Page 15 - National Poultry Newspaper

Australian Poultry Science Symposium
APSS 2020
APSS 2020 a holistic success
DESPITE the recent drought, bushfires and floods in Australia, as well as the internation- al epidemic of coro- navirus, the 31st Aus-
tralian Poultry Science Symposium recorded its highest number of registrations to date.
Even with several in- ternational visitors un-
able to make this year’s rendition of Australia’s premier avian science conference due to trav- el restrictions imposed as a result of coronavi- rus, the event was re- garded as a resounding success.
With an underpin- ning theme of ‘a holis- tic approach to poultry production’ the Syd- ney-based conference hosted a mix of nation- al and international presenters who deliv- ered industry-relevant content for producers.
Given the impact of the drought and sub- sequent bushfires in Australia, it was time- ly that the welcome reception, presented by Assoc Prof David
Phalen, looked at the impact these national disasters are having on native Australian animals and the Uni- versity of Sydney’s commitment to wild- life.
With the support of Sydney University, the Avian Reptile and Ex- otic Pet Hospital has been set up to care for sick and injured ani- mals.
The AREPH is the only purpose-built university-run wildlife hospital in Australia and has over the past four years treated more than 4500 wildlife cas- es.
The welcome recep- tion not only highlight- ed the work being done
by AREPH but it was also a fundraiser, with the initial donation be- ing made by EW Nu- trition who sponsored the welcome reception.
This year’s opening address was delivered by Poultry Research Foundation president Judith O’Keefe who acknowledged long- term sponsors for their ongoing support.
“Looking back over the recent years, there is a sense of pride in what science has brought to industry, which is the key point of this event,” she said.
Following yet an- other successful event, stay tuned for the dates of the 2021 confer- ence.
Assoc Prof David Phalen from Sydney University and David Sherwood from EW Nutrition.
Poster session winnerTerence Zimazile Sibanda.
The benefits of measuring calcium digestibility from raw materials in broilers, meat breeders and layers
TO-date, poultry di- ets have been formu- lated to meet estimated requirements for total calcium, while frequent- ly also maintaining a specified ratio of total calcium:available phos- phorus (AvP).
In vegetable-based diets, limestone can contribute in excess of 50 percent and 90 percent of dietary calcium in broiler diets and laying hen diets, re- spectively.
In laying hens, it is known that limestone particle size can alter the availability of calcium for shell formation and bone mineralisation, and as a consequence, breed recommendations have included specifications for a minimum percent- age coarse limestone grit >2mm in feed formula- tion.
More recent research in broilers has also shown that limestone particle size, as well as the source of limestone, could pro- foundly alter calcium di- gestibility, while simulta- neously having significant effects on phosphorus digestibility and phytase efficacy.
In light of the recent studies that have docu- mented effects of lime- stone quality on the di- gestibility of calcium and phosphorus, it was of interest to quantify dif- ferences in the quality of limestone used in com- mercial feedmills.
With this objective, our laboratory collected 255 limestone samples from feedmills in 16 different countries on the European continent.
GMD>1000 μm.
While analysed calcium
in limestone samples was in most cases high, there was large variation in the GMD particle size of ei- ther fine or grit limestone used in commercial feed- mills.
The dynamic solubility results showed while there was an inverse correla- tion with GMD and solu- bility at all time points, limestone rock (geology) contributed significantly to differences in the solu- bilisation rates between different sources of lime- stone.
With consideration of the recent studies that have elucidated clear ef- fects of limestone particle size and dynamic solubil- ity on calcium and phos- phorus utilisation, these large differences in the dynamic solubility rate arising from differences in the GMD particle size and geology of limestone samples used in commer- cial poultry feed mills can be expected to significant- ly alter the digestibility of calcium and phosphorus in practical diets fed to broilers and laying hens.
A further consequence of this is the ratio of di- gestible calcium:AvP sup- plied to the bird would vary between diets and/or feed mills, dependent on the quality of limestone used.
This highlights the cur- rent practice of formulat- ing to total calcium or maintaining a fixed ratio of calcium:AvP in feed formulation is inaccurate and that there is a need to transition to a digestible calcium system in poultry feed formulation. Introduction
Calcium and phosphorus are two minerals of great concern to poultry nutri- tionists as a result of the relatively large quantities needed in the diet, and the adverse effects on bone
formation, shell quality and overall performance when inadequate amounts of these minerals are sup- plied.
