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J. Anim. Sci. 2003. 81:2653-2659
© 2003 American Society of Animal Science

Relationship between body weight and level of fat supplementation on fatty acid digestion in feedlot cattle

A. Plascencia*,1, G. D. Mendoza{dagger}, C. Vásquez{ddagger} and R. A. Zinn§,2

* Instituto de Investigaciones en Ciencias Veterinarias, UABC, Mexicali, México; and {dagger} Programa de Ganadería, Colegio de Posgraduados, Montecillo, México; and {ddagger} Universidad Nacional Autónoma de México, México City, México; and and § Department of Animal Science, Desert Research and Extension Center, University of California, El Centro 92243


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results and Discussion
 Implications
 Literature Cited
 
Eight Holstein steers with cannulas in the rumen and proximal duodenum were used in a split-plot design experiment to evaluate the interaction of body weight (175 vs. 370 kg) and level of fat supplementation (0, 3, 6, and 9% yellow grease) on characteristics of digestion and feeding value of fat in finishing diets. Dry matter intake was restricted to 2% of BW. There were no interactions between BW and level of fat supplementation (P > 0.10) on ruminal or total-tract digestion. Level of supplemental fat decreased (linear, P < 0.01) ruminal digestion of OM and NDF, and increased (linear, P < 0.05) ruminal N efficiency. There were no treatment effects (P > 0.10) on postruminal digestion of OM, NDF, and N. There tended to be an interaction (P < 0.10) between BW and level of fat supplementation on postruminal starch digestion. Increasing level of fat supplementation increased postruminal digestion of starch in heavier steers but did not affect starch digestion in lighter steers. There were no interactions (P > 0.10) between BW and level of fat supplementation on postruminal fatty acid digestion. Increasing level of fat supplementation decreased (linear, P < 0.01) postruminal fatty acid digestion, which was due to a decreased (linear, P < 0.01) postruminal digestion of C16:0 and C18:0. Supplemental fat decreased (linear, P < 0.01) total-tract digestion of OM and NDF. The estimated NEm (Mcal/kg) of yellow grease averaged (linear, P < 0.01) 6.02, 5.70, and 5.06 for the 3, 6, and 9% of level supplementation, respectively. We conclude that intestinal fatty acid digestion (FAD, %) is a predictable function (r2 = 0.89; P < 0.01) of total fatty acid intake per unit body weight (FAI, g/kg BW): FAD = 87.560 - 8.591FAI. Depressions in fatty acid digestion with increasing level of intake were due primarily to decreased intestinal absorption of palmitic and stearic acid. Level of fatty acids intake did not appreciably affect intestinal absorption of unsaturated fatty acid. Changes in intestinal fatty acid digestion accounted for most of the variation in the NE value of supplemental fat.

Key Words: Body Weight • Cattle • Digestion • Fatty Acid


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results and Discussion
 Implications
 Literature Cited
 
Current standards (NRC, 1996Go) for the NEm and NEg values of supplemental fats are 6.00 and 4.50 Mcal/kg. Estimates based on these values are consistent with empirically derived measures when total fat intake did not exceed 0.96 g/kg of BW (Zinn, 1994Go). When fat intake has exceeded 0.96 g/kg of BW, the NE value of fat declined (Zinn and Plascencia, 2002Go). This decline has been largely attributable to decreased postruminal fatty acid digestion (Zinn, 1994Go). An equation for predicting intestinal fatty acid digestion (IFD, %) was derived based on fat intake (FI, g/kg BW; Zinn, 1994Go): IFD = 83.18 - 4.52FI - 0.68FI3. Estimates based this equation are in reasonably good agreement with observed intestinal fatty acid digestion in light-weight cattle (Zinn, 1989Go; Ramirez and Zinn, 2000Go; Zinn et al., 2000Go). However, the equation appears to underestimate intestinal fat digestion in heavier cattle (>350 kg) fed high-fat diets (>1.2 g fat/kg BW; White et al., 1987Go; Elliot et al., 1996Go; Pantoja et al., 1996Go). The basis for this discrepancy is not certain. A limitation of the Zinn (1994)Go prediction equation is that it was derived using a data set containing only one data point where fat intake exceeded 2 g/kg BW. Furthermore, the interaction of BW and fatty acid intake was not directly assessed. The objective of the present study was to directly evaluate the interaction of body weight and level of fat supplementation on postruminal fatty acid digestion.


