Procedure 2

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Control the mating period to maintain selected annual calving dates

  • Follow guidelines for reducing the spread of calving
  • Supervise heifer and twin calving
  • Manage bulls for high conception
  • Pregnancy diagnosis

Guidelines for reducing the spread of calving

Aim for 95% of cows to calve in a 9-week period

Commercial beef producers who are striving for maximum efficiency should aim for 95% of cows to calve in a 9-week period. This procedure explores the date for removal of bulls or the duration of mating to reduce the spread of calving and to sustain the annual calving date/s. The start of mating is determined in Module 1: Setting directions.

The ideal calving distribution should consist of 65–70% of calves dropped in the first 3 weeks (first cycle), followed by 20% in the second 3 weeks and 10% in the third 3 weeks. This level of reproductive efficiency will produce an even line of calves of roughly the same age, making them easier to manage and market.

To achieve the ideal calving distribution, the guidelines for the length of mating are:

  • maximum 60 days for bulls run with cows
  • minimum 45 days for bulls run with cows (if bulls are not run with the cows for long enough, the calving percentage is decreased).

These recommendations allow all females to complete at least two oestrus cycles during mating. These limits can also be applied strictly for heifers.

When the bulls are run with the cows for too long, the subsequently long calving period results in:

  • reduced ability to maintain a 365-day calving interval
  • unnecessary increase in the use of high quality pasture by the breeding herd and a reduced available pasture for growing stock
  • difficulty obtaining critical mating weight at the nominated mating date for heifers that conceive later in the mating period
  • increased heifer culling and difficulty in maintaining desired herd age structure
  • increased cost of supervision for calving heifers (and twins)
  • wider spread of calf weights that will delay weaning date until the lightest calves reach target weight
  • wider spread of weaning weights that can lead to problems, such as calf marking and associated husbandry procedures during less favourable seasonal conditions.

To achieve the recommended mating periods, apply these rules:

Aim for 80% of cows to conceive by end of second oestrus cycle

  • Manage mating so that 80% of cows conceive by the end of the second oestrus cycle.
  • Remove bulls when the maximum period is reached, providing that the assessment of calving patterns indicates that a 60-day joining is sufficient for a satisfactory pregnancy rate.
  • Adopt a strategy to realign the herd’s calving pattern when more than 20% of the cows are conceiving on the third oestrus cycle (see 'Changing calving time' box, below).
  • Do not use the same bulls in subsequent seasons if the mating histogram shows more than 40% of cows are not conceiving at the first mating. Refer to previous pages on cow fertility (Procedure 1) and bull fertility (see below) if this happens.

Take corrective action when > 20% cows conceive in third oestrus cycle

As a guide, if a calving date histogram of the herd (see Tool 5.4) in the previous year shows that more than 20% of cows conceived in the third cycle, realign the reproductive capacity and age structure of the herd over several years to avoid economic penalties for the enterprise.

The recommended minimum and maximum number of mating days is based on the assumption that more than 80% of cows conceived by the second oestrus cycle in the previous year’s mating. If less than 80% of cows conceived by the end of the second oestrus cycle in the previous year, initiate a program to realign the herd’s calving pattern. In this case, the mating period may need to be extended beyond the recommended maximum limit to ensure satisfactory throughput in the short term.

Changing calving time

The calving pattern of cows is very repeatable, and it is difficult to bring the date of calving for late-calving cows forward by more than a 3-week cycle per year without risking an unacceptably high rate of empty cows.

Where it is necessary to move the calving date forward by more than 6 weeks (over two years), it may best to leave the current cow herd in its established calving pattern and join the replacement heifers to calve at the desired calving time and period. As the number of young breeders (calving at the desired time) increases each year, the older, out-of-sequence cows can be culled. After about five years, the herd will be calving at the required time over two heat cycles with minimal risk of low conception rates.

What to measure and when

  • Record the date on which each cow calved to develop a ‘calving histogram’ (see Tool 5.4).
  • Record the number of days that bulls are with cows.

Ensure that the investment of labour to record information on calving patterns and difficulties benefits the breeding operation.

Mature cows

Mature cows should not need assistance at calving as the cost of labour outweighs the benefits. Aim for cow condition scores of 2.5–3.5 and a minimum of 1,500kg green DM/ha in calving paddocks to minimise weight loss in cows and produce satisfactory milk for calves.

