Push Back on Diet-Sorting by Lactating Dairy Cows

As a dairy nutritionist, I often bag a TMR-sample from the feed-bunk and then later Koster-test its moisture, which should be about 50%. I also do a shaker-box test with a 3-screen Penn State Particle Separator. I like to see 15 -20 % long-stem particles in the top-screen, 35 –40% in the middle and about 50% on the bottom. I also look at the nutrient specs of the lactating cows’ feeding program; it should contain at least 28% NDF (75% from forages) and no more than 37% NFC (non-fibre carbohydrates). When one of these nutritional parameters is outof-balance, lactating cows tend to sort their diet.

I also look for other contributing factors in the same TMR that lead to diet-sorting. But they are not always visible, especially when examining my 1/2 kilo sample. That is why; I like to consult with a few dairy producers in order to get more information.

For example, I know a dairy producer that milks 150 dairy cows, who told me that his cows sort their lactation diet, when he mixes significant amounts of lowquality forages, despite having a final TMR – with correct dietary moisture level and enough effective-forage fibre for good cow rumination. It’s something that he recently noticed on one particular morning’s higher than expected feed refusal (3 - 4%) – caused by adding high-fibre grass hay that also contained unpalatable canola stubble to the previous day’s TMR. He figured that the canola stubble hurt their gums when they tried to eat it. This is something that he never wants to repeat.

Another thing that is not often apparent in my sample bag is when things actually go according to plan in the lactation barn. This is where, there is not a whole lot of sorting, daily feed-intake is consistent and feed refusal is at a minimum. For this testimonial, I can use a 350-cow dairy that follows a wellthought-out protocol, every day. As a result, he delivers an adequately mixed and nutritious TMR to his lactation cows and makes sure it is pushed up several times a day.

It goes something like this - at noontime, every day, he mixes up in his self-propelled mixer-wagon; one mix of feed for 3 – 6 minutes, dumps it in the feed bunk. And, then makes up a second batch, but only dumps ½ of that. Together, this feeds all the lactating cows for one day. The next day, he dumps the remainder ½ mix from the previous day and then makes up a complete batch and dumps that to completely feed the herd for the second day.

His automatic robot feedpusher is programmed to move along the feed-bunk, where it then augers newly dumped feed, remixes it and pushes it up, every 2 1/2 hours. So, this producer has very few issues with TMR sorting in his lactation barn. He sees that by pushing up the feed and making it more available to the cows at all times: cows tend to exhibit less selective feed behaviour. They get a bellyfull of effective forage-fibre that promotes good rumination.

The funny thing is that I have been in a number of dairy barns, where the feed isn’t pushed up as often and there are definite “sorting holes” every few feet along the feed bunk. I would expect that these cows are unfortunately consuming an unbalanced portion of their TMR, namely; a lot of easily digested starches. Without enough effective forage fibres to buffer them, the resulting acids from such rapid NFC breakdown causes frequent digestive upsets or subclinical acidosis (SARA) in lactating dairy cows.

In these diet-sorting SARA situations, I make it a point to watch the cows resting in their stalls and watch them chewing their cud. It’s because cows with SARA and other digestive upsets have little rumination activity. So, when many of these milk producers are rhythmically belching and chewing without a care in the world, I am confident that sorting out their dairy diet is not occurring to a large extent.

Some behavioural studies suggest that dairy cows are just natural feed-selectors, regardless of how their TMR is put together. Yet, I believe we should literally push back on nature to prevent their diet-sorting. Namely, follow some of the above practical suggestions, when mixing up a daily lactation TMR, which needs to be eaten in its entirety by all healthy and productive dairy cows.