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Effect of refined soy oil or whole soybeans on intake, methane output, and performance of young bulls¹

UCD School of Agriculture, Food Science and Veterinary Medicine, University College Dublin, Lyons Research Farm, Newcastle, Co. Dublin, Ireland

	Abstract

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
An experiment was conducted to establish the effects of feeding refined soy oil (RSO) or whole soybeans (WSB) containing soy oil on DMI, animal performance, and enteric methane (CH₄) emissions in young bulls. Thirty-six Charolais and Limousin cross-bred, young beef bulls (338 ± 27 kg of BW, 218 ± 17 d of age at the beginning of the experiment) were blocked by BW, age, and breed before being assigned in a randomized complete block design to 1 of 3 experimental treatments (n = 12). The experimental period lasted for 103 d, with enteric CH₄ output recorded for 2 periods of 5 consecutive days on d 37 to 41 and d 79 to 83. The 3 dietary treatments consisted of a barley/soybean meal-based concentrate with 0 g/d of RSO; oil from WSB as 6% of DMI (WSB treatment); and oil from RSO as 6% of DMI (RSO treatment). Each diet had a 10:90 forage:concentrate ratio, using barley straw as the forage source. Diet affected DMI (P 0.001) and GE intake (P < 0.05 during the CH₄ measurement periods), with the WSB treatment producing the lowest values. The addition of WSB decreased ADG (P < 0.05) compared with the RSO treatment. The WSB treatment also decreased (P < 0.05) average daily carcass gain (ADCG). Both the RSO and WSB concentrates decreased (P <0.05 to P < 0.001) daily enteric CH₄ output when expressed in terms of liters per day, liters per kilogram of DMI, percentage of GE intake, liters per kilogram of ADG, and liters per kilogram of ADCG. Diet had no effect (P = 0.557) on ruminal protozoal numbers. The reductions in enteric CH₄ were achieved at relatively high oil inclusion levels. Such oil levels have previously been reported to decrease DMI of high-forage diets, although no effect on DMI was noted with the low-forage diets fed in this experiment. This impact on DMI of high-forage diets may limit the range of diets for which this CH₄ reduction strategy may be applicable. The inclusion level of WSB in the current experiment (27%) was beyond the palatability threshold of the bulls used and resulted in a marked decline in intake and performance. Therefore, WSB may have a role to play in ruminant diets, but only at a reduced inclusion rate.

Key Words: beef bull • enteric methane • high concentrate diet • soy oil • whole soybean

	INTRODUCTION

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
The world’s climate has always varied naturally; however, there is recent evidence that the majority of the increase in the global temperature over the previous 50 yr is attributable to human activity (IPCC, 2001). Agriculture is the third largest (10%) contributor to the European Union’s (EU) greenhouse gas emissions (EEA, 2004). Agriculture is the single largest emitter of methane (CH₄), through enteric fermentation, accounting for 3% of total EU-15 greenhouse gas emissions (EEA, 2004). Methane accounts for 27% of US agricultural emissions (Environmental Protection Agency, 2003). The use of various plant oils to reduce enteric CH₄ emissions via ruminal defaunation, toxic effects on methanogens, or decreased diet digestibility has been widely reported (Machmüller et al., 1998; Jordan et al., 2004; Jordan et al., 2006). Jordan et al. (2006) identified that a level of 250 g of refined coconut oil/d fed to beef heifers (approximately 500 kg of BW) reduced enteric CH₄ emissions and had little effect on the fatty acid profile of the muscle produced in terms of human health. The objective of this experiment was to determine the potential of refined soy oil (RSO) or whole soybeans (WSB) to reduce CH₄ emissions, as this has not been reported in the literature. This paper deals with the effect of RSO or WSB on DMI, enteric CH₄ output, and animal performance in young Charolais or Limousin cross beef bulls fed a 10:90 forage:concentrate diet under ad-libitum conditions.

	MATERIALS AND METHODS

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
Animals, Experimental Design, and Treatments

The experiment used 36 Charolais or Limousin cross-bred beef bulls (338 ± 27 kg of BW, 218 ± 17 d of age at the beginning of the experiment), which were blocked by weight, age, and breed. Bulls were assigned in a randomized complete block design to 1 of 3 experimental treatments (n = 12). The experimental period lasted for 103 d, with enteric CH₄ output recorded for 2 periods of 5 consecutive days on d 37 to 41 and d 79 to 83. Half of the bulls (blocks 7 to 12) began and finished the experiment 9 d after the first group. This was to facilitate CH₄ measurements, which could only be carried out on half the bulls at any one time. The 3 dietary treatments were a barley/soybean meal-based concentrate with 0 g/d of RSO (C); oil from WSB as 6% of DMI (WSB treatment); and oil from RSO as 6% of DMI (RSO treatment), contained within a diet having a 10:90 forage:concentrate ratio and using barley straw as the roughage source.

