Expert’s view: Rick GRANT about the link between fiber quality and farm profitability

Rick GRANT, William H. Miner Agricultural Research Institute, Chazy, NY USA

How do you define fiber quality and what affects it?

First of all, let’s define fiber quality: it relates to fiber’s intrinsic digestibility, or indigestibility, which is commonly defined by uNDF240, the undegraded neutral detergent fiber at 240 hours of in vitro fermentation. This parameter is sensitive to plant genetics, growing environment, maturity at harvest, as well as harvesting conditions, and it is a useful benchmarking tool on-farm. Another important parameter is particle size, which can be measured by the physical effectiveness factor, or pef, which is the fraction of dried particles retained on the ≥ 1.18-mm sieve.

The combination of these two parameters (pef x uNDF240) appears to be highly related to dry matter intake and energy-corrected milk yield. This relationship is especially true for corn silage and hay crop silage-based rations.

At the farm level, how can we make the most of fiber energy and nutrients?

To optimize energy capture from fiber, we must focus on forage fiber characteristics and feed bunk management. The amount of starch in the ration is an important lever as too much rumen fermentable starch may slow down NDF degradation, and it favors lower rumen pH. Recent research tells us that when the combination of particle size and uNDF240 is low, then even moderately high amounts of rumen fermentable starch may reduce milk fat.

The feeding environment is also an important part of determining rumen pH. The risk of low rumen pH is greatest when: a fermentable ration is fed, excessive competition occurs at the feed bunk, and access to feed is restricted. Under these management conditions, fiber degradability may be actually reduced with lower available nutrients and milk energy. The lesson is that poor feed bunk management will substantially reduce the benefits of high-quality forages.

Time spent eating at the feed bunk is a function of ration forage percentage, fiber degradability, and particle size. The time spent to chew and swallow feed at the bunk is an overlooked component of forage quality. Excessively long particles in the ration may force a trade-off between eating time and recumbent rumination.

Can you make some recommendations about particle size?

Table 1 shows some particle size recommendations with which we have had very good success on farms. With these particle distributions, cows are able to easily eat the daily DM intake within 3-5 hours (which is natural for them) and then have ample time for recumbent rumination. Research from the University of Guelph shows that cows with greater ruminating time while lying down ate more dry matter and produced milk with greater milk fat and protein.

	Sleve mm	PSPS 2013 %	Miner 2020 %	Comments
Top	19	2-8	2-5	Sortable material, too long, increases time neded for eating; especially if >10%
Mid 1	8	30-50	>50	Still long and functional pef, more so than 4 mm material. Maximize amount on this sieve, 50-60%
Mid 2	4	10-20	10-20	Functions aspef sieve, no recommendation for amount to retain here other than total on the top 3 sieves = pef
Pan	—	30-40	25-30	40-50% grain diet results in at least 25-30% in the pan

Table 1: Recommendations for TMR particle size using the Penn State Particle Separator (PSPS), Miner Institute (Cotanch, 2017; rev. 2020)