Poster 8.3: Quality and nutritive value of Napier grass silage at different growth stages and chopped or unchopped in northeast Thailand - Mitsuru Shinoda, Tomoyuki Kawashima, Pimpaporn Pholsen and Taweesak Chuenpreecha

INTRODUCTION

Stable supply of forage throughout the year is the key constraint for further development in cattle production in northeast Thailand. Although Napier grass (Pennisetum purpureum) is not popular in the region, it may have good possibilities under intensive management with high manure input. The present study aimed to evaluate nutritive value and fermentative quality of silages made of either chopped or unchopped Napier grass harvested at different growth stages, and effects on intake and blood composition of cattle.

MATERIALS AND METHODS

Three kinds of silage were made using cylindrical concrete tanks (0.75 m diameter and 0.5 m height), compressed by foot and covered by plastic sheets with sand on top:

(1) Using Napier grass 1 m high (about 30 days regrowth) - chopped.

(2) Using Napier grass 1 m high (about 30 days regrowth) - unchopped.

(3) Using Napier grass of 1.5 m high (about 80 days after transplanting) - chopped.

An aliquot of silage sample from each silo was placed into a bottle with water and kept in a refrigerator overnight. The extracted fluid was analysed for volatile fatty acids (VFAs) using gas chromatography; for lactic acid using a diagnostic kit; and for volatile basic nitrogen (VBN) and total nitrogen content.

Two castrated male native cattle (average body weight 166 kg) were used for digestion trials with the three feeds. All treatments were identical, namely silage was given to the animals ad libitum to measure maximum intake. Nutrient digestibility was examined by total collection method. Blood samples were collected from the jugular vein into a heparinized tube at the end of each collection period, before feeding and 3 hours post-feeding, and analysed.

RESULTS AND DISCUSSION

Although the original grass used in the treatments (1) and (2) was the same, CP and nitrogen-free extract (NFE) contents were lower in unchopped silage, which would be due to the difference in the fermentation process (Table 1).

Table 1. Chemical composition of silage

Key to columns: DM = dry matter; OM = organic matter; CP = crude protein; EE = ether extract; NFE = nitrogen-free extract; CF = crude fibre; ADF = acid detergent fibre; NDF = neutral detergent fibre.

CP content in treatment (3) was lower than in the others, which would be due to the difference in maturity. The fermentative quality of unchopped silage was also worse than that of chopped silage in treatment (1) (Table 2).

Table 2. Fermentative quality of Napier grass silage

Key: VBN/TN = ratio of volatile basic nitrogen to total nitrogen; LSM = least square means; SE = standard error; No. = number of samples. a and b indicate that results with different superscripts among treatments differ significantly (p<0.05).

The unchopped silage showed higher pH and ratio of volatile basic nitrogen to total nitrogen (VBN/TN), and lower lactic acid concentration. If grass was ensiled without chopping, there was considerable space between the pieces of grass, which made anaerobic fermentation difficult. V-score was calculated from VBN/TN, total content of acetate and propionate, and butyrate content (Masaki, 1994), which is one method to evaluate silage quality, and used in Japan to evaluate low- and high-moisture silage using the same criteria. It clearly showed the difference in the fermentative quality in spite of not using the value of lactic acid contents for the calculation. It would be a useful method for the evaluation of silage quality, especially in developing countries, where the analysis of lactic acid is not practicable in terms of cost and facilities. The pH value itself may also be a useful and very simple indicator in the evaluation of silage quality.

The TDN content of the silage in treatment 1 was significantly higher than that in treatment 2 (Table 3). It was therefore concluded that large amounts of nutrients, especially NFE, were lost during the fermentation process in treatment 2. The voluntary intake of silage also decreased in treatment 2. Consequently, TDN intake in treatment 2 was about 68% of treatment 1.

Table 3. Body weight, feed intake and nutrient digestibilities with native cattle given Napier grass silage

Notes: a, b indicate means that differ significantly among treatments (p<0.05).

There was no difference in D-3-hydroxybutyric acid (BHBA) level between 0 hr and at 3 hr after feeding in cattle fed chopped silage (treatment 1). In contrast, BHBA level in cattle fed unchopped silage became higher after feeding (Table 4). It was considered that the difference of butyrate concentration in the silage influenced BHBA level in the blood. However, the physiological effects of butyrate on animals would be minimal even if cattle received such low quality silage for a longer period, as the values of BHBA and NEFA in blood were within the normal range and there was no change in glucose content.

Table 4. The Change of NEFA, glucose, total protein and BHBA contents in plasma of cattle given Napier grass silage, before and after feeding

Key: (1) NEFA = non esterified free acid; TP = total protein; BHBA = D-3-hydroxybutyric acid; Tr = Effect of treatment; Ti = Effect of time after feeding; T*T = Interaction between treatment and time after feeding.

Chopping of original grass before ensiling is highly recommended not only for making better quality silage but also for making better use of silo capacity. Proper preparation of silage minimizes the loss of nutrients during the fermentation process and increases voluntary intake, which results in higher TDN intake.

REFERENCE

Masaki, S. 1994. [Judgement of silage quality.] (in Japanese). p. 79-87, in: Japanese Research Association on Quality Evaluation of Self-supplied feed (ed) Guidebook for quality evaluation of roughage. Japanese Grassland Association