Housing, Feeding Regimen, and Slaughter

During the CH₄ measurement periods, bulls were individually housed and fed in tie-stalls. For the remainder of the experiment, 10 bulls/treatment were group-penned indoors on slatted flooring and fed individually using a Calan Broadbent Feeding System (American Calan, Northwood, NH), with the remaining 2 bulls/treatment group-penned indoors on slatted flooring.

Bulls were fed a diet with a 50:50 forage:concentrate ratio on d 1, composed of grass silage and the respective treatment concentrate. Thereafter, the forage proportion of the diet was decreased by 5% every second day until the target forage:concentrate ratio (10:90) was achieved and maintained for the remainder of the experiment. When a forage:concentrate ratio of 20:80 was achieved, grass silage was replaced by barley straw as the forage source.

Six concentrates were manufactured, 3 treatment concentrates (C, WSB, and RSO) and 3 treatment concentrates plus a proprietary mineral mix, to ensure daily mineral requirements were met (C + mineral, WSB + mineral, and RSO + mineral). The 6 concentrates were formulated to achieve the target inclusion level of oil from RSO or WSB (i.e., 6% of DMI), whereas the treatment plus mineral concentrates were formulated to provide the daily mineral requirements in 1 kg of the concentrate. All concentrates were formulated to be isonitrogenous and to contain calcium, phosphorous, and sodium at a rate of 8, 6, and 2 g/kg as fed, respectively.

Immediately after weighing of orts each morning, 1 kg of the appropriate treatment plus mineral concentrates were fed (i.e., C + mineral, WSB + mineral, and RSO + mineral). When all of the treatment plus mineral concentrates were consumed, the remaining daily roughage and treatment concentrate allowance was fed. The ingredient proportions of the 6 concentrates are shown in Table 1. At the end of the experiment, the bulls were transported to a commercial slaughter facility and slaughtered immediately.

Intake. Dry matter intake was determined by weighing in and weighing out, once daily, the feed offered for the individually fed bulls, and correcting for the DM content of each dietary component. Feedstuffs offered were sampled daily. Weekly samples of the concentrates were compiled and stored at –20°C. Feed refusals were sampled twice weekly, separated by hand into forage and concentrate components, and composited by week after determination of DM (separately on both forage and concentrate components). For calculation of GE intake (GEI), it was assumed that the GE of the concentrate and forage orts were the same as the offered feeds. Forage DM, oven dried at 55°C for 72 h, was determined daily for fresh forage. Feed samples collected daily during the experimental period were pooled to provide 3 samples; d 1 to 33, d 34 to 66, and d 67 to 103, for subsequent chemical analysis.

Enteric Methane Output and Ruminal Protozoal Population. Daily CH₄ emissions were measured from d 37 to 41 and d 79 to 83 using a modification of the SF₆ tracer-gas technique of Johnson et al. (1994), as previously described by Lovett et al. (2003). The 36 bulls were separated into 2 groups for the purpose of CH₄ measurements. Bulls in blocks 1 to 6 were moved to the tie stalls on d 34 of the experimental period, with CH₄ emissions beginning 3 d later and lasting 5 d. Bulls in blocks 7 to 12 were moved to the tie stalls 1 d after the first group returned to their original housing, and they also had 3 d to acclimatize before CH₄ measurements began.

The same procedure was followed for the CH₄ measurements from d 79 to 83. Beginning and finishing the experiment 9 d later for bulls in blocks 7 to 12 than bulls in blocks 1 to 6 meant that CH₄ measurements took place after the same duration of experimental feeding for all bulls. Moving the bulls to a different location for CH₄ measurements placed no noticeable stress on the bulls, and their DMI was slightly greater during the CH₄ measurements periods than during the full experimental period (Table 2). For each day during the measurements, background levels of CH₄ and SF₆ were measured by placing 3 sampling kits (identical to those used on the bulls except that no filter was attached) at strategic locations in the building, which was naturally ventilated. The CH₄ and SF₆ concentrations in the bulls’ samples were subsequently adjusted for these background levels.

Animal Performance. Average daily gain was calculated as the difference between the initial BW and the final BW divided by the total number of days of feeding (103 d). Live-weight measurements were the average of 2 weights taken before feeding on consecutive days. Average daily carcass gain (ADCG) was calculated as the difference between the initial carcass weight (determined as 0.51 of the initial BW) and the final cold carcass weight, divided by the total number of days of feeding. Efficiency of gain was calculated as daily kilograms of gain/kilogram of feed intake, and carcass G:F was calculated as ADCG/daily DMI.

