Nutrient use in chicks during the first week posthatch.

We examined effects of feeding chicks differing levels of macronutrients on performance during the first 7 d posthatch in this study. Four experiments were conducted using male Ross x Ross broiler chicks. The first experiment examined, in a 3 x 3 factorial design, the effect of feeding fat at 3, 7, and 11% and protein at 18, 23, and 28%. With increasing protein and fat levels feed intake and BW decreased. The second experiment examined, in a 3 x 2 factorial design, the effect of fat at 3, 7, and 10% and cellulose at 3 and 13%. Increasing fat in the diet decreased feed intake at both cellulose levels with little effect on BW. High cellulose decreased feed intake and BW. Experiment 3 examined, in a 3 x 2 factorial design, the effect of protein at 19, 23, and 27% and cellulose at 3 and 13%. Increasing protein levels decreased feed intake with little effect on BW. Cellulose decreased feed intake as levels increased. The fourth experiment examined, in a 4 x 2 factorial, the effect of feeding protein at 19, 21, 23, and 25% and fat at 4.5 and 9%, for 1 wk followed by standard diets through marketing. Significant differences in feed intake, BW and feed efficiency were observed at 7 d, but by 18 d differences were not significant and by 31 and 41 d no treatment effects were observed. Fat and protein percentage in the carcass in all experiments were not altered by dietary treatments and thus the efficiency of protein and fat retention decreased with increasing dietary intake. This study indicates that feeding diets with varying macronutrient levels to chicks during the first week post-hatch has distinct effects as compared to older broilers. It appears that once limiting amino acids and energy are provided the influence of dietary composition on immediate posthatch growth is limited.