Puberty in bovines takes place at around 15 months of age. The oestrous cycle of the females lasts about 21 days. Females in heat allow themselves to be mounted by other members of the herd. Ovulation takes place 10 to 12 hours after the end of the heat period. After calving, which triggers the production of milk, the females are not in heat for another 40 to 90 days, depending on the breed; for suckler breeds, this period is lengthened for cows that suckle their calves.

Gestation lasts about 9 months, although this depends on the breed, the age of the female, the number of calves she has had and the number of calves born at each calving. The larger the female, the longer gestation tends to be. The gestation of the heaviest breeds is about 293 days, as compared to 283 days for smaller breeds. Heifers have a slightly shorter gestation period than cows, while twins bring about a fall in the gestation period.

A suckler cow produces from 10 to 20 litres of milk per day during lactation, which lasts until the calf is weaned (from 6 to 8 months depending on systems); on the other hand, a dairy cow, if milked, gives on average 20 to 25 litres per day, 300 days per year.

Natural service or artificial insemination

In dairy production, 90% of females are fertilized by artificial insemination. In selection schemes, a bull which is said to be proven, i.e. which will ‘improve’ the next generation according to the selection criterion chosen, can in this way father from 100 to 200 000 calves in 2 or 3 years. Artificial insemination thus makes it possible to disseminate genetic gain throughout the whole world; it presents many advantages, from both the point of view of production quality and that of health.



Unless dairy breeders wish to obtain replacement females (i.e. replace cows which have reached the end of their working life), they can also use bulls from beef breeds for so-called commercial crossbreeding (crossbreeding with the aim of selling the animals), to obtain livestock with better growth and fattening ability.




In suckler production, natural service is preferred for practical reasons. This is because, during the mating season in spring, the cows are out to pasture, and detecting when the cows are in heat, as well as handling the cows for insemination, is a tricky business. Nonetheless, from 10 to 40% of the females from suckler breeds are fertilized by artificial insemination.

The advantages of artificial insemination are:
> sanitary: it helps to prevent the spread of sexually transmitted diseases and brucellosis,
> genetic: selection of bulls,
> and even economic: there is no need to keep the bulls on the farm.

The disadvantages are:
> the animals require more handling,
> extra personnel are required,
> there are fewer successful pregnancies than with natural service.

Bovine semen can be frozen (unlike pigs’ semen, which has to be used ‘fresh’). It is thus possible to export the breeding value of a bull all over the world and at any time of year, without having to move the animal itself. Each dose of semen is contained in little plastic straws containing 0.125 ml, which are kept in liquid nitrogen at -196°C in insulated containers.

Calving

Calving can be defined as the series of events which enable the calf to be born. However, the term does not only refer to the expulsion of the calf from its mother’s uterus: calving also refers to the expulsion of the fetal membranes, which normally follow the same path as the calf in the hours following the birth. Calving triggers lactation, and the cow will feed the calf by suckling; hence the term suckler cow.

The last phase in the cow’s gestation
The cow’s gestation lasts 9 months in all. However, during this time, the fetus does not grow at a constant rate: Most of its growth occurs during the last three months (from the 190th to the 282nd day). During this time, the weight of the fetus increases on average from 4 kg (a weight which it has taken 6 months to attain) to about 40 kg.

As gestation progresses, the cow requires more and more food. During the last three months of gestation, the pregnant cow’s organism is subject to two rather contradictory needs:
> it must eat enough food to be able to increase the weight of the fetus by 35 kg in 3 months,
> but while the calf is growing in the uterus, it pushes the first stomach forward. This slightly reduces the volume of the first stomach and increases the pressure inside the cow’s belly, both on the digestive system and on the bladder, while increasing the total volume of the abdomen.

The cow thus has to eat more even though its stomach is more compressed. It therefore becomes especially sensitive to any feeding or health problems (such as infection or stress) which may occur over this period.

