fat source and calcium level effects on … · fat source and calcium level effects on finishing...

FAT SOURCE AND CALCIUM LEVEL EFFECTS ON FINISHING STEER PERFORMANCE, DIGESTION, AND METABOLISM’

B. J. Bock2, D. L. Harmon3t4, R. T. Brandt, Jr.3 and J. E. Schneiders

Kansas State University, Manhattan 66506

ABSTRACT

A 11 ld finishing study evaluated animal growth and carcass characteristics using 138 steers (366 kg) in a randomized complete block design with a 2 x 3 factorial arrangement of treatments. The dietary treatments consisted of no supplemental fat or 3.5% tallow or soybean oil soapstock (SS) fed with .6% and .9% dietary Ca. Fat increased DMI (P e .05) but interacted with Ca level (P .05) for gain/feed and ADG. All diets containing fat or .9% Ca were converted more efficiently to gain than the .6% Ca, no supplemental fat diet (P < .05). The .9% Ca interacted with fat source to decrease gain (P < .05) and tended to decrease efficiency in the tallow diet but improved efficiency (P < .05) and tended to improve gain in the no-fat diet. In the SS diet, .9% Ca had no effect on ADG, DMI, or efficiency of gain. Fat addition increased backfat (P .lo) and interacted with Ca on hot carcass weight, final weight, and dressing percentage (P < .05). Feeding fat increased the proportion of 18:O (P c .02) and decreased the proportion of 16:l fatty acids (P < .M) in intermuscular fat. A replicated 3 x 3 Latin square design, using six Holstein steers (349 kg) fed three diets, with no supplemental fat or 3.5% SS or tallow with 1.0% Ca, was used to explore the effects of fat sources when fed with high Ca on digestion and metabolism. Ruminal fluid pH was higher (P e .lo) when steers were fed fat. Adding fat did not affect (P > .lo) duodenal or ileal pH, VFA proportions or total concentration, or ruminal liquid volume or flow rate. Liquid retention time was shorter and liquid rate of passage was higher (P < .OS) with dietary fat addition. Adding fat did not affect site or extent of starch or DM digestion. There was net synthesis of 16:0, 18:0, and 18:l fatty acids in the rumen. When steers were fed tallow, synthesis of 16:O and 18:0 fatty acids in the rumen was lower (P < .IO) than when steers were fed SS. Feeding fat tended to decrease (P = .11) bacterial N flowing at the duodenum but did not affect nonbacterial N or total N. Fat addition seems to affect ruminal kinetics, and the effects may vary with fat source, particularly relative to fatty acid synthesis and digestion. Key Words: Fats, Fatty Acids, Calcium, Beef Cattle, Digestion

J. Anim. Sci. 1991. 69:2211-2224

Introduction

Feeding fat to ruminants can cause palata- bility problems as well as decreased fiber

lConbibution No. 90-516-J, Kansas A@. Exp. Sta. 2Present address: Agway, Inc., P.O. Box 4751.

Syracuse, NY 13221-4751. b p t of Anim. Sci. and Ind. Appreciation is expressed

to Ginger Weir and Valerie Stillwell for their help in preparation of the manuscript.

90 whom reprint requests should be addressed. h p t . of Surg. and Med. Received July 5, 1990. Accepted November 28, 1990.

digestibility (Warner, 1960; Johnson and McClure, 1973), probably because of a toxic effect of long-chain fatty acids (LCFA) on ruminal bacteria (Galbraith et al., 1971; Hen- derson, 1973). Past research has indicated that dietary Ca levels should be increased when fat is fed (Palmquist and Conrad, 1980) to help alleviate negative effects on fiber digestion in high-forage diets (M% forage). The type of fat used may affect these interactions. The low ruminal pH in feedlot cattle would favor the ionized forms of fatty acids and Ca, thereby possibly eliciting more interactions between fatty acids and Ca. Although decreases in fiber

221 1

2212 BOCK ET AL.

digestibility are not a major concern in finishing diets, fat products containing modex- ate to high levels of free fatty acids might be used more effectively if negative effects on ruminal bacteria were suppressed. Two trials were designed 1) to determine the efficacy of feeding two types of fat with two levels of Ca in beef cattle finishing diets and the effects on fatty acid profiles of blood, muscle, and adipose tissue and 2) to assess the effects of fat type when fed with supplemental Ca on metabolism, diet digestion, and blood fatty acid profiles.

Materials and Methods

Finishing Trial. This study, conducted at the Southwest Branch Experiment Station in Garden City, Kansas began on June 1, 1988. One hundred thirty-eight medium-framed yearling crossbred steers of mixed breeding were blocked by weight and assigned randomly to a 2 x 3 factorial arrangement of treatments in a randomized complete block design with four pens per treatment and five to six steers per pen. Pen dimensions were 4.3 m x 7.4 m with automatic waters located near the feedbunk and shared by two pens. The heaviest group averaged 388 kg B W the lightest group averaged 337 kg. The treatments combined no supplemental fat, 3.5% tallow, or 3.5% soybean oil soapstock (SS) with .6% and .9% Ca. The .5% (actual analysis .6%) level of Ca was chosen to fulfill the Ca requirement (.41% according to NRC, 1984) and .9% was a higher level that would not depress intake (Brink et al., 1984). All diets met or exceeded the minimum requirements for CP, Ca, and P as described for medium-framed yearling steers (NRC, 1984). Soapstock is a by-product of edible oil refining. Its fatty acid composition is very similar to that of the original oil but it is much higher in nonesterified fatty acids (83.6% unsaturated, 50% free fatty acids); the tallow is 47% unsaturated, containing 15% free fatty acids. The Ca source was ultrafiie (2325 mesh) limestone6, with a higher solubility than normal feedgrade limestone. Wheat-based diets were chosen to facilitate an optimally low ruminal pH.

%owa Limestone Co., Des Moines, IA. 7 ~ ~ ~ ~ ? %one-poutene hc. , A W ~ GA. 'Model 3064 Perkin-Elmer, Norwalk, CT.

