Introduction

Calving heifers for the first time at two years of age has been commonplace in many beef producing countries since the 1970’s; however, in the UK it is estimated that only 40% of suckler herds carry out the practice, with the average age at first calving being 32.8 months (BCMS, 2019).

When we compare ourselves globally, the UK suckler herds cost of production is significantly higher than elsewhere, and even with a relatively high beef price, often income does not cover cash costs (Figure 1).

Figure 1: Typical farm suckler herd production costs and output, 2018. Source: Agribenchmark, AHDB (2020)

It has been estimated that calving heifers at two years of age, rather than three, reduces costs by £600 per heifer. Heifer development costs equate to around 9% of total cost of production (Davis C., a conversation in 2020) and therefore if more herds implemented a calving at two policy, profitability within the industry could be improved.

In addition, heifers which calve for the first time at two years of age produce more calf weight, wean more calves over their lifetime and remain in the herd longer (Nunez-Dominquez et al., 1985).

Breeding heifers

The first stage in heifer development is identifying suitable sires and dams to breed heifer replacements from and this is where breeding and selection decisions are paramount. Estimated Breeding Values (EBVs) provide producers with information which help them understand the value of the individual as a genetic parent. Uptake of EBVs within the industry is disappointing, with only 30% of producers reporting using them in the most recent Farm Practices Survey (DEFRA, 2020).

The most effective way to create genetic change is through careful bull selection. When choosing sires to breed heifer replacements from, EBVs to primarily consider are calving ease daughters, calving ease direct, age at first calving, scrotal size, mature size and milk. It is also important to consider maternal indexes. The big emphasis placed on maternal traits is driven by the fact that two thirds of the cost of producing a finishing animal equates to the suckler cow (Lardner., a conversation in 2019) and therefore by effectively implementing EBVs within the herd, costs can be reduced.

Over the past 35 years, mature cow weight has been steadily increasing, following the 2.5kg increase in carcase weights each year. Mature cow size is highly correlated with feed costs and is one of the primary reasons why average mature size in the USA, Canada and Australia is much smaller at 550–600 kg. A recent study conducted by AHDB found that the optimum cow size in the UK to be approximately 680 kg. Cows exceeding 700 kg, not only require more feed, but also require feed which is of higher quality, resulting in feed costs increasing at a faster rate (AHDB, 2019).

The replacement heifer index developed by the Irish Cattle Breeders Federation (ICBF) was introduced to ensure more emphasis was placed on maternal traits when breeding decisions were being made. Within the index, 86% of the weighting is allocated to maternal traits and only 14% attributed to carcase traits. Since its creation and incentivisation, the number of calves born per cow has increased by 5%, the number of heifers calving at 24 months has increased by 23% and the calving interval has reduced by 10 days (ICBF, 2020).

However, it is important to remember that selecting superior cows to produce heifers from, is just as fundamental to breeding success, as sire choice. Preferably, replacement females should not be bred from cows which:

• Required assistance at calving
• Calved late in the breeding season
• Failed to wean a calf
• Have large teats making suckling challenging
• Weaned a calf which grew at less than 1 kg/day
• Flighty temperament

Studies have shown that cattle with flightier temperaments have higher levels of the stress hormone, cortisol, in their blood stream, which can disrupt reproductive hormones for ovulation and conception, reducing their reproductive efficiency (Cooke, 2019). Therefore, not only are flighty animals a health and safety risk, they can also impact the productivity and ultimately profitability of the herd.

