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ANIMAL NUTRITION |
* Agriculture and Agri-Food Canada Research Centre, Lethbridge, Alberta T1J 4B1, Canada and
and
Animal Science Research, Pioneer Hi-Bred International, Johnston, IA 50131-0002
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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Key Words: Beef • Fat • Feedlots • Oil • Performance • Sunflower Seeds
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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) and animal health (Cheng et al., 1998). Lipids are often fed to increase dietary energy density without decreasing fiber. Feeding isolated fats (tallow, yellow grease) can be challenging, however, as specialized equipment for handling, heating, and mixing is required.
Sunflower seed (SS) contains over 40% oil, and the majority of its fatty acids are unsaturated. In ruminants, FFA released from consumed fats are partially hydrogenated in the rumen. Microbial hydrogenation of linoleic (18:2) to oleic (18:1) acid gives rise to intermediary CLA, primarily cis-9,trans-11- and trans-10,cis-12-octadecanoic acid. This CLA can be absorbed from the small intestine and incorporated into tissue (Ivan et al., 2001) or milk fat (Chouinard et al., 2001). Recent studies have shown some dietary CLA to be beneficial for human health (Ha et al., 1989; Parodi, 1997). The prevalence of CLA in deposited fat has been elevated by increasing the intake of linoleic acid by sheep (Mir et al., 2000). High-oil SS typically contains approximately 75% linoleic acid; directed selection has produced SS high in oleic acid. Sunflower seed also contains at least 19% protein and 24% NDF (NRC, 2001).
The feeding value of SS has been studied in dairy diets (Boila et al., 1993) but not in diets for feedlot cattle. This study investigated the suitability of SS as a replacement for forage; the effect of processing the SS before feeding; the effects of dietary SS on growth performance, tissue fatty acid profiles, and organoleptic properties of beef; and whether the response(s) differed with the type of diet (barley vs. corn based) and/or fatty acid profile of the SS (high linoleic vs. oleic acid) fed.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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).
Experiment 1
Animals, Housing, and Feeding.
This study was conducted from November 2000 to February 2001 using 60 yearling steers of mixed breeding (primarily Simmental, Charolais, and Limousin; 479 ± 45 kg initial BW) that had been previously adapted to a barley-based finishing diet. The steers were housed individually in an enclosed shelter comprising six wings of 36 pens (three wings along either side of the central building). Each pen (1.85 m x 6.15 m) featured a feed bunk and water trough at one end and a pen access gate at the other end. Adjacent pens were separated by plank fencing. Livestock housed in this facility have no direct exposure to the weather.
The steers were given ad libitum access to feed and water throughout the study. Fresh feed was mixed and delivered daily using a Calan Data Ranger (American Calan, Northwood, NH). The steers were weighed (without withdrawal of feed or water) on two consecutive days at the beginning and end of the study, for calculation of initial and final weights, and at 28-d intervals throughout the study. To equalize initial BW among treatments, the steers were stratified for assignment to five diets (n = 12) on the basis of weights recorded on d 0. Animals within treatment were assigned to contiguous pens to decrease the potential for feeding errors. The absence of effect of pen location has been confirmed in other studies (Zaman et al., 2002; Ralston et al., 2003; Shah et al., 2004) conducted at this facility, including Exp. 2 of the present trial. At processing on d 1, all steers received a Component TE-S implant containing 140 mg trenbolone acetate and 14 mg estrogen (Elanco Animal Health, Guelph, ON). The steers were monitored daily for health status, including symptoms of acidosis.
Dietary Treatments.
Five experimental diets (Table 1) were prepared using the ingredients listed in Table 2. Diets (DM basis) included 1) the control diet, comprising a typical finishing formulation of 84.5% steam-rolled barley, 9% barley silage, and 6.5% supplement; 2) Diet 1 modified by replacing all of the silage (9%) with rolled SS (9RSS-silage); 3) Diet 1 with 9% whole SS replacing both silage and barley so that the ratio of silage to barley was the same as in the control diet (9WSS); 4) Diet 1 with whole SS replacing both barley and silage to 14% (14WSS); and 5) Diet 4 with rolled SS replacing whole SS (14RSS). The 14% replacement level was selected to approximately maximal recommended levels of fat in the diet, on the assumption of 40% oil in the SS. A roller mill (Roskamp Manufacturing Inc., Cedar Falls, IA) with rolls 30 cm in diameter and 76 cm wide and 6.3 corrugations/cm was used to process SS for Diets 2 and 5. Rolls were set to ensure all SS were broken apart. These diets allowed evaluation of SS as a roughage source (Diet 1 vs. 2), the linear and quadratic effects of adding SS (Diets 1, 3, 4), and the value of processing SS before feeding (Diet 4 vs. 5).
