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Although changes in dietary protein levels change metabolism in the broiler chicken, there is little information concerning the time course of the process of adaptation. Therefore, male Hubbard broiler chickens were fed diets containing either 12 or 30% crude protein from 7 to 28 d of age and then were switched to the opposite level for an additional 9 d. Birds were bled and killed at 0, 2, 5, 7and 9 d following the reversals. Data taken at these intervals included those involved in vitro lipogenesis (IVL), growth and feed consumption, hepatic enzyme activities and plasma hormones and metabolites. Birds fed the lower level of crude protein were smaller in growth from 7 to 28 d. Feeding these birds a higher protein diet from 28 to 37 d improved both growth and feed efficiency in comparison to controls. Lipogenesis was also greater and plasma insulin-like growth factor-I (IGF-I) less in birds fed the lower protein diet. Switching dietary treatments increased and decreased lipogenesis as birds were switched from high to low and low to high protein diets, respectively. Half-maximal changes were observed 2 d after the reversal and maximal changes 5 d after the reversal. In contrast, switching dietary treatments decreased and increased plasma IGF-I as birds were switched from high to low and low to high protein diets, respectively. Half-maximal changes were observed 2 d after the reversal. Of the three hepatic enzymes monitored, malic enzyme activity most closely followed the rapid changes in IVL. In the present study, plasma IGF-I may be a more sensitive indicator of changes in dietary protein than changes in intermediary metabolism.
MeSH Terms
- Aging
- Analysis of Variance
- Animals
- Body Weight
- Chickens
- Dietary Fats
- Dietary Proteins
- Lipid Metabolism
- Lipoprotein Lipase
- Liver
- Time Factors
The purpose of this experiment was to study the effects of dietary protein on metabolic adaptations in birds given triiodothyronine (T3) at 28 d of age. Knowledge about the role of dietary protein in thyroid metabolism is lacking. Male broiler chickens were fed diets containing either 120 or 300 g crude protein/kg from 7 to 28 d. At this time, one-half of each group was given that diet supplemented with 1 mg/kg T3. Birds were sampled at 0, 2, 5, 7, 9 and 12 d following the initiation of the T3 treatments. Measurements taken at these intervals included in vitro lipogenesis (IVL), growth and feed consumption, hepatic enzyme activities and plasma thyroid hormones and metabolites. As expected, IVL was greater at 28 d in birds fed the lower level of protein. Moreover, when T3 was added to either diet, IVL decreased by 50% after 5 d. Plasma IGF-I and T4 were greater while T3 and GH were less when birds were fed the higher level of crude protein. Plasma T3 increased and T4 decreased 3 d following the addition of T3 to diets containing either level of crude protein. Most metabolic changes in response to feeding T3 occurred within 2 to 5 d, suggesting that changes in intermediary metabolism preceded morphological changes that we have previously seen. In addition, dietary protein levels may not affect adaptive responses to T3.
MeSH Terms
- Adaptation, Physiological
- Aging
- Animal Feed
- Animals
- Chickens
- Dietary Proteins
- Growth Hormone
- Insulin-Like Growth Factor I
- Liver
- Male
- Radioimmunoassay
- Thyroxine
- Triiodothyronine