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ANIMAL NUTRITION |
* Département des Sciences Animales, Université Laval, Québec, Québec, Canada, G1V 0A6;
and
Organic Dairy Research Centre, Alfred Campus, University of Guelph, Alfred, Ontario, Canada, K0B 1A0; and
Agriculture and Agri-Food Canada, Kapuskasing, Ontario, Canada, P5N 2Y3
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Abstract |
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 Top Abstract INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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Key Words: conjugated linoleic acid • extruded soybean • nursing beef cow • pasture • subcutaneous adipose tissue • suckling calf
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INTRODUCTION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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). These fatty acids are found predominantly in food from ruminants (Ritzenthaler et al., 2001). In particular, dairy products and bovine meat represent 68 and 25% of total CLA consumed in the American diet, respectively (Ritzenthaler et al., 2001). Greater CLA concentrations in bovine milk and meat, therefore, offer an opportunity to increase the consumption of these fatty acids. Increasing CLA content in milk fat of dairy cows or in adipose tissue of beef has been demonstrated with pasture feeding (Kelly et al., 1998; Dhiman et al., 1999; French et al., 2000) or by feeding diets with a high forage-to-concentrate ratio (Steen and Porter, 2003; Elgersma et al., 2004).
Many studies have also been conducted to increase the CLA concentration in milk fat of dairy cows by feeding a fat supplement rich in linoleic acid (Dhiman et al., 2000; Chouinard et al., 2001). As an example, dietary extruded soybeans (ES) supplements have raised the CLA content of milk fat by 3-fold (Chouinard et al., 2001). Increases have also been observed, to a lesser extent, in adipose tissue of steers fed ES (+17%; Madron et al., 2002).
In the Canadian beef industry, a widespread production cycle consists of calving in spring, pasturing animals during summer (suckling period), and sending calves to feedlot in autumn. However, a growing practice is to omit the feedlot period and send calves directly to the abattoir for slaughter at the end of backgrounding. Also, the importance of suckler beef system (i.e., livestock system in which calves are not deliberately weaned until slaughter) has rapidly increased in the last decades. With these production models, pasture forage and milk intakes can, therefore, increase the CLA content in adipose tissue of calves and thus in meat and meat products from these animals.
Because ES are known to increase the CLA content of milk fat in lactating cows, the CLA content of adipose tissue of suckling calves could be increased by the intake of pasture and milk, the latter being naturally enriched in CLA by feeding ES to dams. The objectives of this study were to estimate the effect of ground raw soybeans (RS) vs. ES supplementation of grazing nursing beef cows on the fatty acid composition of milk fat and to examine if the additional CLA in milk fat can influence the composition of s.c. adipose tissue in suckling calves.
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MATERIALS AND METHODS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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All experimental procedures performed in this study were approved by the institutional animal care committee based on the current guidelines of the Canadian Council on Animal Care (1993).
Thirty-two crossbred cows (Simmental x Red Angus and Charolais x Red Angus; BW 624 ± 76 kg; BCS 3.5 ± 0.4; mean ± SD) with their calves (BW 127 ± 15 kg) were selected from a spring calf crop at the experimental station of Agriculture and Agri-Food Canada, Beef Research Farm in Kapuskasing, Ontario. Animals were allotted to 1 of 2 groups containing 8 male and 8 female calves with their respective dams. Cows were sorted to minimize variation in live weight, parity, breed, and calving date in each group. Four experimental groups were then obtained as follows: 8 male and 8 female calves with dams receiving 2 kg of full-fat ground RS daily and 8 male and 8 female calves with dams receiving 2 kg of full-fat ES daily. Table 1 presents the chemical composition of soybean supplements. Full-fat soybeans were chosen as a source of linoleic acid instead of oil because of their availability and their ease of distribution to cows on pasture. Cows were individually provided soybeans once a day in a feed bunk designed with self-locking gates to ensure complete consumption of supplements and avoid competition among cows. To obtain isolipidic supplements, RS were used as a control treatment, because they have been shown to have no effect on CLA content of milk as opposed to heat-treated soybeans (Chouinard et al., 1997a; Dhiman et al., 2000).
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The trial began with a week of control measurements (as detailed below) before animals entered the pasture followed by the grazing season divided into 4 periods of 28 d. Each 28-d period was scheduled similarly. On d 22 of each period, animals were weighed, and BCS of cows was assessed using a scale where 1 = emaciated and 5 = grossly fat (Lowman et al., 1976).