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Fecal samples were collected from eight steers in each of control, 14WSS, and 14RSS diet groups by rectal extraction during weighing on d 84 and again on d 85. The samples were air-dried for 6 d and oven-dried at 55°C for 24 h for DM determination. Fat content of dried fecal samples was determined by extraction with ether (AOAC, 1990).
Dried feed samples were ground to pass a 1-mm screen and analyzed for ADF and NDF (Van Soest et al., 1991) after extraction of the oil with ether (AOAC, 1990). Mineral contents (Ca and P) were determined at an accredited commercial laboratory. Crude protein was estimated from N content determined from Kjeldahl analysis (AOAC, 1990). Fatty acid composition was determined after direct transmethylation as described by Park and Goins (1994). Fatty acid methyl esters were analyzed using a model HP68890 gas chromatograph (Hewlett-Packard, San Fernando, CA) equipped with an automatic sampler (HP7673A).
At slaughter, livers were scored for severity of abscess using a 4-point numeric scale (Brown et al., 1975), in which 0 indicates no visible abscess and 3 indicates severe abscess, defined as more than four small abscesses or one or more abscesses greater than 2.5 cm in diameter. At slaughter, warm carcass weight (with kidneys removed), dressing percent, backfat thickness, LM area, and quality grade were recorded for each carcass. Samples of pars costalis diaphragmatis muscle (diaphragm), liver, and subcutaneous fat (brisket) were also collected from each carcass and frozen immediately on dry ice. Following extraction of tissue lipids with hexane (Hara and Radin, 1978), the triglyceride fraction was isolated from total lipid and the fatty acid content of the triglyceride fraction was determined as described by Kazala et al. (1999).
Experiment 2
Animals, Housing, and Feeding.
In September 2001, 127 British cross (primarily Angus and Hereford) yearling steers (initial BW = 354 ± 25 kg) were housed in individual pens within the facility described above and fed a diet consisting of 59% silage, 33.1% barley, 5.0% supplement, and 2.9% soybean meal (DM basis). After a 2-wk adaptation period, initial weights were determined as the average of unshrunk weights recorded on two consecutive days (d 0 and 1). On the basis of d-0 weights, the seven steers with the lowest rates of gain during the adaptation period were culled, and the remaining 120 were stratified by weight and assigned to six dietary treatments (n = 20). The steers in each diet group were placed in two separate blocks of 10 adjacent pens to allow testing for location effects. No anabolic implants were administered in this experiment.
The six diets were studied in a 2 x 3 factorial arrangement of grain type (barley- or corn-based diets) and SS supplementation (no SS, high–linoleic acid SS, or high–oleic acid SS). In the diets containing SS, both grain and silage were replaced, so that the grain:silage ratios of the control diets were maintained. The ingredients used and the compositions of the final finishing diets are presented in Tables 2
and 3, respectively. The level of SS included in the corn-based diets was adjusted to provide an equal amount of total oil as in the barley-based diets, with calculations based on assumed oil contents of 4, 2, 4, and 40% for corn, barley, silage, and SS, respectively. To ensure the diets were isonitrogenous, soybean meal was included as needed (the highest level was 6.8%). In an attempt to minimize the potential for oxidation of dietary and carcass unsaturated fatty acids, 2,300 IU/kg vitamin E was included in the supplement targeted to provide each steer 1,000 IU/d. Transition from the common initial diet (33.1% barley grain) to the six final experimental diets shown in Table 3 was accomplished over 20 d using five step-up diets specific to each experimental treatment (i.e., corn vs. barley; no SS vs. linoleic or oleic SS). The final diets (Table 3) were fed for 152 d.
