Within all dairy economies, the cost of production and the volume of lifetime ruminant greenhouse gas (GHG) emissions is influenced greatly by the age of first calving. A heifer is likely to be weaned (and therefore commence eructation) at 8 weeks. This means that an animal calving for the first time at 2 years will have been emitting GHG for 674 days before producing food for human consumption, while an animal that calves for the first time at 3 years will have been emitting GHG for 1,039 days. Whilst only 10% of the rearing cost is pre-weaning, management systems that ensure a heifer receives excellent nutrition, whether in the form of high-quality milk powder, or the nutritionally more variable whole milk, during rearing, will give the individual the best possible chance of an Age of First Calving (AFC) of 2 years, and therefore minimise the GHG emissions, see table 1.Â
Age at first calving | Lifetime production (kg) | Total methane produced (kg) |
|---|---|---|
22 months | 31.230 | 76.77 |
23 months | 38.345 | 82.12 |
24 months | 36.154 | 87.92 |
25 months | 32.085 | 93.86 |
26 months | 21.465 | 99.96 |
27 months | 19.960 | 106.22 |
Table 1. Van Laar et al. (2004), Van Straalen (2006)
Minimising the negative energy balance and associated post-partum anoestrus, by satisfying the nutritional needs of a recently calved heifer or cow, will ultimately aid in returning a cow to in-calf ideally after 50-70 days rather than the average of 100 days plus. This will ultimately ensure both the productivity and profitability of a dairy enterprise but also reduce the GHG emissions per litre of milk produced.Â
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