Cold carcass weight (98% of hot carcass weight), carcass conformation, fat score [based on the EU beef classification system, with 5 carcass classification grades (E, U, R, O, and P) and 6 fat grades (1, 2, 3, 4L, 4H, and 5), determined subjectively by a Department of Agriculture and Food official], and dressing percent (cold carcass weight/final BW) were determined immediately postslaughter. The kidney and pelvic fat were removed from the bulls at slaughter and weighed.

Laboratory Analysis

Dried feed samples were ground in a hammer mill fitted with a 1-mm screen before being analyzed in duplicate. Crude protein concentrations of the straw and concentrates were determined as N x 6.25 using a Leco FP 528 (Leco Instruments UK, Ltd., Cheshire, UK) according to the method of Dumas (AOAC, 1990). Crude protein concentration of fresh grass silage was determined in duplicate as Kjeldahl N x 6.25 using a Buchi 435 digestion unit and a Buchi 323 distillation unit (Buchi, Postfach, Flawil/Schweiz, Switzerland) according to AOAC (1990). Crude fiber of the concentrates was determined by the Weende method (AOAC, 1990), whereas NDF, ADF, and ADL were determined using a Fibertec system (Tecator, Hoganas, Sweden) according to the methods of Van Soest (1973) and Van Soest et al. (1991). Ash concentration was determined after ignition at 550°C for 4 h in a muffle furnace and was used to calculate OM. The GE of the concentrates was determined using a Parr 1201 oxygen bomb calorimeter (Parr, Moline, IL), and the GE of the grass silage was determined according to the method of Porter (1992). Ether extract of the concentrates was measured using a Soxtec instrument (Tecator, Hoganas, Sweden).

The buffering capacity of the fresh grass silage was determined by the method of Playne and McDonald (1996), whereas NH₃N concentrations were determined using a modification of the 5.5.2 distillation method (EC, 1984). Dry matter concentrations of the concentrates were determined in an oven at 104°C for a minimum of 16 h. Concentrations of CH₄ and SF₆ in breath were determined by gas chromatography using a Varian 3800 gas chromatograph (Varian, Mulgrave, Australia) as described by Lovett et al. (2003). The relative molar concentrations of the VFA (acetic, propionic, and butyric) in the ruminal fluid were determined by gas chromatography (Varian 3800) using a CP-wax 58, 25 m x 0.53 mm capillary column (Varian), according to the method of Porter and Murray (2001). Rumen ciliate protozoal numbers were determined using a 0.1-mm-depth, Bürker counting chamber (Rudolf Brand, Wertheim, Germany), with duplicate counts carried out for each sample.

Statistical Analysis

The treatment effect of feeding RSO or WSB on DMI and GEI, and, for the CH₄ measurement periods, CH₄ output (liters per day, liters per kilogram of DMI, liters per kilogram of ADG, liters per kilogram of ADCG, and as a percentage of GEI in megajoules per day) were estimated by REML. The model equation for the response from the mth animal in the ith block, receiving the jth level of the diet treatment on the kth day of the lth period, was as follows:

where y_ijklm is the response; µ is the overall constant, or intercept; B_i models the effect of the ith block; T_j models the effect of the jth level of the dietary treatment; D_k models the effect of the kth day; P_l models the effect of the lth period; a_m represents random effects [such that a_m N(0, ) for all m] that model the effect of the mth animal as well as accommodating the correlation between the repeated measurements made on the same animal; ap_lm represent random effects [such that ap_lm N(0, ²_ap) for all l, m] that model the effect of the lth period within the mth animal as well as accounting for the correlation between the consecutive daily measurements taken on the same animal in any given period; and the _ijklm are the residual effects, such that _ijklm N(0, ²).

For variables that had no period effect (DMI and GEI for the entire experimental period, ADG, ADCG, G:F, carcass performance data, VFA, and protozoal numbers), ANOVA for a randomized complete block design was used. Means were compared using standard single degree of freedom tests, based on the estimated SED. All analyses were done using Genstat, version 6 (Lawes Agricultural Trust, 1999).

	RESULTS

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
The composition of the experimental feeds is shown in Table 1. The concentrates ranged in CP concentration from 191 to 230 g/kg of DM. The WSB and RSO concentrates had greater GE values (19.4 and 20.2 MJ/kg of DM for the RSO and WSB concentrates, respectively) than the control concentrates due to the greater oil concentrations. The ether extract content of the WSB concentrate was somewhat greater than expected and resulted in this concentrate having the greatest GE value of the 3 concentrates.