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On the day after slaughter, LM steaks cut from the 13th rib were shipped on ice to the University of Georgia and subjected to sensory analysis by an eight-person panel following the guidelines of the AMSA (1995). Panelists evaluated each sample for juiciness, tenderness, and flavor intensity on an 8-point scale in which 1 is least desirable and 8 is most desirable. Panelists also assessed the presence of off-flavors in each sample from 0 (no off-flavor) to 8 (maximal off-flavor).
Statistical Analyses
Data from steers considered to have exhibited atypical performance (gaining more than 3.2 kg/d or less than 0.68 kg/d) were excluded from the analyses of performance and carcass data. Gain efficiency was analyzed as gain/feed. In Exp. 1, ME and NEg content of each diet were calculated based on DMI and ADG. To more accurately account for carcass gain and retained energy in these calculations, final weight was calculated from carcass weight using an assumed dressing percent of 62. The NEm and NEg contents of the diets were numerically iterated (Hays et al., 1987) using the relationships NEg = 0.877 x NEm – 0.41, and retained energy (Mcal/d) = 0.0635 x equivalent empty BW0.75 x ADG1.097 (NRC, 1996).
Measurements were subjected to analysis of variance using SAS (SAS Institute Inc., Cary, NC) with animal as the experimental unit and diet as the only class variable. Experiment 1 was arranged as a completely randomized design with nonorthogonal contrasts used to assess 1) the roughage value of RSS (control vs. 9RSS-silage); 2) the value of rolling SS (14WSS vs. 14RSS); and 3) the linear and quadratic effects of including 0, 9, or 14% whole SS. The linear regression of diet ME against SS level was calculated so that the ME of the basal diet and of pure SS could be estimated.
The PDIFF option of the GLM procedure of SAS was used to separate least squares means of individual fatty acids from tissues of cattle fed the control diet, 14WSS, or 14RSS for Exp. 1. Orthogonal contrasts were used to compare fatty acid concentrations in tissues of steers fed the control diet against the average for tissues from steers fed diets containing 14% SS.
Experiment 2 was also a completely randomized design with a factorial arrangement of treatments (diets based on two grain types with or without two types of SS). The GLM procedure (SAS Institute Inc.) was used to statistically compare treatments. Animal was the experimental unit with location (each treatment was fed in two locations), grain source (barley or corn), and sunflower seed type (high linoleic vs. high oleic) considered in the statistical model. The LSMEANS and PDIFF options were used for generating LSMEANS and comparison of treatments. Contrasts were used for analysis of taste panel data with covariance adjustment for difference among panelists. In both Exp. 1 and Exp. 2, significance was declared at P 
0.05, with trends declared where P 0.10.
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Results and Discussion |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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Level of Sunflower Seed.
Increasing the amount of whole SS in the diet linearly (P = 0.06) increased DMI during the initial 28 d of the experiment (Table 4). This trend became clearer (P = 0.01) during the second 28-d period (d 29 to 56) so that for the whole experiment, DMI was linearly increased (P = 0.02) by added SS. Quadratic effects of SS were not observed for any of the variables measured.
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). Because both barley and silage were decreased when SS was included, in order to maintain barley:silage ratios, the SS-associated increase in NDF is small when expressed as a percentage of the total diet. However, if SS is considered as a forage component, NDF from forages increased from 4.0% in the control diet to 6.3 with 9% SS, and to 7.6% with 14% SS. Intake of finishing diets typically increases with increasing levels of NDF provided by forage (Galyean and Defoor, 2002). This response often is attributed to decreased energy density of the diet (NRC, 1996); however, in the current experiment, the linear improvement (P = 0.01) in G:F suggests that dietary energy supply increased with the addition of SS. Suppression in DMI of finishing diets in association with increased energy density has been attributed to a decreased ruminal pH (Fulton et al., 1979) or an increased concentration of specific VFA (Baile, 1971; Baile and Forbes, 1974). In the present study, however, most of the energy from SS came from lipid, which is minimally fermented in the rumen (Jenkins, 1993); thus, it seems that the DMI may have been increased because the stimulatory effect on DMI of the increased supply of NDF with SS supplementation exceeded any suppression of DMI resulting from the increased energy supply or possible toxic or inhibitory effects of the added fat on ruminal microbial populations (Jenkins, 1993). Zinn and Plascencia (1996) found that supplemental fat enhanced intake only when forage levels were increased in high-grain diets. Moderate levels of lipid (i.e., <4%) have often (Krehbiel et al., 1995; Zinn and Shen, 1996; Ramirez and Zinn, 2000), although not always (Duckett et al., 2002), decreased DMI when added to corn-based finishing diets, but their effect on DMI of finishing diets containing barley is minimal (Zinn, 1989; Engstrom et al., 1994). Including 3.5 to 4% fat in wheat-based finishing diets was found to increase intake (Brethour et al., 1986; Brandt et al., 1988; Bock et al., 1991). Neutral or positive effects on DMI from fat supplementation might be expected with grains that contain less oil (barley and wheat) rather than with grains that are less rapidly fermented and contain more oil (corn).
