4. Effect of variety and preservation method of cassava leaves on diet digestibility by local and crossbred pigs.

Khieu Borin, Lindberg, J.E., Ogle, R.B., 2005.
British Society for Animal Science 2005, 80: 319-324

Summary: The experiment was carried out from November 2002 to January 2003 at the University of Tropical Agriculture , near Phnom Penh in Cambodia . The mean daily temperature during this period was 27.7 o C (24.2-30.5 ? C). Four indigenous Mong Cai (MC) (17.2 (s.e. 2.61) kg) and four crossbred (Landrace x Yorkshire ) (LxY) (41.5 (s.e. 2.12) kg) castrated male pigs, aged 136 days, were randomly allocated to individual metabolism cages. Each cage had an individual automatic water drinker. The experiment was carried out as a 2 x 2 x 2 factorial arrangement, with two breeds of pig (MC and LxY), two cassava varieties (ST and LT) and two processing methods (sun-drying and grinding to produce a meal and ensiling). The two breeds of pig were each assigned to a 4 x 4 Latin Square . The experimental periods were 10 days, comprising 5 days of adaptation to each diet and 5 days of quantitative data and sample collection. The dietary ingredients were cassava leaf meal (CLM) and cassava leaf silage (CLS) of short (ST) and long term (LT) varieties, sugar palm syrup, crude palm oil, salt and a premix. The sugar palm syrup, palm oil and other dietary ingredients were mixed twice daily with an amount of CLM or CLS corresponding to the body weight of the pigs (30 g and 20 g DM of CLM and CLS respectively, kg-1 body weight) before feeding. Feed offered and residues were recorded twice daily and DM of the residues was determined once daily. Faeces were collected twice daily and dried for 24 h at a temperature of 60 o C in a locally made forced-air oven. Urine was collected in plastic buckets containing 10 ml of 4N H 2 SO 4 to maintain the pH below 4.0. The weights of manure and urine were recorded twice and once daily, respectively, and a 20 ml sub-sample of urine was taken each day.

Abstract: Digestibility and nitrogen (N) balance studies were carried out on the leaves of short-term (ST) and long-term (LT) varieties of cassava, preserved by sun-drying and grinding into a meal or by ensiling. The cassava leaf meal and ensiled leaves (471 and 373 g/kg total diet dry matter, respectively) were mixed with palm syrup and palm oil, to give the experimental diets CLM and CLS, respectively. Four Mong Cai (MC) (17·2 (s.e. 2·61) kg) and four Landrace × Yorkshire (L×Y) (41·5 (s.e. 2·12) kg) male castrate pigs were used. The experiment was designed as a 2 × 2 × 2 factorial, with breed, cassava variety and processing method as factors. The hydrogen cyanide (HCN) levels of the fresh cassava leaves of ST (545 mg/kg dry matter (DM)) and LT (408 mg/kg DM)

varieties were reduced by proportionately 0·63 and 0·33, respectively, after sun-drying and by 0·78 and 0·77, respectively, after ensiling. Intake was higher for DM, crude protein (CP) and organic matter ( OM ) (P <0·001) and neutral- and acid detergent fibre (NDF and ADF) and crude fibre (CF) (P detergent <0·01) in CLM than in CLS. There was a breed by processing method interaction for CF intake (P <0·05). The coefficient of total tract apparent digestibility (CTTAD) was higher in CLS than in CLM for DM, CP, OM and CF (P <0·001) and NDF and ADF (P <0·01). The MC pigs digested ADF (P <0·01) and CF (P<0·001) more effectively than L×Y pigs but there was no difference (P >0·05) in the digestibility of other nutrients or DM. There was a breed by cassava variety interaction for ADF digestibility and breed by processing method for CF digestibility (P <0·01). Daily N intake and faecal N were higher (P <0·001) in CLM than in CLS. Urinary N was lower in CLS than in CLM (P <0·05) and in L×Y than in MC pigs (P <0·001). N utilization (N retained per unit intake) was higher for CLS than CLM (P <0·001) and in L×Y than in MC pigs (P <0·001).

It is concluded that ensiling is a more effective method than sun-drying for reducing HCN in cassava leaves after 60 days re-growth, and also results in higher digestibility of DM and dietary components than sun-drying. However, the bulkiness of the silage limits intake. The MC pigs digested dietary fibre more efficiently than the L×Y pigs, whereas the L×Y pigs utilized N more efficiently than the MC pigs.