Z Mir

Effect of dietary supplementation with either conjugated linoleic acid (CLA) or linoleic acid rich oil on the CLA content of lamb tissues

Conjugated linoleic acid (CLA) is produced in the rumen by isomerization of linoleic acid and has been shown to be a potent anticarcinogen in animal model studies. The objective of this study was to compare the relative increase in the CLA content of lamb tissues by dietary CLA supplementation (0.33 g/d for 21 days prior to weaning) to milk-replacer of preruminant lambs or by feeding linoleic acid rich oil (Safflower oil, 6% DM-SAFF) to weaned ruminating lambs with that of lambs receiving unsupplemented milk-replacer and pelleted feed. Thirteen lambs were randomized to three dietary treatments (CLA-4, SAFF-4 and Control-5) and fed the pelleted diet for 80 days after weaning. Lambs were slaughtered at an average weight of 45 kg and tissue samples were procured from pars costalis diaphragmatis, leg, rib, subcutaneous adipose and liver for determination of fat and CLA content and fatty acid composition. Dietary supplementation with safflower oil increased fat content of subcutaneous adipose tissue only, but the CLA content of all the tissues was increased (P < 0.05) by more than 200%. Dietary safflower oil increased (P < 0.05) C18:2 in all tissues and C16:0 in the diaphragm, and decreased (P < 0.05) C18:1 and C18:3 content in all tissues. Supplementation of the diet with pre-formed CLA prior to weaning decreased (P < 0.05) fat content of the adipose tissue with decreases occurring in C18:0 relative to animals receiving the unsupplemented diet, however, tissue CLA content was not affected by provision of dietary CLA to pre-ruminant lambs. Results indicated that supplementation of lamb feedlot diets with a source of linoleic acid was a successful method of increasing CLA content of tissues. Crown copyright # 2000 Published by Elsevier Science B.V. All rights reserved.

CONJUGATED LINOLEIC ACID-ENRICHED BEEF PRODUCTION

Canadian beef consumption is approximately 31 kg per annum, or a third of all meats consumed. Beef is a nutrient-rich food, providing good quality protein, vitamins B-6 and B-12, niacin, iron, and zinc. However, animal fats have gained the reputation of being less healthy. The identification of the anticarcinogenic effects of beef extracts due to the presence of conjugated linoleic acid (CLA) has heightened interest in increasing the amount of CLA deposited in beef. Beef cattle produce CLA and deposit these compounds in the meat; thus, beef consumers can receive bioformed CLA. Beef contains both of the bioactive CLA isomers, namely, cis-9, trans-11 and trans-10, cis-12. The relative content of these CLA isomers in beef depends on the feeds consumed by the animals during production. Feeding cattle linoleic acid-rich oils for extended periods of time increases the CLA content of beef. Depending on the type and relative maturity of the pasture, beef from pasture-fed cattle may have a higher CLA content than beef from grain- or silage-fed cattle. In feedlot animals fed high-grain diets, inclusion of dietary oil along with hay during both the growth and finishing phases led to an increase in CLA content from 2.8 to 14 mg/g beef fat, which would provide 77 mg CLA in an 85-g serving of beef. The CLAs appear to be concentrated in intramuscular and subcutaneous fat of beef cattle, with the CLA trans-10, cis-12 isomer being greater in the subcutaneous fat.

EFFECTS OF DIETARY SUNFLOWER SEEDS ON RUMEN PROTOZOA AND GROWTH OF LAMBS

Linoleic acid-rich sunflower-seed supplements (SSS) were used in two experiments (experiment 1, high-concentrate diets; experiment 2, high-forage diets) to study effects on rumen protozoa and the growth of lambs. Both experiments consisted of four treatments, two with a low-protein diet (120 g/kg) and two with a high-protein diet (160 g/kg). For both diets, one treatment was without (control) and one with the SSS (140 g/kg dietary DM). The lambs were fed ad libitum for 70 and 140 d in experiments 1 and 2, respectively. Thereafter, the digestibility of organic matter (OM), acid-detergent fibre and neutral-detergent fibre were determined for each diet with four lambs, and then all lambs were slaughtered and rumen fluid samples were collected and analysed. The results showed substantial decreases (P < 0.001) or total elimination of protozoa in the rumen fluid of the SSS-receiving lambs. In the first experiment the SSS also decreased (P < 0.05) feed intake, but an increase in average daily gain (P < 0.06) resulted in an improved (P < 0.05) feed:gain ratio. Also, the SSS increased (P < 0.05) the digestibility of fibre. In the second experiment the SSS decreased (P < 0.05) the OM digestibility, feed intake and growth of lambs. It was concluded that the use of sunflower-seed supplementation in high-concentrate diets of ruminants reduces rumen fauna, resulting in savings on dietary protein supplements and an increased digestion of feed.