It is further difficult to discuss calcium supply in poultry diets without referring to phosphorus, since the dietary require- ment of these two miner- als has previously been shown to be interdepend- ent.
Should plasma calcium or phosphorus concentra- tions decrease, synthesis of 1,25-dihydroxy chole- calciferol (1, 25(OH)2D3) increases and, in turn, promotes increased in- testinal Ca absorption while renal excretion is decreased.
In broilers, when dietary calcium is increased, typi- cally by increasing the in- clusion of limestone, there is a progressive decrease in phosphorus digestibil- ity.
The primary mechanism whereby this occurs has been thought to be di- rectly, or via formation of calcium-phytate complex- es that reduce the digest- ibility of phytate-bound phosphorus.
Since the utilisation of calcium and phosphorus is influenced by the con- centration and digestibil- ity of the other nutrients in the diet, common prac- tice in broilers has been to maintain a ratio of cal- cium to available phos- phorus when specifying requirements of calcium and phosphorus.
Conveniently, this ratio has been set at 2:1 Ca:AvP in broilers.
The obvious limitation of this approach is the in- terdependence of calcium and phosphorus homeo- stasis in the bird is driven by the amount and ratio of these nutrients provided at tissue level and hence by the ratio of digestible calcium:digestible phos- phorus in the diet; and
not by the ratio of total calcium:AvP supplied in the diet.
In recent years, sever- al research groups have shown calcium digestibil- ity in broilers can vary dramatically depending on the calcium source provided, the solubility of limestone, as well as by the source of phytate and addition of phytase.
With the knowledge that the digestibility of total dietary calcium can be significantly altered by the aforementioned di- etary factors, and that the form of calcium provided and absolute amount can alter phosphorus digest- ibility, the specification of calcium requirements for broilers as total calcium in the diet becomes obso- lete, as does the adherence to a fixed ratio of total calcium:AvP.
The need to better un- derstand how to predict variation in calcium di- gestibility, and the in- fluence of calcium on phosphorus digestibility becomes even more criti- cal when considering the high incidence of lame- ness and bone abnormali- ties observed in the indus- try, with over 1 percent of commercial broilers grown to heavy process- ing weights affected after five weeks of age.
A similar case can be made for commercial laying hens for which re- quirements for calcium are still specified on a total basis.
Particle size and solu- bility of limestone are known to influence the availability of calcium to the hen and can alter shell quality and bone ash.
Some authors also sug- gested the daily calcium requirement of laying hens to maintain eggshell quality should be deter- mined based on the solu- bility characteristics of the limestone.
While breed nutrition recommendations for lay- ing hens specify the sup- ply of a portion of lime- stone as coarse limestone grit, potential differences in the solubility charac- teristics of that grit are not considered when formu- lating to meet the calcium demand of the hen.
This observation be- comes increasingly im- portant in the context of modern laying hens where, as a result of in- creasing length of produc- tion cycles, optimising the utilisation of dietary calcium sources as hens age is critical to meet de- mands for shell formation without compromising skeletal integrity and bird welfare.
Variation in limestone quality and in-vitro as- sessment thereof
In vegetable-based broiler diets, limestone can contribute over 50 percent of the total di- etary calcium supplied to broilers, and in excess of 90 percent of the calcium consumed by laying hens.
Given the previous ob- servations by multiple re- search groups that lime- stone particle size and solubility can affect the utilisation of calcium by broilers and laying hens, as well as phosphorus di- gestibility and phytase ef- ficacy in broilers, it was of interest to characterise the observed variation in particle size and solubil- ity of limestones used in commercial feed produc- tion in Europe to quantify differences in limestone quality used in commer- cial poultry diets.
P.W. Plumstead, M. Sinclair-Black and C.R. Angel
To see the full report presented at APSS 2020 and published in the conference proceedings, please email ben@poul trynews.com.au
National Poultry Newspaper, March 2020 – Page 15
Limestone samples were analysed for mineral content, geometric mean diameter and dynamic solubility at five, 15 and 30-minutes for samples with <1000μm GMD and
at 30, 90 and 150 minutes
for grit limestone with www.poultrynews.com.au