In part one we looked at the development of the modern egg laying bird; now we’ll focus on how these genetic characteristics are expressed in practical terms. To help explain, please see the two pie charts below (please note – these charts are used to demonstrate a principle, and do not represent precise ratios);
In both charts, the blue section represents the energy (and for the purpose of this exercise we will broaden that term to “nutrients”) required for normal daily functioning (feeding, fighting, breathing, perching, immunity, temperature regulation, feather replacement etc), while the orange section represents the nutrients required for the bird to produce eggs. As the Jungle Fowl only lays a small number of eggs in the course of a year, it partitions very little to egg production throughout most of its productive life. By stark comparison, the modern laying hen must necessarily devote much more of her nutrient resources to the production of eggs, considering that she has the potential to lay an egg nearly every day of the year! Therefore, looking once again at the pie charts, the Jungle Fowl partitions nearly all of it nutrients into maintenance, while the modern laying hen has around half the available nutrients of the Jungle Fowl available for her maintenance functions. When these birds are housed in environmentally controlled sheds, with stable temperatures, precise rations, no predators and virtually no social interaction they can perform to their full genetic potential because there are few external stressors requiring additional maintenance energy. However, take these birds out of a cage and let them loose on pasture, and the whole picture changes – dramatically! Remember my catch phrase from part one – “Modern laying hens are little more than a life-support system for a reproductive tract”.
I am confident that every commercial pastured egg producer using a modern “brown” bird (Bond, Hyline, Isa or Lohmann) with a normal beak has experienced some (or maybe all!!) of the following production issues:
- Feather pecking and “silver backing” resulting in very “bald” birds by 60+ weeks
- Cannibalism, particularly through vent pecking
- Unreliable or variable egg production
- Decreasing egg shell quality with age
- Decreasing eggs shell colour with age
- Low body weights
- Poor persistence (ability to produce a viable quantity of saleable eggs after 60+ weeks)
- Crowding and “anxiousness” of the birds around vehicles and staff when they approach the laying shed
- Inability to achieve and/or maintain a reasonable “peak” of production
Each of these problems are influenced in varying degrees by the genetics of the birds, some slightly and others almost completely. By way of example, let’s look more closely at a situation that is so common amongst pastured layer flocks that it is considered normal behaviour, and that is the crowding of the birds around vehicles and staff.
In nearly 20 years of consulting to pastured egg and meat bird producers, the phenomenon of crowding layers is something that really strikes me as a huge problem, yet virtually all producers that I visit are unaware of the dreadful implications of this behaviour. I remember very clearly my first experiences with a client that I have worked with for around 15 years. During my very first visit to the site, we inspected the layer flocks out in the field. As we approached one batch of birds, they all raced toward the vehicle, and as we walked, with all the chooks milling around us, vocalising loudly, my client beamed at me with pride and said “Look, my birds are really pleased to see me”. I will never forget the look on this dear man’s face as I delivered my response, “They aren’t pleased to see you, they’re starving!” I thought he was either going to punch me on the nose or burst into tears! I have no doubt that some readers of this article will object to my statement, claiming that the birds have always behaved like this, and that it is a normal behaviour. However, the sad reality is that chickens have a natural aversion or fear of man, and under normal circumstances would prefer to stay out of his or her way. Consider for a moment a flock of young pullets out in the field, say 15 to 16 weeks of age. These birds have not started laying and are settling into their new environment. In most cases these birds show little if any interest in people, although this can vary depending on management practices. However, once these same birds approach peak production, the amount of vocalisation and crowding increases – something I have observed on hundreds of separate occasions on many different locations.
This situation then begs the question “Why ?”; and the answer is as simple as it is disturbing. Before the pullets had started to lay eggs, their demand for nutrients (please refer to the charts above) was comparatively low, and they received all they needed from the ration supplied (I am assuming that the ration has been correctly formulated and presented). However, as they approach peak production at least two significant changes take place. First; the reproductive tract increases markedly in size, with the ova (that ultimately form the yolk) growing from barely visible through to full size, and every size in between. The number of growing egg yolks, known as hierarchal ova, depends on many factors, but in most pullets the number of visible ova can be in the hundreds. Once the bird starts laying eggs, there is a constant demand for nutrients to “grow” the egg within the bird. Second; the birds have been ingesting grass during their time on the range, and almost without exception, every single bird in a pastured flock will have some grass or grass fibres present in their gizzard (the grinding organ that acts as the “teeth” of the chicken). The actual amount of grass will vary between individuals, and after opening several thousand gizzards, I have personally seen every extreme, from virtually nil to 100%. Please note that at 100% the bird ultimately dies of starvation, as they are no longer able to digest any food! There are a number of factors driving the ingestion of grass, and these can be reviewed in the following article: The Phenomenon of Silverbacking in Free Range Hens. So, there are two separate factors conspiring against the birds – an ever-increasing demand for nutrients, and an ever-diminishing capacity to ingest and digest that food. This situation often deteriorates into a savage downward spiral, driven by the birds need for very specific nutrients to produce a ‘life-capsule’ for a developing chick virtually every day of the week.