Milk Production and Intake
Cow milk production was estimated on d –2 and –1 of the pretrial period (period 0) and on d 27 and 28 of each grazing period, using the weigh-suckle-weigh technique described by Loy et al. (2002) with modifications. On the afternoon preceding measurements, calves were separated from dams at 1300 h. Pairs were reunited at 1600 h, and calves were allowed to suckle for 1 h to consume all available milk in the udder. Cows and calves were separated again from 1700 until 0900 h the next day. After the 16-h separation, calves were first weighed. Dams were restrained in a squeeze chute, and a 120-mL milk sample was collected and frozen until it was analyzed for fatty acid composition. Calves were returned to their dams, allowed to nurse for approximately 1 h, and weighed again. Difference between pre- and postnursing weights was recorded as milk intake for a 16-h period and was multiplied by 1.5 to obtain a 24-h estimate of milk yield for each cow. Calf milk intake was assumed to equal cow milk production.
Pasture Forage Sampling
Each paddock was sampled at 10 random locations before grazing (d –1) and at the end of each experimental period (d 28). Pasture was hand-clipped at approximately 3 cm above ground level within quadrats (0.75 m x 0.33 m). Pasture forage was collected, pooled to obtain 1 composite sample per paddock and per sampling time, dried at 50°C for 3 d to determine DM content, ground through a 1-mm screen in a Wiley mill (Standard model 3, Arthur H. Thomas Co., Philadelphia, PA), and stored at ambient temperature for further analysis. Nitrogen of ground forage samples was determined by the Kjeldahl procedure (AOAC, 1990). Crude protein was calculated as total N x 6.25. Neutral detergent fiber and ADF were analyzed with Ankom technology (Ankom Technology Corp, Fairport, NY) using a sample size of 0.5 g. In vitro DM digestibility was also measured as described by Tilley and Terry (1963). Rumen fluid used in this procedure was obtained from a lactating rumen-fistulated cow fed a mid-maturity cool-season grass mixture silage, corn and barley grain, and a protein concentrate according to its requirements (NRC, 2001).
Silage and Pasture Forage Intake
Silage (period 0) and pasture forage (periods 1 to 4) intakes were determined by measuring total fecal production coupled with the determination of DM digestibility. All male calves were fitted with fecal collection bags on the last 7 d of each period. The harness used to accumulate feces was designed according to the description of Tolleson and Erlinger (1989). Bags were emptied every 24 h, in the morning, for 7 consecutive days. Feces were weighed and mixed. Subsamples representing 40, 25, 10, 8, and 5% of total feces were collected for periods 0, 1, 2, 3, and 4, respectively, from each fecal bag and put separately in individual sealed pots. The pots were frozen at –20°C, and sampled feces were added every day to those frozen the day before. At the end of the 7-d collection period, collected feces were thawed, mixed, and an approximately 1-kg sub-sample was dried at 50°C for 7 d to determine DM.
Pasture forage intake was estimated by dividing the adjusted fecal output (as detailed below) by indigestibility of the pasture forage as described by Holloway et al. (1982):
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Assuming a milk total solid content of 12.34% (NRC, 1996), a constant total solid content during the lactation period (Bowden, 1980), and a mean apparent digestibility of milk DM of 96.5% (Blaxter and Wood, 1952), fecal output was adjusted for the milk residual by the equation:
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It was also assumed that the feeding of milk and pasture forage together had no effect on the digestibilities established separately for each component of the diet. Due to technical difficulties, the control measures in period 0 (silage intake) were only performed on 3 animals per group. These data were not used for statistical analysis.
Adipose Tissue Biopsies
On d –2 and –1 of the pretrial period and on d 27 and 28 of each grazing period, s.c. adipose tissue biopsies were collected from male and female calves, respectively. Each calf was restrained in a chute for the intervention. An area of approximately 400 cm2 was shorn using an electric cordless clipper (with a #10 blade; Oster Professional Products, McMinnville, TN) and scrubbed with a povidone-iodine detergent (10%; Becton Dickinson Canada Inc., Mississauga, Ontario). To limit discomfort, calves were locally anesthetized with 1.5 mL of lidocaine (2% HCl solution; MTC Pharmaceuticals, Cambridge, Ontario) injected s.c. in 2 locations around the incision site which was between the 11th and the 12th ribs over the LM. The incision was made on one side for periods 0, 2, and 4 and on the opposite side for periods 1 and 3. A sterile surgical scalpel was used to make an incision of 3 to 4 cm through which a 1-g sample of s.c. adipose tissue was collected with scalpel and dissecting forceps. The underlying muscle was left unharmed. Incision site was sutured, and Boroform (Intervet Canada Ltd., Whitby, Ontario) was sprayed on the incision site to prevent infection. Biopsy samples were stored at –20°C until fatty acid analysis.