Differences in protein levels between treatments also may have affected DMI. Dietary protein levels averaged 13.9, 14.5, and 14.9% for 0, 9, and 14% SS, respectively. DiCostanzo and Zehnder (1997) concluded that much of the gain response to protein supplementation can be attributed to an increase in DMI. When protein was increased from 11.2 to 13.2% using canola meal in barley-based finishing diets, intake increased (Engstrom et al., 1994). However, increasing protein content further, from 13 to 15% (McKinnon et al., 1993a) or to 17 or 19% (McKinnon et al., 1993b) failed to increase DMI of barley-based diets. With corn-based diets, protein supplementation often increased DMI when protein levels were low (i.e., <12%) but rarely increased intake when protein was above this level (Anderson et al., 1988; Milton et al., 1997; Shain et al., 1998). Hence, it seems doubtful that the small increase in protein content above 13.9% with SS supplementation was responsible for the increased DMI seen with an increased amount of dietary SS in this experiment.
Consistent with the increased DMI, added SS linearly increased ADG from d 29 to 56 (P = 0.01), which contributed to an overall positive effect (P = 0.02) over the course of the 100-d trial. Engstrom et al. (1994) also reported a positive response of ADG only during the first 56 d of a 102-d finishing trial in which 4% canola oil was added to a barley-based finishing diet. Inconsistent growth rates throughout feeding periods are not uncommon, likely reflecting compensatory growth patterns that are known to occur in cattle (Berg and Butterfield, 1976). McKinnon et al. (1993a) observed increased daily gain by large-framed cattle when protein was increased from 13 to 15% in one trial in which high-energy barley-based diets were fed. However, this response is not always consistent and seems to be more prevalent with moderate- than with high-energy diets (McKinnon et al., 1993b). Thus, the ADG response to SS in Exp. 1 likely was the result of greater DMI and not an increase in protein concentration in the diet.
A linear improvement in G:F with increasing levels of SS was observed from d 29 to 56 (P = 0.02) as well as averaged over the total experiment (P = 0.01). Greater DMI contributes to improved G:F by increasing the amount of net energy above maintenance that is available for gain. However, very high intakes of feedlot diets containing grains that are not extensively processed are often associated with decreased G:F, presumably owing to decreased digestibility (Owens et al., 1995b). The improvement in G:F from replacing barley and silage with SS likely reflects greater intake of DE from the diet. Fat supplementation has improved the G:F of feedlot cattle fed barley-based finishing diets in most (Zinn, 1988; Zinn, 1989) but not all (Engstrom et al., 1994) experiments. Similarly, with corn-based diets, fat supplementation has improved G:F in some (Brandt et al., 1992; Zinn, 1992; Krehbiel et al., 1995) but not all (Johnson and McClure, 1973; Buchanan-Smith et al., 1974; Huffman et al., 1992) feeding experiments. Supplemental fat should be of greater benefit with diets based on barley or wheat than with diets based on corn (Brandt, 1995) owing to the lower fat content of barley and wheat (Brandt, 1995; Zinn and Plascencia, 2002); however, efficiency is not always improved by adding fat even with wheat-based diets (Zinn, 1992).
Unsaturated fats at high concentrations are toxic to cellulolytic bacteria (Palmquist and Jenkins, 1980), and, consequently, fat supplementation often reduces fiber digestibility (Palmquist and Jenkins, 1980; Zinn and Shen, 1996). No decrease in fiber digestibility was evident from growth performance in this experiment, but NDF concentrations in these diets were reasonably low (<26%). As well, negative effects of added fat can be attenuated by providing the oil as intact seeds (Larson and Schultz, 1970; Steele et al., 1971; Aldrich et al., 1997), because biohydrogenation can proceed as rapidly as oil is released. As a result, toxicity to cellulolytic microorganisms is mitigated (Palmquist, 1995); however, gain and efficiency responses were no better for whole than for rolled SS in this study.
