The six week in calf rate (ICR) of a seasonal calving herd is the best predictor of future performance and directly affects profitability of a herd (Brownlie et al 2014). A 1% increase in 6wk ICR corresponds to a financial gain of £2 per cow (Burke et al 2008) so for a 200 cow herd, a 1% increase equates to a financial gain of £400.
But where does this financial gain come from?
The more obvious gains are from calf health, labour resources, purchasing power, better conception rates in cows that have been calved longer (less semen used) and ease of management of the herd, however the bulk of the gains are through increased efficiency of feed conversion and increased milk production through longer lactations.
Feed conversion efficiency
A cow at the peak of her lactation is metabolically geared up to produce milk from the forage she eats rather than to produce meat. Therefore for every kilogram of food she eats in early lactation she will produce more milk than from the same kilogram of feed in late lactation when more of that energy will go to increasing body condition.
A tight calving pattern will allow you to time more of the herds peak lactations with maximal spring grass growth which will be the cheapest forage available to you. Therefore making the most cost efficient use of the cheapest forage available.
Cows that calve at the beginning of the calving block will have longer lactation lengths and will therefore produce more milk in that lactation.
Take two cows that calve at different times, one on the planned start of calving (PSC) date (i.e. the first cow to calve) and one in the 7th week. They both get in calf on the same day in the middle of the first service block and will both be dried off on the same day but the first cow has given more milk and hence made more profit. If we calculate for an average cow producing 20L per day and a milk price of 24 ppl, we get the following result.
Therefore for the two cows in the example above there is an extra £192 of milk for cow 1, despite based on a traditional ‘all-year-round’ calving mentality and performance assessment, cow 2 performed better!!
Brownlie, T., J. Morton, et al. (2014). “Reproductive performance of seasonal-calving, pasture-based dairy herds in four regions of New Zealand.” New Zealand Veterinary Journal 62(2): 77-86.
Burke, C.R., Tiddy, R.M., Beukes, p.C. (2008) “Case studies exploring the potential impact of farm system changes on herd reproductive performance, production and profitability.” Proc of DCV of the NZVA 25-33