Early warning signs of calving
To forecast when labour will begin, there are several warning signs:

1] if this is the cow’s first calf, the udder swells up (oedema). With older cows, lactogenesis begins a very short time before calving,

2] the ligaments of the cow’s pelvis relax: they become looser, which enables the calf to pass through the pelvis during the birth. This loosening leads to the base of the tail descending between the two tips of the cow’s buttocks when observed from behind. The tip of the tail is also often ‘all limp’. Without this spreading apart, the calf could not be expelled,

3] a translucent discharge appears at the cow’s vulva: this is the plug of mucus which blocked the entrance to the uterus all the way through gestation, and which liquefies in the days preceding the birth.

Keeping an eye on calving
It is important for a farmer to keep an eye on the cows during labour, especially so as have enough time to move them to a quiet area where they can be on their own when they give birth, or so as to spot in time any possible abnormality which may require the intervention of a vet.

However, the cow should not be disturbed during calving: some breeders use a video camera connected to their own bedroom so as to be able to keep an eye on a cow which is in labour during the night.

The fact that the calf is in the normal position in the uterus at the moment of birth is very important: if the calf is in the right position, the cow will be able to give birth without any outside help. However, in around 5% of cases, the calf is wrongly positioned in the uterus. It is then essential that the farmer, or a vet, intervene to save the calf and its mother. It is sometimes impossible to get the calf out naturally. The vet then carries out a caesarian on the cow’s flank.

The three stages of labour
Before giving birth to the calf, the cow lies down. This brings the uterus into a horizontal position and increases the efficiency of the uterine contractions. the first stomach then passively pushes the calf back, and the contractions ‘guide’ it towards the exit.

Stage one: dilatation of the cervix and beginning of contractions
The first stage of calving usually lasts 4 hours (6 hours if it is the first time the cow has calved). The cervix, until then contracted, now dilates. At the same time, the first uterine contractions, which are irregular to begin with, get under way. They begin to push the fetus towards the rear. However, the amniotic sac is located between the fetus and the cervix.

Stage two: expulsion of the calf
This stage lasts from 2 to 10 hours; an adult cow generally gives birth to the calf in 3 hours. The contractions increase in both intensity and regularity, pushing the fetus outwards. The amniotic sac then breaks. The fetus moves along the birth canal: the front legs appear first, followed by the head. This means that the umbilical cord is not broken while the head of the calf is still inside (if it was, the calf wouldn’t be able to breathe).

Stage three: delivery
During this third stage, the calf is on the ground, still sticky, and is being licked by its mother; the umbilical cord is broken. The rest of the placenta is then expelled from the uterus, whose volume has already considerably diminished, although it is still continuing to contract. These remaining bits of placenta, known as afterbirth, are expelled in the 12 hours following the birth of the calf.

If the farmer does not find this afterbirth next to the cow (which happens in 5 to 10% of cases) he calls the vet, who performs the delivery of the placenta, either by injecting a product to intensify the contractions or by removing it manually. This is important, because if the dead tissue was left inside the uterus there is a risk that it could cause infection.

Not all calves weigh the same at birth. It depends especially on the breed of the parents.
> Charolais cattle, for instance, are what is known as a ‘beef breed’: they are very sturdily built, and have an impressive muscle mass. This is true of the newly-born calves, which sometimes weigh over 50 kg.
> on the other hand, the Holstein cow, which is a dairy breed, is of smaller size, and its calves weigh around 40 kg.

First aid for the newly-born calf
When the farmer helps with the calving, the first thing he does after the calf is born is to clean out its nostrils and remove any liquids which may be blocking it up, and make sure that the calf is breathing normally. Sometimes, holding the calf head downwards helps to eliminate these substances from the upper respiratory tract.

It is also important to disinfect the part of the umbilical cord which remains attached, since complications arising from infection of the navel are relatively common.

Finally, the farmer makes sure that the calf has suckled very soon after the birth. This is because the first milk from its mother is rich in antibodies. During the first 24 hours of the calf’s life, its intestine is permeable to large proteins. These antibodies present in the first milk (called colostrum) pass directly from the calf’s alimentary canal into its blood. In this way the calf is vaccinated, as it were, by its mother. These antibodies last only a few weeks, but this is long enough to allow the immune system of the young calf to take over and defend it against infection.