Fatty Acid Analysis
Lipid extraction of milk samples was performed according to Chouinard et al. (1997b). Adipose tissue samples were analyzed for fatty acid composition using a method described previously by Folch et al. (1957), and the extracted lipids were methylated according to Chouinard et al. (1997b). All fatty acid methyl ester analyses were conducted with a gas chromatrograph (HP 5890A Series II, Hewlett Packard, Palo Alto, CA) equipped with a 100-m CP-Sil 88 capillary column (i.d., 0.25 mm; film thickness, 0.20 µm; Chrompack, Middelburg, the Netherlands) and a flame ionization detector. At the time of sample injection, the column temperature was 80°C for 1 min, then ramped at 2°C/min to 215°C and maintained for 30 min. Inlet and detector temperatures were 220 and 230°C, respectively. The split ratio was 100:1. The flow rate for hydrogen carrier gas was 1 mL/min. Each fatty acid peak was identified and quantified using pure methyl ester standards (Nu Chek Prep, Elysian, MN).
Statistical Analysis
Statistical analysis of data for pasture forage and milk intake of male calves, fatty acid profile of adipose tissue for male and female calves, and milk fat composition was carried out by ANOVA for repeated measures utilizing PROC MIXED (SAS Inst. Inc., Cary, NC) as a completely randomized design according to the following model:
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where Yij = record of the animal receiving type of soy-beans i at time j; µ = overall mean; Si = type of soybeans i (i = 1 to 2); Tj = effect of time j (j = 1 to 5); (S x T)ij = effect of the interaction between type of soybeans and effect of time; and eij = random error term.
According to initial analysis, fatty acid profiles and ratios of milk and adipose tissue were not affected by calf sex (P > 0.10). Therefore, this parameter was not included in the final analysis. The subject of the repeated statement was the animal within type of soybeans. The covariance structures were modeled, and the best-fitting structure was selected based on the Schwartz’s Bayesian goodness-of-fit criterion (Littell et al., 1998). First-order autoregressive covariance structure was chosen as the best covariance structure for all parameters except for milk intake and content of C17:0, C18:0, C20:0, and cis-9, trans-11, cis-15 C18:3 in adipose tissue for which compound symmetry was chosen. When a significant time effect was detected, linear and quadratic contrasts were performed to determine the temporal pattern response.
Initial statistical analysis showed no significant effect of calf sex on weight (193.6 and 200.4 kg for females and males, respectively; SEM = 4.4; P = 0.30) or milk intake (7.08 kg/d and 7.31 kg/d for females and males, respectively; SEM = 0.51; P = 0.75) throughout the study. Because pasture forage intake was not measured on female calves, only male performance was included in the final analysis. This decision is supported by the fact that observations have been made in calves in which sex had limited effects on intake of pasture forage and milk (NRC, 1984). Initial and final weights and BW gain of cows and male calves along with G:F for male calves were subjected to ANOVA as a completely randomized design using the MIXED procedure of SAS according to the following model:
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The values reported are least squares means and SEM. In the event that significant treatment effects were established, multiple comparisons were performed using probability of differences (pdiff of SAS) between least squares means. Significance was declared at P < 0.05, and trends were declared at P < 0.10.
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RESULTS AND DISCUSSION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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The chemical composition of pasture forage varied during grazing season. The average forage quality was numerically similar between treatments (Table 1
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Initial (P = 0.83) and final (P = 0.74) weights as well as BW change (P = 0.82) of cows were not different between groups (Table 2). Feeding ES did not influence BW gain of cows compared with RS as shown in several experiments conducted with dairy cows (Block et al., 1981; Guillaume et al., 1991; Chouinard et al., 1997a,b). Lack of effect on BW was expected considering the isolipidic supplementation between treatments. The BW change of both groups of cows was greater than the values obtained by Charmley et al. (1999) with cows at the same stage of lactation on pasture (–0.05 kg/d) but similar to those measured by the same group of researchers on indoor-fed cows receiving silage supplemented with corn gluten meal.
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) was not affected by dietary treatments (P = 0.22). These results are in agreement with previous experiments conducted with dairy cattle, which showed no effect in milk yield when cows were fed ES as compared with RS (Block et al., 1981; Mielke and Schingoethe, 1981; van Dijk et al., 1983; Guillaume et al., 1991). However, the effect was significant for d 56 (P = 0.04) and 112 (P = 0.03; Figure 1).