The steers had been grazing wheat pasture on ranches around Dodge City, Kansas, from which they were purchased. Steers were processed 1 d after arrival, which consisted of ear tagging; vaccination for blackleg and malignant edema, infectious bovine rhinotra- cheitis with parainfluenza-3 (modified live), and bovine virus diarrhea; implanted with 24 mg estradiol; and treating with anthelmintic and grubicide. Decoquinate7 at 180 mg/d, vitamin A at 40,OOO IU/d, and vitamin E at 200 lU/d were included in the receiving diet (25% concentrate, 75% roughage) for 10 d. The trial began (d 0) with weighing the steers and increasing the diet to 50% concentrate for 7 d, then to 72% concentrate (with 2% added fat in designated treatment diets) for 4 d, and finally to 85% concentrate (Table 1). Steers were fed once daily from a truck-mounted mixer-feeder.

Starting and ending weights were the averages of two consecutive early-morning weights. Final weights were calculated using hot carcass weight divided by dressing percentage (.62) to compute ADG. The steers were weighed at 2 8 6 intervals until slaughter (111 d). Steers were weighed at 0700 and fed upon returning to pens. Jugular blood was obtained by venipuncture from two steers per pen (eight animals/treatment) at weighing on d 0,28,56, and 111 of the trial and centrifuged at 2,200 x g for 15 min to obtain serum. Blood was placed on ice immediately after sampling, then kept at 4'C for 48 h or less until it was centrifuged. The same steers were sampled throughout, Serum Ca was measured using .5 ml serum and 9.5 ml .5% La (wt/vol) in 3 N HCl solution on an atomic absorption spectro- photomete8. Total lipids were extracted according to Folch et al. (1957), and LCFA were methylated with 1 ml of 14% (wt/vol) BF3- methanol; the composition was measured on a gas chromatograph according to methods described by Bitman et al. (1984). The steers were slaughtered at a commercial packing plant. The carcasses were electrically stimu- lated and chilled for 24 h at 2'C before evaluation of USDA quality and yield grades by a federal grader. University personnel measured fat over the ribeye (or backfat) at three-fourths the distance from the chine bone and estimated kidney, pelvic, and heart fat. Livers were scored for the presence and severity of abscesses. The animals that were sampled for blood were also measured for

DIETARY FAT SOURCE AND Ca FOR FEEDLOT STEERS 2213

TABLE 1. COMPOSITION OF DIETSa

Fishing trial Metabolism trial Ingredients Control Added fat Control Added fat

Wheatb Corn silage 5 .00 5 .00 Chopped alfalfa hay 5 .00 5 .00 10.00 10.00 supplementc 4.14 4.28 5.00 5.00

% 80.86 80.72 78.00 78.00

- -

Tallow or soybean oil soapstock - 3.50 - 3.50 Blended molassesd 5.00 1.50 5.00 1 S O

Composition, %

Limestone' + + 2.00 2.00

DM 74.25 772 1 89.74 91.93 CP 16.74 16.97 13.91 13.75 Ca .63/.90 .62/.90 1.07 1.05 P .43 .43 .40 .40

apexcentage composition on a DM basis. Formulated to contain .65% K. Monensin and tylosin added at 30 and 11

%inishing trial, steam-roiled; metabolism trial, dry-rolied. 'In the finish@ trial, supplement contained animal protein products, processed rpain by-products, forage products,

vitamins A and q, urea, NacL, KCI, NHqSO4, We, Mgo, ZnO, FeSO4, cuSO4, CoCO3, Na2SQ. and C2HgN212. In the metabolism trial, suppleanen1 contained ground wheat, NaCI, MHqSO4, KCI, Cr2O3, mineral oil, trace miner&, and vitamins A, D, and E.

mgkg, respectively.

kontained 65% corn steep liqnor, 30% cane molasses, and 5% whey. %mestone was added to basal diets in finishing trial to increase. Ca from .60% to .go%.

ribeye area using a USDA ribeye grid, and a single 2.5-cm steak was cut from the 12th rib loin section. The entire longissimus muscle was removed from the steak (except for a l c m outside border), and a sample of intermuscular fat was frozen in liquid N, homoge- nized frozen using a Virtis 459, and kept at -20°C until lyophilization and analysis of LCFA composition by the method of Sukhija and Palmquist (1988). Data were analyzed as a randomized complete block design with a 2 x 3 factorial arrangement of treatments using pen as the experimental unit. The model included fat, Ca, and their interaction as treatment effects, with weight as a blocking factor (Cochran and Cox, 1957). When interactions were not significant (P > .lo), the df associ- ated with fat were further partitioned using orthogonal contrasts. When interactions were present, means were separated by least significant difference. Statistical analyses were per- formed using the GLM procedure (SAS, 1985) with P < .10 as the accepted level of significance.

Metabolism Trial. Six Holstein steers, aver-

'Virtis Research Equipment, Gardenier, NY.

aging 349 kg BW, were prepared with permanent plastisol cannulas in the rumen, duodenum (15 cm posterior to the pylorus), and ileum (30 cm anterior to the ileal-cecal junction) and used in a replicated 3 x 3 Latin square design experiment. Duodenal and ileal cannulas were placed while animals were under general anesthesia using halothane. Ruminal cannulas were inserted using local anesthesia. Dietary treatments (Table 1) were randomized according to procedures described by Cochran and Cox (1957) and consisted of a control (no supplemental fat), 3.5% dietary SS, or 3.5% tallow, all with 1.0% dietary Ca. Fat sources were identical to those used in the finishing trial. The fatty acid profiles of the total diets are shown in Table 2. The diets with the added fat contained approximately twice as much total LCFA (mg/g of sample). Saturated to unsaturated ratios were nearly identical between the control and tallow diets (approximately 4357, respectively); however, these diets differed considerably in proportions of 12:0, 18:0, and 18:l fatty acids. The diet containing SS was considerably higher in unsaturated fatty acids, having a saturated: unsaturated ratio of 27572.5, primarily because of the larger amounts of 18:2.

