INFLUENCE OF AGE AND FEEDING LENGTH ON PHYTASE EFFICACY IN BROILER CHICKENS

2019-01-17T14:23:41Z (GMT) by Olufemi Babatunde
The objective of this thesis was to investigate the effect of age and feeding length on phytase efficacy in broiler chickens during the starter phase. Two studies were carried out to evaluate this objective.
Study 1 was a randomized complete block design with 4 × 5 factorial arrangements of treatments. There were four diets; a positive control (PC), negative control (NC) and two phytase supplemented diets with inclusion levels of 1,000 and 2,000 phytase units/kg. There were five age and duration of feeding groups; Three 2-d feeding lengths terminated at d 8, 14, and 22 (d 6 to 8, d 12 to 14, and d 20 to 22), a 5-d feeding length terminated at d 14 (d 9 to 14) and a 16-d feeding length terminated on d 22 (d 6 to 22). Growth performance and sample collections were collected at the end of each phase i.e. d 8, 14 and 22. There was a difference (P < 0.01) in weight gain, feed intake, and feed efficiency between birds fed the PC diets and birds fed the NC diets across all groups as birds on the NC diets had lower performance (P < 0.05) than birds on the PC diet. However, birds fed the phytase supplemented diets had higher (P < 0.05) growth performance compared with birds fed the NC diet across all groups. Similarly, phosphorus (P) and calcium (Ca) digestibility and retention of birds fed the NC were lower (P < 0.05) as compared with birds fed the PC diet while birds fed the phytase supplemented diets had higher mineral digestibility and retention (P < 0.05) compared with birds on the NC diet. Age effect was evaluated by comparing the performance of birds fed the experimental diets for 2 d until d 8, 14, and 22. Birds fed until d 14 had the highest impact of the NC diet on mineral utilization, and the largest improvement of phytase on mineral utilization as compared with birds fed until d 8 and 22. Similarly, when feeding length effect was considered, birds fed for a shorter period had greater response to phytase (P < 0.05) on nutrient utilization than birds fed for a longer period at d 14 and 22. Tibia ash was higher (P < 0.05) in birds fed phytase supplemented diets for a longer period (i.e. 16 d) compared with birds fed or 2 or 5 d. The results from this study observed that age and duration of feeding influenced phytase efficacy especially in younger birds fed for a short period. However, it could not be determined if feeding birds for a short period at different ages in the starter phase would have a similar effect.
In study 2, the effects of age and feeding low P diets to birds for a short period of time on phytase efficacy and super dosing were evaluated at two critical points in the starter phase. This study had 3 × 2 × 2 factorial arrangements of treatments comprising 3 diets; a PC, NC, and a NC with phytase supplemented at 2,000 phytase units/kg; and 2 ages (i.e d 14 and 22) and 2 feeding lengths (i.e 2-d and 5-d). Thus, birds were fed the experimental diets from d 12 to 14, 9 to 14, 20 to 22, and 17 to 22 respectively. Results observed were similar to the first study. Birds fed the NC diet had lower (P < 0.01) performance as compared with birds fed the PC diets across all age and feeding length groups. Similarly, birds fed diets with the super dose level of phytase had greater growth performance (P < 0.01) compared with birds fed the NC diets. When age effect was considered, birds fed for 2 or 5 d until d 14 had the greatest improvements of phytase on nutrient utilization and bone mineralization compared with birds fed for both periods until d 22. When effect of feeding was considered, birds fed for 2-d at both ages had greater responses to phytase in performance and nutrient utilization compared with birds fed for 5-d at both ages. Plasma myo-inositol was higher (P < 0.01) in birds fed the super dose level of phytase compared with birds fed the NC diet.
In summary, we could conclude that the efficacy of phytase both at 1,000 and 2,000 FTU/kg was higher in birds fed for 2 d until d 14 as compared with the other groups. This could potentially help in designing studies to evaluate new phytase products or for comparing the efficacy of phytase from various sources. Feeding broiler chickens during the suggested time phase would potentially reveal the maximum efficacy of the phytase product.