Influence of age on utilization of supplemental fats by young turkeys.

Male poults were fed diets containing 0, 4, 8, or 12% tallow or 4, 8, or 12% animal-vegetable fat blend (A-V Fat) from 1 day to 8 weeks of age. Supplemental fat improved 8-week body weight and feed efficiency, irrespective of fat source. Fat retention (fat consumed-fat excreted) was not affected by fat level or by fat source after 2 weeks of age. At 2 weeks, fat retention by poults fed tallow was less than that of poults fed A-V Fat. Fat retention increased with age, irrespective of fat source or level. Fat retentions ranged from 66.4 to 83.7 at 2 weeks and from 90.8 to 96.5 at 8 weeks of age. Changes in metabolizable energy (ME) values of the fats with age paralleled those of fat retention, whether ME were estimated by multiplying fat retention percentages times gross energy of the fats or by regression analysis of changes in diet ME associated with increments of fats. On the basis of changes in diet ME, the ME of tallow was 6808 kcal/kg at 2 weeks and 8551 kcal/kg at 8 weeks. Analagous values for A-V Fat were 7114 and 8924 kcal/kg, respectively. Fatty acid analysis of dietary and excreta fat indicated that, as turkeys aged, improvements in retention were greatest for palmitic and stearic acids, especially in the instance of tallow. Fatty acid binding protein (FABP) assay of intestines from poults fed no added fat, 12% tallow, or 12% A-V Fat showed that fat level did not significantly affect FABP activity. There was, however, a marked increase in intestinal FABP in 6- and 8-week-old poults as compared with 2- or 4-week-old poults.