We put a lot of focus on feed sorting issues with lactating cows for very good reason. However, we don"t often look at sorting in close-up dry cow diets.
These rations can be more prone to sorting if using the bulk fill approach with straw in the ration. Miner Institute is currently in the midst of an intensive transition cow trial that includes straw, and also allows us to monitor individual intakes. With individual intakes, it"s readily apparent that, yes, close-up dry cows do sort.
The question is, to what extent – and does it matter?
The use of moderate energy, higher bulk fiber dry cow rations that include straw or other dry forages can result in TMRs where grain and minerals more easily separate out of the base TMR. This then can make it easier for cows to pick and choose, for or against fiber or grain and minerals.
With lactating rations, we"re focused on sorting issues primarily to avoid acidosis. In close-up dry cows, we"re looking at whether they"re getting that high-priced mineral mix we put together for them and, especially in the case of this trial, the protein and fiber sources that can greatly influence MP levels.
The tables below list three close-up TMRs (ZMP 1, 2 and 3), along with orts/refusals from two individual cows on each TMR. Particle distribution was performed with the new Penn State Particle Separator with 4 mm pef sieve (PSPS4). Wet chemistry analyses were performed by Dairy One for DM, NDF, CP and macro-minerals. Warning: this was only a spot check test, so we only have single day sampling and analyses and therefore insufficient replication to conduct proper statistical analyses.
Table 1. Penn State Particle Separation with 4.0mm pef screen: % as fed material retained on each screen. (pef value = proportion of material 4mm and larger).
Table 2. Wet chemistry nutrient analyses of TMR and individual cow orts.
We definitely have a "sorter" in cow #1994, as the particle distribution of her orts greatly differs from that of the TMR, with a PSPS pef value (proportion of material 4 mm or greater) of only 0.47, compared to 0.69 for the TMR. This cow was sorting for fiber consumption and against the smaller grain particles; analyses of her orts show higher CP, Ca and P values compared to the TMR.
However, we can"t simply compare percentage values when it comes to sorting; we must also know the amount she was fed and the amount she refused in order to calculate the grams of CP and minerals she consumed. In this case, she was fed 43 lbs. of DM and refused 7 lbs. of DM. This calculates to her intake of 2.374 kg of CP and 166 g of Ca. In spite of her being a sorter, #1994 was fed enough TMR that she still consumed over 150 g of Ca, which we aim for to prevent milk fever. Had she not been fed so much, her sorting could have resulted in deficiency of mineral intake. In group fed close-up situations it"s critical to not under-feed the group, allowing for differences in individual intakes and sorting behaviors, without risking metabolic problems at calving.
Note, sampling TMR and especially orts/refusals for any chemical analysis especially minerals is extremely difficult. It requires diligent mixing to produce a homogenous blend of the pile for sub-sampling to be sent for analysis. A single rock of calcium carbonate can result in large differences in analyzed Ca levels.
Find the Miner Institute January Farm Report online here: http://whminer.org/farmreport.html