Back-grazing means letting livestock go back across areas that have been previously grazed, usually to access a fixed water point. What we are trying to avoid is allowing animals to bite off regrowth occurring following the prior grazing event on a plant. Back-grazing is acceptable up until the time stock return to take the second bite.
Here are some illustrations of the concept with explanations with each photo.
We’ll start with a nice satellite image showing a 3-day grazing sequence with stock returning to the same water point all three days. The white lines indicate where the daily strip fences had been. Note most of the animals are concentrated in the day 3 allocation where they should be. You can see a few dots in the previously grazed strips as they move from the fresh feed to water. Then they return to the new strip because that is the best feed in the pasture.
The photo below shows a similar situation. Again you can see a few animals moving along the inner circle fence as they go to and from the water point. If you move stock in the morning and check them again in the evening, you should find at least 75-80% of the animals on that day’s strip. If more than a third of the herd are out picking around in the previously grazed areas then you are not giving them enough feed.
This was once-a-day moves. In this particular case I had let the pasture ‘get away’ from me and was in the process of cleaning it up, so this is higher than usual stock density, and right at 210,000 lbs live weight/acre. Generally we are in the 60,000-90,000 lbs/acre range with daily moves.
With proper high stock density grazing there is little motive for the stock to go back to where they just grazed. On irrigated or high natural rainfall pastures you can generally get away with 3 or 4 days of back-grazing. Anything more than that and you will start having issues with cattle grazing the regrowth.
What is the primary variable for when animals will return for the second bite?
In my experience time is the overriding factor. But distance from water points is something to be considered. If you are on such productive pasture that regrowth induces the second bite on day 4, the likelihood of your stock being an excessive distance from water is pretty low. There are over 500 pairs + bred heifers in the aerial pictures so it is a decent sized herd. Even at that, with only six fixed water points on this pivot, it would be very rare that any of them would ever be more than 1500 ft from water. Regarding sward height, on excessively tall forage, you might actually want them to take a second bite to freshen up the sward. There would still likely be adequate post-grazing residual left and CHO stores are fully charged so regrowth would not be impeded.Some folks have also noted that cattle will return to previously grazed areas to loaf, and that the impacts can be quite severe to these areas. This is especially true in absence of shade when cattle seek out a point on the landscape with good air drainage. I have seen these spots that are just as hammered as lone shade trees back in the Midwest or South. So keep that in mind when managing back grazing.