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results and Discussion
 Implications
 Literature Cited
 
Eight Holstein steers with cannulas in the rumen and proximal duodenum (Zinn and Plascencia, 1993Go) were used in a split-plot design, consisting of two 4 x 4 Latin squares to evaluate the influence of body weight and level of fat supplementation on characteristics of digestion and feeding value of fat. Whole plots (Latin squares replicates) consisted of four "lightweight" (175 ± 14.7 kg) and four "heavyweight" (370 ± 6.7 kg) steers. Subplots consisted of 0, 3, 6, and 9% supplemental yellow grease. Composition of experimental diets is shown in Table 1Go. The composition of the yellow grease used in this study (Table 2Go) is similar to the standards set by the American Fats and Oils Association (AFOA, 1988Go) and was very similar to those used in other experiments conducted at this center (Zinn, 1988Go, 1989Go, 1992Go). Supplemental yellow grease was added to the mixer as the next-to-last step, prior to adding molasses.


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  		Table 1. Ingredient and nutrient composition of experimental diets
 

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  		Table 2. Composition of supplemental yellow grease
 
Steers were individually maintained in concrete slotted-floor pens (3.9 m2) with access to water at all times. Dry matter intake was restricted to 2% of BW, 3.5 and 7.4 kg/d for light and heavyweight steers, respectively. Diets were fed in equal portions at 0800 and 2000 daily. Experimental periods consisted of a 10-d diet adjustment period followed by a 4-d collection period. During the collection period, duodenal and fecal samples were taken from all steers twice daily as follows: d 1, 0750 and 1350; d 2, 0900 and 1500; d 3, 1050 and 1650; and d 4, 1200 and 1800. Individual samples consisted of approximately 750 mL of duodenal chyme and 200 g (wet basis) of fecal material. Samples from each steer and within each collection period were composited for analysis. Upon completion of the trial, ruminal fluid was obtained from all steers and composited for isolation of ruminal bacteria via differential centrifugation (Bergen et al., 1968Go). Feed and digesta samples were subjected to all or part of the following analysis: DM (oven drying at 105°C until no further weight loss); ash, Kjeldahl N, ammonia N (AOAC, 1986Go); purines (Zinn and Owens, 1986Go); NDF (ash-corrected; Chai and Uden, 1998Go); fatty acids (Sukhija and Palmquist, 1988Go); and chromic oxide (Hill and Anderson, 1958Go). Composition of supplemental yellow grease was analyzed according to AOCS (1978)Go procedures as follows: moisture (Method Ca 2a-45), impurities (Method Ca 3-46), unsaponifiables (Method Ca 6a-40), iodine value (Method Tg 1a-64). Microbial organic matter and microbial N leaving the abomasum were calculated using purines as a microbial marker (Zinn and Owens, 1986Go). Organic matter fermented in the rumen was considered equal to OM intake minus the difference between the amount of total OM reaching the duodenum and microbial OM reaching the duodenum. Feed N that escapes to the small intestine was considered equal to total N leaving the abomasum minus ammonia-N and microbial N and, thus, includes any endogenous contributions. Data were analyzed using a split-plot design (Hicks, 1973Go). The statistical model for the trial was as follows: Yijkl = µ + Bj + Sj(i) + Pk + Fl + BFil + {varepsilon}ijkl, where µ is the common experimental effect, B is body weight (whole plot), S is steer within body weight level effect (whole-plot error), P is period effect, F is fat-level effect, BF is the interaction of body weight and fat level, and {varepsilon} is the residual error. Subplot treatment effects were tested using the orthogonal polynomials. The protocol for this trial was approved by the University of California Animal Use and Care Administrative Committee.


   Results and Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results and Discussion
Implications
 Literature Cited
 
Treatment effects on characteristics of digestion are shown in Table 3Go. There were no interactions between BW and fat level (P > 0.10) on ruminal or total-tract digestion. However, the proportion of starch digested in rumen was lower (2.8%, P < 0.05) for heavyweight steers than for lightweight steers. The basis for this effect is not certain, although a tendency for lower ruminal starch digestion in older cattle has been observed previously (Rainey et al., 2002Go).