2214 BOCK ET AL.

TABLE 2. LONG-CHAIN FATTY ACID PROFILES OF THE COMPLETE DIETS FED IN THE

METABOLISM TlUAL

Fatty acid,

acid Control oilsoapstock Tallow 120 23.35 8.10 7.91 1 4 0 0 0 1.90 16:O 17.41 16.69 22.24 16: 1 0 0 1.71 18:O 1.64 2.71 11.08 18: 1 14.47 15.81 28.03 18:2 38.5 1 51.65 24.85 18:3 4.62 5.04 2.28 Total, mg/g DM 12.37 24.34 24.85

dl00 g fatty soybean

Steers were housed in an enclosed barn in individual tie-stalls and fed 2% @M basis) of their BW in 12 equal portions daily (2-h intervals) using automated feeders. Steers gained an average of 1.42 kg/d over the 94-d trial. The wheat was dry and coarsely rolled. Chromic oxide was included in the supplement (crumbled pellet form) at 4.4% (or .22% of total diet DM) as the dietary marker. Each period of the Latin square lasted 20 d: 10 d of dietary adaptation, 5 d of total fecal collection, 3 d of digesta (duodenal and ileal) sampling, 1 d of ruminal fluid sampling, and 1 d for blood and ruminal content sampling. Fecal bags were used to make total fecal collections. Bags were weighed, emptied, and rinsed clean after collection, and a 10% subsample was taken once daily (24 h collections). Each subsample was frozen and composited within steer after the collection period, then a representative sample was taken, freeze dried, and ground through a l-mm screen in a Cycloted0 mill. Four duodenal and ileal digesta samples (200 g) were taken every 3 h each day, with each day's collection offset by 1 h so that a sample was taken every hour in a 12-h period. The pH of every sample was recorded immediately using a combination electrode. One milliliter of 10 M NaOH was added to duodenal samples, and .3 ml was

'%eator, Inc., Hemdon, VA. %hatman 4, Whatman International La., Maidstone,

'2Model RFA 300, Alpkem, Clackamas, OR. UK.

added to ileal samples to arrest enzymatic activity for storage. Each day, a composite of 150 g from each sampling hour was frozen. After the collection period, duodenal and ileal samples were cornposited by steer, then a representative sample was taken, freeze-dried, and ground through a Cyclotec mill. Diets, feces, and intestinal digesta samples were analyzed for DM by drying a .5- to 1.0-g sample to a constant weight using a 1 W C oven, for OM by ashing a .5- to 1.0-g sample in a muffle furnace for 8 h at 5WC, for Cr by the method of Williams et al. (1962), for starch by the method of Macrae and Armstrong (1968) with glucose determined by the glucose oxidase procedure (Gochman and Schmitz, 1972). and for LCFA by the method of Sukhija and Palmquist (1988). Insoluble fatty acid salts (IFAS) were measured on ruminal and fecal samples as those fatty acids remaining in the sample after three extractions with a 1:l mixture of ether and acetone (Jenkins and Palmquist, 1982). Total Ca and P were determined using a .5-g sample that had been ashed in a muffle furnace at 5 W C for 8 h and dissolved in 10 ml of 6 N HC1 and heated on a hot plate until the acid began to boil. The sample was removed from the hot plate and filtered through filter paper'l, then the crucible and filter paper were rinsed three times each with distilled water, and the sample was brought to 250 ml volume. Calcium concentration was then measured by atomic absorption spectrophotometry, and P concentration was measured on an autoanalyz- er12 using the ammonium molybdate procedure.

On d 19 of sampling, the steers were intraruminally dosed with 4 g Co-EDTA (dissolved in 200 ml of water) as a fluid marker. The Co-EDTA was prepared according to the procedure of Uden et al. (1980). Ruminal fluid samples were taken before dosing and every 3 h after dosing until 24 h elapsed using a suction strainer that filtered ruminal fluid particles >1.2 mm. The pH of each sample was measured immediately using a combination electrode and recorded, and the samples were then partially processed before freezing; 8 ml of ruminal fluid with 2 ml of 25% metaphosphoric acid was frozen for VFA and 20 ml of ruminal fluid was frozen for Co analysis. Samples were then thawed and centrifuged at 30,000 x g for 20 min, the supernatant fluid was analyzed using gas


~hromatography~~ and atomic absorption spectrophotometry (Kreikemeier et al., 1990). Ruminal volume, liquid dilution rate, and mean retention time of the liquid fraction were calculated by plotting the Ln of declining Co concentrations with time. Ruminal, intestinal, and total tract digestion were calculated by the Cr ratio technique (Schneider and Flatt, 1975), with Cr intake adjusted for Cr recovered in feces during the 5-d total fecal collection.

On the final day of sampling, a jugular blood sample was taken at approximately 1200, placed immediately on ice after sampling, then kept at 4'C for 48 h or less until centrifuging at 2,200 x g for serum. Serum Ca and LCFA were measured as previously described in the finishing trial. A 1-kg sample of total ruminal contents was taken from various locations within the rumen, mixed with 1 liter of cold 10% formalin solution (9 g NaCl and 100 ml of 37% [voVvol] formaldehyde per liter) to preserve the bacteria, then frozen. Later, the samples were thawed and blended at high speed for 1 min in a large blender. A 500-g subsample was taken, freeze-dried, ground through a 1-mm screen using a Cyclotec mill, and analyzed for LCFA and IFAS content. The remaining ruminal contents were strained through two layers of cheese- cloth. The strained ruminal fluid was then centrifuged at 150 x g for 10 min to remove protozoa and feed particles. The supernatant fluid was decanted and centrifuged at 30,000 x g for 15 min to sediment bacteria. The supernatant fluid was decanted and discarded. The bacterial pellets were then resuspended in water using a glass rod with a rubber tip and centrifuged again at 30,000 x g. This washing was repeated two more times, and the bacterial pellets were then freeze-dried, ground, and composited by treatments for analysis of LCFA composition as described above and for purine content as outlined by Zinn and Owens (1986). Kjeldahl N of the feed, duodenal digesta, and bacteria was analyzed on duplicate samples (triplicate for bacteria) by standard procedures (AOAC, 1984). Microbial protein synthesis was calculated from the bacterial purine:N ratio and duodenal purine flow. Data were analyzed as a replicated Latin square design (Cochran and Cox, 1957) using the GLM procedure (SAS, 1985). One steer had an impoperly placed duodenal cannula. Those

13Mdel 5890. Hewlett-Packard Co., Avondale, PA.

duodenal sample data were not included in the analyses; thus, least squares means are reported. The model included square, animal(square), period(square), and treatment. Sums of squares were further partitioned with orthogonal contrasts to compare the no supplemental fat with fat treatments and also to compare the two fat sources. Time and time by treatment were added to the model for analyzing VFA using a split-plot analysis. Animal x period x treatment was the specified whole-plot error term and sampling time was the sub-plot main effect. There were no interactions (P > .lo) between treatment and time. Treatment differences were treated as significant if P < .lo.