What to measure and when

  • Twice-daily routine observations, then two-hourly once a cow is actively engaged in labour.
  • Note the number of hours since ‘waters have broken’, membranes showing, or the cow is actively engaged in labour.

Dystocia

The penalties associated with failure to optimise heifer growth from pre-weaning through to post-weaning and then from joining to first calving are significant, including failure to reach critical mating weight (CMW) and re-conceive, high rates of dystocia and reduced lifetime production.

Around 52% of bovine deaths occur at calving time as a result of dystocia or calf disease from scours and cow losses.

Dystocia is an abnormal or difficult birth or labour, and results from a foetal-pelvic disproportion. Several factors can cause dystocia, including:

  • large calf size – a function of genetics of both maternal and paternal traits, as well as varying rates of maternal nutrition from conception through to birth.
  • placental size – potentially important; a function of nutrition at conception through to about day 80 of gestation. A positive correlation between placental size and birthweight of the calf is well documented, and excessive nutrition immediately post-joining can influence calf size.

Other more complicated mechanisms are at work, and in some cases, cows under nutritional stress can allocate more nutrition to the foetus at the expense of their body condition via a progesterone pathway, and can produce larger calves as a defence mechanism for calf survival in times of energy deficits.

Generally, excessive rates of dystocia are attributable to failure of the cow to reach adequate pelvic size as a two year old. In most cases, this is a management failure to match the growing heifer’s nutritional requirements from pre-weaning to post-weaning and from joining to calving as a two year old.

Losses from dystocia range include:

  • failure to raise a calf
  • culling the empty cow
  • increased labour costs to supervise calving
  • increased mortality rates for surviving devitalised calves in the first month of life.

The influence of heifer nutrition on dystocia rates far outweigh the genetic component affecting birthweight and size.

EBVs for birthweight, calving ease, days to calving etc. are useful tools but it is important to consider nutritional influences.

What to do

  • Aim for maximum pelvic size
  • Ensure the best nutrition for heifers both pre-weaning and post-weaning (the single biggest factor in lowering dystocia loss). 

Supervise heifer (and twin) calving

Guidelines to supervising heifer (and twin) calving

Calving difficulties in beef heifers can be a major source of financial loss, causing calf death rates of up to 10%, and in some cases, death of the cow. Other costs associated with calving difficulty include labour for supervision and assistance, veterinary fees and overall reduction of herd fertility.

As a guide, assist at the birth of a calf in the following instances:

Heifers with a single calf

  • Maximum of two hours after the ‘waters have broken’, membranes showing or heifer is actively engaged in labour.

Cows with twin calves

  • Supervise calving to increase live calves born.
  • Maximum four hours for first calf to be born – after the ‘waters have broken’, membranes showing or cow is actively engaged in labour.
  • Maximum two hours after birth of the first calf and before birth of second calf.

Calve heifers between condition score 2.5 and 3.0, and have them in good physical condition at calving. If the calving of heifers or cows with twins is not carefully supervised, difficulties during the birth process may result in:

  • increased number of stillborn calves
  • calves failing to thrive
  • cows dying or being injured
  • retention of foetal membranes (particularly in twin-bearing cows), which could become infected and reduce future fertility
  • increased veterinary costs.

Ensure heifers are in good physical condition at calving

When a difficult calving occurs, provide assistance in the birth process to improve the chance of cow and calf survival. It is recommended that heifers or cows bearing single calves that need assistance during calving are culled after their calves have been weaned.

Take action when calving difficulties (dystocia) are a sufficiently large issue (as judged by the percentage of heifers or cows experiencing difficulties), a high percentage of calves are stillborn, or considerable time is required to assist heifers and cows experiencing difficulties.

  • Cull any cows that required intensive calving assistance after weaning their calves.
  • Include calving ease in the enterprise breeding objective when selecting bulls for mating (see Module 4: Cattle genetics for information on setting breeding objectives).

Manage bulls for high conception

Guidelines for managing bulls to achieve high conception

Carefully consider the number of bulls allocated to mating groups or herds. Insufficient bulls for the number of cows in a herd can lead to lower pregnancy rates and reduced throughput of animals meeting market specifications.

