Maximise the number of live calves per breeding female

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Profitability in beef production is driven by stocking rate, carrying capacity and herd fertility which are all a function of feed quality (nutrition) and quantity.

Fertility

Basic components of female fertility in the arid zone are:

  • When available pasture permits target liveweights and body condition to be achieved, first calving as a 2 year old in the low rainfall arid zone can be accommodated. However, timing of first calving should be based on an assessment of heifer liveweight and body condition score targets rather than by a particular age to avoid breeder mortality. Young heifers calving during periods of low quality, or low availability, pasture and in low body condition may not conceive again for some time, may not gain sufficient body condition to support the second calf if she does conceive or may not survive. 
  • Conception occurs throughout the year, if continuously mating, but is often concentrated around periods of favourable pasture availability.
  • Dystocia losses in two year old heifers should be minimised.
  • Heifers should achieve liveweight and body condition targets at their first mating and subsequent calving. First calf heifers failing to conceive again quickly are one of the most inefficient parts of an extensive beef cattle herd. 

Nutrition

Nutrition is the key to understanding what really drives efficient reproduction. 

The nutrition available from the native pasture is a major constraint on cattle production across the grazing lands of the arid zone, although there are considerable differences between regions, (see Module 2; Managing your feedbase).

To keep the cow in good condition, breeder and grazing management must match feed requirements to feed availability in terms of both quality and quantity. Planning involves management of the breeder herd, their nutritional demands and pasture quality.

Nutrition also influences the onset of puberty in heifers and the ability to exhibit oestrus (the recurring period of sexual receptivity and fertility, or being ‘in heat’) and then to get in calf quickly either as heifers or return to oestrus post calving in first calf heifers.

Adequate nutrition, principally energy, over and above maintenance and growth requirements is required to drive the onset of oestrus, in both young growing heifers and older cows. Older cattle that have no growth requirements can allocate more energy to reproductive processes than rapidly growing heifers that have high requirements of both energy and protein for growth. 

Significant phosphorus deficiencies in arid pastures can also be a major limitation to reproduction by young heifers as this mineral is required in large quantities for bone development. Supplementation of phosphorus may be required and a key sign of phosphorus deficiency is if cattle are observed chewing bones.

The energy intake for pregnant heifers must be adequate to maintain growth for herself, and also the development of the uterus during pregnancy.

This requirement is around:

  • 40MJ/day for maintenance
  • 34MJ/day for each kilogram of body weight gained by the heifer during growth up to the point of calving.

The developing foetus requires:

  • an extra 5MJ/day up to the fifth month of pregnancy
  • 8MJ/day at six months pregnancy
  • 11MJ/day at seven months
  • 15MJ/day at eight months
  • 20 MJ/day at nine months.

Table 1: Energy (MJ) and protein requirements per day for different livestock classes.

Breeder cows

350kg

400kg

450kg

500kg

550kg

Protein

Dry cow

48

52

57

61

66

6%

Pregnant, last 3 months

60

65

69

74

78

6%

Lactating cow and calf, 0-3 months

74

80

85

90

95

10-11%

Lactating cow and 150 kg calf

111

118

125

133

140

10-11%

Growing cattle

150kg

200kg

300kg

400kg

500kg

Protein

Maintenance

22

26

35

45

55

8%

Gaining 0.5 kg/day

37

44

57

71

82

10-12%

Gaining 1 kg/day

50

59

76

93

108

13%

Older cattle may have body reserves that can be used in times of energy deficit and the loss of 1kg of body weight will release around 29MJ of energy that can be allocated to the reproductive process over and above what has been consumed.

Dry cattle can gain weight rapidly as feed quality improves early in the growing season but lactating cows often only maintain, or may even lose, condition as they allocate nutrition to supporting a calf as well as restoring reproductive processes.

The key indicators of reproductive performance are body condition score for cows (see Tool 5.02) and liveweight for heifers (see Tool 5.01).

