Abstract: This study was performed to evaluate the effect of different feeding systems (choice feeding and conventional system) on performance and emission of carbon dioxide (CO2) and enteric methane (CH4) in dairy Awassi ewes. One chamber was equipped with gas analyzers to measure CH4 and CO2 for 23 h day-1. In total, 16 ewes were used. The ewes were divided into two groups: the Free Choice (FC) group received feed ingredients separately and the Total Mixed Ration (TMR) group received a standard mixed concentrate: forage diet in a ratio of 60:40. The results showed no significant differences between treatments in performance parameters. However, the results of CH4 and CO2 measurement indicated significant differences between groups in the amounts of CH4 and CO2 produced per kg dry matter intake. The ewes in the FC group produced less CH4 per animal than the ewes that received the TMR system. In ewes on the FC system, the level of propionate was greatly increased relative to the total VFA components. There were no significant differences in ruminal pH and acetate level between treatments. The results indicate that the FC system may be a potential mitigating effect on enteric emission of CH4 and CO2.
INTRODUCTION
Ruminants typically lose 2-12% of feed gross energy as emissions of methane (Johnson et al., 1993). Nutritionists have focused on finding methods to mitigate methane emission because of its inefficiency on account of feed conversion ratio and the role of methane in global warming. In the ruminant nutrition, decreased production of CH4 can represent an improvement in feed efficiency. Thus, mitigating CH4 losses from ruminants has both long-term environmental and short-term economic benefits. Carbon dioxide and methane are the main greenhouse gases related to animal nutrition and methane has greater global warming potential than carbon dioxide (IPCC, 1996). The mean volume of methane produced by a dairy ewe each year is 17.8 m3, which is similar to that of a dairy goat (Vermorel, 1997).
The one source of CH4 is hydrogen, which is produced from fermentative reactions in ruminal fluid; excess hydrogen must be utilized in order to decrease the production of methane. Improvements in ruminal fermentation that favor propionic acid may also allow a decrease in methane production, because propionic acid contains more hydrogen than other Volatile Fatty Acids (VFA). Some feed additives (oils, methane inhibitors, ionophores, organic acids, etc.) have been shown to decrease CH4 emissions (Johnson and Johnson, 1995; McGinn et al., 2004). Based on these results, addition of oil to the diet can be used to decrease CH4 emissions, but the total energy intake must not be increased because of its negative effects on usage of fiber. Given that prophylactic usage of antibiotics is not permitted in Europe farming systems, they have been limited their usage in farming. In any event, the effect of ionophore antibiotics on emission of CH4 is short lived (Johnson and Johnson, 1995). The pattern of ruminal fermentation may be changed by the use of different feeding strategies that encourage effective utilization of the feed ingredients. Feeding systems that allow choice may provide one mechanism by which ruminants can alter consumption time, meal size, meal length and meal order to weight the balance of ruminal fermentation in favor of the propionic acid ratio (Askar et al., 2006). In addition, a higher content of fibrous carbohydrates (NDF) in diets of low feeding value has been shown by Moe and Tyrell (1979) to increase the methane emitted per unit digested. An increase in the concentrate ratio may also improve the nutritional status of sheep by standardizing consumption of energy, protein and mineral and will also give an opportunity to increase the ratio of propionic to acetic acid. But there is a risky of metabolic disorders in Standard Mixed Ratios (SMR) having high concentrate: forage. Ruminants can learn the physiological consequences of ingestion of particular foods and can recognize the feed ingredients offered as free choice according to their post-ingestive effects (Provenza, 1995; Yurtseven and Gorgulu, 2004). Thus ruminants can consume high concentrate feed without suffering from metabolic disorders (Fedele et al., 2002; Yurtseven and Gorgulu, 2004). The aim of the present study was to evaluate the effect of two different feeding systems (a free choice feeding system and a conventional diet) as a factor to mitigate enteric emissions of CH4 and CO2 in Awassi dairy ewes.
