Graduate Thesis Or Dissertation
 

Polyunsaturated fatty acid metabolism in broiler chickens : effects of maternal diet

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  • Three experiments were conducted in broiler hens to study the influence of dietary n-3 polyunsaturated fatty acids (PUFA) on egg quality, antioxidant status in progeny, and eicosanoid production in tissue. The objective of experiment 1 was to determine the effect of hen age and dietary n-3 PUFA on egg quality and hatchability. Two-hundred-twenty breeder chicks (males and females) (Cobb Breeders) were raised until 20 weeks of age following the company guidelines. At this age, 3 groups of birds (24 breeder hens and 3 roosters) were randomly allocated to one of the following dietary treatments: 3.5% sunflower oil (Low n-3 diet), 1.75% sunflower oil + 1.75% fish oil (Medium n-3 diet) or 3.5% fish oil (High n-3 diet). Egg quality was evaluated at 29, 37 and 45 weeks of age by determining total egg weight, its components (albumen, yolk and shell) and shell thickness. Total fat content in the yolk and its fatty acid profile was also determined. Egg production was recorded daily. Breeder hens fed the High n-3 diet laid lighter eggs with lighter yolks, albumens and shells than those fed the Medium and Low n-3 diets (p<0.05). Eggs laid by hens fed the Medium n-3 diet had thicker shells than those laid by hens fed the Low n-3 diet (p<0.05). Egg weight, yolk weight, albumen weight, shell weight and shell thickness increased significantly with hen age (p<0.05). Total fat content in the yolk was significantly higher in the eggs laid by 37-week-old and 45-week-old hens than in those laid by 29-week-old hens. Hens fed the high n-3 diet laid eggs with significantly higher n-3 PUFA and lower n-6 PUFA content than hens from the other treatments (p<0.05). Hen age did not affect the n-3 or n-6 PUFA content. Fertility and hatchability were not affected by maternal diet. Total egg weight, yolk weight, albumen weight and shell weight was decreased by feeding n-3 PUFA to breeder hens. The decreased n6:n3 ratio brought about by maternal dietary n-3 PUFA was further investigated in connection with possible effects on antioxidant and eicosanoid status in newly hatched chicks. The objective of experiment 2 was to determine the effect of maternal diet (Low, Medium and High n-3) on the antioxidant and eicosanoid status, tissue fatty acid profile and lipid peroxidation in the newly hatched chick. Two-hundred-ninety-eight eggs were collected from the 29-week-old breeder hens mentioned in experiment 1. After incubation, day-old chicks were randomly selected from a pool of eggs laid by hens fed the three experimental diets. Antioxidant status was established by measuring activity of antioxidant enzymes (glutathione peroxidase, glutathione reductase, superoxide dismutase and catalase) and the content of total glutathione. Hatchability and total fat content in the tissues were not affected by maternal diet. n-3 PUFA content increased and n-6 PUFA decreased significantly in chick’s tissue (p<0.05) hatched from hens fed the fish-oil supplemented diet compared to those hatched from hens fed the Low n-3 diet (p<0.05). Total glutathione and antioxidant enzyme activity was not affected by maternal diet, except for catalase, whose activity was significantly lower in chicks hatched from hens fed the High n-3 and the Medium n-3 diets than in those hatched from hens fed the Low n-3 diets (p<0.05). Malondialdehyde, a measure of lipid peroxidation, was significantly lower in the liver of chicks hatched from eggs laid by hens fed the High n-3 diet than in those hatched from hens fed the Medium n-3 diet. Maternal dietary n-3 PUFA was successfully transferred to the newly hatched chicks without compromising their antioxidant status. The decreased n-6/n-3 ratio observed in chicks hatched from hens fed the fish-oil supplemented diets needs was further investigated relative to its downstream modulatory effects in connection with fat metabolism. The objective of experiment 3 was to establish the effect of maternal diet on fatty acid accretion in heart tissue, and the production of eicosanoids by heart tissue homogenates and peripheral blood mononuclear cells (PBMNC) from broilers fed diet devoid of long-chain PUFA. Broilers were hatched from hens fed the Low, Medium or High n-3 diet. One-hundred-fortyfour 1-day-old chicks were weighed and randomly allocated to four pens housed in three rooms of similar dimensions. Temperature was controlled according to specifications by Cobb Breeders during the 42 days that the experiment lasted. A cardiac morphological study was conducted on a weekly basis starting at 14 days of age to assess the heart weight relative to body weight. Also, the ventricular weights index (right ventricular weight divided by the total ventricular weight) was determined weekly from 14 days onwards. Day-0 chicks hatched from hens fed the High n-3 diet were significantly lighter than those hatched from hens fed the Low n-3 diet. After accounting for age, chicks hatched from hens fed the Low n-3 diet were significantly heavier than those hatched from hens fed the High n-3 diet (p<0.05). Maternal diet did not affect heart weight, after accounting for age. The heart percentage (heart weight relative to body weight) was significantly higher in chicks hatched from hens fed the High n-3 diet than in those hatched from hens fed the Low n-3 diet (p<0.05). The ventricular weights index was not affected by maternal diet. At 7 and 14 days of age, arachidonic acid (AA) content in heart tissue was significantly lower in chicks hatched from hens fed the High n-3 diet than those hatched from hens fed the Low n-3 diet (p<0.05). At 7 days of age, AA content in the heart tissue of chicks hatched from hens fed the High n-3 diet was significantly lower than in those hatched from hens fed the Medium n-3 diet (p<0.05). At day 0, the heart tissue production of prostaglandin E2 (PGE2) was significantly higher in the chicks hatched from hens fed the Low n-3 diet than in those hatched from hens fed the Medium or High n-3 diets (p<0.05). At the same age, thromboxane A3 (TXA3) production was significantly lower in the heart tissue of chicks hatched from hens fed the Low n-3 diet than in that of chicks hatched from hens fed either the Medium or Low n-3 diets (p<0.05). At day 7, PBMNCs isolated from chickens hatched from hens fed the Low and Medium n-3 diets produced significantly higher PGE2 and TXA2 concentrations than those isolated from birds hatched from eggs laid by hens fed the High n-3 diet (p<0.05). At day 31, PBMNCs isolated from chickens hatched from hens fed the Medium and High n-3 diets produced significantly higher PGE2 and TXA2 concentrations than those isolated from chicks hatched from eggs laid by hens fed the Low n-3 diet (p<0.05). Chicks hatched from hens fed the High n-3 diet had a higher heart/body weight than those hatched from the Low n-3 diet. Thus, chicks hatched from hens fed the Low n-3 diet may be at higher risk of developing cardiovascular complications related to high AA concentrations in the heart and blood cells during the first week of age. Further research is encouraged in which the three subpopulations of broilers (i.e.hatched from hens fed the Low, Medium and High n-3 diets) are raised under commercial conditions to investigate how the economic loss, due to a reduction in body weight observed in the High n-3 chickens compares with the potential reduction in mortality during the first week of age. Finally, the mechanistic action of n-3 PUFA needs further investigation, especially molecular aspects related to modulatory effects on gene expression.
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