Use two healthy fertile bulls per 100 cows for normal conception rates

Bulls must be monitored closely during mating.

General guidelines for bull ratios are:

  • maximum 2 bulls/100 cows for intensively managed southern herds
  • maximum 4 bulls/100 cows for extensive grazing (ie pastoral zone)
  • minimum 2 bulls/100 cows or per herd.

Single sire joining is widely practised in the southern beef industry and particular care needs to be taken to achieve high conception rates at every joining. Single bull mating reduces the risk of bull injury from fighting, but increases the potential for low calving percentages within individual mobs due to infertility or sudden loss of service ability. The following guidelines are suggested to reduce the risk.

Take particular care of bulls when single sire mating

  • Assess all bulls every year prior to mating, and only use those that meet the assessment guidelines (described in the 'Bull assessment guidelines' section, below).
  • Join each bull to a maximum of 50 cows.
  • Avoid wasting bull resources; joining sound bulls to less than 40 cows is wasteful and increases the cost of bull purchases.
  • Observe all herds weekly during the joining period to ensure that the bull is working and has not been injured during mating.
  • Have bulls in reserve (at least 20%) to replace injured bulls as soon as they are identified, and consider extending the joining period in that herd by one week (or the period between observations).

Manage bulls carefully pre-mating to achieve high conception rates

The management of bulls has a large impact on herd reproduction. Bulls with low fertility decrease conception rates, which leads to low pregnancy rates, increased calving spans, reduced throughput of weaners and animals meeting market specifications, and consequently reduced enterprise profits.

Additional costs may be incurred because of:

  • the need to replace bulls more often
  • the potential spread of infectious diseases that may reduce the fertility of cows and increase enterprise costs through treatment or eradication of the diseases.

Poor bull management can significantly decrease fertility

Common sources of low bull fertility and conception include:

  • bulls in poor condition two months prior to mating (when semen is produced)
  • insufficient effective bulls for the number of cows in the mating herd
  • use of too many bulls, which encourages fighting and is wasteful (but retain a replacement bull)
  • mixed ages of bulls in mating groups, or mixing bulls shortly before or during mating, which can affect conception while social dominance is being established
  • large mating paddocks where bulls and cows become separated
  • over-fat bulls (condition score 4.0–5.0) and unfit bulls due to lack of exercise (over-fatness can interfere with the heat exchange function of the testicles resulting in infertility with low sperm output)
  • transporting bulls for some distance or feeding high grain supplements close to the start of mating
  • venereal disease (eg vibriosis, trichomoniasis).

Bull condition score

Body condition score is a key factor when monitoring the general health and nutritional well-being of bulls. It is also a means of assessing whether young bulls have been overfed before purchase and may fail semen and serving ability tests.

The ideal condition for a bull prior to mating is condition score 3.0

Aim to keep the condition scores of British breed bulls within the following ranges at start of mating, and then during mating:

  • minimum condition score 2.5
  • maximum condition score 3.5.

Options for adjusting the condition scores of bulls include:

  • checking bull soundness at least two months before the start of mating (allows nutritional adjustments to start with sufficient time to ensure target condition score and testicular size responses are met)
  • increasing or decreasing pasture available or pasture quality for bulls before mating
  • supplementary feeding with a diet containing at least 11.5MJ/kg when condition score is less than 2.0, and considering protein supplements to stimulate testicular development before mating
  • replacing bulls if condition score is below the suggested limit at the start of mating.

Bull physical soundness

Prior to mating, bulls need to be assessed as physically sound, not carrying reproductive infectious diseases and having acceptable levels of libido and semen quality. (See 'Bull assessment guidelines' section, below).

Assess bulls for physical soundness pre-mating

Bull assessment guidelines

Bulls must pass all physical tests specified in the Australian Association of Cattle Veterinarians’ publication, Evaluating and Reporting Bull Fertility. The physical attributes evaluated include:

  • front and hind feet claws and soles
  • angle of pasterns in front and hind legs
  • hind limb conformation from the side (normal, sickle hocked, post legged, swollen or puffy hocks)
  • hind limb conformation from rear (normal, bow legged, cow hocked)
  • stance and gait abnormalities
  • spine and limb defects
  • head examination from front and side for alignment, absence of swellings and normality of eyes
  • scrotal skin pliability, thickness and inflammation
  • scrotal palpations for fat, freedom of movement, head, body and tail of epididymis, shape of testes, hernias
  • prepuce, sheath and umbilicus
  • penis, including palpation through skin, protrusion of penis and examination of erect penis (to exclude a potentially large number of penile and prepuce abnormalities).