MATERIALS AND METHODS
Animals and Diets
The study was carried out at the Sanliurfa Harran University in the Southeast
Anatolian Region of Turkey, which lies on longitude 38°46' E and latitude
37°08' N. The mean temperature and relative humidity for the experimental
period (from the end of May through June) were 32.12°C and 25.3%. The experiment
was conducted with a total of 16 Awassi dairy ewes in their second and third
lactation, each with a single lamb. The ewes were allocated after weaning of
their lambs to two experimental groups (free choice feeding-FC and total mixed
ratio-TMR), with eight replicates comprising one ewe in a 2.25 m2
(1.5x1.5) pen. The ewes were assigned to each treatment according to their live
weight (FC:51.75±7.6 kg; TMR: 52.17±18.2 kg) and milk yield (FC:
802.5±242.8 g day-1; TMR: 804.75±310.5 g day-1)
at the beginning of the experiment. Each pen contained a 15 L bucket for fresh
water, which was available during the entire experimental period (training and
testing). The feed fed by free choice was divided into six equal parts so that
the feed ingredients were presented separately, but ad libitum. The experiment,
including a two-week preliminary period, lasted for a total of 4 weeks plus
two days. During the second week of the preliminary period, the ewes of the
Free Choice (FC) feeding group were given the opportunity again to experience
the ingredients that were subsequently given as choices. During this training
period, lucerne straw was available at all times and the other ingredients (corn,
barley, soybean meal (SBM), cottonseed meal (CSM) and wheat bran) were offered
alternately every six days for a period of 14 days. Each feed ingredient, except
alfalfa hay, was mixed with 1.33% limestone, 1% salt and 0.11% vitamin-mineral
mixture in order to ensure adequate intake of micronutrients and also to prevent
any possible effect of micronutrients on selection of feed ingredients. The
Total Mixed Ration (TMR) group received compound feed supplied as a concentrate
and lucerne hay, made from hay by chopping to lengths of 1-2 cm, as roughage
were used in the experiment. The composition and nutrient contents of the TMR
diet, based on 60:40 concentrate: forage. The metabolizable energy content of
the diets was calculated based on the values published by National
Research Council (1985). Each of feed ingredients given to FC groups and
TMR was added daily but residual feed checking control was done manually by
first and second half of the experiment to prevent any stress changing feeding
behavior especially in FC groups. Live weight changes of both groups were measured
at the beginning and end of experiment in order to see any effect of feeding
system on live weight.
Methane and Carbon Dioxide Measurement: Respiration Chamber
During the second 14 days of the data collection period, the ewes were taken
into one chamber one by one with own manger. In experiment, all of the animals
(16) in each treatment group were used and CH4 measurements were
made using a ventilated respiration chamber. The respiration chamber formed
a closed system in which the fresh intake airflow, based on a continuous system,
was controlled. The calculation of the volume of methane emissions was based
on the concentration measured in the airflows into and out of the chamber. The
chamber was 2.5x3.9x3.7 m wide, tall and deep, respectively. The walls and windows
of the chamber were insulated to prevent risk of gas leakage. During the experiment,
no significant difference was seen between the outside and inside barometric
pressure, which would have encouraged leakage of gas (941-952 MB). Ventilation
of the chamber was provided by means of individual fresh air intake and chamber
exhaust ducts. The ducts were 10 cm diameter and 30 cm long. Fresh intake and
exhaust air (90 m3 h-1 = 0.25 m3 sec-1)
was fed directly into the duct, which contained a pair of fans of the same turning
velocity (31.8 m sec-1). The chamber was equipped with a dedicated
infrared gas analyzer to detect CH4 and CO2. The ewes
were left with their feed trough in the chamber for 23 h, from early morning
(08:30) until the following day (07:30) in order to measure differences according
as time and feeding behavior between the emissions during day and night. The
concentration (ppm, on a volume basis) of CH4 in the intake and exhaust
ducts of chamber was measured by pumping a sample of the air stream in each
duct through the infrared gas analyzer. The level of CH4 and CO2
emission generated from the chamber (FCH4, g sec-1)
was calculated via data loggers for each 3-min period from the concentrations
in the fresh air intake and the chamber exhaust (Ci and Ce,
respectively; ppm) (McGinn et al., 2004).
where, Ve and Vi are the mean air velocity (m sec-1) in the fresh air and the chamber exhaust, MW is the molecular weight of CH4 (16 g moL-1) or CO2 (14 g moL-1), P is barometric Pressure (Pa), R is the universal gas constant (8.31 J moL-1 deg K-1), T is the temperature of the air stream (°K) and A is the cross-sectional area of the duct (0.0250 m2).
