Abstract
The use of alternative, often bulky ingredients is becoming widespread in poultry diets as the industry seeks to reduce its economic and environmental costs. Consequently, there is an increased need to accurately predict the performance of birds given such diets and identify their maximum capacity for bulk. We offered diets diluted with a range of bulky ingredients to male Ross 308 broilers to assess their capacity for bulk and identify a bulk characteristic responsible for limiting intake. Four hundred ninety-five day-old broilers allocated into 45 pens, were offered a common starter diet until day (d) 7, and 1 of 9 grower diets from d 8 to 29 (Period 1). Each of the grower diets was diluted with either 30 or 60% of oat hulls (OH), wheat bran (WB), or grass meal (GM), or a mixture of 2 bulky ingredients at an inclusion level of 30% each (OHWB, OHGM, WBGM). From d 29 to 43 (Period 2), all birds were offered the bulkiest diet (GM60). A number of bulk characteristics were measured on the diets. Feed intake was measured daily, and birds were dissected on d 29 and 43 for organ and carcass measurements. During d 8 to 14 diet water-holding capacity (WHC) was more consistent in predicting feed intake when scaled per unit of body weight than any other bulk characteristic. However, this was no longer the case during d 15 to 28. In Period 2, the response and adaptation to the bulkiest diet was determined by previous experience to bulk. Birds offered a bulkier diet during Period 1, were better able to adapt the size of their digestive organs and increase scaled feed intake, such that there were no differences between these birds and those offered the GM60; the converse was the case for birds on the least bulky diets. We conclude that WHC is able to predict maximum intake on bulky diets in unadapted birds. Adaptation to bulky diets can be very fast, so that their high bulk content no longer limits feed intake and performance.
Highlights
Prediction of voluntary food intake is the basis of any simulation model that aims to account for bird performance under different management conditions (Kyriazakis and Emmans, 1999; Gous, 2007)
The lowest crude fiber, acid detergent fiber, acid detergent lignin, and feed density were seen in the WB30 diet, whereas the lowest neutral detergent fiber and dietary water-holding capacity (WHC) were seen in the OH30 diet
We used 3 bulky ingredients to investigate the capacity of a modern broiler strain for bulk, with the overarching objective of reaching a prediction of maximum capacity of the birds for bulky diets. This is of particular relevance in informing models and predictions of broiler feed intake and performance (Nascimento et al, 2020), especially that there is an increased interest in the use of alternative, potentially bulky ingredients in broiler diets (Morgan and Choct, 2016; Scholey et al, 2020)
Summary
Prediction of voluntary food intake is the basis of any simulation model that aims to account for bird performance under different management conditions (Kyriazakis and Emmans, 1999; Gous, 2007). The inclusion of alternative ingredients in poultry diets is becoming increasingly common to achieve sustainable food production and ensure global food security (Morgan and Choct, 2016; Tallentire et al, 2018; Tufarelli et al, 2018; Wyngaarden et al, 2020) As such there is an urgent need to understand and predict the ability of modern broiler genotypes to cope with such alternative ingredients, which are typically bulky in nature. There is evidence to suggest that modern broiler genotypes have retained the ability to regulate energy intake, as the energy content of the diet is reduced (Linares and Huang, 2010; Nascimento et al, 2020; Taylor et al, 2021) This ability is not infinite and holds only up to a maximum feed intake, which presumably relates to the maximum capacity of the gastrointestinal tract (GIT) for volume or bulk. Nascimento et al (2020) did not find any adaptation to the bulky ingredients over time (for 45 d), whereas Taylor et al (2021) suggested that adaptation on their bulky diets took approximately 15 d, this depended on the nature of the bulky ingredient
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