Infectious disease assessment as set out by the Australian Cattle Veterinarians is summarised in Module 6: Herd health and welfare.

Table 1: Guidelines for minimum scrotal circumference in healthy bulls
Age Bos taurus bulls and Bos indicus derived bulls Bos indicus bulls
12–15 months 30cm 24cm
18 months 32cm 28cm
2 years and older 34cm 30cm

 

Serving ability

It is important to know the serving ability of each bull. The serving ability test is a useful procedure, but a meaningful result requires a trained person to use careful application of animal husbandry skills. It is recommended that a local veterinarian carry out the test under approved guidelines. The close observance of a bull during a serving ability test allows observance of sexual behaviour and libido, mounting behaviour, exteriorisation of the penis and ejaculation. Many problems are detectable on serving ability testing that may not be apparent just on a physical examination

A serving ability of 2–3 servings in 10 minutes is essential for high conception

Guidelines to serving ability:

  • minimum serving ability of 2 or 3 servings in 10 minutes
  • minimum time since bulls exposed to excessively hot conditions of 60 days before mating.

Preparation of bulls for mating should include:

  • mating bulls of highest serving ability to heifers so that they get in calf at their first joining (cows that calve early in their first season tend to be early calvers for the rest of their lives)

Join high serving ability bulls with heifers

  • selecting bulls for mating that meet the specifications set out in Evaluating and Reporting Bull Fertility (2003) available from the Australian Cattle Veterinarians website.
  • ensuring access to at least one replacement bull (more in larger herds) from four weeks before mating begins
  • planning mating groups eight weeks before joining and running bulls together before mating to allow social groupings to establish (mixing bulls shortly before or during mating can reduce conception rate due to distraction when fighting, and possible injury to bulls)
  • vaccinating bulls with appropriate vaccine to keep the herd protected against diseases that affect fertility (described in Module 6: Herd health and welfare).

What to measure and when

  • Ratio of bulls per 100 cows before mating each year.
  • Body condition score weekly from eight weeks before mating until the end of mating.
  • Physical and health check-up at eight to four weeks before and at start of mating and weekly during mating.
  • Semen examination at eight and four weeks before, and at mating if infertility is suspected.
  • Libido test completed at eight to four weeks before mating.
  • Calving histogram prior to mating (see Tool 5.4).

Artificial insemination as a mating option

If artificial insemination (AI) is used, the correct procedures are required to ensure high conception and calving rates. Results from an AI program are optimised by managing:

  • cow/heifer selection – all females in an AI program must be on a rising plane of nutrition with sufficient time post-calving to return to oestrus. As a guide for best results, maiden heifers are under less stress than mature cows, but mature cows are easier to get in calf than first-time calvers if nutrition adequate.
  • heat detection  – the accurate detection of standing heat and the resulting timing of insemination are critical to the success of an AI program. Clear identification of individual animals, record keeping, visual observation for signs of heat and where necessary, the use of heat detection aids, are critical factors in an AI program.
  • oestrus synchronisation – manipulation of oestrous cycles of heifers or cows to cause them to exhibit standing oestrus around the same time can greatly reduce the number of days needed to detect a group of animals in standing oestrus. Hormones common to many protocols are prostaglandin F2α (PG), gonadotropin releasing hormone (GnRH) and progestins.  
    • Prostaglandins – a hormone (administered by injection) that shortens the reproductive cycle by removal of the corpus luteum from the ovary between day 4 and day 17 of the normal oestrus cycle.
    • Progesterone implants – placed under the skin behind the ear or in the vagina (eg intravaginal CIDR or controlled internal drug release). Implants are usually left in place for 11 days to postpone the onset of oestrus until two days after removal (see Tool 5.6 for different schedules).

Synchronisation of females will fail in animals that are anoestrus (no ovarian activity and not cycling).

