PhD student, University of Alberta
Overcoming reproductive issues related to light schedules and feed intake in meat type chickens.
Broiler breeders are the parents of the meat type chicken used for human food production. In the current poultry industry, this type of chicken is fed at severely restricted levels during rearing, around 25 to 50% of their voluntary intake. This prepares them the best for the reproductive phase of their life, but also implies a significant reduction of the welfare of the birds due to hunger and stress at feeding time. My doctoral research is therefore focusing on the effects of feed restriction in chickens on metabolism, growth, and reproduction under different circumstances. In my studies, I use the Precision Feeding System, designed by Dr. Martin Zuidhof, with which real time feed intake and body weight data can be collected and feeding decisions can be made. In April 2016, I started the final project of my degree, where I looked at the interaction between different day lengths during rearing and various levels of feed restriction on subsequent reproductive performance in broiler breeders. For this 60-week study I recorded egg production and egg weight, but I also dived into the physiology of the bird and measured reproductive hormones levels in their blood. The expectation is that there is no interaction between day length and restriction level, but that hens with a less severe restriction will come into production earlier, and that hens with a shorter day length during rearing will produce more eggs. My studies will have large implications for the poultry industry. The poultry industry produces worldwide around 90 million tons of meat and around 70 million tons of eggs per year, and the demand for chicken products continues to increase. With these large numbers, even a minor increase in growth, egg production, or efficiency can have a massive influence on a global scale. In addition, in many western countries serious societal concerns about animal welfare arise. If it can be shown that broiler breeders can be less severely restricted without production loss, this can relieve hunger and stress in many birds.
Abstract: Natural antibodies (NAb) are an important component of the first line of immune defense. Selective breeding for enhanced NAb levels in chickens may improve general disease resistance. It is unknown what the consequences of selection for NAb will be on the productive performance of laying hens. In this paper we describe the genetic relations between NAb titers binding keyhole limpet hemocyanin at 19 wk age and production traits in a white purebred leghorn chicken line observed in several time periods. A linear animal model was used to estimate (co)variance components, heritabilities, and correlations. Negative genetic correlations were found between egg weight and NAb titers, and between egg breaking strength and NAb titers. Positive genetic correlations were found between the feed conversion ratio (consumed feed/egg mass produced) and NAb titers, and egg production and NAb titers. Negative phenotypic correlations were found between body weight and NAb titers, between egg weight and NAb titers, and between egg breaking strength and NAb titers. Positive phenotypic correlations were found between egg production and NAb titers, and feed conversion ratio and NAb titers. In general, phenotypic correlations were more often significant, but less pronounced than genetic correlations. Other production traits were not found to be significant related to NAb titers. These findings suggest that there is a genetic tradeoff between levels of immunity and some production traits, although the underlying mechanism(s) remain(s) unclear. The results suggest possible consequences for production efficiency as a result of selective breeding for improved general disease resistance by natural antibodies.
Pub.: 07 Mar '15, Pinned: 27 Jun '17
Abstract: Delayed feed and water access is known to impair growth performance of day old broiler chickens. Although effects of feed access on growth performance and immune function of broilers have been examined before, effects of dietary composition and its potential interaction with feed access are hardly investigated. This experiment aimed to determine whether moment of first feed and water access after hatch and pre-starter composition (0 to 7 days) affect growth rate and humoral immune function in broiler chickens. Direct fed chickens received feed and water directly after placement in the grow-out facility, whilst delayed fed chickens only after 48 h. Direct and delayed fed chickens received a control pre-starter diet, or a diet containing medium chain fatty acids (MCFA) or fish oil. At 21 days, chickens were immunized by injection of sheep red blood cells. The mortality rate depended on an interaction between feed access and pre-starter composition (P=0.014). Chickens with direct feed access fed the control pre-starter diet had a higher risk for mortality than chickens with delayed feed access fed the control pre-starter diet (16.4% v. 4.2%) whereas the other treatment groups were in-between. BW gain and feed intake till 25 days in direct fed chickens were higher compared with delayed fed chickens, whilst gain to feed ratio was lower. Within the direct fed chickens, the control pre-starter diet resulted in the highest BW at 28 days and the MCFA pre-starter diet the lowest (Δ=2.4%), whereas this was opposite for delayed fed chickens (Δ=3.0%; P=0.033). Provision of MCFA resulted in a 4.6% higher BW gain and a higher gain to feed ratio compared with other pre-starter diets, but only during the period it was provided (2 to 7 days). Minor treatment effects were found for humoral immune response by measuring immunoglobulins, agglutination titers, interferon gamma (IFN- γ ), and complement activity. Concluding, current inclusion levels of fish oil (5 g/kg) and MCFA (30 g/kg) in the pre-starter diet appear to have limited (carryover) effects on growth and development, as well as on humoral immune function.
Pub.: 08 Mar '16, Pinned: 27 Jun '17
Abstract: Natural antibodies (NAb) are defined as antibodies present in individuals without known antigenic challenge. Levels of NAb binding keyhole limpet hemocyanin (KLH) in chickens were earlier shown to be heritable, and to be associated with survival. Selective breeding may thus provide a strategy to improve natural disease resistance. We phenotyped 3,689 white purebred laying chickens for KLH binding NAb of different isotypes around 16 weeks of age. Heritabilities of 0.12 for the titers of total antibodies (IgT), 0.14 for IgM, 0.10 for IgA, and 0.07 for IgG were estimated. We also estimated high, positive genetic, and moderate to high, positive phenotypic correlations of IgT, IgM, IgA, and IgG, suggesting that selective breeding for NAb can be done on all antibody isotypes simultaneously. In addition, a relatively substantial non-genetic maternal environmental effect of 0.06 was detected for IgM, which may reflect a transgenerational effect. This suggests that not only the genes of the mother, but also the maternal environment affects the immune system of the offspring. Breaking strength and early eggshell whiteness of the mother's eggs were predictive for IgM levels in the offspring, and partly explained the observed maternal environmental effects. The present results confirm that NAb are heritable, however maternal effects should be taken into account.
Pub.: 27 Jun '15, Pinned: 27 Jun '17
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