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  		Table 3. Influence of body weight and level of fat supplementation on characteristics of digestion
 
Increasing the level of supplemental fat from 0 to 9% depressed (linear component, P < 0.01) the ruminal digestion of OM and NDF and increased (linear component, P < 0.05) ruminal N efficiency (nonammonia N flow to the small intestine/N intake). The negative effects of supplemental fat on ruminal OM and NDF digestion have been reported previously (Boggs et al., 1987Go; Zinn, 1989Go; Elliot et al., 1996Go). In vitro studies (Henderson, 1973Go; Maczulak et al., 1981Go) demonstrated that the unsaturated fatty acids, particularly C18:1, inhibit ruminal cellulolytic microbes. MacLeod and Buchanan-Smith (1972)Go postulated that the depressing effects of fat on fiber digestion might also be partially due to a physical coating of fiber particles, forming a lipid barrier that impedes enzyme penetration. However, no differences in ruminal fiber digestion were noted when supplemental fat was added directly to the grain, the forage, or as the final ingredient in the feed mix (Zinn et al., 1998Go; Plascencia et al., 2001Go; Plascencia and Zinn, 2002Go).

The depression in ruminal OM digestion observed here can be attributed partially (~28%) to differences in NDF digestion, and partially to ruminal indigestibility of fat. Consistent with previous studies, supplemental fat did not affect (P > 0.10) ruminal digestion of starch (McAllan et al., 1983Go; Krehbiel et al., 1995Go) or N (Elliot et al., 1996Go; Plascencia et al., 1999Go).

There were no treatment effects (P > 0.10) on postruminal digestion of OM, NDF, and N. There tended to be an interaction (P < 0.10) between BW and level of fat supplementation on postruminal starch digestion. Increasing level of fat supplementation increased postruminal digestion of starch in heavyweight steers but did not affect starch digestion in the lightweight steers.

Treatment effects on postruminal fatty acid digestion are shown in Table 4Go. There were no interactions between BW and fat level (P > 0.10) on fatty acid digestion. Across BW (whole-plot effects), the flow of fatty acids to the small intestine was 113, 112, 102, and 101% of intake for the 0, 3, 6, and 9% levels of supplemental fat, respectively, reflecting decreased de novo microbial fatty acid synthesis at the higher levels of fat supplementation (Klusmeyer and Clark, 1991Go; Pantoja et al., 1996Go; Ramirez and Zinn, 2000Go). Postruminal fatty acid digestion decreased (linear, P < 0.01) with increasing level of fat supplementation, averaging 82.6, 80.7, 75.5, and 67.4% for the 0, 3, 6, and 9% level of fat supplementation, respectively.


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  		Table 4. Main effects of level of fat supplementation on fatty acid digestion in Holstein steers
 
Intestinal digestion of unsaturated fatty acids was not affected (P > 0.10) by level of fat intake, averaging 87 and 77% for C18:1 and C18:2, respectively. The lower digestibility observed for C18:2 vs. C18:1 in this study may be more apparent than real. Very little C18:2 (<0.5% of duodenal DM) was supplied to the small intestine, affecting the analytical accuracy of the measure. The coefficient of variation associated with intestinal digestion of C18:2 (9.5%) was threefold greater than that of the other fatty acids.

Postruminal digestion of saturated fatty acids declined markedly (linear, P < 0.01) with increasing levels of fat intake. The decline in postruminal digestion with increasing level of fat intake was 121% greater for C18:0 than for C16:0 (consistent with the concept that intestinal digestion of saturated fatty acids decreases with increasing chain length; Steele and Moore, 1968Go; Zinn, 1989Go). Furthermore, whereas C18:0 comprised only 4 to 13% of fatty acid intake, it comprised 56 to 64% of total fatty acid flow to the small intestine. Hence, decreased digestion of C18:0 explained most of the depression in total intestinal fatty acid digestion with increasing levels of fat intake (Coppock and Wilks, 1991Go; Wu et al., 1991Go; Plascencia et al., 1999Go).

