Do you know someone who picks and chooses what they eat on their plate? Maybe this is someone that likes to eat healthy and sorts for all the veggies, or maybe it’s someone who can’t stand the thought of eating something green and sorts against all the veggies. Just like people, cows can have preferences in what they choose to consume, which can sometimes lead to sorting.
We evaluated sorting in a Calan bin study at Miner Institute. To determine the extent of sorting, if any, we took a TMR sample and then an orts sample from all cows on two days. We then used the Penn State Particle Separator (PSPS) to determine the amount of feed that was on each screen (19 mm, 8 mm, 4 mm, and pan) for both the orts and the corresponding TMR. We discovered that not all cows sorted, and cows that did so didn’t consistently sort from day to day. It was interesting to find that some cows changed their behavior from day to day and possibly chose fiber vs. grain based on how they felt that day. For instance, when walking the Calan bins I noticed a cow that had eaten every last piece of long fiber she could from her TMR. This cow had also been sick four days earlier and treated for indigestion, so maybe she was sorting for the fiber because she was still in the recovery phase and the fiber helped buffer her rumen and reduce the risk of subacute ruminal acidosis (SARA). A study conducted at Pennsylvania State University found similar results when cows were allowed a choice between a long forage and slow fermentable starch diet (LC) vs. a short forage and fast fermentable starch diet (SC). Cows increased their intake of LC from 18.1% of total daily DMI to 38.3% when they were given a rumen challenge.
After shaking out nearly 150 PSPS, we next had to determine what was considered sorting. A recent review at the University of Guelph calculated sorting activity by first multiplying the DMI of the cow by the DM percentage of each fraction of the PSPS to get predicted intake of each fraction. Then actual intake of each fraction was expressed as a percentage of the predicted intake of that fraction. Values equaling 100% indicated no sorting, <100% indicated sorting against that fraction, and >100% indicated sorting for that fraction. In a perfect world every cow would be at 100% for each fraction but that’s nearly impossible in the real world. For our study we looked at the number of cows that deviated ±10% from 100% for each fraction. When we averaged the percent actual intake of each fraction from both days sampled for each cow we found that 11 of 65 cows sorted for the long particles (19 mm screen) and 5 cows sorted against the long particles. We saw the most sorting with this fraction, which makes sense since this was the smallest fraction (approximately 5.5% of the diet) so any variation would have a greater impact. In comparison, the bottom pan (approximately 36.0% of the diet) had 2 cows sorting against the long particles and 3 cows sorting for the long particles. We also averaged the percent actual intake of each fraction of all cows from all days and found 104% actual intake for the 19 mm screen, 99% for the 8 mm screen, 100% for the 4 mm screen, and 100% for the pan, so overall cows were sorting for the long particles but not to an extent that we would be highly concerned.
Certain characteristics including forage inclusion rate, DM content, particle size, and number of times feed is delivered can lead to sorting. It’s important to regularly check your TMR for sorting so that you can monitor your herd’s sorting rate. If your cows tend to sort on a regular basis or if your cows suddenly start to sort, you can identify potential causes of the sorting including changes you recently made that could have caused the cows to start sorting. If you’re identifying TMR sorting in your herd on a pen basis, take multiple samples along the feedbunk when fresh feed is delivered as well as multiple samples when orts are collected. Then use a PSPS to evaluate sorting levels using the methods listed above.
Sorting on dairy farms can lead to big problems if the cows don’t eat what you formulate for them. For example, a study conducted at the University of Guelph found that every 2% increase in selection against long particles led to nearly 2 lb/day decrease in 4% fat corrected milk per cow. In addition to production impacts, sorting can also increase the risk of SARA. Monitoring sorting in your herd and taking necessary steps to reduce sorting can help increase production and maintain herd health.