Feed restriction in the parental stock of meat producing chickens, broiler breeders, is essential in order to decrease the high growth rate that they are genetically selected for. The feed restriction does however lead to chronic hunger and stress. Stress can be measured by counting H/L ratios and the method of manually counting H/L ratios was evaluated. The method was not a good way to ensure reliable individual H/L ratios but still gives an H/L ratio indication on a group level and was therefore still used in the study. Two different feeding regimens were investigated in the study: 5:2 skip-a-day (SKIP) with two fasting days and daily feed restriction (CTRL), with chickens sampled at 9 and 12 weeks of age. There was no significant difference in body mass between the treatments at either age. SKIP chickens had significantly higher H/L ratios compared to CTRL at 12 weeks of age (P=0.020), but both treatments had H/L ratios above the reported limit of stress (0.5). The SKIP group on a feeding day significantly increased plasma glucose levels during the day (10.3 to 11.5 mmol/L, P=0.020) and had significantly higher liver mass and liver glycogen levels compared to the CTRL (P≤0.001). The SKIP group were also less fearful on fasting days and significantly less active than the CTRL (P≤0.050), regardless of age or daily feed differences. The conclusion was that both treatments were stressed but skip-a-day chickens were habituated to their regimen and did not experience worse welfare than daily fed broiler breeders.

The parental stock of meat type chickens (broiler breeders) are commonly feed restricted to decrease their rapid growth and the issues associated with it. Among these birds, chronic hunger and stress are the most prominent welfare concerns and mass heterogeneity within flocks a major management challenge. The present study compared small and large broiler breeders of the same age within a flock, with the hypothesis that small birds would show signs of poorer welfare indicated by higher corticosterone concentration and heterophil/lymphocyte ratio as a consequence of higher experienced feed restriction due to competition. It also aimed to characterize morphometric differences between small and large birds within flocks as well as between birds on different feeding regimens; skip-a-day vs. every-day-fed. Heterophil/lymphocyte ratio at 4 weeks was significantly higher in large birds compared to small birds, but corticosterone concentration did not differ. Relative mass of the upper gastrointestinal tract, pancreas and liver of small birds at 4 weeks of age were significantly larger, while relative muscle and gizzard fat mass were significantly lower compared to large birds. 12 weeks old skip-a-day fed birds largely followed the pattern of 4 weeks old small birds. In the present study, no clear signs of poorer welfare in small broiler breeders could be seen and the morphometric differences might suggest different ways to cope with feed competition. A larger gastrointestinal tract might indicate long-term investments and maybe that smaller broiler breeders, and skip-a-day fed birds, are better habituated to feed restriction.

There has long been evidence for increased lipids in the liver of chickens exposed to feed restriction, commonly used for production hens. Lipogenesis is an important part of the metabolism and storing of glucose, a source of energy. Few studies compare the difference of lipids in the liver in chickens between regular feed restriction and skip-a-day diets, despite differences in lipid content found in other organs and in overall carcass. In this study I experimentally investigate if a difference in lipid content can be found in broiler breeders exposed to two different feeding regimes, 65 % feed restriction and 5:2 skip-a-day, along with the difference between days and time points (a.m. and p.m.). I also experimentally investigate the effect on dry weights of the liver. I expected to see a difference in lipids of the liver, with an increase found in skip-a-day birds. However, a difference could only be observed in the dry weights of the livers in birds exposed to skip-a-day feeding. Although there was no significant change in lipids, there is a pattern for increase in lipids in skip-a-day birds. Therefore, the conclusion can be drawn that an increase in lipogenesis caused by skip-a-day diet exists but it was not big enough to cause a significant difference in lipid content. For the dry weights of the livers, we can suspect lipids and glycogen as the reason for the increased weight but to determine exactly how these two components affect the skip-a-day birds’ further inquiry is needed.