On the following day the ewes were removed from the chamber and the air inside the chamber was ventilated for one hour. Manure and urine were removed and the chamber floor was prepared for new gas measurements the following day. Thereby, gas emissions from animals from different groups (FC vs. TMR) were analyzed in the different time but during the experiment, the temperature and barometric pressure inside and outside the chamber were recorded for each 3 min period by data loggers. The concentrations of CH4 and CO2 were calculated after adjustment (P/RT) for the temperature, humidity and barometric pressure. The values shown also include emissions of gas from the manure.
Ruminal Fermentation Measurement
Ruminal pH was measured once for four animals per group 32th day after the
experiment, in order to prevent changes in their feeding behavior and diet selection
caused by stress. A rubber tube was inserted into the rumen via the esophagus
5 h after the feeding and a sample of the ruminal contents (250 mL) were removed
using a manual pump. After sampling per content, rubber tube was wiped out again
and again to prevent any contamination with saliva. The pH was measured immediately
using a pH meter. The ruminal contents were filtered through four layers of
cheesecloth. After filtration, the filtrate was centrifuged at 3000 x g for
15 min according to the method of Erwin et al. (1961).
Five milliliters of the filtrate was combined with 1 mL of 25% (w/v) metaphosphoric
acid and stored frozen (-25°C) until VFA analysis.
Chemical and Statistical Analysis
The compositions of the feed ingredients were determined by the method of
AOAC (1998). The Neutral Detergent Fiber (NDF) and Acid
Detergent Fiber (ADF) were analyzed based on the method of Van
Soest et al. (1991) using an ANKOM fiber analyzer. The metabolizable
energy content of the diets was calculated based on the tabulated values published
by National Research Council (1985). Milk yield and feed
intake were determined every 2 weeks. The animals were milked by hand during
the morning and milk samples were analyzed for milk fat, total solid, ash, milk
protein, Non Protein Nitrogen (NPN) and casein nitrogen using a FOSS Milco Scan
FT120 (Denmark). The composition of TMR’s and the diet selected by the
ewes were compared by one sample t-test for independent samples of FC and TMR
in the Compare Means procedure of SPSS (SPSS, 2006). Independent
sample t-test was also carried out to determine the significance of the effect
of the treatments on the other performance parameter and cumulative standardized
fluxes of CO2 and CH4 according to temperature and barometric
pressure.
RESULTS
The components of the ration selected by the ewes are shown in Table 1 for the total experimental period because there were no significant differences between the first and the second half of the experiment.
| Table 1: | Compositions of the diets selected by Awassi ewes offered different grain and protein sources vs. TMR ration (DM basis) |
| ACalculation based on the values published by NRC (1985); BEach kg vitamin-mineral premix provides vit. A 8.000.000 IU; vit. D3 1.000.000 IU; vit. E 30.000 mg; Mn 50.000 mg; Fe 50.000 mg; Cu 10.000 mg; Co 150 mg; I 800 mg and Se 150 mg; *There is a significant difference between the two groups (p<0.05); **NP: Statistical analysis not performed because each feed ingredient in FC, except alfalfa hay, was mixed with limestone, salt and vitamin-mineral mixture in order to prevent any possible effect of micronutrients on selection of feed ingredients | |
The results showed that diet selection, with respect to consumption of feed ingredients and nutrient intake was different for the FC and the TMR rations. The ewes receiving feed ingredients as free choice selected a ration that contained more maize (FC: 28.38; TMR: 13.56%) and cottonseed meal (FC: 18.82; TMR: 3%) but less wheat bran (FC: 8.56; TMR: 16%) and lucerne hay (FC: 18.96; TMR: 40%) compared with the TMR group (p<0.05). The differences for barley and soybean meal were not statistically significant (p>0.05). The different composition of the ration in the two groups affected the nutrient composition of the diet. The FC group selected a ration with a higher content of dry matter (93.3 vs. 90.9%), metabolizable energy (2.57 vs. 2.38 Mcal kg-1) and ether extract (3.6 vs. 2.5%). Given that the ewes in the FC group preferred a ration with a lower content of lucerne hay, this group consumed a ration with a lower ADF (19.22 vs. 22.69%) and NDF (28.66 vs. 34.31%). However, there were no differences between the two groups in the protein and crude fiber content of the diet. The ewes in the FC group consumed more dry matter, metabolizable energy, digestible energy, crude protein and crude fat than the ewes in the TMR group (Table 2, p<0.05).