The bulls fed the diet containing WSB consumed less DM and GE during the CH₄ measurement periods and during the entire study compared with bulls fed the control and RSO diets (Table 2). The observed forage:concentrate ratio was greater (P < 0.001) for the RSO-fed bulls, but this difference was biologically quite small. For all treatments the forage:concentrate ratio was close to the target value.

There was no overall effect of diet on ADG (P = 0.07; Table 3). When treatment comparisons were carried out, ADG for the WSB treatment was decreased (P < 0.05) compared with the RSO treatment only. Carcass conformation score was decreased for bulls receiving the WSB treatment (P < 0.05) compared with bulls on the C diet. Also kidney and pelvic fat weight was increased (P < 0.01) for the RSO treatment compared with both other treatments. The addition of RSO or WSB had no effect (P > 0.05) on G:F, carcass G:F, dressing percent, and carcass fat score, but addition of WSB reduced ADCG (P < 0.05) compared with the other 2 treatments (Table 3).

	DISCUSSION

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

Reductions in DMI have been widely reported after the inclusion of high levels of oils to ruminant diets (Sutton et al., 1983; Sutter et al., 2000; Jordan et al., 2004). In the current experiment, the authors observed a reduction in DMI for the WSB treatment only. The absence of a reduction in DMI for the RSO bulls may be due to the low dietary fiber level reducing the impact of any reduction in fiber digestibility. Among the possible factors involved in the reduction in DMI when oil is fed is a decline in rumen protozoal numbers (Sutton et al., 1983; Machmüller et al., 2003), leading to an increased rumen retention time due to reduced fiber digestion and particle outflow rates (Demeyer, 1987). In the current experiment, the proportion of concentrate in the experimental diet was greater than 88%, thereby reducing the fiber content of the diet and the impact of any subsequent reductions in fiber digestion or rumen particle outflow rates. The reduction observed in DMI for the WSB treatment might be attributed to palatability. Felton and Kerley (2004) reported a linear decline in DMI with increasing levels of WSB inclusion and the inclusion level in the current experiment (27% of DMI) is in excess of the greatest level (24%) used in their experiment. Sieving of the concentrate orts (approximately 1 kg/d) from individual bulls during the CH₄ measurements revealed a doubling of the WSB concentration in the orts (61% orts vs. 30% feed offered) and suggests some avoidance of WSB by bulls for this treatment. The difference (P < 0.001) observed in forage:concentrate ratio was of a magnitude unlikely to reach biological significance and therefore should have no effect on animal performance.

Animal Performance

Whereas no overall significant differences were observed, when treatments were compared, the RSO treatment improved ADG compared with the WSB treatment. This improvement in ADG can be attributed to the greater DMI for the RSO treatment compared with the WSB treatment, a reduction in CH₄ energy loss, and/or the greater GEI for the RSO treatment. In line with the lower ADG, lower ADCG was observed for bulls on the WSB treatment. This decrease in carcass gain can be attributed to the lower DMI, smaller reduction in CH₄ energy losses compared with the RSO treatment, a reduction in the energy density of the feed consumed due to palatability problems with the WSB, or some combination of these factors. Despite the decrease in ADCG, carcass G:F for the WSB treatment was not affected due to comparable reductions in DMI for this treatment. The WSB treatment also resulted in a reduction in carcass conformation score compared with the C treatment only. This agrees with the previously recorded phenomenon of improving conformation score with increasing slaughter weight (Keane, 2003) and reflects the lower slaughter weight of the WSB bulls. The weight of kidney pelvic fat for the RSO treatment was increased over both the C and WSB treatments and is in agreement with Santos-Silva et al. (2004) who recorded a significant increase in kidney, knob, and channel fat after the addition of soy oil (8%) to the diet of finishing lambs. The high proportion of WSB, which were not consumed due to palatability problems (determined from sieving the orts during the CH₄ measurement periods), may explain the absence of an increase in the weight of kidney pelvic fat for the WSB treatment because daily oil intake was decreased by 10%.

