By Bill Mahanna, PhD, Dipl. ACAN, Pioneer Global Nutritional Sciences Manager
March marked the alternate year in which the Western Dairy Management Conference was held in Reno, Nev., and as usual, it was extremely well attended by producers, consultants and academics.
While all of the presentations were excellent, this column will focus on practical advice offered by Dr. Bill Weiss of The Ohio State University regarding the amount of variation cows can handle when it comes to short-term changes in dietary concentrations of dry matter and fiber.
It is a common adage that ration consistency is paramount to maintaining the high intakes that drive high production. However, every cattle feeder has experienced the short-term intake effects of a drop in barometric pressure, indicating an oncoming storm, and how storm conditions cause cattle to consume a greater amount of feed before and after the weather event.
Several recent studies (Stone et al., 2003; Mertens and Berzaghi, 2009) have also documented the variation existing in forage dry matter (DM) and nutrient concentrations due to the differing harvest maturity and ensiling moisture content of the forage. Abrupt changes in forage DM also occur from rain or snow seeping into the open faces of forage bunkers or piles.
If not accounted for, dietary forage-to-grain concentrations will be altered, coupled with a decrease in the amount of ration provided due to water displacing DM in every bucket of feed put into the total mixed ration (TMR) mixer.
Feed bunk management also plays a role if the bunk ends up empty from a shortage of actual DM being delivered due to a rain event soaking the silage. The typical response to this would be overfeeding the next day in response to observing a slick bunk.
Many experts in subclinical acidosis (Zinn, 2014) also believe that feed delivery and bunk management are likely more to blame than diet formulation, based on their experience with the difficulty of inducing acidosis in a research setting without initiating at least two management challenges (nutritional insults) about four to six hours apart.
Given all this background on possible causes for variation in DM intake, what has been lacking is solid research data on how quickly, and to what extent, high-producing cows respond to relatively transient changes in diet DM and nutrient composition and if short-term cyclical intakes truly result in lowered production or rumen health issues.
Enter the applied results from an excellent series of research studies by Weiss and colleagues at Ohio State (Weiss and St.-Pierre, 2015).
To determine the effect of short-term changes in silage DM, a 24-cow study was conducted for 21 days (McBeth et al., 2013) in which control cows were fed a diet that was two-thirds alfalfa silage and one-third corn silage, resulting in a 55:45 forage-to-grain ratio on a DM basis.
The second treatment (UNBAL) was the same control diet, but water was added to the silage to reduce the DM concentration by 10%, resulting in a forage:grain ratio of 49:51 and providing less neutral detergent fiber (NDF) and more starch.
The third treatment group (BAL) was fed the same UNBAL diet, but cows in this group were given additional as-fed forage to maintain the same NDF, starch and forage:grain as the control cows.
During the 21-day trial, the researchers imposed two 3-day bouts in which treatment groups received the UNBAL and BAL diets.
Over the entire trial, DM intake of the two wet silage treatments (UNBAL and BAL) did not differ from the control group. Milk yield was the same for cows fed the control diet and the BAL treatment, where excess feed was offered. However, milk yield averaged slightly higher (87.6 versus 86.5 lb. per day) for the UNBAL group, which the researchers attributed to increased concentrate during the three-day bouts.
The practical implications of this trial were that all cows in the experiment were offered excess feed so that when the wetter diets were provided, cows did not run out of feed. The researchers proposed that this approach was likely the reason they did not observe any negative effects from feeding wetter silages.
In general, DM intake was depressed the first day of feeding wetted silage, but cows were able to adapt by the second day and consumed more of the wet diet. This increase in intake continued for about one day after the cows were placed back on the control diet before they readjusted and lowered intake to the level of the control cows (Weiss and St.-Pierre, 2015)
A second trial (Yoder et al., 2013) investigated the short-term effect of varying the dietary forage NDF (FNDF) concentrations among early-lactation - 73 days in milk - Holstein cows.
The 21-day experiment compared control cows fed a consistent diet containing 24.7% FNDF. Another group was fed a diet in which the proportion of alfalfa and grass silages was randomly altered, resulting in diets ranging from 21.5% to 28.0% FNDF. A third treatment group was provided a diet in which there was a five-day cyclical pattern in total forage and FNDF concentrations: 26.0%, 24.0%, 28.0% and 21.5% FNDF.
Surprisingly, when averaged across the entire 21-day trial, extreme daily fluctuations in FNDF had no negative cumulative effect on production. It appears that cows have the ability to dampen the response to repeated shortterm bouts (one to three days) of higher-FDNF and reduced-energy diets (Yoder et al., 2013).
Milk production, milk fat and milk protein were not affected by treatment. Furthermore, daily responses to shortterm increases in FNDF were variable but less than expected among high-producing cows typically limited by physical fill.
The researchers noted that on days when cows were given high-FNDF diets, DM intake was reduced, but cows compensated with mobilizing adipose tissue. However, on days when lower- FNDF diets were fed, excess feed delivery allowed the cows to consume additional feed (Weiss and St.-Pierre, 2015).
Cows seem resilient to short-term ration balancing mishaps, just as they are resilient in managing intake around a storm event.
Research from Weiss and colleagues at Ohio State suggests that rebalancing diets for a few days’ change in silage DM or NDF content is not necessary. Avoid overreacting to variation in feed analysis either due to poor sampling or actual feed quality differences by averaging results from multiple samples (near-infrared analysis can reduce this cost).
Unless changing to an entirely new forage source, also avoid making abrupt ration changes based on the latest forage analysis by using a rolling average of the last three to four analysis results.
To mitigate issues with short-term variations in dietary DM or fiber content, research lends credence to allowing feed refusals, suggesting that providing cows with excess feed appears to be the key to giving cows the ability to adapt and compensate.
Originally published in the April 2015 Feedstuffs issue. Reproduced with permission.
The foregoing is provided for informational purposes only. Please consult with your nutritionist or veterinarian for suggestions specific to your operation. Product performance is variable and subject to a variety of environmental, disease, and pest pressures. Individual results may vary.