Measuring motivation for appetitive behaviour: food-restricted broiler breeder chickens cross a water barrier to forage in an area of wood shavings without food

Broiler breeders (parents of meat chickens) are selected for fast growth and become obese if fed ad libitum. To avoid this and maintain good health and reproductive ability, they are feed restricted to about 1/3 of what they would eat ad libitum. As a result, they experience chronic hunger and exhibit abnormal behaviour patterns that may indicate stress and frustration. One approach to measuring hunger is to observe how much birds will work, such as pecking a key, for access to more or different types of food. However, the sight, smell, and feedback from consumption of the feed reward changes the context and may artificially raise feeding motivation. To avoid this, we tested broiler breeders in an apparatus in which they could work for access to a wooden platform covered in wood shavings by crossing a water runway which increased in length and depth in 8 successive tests. In the wood shavings area, they could perform exploratory and foraging behaviour (the appetitive phase of feeding) but were never rewarded with feed. Sixty birds were divided into three feed quantity treatments: commercial restriction (R), and twice (2R) or three times (3R) this amount. Overall, birds fed R worked harder to reach the wood shavings area (reached it in a larger number of tests) than 2R and 3R birds (P2R>3R). This indicates that restricted-fed birds were hungry and willing to work for the opportunity to forage even though food was never provided, suggesting that their motivation to perform the appetitive component of feeding behaviour (foraging/food searching) was sufficient to sustain their response. Thus food restriction in broiler breeders is a welfare concern. However these methods could be used to test alternative feeding regimes to attempt to find ways of alleviating hunger while still maintaining healthy growth and reproduction in these birds

Diagram of the water runway apparatus.

<p>Birds were placed on the start platform and could chose to walk down the ramp into the water runway, up the second ramp and go onto the wood shavings area. The wood shavings area could be moved along the runway so that the distance travelled through the water could be increased up to a maximum of 4</p

Bird weights for the 3 feed treatments (mean ± SD) from 14 days of age to the end of the trial.

<p>Birds began different feed treatments at 35 days of age and testing began at 50 days of age.</p

Latency to reach the wood shavings area for tests for which birds were successful across eight tests with increasing water runway length and depth for the three food treatments for a) means (±SE) estimated from LMM on log scale and b) back transformed to the latency to reach the wood shavings area.

<p>Latency to reach the wood shavings area for tests for which birds were successful across eight tests with increasing water runway length and depth for the three food treatments for a) means (±SE) estimated from LMM on log scale and b) back transformed to the latency to reach the wood shavings area.</p

Proportion of time spent foraging while in the wood shavings area for tests for which birds were successful across eight tests with increasing water runway length and depth for the three food treatments for a) means (±SE) estimated from LMM on angular scale and b) back transformed to the proportion of time spent foraging while in the wood shavings area.

<p>Proportion of time spent foraging while in the wood shavings area for tests for which birds were successful across eight tests with increasing water runway length and depth for the three food treatments for a) means (±SE) estimated from LMM on angular scale and b) back transformed to the proportion of time spent foraging while in the wood shavings area.</p

Cost increases (runway length between the two ramps and water depth) with increasing test number for the 3 feed treatments.

<p>Water depth is based on percentage of the mean length of the birds' legs, from the ground to top of the hock, for each food treatment. The initial water depth was 1/6^th of the average leg length and increments of 1/6^th were then made at successive tests so that in the last two tests the water was deeper than the birds' legs were long, meaning that her body was getting wet.</p

Proportion of birds reaching the wood shavings area across eight tests with increasing water runway length and depth for the three food treatments for a) means (±SE) estimated from GLMM on logit scale and b) back transformed to the proportion of birds reaching the wood shavings area.

<p>Proportion of birds reaching the wood shavings area across eight tests with increasing water runway length and depth for the three food treatments for a) means (±SE) estimated from GLMM on logit scale and b) back transformed to the proportion of birds reaching the wood shavings area.</p