Slowing Down Chicken Growth

Tue, 18, January, 2022 by Food from Thought

A wide-ranging, comprehensive research project investigating how different growth rates affect chickens’ health and welfare may change the poultry industry with a shift to slower-growing birds in the future.

“Fast-growing broilers have been highly selected over the past 50 years to efficiently turn chicken feed into meat,” says Dr. Tina Widowski, a professor in the University of Guelph’s Department of Animal Bioscience, holder of the Egg Farmers of Canada Research Chair in Poultry Welfare and a researcher with Food from Thought.

“They’ve also been selected for large breast muscles because of consumer demand.”

Animal Welfare Issues

Widowski says that while the result has been an inexpensive, highly efficient, environmentally friendly animal protein product, high rates of growth coupled with large breast sizes have had a lot of adverse consequences for the birds. Through selective breeding, the birds’ body composition, appetite and metabolism have changed so that they grow really fast – from chick to slaughter in about five to six weeks in a commercial operation. The growth of muscle meat outpaces the skeleton and heart, so the chickens have trouble with mobility and lameness and are much less active.

“There are biological limits, and speeding up growth rates produces adverse consequences to the chickens’ health and physiology,” she says, pointing out that these problems have existed for decades. Consumer concerns about the animal welfare issues prompted poultry producers and retailers in the Netherlands to develop the Dutch Retail Broiler, also known as the “Chicken of Tomorrow.” This slower growing breed is allowed to gain only up to 50 grams per day, is stocked at a density of up to 38 kilograms per square metre and is provided with environmental enrichment.

In North America, Global Animal Partnership (GAP), a U.S. animal welfare standards organization founded by Whole Foods Market CEO John Mackey, approached University of Guelph researchers to conduct this project. The University’s Food from Thought program, the Ontario Agri-food Innovation Alliance – a partnership between the University and the Ontario Ministry of Agriculture, Food and Rural Affairs – and several major poultry genetics companies provided support for the project. Food from Thought aims to position Canada as a global leader in the development of innovative solutions that improve both the sustainability and the productivity of agricultural production at global, landscape and micro scales.

The Research

The project was an interdisciplinary effort that examined everything from animal welfare and behaviour to feed efficiency, meat quality, anatomy and mobility. Working with Widowski, research associate Stephanie Torrey managed a large team of post-doctoral students, technicians, graduates and undergraduates, in collaboration with faculty from across the Ontario Agricultural College and the Ontario Veterinary College.

A total of 7,528 broilers from 14 different genetic strains were examined over two years. They consisted of 12 slow-growing strains and two conventional strains that were categorized into conventional, fast slow-growing birds, moderate slow-growing birds and slow slow-growing birds. All of them were incubated, hatched, housed, managed and fed in the same way, and the categories of strains differed in body weights, growth rates, feed intake and feed efficiency. At 48 days of age, for example, strains in the conventional category were 835 to 1,264 grams heavier than strains in the other categories.

An article prepared by the research team and published by GAP in fall 2020 said: “In summary, we found that conventional strains of broiler chickens grew faster, more efficiently and had higher breast yields than did slower growing strains.

However, there are significant trade-offs for this high productivity. In comparison to strains with slower growth rates and lighter breast yields, strains with faster growth rates and higher breast yields had lower activity levels, poorer indicators of mobility, poorer foot and hock health, higher biochemical markers of muscle damage, higher rates of muscle myopathies, and potentially inadequate organ development. Fast growth rate coupled with high breast yield is associated with poor welfare outcomes.” The broiler chickens were raised in identical pens. Researchers observed their behaviour to quantify levels of activity, use of environmental enrichments and bird mobility. They also monitored litter quality and foot health

The Future

Going forward, GAP will use the data from the study to help develop welfare standards and assessment protocols for the broilers they certify. According to its website, GAP has certified more than 1,200 products and 3,900 livestock farms. More than 5,000 outlets carry GAP-certified products.

“A number of retailers and companies in the food service industry will be using the GAP standards to obtain genetic strains that have better welfare outcomes,” Widowski says.

In August 2021, seven large U.S. companies– including Aramark, Sodexo and Target –formed the U.S. Working Group for Broiler Welfare. By 2026, the group will compel suppliers to use broiler breeds whose higher welfare outcomes meet the criteria of the RSPCA Broiler Welfare Assessment Protocol or Global Animal Partnership.

This story is a part of the 2020-21 Food from Thought Annual Impact Report