Editor's note: The following case study was contributed by Alan S. Vaage, ruminant nutritionist with Jaylor.

A herd I worked with in Alberta, Canada, had an acceptable level of milk production (83 pounds); however, it continued to struggle with lower-than-desired milk fat (3.4 percent fat, 3.0 percent protein).

The feeding system on this older style free-stall farm was comprised of a partial mixed TMR (PMR), fed in a feedbunk in a cross-alley next to the free-stall barn, with a dead-end at one end and capable of only accommodating a third of the cows at a time; a limited amount of loose hay, fed in a feeder within the free-stall area that could accommodate about half the herd at one time; and 4 pounds concentrate per milking (2x), fed in the parlor.

The overall ration was relatively high in forage, and the PMR contained haylage, barley silage as well as added hay. In an attempt to increase milk fat, the dairyman continually wanted to increase the amount of hay fed, but was limited in what could be added to the PMR as he was using a horizontal auger mixer that did not have blades.

I suspected the problem was related to animals eating variable ratios of hay and PMR, sorting of the PMR, or both. The dairy producer doubted this could be the problem since he felt the cows preferred the hay and that all the animals ate their share. The issue was finally settled by an analysis of Dairy Herd Improvement records.

Cows having milk fat minus protein percent equal to or below 0.1 were identified as being “inverted,” and classified into three groups based on days in milk (DIM), as either 1-100, 101-200 or 201+ DIM. The results showed that 21.1, 34.6 and 50.0 percent of each group (35.8 percent overall) were inverted, respectively, with many animals having milk fat 0.5 units lower than protein, especially in the 200+ group. These results provided evidence that a relatively large number of cows were sorting the PMR, as well as possibly eating a higher proportion of the PMR than intended. As expected, the feed in the feedbunk showed characteristic signs of sorting.

Personal observation had shown that the extent of the increase in the incidence of milk fat-protein inversion with increasing DIM is a good indicator of the degree of ration sorting in TMR-fed herds. Later-lactation cows seem to have the luxury of time, due to a lower level of hunger and intake, which enables them to be more active in this pastime. Similar high levels of inversion (>25 percent) across DIM can be an indication of excessive NFC or total fermentable carbohydrate in the diet, lack of effective fiber, or both.

Convinced by the DHI analysis, the dairyman agreed to reduce both the hay in the PMR and that fed separately. Only better-quality alfalfa hay was included in the PMR to ensure that it would break down easier as well as be preferentially eaten if it remained long. It was also recommended that the TMR be fed twice daily to reduce the potential for sorting.

These simple changes helped increase milk production to 88 pounds, with 3.7 percent fat and 3.1 percent protein, in a relatively short time. Analysis of DHI records then showed the proportions of inverted cows as 18.2, 16.7 and 20.0 percent (18.5 percent overall) for 1-100, 101-200 and 201+ DIM, respectively — well within the expected range.

Though the herd was capable of higher milk fat content, it was concluded that this was near the best possible result given the current farm configuration and TMR mixer. A vertical mixer such as marketed by Jaylor would eliminate much of the challenges with hay use and PMR sorting on a farm such as this, but the time for building and equipment changes in the current case was still in the future.