An Introduction to Practical Animal Breeding
By Dr Clive Dalton
PART 1. The Traits in Farm Animals
Man and his animals
Most of the animals currently husbanded by man were domesticated in neolithic times with the exception of the dog which was used in the earlier paleolithic era. Few further attempts have been made in recent times to domesticate animals except for the Eland. Most effort seems to have gone into improving the animals already in use.
The modern farmer can improve animal performance in many ways. He can feed his stock better, improve their physical environment by housing, reduce the ravages of pests and disease and so on. These are management or environmental improvements and should go hand-in-hand with better breeding or genetic improvements.
Man's association with animals has always been complex and it remains so. It is wrong to assume that all farmers keep livestock for the same reason i.e. financial gain, and that all breeders have similar aims. This highlights one of the biggest problems in breeding, that of defining the objectives in breeding programmes.
Traits: a general comment
A major difficulty in farm animal breeding is that often breeders try to breed far too many things at once, and are usually disappointed at the slow rate of overall success. It must be accepted that one of the basic principles of breeding is that the larger the number of traits included in a breeding programme, the slower is the rate of progress in any one of them.
The main challenge is to decide on a priority order for the required characters, to keep the list short and to stick to this decision. This is where the greatest arguments usually arise-especially between breeders and geneticists. As Lerner and Donald (Ref 1) pointed out, any controversy between breeders and geneticists is mostly about aims, less about methods and not at all about theory.
Traits in farm animals can be classified in a number of ways. They can be divided into either simple traits like coat colour or complex traits like growth and survival, or they can be classified as either objective or subjective.
Objective traits can be measured in positive terms such as weight, length, area, percentage, etc., whereas subjective traits are measured by scores, grades, proportions, etc., where a person's opinion greatly affects the assessment. Both objective and subjective traits are used in farm animal improvement.
Reproduction is basic to all livestock production but must be very clearly defined as a trait to be considered by breeders. In the female, the breeder is concerned with a considerable number of different ways of measuring reproductive merit. Here are some examples:
(a) The number of eggs shed from the ovary (ovulation rate).
(b) The number of fertilised ova implanted in the uterus.
(c) The number of dams pregnant per 100 joined with the male, or per 100 inseminated. This may be called the pregnancy rate. Pregnancy may be diagnosed at a standard number of days (e.g. 60) after mating or insemination.
(d) The number of offspring born per animal giving birth or per animal joined with the male. Here some breeders may measure total (live + dead) offspring born, whereas others may use only live offspring born. Live offspring born per birth is often called 'litter size' in pigs and sheep.
(e) The number of offspring castrated (testicles removed) or docked (tail removed) at standard ages.
(f) The number of offspring weaned from the dam at standard ages such as six months for beef calves, four months for lambs and three, six, or eight weeks for pigs.
The terms fertility and fecundity are often confused and their definition may vary throughout the world. Generally the term fertility is restricted to points (a) to (d) above and fecundity to points (e) and (f) . Fecundity generally includes aspects of rearing ability. However, the point to stress here is that clear definition is needed for whatever measure of reproductive performance is used.
In the male, fertility covers aspects of quantity and quality of the sperm (spermatozoa) produced. Here motility is important as sperm have to move through the female reproductive tract to fertilise the ovum. The proportion of live to dead sperm or the proportion of abnormal to normal sperm is also noted as other factors affecting fertilising ability of the male (see fig. 1).
Characteristics of sperm are especially important in artificial insemination (A.I.) where sperm are collected, concentrated, deep frozen, thawed, diluted and then used in low concentrations. The final merit of sperm is measured by the pregnancy rate of the females inseminated.
Fig. I Normal bull and abnormal bull semen (X 500)
In natural service, perhaps more so than in artificial insemination, the libido or sex drive of the male can be critical to the final pregnancy rate. Libido is of special concern to breeders in difficult environments such as the very hot and humid conditions of the tropics or the severe cold of the great plains. The desire of the male to seek and serve females in oestrus (heat) should always be a primary instinct.
BIRTH TRAITS AND SURVIVAL
Breeders are especially concerned with the animal's ability to survive: the more animals that survive then the more there are to provide potential for improvement. Birth and the first three or four days of life are the most hazardous times. First there are the mechanical problems of the birth process in which the offspring has to pass through its dam's pelvis, break free from the birth sack and amniotic fluids and then breathe without suffocating. It has also to withstand a large temperature drop from the dam's body temperature to perhaps ice and snow on a winter range.