Processing
Equal performance with 14WSS and 14RSS indicates little if any advantage from rolling SS before feeding. Steers fed 14RSS diets exhibited DMI, ADG, and G:F only 2.9, 3.7, and 0.6% lower, respectively, than those fed 14WSS (P = 0.65, 0.64, and 0.85, respectively). Using recorded performance data (Table 4) with NRC (1996) equations to calculate energy content revealed that diets containing whole SS surprisingly had slightly higher ME values than diets containing rolled SS (3.02 vs. 2.93 Mcal/kg; Table 4). In addition, an unexplainable increase (P < 0.05) in LM area was detected when whole rather than rolled SS was fed (Table 5).
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reported 86% digestibility for oil from whole SS included at 20% of the diet. When partially crushed, high-oleic acid SS was included at 20% of the diet, 95% of the fatty acids from the SS were absorbed (Chang et al., 1992). Digestibilities of saturated fatty acids (18:0 and 16:0) from SS, however, have been reported to be as low as 69 and 78%, respectively (Hogan and Hogan, 1976). Similarities (P = 0.33) in ether extract content of feces from steers fed diets containing 14% whole vs. 14% rolled SS, combined with similarities in intake and performance, indicate that processing the seed did not enhance digestibility of the oil. Whole SS must have been adequately masticated and/or ruminated to maximize digestibility of the lipid because whole SS is resistant to microbial fermentation (White et al., 1987; Palmquist, 1995). Increased fecal ether extract with supplementation of 14% whole SS would be expected as the dietary concentration of fat increased (Brandt, 1995; Zinn and Plascencia, 2002).
Sunflower Seed as a Roughage Source
Replacing silage with SS resulted in an improvement (P < 0.01) in G:F (0.157 vs. 0.129). This improved G:F reflects superior (P = 0.10) ADG with no effect (P = 0.50) on DMI. Improved efficiencies frequently are observed (Stock et al., 1990; Bartle et al., 1994; Traxler et al., 1995) when higher energy ingredients (i.e., SS) replace lower energy feeds (i.e., silage) in the diet unless fiber levels are inadequate for ruminal function (Bull et al., 1965; Hinders and Owen, 1965; Thorlacius and Lodge, 1973). Replacing silage with SS did not (P = 0.88) increase the incidence of liver abscesses (Table 5), indicating that despite its small particle size, effectiveness of roughage from SS may equal that of barley silage. The linear increase in DMI with increasing levels of whole SS supports this theory; however, steers penned and fed individually consume feed less aggressively (Kidwell et al., 1954; Coppock et al., 1972; Phipps et al., 1983) than when fed as a group, so this experiment may lack the sensitivity needed to detect digestive challenges associated with low fiber levels. With no negative control treatment (0% roughage) to determine the necessity of including roughage in these diets, one cannot draw firm conclusions about the roughage value of SS. However, results indicate that SS could fully replace barley silage in diets of individually fed steers without negative effects on intake, performance, or liver abscess incidence or severity.
Energy Value of Sunflower Seed
Energy contents of the diets were calculated using DMI, ADG, and average animal weight (Table 4). Metabolizable energy and NEg of diets increased linearly (P = 0.01) with SS content. Regression of ME against the percentage of SS in the diet yielded the following equation (R2 = 0.23; P < 0.01):
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with SE of 0.079 and 0.0071 for the y-intercept and slope, respectively. According to this formula, a diet with 100% SS would have an ME content of 5.13 Mcal/kg, almost 9% higher than the 4.71 Mcal/kg cited ME content of high-oil SS for dairy cows fed at 3x maintenance (NRC, 2001).
Effects of Sunflower Seed on Carcass Traits
Feeding whole SS tended to linearly increase (P = 0.08) final live weight and dressing percent and increased (P = 0.03) carcass weights (Tables 4 and 5). Backfat thickness tended (P = 0.11) to increase with SS content of the diet. At modest rates of gain (<1.3 kg/d), carcass fat usually increases with increases in growth rates (Owens et al., 1995a). Supplemental lipid often results in increased carcass fat that is in turn associated with an increased dressing percent (Owens et al., 1993). The higher dressing percent observed with feeding SS in the present study would not reflect increases in kidney, pelvic, and heart fat alone, as is often observed with fat supplementation in the United States (Cameron and Hogue, 1968; Zinn, 1989; Clary et al., 1993) because these deposits are removed from the carcasses in Canadian slaughter plants.
