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Metabolic status and reproduction in precision-fed broiler breeders: Impact of growth trajectories
- Author / Creator
- Afrouziyeh, Mohammad
Broiler breeders are subjected to feed restriction programs to control excessive growth. However, current levels of feed restriction are becoming severe, raising welfare and suboptimal reproductive performance concerns in underfed breeders. To circumvent the issue, we studied new strategic growth curves in this thesis. Birds in all studies were fed using a precision feeding (PF) system.
The first study investigated the effect of minor feed restriction on feed efficiency in New Hampshire and Brown Leghorn strains. The growth data of the birds were fit to a mixed Gompertz model with bird-specific random coefficients for mature BW, rate of maturing, and both to evaluate the effects of random terms on the fitting and predictive performance of the models. The model with both random coefficients was determined to be the most parsimonious model. Minor feed restriction increased production efficiency, but this was not confirmed for the New Hampshire strain.
The second study was conducted with 40 broiler breeder pullets reared on one of ten target growth trajectories, which were designed with 2 levels of the amount of prepubertal growth (Standard g1 and High g1) and 5 levels of pubertal growth timing (I2 that was advanced by 0, 5, 10, 15, or 20% of the coefficient estimated from the breeder-recommended target BW). Analysis of covariance showed that for every week of earlier I2, 24 wk body fat increased by 0.38%; pullets came to lay earlier by 0.49 day; egg production increased by 0.33 egg/hen/d in the High g1 treatment but decreased by 0.27 egg/hen/d in the Standard g1 treatment, respectively. Increasing g1 reduced feeding motivation index by 1.6 and 0.8 visits/meal during rearing and laying phase, respectively.
The third study investigated effects of the growth trajectories on energy efficiency of birds. It also tested the effects of chunking data into different sizes and inclusion of random terms associated with individual maintenance ME and ADG requirements on fitting and predictive performance of ME partitioning models. A model including a random term associated with individual maintenance requirement in a 3 wk chunk size was chosen as the most parsimonious based on greater fitting and predictive performance among the models. Standard g1 treatment had lower residual heat production compared to the High g1 treatment, indicating greater efficiency in utilizing the ME consumed.
The fourth experiment was an extension of the second experiment to evaluate the intergenerational effects of a reduced degree of maternal pre-pubertal phase growth restriction and earlier maternal pubertal phase growth on offspring growth and development. Two replicated broiler studies were conducted that varied in maternal age (35 and 42 wk). Overall, relaxed growth restriction during pre-pubertal and earlier pubertal growth increased male offspring growth by 2.2% and produced more efficient female broilers by reducing FCR by 0.017.
The fifth study evaluated some metabolic biomarkers that gave clues to the metabolic shifts resulting from sexual maturation. A total of 36 broiler breeder pullets were used, of which 30 were randomly assigned to one of 10 unique growth trajectories, and 6 were assigned to an unrestricted group. The growth trajectories varied in total gain in the prepubertal and pubertal growth phases ranging from the breeder-recommended target BW to 22.5% higher, in 2.5% increments. Increasing prepubertal and pubertal BW gains by more than 15% of the breeder-recommended target BW triggered fat metabolism and yolk precursor synthesis, which consequently advanced sexual maturity. We concluded that certain metabolic signatures can be used to predict the metabolic status linked to the bird’s maturity.
The sixth experiment was an extension of the fifth experiment to determine correlation between plasma concentrations of corticosterone measured by Enzyme Linked Immunosorbent Assay (ELISA) and Liquid Chromatography-tandem Mass Spectrometry (LC-MS/MS) methods. Plasma corticosterone levels were not affected by photostimulation BW, indicating the same welfare status between the precision fed high and low BW groups. Concentrations of plasma corticosterone measured using ELISA method were highly correlated (r = 0.95) with values measured using LC-MS/MS method.
In conclusion, the current breeder-recommended target BW is low for optimal reproductive performance. Increasing prepubertal BW gain by 10% and advancing the pubertal growth phase by 20% could increase margin over feed and chick cost for the hatching egg producers and the broiler chicken supply chain as a whole.
- Graduation date
- Fall 2021
- Type of Item
- Doctor of Philosophy
- This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.