The effect of absolute alterations in energy concentration of developing and finishing diets for the large white Turkey on performance and carcass quality with a note on the correlation of back skin fat and grade of finish 1

A commercial strain of large white turkey was fed maize‐soybean meal type rations from 8 to 21 (for hens) and 23 weeks of age (for toms). During the developing period (8–18 weeks) each sex was offered diets having either a “high” or “low” energy concentration. To assure energy as the only dietary variable while con‐comitantly effecting a reasonable separation in caloric density, 3 per cent tallow was substituted by an equal amount of cellulose. At 18 weeks of age, the birds representing each of the developing period treatments, were subdivided into 3 further groups and subsequently offered the experimental finishing rations. These terminal diets, through the use of tallow, glucose and cellulose, were altered in energy content (2202, 2642, and 3083 kcal ME/kg) and respectively rated “low”, “moderate” and “high” in caloric concent. All birds were slaughtered, their specific gravity determined, and the quantity of fat in skin taken from the dorsal surface determined.

Though there was a reduced weight gain with those birds fed the “low” energy finishing diet, growth of all other turkeys, irrespective of sex, was comparable regardless of treatment during the developing period while the F/G ratio was altered to accommodate caloric density alterations. Excepting those groups offered the “low” energy finisher, period and cumulative consumption of metabolisable calories, like weight gain, was near equal. Dressing percentage and grade of fleshing essentially paralleled what was obtained with growth. There were no obvious effects due to developing period treatment or with the upper two levels of energy in the finishing ration; however, both of the aforementioned parameters were noticeably poorer when the “low” energy finisher was fed. The grade of finish of both the breast and back was found to improve with an increasing dietary caloric density of the terminal ration. Though there were no apparent effects on breast finish due to development period treatment, differences were noticed with the quality of back finish.

It is speculated that the grade of back finish can be confounded by a subdermal fat depot. This additional lipid deposit is probably a carry‐over from the developing period; hence, dietary adequacy during this time could influence ultimate grade of back finish.

Back skin fat, expressed as a percentage of dry weight, was found to be highly correlated with grade of finish on both the breast and back. Calculation of linear least squares lines indicated little or no difference with area of finish assessment; however, the correlation coefficient, apparently because of variations caused by developmental period dietary energy alterations, was lower on the back than the breast (r = ‐0.756 vs r = ‐0.771).