Results

Finishing Trial. Steer gains, intake, or gain/ feed ratios (feed efficiency) were not affected by fat addition during the first 28 d (Table 3); however, .9% Ca decreased ADG (P < .08). From d 29 to 56, steers fed .9% Ca with the soapstock or the .6% Ca tallow diets increased feed intake compared with animals consuming the .9% Ca diet not containing fat (P < .05). From d 57 to 84, Ca affected gains differently within the different fat sources, increasing gains in the SS diets and decreasing gains in the tallow diets. During the fiial period (d 85 to 111). fat increased ADG (P < .05), DMI, and efficiency of gain (P < .07). The overall (0 to 11 1 d) effect of fat was to increase DMI (P c .05). The .9% Ca interacted with fat source to decrease gain (P < .OS) and tended to decrease efficiency in the tallow diet but improved efficiency (P c .05) and tended to increase gain in the no supplemental fat diet. In the SS diet, the .9% Ca had no effect on ADG, DMI, or efficiency of gain.

Fat source and Ca interacted on hot carcass weight, final weight, and dressing percentage (Table 4). Including fat in the diet increased the amount of subcutaneous fat or backfat on the animal, as would be expected by the increased energy intake. Ribeye area, yield grade, marbling score, liver score, and kidney, pelvic, and heart fat (data for latter two not reported) were not affected by feeding fat and(or) .9% Ca.

Animals fed fat had lower (P < .06) percentages of 16:l LCFA but higher (P < .02) percentages of 18:O in the intermuscular fat (Table 5). Dietary fat source and(or) .9% Ca

2216 BOCK ET AL.

TABLE 3. DIETARY FAT AND CALCIUM EFFECTS ON FEEDLOT PERFORMANCE (FINISHING TRIAL)a

Treatments fsuuolementsl ~~ ~~~~

soybean oil Control + Ca% soapstock + Ca% Tallow + Ca%

Item .6 .9 .6 .9 .6 .9 SE No. of steers 23 23 23 23 23 23 Oto28d

1.58 1.51 1.63 1.50 1.72 1.55 .OS DMI, kg 8.42 8.11 8.46 8.70 8.68 8.35 .17 Gain/Eeed .188 .187 .194 .174 200 .185 .010

ADGb 1.60 1.80 1.87 1.94 1.88 1.92 .07 DMF 9.7od" 9.11d 9.65* 10.32' 9.96' 9.63& .24 GWeedC .165d .1* ,195' . l 8 7 . 1 w 200' .007

AD@ 1.46" 1.49d" 1229d 1 . 5 e 1.61' 1.36& .10 DMI 9.95 9.73 10.17 10.40 10.59 10.21 .30 Gain/feed .147 .154 .128 .152 ,152 .134 .010

kg

29 to 56 d

57to8pd

85 to 111 d ADGb 1.21 1.20 1.51 1.42 1.37 1 S O .07

Gain/feedj ,136 .125 ,156 .141 .137 .154 .007 DMIJ 8.93 9.74 9.76 9.99 9.97 9.74 .24

Oto 111 d ADGC 1.41d 1.51df l.5ecf 1 . w h 1.71& 1.56f .03 DMIb 9.25 9.17 9.5 1 9.85 9.80 9.48 .17 Gain/feedc . 153d . 164' .16? .17@ .175' .164' .004

~

aMeans, n = 4 (pen as the experimental unit). Final weight equals hot cawass weighV.62. "Fat effect (P e .05). 'Fat x Ca interaction (P < .05). +*~C.%J'M- without a cornmoil rmperscript difftr (P < .OS). kat x ca interaction (P < .in).

bat effect (P e .on.

did not affect any of the other LCFA or percentage of saturated or unsaturated fatty acids measured in the intermuscular fat. Calcium decreased (P < .08) the total concentration of fatty acids in the intermuscular fat. Treatment did not affect the LCFA composition of the longissimus muscle.

The serum LCFA profiles taken on the final day of the finishing study (111 d) are presented in Table 5. Feeding fat decreased (P < .OS) the percentages of 14:O LCFA on the final day of the finishing trial (Table 5). Calcium at the .9% level decreased (P e .05) the percentage of 18:O and, therefore, the percentage of saturated LCFA observed in the serum. The proportions of other serum LCFA were not different among treatments. Serum Ca was not different between treatments.

Metabolism Trial. No differences in molar percentages or concentration of total VFA were measured (Table 6). RuminaI pH was higher (P < .lo) when steers were fed fat and

was higher (P = .lo) when steers were fed SS compared with when they were fed tallow. Duodenal and ileal pH, ruminal liquid volume or flow rates were unaffected by treatment; however, when steers were fed fat, ruminal liquid retention times were 22% shorter (P < .05) and turnover rates were faster (P < .05). Dry matter intake was not different between

treatments ("able 7). Starch and N intake were lower and fatty acid intake, ruminal LCFA, and ruminal IFAS were higher in the diets containing fat (P < .lo). Intakes of starch, LCFA, DM, N, or ruminal IFAS (as a percentage of ruminal LCFA) were not different between fat sources; however, when steers were fed tallow they tended to have lower amounts of ruminal LCFA (P = .11) and ruminal WAS (P = .W). Fat presence or type did not affect ruminal IFAS content expressed as a percentage of ruminal LCFA or digestibility of DM or starch. As shown by the negative numbers, there was net synthesis of LCFA in


TABLE 4. CARCASS CHARACTERISTICS (pINISHtNG TRIAL.)'