The feeding method had no significant effects on milk yield, 4% fat corrected milk yield or milk components (p>0.05). However, the efficiency of milk production deteriorated in the FC group and the ewes in the FC group consumed more dry matter per kg milk production than those that received the TMR (FC 4.16 vs. TMR 2.55). Ruminal pH values were not affected by the treatments (Table 3). Although, there was no difference in the proportion of acetate between the treatments, the proportion of propionate and butyrate and the acetate:propionate ratio differed (p<0.05). Ewes fed separate feed ingredients (the FC group) had higher propionic acid concentrations than those in the TMR group. Consequently, the acetate:propionate ratio averaged 3.46 for the FC treatment compared with 4.93 for the TMR treatment (p<0.05). The CH4 and CO2 emissions per animal were not significantly different, but tended to be lower in the FC group (p>0.05); however the emission value per kg dry matter intake decreased significantly in the FC group (FC 10.65 vs. TMR 18.12 g DMI-1).
| Table 2: | Dry matter and nutrient intakes and milk yield and composition of Awassi ewes fed using different methods |
| DMI: Dry matter intake SEM: Standard error of the mean,. ME: Metabolizable energy, DE: Digestible energy, CP: Crude protein, FCM: 4% fat corrected milk, MPE: Milk production efficiency, LWC: Live weight change, TS: Total solids, SNPN: Nonprotein nitrogen | |
| Table 3: | CO2 and CH4 emissions and ruminal fermentation variables for Awassi ewes offered different grain and protein sources vs. TMR diet |
| DMI: Dry matter intake, VFA: Volatile fatty acids, SEM: Standard error of the mean | |
DISCUSSION
Diet Preference and Performance
The ewes in the FC group selected a diet that contained a higher concentrate
ration than that received by the TMR group. There were important differences
between groups in the energy, ADF, NDF and ether extract of the diets, but not
in the level of protein and crude fiber. The diets consumed by the ewes in the
FC group contained less lucerne hay than the TMR diet, thus their diet had lower
bulk and higher dry matter content than the TMR diet. The changes in diet preferences
in FC group according to the TMR (Table 1) diet in the present
study could be also a reflection of the freedom in feed intake and feeding behavior
of the sheep with environmental conditions. The ambient temperature and relative
humidity were higher (42.9 vs. 21.7°C and 29.1 vs. 23.4%) in the second
half of the experiment. It is well documented that ruminants increase their
intake of concentrate and reduce their intake of roughage to minimize the heat
increment in their bodies under high environmental temperature, when concentrate
and roughage are available as free choices (Fedele et
al., 2002; Yurtseven and Gorgulu, 2004, 2007).
Yurtseven and Gorgulu (2004) suggested that goats having
free access to feed ingredient tended to decrease forage intake as the temperature
was in progress. This could be also explained by the changes in feeding behavior
(the order of consumption of feed ingredients, the interval between meals, the
meal size and meal length, etc.) of the ewes that had free access to feed ingredients
(Abijaoude et al., 2000; Gorgulu
et al., 2003). In this experiment, no metabolic disorder derived
from feeding of a high concentrate ration was seen in the FC group during the
experiment. The results also showed that the ewes in the FC group consumed a
larger amount of corn and CSM and less wheat bran and lucerne hay than those
that received the TMR diet. The present study also showed that the ewes in the
FC group consumed more corn than barley, probably because of the high fiber
content and lower energy level of barley. The FC ewes ate a diet with lower
ADF and NDF content because they consumed a larger amount of grain and cottonseed
meal during the experiment compared with the TMR group. Small ruminants have
a lower capacity to digest forage than larger ruminants. Their gastrointestinal
size and capacity may also limit the intake and utilization of a TMR, because
this diet contains more forage.
