Kimberly - Energy density in dairy heifer diets. Sorting behaviors by heifers on ingredients in those diets. Variability of weight gains by heifers within groups. Effects of overstocking of heifers in penned facilities.
What do they have in common? All have been the subjects of research projects at the United States Dairy Forage Research Center at Marshfield and in which Wayne Coblentz was involved in some ways.
Coblentz, who is a research agronomist and dairy scientist with the U.S. Department of Agriculture's agricultural research service, was a presenter at the Extension Service's 2017 “Raising Quality Dairy Heifers” programs.
The three experiments that Coblentz reported on were prompted by earlier observations that the dairy heifers being grown at the Marshfield research station were putting on too much weight – most likely because of the energy contained in the corn silage in their diet, he indicated.
From his own familiarity with the forage, Coblentz believed that using eastern gamagrass as an energy dilutant and source of fiber in the diet might make a difference. In lieu of limited or precision feeding to address the excess energy phenomenon, he launched an experiment to dilute the diet with low energy forages, including gamagrass.
Coblentz explained that eastern gamagrass is a warm season plant that is better suited to a climate that is a bit warmer than Wisconsin's. He said it fares well on wet sites but is vulnerable to competition from weeds because of its slow establishment pace.
With the feeding of corn silage and corn byproducts from ethanol manufacturers being popular in the diets for dairy heifers, Coblentz said there is a challenge of keeping the energy density low enough to deter excessive weight gains.
One way to address that challenge is to dilute the diet with “cutter forages,” Coblentz stated. The not easily met ideal traits of those forages would be a high dry matter yield, high fiber content (close to 70 percent neutral detergent fiber or NDF)), low energy (40 to 50 percent in total digestive nutrients or TDN), high protein (15 percent), low potassium content (1.5 percent), and low sortability at feed bunks, he indicated.
As an option to having the readily available wheat straw satisfy some of those goals, Coblentz proposed an experiment with eastern gamagrass at Marshfield. Grown and harvested there from 2010 to 2013, it met the standards set by Coblentz, including for yields, NDF, and TDN.
Conducted in 2011, Coblentz's first trial covered 105 days with 120 Holstein heifers – 8 of each in 15 pens starting with group average weights of 714, 813, and 934 pounds. Five different diets with varying amounts of corn silage, alfalfa haylage, and eastern gamagrass haylage (0 to 30 percent of the forage) were fed.
As was suggested from previous heifer feeding at the research station, the diet without any gamagrass resulted in the greatest weight gains – an average of 2.4 pounds per day, which is considered to be too much for heifers, Coblentz observed. With 30 percent of gamagrass, the gain was a very acceptable 1.87 pounds per day, he pointed out.
Those differences were attributed to the limit on the intake of calories because the energy density of the diet was reduced, Coblentz said. An additional observation was that bunk sorting did not occur in the rations with the gamagrass, perhaps because it is very palatable, he noted.
For his second experiment at Marshfield, conducted in 2015, Coblentz worked with 128 Holstein heifers – 8 each in 16 pens – for 118 days. An additional variable in that experiment was a 33 percent overstocking at the feed bunk.
Four different diets, each with varying percentage of corn silage and alfalfa haylage, were fed. Gamagrass, wheat straw, and corn fodder were included in one diet each. As with the first experiment, efforts were made to standardize the crude protein, NDF, and TDN.
After feed was provided once a day at 10 a.m., the feed bunks were checked six times in the next 24 hours. Among the findings were that the heifers had a preference for protein and energy ingredients, that corn fodder had the most sorting while the gamagrass again had very little, and that the weight gains were lowest with the wheat straw, just a bit over the goal with both the gamagrass and corn fodder, and too high without the inclusion of the energy density dilutants, Coblentz reported.
No statistically reliable link could be made between sorting and the growth rates, Coblentz added. The feed bunk management also led to having virtually all of the feed being consumed every 24 hours, he noted.
For the third study, Coblentz introduced overstockings of 25 and 50 percent in some of the pens for 90 days of feeding 240 Holstein heifers starting with an average weight of 903 pounds. This time the main variable in the two diets was either well-processed wheat straw (cut to 3 inches) or non-processed wheat straw.
Noticeable differences were seen in the sorting between the two types of straw and in the variability of weight gains between individual heifers, most often among those in the overstocked pens, Coblentz pointed out. Delays in eating and the lying in alleys instead of the free-stalls were also more frequent in the overstocked pens, he added.
Accordingly, the hygiene scores on the heifers' flanks and legs were significantly lower for the groups in the overstocked pens, Coblentz observed. Although he suggested that behaviors could be attributed to “bored animals,” Coblentz noted that standing time and bouts between heifers increased with the higher stocking rates.
From the three studies, Coblentz concluded that the standing recommendation for dairy heifers to have a daily NDF intake of 1 percent of their body weight is appropriate, that statistical significance for difference in weight gains due to the sortability of the feed is not yet proven, and that the sorting behaviors prompted by differing diluting ingredients are not yet definitely linked to rate of growth.
More information on the U.S. Dairy Forage Research Center is available on the www.ars.usda.gov/mwa/madison/dfrc website.