Disadvantages of calving ‘in the field’
When calving takes place outside with no human intervention, which is relatively common for beef breed cows, the greatest risk for a calf is to be born in bad weather conditions: most calving takes place from the end of winter until spring. Cold is not especially dangerous for a dry calf. However, damp, cold weather rapidly uses up the calf’s energy reserves. The dam plays a crucial role by licking the calf all over as soon as it is born, by getting it to suckle and by protecting it from predators.

In the US, a national survey has shown that bad weather conditions at the moment of birth are the main cause of calf mortality (one calf in five).

Here again, the farmer’s role in keeping an eye on the animals can help to minimize losses.

Breeding

Different players in the industry have different aims
In beef production, selection aims can be put into 3 categories:
> cow-calf producers seek breeding ability, i.e. everything connected to reproduction, suckling, calving, mothering ability, etc.
> fatteners are more interested in the animal’s growth performance, its feed conversion efficiency, its morphology, its fattening capacity, etc.
> processors are more interested in criteria which affect carcass quality in order to obtain a high dressing percentage and meat of good quality.

Pure breeding or crossbreeding?
The farmer can use breeding in order to improve the livestock’s production performance, either by selecting breeding stock from within one breed (a system much used in France, but considerably less in other EU countries), or by the judicious use of crossbreeding between different breeds.

>pure breeding provides breeders with good breeding stock. It is on this basis that breeding is organized, and that herd-books are created (the animals that are listed there are said to be ‘registered’ in the herd-book). But pure bred livestock do not adapt as easily to economic fluctuations and to consumer demand,

> the interest of crossbreeding is that it can bring about novel traits within the same species by mixing the different breeds of which the species is made up.
A distinction is made between crossbreeding for genetic purposes (to improve or create a breed within a species) and commercial crossbreeding (generally used to produce livestock for slaughter), the latter being the most frequent.

For instance, in order to improve the meat producing capacity of local breeds, which, although often not very productive are acclimatized to the area, crossing with paternal beef breeds is used.

In many tropical countries, female zebus are crossed with beef breeds to increase carcass weight; zebus are highly resistant to local parasites, heat and to moving over long distances, which is beneficial to the resulting calves.

Crossbreeding is also used to change the nature of a herd. For instance, when a dairy producer wishes to turn his dairy herd into a beef herd, so-called substitution crossing enables him to obtain, over the generations, livestock which produce increasing amounts of beef.

But in all cases, if producers wish to improve their livestock, they must be clear about their goals and about which selection criteria (i.e. features or abilities which can be measured in the candidates to be selected) they wish to improve. It is also important to understand the selection schemes (programmes that must be completed in order for selection to be successful) which are used.

The general principles on which a selection programme is built
To select is to continuously adapt the performance (i.e. specific characteristics such as growth, conformation, milk yield, fertility, etc) of today’s breeding stock to the needs of tomorrow’s livestock industry. To achieve this requires:

1/ A judicious choice of selection aims and selection criteria. This means answering two questions: what do we want to select and what can we select?

2/ The efficient use of the instruments and methods by which the breeding value of breeding stock is estimated, and their rational implementation by means of ‘Breed selection programmes’. This is equivalent to asking: what measures can we take, and with what means, in order to achieve the selection aims we have determined?

A selection programme is a series of different stages involving first the estimation of breeding value, and then the selection of breeding animals based on these selection criteria, in line with the aims that have previously been defined.

Issues and limitations in the selection of beef breeds
The presence of many different players, each with their own economic aims, brings with it the need to take into account a wide range of goals, and accordingly a large number of criteria to select simultaneously. However, with regard to beef breeds, these abilities can be classified from the breeder’s point of view into two broad categories:

> slaughter qualities, which are associated with the productivity of cattle that are still growing (fattening and carcass quality). They aim to obtain a high yield in marketable beef in relation to production costs. They concern not only yield in terms of carcass weight (growth rate, feed efficiency, carcass composition, dressing percentage), but also improvement in carcass quality (finishing, muscle quality, beef quality),

> mothering ability, which is associated with yield in weaned calves per breeding female (cow-calf production, rearing and breeding). These aim to increase the number and individual slaughter value of calves weaned by the dam during her breeding life, by using production systems where humans play a smaller role, and where the food needs of the dams are increasingly met by the use of forage which varies in quality and quantity in the course of the year. The abilities concerned are very varied: production capacity of the dams (early maturity, longevity, fertility, etc), calf rearing ability (suckling, behaviour, etc), short and long term adaptation to the feeding, physical or social constraints inherent to livestock production (mobilization and regeneration of bodily reserves, etc).