It is appropriate to pause for a moment and consider the statement highlighted above. Every day these birds lay an egg, and that egg is a great source of nourishment for people. But have you ever stopped to consider that the purpose of that egg is not to feed you, but to nourish and protect a chicken from fertilization to hatching? That is 21 days without any external input apart from the warmth of the mother hen (or the incubator). This means that the egg contains a very precise range of nutrients and physical characteristics to complete that important task, and all the inputs for that egg must come to the hen from external sources, particularly through food. Therefore, the modern laying hen, laying an egg nearly every day, is constantly seeking a range of very specific nutrients to meet that need, and this is the cause of most of the behavioural, physiological and metabolic maladies that plague the modern layer more than other types of poultry.
Returning to our crowding hens; it should be clearly understood that chickens have a brilliant ability to identify specific nutrients for their daily needs, sometimes called “dietary intelligence”. The processes by which this takes place are complex, but in simple terms rely on feedback from the bottom end of the digestive tract and other organs to the top end of the bird, namely the eyes and beak. Consider, for example, the amino acid methionine. Methionine is an essential nutrient, meaning it cannot be synthesised by the bird, and must come from external sources. Under normal circumstances a well-balanced ration should meet the needs of a laying hen, and in a caged environment this is generally the case. However, as a result of the dual factors of gizzard impaction and the onset of peak production, a pastured laying hen cannot get all she needs from the prepared ration and seeks other sources of this specific nutrient. In her search for this nutrient she will go to extreme lengths, including crowding around visitors and vehicles, the amount of associated vocalisation often corresponding to the extent of the nutrient deficit. However, that same search for nutrients can also lead to destructive and costly behaviours, most of which will be familiar to pastured egg producers:
There has been a huge amount of research conducted in an effort to better understand this behaviour, and there are a range of factors that can contribute to its expression. In this particular situation, birds start eating feathers in increasing quantities due to the high level of methionine and other sulphur amino acids they contain. The onset of this behaviour in adult birds can be exacerbated by poor rearing techniques in which the growing birds started feather pecking at an early age. It is important to note that extreme feather pecking has at least two compounding factors to consider – the first is that as the bird increases her consumption of feathers they can “entangle” in the gizzard, creating a very similar situation to gizzard impaction with grass, decreasing the capacity to consume the prepared ration and increasing the desire to eat feathers. The second is the progression from feather pecking to cannibalism, where the birds inadvertently cause their flock mate to bleed by pulling a large quill feather or peck at flesh. Once the “pecker” establishes the value of blood and flesh as a source of methionine, it will actively and aggressively peck its flock mates to meet that dietary need. Sadly, this behaviour is rapidly learned by other birds in the flock, and severe losses from cannibalism can result.
- Vent pecking
Driven by similar circumstances to feather-pecking, vent pecking is commonly associated with poor nesting training, resulting in large numbers of pullets laying their eggs on the ground rather than in the nest boxes provided. Under these circumstances (which are completely avoidable) a bird laying an egg under the shed for example, presents it everted reproductive tract during the act of oviposition (laying an egg) to its surrounding flock mates. Due to the blood red colour of the everted tract, it is not uncommon for another bird to peck aggressively at the exposed flesh, causing bleeding. This is often indicated by eggs with blood streaks being collected. There are a couple of negative outcomes from this behaviour. The first is that the pecked bird may develop an infection of the reproductive tract, which results in a condition known as ascending salpingitis. Birds so affected rarely recover, and normally deteriorate, loosing bodyweight and condition until they die. The second is the pecking birds become aggressive in their behaviour, and actually eat their flock mates from the inside out. I have seen this distressing and costly behaviour on thousands of occasions, and always under pastured, free range conditions, and as noted above, is quickly learned by other birds.
- Gizzard impaction with grass
In my opinion this is the single greatest threat to pastured egg production using modern brown birds, and I have yet to visit a pastured site that was not affected to some degree by gizzard impaction. To date there has been no definitive condition or circumstance acknowledged as the cause, but I have developed a theory supported by a mountain of practical evidence. Most people are not aware that chickens (and other birds) can move digesta (the food passing through the digestive tract) in both directions, forwards towards the cloaca (bottom) and backwards, towards the beak. This very precise capability must serve an important part in effective digestion, and this is where the largely misunderstood or ignored part of the lower digestive tract, known as the caeca, have a critical role. The caeca are a pair of blind sacs connected to the digestive tract at the end of the small intestine and the commencement of the rectum. A portion of the digestive tract known as the ileocaecal junction controls the flow of digesta into the caeca, preventing even very small solid particles, only allowing liquid to enter. In the caeca a number of functions are performed, including the anaerobic fermentation of the soluble cellulose fraction of the birds’ diet. While this specific component is present in a range of feed ingredients, it is prevalent in grass, particularly the fibrous portions of monocotyledon grasses. During the process of fermentation, it is my contention that a range of endogenous (produced within the bird) nutrients or metabolites are created, and these are then moved back up the digestive tract to catalyse, augment or assist in the digestion and absorption of a range of nutrients, including sulphur amino acids like methionine. Given the effectiveness of the birds’ “dietary intelligence”, it is reasonable to suggest that they soon recognise the relationship between grass and methionine (or a similar nutrient) and consume increasing quantities. It is interesting to note that in my experience birds favour fibrous, long grasses over soft green plants, such as clover. As the birds increase their consumption of grass, the amount of space in the gizzard decreases, increasing the need for more methionine. Ultimately, the bird’s gizzard can become completely impacted with grass, and they die of starvation.
Although these observations are disturbing and confronting, they also serve to demonstrate the antagonism that exists between the genetics of the modern layer and the realities of a pastured production environment. In the third and final part of this series, we will investigate strategies to stay in the game and manage these limitations and constraints.