Elders Livestock Production Manager Rob Inglis discusses key factors in managing your heifers to improve their reproductive performance.
The success of your heifer raising programs hinges on the reproductive health of the heifers, and how well they have been prepared for their first breeding season.
The weight of heifers at their first joining has a profound effect on their future reproductive performance.
The weight at first joining is expressed as the Critical Mating Weight (CMW) and is quantified as 66 per cent (pc) of the adult Standard Reference Weight (SRW). Heifers usually reach sexual maturity at 52 pc of SRW, however joining heifers at weights below the critical mating weight (66 pc of SRW) may result in calving difficulties and/or failure to return to oestrus at the subsequent joining.
Nutritional needs
Nutrition is clearly the most influential factor determining critical mating weight. Poorly reared heifers reach puberty later, take longer to get in calf, and will calve late.
The chart below from Zoetis Repro active® shows the required growth rates from weaning to joining, and weaning to calving for a 500kg SRW heifer.
| Growth rates required bewteen weaning and mating to reach CMV 300kg at 15 months | ||||
|---|---|---|---|---|
| Weaning weight (kg) at 8 months | 200 | 220 | 240 | 260 |
| Average daily growth, weaning to joining (210 days kg/day) | 0.48 | 0.38 | 0.29 | 0.19 |
| Growth rates required between weaning and calving to reach target weight 450kg at 24 months | ||||
| Weaning weight (kg) at 8 months | 200 | 220 | 240 | 260 |
| Average daily growth, weaning to calving (480 days kg/day) | 0.52 | 0.48 | 0.44 | 0.40 |
Table shows growth rates required between weaning and calving to reach certain milestones. Source: Zoetis Repro Active.
Animal health
Ensure your heifers are in the best possible health. Better management of parasites, disease and nutrition will clear the way for timely joining of fit to join heifers.
While spring pastures are highly digestible, high in protein and energy, they are usually low in dry matter, low in starch, magnesium and other essential trace nutrients. Supplementary feeding is often necessary to ensure optimum health. Read Elders' Livestock Production Specialist Adam Turnbull' tips for supplementary feeding.
The table below shows the frame score of heifers and weights at various ages and milestones. All weights are expressed in kilograms. Source: Zoetis Repro Active and Meat & Livestock Australia.
| Frame score | Weight at puberty | Mating weight 15mths | Weight 0-3mths pregnacy | Weight 4-6mths pregnancy | Calving weight 24 mths | Mature weight |
|---|---|---|---|---|---|---|
| 1 | 240 | 260 | 296 | 319 | 333 | 400 |
| 2 | 270 | 300 | 342 | 369 | 387 | 470 |
| 3 | 290 | 330 | 377 | 409 | 430 | 530 |
| 4 | 310 | 365 | 419 | 454 | 487 | 600 |
| 5 | 340 | 400 | 455 | 499 | 525 | 670 |
Achieving critical mating weight can increase herd productivity, profitability and longevity.
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