Tissue Fatty Acid Profiles
Despite the fact that unsaturated fatty acids are extensively biohydrogenated in the rumen (Palmquist and Jenkins, 1980), alterations in fatty acid profiles of liver, diaphragm, and brisket fat were observed when SS was fed (Table 6). Differences between diets, however, were not consistent across these tissues. Fatty acid profiles differ among tissues (Dryden and Marchello, 1973; Garrett et al., 1976; Hogan and Hogan, 1976) presumably as a result of differences in their accretion of specific fatty acids (Hood and Thornton, 1976) and desaturase activity (Chang et al., 1992). The effects of dietary SS on carcass subcutaneous and diaphragm fat were similar, but effects on liver lipids often opposed those observed in subcutaneous and diaphragm fat.
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that CLA may be deposited preferentially in subcutaneous fat. Contrast comparisons also indicated that the prevalence of 18:3 and saturation of fatty acids were decreased (both at P = 0.05) by including 14% SS in the diet.
Surprisingly, changes in fatty acid profiles with SS supplementation were not consistent between whole and rolled SS. For example, decreases in 14:1 (P = 0.03) and 16:0 (P = 0.02) in subcutaneous fat were seen only with whole SS, whereas only rolled SS decreased concentrations of 17:0 (P = 0.02) and 18:3 (P = 0.005) in subcutaneous fat. Processing the SS probably increased both the rate and extent of fatty acid exposure and hydrogenation in the rumen, which could influence both the microbial populations in the rumen and the type of fatty acids available for absorption. Consistent with this theory, only whole SS increased (P = 0.01) the prevalence of 18:2 in diaphragm tissue. The reason why whole SS increased (P < 0.001) the prevalence of 18:2 in subcutaneous fat, however, is not clear. Decreased hydrogenation of oil from whole compared with processed oilseeds, which has been suggested previously (Baldwin and Allison, 1983; Aldrich et al., 1997), may have led to greater deposition of unsaturated fatty acids in target tissues with whole than with rolled SS.
Including 14% SS in the diet reduced (P < 0.05) the prevalence of 16:0 in both diaphragm and subcutaneous fat, more so with whole than with rolled seeds. This is consistent with reported milk fat responses to supplemental SS (McGuffey and Schingoethe, 1982; Rafalowski and Park, 1982; Markus et al., 1996). Increased dietary fat reduces the rate of de novo fatty acid synthesis in ruminants (Vernon, 1976) by inhibiting acetyl-CoA carboxylase activity (Palmquist and Jenkins, 1980). Thus, the SS-mediated decreases in 16:0 concentrations observed in the present study could presumably have arisen from depressed de novo synthesis as a result of the increased dietary supply of lipid from SS.
The effects of dietary vegetable oils on duodenal flow of the cis-9,trans-11-CLA isomer (Duckett et al., 2002) or its incorporation into carcass fat (McGuire et al., 1998; Beaulieu et al., 2002) in cattle have been minimal. In contrast, the effect of supplementary oil in diets for lambs on the CLA content of tissues has been dramatic. Feeding 6% sunflower seed oil to lambs increased total CLA content by 33 to 55% in diaphragm, leg, rib, heart, liver, kidney, and subcutaneous fat (Ivan et al., 2001). Similarly, 6% safflower oil in the diet increased CLA content more than 200% in each of these tissues (Mir et al., 2000). The cis-9,trans-11 isomer, which was increased in diaphragm and subcutaneous fat by feeding SS in the present study, is thought to provide the greater anticancer benefits for humans (MacDonald, 2000), although other isomers may offer benefits in animal production by altering energy retention through modulation of fat synthesis or catabolism.
Experiment 2
Interactive effects of location of pen within the barn and dietary treatment were not detected (P > 0.20) during any period of the experiment for any of the variables considered. Consequently, location was removed from the statistical model. Initial full weight averaged 354 kg with no differences among treatments (P = 0.89). As in Exp. 1, the performance indicators were analyzed for the first two 28-d periods, for the remainder of the experiment (d 57 to 172), and over the entire 172-d experiment (Table 7).