Treatments (supplement)

Control + Ca% soapstock + Ca96 Tallow + Ca% soybean oil

Item .6 .9 .6 .9 .6 .9 SE

No. of steers 23 23 23 23 23 23 Initialwt,x 367 365 367 366 367 366 .5 FiaalwZkg 524d 532df 542'' 5Soeh 55@ 539ef 4

Dressing s: 61.3d 62.0& 6 2 . e 62.6' 62.F 61.7d" .4

Yield gradek] 2.62 2.93 3.23 3.01 3.21 2.97 .21

Hotcarcass.wt,kgb 325d 332df 33acf 341d 345fi 334ef 2.3

Bacldat, c d 1.19 1.22 1.31 1.29 1.39 1.26 .05 Ribeye =ea, cmZk 82.3 77.6 775 83.2 81.5 80.3 2.4 Marbling scod 210 203 199 215 218 212 14

a ~ , n = 4 @en as the experimental unit). %at x ca interaction (P < .OQ. %pals hot carcass weightL62. 4e.fab- without a common superscript differ. 'pat x ca interaction (P < .MI. bat effect (P < .lo). k ~ m ~ r e d on eight steasmtment (two steers/pen), n = 4 (pen as the experimental unit).

'small = 200 to 300.

the rumen for all treatments. Net synthesis of LCFA was lower (P < .05, measured as percentage of LCFA intake) in the rumen and total tract of steers fed fat than in the rumen and total tract of those not fed fat. Net ruminal synthesis of LCFA was lower (P < .lo, measured as a percentage of LCFA intake) when the steers were fed tallow than when steers were fed SS. The latter steers had the lowest digestibilities of insoluble salts, fol- Iowed by those on the tallow diet, but digestibility nearly doubled for steers on the no supplemental fat diet.

Feeding fat tended (P = .11) to decrease bacterial N flowing to the duodenum (Table 7). Treatment did not affect nonbacterial N or total N measured at the duodenum. Values were similar between the two fat sources.

Moderate amounts of 16:O and 18:l LCFA and extremely large amounts of 18:O (particularly for the no fat and SS diets) were apparently synthesized in the rumen (Table 8). At least 50% or more of 18:2 and 18:3 disappeared in the rumen and more than 90% of 12:O was used. The majority of LCFA that were either produced or not metabolized in the rumen disappeared in the small intestine. Disappearance in the small intestine ranged from 54 to 89% for all fatty acids measured, when calculated as a percentage of LCFA entering the small intestine. Total tract net

disappearance of all the individual LCFA (except for 18:O) ranged from 56 to 97%.

When steers were fed fat they had lower ruminal (P e .01) net disappearances of 16:0, 18:0, and 18:l and higher nuninal net disappearances of 18:2 LCFA than when steers were not fed fat. Ruminal LCFA net disappearance of 12:O and 18:3 were unaffected by fat feeding. Net disappearance of LCFA in the small intestine was lower when steers were fed fat, except that net disappearance of 18:3 LCFA was unaffected by fat inclusion. When steers were fed fat, total tract apparent digestibility was lower (P e .05) for 12:O and higher (P < .OS) for 18:l and 18:2 than when steers were not fed fat. Total tract apparent digestibility of the remaining LCFA was not affected by fat inclusion.

Net disappearance was lower for 18:0, 18:1, 18:3 (P e .05) and 16:O (P e .lo) when steers were fed tallow, but disappearance of 12:O and 18:2 were not different between steers when fed tallow or SS (Table 8). Disappearance of LCFA was not different between steers fed tallow or SS, except for 18:2, which tended to be lower when the steers were fed tallow (P e .lo). In steers fed tallow vs SS, total tract apparent digestibilities were lower (P < .05) for 18:O. 18:2, and 18:3 LCFA, higher (P < .Ol) for 18:1, and not different for 12:O and 16: 0.

221 8 BOCK ET AL.

Composition of serum LCFA for steers used in the metabolism trial was similar to composition of those for steers in the finishing trial (Table 9). In general, when steers were fed fat they had lower percentages of 14:0, 16: 0, and 16:l. Compared with steers fed tallow, the animals fed SS had lower proportions of 16:0, 161. and 18:l but much higher proportions of 18:2. When steers were fed the SS diets they had the highest proportion of unsaturated fatty acids and when not fed fat they had the lowest; proportions of unsaturated

fatty acids were intermediate when the steers were fed tallow. Serum Ca concentration was not different between treatments.

Calcium and P digesta flows and digestibilities were determined but are not presented in tabular form. They were both unaffected by dietary treatment. Average apparent digestibilities in the rumen, smal l intestine, large intestine, and total tract were 28.4, 7.3, -7.2, and 27.3 for Ca and -37.2, 80.8, -12.2, and 40.5 for P, respectively, all reported as a percentage of intake.

TABLE 5, INTERMUSCULAR FAT, LONGISSIMUS MUSCLE FATTY ACID, AND SERUM (DAY 111) COMPOSITION AND SERUM CALCIUM L .EW (FINISHING TRIAL,))'

Treatments (supplement)

Control + Ca% soapstock + Ca% Tallow + Ca% soybean oil

Fatty acid, g100 g fatty acid .6 .9 .6 .9 .6 .9 SE Intermuscular fat

140 160

18:OC 18:l 18:2 183 TOW wet sampled, mg/g Saturated, % unsaturated, %

120 140 16:O 18:O 18: 1 18:2 18:3 Total, mg/g wet sample Saturated, 96 unsaturated, %

Senun(dl11) 14OC 16:O 16: 1 18:v 18:l 18:2 18:3 Saturated, %e Unsaturated.

