Laying hens selected and bred for high performance in a controlled environment face various challenges when exposed to free-range housing systems. Gut impaction with grass, nutritional imbalances, and social stress such as feather pecking are some of the major challenges that the modern free-range egg industry in Australia is facing. The research subject to this thesis aims to improve the performance of commercial laying hens by comprehending the aforementioned challenges with the use of feed additives.

In this thesis, it was demonstrated that pasture consumption significantly (P < 0.05) reduced the digestibility of crude protein (CP), acid detergent fibre (ADF), neutral detergent fibre (NDF), insoluble arabinose and insoluble xylose. The digestibility of CP, ADF and NDF was significantly (P < 0.05) improved in hens fed a diet supplemented with multi enzymes (T2) or a diet supplemented with organic acid and essential oils (T3), compared to hens fed a control diet (T1). Similarly, hens fed the T2 diet had a greater digestibility (P < 0.05) of free oligosaccharides containing arabinose and xylose compared to hens fed T1 or T3 as discussed in Chapter 3. This higher digestibility of nutrients and non-starch polysaccharides can be linked to the heavier body weight of hens fed T2. In general, pasture consumption increased the body weight and egg weights of hens. However, non significant changes were observed on internal and external egg quality except a significant increase in yolk color colour score as a result of pasture consumption as discussed in Chapter 4.

The effect of pecking stones were tested in two commercial free range layer farms. On Farm A, using fixed sheds and flock sizes of 20,000 hens, access to pecking stones reduced (P = 0.001) hen mortality per week. Hens with access to pecking stones also had better wing feather conditions compared to hens of the control group (pecking stone × age, P = 0.002). These results provide evidence that access to pecking stones reduces feather loss and mortality. However, pecking stone consumption also caused hens to decrease large sized feed particles consumption and subsequently modified feed intake as discussed in Chapter 6.

The results of these experiments indicated that feed additives (dietary enzymes as well as freely available pecking stones) can be powerful tools to improve hen performance and welfare under free range conditions. In conclusion, the negative effects associated gut impaction, feather pecking in free-range hens' performance, health and welfare can be reduced with feed additives. However, further research is warranted to establish the role of various feed additives in freerange layer diets on commercial farms.

Rabies is a preventable viral zoonosis that causes inflammation of the brain, and eventually death, in infected mammals. With few exceptions, including Australia, terrestrial rabies can be found worldwide. More than 55,000 deaths from rabies infection are reported annually; these are mainly in Asia and Africa where the primary reservoir is the domestic dog.

Despite ongoing control efforts in Indonesia, canine rabies remains a disease of critical concern there. Although rabies is not endemic in Australia, at less than 300km away in Indonesia, a rabies incursion is a likely and imminent threat.

To improve preparedness for a canine rabies outbreak in Australia, I collected data on a number of extant dog populations in northern and eastern Australia. I used a range of methods including self-administered questionnaires, GPS telemetry collars, camera trapping and mark-recapture studies. Using my own data and parameters collected from the wider literature, I developed state-transition models to determine how rabies could spread through these dog populations. Finally, I used these same models to evaluate a range of control strategies, including dog removal and vaccination, to identify the most effective options for reducing impacts in Australian communities following a rabies incursion.

Model outputs suggested that rabies will progress differently within functionally different dog populations present within Australia. Restrained domestic dogs posed limited risk for rabies transmission, because interactions with other dogs were limited and generally supervised by owners. Free-roaming domestic and hunting dogs will likely play an important role in rabies transmission in some situations only, primarily based on their ability to roam, access to other free-roaming dogs and their interactions within and between dog groups. Wild dogs (including dingoes) proved the most critical type of dog for rabies spread and maintenance in Australia, because they are widely distributed, often in high abundance, roam over large distances and frequently interact.

I found that time to detection for rabies in wild dogs will likely be lengthy, probably due to low infection rates prior to an epidemic and limited contact with humans, relative to the other categories of dog that I studied. Further, the capacity of authorities to implement effective control strategies for wild dogs will likely be restricted because of limited access to individual animals. The economic costs of controlling a rabies outbreak involving wild dogs will be substantial and likely equivalent to the costs for extensive aerially-based wild dog control that are currently used in some areas of Australia (~Aus$34 km-2).

Australia’s current plans to address rabies incursions, which were developed in the 1990s are clearly outdated. My findings reveal that revision of these plans, taking specific account of relevant differences between restrained domestic dogs, free-roaming domestic dogs and extensive wild dog populations is necessary to ensure that Australia is adequately prepared for the arrival of canine rabies.