The experimental data showed that the protein deficiency in the FC group that originated from consumption of less lucerne hay was compensated for by the increased consumption of CSM. Although, SBM and CSM have similar contents of rumen undegradable protein, when SBM was presented as a choice with CSM, the ewes consumed almost 6.6 times more CSM than SBM. This is probably, a reflection of the high protein content of SBM (51.94% CP) and the ewes fed FC could meet their protein requirements by consuming less SBM than CSM (21.4% CP). The high protein content of SBM may have also induced negative post-ingestive feedback based on high protein (Provenza, 1995) and thus it was consumed less by ewes in the FC group. The ewes given free access to feed ingredients had higher daily dry matter intake (3.1 vs. 2.16), therefore, they consumed higher levels of nutrients (ME, CP, ADF, NDF and ether extract) compared with the ewes that received the TMR (Table 2). It is concluded that the feeding behavior of ewes consuming an alternative fiber source to lucerne hay, such as CSM, is a reflection of resistance to the potential risk of acidosis. These results suggest that when given a choice of feeds, ruminants alter their diet selection to attempt to attenuate acidosis (Keunen et al., 2002).
Milk yield and the components of milk, especially the N fraction, were not affected significantly by the treatments. The results are attributed to high variation in terms milk yield among groups and some ewes have dried early than target date. There was no important difference in milk NPN content between the FC and TMR groups. It was revealed that the ewes in the FC group selected a synchronized diet from among the different energy and nitrogen sources. Gorgulu et al. (2008) reported that does given free access only to SBM with barley produced higher milk NPN, although all does had similar protein intake. This probably resulted from inefficient use of ammonia nitrogen released from the highly degradable soybean protein used in their experiment. However, in the present study, the sheep used alternative energy and protein sources (corn and CSM) to provide a synchronized diet (Table 2).
Methane Emission and VFA Concentrations
A diet selection that leads to substantial reductions in CH4
emissions may maintain an optimal rumen ecosystem. Although, the reductions
in CH4 and CO2 were small on the basis of an individual
animal and were not statistically significant, the decrease in energy lost as
CH4 was significant and was the result of higher feed intake in the
FC group compared with the TMR group. Johnson et al.
(1993) reported that, as the daily amount of feed eaten by any given animal
increases, the percentage of the dietary gross energy lost as methane decreases
per unit of intake. However, in our study, the FC system had a significant effect
on the ruminal content of VFA and clearly decreased the acetate:propionate ratio.
The ewes in the FC group consumed larger amounts of concentrate, which contained
readily fermentable components such as starch. Daily CH4 emissions
per kg dry matter intake were decreased significantly in the FC group. The differences
between the two groups are attributed to the differences in composition of the
diets. This agrees with another report in which the net production of VFA was
highly correlated with diet composition (Castillejos et
al., 2005). Moe and Tyrell (1979) found fermentation
of soluble carbohydrate to be less methanogenic than that of cell wall carbohydrates.
On the other hand, the reduction in ruminal fiber intake in the FC group probably
accounted. Although, ruminal fiber digestion was not measured for a large proportion
of the reduction in CH4 emissions. Although, ruminal fiber digestion
was not measured directly in this study, other variables (for example the acetate:propionate
ratio) indicated a considerable reduction in ruminal fiber digestion. These
data suggest that the FC system had a potential mitigating effect on enteric
methane emissions in dairy ewes. These results also indicated that there was
a relationship between dry matter intake and emission of methane. The values
of daily methane emission showed a similar trend with time and followed the
feeding and digestive processes. For example, after each feed the emissions
of CO2 and CH4 increased sharply and then slowly decreased
overnight to the lowest values at 08:30 h, just before the morning feed (Fig.
1).