The most common causes of death in farm animals in the early stages of life are dystocia (difficult delivery) and starvation/exposure. The number of offspring born to the dam at any one time also affects survival: for example, single-born offspring have better chances than individuals in litters. The breeder often finds it helpful to apportion blame for mortality, which can be classed very simply as: dam's fault, offspring's fault and unspecified (i.e. not sure).
Even this presents some problems in assessment and depends a lot on the stockman's opinion. However, the information is valuable because although faults in the offspring can be due to the sire, the faults caused by poor mothering cannot be blamed on the sire; and the true position becomes clear when the sire is mated to different dams. In assessing mothering ability, faults of the dam would be under scrutiny while factors classified as the offspring's fault would be ignored.
The complexity of these traits is well recognised by breeders but great efforts are justified in improving them. If a calf dies at birth, not only will the nine months' care during pregnancy have been wasted but the whole twelve months' investment in the dam will have brought no financial return. Diagnosing the cause of death by post-mortem examination requires considerable expertise and usually back-up laboratory servicing.
An accurate diagnosis of the cause of death is often difficult, particularly if the dead animal has not been examined promptly after death. Even apparently simple matters like accurately defining an abortion and a premature birth can be hard. The stockman usually assumes that an abortion has occurred if the animal is not born fully-formed, but this assumption is prone to error. Because of these problems, many breeders take the more positive approach of being more concerned about survival than mortality.
This means that they are more interested in why the living offspring live, than why the dead ones die. They thus must select for survival characters rather than against mortality ones. Birth is also the time when breeders usually establish the correct parentage of an offspring-the dam can be seen, and the sire to which she became pregnant is known from the records.
Problems can arise where dams give birth to their offspring together e.g. under range conditions. Here through mixing of birth fluids and hence the smell of all the newly-born offspring, dams may suckle any of the young. The stockman cannot determine true parentage, and blood typing is the only guaranteed way to establish parentage accurately. Range cattle often leave their calves in groups or crèches while the dams graze, and as the calves do not usually run to their dams like lambs do, establishing parentage after birth can be difficult. This is an example of how animal
behaviour can have profound implications for genetics.
Good maternal ability or 'mothering' is essential in farm stock that suckle their own offspring. It is a complex trait closely associated with survival, as a young animal's apparent desire to live is strongly affected by its dam's ability to feed, shelter and perhaps protect it from predators.
Although stockmen can readily recognise good and bad maternal ability in an animal, the trait is difficult to describe objectively. Because of this, breeders often use indirect measures of mothering ability such as the total weight of the offspring at weaning.
Milk production is obviously an important part of mothering, and is under hormonal control along with the processes of reproduction and birth. It is well recognised by stockmen that dams which have a poor milk supply when they give birth also have poor mothering instincts and may not be interested in their offspring. This may be a problem with young dams at the birth of their first offspring.
While considering these traits, the breeder must remember the importance of the level of feeding of the dam during the later stages of pregnancy and in lactation measured by her live weight and condition: these are environmental factors. Some take the approach of deliberately not assisting their animals at birth or up to weaning so that they can identify those dams with good natural maternal ability.
It is argued by these breeders that generations of 'good husbandry' (by assisting animals at birth and up to weaning) have retained such defects or weaknesses in livestock. Their approach is one of 'easy-care' where the animals look after themselves and is very applicable under conditions where labour has to be reduced.
Lactation requires special attention in farm animals whether they suckle their own young as in beef cattle, sheep and pigs, or whether they are used for milking as in the dairy cow, the dairy goat, and in some countries milking sheep.
Lactation involves the whole complex reproductive system which is under intricate hormonal control. Mammary (udder) tissue develops during pregnancy and is ready to function to coincide with birth. Without pregnancy there can be no effective lactation ion. The survival of the young animal is highly dependent on whether or not it receives the colostrum from its dam.
Colostrum is the first milk from the udder - it has a thick creamy consistency and is especially rich in antibodies (defence mechanisms) built up against disease organisms by the dam during pregnancy. The intestine of the newly-born animal can only absorb these in the first hours of life.
The udder is of great importance to breeders. In animals that suckle their own offspring it is highly desirable that the teats are of a suitable size and shape to allow the young to suckle and can stand up to the considerable chewing and wear that they get, especially where litters are involved. In such animals, the number of teats is important too. Large teats that young animals cannot get into their mouths are especially bad - the udder pressure builds up causing stress and disease, and the offspring may die of starvation.