Potential problems associated with CIDRs

Controlled internal drug release (CIDR) is an intravaginal device that contains progesterone and acts like an artificial corpus luteum. Information on the proper handling and administration of CIDRs is provided in Tool 5.6.

There are normally few problems associated with CIDR treatment.

CIDRs should not be inserted in cows that are less than 21 days postpartum because the probability of inducing cyclicity is low. CIDR insertion should be performed as cleanly as possible to reduce the risk of spreading disease (see Tool 5.6).

When removing CIDRs, it is not uncommon to detect a whitish discharge due to vaginal irritation from the wings of the CIDR, which does not necessarily mean the animal has a vaginal infection. A difference in conception rate or pregnancy rate has not been detected between CIDR-treated animals that do or do not have a discharge.

  • Care when handling semen – semen is a live biological product that must be handled correctly and stored at the correct temperature with liquid nitrogen. It is susceptible to temperature shock and exposure to sunlight, water, blood and poor hygiene.
  • Insemination technique – rectovaginal technique of insemination gives the best results. Insemination can be done approximately 12 hours after the onset of observed oestrus. Fixed time insemination can occur with different programs involving CIDRs and specific hormone injections, and reduces the labour and time taken up in inseminations that are timed to observed oestrus.

Proper artificial insemination technique

High pregnancy rates to fixed-time artificial insemination (FTAI) depend on a series of events, including proper storage and thawing of semen, and depositing semen in the correct location (uterine body).

When synchronising heifers or cows for FTAI, consider how many animals can be inseminated properly in a designated time. This will determine how many heifers or cows you synchronise, and whether you will require assistance with the insemination process.

Representatives of AI companies are available to assist with the entire oestrus synchronisation and AI process. They can assist you with choosing an appropriate FTAI protocol, administration of the oestrus synchronisation products, sire selection, purchase of semen, and insemination.

If you are conducting the AI process, remember that the location of semen placement within the reproductive tract will have a significant impact on pregnancy rates. It is important to deposit the semen in the body of the uterus (target area) and not the cervix. Deposition in the cervix will significantly reduce the pregnancy rate to FTAI. Placing the semen beyond the uterine body into one or both of the uterine horns is not beneficial.

During the artificial insemination process, it is important to know where the tip of the AI catheter is at all times. Some helpful tips when performing AI include:

  • pay careful attention to the storage of semen
  • ensure the thaw unit is at the correct temperature (37°C)
  • follow the AI company’s recommendations for thawing semen.

If an AI program is being considered, carefully assess the benefits and costs of the options. Calculate the costs of the various options in terms of dollars per calf born to enable a comparison of mating systems. Attend a special AI training course to gain the knowledge and skills to obtain the best results.

Pregnancy diagnosis

Guidelines to implementing pregnancy diagnosis

Aim to conduct a pregnancy diagnosis as soon as possible after either the maximum number of days from the last day of mating has been exceeded, or calves have been weaned from the cows, except in drought when calves have been weaned earlier (see Procedure 3 for guidelines).

Schedule pregnancy diagnosis at the appropriate time for accuracy

Recommended guidelines for timing of pregnancy testing and diagnosis are:

Heifers

Ultrasound technology

  • minimum 28–35 days after last day of mating
  • limited use on foetus once advanced beyond 15 weeks when it drops lower over the pelvis
  • very accurate on positive pregnancy diagnosis but can give false negatives
  • useful in accurately ageing the foetus.

Manual palpation

  • minimum 35–50 days after last day of mating
  • requires experienced operators for early diagnosis at 7–10 weeks in heavy cows.
Cows with calves
  • ultrasound 30 days after last day of mating
  • manual palpation 50 days after last mating
  • at weaning, at the very latest.

Cull all non-pregnant cows, and assess and record reasons for failure to conceive to aid future management decisions.

Use pregnancy diagnosis to cull all empty cows

It is important that pregnancy diagnosis is conducted at the correct time so that infertile heifers can be culled from the breeding herd and managed to meet market specifications for sale.

What to measure and when

  • Check for presence of a foetus (or twins) on day of pregnancy diagnosis.
  • Estimate age of foetus to plot calving pattern, which will assist with labour planning for calving supervision.