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Broiler BW at 56 D of age has increased by over 450% due to intensive genetic selection from 1957 to 2005, whereas the target BW for broiler breeders has remained almost constant. As a result, the degree of feed restriction in broiler breeders became more severe and modern broiler breeders have reduced fat deposition. This can reduce egg production during the laying period. To increase efficiency, ensure equitable feed distribution for every individual bird, and increase consistency in supply of nutrients to increase egg production, new feed restriction methods or new feeding technologies may be needed for modern broiler breeders. A novel precision feeding (PF) system was developed at the University of Alberta to provide the right amount of feed to each bird, increase BW uniformity, and increase efficiency. The first objective for the current experiment was to develop an ME intake model whose coefficients quantified the amount of ME partitioned to total HP, ADG, and egg mass of broiler breeder hens. The second objective was to use this model to compare energetic efficiency between a conventional daily-restricted feeding program and the PF system. The third objective was to evaluate the effect of a conventional daily restricted feeding program and the PF system on egg production, egg mass, total HP, ADG, carcass composition, and age at 50% production as an indicator of sexual maturation.
A total of 480 Ross 308 broiler breeder hens were randomly and equally assigned to 2 treatments (8 pens of 30 hens in each treatment): 1) precision feeding system (PF) and 2) conventional daily restricted feeding (CON) in a randomized complete block design. The PF and the CON hens were reared to achieve the breeder-recommended Ross 308 BW target. A single broiler breeder layer diet was formulated according to the Ross 308 recommendations and was provided in pellet form to both treatments for the duration of the study. Diet and ileal digesta samples were collected from 16 hens per treatment to calculate AME. For carcass characteristics, 42 birds per treatment were euthanized at each of 23, 28, 32, and 34 wk of age, and the weights of breast muscle (pectoralis major + pectoralis minor) and abdominal fat pad were recorded. The weights of fat pad and breast muscle were reported as a percentage of live BW. At each dissection age, the ovarian stroma and oviduct were weighed and expressed as a percentage of BW. Each large yellow follicle was individually weighed at 34 wk of age and the number of hierarchical LYF was counted. Eggs were collected daily and average egg weight was determined for each pen.
The CON hens had a 3% higher ME intake (366 kcal/d) compared with the PF hens (354 kcal/d) from 23 to 34 wk of age. The ADG of CON hens was higher than PF hens from 23 to 28 wk of age, after which ADG did not differ between treatments. The lower ME intake for the PF hens during the first 5 wk of the experiment than for the CON hens could have been due to several factors. First, the CON hens were weighed only once per week and the feed allocation decisions were made weekly, considering their BW and desired rate of gain for the subsequent week. The BW of CON hens at the start of the laying period was lower than the PF hens (2,477 vs. 2,602 g respectively); thus, the feed allocation for the CON hens was increased compared with PF hens which resulted in their higher ME intake. Breast muscle as a percentage of BW did not differ between the CON and the PF hens at any age. At 23 and 28 wk of age, hens in the CON treatment had increased fat pad compared with hens in the PF treatment. However, there was no difference in fat pad percentage after 28 wk of age. In the current study, the CON hens deposited more energy in the fat pad; thus, they had more energy available for reproductive development and egg production. Overall, HDEP from 24 to 34 wk of age was higher for the CON hens (65.5%) compared with the PF hens (55.2%). The peak of HDEP for the CON treatment was 87.6% from 32 to 33 wk of age, compared with 82.0% for the PF treatment from 33 to 34 wk of age. The PF hens likely did not peak by 34 wk of age. Age at 50% production was estimated to be 192.7 d ± 0.56 for the CON hens, 8.5 d earlier than the PF hens (201.2 d ± 0.75; P < 0.05). The CON hens had higher relative ovary and stroma weights than the PF hens at 28 and 32 wk of age. Weight and number of LYF (F1 to F7) did not differ between the CON and the PF hens at 34 wk of age. In the current study, the CON hens had lower RFI compared with the PF hens (–5.9 and 6.7 kcal/d, respectively); thus, they were more energetically efficient than the PF hens. These results indicated that the CON hens partitioned ME intake more efficiently than the PF hens.
The feed allocation decisions for the PF treatment were based on the individual BW of each hen, and the increase in feed allocation was provided after the hen laid the egg; thus, the PF hens had limited nutrients to form the egg. Conversely, feed increases for the CON treatment allowed for all hens to increase feed intake simultaneously prior to lay an egg. Thus, the PF hens had lower ME intake than the CON hens from 23 to 28 wk of age. Increased diet-induced thermogenesis and body size likely contributed at least in part to the higher total HP by the CON hens. However, the model predicted that the CON hens compared with the PF hens would partition less energy toward total HP and more energy toward growth and egg mass and eventually they increased egg production. This resulted in the higher energetic efficiency of the CON hens than the PF hens. The CON hens compared with the PF hens had higher fat pad content at 23 and 28 wk of age, greater ovary and stroma weight at 28 and 32 wk of age, and greater oviduct weight at 28 wk of age. These results showed that the CON hens likely had more resources available for egg production and partitioned more energy toward developing reproductive tissues which advanced the age at 50% production. To provide the practical conclusion whether use the PF system in the industry for the maximum egg production in broiler breeders, the results of the current study should be taken in the context of other research results that used the PF system to feed broiler breeders. The PF system can be used for increasing egg production in broiler breeders. Because it was shown by the previous research in our group that increasing the target BW for 22% compared with the standard breeder-recommended target BW increased egg production. Therefore, we hypothesized that the target BW for the PF birds should be increased before the laying period and around the time of sexual maturation to help the PF birds to increase their ME intake and the body fat deposition to increase their productivity. The MEe (0.75 kcal/g) predicted from the ME intake model did not have biological meaning which showed that the predicted ME intake model was not great. The reasons could be due to the relatively small sample size for the number of experimental units and the short duration of the egg collection.