As the udder in the dairy animal has to hold large volumes of milk at peak lactation, its attachment through the suspensory ligaments to the pelvis is important. With repeated lactation, poorly attached udders become pendulous and are easily damaged when the animal walks or is housed in close confinement with others. Modern machine milking systems require rapid release or 'let down' of the milk by the dairy animal.
This 'let down' mechanism is called a conditioned reflex whereby the animals can be trained to let down the milk. Training is usually done by handling or washing the udder, or giving the cow some extra feed while milking. Fear or stress can effectively 'switch off the let down hormone. Breeders are thus very concerned to conserve and improve these dairy traits. In some countries, milk is obtained from non-dairy animals by milking while the calf is suckling or with the calf tied up near the cow's head so she can see it.
Milking machines have caused breeders to pay attention to teat shapes which are suitable for efficient milking but also prevent damage by 'over-milking'. Over-milking is said to occur when the machine continues to squeeze the teat when no milk is left. As milking becomes even more automated in future the physical form of the udder and teats will become even more important.
In the milking animal that has to walk to obtain food and to the milking shed twice daily, overall conformation is important. This involves the udder and teats, large pelvis, good legs and feet, large body capacity for food digestion organs, etc. The breeder of dairy animals is concerned with the quality as well as the quantity of the milk produced. Milk is a complex product and breeders are interested in many of the physical traits such as size of fat globules and chemical traits such as fat, protein, sugar and mineral contents.
Growth and development
Growth and development are given high priority in breeding. 'Growth' is best visualised as an increase in weight and or size. Sometimes size is inferred from the weight of the animal, but this can be misleading. 'Development' is more the change in proportion of the various parts of the animal seen through changes that start at conception and continue through to maturity (Refs 3,4,5). Growth is the increase in weight and or size that occurs over time (i.e. age), and can be drawn as an S-shaped (sigmoid) curve in fig. 2.
This curve shows that life begins at conception and growth is rapid up to birth and thereafter to puberty or sexual maturity. Puberty is usually taken as the point of inflexion of the curve or where it changes direction. After puberty the rate of growth slows down until final maturity is reached.
The different tissues vary in their priority for the available nutrients (Refs 3,4,5). For example the placenta and foetus have first priority, then the brain and central nervous system followed by bone, muscle and fat. It is the relationship between these last three tissues that breeders aim to alter and control.(Ref 4).
Breeders are concerned with animals that vary in their mature size and weight (e.g. Angus versus Charolais cattle and Southdown versus Oxford downsheep), hence the actual rate of growth and tissue composition at any one time can vary greatly.(Ref 4)
The point to remember in breeding is that all the stages on the growth curve (e.g. birth weight, weaning weight, weight at puberty and maturity) cannot be viewed as isolated traits. If one is altered then the others are affected too. The live weight of an animal is a simple trait to measure. However, scales do not show what makes up this weight.
In ruminants (cattle and sheep) the contents of the digestive tract (gut fill) can account for 10 - 25% of actual weight. So for valid comparisons, animals should be weighed either uniformly full as when straight off feed, or uniformly empty after a standardised period of starvation. Also, in sheep carrying heavy fleeces variation can be caused by the quantity of water in the wool or whether the sheep were all at the same stage of wool growth when weighed.
Breeders are interested in the carcass of most farm animals as it is a stage nearer the consumer than the live animal. However, as the animal has to be killed to examine the carcass, special breeding plans are necessary to select for carcass traits of breeding stock by examining carcasses of offspring or relatives; or ultrasonic aids can be used to study carcass traits on the live animal itself.
The weight of the cold carcass as a trait for improvement can be most easily obtained at the point of slaughter. The weight of the carcass as a proportion of the live weight (usually starved live weight) is termed the killing-out percentage (KO%) or dressing percentage. There are many aspects of the carcass, both objective and subjective, that are important to the consumer and hence to the breeder.
The consumer is most interested in the muscle or lean-meat part of the carcass - not the bone or the fat that lies both inside the muscles (intramuscular) and between the muscles (inter-muscular). Fat can be measured objectively by fat depth at defined points using probes that cut through the external fat layers of the carcass, or sample joints can be minced and a sample analysed chemically. Fat can even be measured by specific gravity -weighing the carcass in air, then in water.