Methane Output and Rumen Protozoal Population

Reductions in enteric CH₄ emissions have been widely reported after the addition of a variety of plant oils to the rumen (Czerkawski et al., 1966; Machmüller et al., 1998; Jordan et al., 2004). Oils rich in medium chain saturated fatty acids (e.g., coconut oil) have shown the greatest reductions in enteric CH₄ emissions followed by oils rich in polyenoic fatty acids (Machmüller et al., 1998). The reductions in enteric CH₄ in the present experiment using RSO, a plant oil rich in polyenoic fatty acids, are in agreement with those observed in vitro by Machmüller et al. (1998). Whereas the reductions (40%) in enteric CH₄ with RSO in the present experiment are comparable with those previously identified at this institute (Jordan et al., 2004) using coconut oil, it should be noted that a greater oil inclusion level was used in the present experiment (6.0 vs. 4.75% DMI). When WSB was included in the diet, the magnitude of the reduction in CH₄ (liters per day and liters per kilogram of DMI) was decreased, which may be attributed to less oil being consumed by the bulls due to the high level of WSB (60%) contained in the orts. In addition, when oilseeds have been added to the rumen, reductions in CH₄ have been lower due to the partial rumen protection of the oil (Machmüller et al., 2000). A significant period effect was recorded for CH₄ emissions in terms of liters per day. This reflects the high growth rate exhibited by the bulls on the high concentrate diet, which was accompanied by an increase in DMI, due to increasing body size, between periods (data not shown). The increase observed in DMI explains the lack of any period effect for CH₄ output in terms of liters per kilogram of DMI or as a percentage of GEI.

A decrease in fiber digestion was observed after the addition of soy oil to the diet of sheep (Broudiscou et al., 1990), and decreased NDF digestion has been identified as an explanation for the reduction in CH₄ emissions after the inclusion of other plant oils in the diet (Dohme et al., 1999). In the present experiment, the low level of forage in the overall diet (12% or less) would greatly reduce the impact of a decrease in NDF digestibility on CH₄ emissions. Thus the reduction in CH₄ output is more likely to be as a result of the decline in protozoal numbers, the shift in the molar concentration of VFA from acetate to propionate, a direct CH₄ suppressing effect of the polyenoic oils on the rumen methanogenic bacteria, or a combination of these factors. The toxic effect of oils on ruminal microbes has been attributed to surface-active fatty acids attaching to the cell wall and hindering the transfer of essential nutrients (Henderson, 1973). Machmüller et al. (2003) demonstrated increasing methanogen numbers after the addition of coconut oil to the diet though their metabolic activity seemed to be inhibited (based on the number of rRNA copies present) and CH₄ emissions were significantly decreased. Thus the toxic effect of lipids toward the methanogenic bacteria may not be to eliminate the methanogens from the rumen but rather to inhibit their metabolic efficiency. A reduction in protozoal numbers is of significance because a symbiotic relationship between protozoa and rumen methanogens has been observed (Finlay et al., 1994), allowing interspecies H₂ transfer (Finlay et al., 1994). Less H₂ is therefore available for the formation of CH₄ after defaunation, along with a reduction in numbers of symbiotic methanogens. However, a corresponding increase in free-living methanogens has been reported (Sharp et al., 1998).

The shift in molar concentration of ruminal VFA from acetate to propionate further contributes to the reduction in CH₄ production as propionate provides a larger sink for available H⁺. The formation of propionate is a H⁺ consuming reaction, whereas formation of acetate is a H⁺ liberating reaction, thus leaving less H⁺ available for the formation of CH₄.

With beef cattle, CH₄ mitigation strategies should consider the effect on animal performance and thus lifetime emissions. The poor animal performance observed in terms of ADG for the WSB treatment resulted in greater CH₄ per kilogram of ADG compared with other treatments. Therefore, if bulls were slaughtered at a common BW, as is the practice on many farms, some of the reductions in CH₄ would be negated by greater lifetime emissions.

Summary and Conclusions

The addition of dietary oil (6% of DMI) from RSO decreased (40%) CH₄ output and maintained intake. The inclusion of RSO had no impact on animal performance, which may affect the economics of including RSO in the diet and has implications for acceptance by producers. In addition, the reductions achieved were at high oil inclusion levels, which have produced a detrimental effect on DMI for diets containing a greater forage proportion and thus may limit the range of diets for which this CH₄ reduction strategy may be applicable. The inclusion level of WSB in the present experiment (27%) was beyond the palatability threshold of the bulls used and resulted in a marked decline in intake and performance. Therefore, WSB may have a role to play in ruminant diets but only at a reduced inclusion rate. Further work is required to determine the suitability of RSO to reduce CH₄ emissions across a range of diets and also to determine the optimum inclusion level of WSB in terms of CH₄ reduction.

	Footnotes

 
¹ The provision of an IRCSET postgraduate scholarship is appreciated.

² UCD School of Mathematical Sciences, University College Dublin, Belfield, Dublin 4, Ireland.

³ Corresponding author: frank.omara{at}ucd.ie

Received for publication July 4, 2005. Accepted for publication March 7, 2006.

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