Energy partitioning by broiler breeder pullets in skip-a-day and precision feeding systems

S.H. Hadinia, P.R.O. Carneiro, C.A. Ouellette, M.J. Zuidhof, Energy partitioning by broiler breeder pullets in skip-a-day and precision feeding systems, Poultry Science, Volume 97, Issue 12, 2018, Pages 4279-4289, ISSN 0032-5791, https://doi.org/10.3382/ps/pey283

energy partitioning model, maintenance, peer-reviewed, Precision Feeding, Publication

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Residual feed intake is the difference between observed and expected ME intake (MEI) and it is an efficiency indicator that can account for variations in maintenance requirements and growth. Metabolizable energy intake models can be used to estimate RFI as an efficiency indicator. The error term of MEI models is referred to RFI. The first objective of the current study was to develop a model whose coefficients describe ME cost for total HP and growth in broiler breeder pullets. Partitioning MEI by modern broiler breeders has not been assessed as comprehensively during the rearing period. Additionally, using an energy partitioning model to measure energetic efficiency has not been studied thoroughly. The second objective was to evaluate energy efficiency and feed conversion rate of broiler breeder pullets fed using precision feeding and skip-a-day feeding systems. Efficiency was calculated using RFI, RHP, and feed conversion ratio (FCR). It was hypothesized that precision-fed broiler breeder pullets would be more efficient compared to pullets fed using conventional skip-a-day feeding method because of a higher feeding frequency.

Approach

A total of 630 Ross 308 broiler breeder pullets were reared using pan feeders from 0 to 9 wk of age in floor pens. From 10 to 23 wk of age, they were randomly allocated to 2 treatments (7 pens of 45 birds in each treatment): precision feeding system (PF) and conventional skip-a-day feeding (CON). PF pullets could access feed 24 h/d and sequentially received several small meals over a full 24 h/d rather than 1 large meal. In the CON treatment, pullets were fed on alternate mornings. At the end of each week in the morning, all pullets in both treatments were individually weighed manually. The ADG was calculated for each experimental unit (pen). The cumulative FCR for each experimental unit was calculated weekly by dividing the total feed intake to the total ADG. The AME content of the diet was determined by adding 2% acid-insoluble ash marker for 4 d in the diet at both 16 and 23 wk of age. Two birds in each pen (14 per treatment) were randomly selected at 16 and 23 wk of age and euthanized 4 h after the CON treatment birds were fed. Ileal digesta samples were collected and gross energy (GE) was measured using bomb calorimetry for feed and digesta samples. At 16 and 23 wk of age, 28 birds per treatment were euthanized and breast muscle and fat pad weights were recorded. Fat pad weight and breast muscle weight as a percentage of live BW were calculated for both treatments.

Analysis of Results

Overall MEI for both treatments increased from 10 to 23 wk of age primarily because BW increased with age and broiler breeder pullets needed more ME to meet their maintenance requirements, and ADG also increased with age, for which ME was also required. In the present study, the average MEI of broiler breeder pullets from 10 to 12 wk of age was 147 and from 20 to 23 wk of age was 241 kcal/d. The overall average daily MEI for PF treatment (174 kcal/d) was 90% of the CON treatment (194 kcal/d; P < 0.001). Increased feeding frequency in PF pullets could have increased their efficiency, thereby requiring a lower MEI to photostimulation age compared with the CON treatment. Although PF hens had lower MEI compared to CON hens during the entire experimental period, they had greater BW relative to CON birds. The CON and PF pullets in the present study partitioned 89.0 vs. 86.9% of the MEI into total HP, respectively, during the entire experimental period (P = 0.020). Conversely, birds in the CON and PF treatments partitioned 11.0 and 13.1% of MEI into BW gain (growth), respectively (P = 0.02). Weekly and overall ADG did not differ between PF and CON pullets from 10 to 23 wk of age. In the current study, RFI was not affected by treatment at the P < 0.05 level (–3.8 and 3.7 kcal/d, respectively; P = 0.064).

Application

In conclusion, although CON pullets actually had lower BW, they had higher MEI and higher total HP compared to PF pullets. The PF pullets had lower cumulative FCR compared to CON pullets; thus, PF pullets used their feed more efficiently. However, residual HP analysis suggests that both treatments had similar biological efficiency. The CON treatment pullets did not appear to lose more energy as heat as a result of diet-induced thermogenesis, but because they were fed less frequently, probably used the extra energy they consumed to store and mobilize nutrients, and to deposit fat in their body.

Abstract

An empirical nonlinear mixed model was derived to describe metabolizable energy (ME) partitioning in Ross 308 broiler breeder pullets. Its coefficients described ME used for total heat production (HP) and growth. A total of 630 pullets were randomly and equally assigned to 2 treatments: precision feeding (PF) and conventional skip-a-day feeding (CON) from 10 to 23 wk of age. The PF system allowed birds to enter voluntarily at any time, weighed them, and provided access to feed for 60 s if their BW was less than the target BW. Birds in the CON treatment were fed as a group on alternate days. Energetic efficiency of pullets was evaluated using residual total heat production (RHP), defined as the difference between observed and predicted total HP. Additionally, ME intake (MEI), ADG, HP, and cumulative feed conversion ratio (FCR) were calculated for the entire experimental period. The energy partitioning model (P < 0.05) predicted MEI = (120+u)BW^0.68 + 1.52(ADG) + ε. Total HP was (120 kcal/kg^0.68 + u); the energy requirement for each g of BW gain was 1.52 kcal/d. The random variable u ∼ N (0, σ_u²) indicated a pen level HP standard deviation σ_u = 12.1 kcal/kg^0.68. Over the experimental period, for CON and PF treatments, respectively, MEI was 194 and 174 kcal/d (P < 0.001); ADG was 15.3 and 15.4 g/d (P = 0.94); HP was 129 and 111 kcal/kg^0.68 (P < 0.001); FCR was 4.888 and 4.057 (P < 0.001); and RHP was 0.12 and –0.12 kcal/kg^0.68 (P = 0.73). The CON pullets had similar ADG, but higher MEI relative to PF, consistent with levels of heat production predicted by RHP. The PF pullets had lower cumulative FCR compared to CON pullets. The PF pullets lost less energy as heat, likely because they were fed continuously, reducing the need to store and mobilize nutrients compared to CON pullets. Thus, increased feeding frequency likely increased PF pullet efficiency.