The weaner as currency

The pig’s reproductive cycle lasts for 20 weeks, with weaning at 21 days: 16,5 gestation period + 3 lactating + average time on heat. Supposing that the sows wean 10 piglets, we can then come to the following conclusion: it takes two weeks to produce a piglet.
The pig’s reproductive cycle lasts for 20 weeks, with weaning at 21 days: 16,5 gestation period + 3 lactating + average time on heat. Supposing that the sows wean 10 piglets, we can then come to the following conclusion: it takes two weeks to produce a piglet.

I am aware that, in reality, I am mistaken: not all the sows in the farm have a reproductive cycle with an interval of 20 weeks. If it were so, we would have an average of 2,6 births a year. However, it is also true that these days it is possible that sows can wean more than 10 piglets at each birth. So we could say that one mistake compensates for the other and, in this way, we can “round up” some of the numbers.

Using this statement we can make comparisons between the consequences of certain production gains and losses. If it takes two weeks to produce a piglet then …..
  • One return at 21 days is equivalent to the loss of one and a half weaned piglets.
  • When the ultrasound shows an empty sow 42 days of gestation are lost, which is the equivalent of losing 3 weaned piglets.
  • To increase to 3,5 days the average weaning to mating interval is the equivalent of losing 0,25 weaned piglets.
  • Etc.


This formula can also help us to decide at what age weaning would give us the best results, answering the question: How many more piglets must be weaned to compensate for the production lost by increasing the weaning age from 21 to 28 days?

If it takes two weeks to produce a piglet with weaning at 21 days then, if we change the weaning to 28 days and continue weaning 10 piglets per birth, we are losing 5% productivity as a result of increasing the reproductive cycle from 20 to 21 weeks.

This means that “only” weaning half a piglet more per sow, we have already compensated for the loss due to the lower potential capacity of the rotation of births. Sometimes it is not an easy task to produce a half a piglet more, but it is likely that in many cases the prolonging of lactation and the corresponding better uterine involution, results in an increase in the total piglets born. What is lacking is that this increase in births be sufficient to stop increasing by 0,5 the weaned piglets.

Weaning half a piglet more per sow is the equivalent of adding one week to the cycle of all the sows on the farm.

These comparisons also allow us to consider other parameters that affect the ratio, as well as the percentage of returns. For example, how many weaners is equivalent to 10% of returns?

Let’s imagine a farm that is weaning 10 piglets per birth. If they manage to wean an extra 1,5 piglets per birth we could allow ourselves the luxury of increasing by 100% the repeats at 21 days (so that all the sows on the farm repeat once more) and we would achieve the same result. If instead of increasing by 100% the repeats, we increased them by 10%, this would be the equivalent of losing 0,15 weaners per birth.

With an increase of 0,15 weaners per birth we compensate 10% of the repetitions to 21 days.

The truth is that the first time I made this calculation I was surprised. Often we pull our hair out because in a batch we pass from 10 to 20% of repeats at 21 days. However, we don’t give so much importance to having weaned another batch at 9,8 when, usually, we are doing it at 10,1. In the latter case we are losing double that of the former! This data should convince us of the importance of good maternity management.

As we can see, employing the weaner as “currency” makes us more aware of the magnitude of the production variations and helps us to determine which of them are the most important.

Finally, judging the cost of a weaner, we will always be able to translate the production variations into Euros. According to SIP Consultors, this cost is around 30€ from which we can quickly arrive at the following conclusions:
  • One repeat at 21 days is the equivalent of losing 45 Euros (1,5 weaned piglets).
  • To maintain a sow for a day costs approximately 2,15 Euros.
  • Etc.

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