Last month we discussed the batch management of the sow herd in terms of the choices for the number of batches, in other words whether new groups of weaned sows should be formed on a weekly cycle or every 2 or more weeks. The second point we need to know is the rotation time of the farrowing facility for the batch management system chosen. This will alter the number of farrowings obtained from a set of pens during a certain period. As the rotation time decreases, the farm can win more litters born from the same number of crates.

The easiest example of how farrowing facilities rotate comes with a batch management system in which the groups are formed every 5 weeks. The process starts in Week 1 with Batch-1 sows either farrowing or in lactation. They will have entered the room some 5-7 days before they were due to farrow. Say these sows were weaned on a Thursday and mated the following Monday, 16.5 weeks earlier. It means most of them will begin to farrow on Thursday.

For Weeks 2 and 3 the sows are in their lactation period. On another Thursday, but now in Week 4, most of them have completed a lactation of 21 days and are going to be weaned. We can start cleaning and disinfecting the room they vacate. The compartment stays empty in Week 5 until the next sows (Batch 2) arrive. They can enter the farrowing pens on the Friday of this week, 6 days before their piglets are due. Then as Week 6 begins, the sows of Batch 2 start to farrow — and we have completed the rotation of the room.

As you can see, with a production system that works on batches every 5 weeks, the total rotation time of the farrowing facility has a length of 5 weeks and only one room is needed. An interval of 2 weeks separates weaning of Batch 1 and the start of the expected farrowings of the next batch. That means we have plenty of time to clean, disinfect and rest the room (for one week, for example) and enter sows before they begin to farrow. In the event that we decided to introduce them on Friday, we would gain another week.

On a 4-weeks cycle

Now consider the rotation time for farrowing places in a herd working with batches every 4 weeks. Again the system needs only one farrowing room. In this case, however, the total rotation time reduces to 4 weeks so we have a shorter period for cleaning and disinfecting. Probably it will involve cutting back on the room-resting time and introducing the new sows only 3-4 days before they are due to start farrowing.

Week 1 sees Batch-1 sows introduced 3-4 days before the expected farrowing date. Most of them begin to farrow soon afterwards. Three weeks later we are in Week 4 and most sows are going to be weaned after a 21-day lactation. Cleaning and disinfection of the room must be done urgently because Batch 2 has to enter by the next Monday at the latest. Rotation is completed in Week 5 when the first Batch-2 sows start to farrow.

Compare that with the farrowing rotation time when batches are formed every 2 weeks. In fact the total rotation time stays at 4 weeks, as with 4-week batches. Even so, we must still recognise that it gives us only a few days to clean/disinfect and rest the facility and it involves a short pre-farrowing introductory period for the next sows. The difference on this occasion is that we will need a second farrowing room because a second batch of sows will be introduced only 2 weeks after the first one.

In Week 1, Batch 1 enters Room A 3-4 days before anticipated farrowing. Week 2 finds the sows of Room A in their first week of lactation. But see the changeover in Week 3. That is when Batch 2 arrives in room B while the sows of room A are into lactation by 2-2.5 weeks. This Batch 1 is weaned in Week 4 so the sows' lactation has lasted a maximum of 3 weeks. Follow-up cleaning and disinfecting prepare Room A to receive Batch 3 in Week 5. At this stage, therefore, the rotation of the 2 rooms needed for the system has been completed.

Batches every 3 weeks

Working with batches every 3 weeks, the total rotation time is 6 weeks and 2 farrowing rooms are needed. As with the 5-week system, we have longer for cleaning, disinfection and resting of the farrowing place and sows can be brought into it more than 5 days before farrowing is due to commence.

The sequence has sows introduced at the beginning of Week 1 although they could in fact arrive in the previous week. They start to farrow and lactate in Week 1 and lactation continues in Week 2. At the end of Week 3, Room A is still full, but Room B can be filled with the sows of Batch 2. The alternative in theory fills Room A with Batch 2 in Week 3, but it would require the first batch to be weaned after only 10 days and that is not workable in normal circumstances. That is why a second room is needed. Back to Week 4 for the sequence shown and the sows of Room A are in their third week of lactation while those of Room B are farrowing.

Worth noting here is that if we weaned at 21 days, Room A would not be filled again until the end of Week 6 as batches cannot arrive before 3 weeks. More profit is won from the rooms by weaning at 28 days. The full cycle lasts 21 weeks and this suits management because it divides exactly by 3 to give 7 batches needed.

Week 5 has the litters of Room A being weaned (say, on the Thursday) and the facility can be cleaned. Meanwhile, sows in Room B are in their first lactation week. At the end of Week 6 it is the turn of the Batch-3 sow to enter Room A after its cleaning and resting. The cycle is closed and we can see why 2 farrowing rooms are needed.

However, perhaps we should look again at why a rotation of the farrowing facility needs to have 6 weeks when the lactation itself is just 4 weeks in length. That is due to the fact that the batches are organised every 3 weeks, so the only possibilities for rotation time are 3 or 6 weeks. In practice, rotating in 3 weeks is nearly impossible. The sows would have to be weaned after no more than 14 days of lactation and only one week would be left for the clean-up and the introduction period of the new sows.

On the other hand, herd management gains a practical advantage from the longer period that farrowing rooms are empty in 3-week and 5-week batch systems. It opens the possibility of introducing sows early where necessary. Say they were mated up to 7 days before the main part of the batch. Even at that stage they could still be introduced into the farrowing room as it is already clean and empty. This would be impossible working with batches every 4 and 2 weeks. These sows would have to farrow while penned with members of the previous batch and afterwards be weaned very early.

Furthermore, with a 3-week batch system, a sow mated even a week later than the main part of the batch can be brought into the farrowing room. This sow will be weaned relatively early after 21 days of lactation. But this is not the weaning at 14 days or less which could be involved if we were dealing with one of the other systems.