Dissection of the carcass is labour intensive and thus expensive, so it is used mainly in research. Most countries however have grading or classification systems to assess or describe the important commercial aspects of the carcass. These are based on some objective (e.g. fat depth) and many subjective criteria such as distribution of fat cover, fat colour, shape of carcass and proportion of hind end (the first quality or expensive cuts) to fore end (the cheaper cuts). Grading systems are usually criticised for not achieving their aims, but critics often find it hard to suggest workable alternative schemes. Photographic standards are often used in an attempt to retain consistency between graders.
Specially trained taste panels are sometimes used to assess meat qualities after standardised cooking procedures. These include such properties as colour, texture, tenderness, juiciness and flavour. An alternative technique used by some workers is to survey consumers and ask them for their opinions of the product. This technique gives only general information compared to the taste panel, and is similar to that obtained by measuring consumer demand by recording what sells best from the shelves in modern supermarkets.
Modern consumers demand tenderness, flavour, more lean and less fat. It would seem sometimes that breeders are expected to produce an animal that is all hind-quarter! Unfortunately the prospects of altering the proportions of muscles in the body are not high.(Ref 4).
The main difficulty facing breeders is to look at a live animal and predict what its carcass will look like or, what is even more difficult, to predict consumers' reactions when they eat the meat. Despite electronic aids that can measure fat depth and eye-muscle area on the living animal, this is still an area for individual skill and experience.
Breeders may have to learn to predict live weight (if scales are not available), killing-out percentage and hence carcass weight and grade. Some even attempt to predict the yield of lean edible meat from the carcass. Clearly, there is scope for enormous errors of judgment but these risks will remain until cheap and effective methods are evolved to measure these 1 traits objectively so that the breeder can use them in a programme.
Compared to some of the other traits discussed in Part I, wool appears to pose fewer problems for breeders. However, the greasy fleece as shorn from the sheep is made up of various components that may need the special attention of breeders.
The shorn fleece is made up of fibres, water, grease or wax, suint and various contaminants such as marking fluids, vegetable matter and bacterial, fungal and water stains. The breeder has to know which of these can be genetically controlled and which are solely environmental. In most situations, the economic return to the farmer is based mainly on greasy fleece weight.
A fibre is produced from a follicle in the skin of the animal (see fig. 3).
There are large primary follicles (coded P) that grow coarse fibres and are seen in the British Mountain breeds and some of the hair breeds in other countries. Then there are smaller secondary follicles (coded S) that produce finer fibres as seen in the Merino.
Fig. 4 shows the fibres found in two contrasting sheep breeds -Merino and Scottish Blackface. The ratio between secondary and primary follicles (called the S:P ratio) dictates the type of fleece produced by the sheep. There are broadly three kinds of fibres shorn from the sheep and their proportion depends greatly on the breed concerned. There are wool fibres that have a solid core, and medullated fibres (or hairy fibres) that have a medulla, or hollow centre, which may or may not be continuous. Kemp fibres may be present and these are notable because they are brittle, they have a medulla and are shed (fall out) from the skin. Fig.5 is a simplified drawings of these fibres.
The manufacturer's needs are dictated by the end-use of the wool purchased. The trade's needs are broadly classified into the clothing trade and the carpet trade, and each involves many different aspects of wool such as staple length, fibre diameter, fibre soundness (so that it does not break when put under tension), freedom from contaminants, colour, etc.
The traits considered are shown later. Technical equipment is continually being developed to measure traits that have traditionally been assessed subjectively; for instance, using fibre diameter measurements instead of the traditional quality number or count. There is now a much greater awareness by breeders of the needs of manufacturers and fashion houses. The International Wool Secretariat (IWS) is actively involved in this area.
DRAUGHT AND SPEED
These traits are of interest to breeders of horses and some cattle breeds in particular countries. Indeed, animal power may increase in importance in future as fossil-fuel supplies decrease and draught power from ruminants that eat fibre still remains a cheap source of energy.
Pulling power can be measured objectively by a dynamometer and individual animal performance can be easily recognised. Speed likewise can be assessed by distance traveled in a time period. Despite the fact that speed in racehorses is affected by the official handicapping system and the experience of the jockey, it is still a trait that can be selected successfully by breeders.
Improvement of cattle for draught purposes has had indirect benefits in increased size, improved muscling and reduction of fat. These formerly draught breeds (e.g. Charolais and Limousin) have been widely exploited for beef production throughout the world in recent years.
Breeders of every class of farm animal are greatly concerned with the physical features of their stock. There is an apparently endless list of traits to consider under the headings of ‘physical form’ including conformation, structural soundness, visual appraisal, type, and many more.