Body condition of the cow can be assessed on a scale of 0 to 5 with a body condition score (BCS) of 1 being poor, BCS 3 being moderate/store and a BSC 5 being fat. These scores are a good guide to the cow’s reproductive potential. For example, a cow in:

  • BCS 1-2 may have dormant ovaries and will probably not cycle and conceive again while lactating during the following growing season
  • BCS 3 should start cycling soon after calving.
  • BCS 5 has usually not reared a calf for some time and is a poor breeder.

To keep the cow in good condition, breeder and grazing management must match feed requirements to both feed availability and feed quality. Planning involves management of the breeder herds’ nutritional demands and the quality of pasture. Breeder management strategies include:

  • timing mating so that the calf's highest milk requirement in its second and third month is matched to peak pasture quality
  • weaning to remove the nutritional stress on the cow as pasture quality declines
  • supplementing to reduce specific diet deficiencies.

Guidelines for heifer management and nutrition

Management for joining for first calving heifers and their subsequent performance is entirely governed by controlling the liveweight prior to their first pregnancy, through to pre-weaning, post-weaning and joining, and then from joining to calving.

Critical mating weight (CMW) for heifers

The concept of a target weight for joining that exceeds the weight required for the onset of puberty will ensure that all heifers are actively cycling and are fully fertile when first exposed to a bull. This will ensure that the maximum number of heifers conceive in the first oestrus cycle during the joining period.

Management of heifers from weaning to joining to reach Critical Mating Weight (CMW)

CMW is defined as the weight at which 85% of heifers fall pregnant over 45 days (two cycles).
  • Fertility at first oestrus is 21% lower than the third oestrus so it is important to ensure all heifers are cycling in unison before mating.
  • Selenium is important to reproductive efficiency and achieving high conception rates, (NB Selenium is naturally low in the native pasture plants of the arid zone).
  • Maximise number of heifers to reach CMW 2-3 cycles before joining.

Importance of a tight calving span in heifers and cows

How a heifer calves in her first gestation in relation to the herd calving span, determines the relationship of that cow to the herd for the rest of her life. Heifers that calve early in the calving season often continue to do so for the rest of their life.

Tight calving spans allow even calf drops, even lines of sellable cattle, easier management, and use of labour, and a herd that consistently reproduces within a 365-day time frame.

Management of heifers from joining to calving

  • It is critical to keep heifers growing from joining to calving to obtain maximum pelvic size for the calving process.
  • Heifer condition score and energy intake at calving determines the ability to return to oestrus and maintain a 365-day calving interval.
  • Cattle with a low body condition score at calving and then poor nutrition post calving will fail to cycle.
  • Use cow body condition scores and heifer liveweight as indicators of herd fertility

Genetics, as reflected through various EBVs, also has a minor role in breeding for herd fertility:
  • Selecting sires with a high EBV for scrotal circumference results in earlier onset of puberty in their heifer progeny.
  • The EBV which estimates the days to calving will also help to decrease the interval between calving and conception by decreasing the gestational length.
  • Calving difficulties are reduced by selecting sires with a low score EBV for gestation length.
  • A low EBV for birthweight will decrease calf size for that generation but cannot guarantee dystocia will be avoided, as most cases of dystocia are a result of a failure to maximise maternal pelvic size through poor nutritional management rather than birthweight. Managing nutrition is a far more immediate way to manage calving ease. Also in the long term if the heifer grows properly she should have easy calving in the future.
  • If the phenotype of the herd, especially heifers, is high yielding with a larger mature body size, they tend to be mature later with a later onset of oestrus.
    Manage fertility to maintain a calving interval <365 days

    Calving to conception interval

    The time between calving and conception has a major impact on the overall reproductive performance of beef herds. To achieve the same calving period every year (ie. a 365-day calving interval), cows must mate and conceive by around day 82 after calving. This puts considerable nutritional demand on cows to return to oestrus and lactate.