Birth to breeding

The main aim of this stage of heifer development is to ensure that heifers reach 65% of their mature weight before breeding; this is mainly achieved through effective nutrition. Whilst suckling their dams, heifers are required to grow at least 1 kg/day without creep feed and 0.7 kg/day until maturity. This can be achieved through good quality silage or if required, supplementation with concentrates. Ideally the development ration should mirror the diet which they will be expected to thrive on as mature cows. Selection is key during this stage with studies suggesting that it is more economically viable to cull heifers before the breeding season, rather than retain unsuitable heifers for an extended period of time (Lamb, 2013). Heifer selection is driven by:

• Size: Heifers which do not retain 65% of mature weight by 14 months should not be retained
• Birth date: Retain heifers born in the first cycle of the calving season
• Temperament: Flighty animals should not be retained

Breeding to calving

The main aim between breeding and calving is for the majority of heifers to conceive within the first three weeks of the breeding season; pregnancies to be maintained and that the heifers reach 85% of their mature weight by calving time.

One of the key factors determining the success of calving heifers at two years of age is bull choice. Heifers that experience calving difficulties at two years of age produce fewer calves over their lifetime, and the calves are younger and lighter at weaning. Dystocia also extends post-partum anoestrus, reduces conception rates and increases the likelihood of the heifer being culled from the herd (Perry and Cushman, 2019).

Bull selection for heifers must focus on calving ease direct, birth weight and gestation length traits. In Canada and the US producers would not use a bull which weighed more than 30 kg at birth to prevent calving difficulties. A breeding period of between 45–60 days is also advised; this is a great way of selecting for long term fertility whilst also ensuring that most calves are born early in the breeding season.

Nutrition is also key during this stage. Inadequate maternal nutrition at any stage of foetal development has been shown to impact calf development, producing calves with lower birth weights; which have a higher chance of morbidity and mortality. Even though 75% of the foetal growth occurs during the last trimester (Reynolds et al., 2006), most of the placental growth occurs during the first two thirds of gestation (Reynolds et al., 1990) and therefore any disruption caused during this stage can have a big impact on future development of the calf.

Approximately 75–80% of calf losses from breeding to calving are due to early embryonic death (Edwards and Schrick, 2019). This is because the embryo does not attach fully to the uterus until 42 days after fertilisation and therefore any dietary changes during this time can impact embryo survivability by altering the uterine environment (Perry et al., 2013).

Nutrition in late gestation is also important. Heifers have an extended post-partum interval (time between calving and first oestrus) because they require energy for growth and lactation before finally directing some of it towards reproduction. The post-partum interval for heifers is around 86 days, 18 days longer than cows, and therefore it is important heifers calve early in the breeding season or alternatively calve a couple of weeks before the cows to ensure they are cycling before the onset of the breeding season (Anderson and Crites, 2019).

Body condition is the single most important factor linked to resumption of oestrus cycles. Nutrition pre-calving has an increased impact on post-partum interval, compared with nutrition post calving. Thin heifers have a 30-day extended post-partum interval compared to those which calve at body condition score 3 (Anderson and Crites, 2019). In addition, heifers which are thin at calving, have increased risk of dystocia (Corah et al., 1975) and their colostrum is often of poorer quality which impacts calf survivability (Odde, 1988). The most successful way of reducing dystocia is through genetics.

Post calving

Post calving management is key to ensuring heifers rebreed successfully and calve again within 365 days. Cattle prioritise growth and lactation over initiation of the next pregnancy and therefore adequate rationing is vital to ensure heifers remain in good body condition. This can be achieved by ensuring that spring calving heifers are provided with preferential pastures and kept separate from the main herd until they have produced their second calf.

Heifers who fail to rebreed successfully within a 60-day breeding period should be culled from the herd. This strong culling policy will increase selection for more fertile females.

Conclusion

Calving at two years of age is commonplace across the world. It undoubtedly reduces cost of production, but is very dependent upon the effective use of genetics, selection and management practices. By developing heifers effectively this will inevitably produce a functional suckler herd, where cows calve unassisted every 365 days and wean a live calf, have low maintenance costs and remain productive for a sufficient period of time to cover their development costs.

Thank you to the Worshipful Company of Butchers and the Yorkshire Agricultural Society for funding my Nuffield Farming Scholarship.

References

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