1 6 lb

Longissimus muscle

4.70 32.92 4.38

15.87 40.62

.52

.22 944.9 53.5 45.7

.18 3.29

29.4 5.12

45.60 229 2 6

40.1 46.7 53.3

2.66 19.62 5.75

21.40 18.71 28.21 3.63

43.69 56.31

calcium, &dl 10.22

4.81 32.38 4.46

16.80 41.46

.60

.22 864.1 54.0 46.7

.33 3 -29

29.6 5.25

44.71 3.34 .34

28.8 46.4 53.6

2.65 18.53 6.28

19.10 18.25 32.10 3.10

40.27 59.73 10.58

4.48 29.64 3.88

18.91 43.45

A 1 .18

922 A 53.0 47.9

.25 3.53

28.6 5.07

45.36 2.60

.23 31.4 46.7 53.3

1.59 17.98 4.80

21.45 15.80 35.43 2.%

41.01 58.99 10.69

4.61 30.73 3 .w

17.98 42.66 .46 .18

852.7 53.3 472

2 0 3.45

28.6 4.99

46.34 2.62 2 2

37.4 45.8 54.2

1.80 1828 5.68

18.53 18.67 3428

38.60 61.40 10.53

2.78

4.22 30.08 4.11

18.16 42.87 .40 .22

877.6 52.5 47.6

.29 3.22

28.8 4.94

45.95 2.46

2 3 33.9 46.4 53.6

2.17 19.32 7.05

20.71 20.02 28.03 2.70

4220 57.80 10.30

4.63 31.36 3.67

19.75 41.14

.39

.18 860.2 55.7 45.4

.23 3.35

29.1 4.65

44.93 2.29 2 9

36.2 47.8 52.2

2.07 19.10 6.54

19.5 1 18.83 30.24 3.71

40.69 59.31 10.48

.27 1.09 .22 .82

1.04 .09 .04

36.8 1.6 1.1

.06

.20

.78

.24

.88

.43

.05 4.9 1.1 1.1

2 1 .83 .83 .82

2.18 2.56

.43 1.29 1.29 .16

)'Means, measured on eight steedtreatment, n = 4 @en as the experimmtal unit). %at effect (P = .M). 'Fat effect (P < .05).

%a effect (P = .OS). eCa effect (P < .m).


Discussion

In terms of overall performance, adding fat or supplemental Ca improved feed utilization compared with the .6% Ca no-fat diet (Table 3). These results are consistent with past research using 280% concentrate diets (Ca: Zinn and Owens, 1980; Turgeon et al., 1982; Steele et al., 1983; fat: Brethour et al., 1986; Brandt et al., 1988a.b; Zinn, 1989a). Higher levels of Ca, supplied by limestone, have been shown to increase ruminal or small intestinal starch digestion (Zinn and Owens, 1980; Goetsch and Owens, 1984; Brink and Steele, 1985). Because wheat-based diets were used, a buffering effect from Ca might have been the cause of the improved performance of the nonfat diet. Brink et al. (1984) reported results from five experiments with limestone added at .8 vs 1.7% of the DM in highcorn diets (80 to 85%) that contained either various ratios of dry corn (whole or rolled) or high-moisture corn. The 1.7% level of limestone did not affect gain, DMI, or efficiency in the three experiments using dry corn and in one of the experiments using high-moisture corn. Howev- er, in the other experiment using high-moisture corn (Brink et al., 1984), steers fed the 1.7% level of limestone were more efficient (P = .02) than those fed the 3% level.

Improved gain and feed utilization when feeding fat have been related to its increased

energy density. Feeding additional Ca with tallow decreased ADG by 9.6%, whereas Ca improved ADG approximately 6% through improved feed utilization or intake of the no supplemental fat and SS diets. This decreased ADG was due to the combined nonsignificant decreases in DMI. Fat increased DMI in this study. A reduction in feed intake when fat is fed has been the common result in past research (Brent et al., 1971; Hatch et al., 1972; Zinn, 1985; Cole and Hutcheson, 1987; Brandt et al., 1988a). The critical factor of the intake effect in this study is the type of grain fed (i.e., wheat). In several trials by Brethour et al. (1986) and a study by Brandt (1988b), fat increased the feeding value of wheat (in 50 or 100% wheat diets) by consistently increasing DMI. Brandt (1988b) found that adding fat increased ADG by an average of 1 1 % (1.40 vs 1.25 kg/d) whether wheat was dry-rolled or steam-flaked. Steam-flaking wheat and adding fat produced additive increases in ADG compared with dry-rolled wheat. Although the metabolism study in that research used dry- rolled wheat and the finishing study used steam-flaked wheat, Brandt et al. (1988b) indicated that the response to fat was simiIar for both forms of wheat. However, steam- flaking compared with dry-rolling often results in better performance when feeding wheat

TABLE 6. VOLATILE FATTY ACID CONCENTRATIONS, pH, A N D RUMINAL LIQUID KINETICS (METABOLISM

Treatments (supplement)b P = Control ssvs Volatile fatty acid, soybean oil

mol/l00 mol Control soaustock (SS) Tallow SE vs fat tallow Acetate 53.68 53.39 52.20 1.81 .70 .66 Propionate 29.03 3 1.05 32.49 3.01 .49 .74 Butyrate 12.92 11.73 11.57 1.97 .62 .96 Isobutyrate .98 .73 .65 .13 -12 .65 Valerate 1.64 1.66 1.57 .18 -93 .73 Isovalerate 1.75 1.45 1.52 21 .34 .84 Total, mM 97.73 102.57 100.80 6.11 .62 '84

PH Rumioal 5.65 5.99 5.75 .09 .09 .10 Duodenal 2.76 2.90 2.80 .10 .5 1 .53 Ileal 6.95 7.04 7.06 .ll S O .90

Volume, liter 40.80 44.78 39.08 4.87 .86 .44 R u m i d 4 u i d

Flow rate, literh 2.72 3.35 3.15 .29 .19 .65 Retention time, h 16.72 13.41 12.74 1.21 .05 .7 1 Turnover rate, per h .067 .079 .080 .004 .04 .82

aMeans, n = 6. bAll diets contained 1.0% DM as Ca.

2220 BOCK ET AL.

(Brandt et al., 1987) by altering ruminal fermentability, specifically by decreasing the rate of starch digestion (Kreikemeier et al., 1990).