    If this 365-day interval is not maintained, over time the mean calving date will become later and as a result the calving period will change. This may mean more late calves are born, more will cows fail to join on the next joining and drop out empty. The late drop calves have less growing days to weaning. It also pushes the period of greatest nutritional demand away from the pasture’s most productive time.

    There is strong evidence that body weight, particularly body condition score of cows at calving, has a substantial effect on the post-partum anoestrus interval. Increases in condition score during late pregnancy through the provision of good nutrition, particularly energy, can reduce the interval between calving and first oestrus for all cows except those in good condition where it has no effect. A similar outcome can be achieved through the provision of good nutrition during early lactation.

    As Table 2 indicates, the real challenge in maintaining a 365-day calving interval lies with the heifer population. Only 68% of heifers are cycling within the 82 day timeframe required to maintain the calving interval of 365 days.

    Table 2: Return to oestrus post calving.

    Days after calving

    First calf heifers return to oestrus (%)

    Old cows return to oestrus (%)

    40

    15

    30

    50

    24

    53

    60

    47

    72

    70

    62

    82

    80

    68

    89

    90

    79

    94

    100

    91

    96

    Source: Merial Opportunity of a Lifetime

    Some important considerations for calving heifers in order to improve their return to oestrus within 80 days of calving are:
    • first calf heifers take longer to return to cycling post calving
    • heifers with dystocia take longer to return cycling
    • heifers are particularly sensitive to body weight at calving and post calving nutrition and this is reflected in slow return to oestrus
    • prioritise resources to meet the needs of heifers in the lead up to and following calving. This might mean putting them in your ‘best paddock’ prior to their first joining and/or calving and/or providing supplementary feed/nutrition post calving. Some considerations to working out your ‘best paddock’ for first calf heifers may be include the type of pastures, the distance between water points and nutritious pastures, water quality and topography
      • to increase conception rates, remember it is important to join all females and have them conceive on a rising plane of nutrition.
      If possible, heifers should be joined 2-3 weeks before the main herd as this allows an additional 2-3 weeks for them cycle post calving and to slot into the main herd to maintain a tight calving pattern.

      Heifer performance is critical. Underperforming animals are inherently less fertile, can fail to achieve maximum pelvic size leading to dystocia and can fail to get into calf quickly as second calvers.

      The effects of nutrition on reproductive efficiency in the older cows is much less apparent and allows re-allocation of the limiting factor in production, namely to feed to younger cattle.

      Select cows capable of conceiving within two mating cycles

      In seeking to strictly maintain a 365-day calving interval, high culling rates of underperforming cows may be required, which in turn increases the number of replacement heifers required to maintain the breeding herd. 

      This practice results in a higher proportion of quality pasture being used for maintenance of the breeding herd because of the amount of pasture needed to grow females up to first mating. The benefits of higher heifer retention rates do, however, far outweigh the perceived downside of having to allocate quality feed to breeders.

      What to measure and when
      • Conception rates from natural mating or when an artificial insemination (AI) program is implemented through pregnancy testing.
      • Body condition score of cows at regular intervals according to the seasonal conditions – monitor after weaning of the last calves, from six weeks before calving, and then from calving to mating.
      • Nutritional deficiencies that may limit oestrus and heifer growing including energy, phosphorous and other trace elements (selenium etc).
        You should also observe the breeding herd for evidence of female activity (cycling) prior to the commencement of mating.

        Further information

        Contact your state departments of agriculture for more information.

        Manage bulls for 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. Bulls should be monitored closely during mating, if possible and practical.

