YOUNG heifers represent one of the most vulnerable groups in Northern Australia’s beef herds, facing significant risks of mortality and reproductive challenges. High mortality rates, particularly in first-calf heifers, can drastically reduce herd productivity and profitability.

The Calf Alive project has been instrumental in identifying the causes of these losses and recommending strategies to manage both mortality and maximise re-conception rates in young heifers.

First-calf heifers have an inherently higher risk of mortality compared to mature cows. This is due to several physiological and management-related factors, including:

• Dystocia (calving difficulty): One of the leading causes of mortality in heifers, particularly younger heifers calving for the first time, is dystocia, often caused by foetal-maternal disproportion. Smaller pelvic sizes make it difficult for heifers to deliver calves, increasing risks of injury or death for both the calf and the mother.
• Nutritional demands: Heifers are unique because they are still growing while supporting both a pregnancy and lactation. This dual demand strains their energy reserves, making them more susceptible to health complications and, in some cases, death.

Key Findings from the Calf Alive Project:

• Age-related mortality: Heifers calving before two years of age have a significantly higher risk of mortality in northern Australia, with a 4.3pc higher missing rate compared to non-pregnant heifers of the same age. Even two-year-olds face 2.3pc higher mortality risk, while three-year-olds show a 1.6pc increase.
• Critical pregnancy status: Pregnancy is a crucial factor contributing to heifer mortality. Younger heifers have a harder time managing the energy and nutritional needs required for both growth and reproduction.

Nutritional deficiencies are a leading cause of poor reproductive outcomes and mortality in heifers. Managing the diet of first-calf heifers is critical, especially in regions like Northern Australia where pasture quality declines sharply during the dry season.

Heifers, particularly those in late gestation, need significantly more protein and energy to maintain body condition, support pregnancy, and ensure a successful calving and lactation process.

Protein and Energy Supplementation:

• Protein needs: Pregnant heifers need at least 1kg of protein per day, but dry season pastures often provide only 500g of protein, creating a severe nutritional shortfall. This lack of protein can lead to malnutrition, poor growth, and higher rates of dystocia, increasing the risk of both heifer and calf mortality.
• Energy supplementation: During the dry season, heifers should be given energy-dense supplements to compensate for low pasture digestibility, which typically drops below 55pc dry matter digestibility (DMD). This ensures they maintain sufficient body reserves to sustain both their growth and reproductive needs.

Improving Body Condition Scores (BCS):

• Target BCS: Maintaining a BCS of at least 3 is crucial for heifers. A BCS below 3 significantly increases the odds of non-pregnancy and mortality. Heifers with a BCS of less than 3 are 2.3 to 4.1 times more likely to experience non-pregnancy and calving complications.
• Ensuring heifers maintain a BCS above 3 improves their ability to conceive after calving and reduces mortality risks.

Aligning Calving with Nutritional Peaks:

• Timing calving with the wet season (November to April) ensures that heifers have access to higher-quality pasture during the critical periods of lactation and early post-calving recovery. Aligning calving with periods of abundant forage helps maintain heifer body condition and enhances calf survival rates.
• This strategic calving period also improves the chances of re-conception, as heifers have more time to recover body reserves before the onset of the dry season.

The Calf Alive study emphasises the importance of utilising data on animal performance to make informed management decisions. By monitoring factors such as age, pregnancy status and mortality trends, producers can identify high-risk heifers and apply targeted interventions. This includes:

• Supplementing diets during critical periods (e.g., late gestation and early lactation) based on Body Condition Scores and overall herd health data.
• Adjusting management practices, such as weaning earlier, to reduce the nutritional strain on younger heifers.
• Implementing reproductive management strategies, like delaying the age of first calving, to allow heifers more time to grow and mature before facing the stress of pregnancy and lactation.

The findings from the Calf Alive project highlight the critical need for targeted management strategies to improve the survival and reproductive performance of first-calf heifers. Key strategies include:

• Delaying the age of first calving to allow for greater growth and reduce risks of dystocia and mortality.
• Providing adequate nutrition, particularly in the form of protein and energy supplements, during the dry season when pasture quality is poor.
• Aligning calving with the wet season to ensure heifers have access to better quality forage during critical periods of pregnancy and lactation.

Genetic selection using Estimated Breeding Values and genomic EBVs plays a pivotal role in improving heifer fertility and body condition in northern herds, particularly in challenging environments.

Utilising higher accuracy information such as Genomic Breeding Values, along with high accuracy EBVs offer the opportunity to move a herd towards more favourable performance in areas such as age at puberty and post-partum anoestrus intervals.

Alastair Rayner is the General Manager of Extension & Operations with Cibo Labs and Principal of RaynerAg.  Alastair has over 28 years’ experience advising beef producers & graziers across Australia.   He can be contacted here or through his website www.raynerag.com.au