Altering tissue LCFA composition by feeding fat is much more difficult in ruminants than in nonruminants; however, significant but s m a l l changes have been shown by numerous researchers (Faichney et al., 1972; Dryden and Marchello, 1973; Garrett et al., 1976; Rule and Beitz, 1986). In the present study, the increase in proportion of 18:O and decrease in 16:l of animals fed fat is reflective of dietary changes (Table 5). Duodenal contents when steers were fed fat in the metabolism trial contained 48% 18:0, compared with 36% when steers were not fed fat (P < .02) and .61% 16:l compared with 1.13% (P < .Ol), respectively. How Ca

decreased the concentration of LCFA in the fat tissue is not known. A possible explanation is an overall reduced absorption of LCFA because of increased amounts of insoluble, undigested fatty acid salts. However, this does not explain how Ca affected the concentration of LCFA (Table 5) in the intermuscular fat but not the total amount of fat (subcutaneous fat or backfat, Table 3).

The lower levels of serum 18:O in animals fed the Ca-supplemented diets (Table 5) may have been due to decreased absorption of 18:O. Drackley et al. (1985) reported that 18:O made up approximately 60% of ruminal IFAS. In the metabolism trial, 18:O made up 44% of the ruminal IFAS. Possibly greater amounts of indigestible salts were formed at the .9% Ca level; however, Drackley et al. (1985) and

TABLE 7. APPARENT DIGESTION OF DM, STARCH, FATTY ACID, AND INSOLUBLE FATTY ACID SALT (PAS) (METABOLISM TRIAL)a

~reahnents (supplement)b P = soybean oil Control Ssvs

Item Control soapstock (SS) Tallow SE vs fat tallow

D W W d N intake, gld Starch intake, g/d Patty acid intake, g/d Ruminal LCPA, mgl& Ruminal WAS, mglg Ruminal WAS, % of ruminal LCFA DM digestibility, 96 Ruminal small intestinal Total tmct

Ruminal Small intestinal % of intake % of duodenal flow

Fatty acid digestibility, %

Starch digestibility, %

Total tract

Ruminal small inksti@ % of duodenal flow

WAS digestibility, % Total tract

Total tract

Duodenum, g/d Bacterial N Nonbacterial N Total N

7.98 177.6

4342 98.68 44.3 35.0

792

58.24 23.49 82.59

86.76

7.97 78.40 95.90

-66.04

86.00 72.46

82.45

90.2 43.3 133.5

7.88 174.8

191.79 87.2 62.0

71.8

57.72 25.15 82.23

84.77

11.82 7220 96.11

4118

-55.28

78.62 59.79

24.77

75.7 45.1

7.89 172.1

192.89 74.5 54.2

73.3

61.31 22.49 82.77

86.50

8.97 66.62 96.04

-37.95

77.14 65.48

46.52

71.5 42.5

4090

.81 1.7

4.34 4.7 2.7

3 .O

2.94 1.31 1.39

2.91

1.75 3.85 .69

5.81

2.54 2.80

426

7.2 4.3

38

.37

.10 <.01 1.01 eo1 <.01

.13

.74

.85

.96

.76

.33

.13

.85

.03

.06

.03

<.01

.11

.93

.95

.32

.63

.20

.ll

.09

.74

.42

.23

.79

.69

.32

.37

.95

.08

.70 20

.a?.

.69

.6% ~ _ _ ~ 120.8 114.0 9.0 .19 .6 1

h t squares means, n = 6. Digestibilities reported as a percentage of intake.

‘LCPA = long-chain fatty acids. b~ diets contained 1.0% DM as ca


Palmquist et al. (1986) have shown that supplemental Ca did not affect salt formation. The lower amounts of 18:O caused the percentages of saturated and unsaturated LCFA to be affected also by the .9% level of Ca. The sem profiles of the steers used in the metabolism study reflected differences strictly related to fat preswce and source. When the steers were fed fat, serum profiles contained higher proportions of unsaturated LCFA (Ta- ble 9). The differences between the steers when fed SS and tallow are reflective of dietary profiles, except for 18:0, which was greatly affected by ruminal bacterial production.

The lack of difference in molar percentages of VFA agrees with the data of Esplin et al. (1963), Riley and Newby (1978), and Grum- mer (1988). The analyzed level of 1.2% added LCFA may have been too low to substantially (Table 2) affect VFA. However, the majority of the other data suggests that it was adequate to affect ruminal fat metabolism. In contrast, feeding fat has more frequently caused decreased acetate:propionate ratios (Sutton et al., 1983; Boggs et al., 1987; Zinn 1989b).

Possibly the high level of Ca (1.0%) acted to alleviate effects on fermentation, as suggested by Brooks et al. (1954), who added alfalfa ash to a 90% cottonseed hull diet. However, the tendency for decreased bacterial N and decreased ruminal synthesis of LCFA (Table 7) when steers were fed fat suggests that the bacteria were affected by fat addition. Total numbers of protozoa were reduced (I' < .OS) in the steers fed fat in the finishing trial reported by Towne et al. (1990).

The increase in ruminal pH from fat consumption is best explained by the increased ruminal liquid turnover rates and decreased retention time when steers were fed fat (Table 6). The increased dilution rates when steers were fed fat did not result in increased feed or total N entering the duodenum. This increased xuminal pH when feeding fat may have importance relative to maintaining a more optimum rumen environment. However, how the high levels of Ca, grain type (wheat), or other factors may be related is unknown. The literature in this area is also limited Boggs et al. (1987) reported that feeding 7.6% tallow in a 75% ground corn diet decreased ruminal

TABLE 8. INDIVIDUAL FATlY ACID NET DISAppeARANcE IN THE DIGESTIVE TRACT AND TOTAL. TRACT APPAFUWT DIGESTIBILITY (METABOLISM

soybean oil Control ss vs Dkestibilitv. 96 Control BoaDstock 6s) Tallow SE vs fat tallow

Ruminal, % of mtake 120 93.92 160 -108.41 18:O -3521.9 18: 1 -173.45 18:2 50.26 18:3 55.84