Although, emission of CH4 reflects the fermentation activity of the digestive tract, the output of CO2 is primarily an indicator of the respiratory activity of the ewes. For this reason, in the experiment, the level of CH4 emission was higher than that of CO2 (Fig. 2). A similar diurnal pattern of gas emission was observed by Kirchgessner et al. (1991). In these trials also, CH4 emissions increased after feeding and then declined until the next fresh feed was distributed.
| Fig. 1: | Diurnal CH4 (g sec-1) emissions profiles from ewes receiving FC and TMR diets recorded over the experimental period (this figure based on data of 8 animals/treatment) |
| Fig. 2: | Diurnal CO2 (g sec-1) emission profiles from ewes receiving FC and TMR diets recorded over experimental period (this figure based on data of 8 animals/treatment) |
Figure 1 shows a clear pattern throughout experiment CH4 emission reaching a peak at or around sunset and then falling through the night to a minimum at dawn. Feeding behavior was not assessed in the present studies. However, the pattern of CH4 emission is certainly compatible with the feeding behavior: from sunrise, as feeding activity increased so did CH4 emission, with the accumulation of ingesta in the rumen. Later, after sunset, feeding gave way to rumination or idling and emissions fell as the content of the rumen was reduced. Lockyer (1997) also found peaks of CH4 emission during daylight periods in grazing sheep. Present study has shown that CH4 emissions from sheep may be linked to diurnal patterns of feeding behavior and to changing levels of dry matter intake.
The ecosystem of the rumen microbial flora was not investigated in this study because the experiment focused especially on the measurement of methane emissions. However, it is well known that cellulolytic microbes tend to diminish in the presence of competitive substrates such as starch. The results showed that there was an important relationship between ruminal VFA and ruminal production of methane. The decreased production of methane by ewes that received separate feed ingredients may be related to an increased rumen turnover ratio and digestibility of organic matter in the FC group. In addition, the CSM may have affected the dry matter intake and so ruminal turnover ratio for ewes in the FC group may have been affected positively. Redman et al. (1980) reported increased digestion of organic matter in the reticulorumen of steers fed oaten chaff, as a result of protein supplementation. Voluntary intake of low quality forages may be enhanced by ruminal escape of supplemental protein and its subsequent metabolic effects on voluntary intake (Kempton et al., 1977). The methanogenic bacteria are the most sensitive to changes in the rumen environment and are affected by many dietary factors. Given that the methanogens are the principal utilizers of hydrogen, their welfare affects ruminal and enteric metabolism and carbon balance. Increased rumen turnover may also restrict methanogens through competition for sufficient generation time. Reduction of methanogenesis tends to promote hydrogen production and shifts the carbon balance toward propionate (Van Soest, 1994). Ruminal pH values were not affected by the treatments in the current study, although the ewes in the FC group selected a diet with a lower forage:concentrate ratio (21.4/78.6). Ruminal pH value was too low in both group and results indicated the effects of feeding system on ruminal pH to be minimal. This result may have been concluded that high concentrate ratio in FC and high ground (1-2 cm) forage in TMR. On the other hand, the rumen of a grain-fed dairy cow may show a reduction in cellulose digestion without any change in pH (Murphy, 1989) and this occurs even if the ruminal pH rises to 6. Total cellulolytic activity may be as high in the grain-fed animal as in the forage-fed animal.
Given that there is very limited information on the effects of FC systems on methane emission and rumen VFA content, the results of this study are important and indicate that FC systems have the potential to decrease methane production in the rumen. The factors that influence methanogenic bacteria include those that create a less favorable rumen environment for methanogenesis through an increased rate of passage and rate of digestion, depression of rumination and depression of rumen pH. In the FC system, these conditions may favor propionate-producing bacteria over acetate producers, making less hydrogen available to methanogens (Van Soest, 1994), as seen this experiment. Results also indicated that sheep having free access to feed ingredient tended to decrease forage intake in hot climate. Similar experiments in winter tide will improve the knowledge of sheep’s behavior and requirements and provide some useful information on how to modulate rations and methane emission. Additionally the experiment using low-roughage based TMR with free choice method will be required to prove that FC systems have a potential to decrease CH4 production in ewes.