Additionally, the relative importance given to slaughter qualities or to mothering abilities in the overall selection aim of a beef breed depends on how it is principally used:

> for crossbreeding (slaughter quality for paternal breeds, or mothering ability for maternal breeds),
> for pure breeding (slaughter quality plus mothering ability),
> for extensive production (mothering ability more important than slaughter quality),
> for intensive production (slaughter quality more important than mothering ability).

Similarly, within the range of slaughter qualities or mothering abilities, the relative importance given to the different criteria depends on the breed. A balance needs to be found between:

> growth and conformation, for slaughter qualities,
> morphology, fertility, ease of calving, and suckling, for mothering abilities.

It is also worth stressing that these two groups of abilities are not genetically independent! In fact, they are usually conflicting. Livestock therefore needs to be selected using both groups of criteria at the same time in order to avoid one of them deteriorating.

Moreover, it shouldn’t be forgotten that heritability, i.e. that part of the variability in livestock performance that is of genetic origin, varies considerably according to the characters that are selected. Heritability is expressed by a coefficient which can vary from 0 to 1. It is fairly low for characters related to reproduction (under 0.25), since here the influence of the environment (rearing conditions in the broad meaning of the term) is very great; it is average (0.25 to 0.40) for characters connected with the production of the animal (such as growth rate or milk production), and it is fairly high (over 0.40) for the make up of the animal (the quantity of muscle or fat in the carcass);

Progress is all the slower when many characters are selected, as is the case with beef breeds, and also when there is a long interval between generations. The immediate response time, which results from the choice of one sire rather than another, varies according to the character that we seek to improve: from as little as 13 months for the conformation of beef calves (9 months of gestation + 4 months of actual production) to as much as 4 ½ years for the milk yield of suckling cows (9 months of gestation + 3 years of rearing until the first calving + 9 months until the weaning of the first calf). The replacement of all the females in a herd theoretically takes 8 years, on the basis of an ‘annual replacement rate’ of 20% and an age at first calving of 3 years.

It is therefore clear that improvement in slaughter performance is more effective and faster than improvement in mothering ability, which is less heritable and takes longer to emerge. Maintaining a reasonable balance between the two requires continual compromise.

Pedigree, individual or progeny selection
In pedigree selection, the choice of the animal is based on its pedigree, i.e. on the performance of its parentage over several generations. The method is quick and simple, and makes it possible to work on the basis of the criteria of the sire and dam. It is one of the best methods for selecting females, but it is not very reliable for characters with little heritability.

In individual (or mass) selection methods, the animals are selected according to their individual performance. A series of measurements is taken of the animal’s weight, size, conformation, etc, together with an analysis of the state of its health, its temperament, etc. This method is simple and cheap, and works well for characters with high heritability. However, certain criteria cannot be measured in male animals, such as their capacity for milk production.

In progeny selection methods, a technique called progeny testing is used to estimate a male’s breeding worth. Progeny testing is a way of estimating the breeding worth of a male by measuring the performance of its offspring collected from farms, either under normal production conditions, or else in testing stations, which facilitates comparisons between animals and between blood lines. It is thus possible to measure the carcass of at least 30 of the male offspring of the same bull in order to evaluate its slaughter quality, and similarly the mothering ability and calf production performance of at least 20 female offspring of the same bull can be used to estimate its breeding ability. The more offspring it has, the more reliable the results are. When the progeny testing is complete, the bull can be classified on a scale with 100 as the mean. When a bull scores over 100 for a particular criterion, it is ‘proven’ for that particular criterion. There is no doubt that this is the most efficient method for males, but it requires time and is expensive: it is sometimes necessary to keep the offspring for several years, and taking the measurements requires staff.

Modern techniques that use biomolecular genetics and the components of DNA are being developed, in order to eliminate more rapidly blood lines of animals of no value from the selection programme, thereby reducing costs.