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; d 112: P = 0.007, soybeans x time: P = 0.006). However, average pasture forage intake during the entire grazing period was not affected by treatment (Table 2; P = 0.13). As a result, dietary supplementation of full-fat soybeans to nursing cows had no effect on the ADG (P = 0.26) during the pasture season and weaning weight (P = 0.53) of calves. Average daily gains observed for both treatments in the current experiment are similar to those reported previously by Charmley et al. (1999) in calves nursing cows on pasture and receiving no dietary supplements.
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; P = 0.08). As shown in Figures 1 and 2, calves whose dams received ES consumed less milk on d 56 (P = 0.04) and d 112 (P = 0.03) and more pasture forage on d 112 (P = 0.007). Cow milk is known to have greater digestibility and energy content as compared with pasture forage (NRC, 1996). Replacing milk with pasture at specific period of the grazing season would, therefore, be expected to decrease overall feed efficiency. The effect of treatments on intake of pasture and milk was not consistent throughout the grazing season and could be attributed to other unexplainable factors. Fatty Acid Composition
Milk.
Milk fat from cows fed RS contained 15.4 mg of CLA/g of total fatty acids. The CLA concentration in milk fat of ruminants fed total mixed rations is normally in the range of 3 to 6 mg/g (Jahreis et al., 1999). Feeding pasture has been reported to increase milk CLA concentration up to 10 to 22 mg/g (Stanton et al., 2003). However, Dhiman et al. (2000) showed that RS supplementation had no effect on CLA secretion in milk fat by dairy cows when compared with a low-fat alfalfa and corn silage diet.
The concentration of CLA in milk fat increased by 57% in cows fed ES, a source of rumen-available linoleic acid (Table 3; P = 0.02). Khanal et al. (2005) reported no effect of supplementing dairy cows on pasture with 2.4 kg of ES daily on milk CLA concentration. However, Lawless et al. (1998) observed an increase of CLA in milk fat content from 17.4 to 22.3 mg/g when cows on pasture received toasted soybeans at a rate of 3.1 kg/ d. Greater levels of ES supplementation (3.5 and 4.8 kg/d) were evaluated by Chouinard et al. (2001) in dairy cattle fed total mixed diets based on silages and concentrates. The CLA content in milk fat was increased in those experiments as compared with respective RS control diets. The final CLA concentrations observed in dairy cows fed ES in silage-based diets were, however, lower (<20 mg/g) when compared with the values observed with cows fed ES on pasture as in the current experiment.
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; linear effect of time x soybeans: P < 0.001; quadratic effect of time x soybeans: P < 0.001) shows that CLA concentration in milk from dairy cows fed ES was over 25 mg/g at the end of the first sampling period in July and remained stable until the end of the experiment. The level of CLA with RS increased gradually from 10 to 15 mg/g over the summer season.
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9, 10, 11, and 12; P = 0.03; Table 3) in milk fat. Those fatty acids are known to be intermediates in the process of rumen biohydro-genation of unsaturated fatty acids (Griinari and Bauman, 1999). Among them, trans-11 C18:1 is the dominant isomer and represents 58% of total trans C18:1 for cows fed both RS and ES. Trans-11 C18:1 is produced in the rumen after the hydrogenation of the cis-9 double bond on cis-9, trans-11 CLA (Griinari and Bauman, 1999). These 2 fatty acid intermediates can escape complete biohydrogenation in the rumen. They are then absorbed from the digestive tract and transported in circulation for use by different tissues and organs. At the mammary gland in lactating ruminants, a portion of circulating trans-11 C18:1 is converted back to cis-9, trans-11 CLA via the action of the enzyme 9-desaturase. Activity of the 9-desaturase is important, because a major portion of CLA in milk originates from the desaturation process (Griinari and Bauman, 1999). This precursor-product relationship explains the strong positive correlation observed between trans-11 C18:1 and cis-9, trans-11 CLA in milk fat (Griinari and Bauman, 1999). In the current experiment, the ratio of cis-9, trans-11 CLA to cis-9, trans-11 CLA + trans-11 C18:1 remained constant between treatments (Table 3; P = 0.29), and was similar to relative proportions of these 2 fatty acids reported previously (Griinari and Bauman, 1999).
