A study was carried out to evaluate the effect of feed processing (pelleting) on bodyweight, feed conversion and mortality in male broilers. Pelleted feed was compared to mash feed with the same specification. In addition, the effect of feed texture (feed particle size) on bodyweight, feed conversion and mortality, by using crumbles and pellets, ground crumbles and pellets, and mash was evaluated. Six thousand day-old Ross 788 male broiler chickens, originating from a specific broiler breeder flock (37 weeks old) were divided into three treatment groups of 2000 birds by systematic random sampling. The experiment was an 8 x 3 block design, with 250 broilers randomly and equally assigned to each pen. The birds were kept in a controlled environmental house and vaccinated against NCD, IB, IBD and Pneumovirus. The experiment was carried out at 1517 m above sea level, on the Highveld of South Africa. At this altitude and together with the fact that the experiment was carried out during winter (June and July 1997), no inducing methods were necessary. Mortalities were recorded daily and post mortems were done on all dead chickens and the cause of death recorded. Dead chickens were weighed individually and the weight recorded. Bacteriology was done on all the chickens that died from infectious causes to identify the specific bacteria. The bodyweight per pen was determined by weighing all the chickens per pen on day 0, 7, 14, 21, 28, 35 and 42 and weighing at least 20% of the chickens per pen on day 4, 11, 18, 25, 32 and 39. The feed conversion and mortality corrected feed conversion were determined on day 7, 14, 21, 28, 35 and 42. The mean live mass in kg, the percentage survivors, the feed conversion and age in days were used to calculate the production efficiency factor for each treatment group at 42 days of age. Chickens on crumbles and pellets had the highest bodyweight (2304,0 g) at 42 days of age. They were followed by the chickens on the mash diet (2054,1 g) and the lowest bodyweight was recorded on the ground crumbles and pellets (1993,5 g). The difference in bodyweight for the three treatment groups was significant (p#0,05). The pelleting process therefore did not result in better bodyweight, but the bodyweight were determined by the particle size of the feed (feed texture). The percentage weight gain per week, decreased from week one to week six. During the first week and to a lesser extent during the second week, there was a big difference in percentage weight gain between treatment groups. The chickens on the crumbles and pellets grew the fastest (230,1% during week one and 159% during week two). The weight gain for the chickens on the all-mash diet was 187,7% for week one and 153,1% for week two. The slowest weight gain was in the chickens on the ground crumbles and pellets (179,7% during week one and 143,5% during week two). The weekly weight gain in the three treatment groups from week three to week six was similar. The difference in weight gain over the first two weeks, was probably due to the difference in feed texture, because the chickens on the crumbles grew the fastest and the chickens on the ground crumbles the slowest. Eleven percent of the crumbles and 5% of the pellets were smaller than 0,6 mm. In the mash 25,0% and in the ground crumbles and pellets 41,5% of the particles were smaller than 0,6 mm. In the crumbles 44% and in the pellets 76,7% particles were greater than 3,6 mm. In the mash 7,5% and in the ground crumbles and pellets 3,5% of the particles were greater than 3,6 mm. The best FC (1,900) and mortality corrected FC (1,852) were achieved on crumbles and pellets. It differed significantly (p#0,05) from the FC (1,946) and mortality corrected FC (1,921) of chickens on ground crumbles and pellets, as well as the FC (1,963) and mortality corrected FC (1,945) of chickens on mash. There was no significant (p>0,05) difference in the FC and mortality corrected FC in the ground crumbles and pellets, and mash rations. The pelleting process on its own, did not significantly improve feed efficiency. Grinding of crumbles and pellets abolished the feed efficiency responses observed when the physical form was preserved. Particle size (feed texture) was therefore the most important factor determining feed efficiency. Mortality was the highest in chickens on crumbles and pellets (6,57%), followed by 4,03% in chickens on ground crumbles and pellets and 2,85% in chickens on mash. These differences in mortality were significant (p#0,05). The higher mortality on crumbles and pellets was mainly caused by ascites (2,11%) and SDS (1,39%), which caused 3,5% of the mortality. The most important cause of mortality in the group receiving ground crumbles and pellets was SDS (1,01%). Although the total mortality in the chickens on crumbles and pellets was the highest, the better bodyweight and FC in this group resulted in the highest PEF (269,8) at 42 days. The chickens on mash had a PEF of 242,4 and in the chickens on ground crumbles and pellets it was 233,6. The better results on crumbles and pellets are further accentuated by the net return per 2000 day-old chickens placed of R1694.70 when compared to the chickens on ground crumbles and pellets, and R1196.36 when compared to the chickens on mash. This study therefore, showed that particle size (feed texture), played the most important role in determining bodyweight and feed efficiency in broilers. To ensure the heaviest bodyweight and most efficient feed conversion on any given feed specification, it is of utmost importance that broilers receive feed as intact crumbles and pellets, with minimum damage to the crumbles and pellets.
Dissertation (MMedVet (Altil))--University of Pretoria, 2001.