EFFECT OF AGE OF GUINEA GRASS (Panicum maximum) ON SILAGE QUALITY AND ITS NUTRITIVE VALUE IN WEST AFRICAN DWARF GOAT (WAD)
One of the major physiological disorders of grazing goat in the early wet season is bloat. In the early wet season, grasses are just coming up, being tender and with a lot of water in it could results to distention of the stomach orchestrated by gas accumulation. Also, ruminants benefit a little from fermentation of over matured grass due to lignifications. In the light of this, there is need to adequately cater for all stages of pasture growth in order to meet the normal feed requirements of ruminants (Babayemi, 2009).
Young pastures are high in crude protein, low in fibre but very low in dry matter (Bamikole et al., 2004). On the other hand, older grasses are low in crude protein but high in fibre and dry matter (Babayemi and Bamikole, 2006). Young pastures may be low in fermentable carbohydrates or water soluble carbohydrates and high buffering solutions or capacities, making them practically difficult to ensile without injecting additives (Salawu et al., 2001; Ohba et al., 2004).
Pasture quality decreases from the young to mature stages as a result of difference in plant composition between levels of maturity. The presence of an increased proportion of plants stems, typical of older plants, may restrict access to leafy parts and force animals to consume lower quality herbage (Reiling et al., 2001). The quality of available bites is depressed when green leaf material is scarce and largely dispersed among senescent material especially in the case of older pasture for which the neutral detergent fibre (NDF) fractions increased with level of maturity. The nitrogen content (CP) of pasture also decrease from the young to mature stages. Increased pasture maturity has a negative effect on the nutritional value of Panicum maximum (Guinea grass) cv. gatton pasture (Reiling et al., 2001).
A major constraint to livestock production in developing countries is the scarcity and fluctuating quantity and quality of year round forage supply. (Dixon and Egan 1987) reported that during the dry season, the natural pastures and crop harvest are usually fibrous and devoid of most essential nutrients which are required for improved microbial fermentation and improved performance of the animal. This manifest in loss of weight reduced reproduction capacity and increased mortality rate. Ensiling is a potent general method for forage preservation and also a form of treatment to occasionally salvage the under-utilized pastures for better acceptability and degradability (Salawu et al., 2001; Ohba et al., 2004). Silage is one way of improving the utilization of low quality roughages. Silage production in the tropics is a sustainable means of supplementing feed for ruminants in the dry season (Babayemi and Igbekoyi, 2008).
The role of silage is to build up feed reserve for utilization during period of feed deficiency e.g. dry season or winter. It also acts as a routine feed supplement to increase productivity of animals; to utilize excess growth of pasture for better management and utilization. Silage making is practiced widely in intensive animal production system in temperate regions, because during the winter period, there is no high quality feed available and there is need to feed high quality feed supplement to complement available grass in order to improve production and to ensure good conditions for breeding. Silage making is useful only if the ensiled product is of good quality, that is well-preserved and of high digestibility and protein content. Quality silage is achieved when lactic acid is the predominant acid produced as it is the most efficient fermentation acid and will drop the pH of the silage the fastest (Ogunjobi et al., 2010). The faster the fermentation is complete; the more nutrients will be retained in the silage. Speed of harvesting, moisture content, length of chop, silage distribution and compaction can greatly influence the fermentation process and storage losses.
Efficient fermentation ensures a more palatable and ingestible feed, which encourages optimal dry matter intake that translates into improved animal performance. It is important that bacteria responsible for production of acetic and lactic acid grow and multiply immediately after storing the forage for maximum quality haulage. Proper packaging of the silage and voiding of air provides the environment needed by bacteria to break down fibre components and sugar (Ogunjobi et al., 2010). Oxygen must be removed from the silage to maximize reproduction of acetic and lactic acid producing bacteria.
Microbes responsible for fermentation need anaerobic conditions. As bacteria consume sugars, and product produced (acetic and lactic acid) cause the pH to drop. Quality silage is achieved when lactic acid is the predominant acid produced, as it is the most efficient fermentation acid and will drop the pH of the silage. The faster the fermentation is completed; the more nutrients will be retained in the silage. Bacteria inoculants can be added to increase the number of lactic acid producing bacteria, thus, encouraging more lactic acid production and a well-preserved forage mass (Ogunjobi et al., 2010). A critical time during the ensiling process occurs after the initial three to five days and requires some 15 to 20 days for completion (Ogunjobi et al., 2010). The success of the ensiling process is determined during two weeks, during this period there is a gradual increase in lactic acid producing bacteria which breakdown simple sugars to accelerate the fermentation process. The resultant effect of this process is the gradual drop of pH level to a range of 3.8 – 4.2 leading to further bacterial action.
Harvesting of pasture before maturity and conserving as silage provides the opportunity of getting the best for our livestock. Previous studies have reported the effect of harvesting age on the nutrient composition of grass (Oyenuga and Olubajo, 1975., Bamikole, et al., 2004). In a situation where grasses harvested prior to maturity are stored as silage there is a need to know if the nutrient content can be retained and at what age can this be best achieved. In this study therefore, the chemical component and nutritive value of fresh and ensiled Guinea grass harvested at different stages of maturity was monitored.
The general objective of this study is to determine the effect of age of Guinea grass on the silage quality and nutritive value in West African dwarf goat (WAD). Specific objectives of this study are;
1. To determine the chemical composition of silage produced from Guinea grass harvested at different age.
2. To determine the in vitro gas production characteristics of ensiled Guinea grass at different ages.