However, a limitation of metabolism studies of this nature is that they do not take into consideration the potential for biohydrogenation of unsaturated fatty acids in the lower intestinal tract. To the extent that some C18:1 entering the small intestine was hydrogenated to C18:0 before excretion in the feces, the intestinal digestion of C18:1 and C18:0 would be overestimated and underestimated, respectively.

Shown in Figure 1Go is the relationship between fatty acid intake (FAI, g/kg of BW, mean) and intestinal fatty acid digestion observed in this and six other studies conducted at this center and elsewhere (Wu et al., 1991Go; Pantoja et al., 1996Go; Zinn and Shen, 1996Go; Ramirez and Zinn, 2000Go; Zinn et al., 2000Go; Plascencia and Zinn, 2002Go). Fatty acid digestion decreased linearly with increasing intake: fatty acid digestion, % = 87.560 - 8.591 FAI; r2 = 0.89 (P < 0.01). Fatty acid digestion exceeded 80% when fatty acid intake was less than 0.86 g/kg of BW, decreasing by 0.85% for each 0.1 g/kg BW increase in total fatty acid intake. In contrast, Zinn (1994)Go observed a curvilinear decrease in intestinal lipid digestion with increasing lipid intake. A comparison of the two models is shown in Figure 2Go. Both models give similar results when fatty acid intakes are less than 2.0 g/kg of BW. However, at higher intakes, the earlier model (Zinn, 1994Go) underestimates intestinal fatty acid digestion. As stated previously, a limitation of the earlier model is that it contained only one data point where fatty acid intake exceeded 2.0 g/kg BW.



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  		Figure 1. Influence of fatty acid intake on intestinal fatty acid digestion.

 


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  		Figure 2. Comparision of the models for predicting intestinal fatty acid digestion (present study vs. Zinn, 1994Go).

 
Given that 1 g of intestinally digestible fat (IDF) has a ME value of 9 kcal (100% of its physiological fuel value) and the partial efficiency of utilization of ME from dietary fat for BW gain is 67% (Czerkawsky et al., 1966Go; Garrett, 1980; Zinn, 1994Go), the NEg value of dietary fat can be calculated as 6.03 kcal/g IDF. Accordingly, applying digestibility values, the NEg values for the yellow grease used in this study are 4.87, 4.55, and 4.06 Mcal/kg for the 3, 6, and 9% of level supplementation, respectively. Corresponding NEm values are 6.02, 5.66, and 5.10 Mcal/kg, respectively, where NEm = (NEg + 0.41)/0.877 (derived from NRC, 1984Go).

The NE values obtained for yellow grease supplemented at the rate of 3, 6, and 9% of dietary DM (fatty acid intake = 1.17, 1.67, and 2.14 g/kg BW) were 100, 94, and 85% of the tabular value (NRC, 1996Go). The linear decrease in NE value of supplemental fat with increasing level of fat intake observed in this study is in close agreement with NE values obtained at this center based on growth performance (Zinn, 1994Go; Zinn and Plascencia, 2002Go). The good agreement observed between NE measures based on metabolism studies and NE measures based on growth performance is supportive of the concept that intestinal fatty acid digestion is the primary determinant of level of intake effects on NE value of supplemental fats.

Supplemental fat decreased (Table 3Go; linear, P < 0.01) total-tract digestion of OM and NDF. Depressed total-tract fiber and OM digestion due to fat supplementation is well documented (Moore et al., 1986Go; Zinn and Plascencia, 1993Go).


   Implications
Top
 Abstract
 Introduction
 Materials and Methods
 Results and Discussion
 Implications
Literature Cited
 
Intestinal fatty acid digestion was a predictable function of level of total fatty acid intake per unit of body weight. Depressions in fatty acid digestion with increasing level of intake were due primarily to decreased intestinal absorption of palmitic and stearic acids. Level of fatty acid intake did not affect intestinal absorption of unsaturated fatty acids. Changes in intestinal fatty acid digestion accounted for most of the variation in net energy value of supplemental fat.


   Footnotes
 
1 Fellowship PROMEP-SEP, México. Back

2 Correspondence—phone: 760-357-3086; E-mail: razinn{at}ucdavis.edu.

Received for publication January 7, 2003. Accepted for publication July 15, 2003.


   Literature Cited
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 Abstract
 Introduction
 Materials and Methods
 Results and Discussion
 Implications
 Literature Cited
 


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