Abstract:
The seven day period post hatching is considered critical as it is thought to account for 8-10% of the final body weight of broilers at 40 days of age. The digestive capacity of newly hatched chicks is quite low, and increases with age to support growth. By meeting the nutritional requirements of the young chick, broiler performance may be improved throughout the production cycle by means of carryover effects. Not only will this increase the return of investment on feed costs but will also reduce the negative environmental effects that result from broiler production. Despite models using 21 day old birds having proven to yield better estimates of nutritional requirements during the early feeding phase, birds older than 40 days of age are still widely used in models for determination thereof.
This trial was conducted in an effort to identify the optimal dietary energy (metabolisable energy) to protein ratio (expressed on the basis of total lysine) for Ross 308 broiler chicks from 0 to 21 days of age. Birds were provided with 12 treatments comprising of three metabolisable energy (ME) levels (11.31, 12.13 and 12.97 MJ/kg) in combinations with four total lysine (TLys) levels (1.3%, 1.4%, 1.6% and 1.7%). Each treatment was replicated 4 times. Following the experimental feeding phase, all birds were fed the same Grower, Finisher and Post-finisher diets until slaughter at 35 days of age. At day twenty-one of the trial, two male birds were randomly selected from each pen, euthanised and these carcasses were analysed for crude fat, fibre and protein. Body weight, feed intake and mortality were measured on days zero, three, seven, 10, 14, 21, 28 and 35 of the trial.
Optimal broiler growth was found at TLys1.4 with no differences between ME levels. However, at the lowest TLys level body weight (BW) improved with every increase in ME level. Body weight gain (BWG) was similarly favoured by TLys1.4 during the experimental feeding phase but an inversed effect was observed in the carryover phase, where improved BWG was noted at high TLys levels and low ME levels. Feed intake (FI) was more influenced by TLys than ME levels, with increased FI when TLys increased from TLys1.3 to 1.4 at ME 11.30 and 12.13. Resultant 35 day feed conversion ratio (FCR) did not improve beyond TLys1.4 and differences due to ME levels were only observed at the lowest and highest TLys levels (ME 11.30 being the least favourable). No treatment effects were observed for mortality. The calculated performance efficiency factor (PEF) of the broilers in this study was maximised at TLys1.4 with no differences between ME levels; however, these results were matched when TLys1.3 was combined with ME 11.30. Carcass fat was observed to decrease with increasing TLys levels across all ME levels and carcass protein conformed to expected trends by increasing with increased TLys levels. Results based on broiler performance suggest that TLys of 1.4% in combination with ME levels as low as 11.30 MJ/kg may be successfully used in the early feeding phase.