120 73.5 1 160 86.15 18:O 88.46 18: 1 88.79 18:2 76.22 18:3 72.26

12:o 97.42 16:O 56.81

18:l 64.78 18:2 89.92 18:3 88.21

Small intestine, % of duodenal flow

Total tract, % of intake

18:O -308.14

92.28 -74.42

-2571.7 -1 17.80

73.01 69.84

61.00 80.69 77.15 83.41 73.07 69.15

96.29 56.22

-711.37 62.78 94.57 90.78

92.90 .62 .I3 -55.06 6.39 .01

-513.9 303.9 .01 22.91 25.98 .01 67.98 4.15 .01 49.09 5.11 .58

54.01 5.19 .07 80.98 1.77 .w 75.53 4.36 .09 81.42 1.38 .02 60.09 3.70 .10 66.2 1 3.72 .38

96.26 .32 .03 6359 3.13 .45

-57.17 6256 .36 84.6 1 1.85 .o 1 91.40 .80 .m 81.59 1.31 .25

.5 1

.08

.01

.01

.42

.03

.40

.9 1

.81

.37

.07

.6 1

.95

.15

.01

.o 1

.03

.01

%east squares means, n = 6; 14:O and 161 were not present in diet. b~ diets contained 1.046 DM BS ca

2222 BOCK ET AL.

TABLE 9. SERUM LONG-CHAIN FAlTY ACTD COMPOSITION AND CALCIUM CONCENTRATION (METABOLISM TRIAL)'

~ ~~ ~

~reatments (supplement)b P= Fatty acid, Soybean oil Control ss vs dl00 g fatty acid Control soapstock (SS) Tallow SE vs fat tallow

140 4.01 2.1 1 2.94 .30 .01 .ll 16:O 22.02 18.12 18.80 .16 .01 .01 16 1 5.85 4.47 5.73 .12 .01 .01 18:O 14.35 14.99 14.85 .40 .30 .82 18:l 21.46 19.31 23.75 1.24 .% .oQ 18:2 29.52 38.30 29.75 1 .oo .a2 .01 18:3 2.79 2.7 1 3.18 .t8 .52 .13 Saturated, % 40.4 35.2 37.6 .31 .01 .01 unsaturated, % 59.6 64.8 62.4 .3 1 .01 .01 Saum calcium, mddl 9.48 9.45 9.29 .29 .76 .72

'Ueans, n = 6. bAll diets contained 1.0% DM as Ca

liquid volume and increased solid turnover rate. Although not significant because of protein level interactions, tallow numerically increased (6.79 vs 5.63 %/h) liquid dilution in the higher-protein (12% CP) diets only. Czer- kawski et al. (1975) fed linseed oil and reported an increase in ruminal dilution rate but also a contrasting increase in ruminal volume.

In spite of an increased liquid dilution rate, the lack of effect of fat on site and extent of DM and starch digestibility (Table 7) is similar to results of other research (Esplin et al., 1963; Hatch et al., 1972; McAllan et al., 1983; Drackley et al., 1985; Zinn, 1988, 1989b). Boggs et al. (1987) and Zinn (1989b) reported decreased total tract OM and(or) DM digestion in diets containing fat. This was due to decreased ruminal OM digestion, which was attributed partially to depressed ADF digestion in the fat-containing diets, according to Zinn (1989a,b). In the research by Boggs et al. (1983, dietary Ca levels were low (<.30%) and possibly not adequate to alleviate the negative effects of fat on fiber digestion. However, in the trial by Z i (1989b), Ca levels were quite adequate (.9%).

Results for LCFA digestibility (Table 7) agree closely with those of Zinn (1988, 1989b). The difference in apparent ruminal synthesis between SS and tallow may be related to ruminal pH. As ruminal pH declines, bacteria become more sensitive to the toxic effect of LCFA (Galbraith and Miller, 1973). It was interesting that the percentages of LCFA in the bacteria for the control, SS, and tallow

diets were 10.2, 18.3, and 12.9, respectively. Uptake, adsorption, and, possibly, synthesis of LCFA were much greater in the bacteria from the SS diets. Although IFAS (as percentage of fatty acids present) were not affected by treatment (data not shown) in the rumen, duodenum (avg 46.3%), or ileum (avg 79.6%), the percentage of IFAS or soaps remaining in the feces was higher for the steers when fed fat (70.5, 79.7 and 81.9% for control, SS, and tallow diets, respectively) and made up a higher proportion of LCFA excreted. One possible confounding effect was the addition of NaOH to the duodenal and ileal samples. This may have influenced the proportion of IFAS measured in these samples. The increase in fecal IFAS is consistent with many other studies (Esplin et al., 1963; Dryden et al., 1974; Drackley et al., 1985). This concurs with the lower IFAS digestibilities when the steers were fed fat. In general, LCFA that were synthesized in the rumen were utilized in the small intestine. The large amounts of 18:O produced were probably from bacterial cells (containing 50%) and to a lesser extent from saturation of dietary 18:1, 18:2, and 18:3 LCFA. The increased LCFA also might have been from endogenous sources, such as sloughed r~minal epithelium, saliva, or gastric juices (Sutton et al., 1970). The general pattern observed in this study is that when steers were fed tallow they synthesized and digested fewer LCFA than when steers were fed SS. Also, when steers were fed fat they had a lower percentage of ruminal and small intestinal digestion for the majority of the LCFA. Small


intestinal digestibility of LCFA was very similar (avg 75%). The large amounts of 18:O st i l l remaining in the feces as reflected in total tract digestion is in agreement with results of Dryden et al. (1974) and Drackley et al. (1985).

In summary, increasing dietary Ca levels to .9% in wheat-based finishing diets did not seem to improve the feeding value of added fat. However, it did improve gain/feed ratios when fat was not included in the 85% wheat diets. Fat source interacted differently with Ca level and seemed to do so in the rumen, primarily through decreased LCFA synthesis. Rumen kinetics were affected by feeding fat but did not alter DM or starch digestion or fermentation profiles in wheat-based finishing diets.

Implications

Increasing dietary Ca levels from .6 to .9% in wheat-based finishing diets did not increase the feeding value of added fat; in fact, it caused a decrease in weight gains of steers fed tallow. Adding 3.5% fat or Ca to .9% (dry matter basis) or both to a 85% steam-rolled wheat finishing diet increased gain/feed ratios by 9.8%. Average daily gain and dry matter intake were also increased by adding fat to 85% wheat f ~ s h i n g diets. Adding 3.5% fat did not affect dry matter or starch digestibility.

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