Basically they all concern what the animal looks like. They are visual traits, aptly called 'eye-ball traits' by some Americans. This is a rather difficult area in practice as people usually hold strong views on the importance or otherwise of particular physical traits. There tends to be a polarisation of breeders at one extreme saying that these characters are important, and geneticists at the other extreme claiming there is no scientific evidence to support that they are related to productive merit.
There are many reasons for the contrasting opinions associated with these physical features:
• Many of these traits or their components are difficult to measure in objective terms.
• The way in which some of these traits are inherited is not known.
• Some of the simple traits like colour of hair or wool, presence or absence of horns, may be part of the officially recognised features of the breed association and as such are important to pedigree breeders even if they do not affect the end product - meat, milk or wool, etc.
• As physical traits are assessed by eye, they tend to receive far more attention than do subjective traits seen in the animal's records.
The most difficult part of animal breeding seems to be maintaining a balance between the performance records and visual assessment. However, whether physical traits are based on scientific fact or traditional fancy, they are ‘economic’ traits. In other words, people pay money for them, and they must be considered as such. Why people pay money for characters that are ill-defined but personally satisfying is just part of the wider complex of why people keep animals.
Learning ability - sometimes loosely termed intelligence - is most commonly recognised as being an important feature in sheep- and cattle-dogs. Without dogs, many extensive pastoral areas of the world could not be farmed, and there seems little chance of them being replaced in the near future.
Sheep- and cattle-dogs have learning ability developed to a very high degree and the range of tasks they can execute under command is extensive. The sheep-dog trials held throughout the world vary but the basic tests of gathering, driving and penning sheep are common to all. This means that trial performance can be used to describe the ability of a dog. It is recognised by breeders that luck (chance) can affect a particular trial result, as with a difficult group of sheep that did not herd together.
The relationship between the dog and handler is also recognised as important and good dogs are frequently sold on a trial basis until the new owner tests his relationship with a new dog. This applies especially to commands by word (perhaps a different language), whistle or body signal. The dog's learning ability is critical in this. (Ref 5).
Breeders are now developing an interest in the ability of farm animals to learn the simple routines that will allow them to do some of their own chores. This is an exciting area for the future and is currently being studied by animal behaviourists and psychologists.
Examples of these chores would be operating watering and feeding devices, control lighting, temperature and humidity, treating themselves for external parasites, eating special supplements to counteract deficiencies, operating cleaning out mechanisms, and so on. Economic pressures on breeders will generate a continuing interest in this in future.
Whatever farm animal is considered and whatever the environment, good temperament is of importance. Breeders have paid great attention to this in the past and modern mechanised systems rely on animal cooperation that comes through a good i.e. non-aggressive temperament.
A good temperament in the animal is required in every aspect of the farm routine. Examples are: moving animals around the farm, treating them for ailments, milking, riding, yoking them for pulling and so on. An aggressive animal is a danger to itself (by jumping out of yards), to its fellow animals (by fighting and kicking) and to the people who handle it.
It can be argued that fear of man and dogs can be useful as in mustering animals in extensive situations. If they are not afraid they will not move at the sight or sound of man. It is also argued that fear of man by the animal encourages respect. This is the case with the bull. A hand reared, over-friendly bull can be a potential danger, but so can a bull that is terrified of his handlers. So clearly somewhere there is a happy medium between the two extremes where the animal is tractable and safe.
The temperament of the animal is controlled by its hormonal condition. At birth an extremely good mother will fight off predators (including the stockman) to protect its young although it is otherwise very friendly. This can be an important quality, as for example, in sheep protecting lambs against foxes.
A quiet temperament is needed in draught animals that may have to spend long periods of time waiting between spells of work. This is often done in noisy, busy conditions and when they cannot eat. In groups of animals there is usually a social hierarchy or 'peck order', in which aggressive animals will push less aggressive animals down the order.
The higher-order animals usually obtain more to eat, may be milked first, rest first and so on. The lower-order animals eat less, thus produce less and are more prone to disease. These problems are especially important in large groups of animals in confined areas such as poultry in deep litter houses, milking cows in yards or sheep or cattle confined indoors.
Stockmen now recognise that there is an optimal group size to reduce these 'stress' factors. However, producing animals to cope with stress situations is a task for breeders and has been especially so for poultry and pigs that are housed intensively.