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). However, DMI by steers fed barley with high-linoleic SS was lower (P < 0.05) than DMI by those fed the other diets. Averaged across grain types, SS did not affect DMI (P = 0.46), ADG (P = 0.29), or G:F (P = 0.20). Cattle fed corn-based diets ate more DM (9.48 vs. 9.00 kg/d; P = 0.02) than cattle fed barley, but their ADG (1.60 vs. 1.55 kg; P = 0.59) and G:F (0.169 vs. 0.173; P = 0.64) were similar between grain types. During this initial period, the steers fed high-oleic SS tended (P = 0.07) to be less efficient than those fed no SS (0.162 vs. 0.180). During the second 4 wk of the experiment (d 29 to 56), a trend toward an interaction of grain type and SS type on DMI was observed (P = 0.08). When the diets were barley-based, DMI was lower (P = 0.02) when high-linoleic SS was fed than when high-oleic SS was fed, whereas, with corn-based diets, the steers receiving high-linoleic SS had the numerically highest DMI. No other differences in performance were detected during this period.
Over the remainder of the feeding trial (d 57 to 172), the effects of SS on performance indicators were inconsistent across grain types, and SS x grain type interactions (P < 0.05) were detected for DMI, ADG, and G:F. Feeding high-linoleic SS negatively affected (P < 0.05) DMI and ADG with barley-based diets but not (P = 0.19) with those based on corn.
Similar to the latter portion of the study, the effects of SS on DMI over the entire feeding period (d 1 to 172) were inconsistent, and grain type x SS source interactions were detected for G:F and DMI (trends at P = 0.11 and P = 0.06, respectively) and ADG (P = 0.01). When diets were barley based, including high-linoleic SS decreased DMI (P = 0.02) and ADG (P = 0.007) compared with no SS supplementation. In contrast, when diets were corn based, SS did not affect (P > 0.55) DMI, ADG, or G:F. Final live weights (Table 7) and carcass weights (Table 8) were lower (P < 0.05 and P < 0.06, respectively) for steers fed high-linoleic SS with barley than for steers fed any of the other diets.
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; interactive effect at P = 0.005). Longissimus muscle area was lower (P < 0.05) with the high-linoleic SS, corn-based diet than with the other corn-based diets. Among steers fed barley, those fed high-linoleic SS had less backfat compared with those receiving no SS (P = 0.02), which is reflective of the slower gain rate, but LM area was not altered (P = 0.75). The decreased backfat thickness contributed to a greater saleable meat (P = 0.02) for steers fed high-linoleic SS compared with those fed high-oleic SS. No differences were observed in quality grade among treatments. The incidence of abscessed livers ranged from 5 to 20% across treatments, whereas the incidence of severe abscess ranged from 0 to 10%. Statistically significant differences in liver abscess rates among treatments were not detected.
Sunflower seed did not affect organoleptic properties of meat from barley-fed cattle, but minor differences were detected when diets were corn based (Table 9). When corn diets were fed, added high-oleic acid SS increased (P = 0.02) juiciness (6.0 vs. 4.7 on a hedonistic scale, where 1 is least desirable and 8 is most desirable), whereas linoleic SS increased initial and overall tenderness (6.4 vs. 5.4; P = 0.02). Level or source of SS did not affect warmed-over flavor of meat. On the basis of observed DMI, the additional vitamin E that was incorporated into the diets in Exp. 2 to mitigate the tendency of supplemental dietary oil to increase carcass fat oxidation provided an average of approximately 900 IU daily to each steer.
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; Tatum et al., 1988; McKinnon et al., 1993a) have found that cattle with larger frame size are more responsive to increased energy levels than are medium-framed animals. Decreased genetic potential to utilize increased energy as well as increased carcass fat might be responsible for the lack of response to SS supplementation in Exp. 2. |
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Footnotes |
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2 Presented in part at the annual meeting, Canadian Society of Animal Science, Guelph, Ontario, July 2001.
3 Correspondence: P.O. Box 3000 (phone: 403-327-2240; fax: 403-382-3156; e-mail: mcallister{at}agr.gc.ca).
Received for publication November 24, 2003. Accepted for publication May 18, 2004.
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