Effluent control
Absorbing Silage Effluent Costs Money
The prevention of loss of effluent is an annual challenge when making silage. Silage effluent is not desirable for two main reasons
- it requires expensive storage facilities because of its corrosive nature and because it is a major source of pollution of watercourses if it escapes into rivers
- it represents a loss of nutrients during ensilage. The single biggest factor influencing the volume of silage effluent produced is the dry matter content of the grass at ensiling. Increasing the dry matter content of the crop to over 25 percent in order to eliminate effluent production is often not feasible in the soft climate of the Western regions of the British Isles.
Absorbent materials
At farm level the materials most commonly used to absorb silage effluent are sugar beet pulp, sugar beet pulp based products, barley and straw. Straw should not be placed in a layer on the floor of the silo as this can actually increase the flow of effluent from the clamp. The inclusion of chopped straw throughout the clamp will reduce the nutritive value of the silage produced, due to the inclusion of a material of low feed value. Absorbents based on sugar beet pulp generally have a greater capacity to absorb effluent than those based on cereals.Effluent production
Over three years sugar beet pulp and sugar beet pulp based additives (SBP) were applied to grass at ensiling at levels ranging from 30 to 150 KG of SBP / tonne of grass ensiled. It was evident that effluent retention decreased with increased level of inclusion of SBP and with higher grass dry matter, ranging from 1.3 to 0.3 litres effluent per kilogram of SBP. The influence of absorbent inclusion at 50, 100 and 150 KG SBP / t grass ensiled on effluent production, in one experiment.Although the inclusion of absorbent with grass ensiled at less than 20 percent dry matter reduced the total volume of effluent considerable quantities of effluent were still produced. For example, direct cut grass ensiled at 18 percent dry matter might be expected to produce in the region of 160 litres effluent / tonne grass ensiled. The addition of 50 KG sugar beet pulp / tonne of grass would be expected to reduce effluent by approximately 40 percent. The application of absorbent often reduces effluent flow to a greater extent during the first few days immediately following ensiling. This can ease the pressure on storage facilities and allow a little more time in which to get tanks emptied.
Silage fermentation
The inclusion of absorbent materials with grass at ensiling should improve silage preservation under difficult ensiling conditions as a result of an increase in dry matter content of the material ensiled and, in the case of materials with high water soluble carbohydrate content, from the provision of additional substrate for lactic acid bacteria. The results at Greenmount showed absorbent treated silage to have improved silage fermentation characteristics when compared with untreated silage. Similar improvements in fermentation have also been observed by other workers. However, high levels (in the region of 100 KG SBP / tonne grass) of absorbent inclusion would be necessary to counteract difficult ensiling conditions.In-silo losses
The inclusion of absorbent generally reduced in-silo dry matter losses. Losses of dry matter in effluent were reduced with increasing level of absorbent inclusion, reflecting the smaller volumes of effluent produced. There was, however, a tendency for dry matter lost as visible waste to be increased in absorbent treated silages, suggesting that such silages are more prone to aerobic deterioration. Animal production
There have been suggestions that the incorporation of absorbent products into grass at ensiling has resulted in better animal performance and food conversion efficiency than when a similar quantity of the same absorbent product has been fed with untreated silage. Animal performance
In the work at Greenmount beef cattle offered silage treated with 50 KG SBP per tonne of grass ensiled had 13 - 25 percent higher intakes than those offered untreated silage. Cattle offered absorbent-treated silage without supplementation had 33 - 95 percent higher liveweight and carcass gains than those offered untreated silage without supplementation. As the inclusion rate of absorbent was increased, intake and liveweight gain were both increased. Feed efficiency
In order to determine how efficiently ensiled blends of absorbent were utilised untreated silage was also fed with absorbent offered as a supplement. The absorbent intakes from the ensiled blends were calculated assuming no loss of absorbent from the silo, as it was impossible to quantify the loss of absorbent in the effluent, as waste silage or through the fermentation process. This approach ensured that all of the absorbent applied to the grass at ensiling was accounted for. The calculations took account of total dry matter lost through effluent, fermentation and waste. In one experiment, involving fifty-six growing cattle, similar animal performance could have been achieved by feeding untreated silage with 1.18 KG DM absorbent or feeding silage containing 1.60 KG DM absorbent. This would indicate that 36% more absorbent was required to achieve similar levels of individual animal performance when it was included at ensiling rather than being offered as a supplement with untreated silage. In another experiment involving sixty finishing cattle, up to 21 percent more absorbent was required to produce similar outputs of beef per unit of grass ensiled when the absorbent was ensiled with grass rather than being offered as a supplement with untreated silage. In these two experiments absorbent inclusion rate ranged from 30 - 70 KG per tonne of grass. In a further experiment where sugar beet pulp was included at 50, 100 and 150 KG per tonne of grass ensiled, and silage fed to fifty-six finishing beef cattle, absorbent was also used less efficiently when low levels of absorbent were included. However, at higher levels of absorbent inclusion the overall efficiency of feed use was higher when the absorbent was ensiled rather than offered as a supplement.
These results are contradictory to much of the work reported in GB but are in general agreement with the work at the Agricultural Research Institute of Northern Ireland where absorbent treated silages were offered to dairy cows.
Conclusions
Although the use of sugar beet pulp based absorbents may appear attractive because of the possibility of reducing effluent production, improved fermentation, lower in-silo DM losses, higher intake and daily liveweight gain there are a number of drawbacks. Absorbent is bulky and cumbersome to apply, occupies considerable space and generally slows down the rate of filling the silo. The purchase of absorbent can represent a considerable expenditure although this may be partly offset against the cost of other silage additive. The biggest drawback is the apparent reduction in overall feed utilisation when applied at moderate levels of inclusion, when compared to feeding the absorbent as a supplement to untreated silage. Although feed efficiency is good at high absorbent inclusion rates, application of 100 KG and above are unlikely to be used in practice as a result of cost and physical handling difficulties.