POULTRY MEAT AND EGG PRODUCTION
Poultry breeders have probably used the recent advances brought about by genetics more than any other of the breeders of farm livestock. Modern poultry are kept solely for their function: the showing of poultry passed into the fanciers' domain many years ago.
The very concept of 'breed' in poultry has become outdated in any commercial sense. As the cost of food makes up such a large proportion of the total cost of a bird, the efficiency of feed conversion to meat and eggs is the critical trait in profitability.
Breeders of meat birds (broilers) are interested primarily in growth rate. This can easily be measured and generally the fast-growing bird converts its feed most efficiently. The main management concerns for profit are, then, to eliminate feed wastage by spillage and fouling and to reduce deaths through disease.
In meat birds, the breeders are concerned with the conformation of the bird as it appears pre-packed in the supermarket. The bird must have a large breast with fleshy thighs and short legs. Colour of skin can be important for some markets. The bird lays down fat inside its body cavity and this can be easily noticed (and probably removed) by the consumer. Hence attempts are being made to reduce this fat depot so that feed consumed is converted directly to edible meat. Breeders have made great progress towards this end.
In egg production, breeders are concerned with egg number, egg size and weight as well as good hatchability. Body weight and feed conversion of the bird are vital to profit. One extreme would be a small bird that had a low maintenance (feed) cost, laid many medium to small sized eggs and had a carcass that was of no value at the end of the production period.
The other extreme would be a heavier bird that ate more, produced fewer larger eggs but had a good carcass value at the end. Breeders are interested in the most efficient combinations among these traits. Breeders want birds that mature early so that they start to lay at an early age, that do not pause (stop laying) during production and do not go broody.
Persistency is needed too, which is the ability to keep laying for a long time. The various qualities of the egg itself have to be considered as they are important in consumer preference. Such traits are shell colour (white, tinted or brown), shell texture (smooth versus rough), shell thickness as thin shells increase waste through breakages. Inside the egg important qualities are yolk colour, thickness of the white and absence of blood and meat spots.
The traits discussed so far have been summarised by listing in Table I according to each class of stock. It is important to note that this is by no means an exhaustive list and is not given in any priority order. Deciding what is the priority order is the breeder's main problem and generally it would be based firmly on the economic importance of traits at a particular time. The main concern here is not just the actual value of each trait but their relative economic value (REV). This concept is of paramount importance in animal breeding.
DAIRY CATTLE: Objective traits
- Milk yield per lactation of specified length
- Fat yield per lactation
- Fat and solids not fat %
- Live weight
- Size (height at withers)
- Lifetime milk yield
- Milk flow rate
- Calving interval
- Heat resistance (heart rate)
- Conformation-udder, teats and structural soundness
- Breed specifications
- Disease resistance
- Fertility - number born and age at puberty
- Birth, weaning and yearling weight
- Weight of calf weaned/cow
- Cow weight:calf weaning weight
- Mature size and weight
- Draught ability
- Heat resistance
- Fat depth and eye muscle area
- Cold carcass weight
- Weight of hind: fore quarter
- Weight of commercial joints
- Bone, muscle, fat weight and proportions
- Conformation- muscling and structural soundness
- Beef specifications
- Disease resistance
- Carcass conformation- shape and proportions
SHEEP (MEAT): Objective traits
- Fertility - number born, number docked, number weaned
- Birth, weaning and yearling weight
- Weight of lamb weaned/ewe
- Fleece weight and slipe wool production
- Milk production
- Conformation - muscling, fatness, structural soundness
- Breed specifications
- Fleece weigth
- Staple length
- Fibre diameter
- Medullation (hairiness)
- Follicle parameters - S/P ratio
- Count or quality number
- Fertility - litter size, no litters/year
- No reared/weaned
- Weaning weight/piglet and total weaning weight
- Slaughter weight for pork or bacon
- Cold carcass weight
- Fat depth
- Eye muscle area
- Carcass length
- Colour of skin
- Teat number
- Conformation - structural soundness
- Breed specifications
- Disease resistance
- Egg number
- Egg size and weight
- Hen-housed average
- Feed conversion efficiency - feed consumed/dozen eggs
- Yolk colour
- Shell texture and colour
- Body weight
- Carcass weight
- Proportion of breast meat to total carcass
- Shank length
- Feed conversion - Feed consumed per unit of dressed carcass
- Feather colour
- Comb shape
- Disease resistance
- Working performance - number of official trials won
- Conformation - length of hair for hot or cold conditions, feet pads