1 - Maximise the number of live calves per breeding female

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.

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

Critical mating weight (CMW) for heifers

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

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

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. 

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

Bull assessment guidelines

Table 3: Guidelines to minimum scrotal circumference in healthy bulls.

Serving ability

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

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

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.