Studies on the measurement of calcium digestibility in raw materials for poultry and of digestible calcium requirement of broiler starters : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science (Poultry Nutrition) at Massey University, Palmerston North, Manawatu, New Zealand
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Date
2021
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Massey University
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Abstract
The measurement of calcium (Ca) digestibility in feed ingredients for poultry is receiving increasing attention because of recent interest in formulating diets based on digestible phosphorous (P) and the close relationship between these two minerals in their absorption and post absorptive utilisation. Data on the ileal Ca digestibility of Ca sources and factors influencing Ca digestibility in poultry are scant. The current thesis presents follow-up studies of the previous work conducted at Massey University. The Ca digestibility values of Ca sources determined in the thesis, along with previous published data, were then used to develop dietary treatments to assess the digestible Ca requirement of broiler starters.
The first study reported in Chapter 3 was conducted to examine the effect of basal diet composition on true ileal Ca digestibility of four Ca sources namely, limestone, meat and bone meal (MBM), monocalcium phosphate (MCP) and dicalcium phosphate (DCP) in broiler chickens. Two basal diets, namely a maize-based diet and a maize-starch-based purified diet, with each Ca source were tested. The results showed that the average true ileal Ca digestibility was higher in the maize-based diet (0.46) than that in the purified diet (0.37). True ileal Ca digestibility of limestone, MBM, MCP and DCP were determined to be 0.51, 0.41, 0.43 and 0.32, respectively.
In the study reported in Chapter 4, the effect of dietary indicator-type and dietary adaptation length on the apparent ileal Ca digestibility of limestone were evaluated. In Experiment 1, the use of two indicators namely, titanium dioxide and acid insoluble ash (Celite) were compared and the findings showed that the ileal Ca digestibility was unaffected by dietary indicator. In Experiment 2, four dietary adaptation lengths namely, 24, 72, 120 and 168 hours were examined and it was found that the Ca digestibility was unchanged between 72 and 120 hours but decreased at 168 hours of adaptation length.
The third study, presented in Chapter 5, was conducted to measure the influence of age (7, 14, 21, 28, 35 and 42 days post-hatch) on the Ca digestibility of limestone for broiler chickens. The findings revealed that the apparent ileal Ca digestibility coefficients were linearly decreased from day 7 to day 42. The ileal Ca digestibility coefficients were determined to be 0.51, 0.53, 0.36, 0.34, 0.41 and 0.27 at days 7, 14, 21, 28, 35 and 42, respectively. A secondary objective of this study was to examine the influence of dietary crude protein concentration (79 and 153 g/kg) on the apparent ileal Ca digestibility at 21 days of age. It was found the apparent ileal Ca digestibility was not influenced by dietary protein concentrations.
The studies reported in Chapter 6 were conducted to measure the influence of phytase doses (0, 500 and 2000 FTU/kg) on the Ca and P digestibility of soybean meal (SBM) and canola meal (CM) in broiler starters (Experiment 1) and finishers (Experiment 2). True ileal Ca digestibility coefficients of SBM and CM, with no supplemental phytase, were determined to be 0.51 and 0.53, respectively, for broiler starters and 0.33 and 0.22, respectively, for broiler finishers. True ileal P digestibility coefficients of maize-SBM diet and maize-CM diet, with no phytase were determined to be 0.89 and 0.66, respectively, for broiler starters and 0.82 and 0.57, respectively, for broiler finishers. Microbial phytase increased the true ileal digestibility of Ca and P in maize-SBM diet and maize-CM diet, but the effect was more pronounced for the maize-CM diet. Superdosing of phytase (2000 FTU/kg) increased the Ca digestibility in CM and SBM by two-fold compared to the normal phytase dose (500 FTU/kg).
The studies reported in Chapter 7 were conducted to determine the ileal Ca digestibility coefficients of two limestone sources in broilers and layers. The results showed that, in both sources, the apparent ileal Ca digestibility of limestone was found to be higher in laying hens (0.62 and 0.70) compared to broilers (0.50 and 0.43). The findings indicated that laying hens absorb Ca more efficiently than broilers which may be attributed to their high demand of Ca for eggshell formation.
Using Ca digestibility values of Ca sources measured in this thesis work and previous published data, a growth study (Chapter 8) was conducted to estimate the standardised ileal digestible (SID) Ca requirement for 1 to 10 day-old broilers fed different dietary concentrations of both SID Ca (3.3, 3.9, 4.4, 5.0 and 5.5 g/kg) and SID P (4, 5 and 6 g/kg). Based on response surface models, the growth performance, bone mineralisation and mineral utilisation of broiler starters were found to be optimised at 5 g/kg SID P concentration. The concentrations of SID Ca that maximised body weight gain, tibia ash, tibia Ca, tibia P and toe ash were estimated to be 3.32, 4.51, 4.72, 4.36 and 4.78 g/kg, respectively, which corresponds to SID Ca to SID P ratios of 0.66, 0.90, 0.94, 0.87 and 0.96, respectively. Bone mineralisation required more SID Ca than for growth.
Most of the findings reported in this thesis are novel and contribute to the advancement of current knowledge on the measurement of ileal Ca digestibility in poultry and the factors influencing Ca digestibility. The array of factors examined were hitherto unexplored and included the effects of basal diet type, dietary adaptation length, broiler age, phytase dose, Ca source and bird type (broilers vs. layers). Another notable contribution was to establish the requirements of digestible Ca, digestible P and the ratio of digestible Ca to digestible P for broiler starters (1-10-day old).
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Listed in 2021 Dean's List of Exceptional Theses
Keywords
Broilers (Chickens), Poultry, Feed utilization efficiency, Feeding and feeds, Calcium in animal nutrition, Feed utilization efficiency, Dean's List of Exceptional Theses