Feeding calcium and phosphorus to stop broiler leg issues

Feeding broilers more calcium and phosphorous early in life may help alleviate leg and bone problems.

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(Dancu Aleksandar | iStock.com)
(Dancu Aleksandar | iStock.com)

Feeding broilers more phosphorous early in life, while simultaneously optimizing the supply of digestible calcium, may help alleviate leg and bone problems.

As part of the Virtual 2020 Poultry Science Association Annual Meeting, Dr. Peter Plumstead, innovation director at Chemuniqué (Pty) Ltd. in South Africa, spoke about research conducted by Dr. Roselina Angel, a professor of animal and avian sciences at the University of Maryland’s College of Agriculture and Natural Sciences, about the role of calcium and phosphorus in the skeletal health of broilers.

“We do not sell bones, we sell meat. This is why nobody has ever wanted to feed calcium and phosphorus levels to maximize bone mineralization,” Plumstead said. “But because of the carryover effect, that the first 10 days has on the life of the bird – and also the relative low economic impact of feeding higher levels of calcium and phosphorus during that phase – I think it’s quite a cheap strategy to ensure better bone integrity.”

limestone-quarry-surface

Limestone is a key source of calcium in feed formulas, but the chemical composition of the rock varies greatly depending on the source leading to issues with consistent formulation. | (IvanSpasic | BigStock.com)

Leg issues with modern broilers

In the past decades, broiler genetics are enabling the birds to reach greater weights in a shorter amount of time than ever before. However, those gains come with the tradeoff of placing excessive stress on the legs of the animal.

Plumstead said about 2% to 6% of heavy broilers are lost due to skeletal issues. Leg deformities, bone infections and other problems are both significant animal health and welfare issues. These symptoms happen because the rate of bone mineralization does not keep pace with the growth of the bird.

Since slowing down the growth rate of the bird is not commercially viable, the best solution may be to better-optimize the supply of digestible calcium and phosphorus with the varying rate of bone mineralization.

Feeding from hatch

When a chick hatches, it's already used up most of the mineral reserves in the yolk – notably phosphorus, zinc and copper. Therefore, it does not have the minerals it needs to support the rapid rate of skeletal growth after hatch.

Studies referenced by Plumstead show during the first 10 days of life, the bird is mineralizing bone at six -times greater than any other time of its life, so feeding calcium and phosphorus at that time is critical.

Finding out exactly how much to feed at this time is complex. Studies conducted by Angel show the requirement for phosphorus is dependent on the supply of digestible calcium. An under supply of calcium could therefore lead to lower estimates of the phosphorus requirement for bone mineralization. This could negate a lot of conventional thinking about feeding these minerals, since the amount of calcium and phosphorus needed for ideal weight gain is much lower than what’s needed for ideal bone structure.

Angel recommended that in the first 10 days that birds require 0.53% digestible phosphorus in order to maximize bone mineralization, or about 0.6% available phosphorus. The calcium level is 0.85% analyzable calcium, or about 1% calcium when formulating with a high dose of phytase assuming a phytase contribution of 0.15%.

This is a much higher recommendation for phosphorus than the breed recommendations provide. That’s because the breeder recommendations are likely based on maximizing body weight gain not skeletal composition.

Commercial feeding recommendations

Angel tested the feeding tables in a commercial broiler operation by comparing the breeder’s recommended levels with her own recommendations for the first 10 days. After 10 days, all birds received the same, breeder recommended diet. She observed a carryover effect in that birds fed her recommended diet had significantly higher bone mineralization than the control birds at 42 and 52 days of age.

Therefore, Angel and Plumstead recommended birds should be fed for maximum bone mineralization for the first 10 days of life, then for the rest of their life, they should be fed for maximum bodyweight gain and feed conversion ratio.

Moreover, the research shows that birds can be fed even less calcium and available phosphorus after 16 days than breeders recommend and still maximize bodyweight. However, that can only work if the birds are fed the phosphorus and calcium they need to maximize bone mineralization in the first 10 days and the supply of calcium relative to phosphorus thereafter is optimized.

The limestone problem

This also means the fixed recommendation of a 2 to 1 ratio of total calcium to available phosphorus throughout the life of the bird offered by the leading breeding companies is outdated.

A major issue with that recommendation is diets are formulated with limestone. Limestone is a carbonate sedimentary rock often composed of the skeletal fragments of fossilized marine animals. Limestone contributes about 60% to 70% of the calcium a bird will consume. However, the exact geological formation of limestone varies greatly depending on where it is mined.

Research conducted on limestone sourced from around the globe found significant variance in the actual digestible calcium coming from limestone. In some samples it was as low as 19.9% percent and in others it was as high as 68%.

Therefore, in order to formulate feed more accurately, the digestibility of calcium from limestone and its subsequent impact of dietary phosphorus digestibility and phytase efficacy must be better understood. Without that understanding, it can throw the levels of calcium and phosphorus the bird needs, and is receiving, out of balance.

To solve this problem, Plumstead said current studies are working on understanding the relationship between the quality of limestone and the mineral needs in broiler feed. This is a need because excess calcium in a diet will affect the birds’ ability to digest phosphorus.

“There’s huge opportunity to decrease calcium and phosphorus levels from around about 16 days of age that can provide significant cost-savings and environmental benefits” Plumstead said. “But we can only do that when we start formulating more accurately for calcium both in understanding the digestibility of the calcium from the limestone as well as in preventing excesses of calcium or too little calcium.”

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