Step-Up Protein Diets for Growing Pullets

Abstract

A pullet rearing program involving step-up protein diets was developed from studies on diet self selection. Day-old Single Comb White Leghorn chicks of a commercial strain were reared conventionally [0 to 8 weeks, 18% crude protein (CP), 3049 metabolizable energy (ME) (kcal/kg); 8 to 12 weeks, 15% CP, 2992 ME; 12 to 20 weeks, 13% CP, 2952 ME] or on a step-up protein regime: [0 to 12 weeks, 12% CP, 3080 ME; 12 to 16 weeks, 16% CP, 2974 ME; 16 to 20 weeks, 19% CP, 2972 ME]. These mash diets were offered ad lib. Twenty-four replicate cages of 10 birds were used for each program. Feed intake and replicate mean body weight were recorded at 8 and 12 weeks. At 20 weeks, birds were individually weighed and transferred to laying cages, with four replicate groups of 12 birds being offered isocaloric diets containing either 13, 15, 17, or 19% CP. Conventional production parameters were measured. Pullets reared on the step-up protein diets were significantly (P<.01) smaller than control birds at 20 weeks of age, although without loss of uniformity in body size. These birds consumed 100 g CP and 2000 kcal ME less than the controls from 0 to 20 weeks. During the subsequent 40-week laying period, step-up protein reared birds consumed significantly (P<.05) less feed than did control reared birds while producing a comparable number of eggs of smaller size and greater shell deformation. Test reared birds were significantly (P<.05) smaller in body size at the end of the laying period. There was no significant (P<.05) interaction between rearing treatment and laying diet protein level. Protein per se had no effect on egg production, although birds produced significantly (P<.05) larger eggs when offered 17 vs. 13% CP. Birds on 19% CP were significantly (P<.05) heavier at end-of-lay than birds offered 13% CP. Mortality was not influenced by either rearing treatment or laying diet CP. It is concluded that pullets can be reared on step-up protein diets as a means of controlling body weight without recourse to physical feed restriction and associated loss in uniformity of body weight.