Evaluation of the use of plastic syringes instead of glass syringes in the gas production technique for evaluating some feedstuffs

Determining the nutritional value of nutrients used in animal feed or diets using live livestock are costly and time-consuming; so, there is a great tendency to evaluate them using laboratory methods. Measurement of the gas production parameters from in vitro fermentation of feedstuffs was established by Menck et al. (1979). In this method, the fermentation of the feed sample and measurement of gas production parameters take place in glass syringes by a rotary incubator, which was positioned horizontally at specific locations to mimic ruminal conditions. In order to eliminate the disadvantages and improve the original method of gas production test proposed by Menek and Steingass (1988), several studies have been carried out by various researchers. Changing laboratory equipment’s of gas test was carried out mainly by Blümmel and Ørskov (1993), using a water bath or Bin Marie instead of a rotating incubator and the rotation of the syringes in the incubator was compensated by shaking the syringes by hand. In a report by Fedorak and Hrudey (1983), a simple method was used to measure the volume of produced gas using a graded petite-like, thin-walled glass tube attached to a culture medium containing bottle and based on the displacement of water inside the pet. In another report, Theodorou et al. (1994) also used a barometer to connect the hose to a bottle containing the culture medium to estimate the gas production. The cost of producing a rotary incubator for measuring the gas test with glass syringes is high and has the potential to be difficult to install and operate, due to the sensitivity and fragility of the syringes. It seems that most efforts of previous researchers have been based on the improvement and simplification of the original method. Glass syringes are an imported commodity and will cause the currency to exit the country; thus, replacing it with plastic syringes can reduce country's dependence on imports and reduce the costs of related research. A search of reliable scientific sources at home and abroad shows that there has been no report on the comparison of plastic syringes with glass in the gas production test. This study was conducted to evaluate the use of plastic syringes instead of glass syringes in the parameters of gas production of some feedstuffs.

The feedstuffs included alfalfa hay, perennial ryegrass, barley grain, corn grain, soybean meal, and rapeseed meal. Glass syringes and two types of plastic syringes of type I and II (high and medium quality respectively) were used. The gas production parameters were determined using commonly used models and the data were analyzed based on a completely randomized design.  Menke et al. (1979) method was used to measure the amount of gas production. The amounts of short chain fatty acids, digestibility of dry matter, organic matter in dry matter, and metabolizable energy were estimated using related equations (Menke and Steinggass, 1988). The data obtained from the method of gas production were analyzed based on a completely randomized design with repeated measurements design using SAS (2003) software.

The results of the net volume of gas produced from the feedstuffs (except barley grain) at 6 h did not show a significant difference between glass syringes and type I plastic syringes (P>0.05). There was no significant difference between the three types of syringes at 6 h in rye forage. At 24 h, there was a significant difference between glass syringes and plastic syringes in terms of gas volume (P<0.05), except for corn grain and rapeseed meal. At 96 h, there was a significant difference between glass and plastic syringes in terms of volume of gas production (P<0.05), except for rapeseed meal. Between glass syringes and plastic syringes type I and II, there was a significant difference in terms of gas production potential for all feedstuffs (P<0.05), except for rapeseed meal. Overall, these results showed that the volume of gas production in type I and type II plastic syringes was lower than that of glass syringes. There was a significant difference between the glass and plastic syringes of types I and II in terms of A or gas production potential (P<0.05), except for rapeseed meal. The potential of gas production was lower than that of glass syringes, similar to the volume of gas production in plastic syringes, especially its second type. There was no significant difference between the glass and plastic syringes of the first type in terms of c parameter or gas production rate, except for alfalfa hay and barley grain. There was no significant difference between type I glass and plastic syringes in terms of lag or lag time for all feedstuffs, except for barley grain. In terms of lag time, there was a significant difference between type II syringes and plastic syringes for soybean meal and rapeseed. However, for alfalfa hay, ryegrass, barley grain, and corn grain, there were no significant differences in terms of Metabolizable energy, short-chain fatty acids, and organic matter digestibility estimated from feedstuffs showed that there was no significant difference between glass syringes and plastic syringes of type I only for corn grain and canola meal. High correlation coefficients (r = 0.90 to 0.98) were found between the results of glass syringes with type I plastic syringes.
When feed is fermented with ruminal liquid in vitro conditions, its carbohydrates are converted to short-chain fatty acids such as acetic, propionic, butyric, valeric, lactic, etc., and gases (such as carbon dioxide and methane (Blümmel and Ørskov, 1993). However, regression relationships do not take into account the different physical properties of feeds in the rumen, as well as digestive differences in the lower parts of the gastrointestinal tract. But, regression relations estimate only the total amount of volatile fatty acids (Parand and Taghizadeh, 2011, Mirshadi et al., 2016).

The results showed that the measured volumes of gas production and estimated parameters in plastic syringes, especially its second type, were lower than those of glass syringes; though, in some feeds inclusions of maize seed and rapeseed were similar in most cases to glass and plastic syringes of the first type. The high correlation coefficients between the results of the syringes indicate that it is possible to develop mathematical models for estimating the desirable results when using plastic syringes. However, more research is needed and more feedstuffs should be used to provide regression models to estimate the results equivalent to glass syringes, when using plastic syringes. The lack of significance of the results in some feedstuffs and the high correlation coefficients between the results of the syringes show that it is possible to replace high-quality plastic syringes instead of glass syringes.