Storage lipid accumulation and acyltransferase action in developing flaxseed

Investigations of storage lipid synthesis in developing flaxseed (Linum usitatissimum) provide useful information for designing strategies to enhance the oil content and nutritional value of this crop. Lipid content and changes in the FA composition during seed development were examined in two cultivars of flax (AC Emerson and Vimy). The oil content on a dry weight basis increased steadily until about 20 d after flowering (DAF). The proportion of α-linolenic acid (α-18∶3, 18∶3cisΔ9, 12, 15) in TAG increased during seed development in both cultivars while the proportions of linoleic acid (18∶2cisΔ9, 12) and saturated FA decreased. The developmental and substrate specificity characteristics of microsomal DAG acyltransferase (DGAT, Ec 2.3.1.20) and lysophosphatidic acid acyltransferase (LPAAT, EC 2.3.1.51) were examined using cultivar AC Emerson. The maximal acyltransferase specific activities occurred in the range of 8–14 DAF, during rapid lipid accumulation on a per seed basis. Acyl-CoA of EPA (20∶5cisΔ5,8,11,14,17) or DHA (22∶6cis4,7,10,13,16,19) were included in the specificity studies. DGAT displayed enhanced specificity for α-18∶3-CoA, whereas the preferred substrate of LPAAT was 18∶2-CoA. Both enzymes could use EPA- or DHA-CoA to varying extents. Developing flax embryos were able to take up and incorporate these nutritional FA into TAG and other intermediates in the TAG-formation pathway. This study suggests that if the appropriate acyl-CoA-dependent desaturation/elongation pathways are introduced and efficiently expressed in flax, this may lead to the conversion of α-18∶3-CoA into EPA-CoA, thereby providing an activated substrate for TAG formation.

Localization and activity of rRNA genes on fenugreek (Trigonella foenum-graecum L.) chromosomes by fluorescent in situ hybridization and silver staining

Abstract Fenugreek (Trigonella foenum-graecum L.), an annual legume crop grown mainly for seed at present, has the potential to be a high-quality forage crop in western Canada. A cytological survey of germplasm stored at the USDA germplasm center demonstrated a somatic karyotype with a chromosome number of 2n=16. Structural details of two pairs of chromosomes (numbers 1 and 2) showed secondary constrictions that were presumed to be the site of rRNA genes. Fluorescent in situ hybridization (FISH) with a heterologous rRNA gene probe from wheat was utilized to physically map their location for the first time on fenugreek chromosomes. Strong hybridization signals of apparently similar copy-number sequences were detected primarily near the centromere on the metacentric chromosome 1 and near the telomere on the acrocentric chromosome 2. Silver staining of the nucleolar organizing region provided evidence that both the sites were transcriptionally active and independently capable of forming a nucleolus. However, the site on chromosome number 2 was relatively more active than the one on chromosome number 1.

Positional distribution of CLA in TAG of lamb tissues

The content and positional distribution of CLA in TAG fractions of lamb tissues was examined with either preformed CLA or the linoleic acid precursor of CLA in the diet as experimental treatments. The CLA content of phospholipid (PL) from these tissues was also examined. Thirteen lambs were randomized to the following dietary treatments: (i) control diet (no supplement); (ii) CLA supplementation (0.33 g d−1 for 21 d prior to weaning) to milk-replacer of pre-ruminating lambs, or (iii) feeding linoleic acid-rich oil (6% safflower oil on a dry matter basis) to weaned ruminating lambs. At slaughter, tissue samples were procured from diaphragm, rib muscle, and subcutaneous (SC) adipose tissue. Safflower oil supplementation in the diet resulted in an increase in CLA content of the TAG from diaphragm, rib muscle, and SC adipose tissue by about threefold (P<0.05) on a mol% basis. CLA was localized to the sn-1/3 positions of TAG. Animals that received pre-formed CLA, however, had increased proportions of CLA at the sn-2 position of TAG from SC adipose tissue, suggesting that there were tissue-specific dietary effects and possible age-related effects on the mode of FA incorporation into TAG. Safflower oil supplementation in the diet had no effect on the CLA content of PL from diaphragm, rib muscle, and SC adipose tissue, suggesting that CLA was preferentially incorporated into the TAG of these tissues.