Milk from cows fed RS had greater C18:0 (P = 0.002); cis-9, cis-12 C18:2 (P = 0.05); and cis-9, cis-12, cis-15 C18:3 (tendency, P = 0.10) as compared with ES. Similar effects were observed in dairy cattle by Chouinard et al. (1997b) with greater levels of soybean supplementation (4.8 kg/d). A greater C18:0 concentration would suggest a more complete biohydrogenation with RS, which may be in contradiction with the greater proportion of cis-9, cis-12 C18:2 observed in milk fat. An in situ study of the biohydrogenation process revealed that PUFA in RS are released more rapidly in the rumen than PUFA in ES as degradation of the seeds takes place (Chouinard et al., 1997b). These fatty acids seem to disperse in the rumen, which allows for efficient bio-hydrogenation by the bacterial population. A tentative explanation for the greater cis-9, cis-12 C18:2 content in milk fat might be that, because RS PUFA are liberated more rapidly than ES PUFA in the rumen, a fraction could leave the rumen with the liquid phase, thus escaping hydrogenation (Chouinard et al., 1997b). The extrusion process, on the contrary, is known to break the matrix of the seed, making the oil more available in the rumen. The in situ study conducted by Chouinard et al. (1997b) has suggested that the oil remained adsorbed on soybean particles within the rumen. Such free oil concentrated on feed particles might inhibit the activity of the microorganisms responsible for the last step of rumen biohydrogenation, thus reducing the production of C18:0. More intermediates, including trans-11 C18:1 and cis-9, trans-11 C18:2, therefore, accumulate in the rumen and can eventually be absorbed by the animals.
The mean content of cis-9, cis-12, cis-15 C18:3 in milk fat showed several variations during the pasture season; cis-9, cis-12, cis-15 C18:3 concentrations seemed to be negatively correlated with the percentage of ADF measured in silage and pasture (Figure 4). At the beginning of the study, cows were receiving a 39.4% ADF silage, whereas after 1 mo on pasture, the mean ADF content of pasture was 31.5%. The cis-9, cis-12, cis-15 C18:3 concentration had increased from 8.0 to 9.6 mg/g of total fatty acids. Maturity increased again in August, declined in September, and increased again in October; the cis-9, cis-12, cis-15 C18:3 content in milk fat followed the opposite temporal pattern. These observations support the results of Boufaïed et al. (2003), which have shown a decline in cis-9, cis-12, cis-15 C18:3 concentrations with forage maturity.
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). This value is greater than the CLA concentration reported by French et al. (2000) in growing cattle fed harvested pasture grass (10.8 mg/ g). The greater CLA concentration observed in the current experiment may be explained by milk intake, which is a source of preformed trans-11 C18:1 and CLA. The CLA content was 48% greater in adipose tissue of calves from dams fed ES as compared with RS (Table 4; P < 0.001). These observations are supported by the results of Lake et al. (2006), who observed a linear relationship between the CLA content in adipose tissue of suckling calves and the concentrations of trans-11 C18:1 + CLA in milk fat of nursing beef cows.
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) shows that CLA concentrations increased gradually over the pasture season and had not reached a plateau at weaning (linear effect of time: P < 0.001). This gradual increase of CLA in adipose tissue appears to be inconsistent with the decrease in milk intake over the pasture season (effect of time; linear: P = 0.015, quadratic: P = 0.001; Figure 1), which lowered the supply of trans-11 C18:1 and CLA from the dams. However, the consumption of pasture forage increased during the experiment (linear and quadratic effects of time: P < 0.001; Figure 2). Fresh grass is a source of cis-9, cis-12, cis-15 C18:3 (Boufaïed et al., 2003). The biohydrogenation process of this fatty acid in the rumen leads to the formation of trans-11 C18:1, an intermediate that can be absorbed by the animal and used as a substrate for the enzyme 9-desaturase to produce cis-9, trans-11 CLA (Griinari and Bauman, 1999). Noci et al. (2005) also observed a linear increase in the CLA proportion of neutral lipids from the LM of beef heifers during the pasture season.
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). Ryegrass is known to contain a greater level of cis-9, cis-12, cis-15 C18:3 as compared with several other graminaceous species (Boufaïed et al., 2003). A greater CLA concentration could therefore be obtained in older animals on pasture with appropriate forage species.
As observed in milk fat, adipose tissue of calves whose dams received RS compared with ES had greater concentrations of cis-9, cis-12 C18:2 (P = 0.002) and cis-9, cis-12, cis-15 C18:3 (P = 0.04; Table 4). Trans-11 C18:1 was again the dominant trans C18:1 isomer, representing 59 and 57% of total trans C18:1 in s.c. tissues of calves for RS and ES, respectively (Table 4).
