al. (2000), the DMI and apparent DM digestibility of Stylosanthes guianensis hay by Dorper wethers were 50.9 g/kg metabolic body weight (W^0.75) and 577 g/kg DM, respectively. The daily intake of organic matter (OM) by Blackhead Persian rams fed a diet consisting of Stylosanthes scabra cv. Seca hay was 216 g/kg body weight (BW) and digestibility of OM was 577 g/kg (Mero and Udén, 2000).

 

Cassava is a tropical feed resource with a high biomass production and is also a potential source of protein and vitamins. Cassava roots are used for human consumption and the leaves can be used as a feed for animals. The CP concentration in cassava leaves ranges from 160 g to 250 g per kg DM, with 85% of the CP as true protein (Ravindran, 1993). Moore (1976) found that the feed intake, growth rate and feed efficiency of steers were improved when they were fed diets containing Cassava foliage. Cassava has also been used as a supplement in diets of lactating cows (Wanapat, 2001). Phengvichith and Ledin (2007) indicated that the daily live weight gain of growing goats ranged from 52 g to 54 g/day when given 30% to 40% of the DMI in the form of wilted cassava foliage. Seng and Rodriguez (2001) showed that the growth rate of confined goats was higher and nematode infestation lower, when the forage supplement was Cassava foliage. Muller (1977) suggested that the Cassava foliage should be harvested at 3-4 months of age to ensure high nutrient content.

 

Jackfruit is a popular fruit tree, distributed widely throughout Vietnam, and used as a multipurpose tree for producing fruit for human consumption, making fences and harvesting foliage as feed for animals. Live weight gain (LWG) of growing goats and sheep was high when Jackfruit foliage was used as a protein supplement in the diets (Mui et al, 2001; Mui et al., 2002; Van et al., 2006). The leaves contain 330 g DM/kg and the CP concentration is 171 g/kg DM (Lin et al., 2003). The total tannin in leaves and 35 cm to 45 cm stem of Jackfruit was found to be 33.2 g/kg DM according to Mui et al. (2002). The voluntary feed intake by goats is high, 38.5 g to 49.7 g DM/kg BW and LWG was 43.9 g/day (Keir et al., 1997; Mui et al., 2001; Kibria et al., 1994; Kouch et al., 2003).

 

Leaves or foliages of multipurpose tree species often contain secondary compounds, especially tannins, which in low amounts may increase the productivity of the animals by binding with the dietary proteins during mastication and protecting the protein from microbial attack in the rumen. The protein-tannin complex will then be digested and utilised in the lower part of the digestive tract, thus acting as a by-pass protein source (Barry and McNabb, 1999; Norton, 2000). Leaves from some foliages have been introduced in practice for the control of parasites in ruminants (Mui et al., 2005). Cassava or Jackfruit in the diet of cattle, goats and sheep reduced the number of parasite eggs in the faeces with time (Athanasiadou et al., 2001; Lin et al., 2003; Khuong et al., 2005).

 

The objectives of the present study were to evaluate:

·        The effect of supplementing a basal diet of urea treated rice straw with protein rich forage species (Cassava, Stylosanthes or Jackfruit) on intake, growth rate, digestibility and nitrogen retention of growing lambs

·         The effect of secondary compounds (mainly tannins) in the foliages on number of parasite eggs in the sheep faeces.

Material and methods

Location and climate

The experiments were conducted in The Goat and Rabbit Research Center, Sontay, Hatay, Vietnam, 40 km West of Hanoi, longitude E 105^o25 and latitude N 21^o06. The altitude is about 220 m above sea level. The climate in this area is tropical monsoon with a wet season between April and November and a dry season from December to March. Average annual rainfall is 1850 mm. The two trials were conducted during March to September 2006.

Animals and management

The animals in the experiment were weaned lambs, bought at the Goat and Rabbit Research Centre. The breed was the local Phan Rang breed, which is used for meat production only, with brown wool colour and long thin tail. The mean initial body weight and SD were 14.9 (1.34) kg around 3.5 months of age. Before starting the experiments, the lambs were treated against parasites with injections of Ivermectin solution (1 ml per 4 kg BW) and were vaccinated against Pasteurellosis, Pneumonia and Enterotoxaemia.

 

Water was supplied in plastic buckets in both trials at all times. Mineral lick blocks [730 g minerals (700 stone meal, Ca₃(PO₄)₂ and 300 g bone meal/kg mineral) 170 g cement as a binding agent and 100 g salt/kg mineral lick block] were available ad libitum.

The animals were allowed to exercise once daily for one hour in the afternoon at 14 h to 15 h (for the growth trial only). During the exercise time, males and females were separated to avoid mating.

     

The animals were weighed in the morning before feeding at the start and end of the experiments, and at two week intervals for the growth trial. For the digestibility trial the animals were weighed at the start of the adaptation period, at the start of the collection period and at the end of the collection period. The animal cages, houses and troughs were cleaned every day.

 

Experimental feeds and feeding

 

The feeds used in the experiments were UTR, molasses, concentrate and forages from Cassava, Stylosanthes and Jackfruit.

To produce UTR the straw was chopped into pieces of 7 cm to 10 cm in length before treatment. The formula for treatment was 100 kg rice straw + 50 kg water + 4 kg urea + 1 kg salt +1 kg lime. The urea, salt and lime were dissolved in water before mixing with the rice straw. After mixing, the rice straw was stored in plastic bags under anaerobic conditions for 10 to 15 days before feeding. The quality of the UTR was estimated according to colour and smell (bright-yellow colour and good smell)

The molasses was bought at the same time for the two experiments at Thanh Hoa Sugar Company and was stored in plastic tanks. The tanks were kept inside the house to avoid the negative effects of rain, sunshine or high temperatures.

The concentrate was a commercial concentrate produced by Guyomach feed company. The nutritive value of the concentrate according to the producer was 180 g CP and 11.7 MJ ME/kg DM and the DM content was 890 g/kg. The concentrate was based mainly on fish meal, soybean meal, maize and rice bran, and was stored in plastic bags. All concentrate for the experiment was bought at the same time to avoid variations in feed composition.

 

Cassava, Stylosanthes and Jackfruit were harvested by cutting or breaking from the fields around the centre 1 to 2 hours before feeding. If it was raining, the forages were harvested the day before feeding to limit the effects of low DM content. The Stylosanthes was harvested at an approximate age of 50 to 60 days. Before the start of the experiment, the area with the Stylosanthes was divided into 6 plots, each plot big enough to provide feed for 10 lambs during one week. The plots were harvested one by one with one-week delay to be able to provide the Stylosanthes at the same age during the experiment. The Cassava foliage was harvested at an age of 3 to 4 months when the length of the cassava stems was about 50 cm to 60 cm.

 

The animals were fed concentrate and foliage twice per day at 7:00 h and 14:00 h. Molasses was added at a level of 20% of the fresh weight of the UTR and mixed thoroughly before feeding 4 times per day, the same times as the concentrate and foliage but also at 10:30 h and 16:30 h. The UTR-molasses and the concentrate were put in separate troughs. The forages were tied in bunches in the front above the trough.

 

Experimental design

 In the growth trial 32 lambs were randomly allocated to 4 treatments with 3 males and 5 females per treatment. The length of the trial was 12 weeks. Before the start of the experiment, the lambs were adapted to the feeds for 10 days. The treatments were:

·        Control: UTR + molasses + concentrate

·        UTR-S: UTR + molasses + Stylosanthes

·        UTR-C: UTR + molasses + Cassava foliage

·        UTR-J: UTR + molasses + Jackfruit