Do you have a fertility problem in your herd? Use weaning data to separate nutrition from genetics

# Why weaning is the right place to start Weaning gives producers consistent, comparable numbers across a herd: how many calves made it to weaning, and their weights and ages. Those are direct, usable metrics. When numbers are poor, producers often point to a single cause — nutrition or genetics — but the answer is usually a mix of both.

# Nutrition matters — a lot Across Australian systems, underestimating cow energy and protein demand is a common problem. When cows mobilise body reserves to meet production needs, their chance of getting back in calf falls. The CashCow project followed about 78,000 cows in 142 mobs across 72 northern properties and found body condition and timing of calving strongly influence reproductive performance. If cows routinely calve in poor condition or stocking rates are too high, genetics alone won't fix the outcome.

# Genetics is real and measurable

# Think measurement, then action Producers should move beyond assigning blame and start measuring the variation inside their own herds. Key data points to collect at weaning and across the season include:

• Numbers weaned and individual weaning weights with ages.
• Calving dates and interval to re-conception targets (Days to Calving metrics already in industry use).
• Body condition scores recorded at strategic points (pre-joining, calving, weaning).

Accounting for age, lactation demand, disease history, and social or grazing behaviour will explain much of the within-mob spread. After accounting for those effects, remaining consistent differences are likely genetic and can be selected on.

# Practical approach for producers Start with the herd-level basics. If cows are consistently underfed, no amount of genetic change will overcome the nutritional shortfall. Conversely, if management and nutrition are commercially sensible, selecting for animals that perform above the mob average will improve reproductive performance over time.

• Improve the quality and consistency of weaning records so selection decisions rest on solid data.
• Use calving date and Days to Calving measures to identify females that re-conceive quickly under your environment.
• Account for known non-genetic influences (age, health history, lactation stage) when comparing animals.

# How to balance fixes Do not treat nutrition and genetics as mutually exclusive. Remove obvious nutritional shortfalls first so animals have the opportunity to express genetic potential. Then use measured performance to select females and bulls that do better in your system. In northern and extensive systems where seasonal stress is inevitable, selection for animals that cope better in real commercial conditions is a practical way to raise herd-level fertility without unrealistic management changes.

# Bottom line Weaning data tell a clear story if you pay attention. Fix the major nutritional problems first, then use consistent measurement and selection to capture genetic gains that improve reproductive performance in your environment.