Dietary treatments applied to cows did not affect the specific ratios of fatty acid pairs representing 9-desa-turase activity, except for the ratio of cis-9, trans-11 CLA to trans-11 C18:1 + cis-9, trans-11 CLA, which was greater for calves whose dams received ES (Table 4; P = 0.007). This ratio in s.c. adipose tissue of calves was numerically greater (0.42) than in milk fat of dams (0.35). The efficiency of 9-desaturase is known to be of a lower magnitude in adipose tissue as compared with the mammary gland. The consumption of preformed cis-9, trans-11 CLA in milk of dams may then explain the greater CLA desaturase index in calf tissues as compared with cow milk fat.
Only s.c. adipose tissue was analyzed in the current study through periodic biopsies harvested over the pasture season. Madron et al. (2002) examined 3 distinct fat depots in individual retail cuts. The comparison of CLA concentrations of adipose tissue from different locations indicated variations, but they tended to be minor (6.7, 7.0, and 7.8 mg/g of total fatty acids for inter-muscular, intramuscular, and s.c. adipose tissues, respectively). Moreover, Basarab et al. (2007) showed a strong positive linear relationship in cis-9, trans-11 CLA content of the LM and the content in the s.c. fat. Considering the results from these previous studies (Madron et al., 2002; Basarab et al., 2007), the increased CLA concentration observed in the s.c. tissue of calves (Table 4; P < 0.001) would suggest a comparable increase of CLA content in the meat.
Because CLA content of s.c. fat was significantly different between the 2 groups of calves, it can be concluded that CLA in milk fat is transferred to adipose tissue of the calf. The efficiency of the esophageal groove reflex has not been assessed in the present study, but considering the greater CLA contents observed in biopsies from calves whose dams received ES, we can assume that an important fraction of CLA in milk fat was protected against rumen biohydrogenation.
It is therefore likely that CLA secreted in milk fat of nursing cows can be transferred to adipose tissue of suckling calves. Little information is available on the efficiency of fatty acid transfer from milk to calf. Guilhermet et al. (1975) reported that more than 85% of the milk ingested by ruminant calves bypasses rumen fermentation. This experiment was conducted from 6 to 60 wk of age, and calves also received hay, grain, and water. Moreover, work from the same authors showed that a frequent distribution of milk helped to maintain the closure reflex of the esophageal groove. Even if the efficacy of the mechanism was not complete, especially in the ruminant calf, Guilhermet et al. (1975) concluded that it remains functional until 1 yr of age.
In summary, dietary treatments fed to nursing beef cows had no effect on overall milk intake, overall pasture forage intake, and ADG of their suckling calves. Feeding ES to nursing beef cows as a rapidly available source of cis-9, cis-12 C18:2 to the rumen microorganisms leads to greater proportions of trans-11 C18:1 and cis-9, trans-11 CLA in milk fat. Pasture forage increased trans-11 C18:1 and cis-9, trans-11 CLA contents in milk from grazing cows and in s.c. adipose tissue from grazing calves. The cis-9, trans-11 CLA content in adipose tissue of suckling calves was increased along with trans-11 C18:1 and cis-9, trans-11 CLA contents in milk from dams. Results from the current study bring new understanding on the utilization of milk fatty acids by calves. In light of these observations, feeding ES to nursing beef cows on pasture seems to be an innovative approach to increase CLA content in adipose tissue of calves and thus in meat and meat products from these animals.
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Footnotes |
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2 We gratefully acknowledge the assistance given by the farm crew at Kapuskasing Experimental Farm. The authors also thank Marcelle Mercier (Agriculture and Agri-Food Canada, Kapuskasing, Ontario) and the team of Gaëtan F. Tremblay (Agriculture and Agri-Food Canada, Québec) for their assistance with laboratory analysis.
3 Corresponding author: Yvan.Chouinard{at}san.ulaval.ca
Received for publication November 1, 2007. Accepted for publication March 10, 2008.
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LITERATURE CITED |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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) or extruded (
) soybeans on pasture. Initial measurements (d 0) were made during the pretrial period when animals were fed silage. Values are least squares means; n = 8 male calves per treatment; SEM = 1.0 kg/d. Effect of soybean treatment; *P < 0.05.
; SD ± 2.7%; n = 2 per sampling time) of pasture forage. Initial measurements (d 0) were made during the pretrial period when animals were fed silage.