Fresh cows are typically maintained on a slightly modified high-production cow diet. Unlike dry cow diets, where much of the research on transition cow nutrition has been focused, the postpartum period dietary requirements have been overlooked. But that will be changing, as researchers focus on fresh cow feeding strategies over the next few years, predicts Dr. Tom Overton, Cornell University, Professor Director, PRO-DAIRY.
Most research has been conducted from the “transition cow standpoint,” Overton said. “We’ve gained a lot through some of these types of approaches,” including the need to control energy intake, increasing metabolizable protein pre-partum, and the use of dietary cation-anion difference (DCAD) diets.
But there hasn’t been an emphasis on the specific needs of the fresh cow. Overton and his colleagues have recently examined data and conducted experiments on fresh cow feeding. As a result, they’ve formulated several important questions that need to be asked as researchers forge ahead and examine feeding strategies during this stage of the reproductive cycle.
Two separate studies — one conducted at William H. Miner Agricultural Research Institute (Dann and Nelson, 2011) and the other at Cornell (McCarthy, 2015) — yielded seemingly conflicting results. Upon closer examination, however, the discrepancy has led to some unanswered questions that warrant further explanation.
The 2011 Miner Institute study measured dry matter intake (DMI) and milk production during 13 weeks of lactation, comparing cows fed varying levels of starch in the diet. Cows were fed either a low-starch diet for 91 days postpartum; a medium starch diet for 21 days, then a high starch diet for the remaining 70 days; or a high-starch diet for the full 91-day postpartum period. Starch was provided by corn meal and kernel-processed corn silage, with soybean hulls and wheat middlings altering the starch content of the feed as needed for the groups.
According to Overton, the results indicated that the DMI and milk yield were lowest for cows which were fed a high starch diet immediately following calving. Cows fed the medium level of starch immediately postpartum, then switched to a high starch diet, showed the best performance. Cows on the low starch diet had higher milk yields and higher DMI than those on the high starch feed.
“This would tell us that a higher starch diet out of the gate,” was “not so good,” and that producers should feed a lower starch diet, and increase the amount of starch gradually, postpartum, Overton said.
However, the Cornell study had results which seem to conflict with that approach. In this study, cows were all fed the same diet pre-calving, then fed either high or low starch diets, with our without monensin postpartum. Monensin is a feed additive that increases milk production efficiency. At day 22 postpartum, all cows were fed the high starch diet for remainder of the study, at 63 days postpartum.
In this study, higher starch intake immediately postpartum led to increased DMI. While starch level had no impact on overall milk yield, cows on the high starch diet did show a faster rate of yield increase than those on the low starch diet. Adding monensin to either diet increased post-calving intake. Increased starch in the diet also decreased common problems such as ketosis.
So why were the results of the two studies apparently conflicting?
“Maybe the difference between pre-calving diet is influencing the results,” Overton said.
Pre-calving diets in the Cornell study consisted of 17.5 percent starch. At Miner, the starch level was 13.5 percent. The Cornell diet had more fermentable starch. Differences in feed digestibility and Neutral Detergent Fiber (NDF) digestibility between the two diets may have impacted results.
When the pre-calving diet is examined, it appears that cows on a low starch diet cannot make the transition to high-starch immediately after calving. For cows who are on a high starch diet pre-calving, a high-starch fresh cow diet makes more sense, and may jump-start lactation.
Fiber and the rumen
The results, along with other data from earlier studies, have led to more questions and speculation.
“Is there something going on here ruminally?” is one question to be explored, Overton said.
Cows fed a high starch diet had lower rumen pH and increase time where the rumen pH was below 5.8 during the first three weeks post-calving. They also had increased haptoglobin and serum amyloid A during this period.
A decrease in rumen pH below 5.8 is “consistent with much higher fermentability,” Overton said. “There is a potential for inflammatory response when feeding a high starch diet right after lactation.”
Results from the Cornell study, where some cows experienced health concerns, including ketosis developing three to seven days postpartum, most notably on the high starch diets, led the researchers to change the ration. Straw was incorporated into the ration, replacing an equal portion of BMR corn silage, altering NDF levels.
Postpartum data from cows on high starch/low fiber, high starch/high fiber, low starch/low fiber, and low starch/high fiber rations seem to demonstrate an interaction between starch levels and fiber levels which has an impact on DMI and milk yield.
In order for fresh cows to adjust to a high starch diet, fiber is needed to provide good rumen adaptation, based on study results. Results show that adequate physically effective NDF seems to play a role in fresh cow productivity. NDF levels higher than what nutritionist currently recommend may be fine under these circumstances.
If producers are using “rocket fuel forage,” the need may exist to “push the envelope and make sure we have rumen structure there to go along with the fermentability,” Overton said, and research is ongoing.
A relationship between pre-calving feeding strategy and fresh cow rations and results appears to exist, based on recent fresh cow studies. Interactions between starch and fiber also seem to impact fresh cow health and productivity.
Non-nutritional factors, such as optimal stocking density; reductions in heat stress; and segregation of cows and heifers during the transition period are all known to impact fresh cow productivity. But more research focused on the diet during the fresh cow period is needed.
“As much as our herds have gained, we still have a ways to go,” Overton said of fresh cow needs.
Dr. Overton presented this workshop at the recent 2015 Cornell Nutrition Conference.