        General guidelines for bull ratios are:
        • extensive grazing in pastoral zone – maximum 4 bulls/100 cows
        • minimum of 2 bulls/100 cows or per herd.
          Assess all bulls every year prior to mating and only use those that pass assessment guidelines (as described in ‘Bull assessment guidelines’ section below).
          • Join each bull to a maximum of 50 cows. There is no minimum, but joining sound bulls to less than 40 cows is wasteful and increases costs of bull purchases.
          • Observe all herds during the joining period to ensure that the bull is working and has not been injured during mating or fighting with other bulls.
          • 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.
            Manage bulls carefully pre-mating to achieve high conception rates
            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 and/or eradication of the diseases.
              Fertility can be significantly decreased by poor bull management. Common sources of low bull fertility and conception include:
              • bulls in poor condition prior to mating when the semen is produced. They may also not be strong enough to mount cows effectively
              • insufficient effective bulls for the number of cows in the mating herd
              • using too many bulls, which encourages fighting and is wasteful (but be sure to retain access to a replacement bull)
              • mixed ages of bulls in mating groups, which can affect conception while social dominance is being established
              • large mating paddocks where bulls and cows become separated
              • overly fat bulls (condition score 4 or 5) 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
              • venereal disease such as vibriosis and trichomoniasis.
                Bull condition score
                Body condition score (see Tool 5.01) 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
                Options for adjusting the condition scores of bulls include:
                • increasing or decreasing pasture available and/or pasture quality for bulls before mating
                • replacing bulls if condition score is below the suggested limit at the start of mating.
                  Bull physical soundness

                  Bulls that are about to be mated need to be assessed as being physically sound, not carrying reproductive infectious diseases and having acceptable levels of libido and semen quality. See below for bull assessment guidelines.
                  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; there are a potentially large number of penile and prepuce abnormalities
                    Infectious disease assessment as set out by the Australian Association of Cattle Veterinarians is summarised in Module 6: Herd health and welfare.

                    Table 3: Guidelines to 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 it does require a trained person to use careful application of animal husbandry skills to obtain a meaningful result. 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 or 3 in 10 minutes is essential for high conception
                    Guidelines to serving ability:
                    • minimum serving ability – 2 or 3 servings in 10 minutes
                    • minimum time since bulls exposed to excessively hot conditions – 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

                        Preparation of bulls for mating should include:
                        • Selecting bulls for mating that meet the specifications set out in the AACV publication, Evaluating and Reporting Bull Fertility.
                        • Planning mating groups eight weeks before joining and running bulls together before mating to allow social groupings to establish. Mixing bulls either shortly before or during mating can reduce conception rate due to distraction when fighting and possible injury to bulls.
                        • Vaccinating bulls appropriately to keep the herd protected against diseases that affect fertility, as described in Module 6: Herd health and welfare.
                        • Joining experienced bulls, rather than young bulls, with heifers.
                          What to measure and when
                          • Ratio of bulls per 100 cows before mating each year
                          • Body condition score of bulls before mating until the end of mating
                          • Semen examination when infertility is suspected
                          • Libido tests completed before mating.
                            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 and have had sufficient time post calving to return to oestrus. As a guide to 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 is 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 all critical factors in an AI program.
                            • Oestrus synchronisation. Oestrus synchronisation simply implies the manipulation of oestrous cycles of heifers/cows to cause them to exhibit standing oestrus around the same time. This 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 luteam from the ovary between day 4 and day17 of the normal oestrus cycle.
                              • Progesterone implants – placed under the skin behind the ear or in the vagina such as the intra vaginal CIDR (Controlled Internal Drug Release). The implants are usually left in place for 11 days. This postpones the onset of oestrus until two days after removal. 
                              Synchronisation of females will fail in the animal that is anoestrus with 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. 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 in order to reduce the risk of spreading disease.
                              When removing CIDRs it is not uncommon to detect a whitish discharge which is due to vaginal irritation from the wings of the CIDR and 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. The retro/vaginal 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 AI (FTAI) are dependent upon a series of events including proper storage and thawing of semen as well as depositing semen in the correct location (uterine body).

                                When synchronising heifers or cows for FTAI an important question to ask is “How many animals can be inseminated properly in a designated period of time?” The answer to this question 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; whereas, 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
                                • make sure 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 $ per calf born to enable a comparison of mating systems. Attending a special AI training course is also recommended to gain the knowledge and skills to obtain the best results.