Alfalfa is a widely used ingredient in animal nutrition, due to its excellent nutritional values per se. Harvested at proper time, it is an excellent source of highly digestible protein, as well as vitamins and minerals.
This post however,
is focused on Alfalfa as a source of physically effective Neutral Detergent
Fiber (peNDF). An essential nutrient in ruminant diets, whose role in rumen
health as well as in the digestion of other nutrients, has been widely assessed
by a large number of scientific works.
Most of the
ingredients from plants (cereal grains, oleaginous seeds, forages, etc.), used in livestock diets, content a varying amount of NDF, which
is directly related to their fiber content.
However,
not all of NDF has the capacity of promoting ruminal contractions, ruminal net
formation, salivation and hence stimulating an appropiate ruminal pH. It will depend on their
physic and chemical characteristics. This NDF that can promote these activities,
previously named, is considered as physically effective NDF.
Actually,
there are different methods and systems which try to estimate the effectiveness
of NDF from different ingredients. Among these, the most remarkable are the recommendations
made from NRC (2001), Michigan University and Cornell University. As for this
last reference, Cornell University has developed
the Cornell Net Carbohydrate and Protein
System. This system assigns different values to the effectiveness of NDF
from non forages, as well as modifies the effective values of NDF from forages,
depending on their processing and particle size.
Many
previous scientific studies have been performed in order to assess the role of
peNDF in ruminant diets with a common factor. They all used Alfalfa as the main
source of peNDF, trying to evaluate how their presentation (Alfalfa silo vs Alfalfa
hay) and particle size (long stem, chopped or ground) affected its
effectiveness.
Nowadays, researches continue in order to quantify the peNDF requirements of ruminants (depending on the species, type and level of production), as well as to assign proper values of peNDF to different ingredients.
But… Why is
so important peNDF in Ruminant diets?
One of the
main reasons for making up diets with an adequate level of peNDF is to prevent subacute
ruminal acidosis (SARA). Ruminant fed diets high in cereal grains, are exposed
to suffer a chronically low ruminal pH because
of the accumulation of acids (mainly Volatile fatty acids - VFA and lactic
acid) from ruminal fermentation of daily intake.
This situation isn’t desirable
at all, firstly because it decreases the digestion of certain nutrients from diet
which potentially leads to a yield decrease.
Secondly, if this situation
persists and due to rumen wall isn’t cover with mucous unlike monogastric, acids
will cause ulcerations and scars. This situation can be approached by Fusobacterium
necrophorum, present in rumen fluid, to migrate from the ruminal ulcers to the
liver via the portal blood. This bacterium
produces toxins, which cause liver abscesses and a variety of dysfunctions.
How can peNDF prevent digestion disorders?
As for
this, SARA can be prevented with an adequate amount of peNDF in daily diet. It will
help to the ruminal health, acting in different ways:
-The presence
of peNDF promotes ruminal contractions which help washing out VFA from rumen to
abomasum, where they are absorbed more efficiently, avoiding their accumulation,
hence contributing to increase pH value in the rumen.
-Promoting
chewing activity and saliva production. Saliva is the main source of
bicarbonate to the rumen as well as it serves to dilute acids, produced in
rumen fermentation. Bicarbonate acts as a buffer against the action of acids
and serves to raise pH value in the rumen.
How can peNDF
enhance the utilization of nutrients from diet?
Another
important action of peNDF into the rumen is to contribute in the formation of ruminal
mat. One of the main functions of ruminal mat is to promote particle retention.
Some authors have described ruminal mat as a very effective filter for
undigested small feed particles. Ruminal mat acts decreasing the escape of these
potentially degradable feed particles from the rumen, thus enhancing fiber
degradation and feed utilization.
Furthermore,
adding to this latter effect, the effect of promoting ruminal contractions previously
named. It has been described that an adecuate level of peNDF together with a suitable
particle size lead to a higher microbial protein synthesis into the rumen and a
greater flow of microbial nitrogen to the duodenum.
To
summarize, with the inclusion of appropriate amounts of Alfalfa or other high
quality forages in ruminant diets, we are not only covering their nutritional requirements,
but also due to their peNDF content, we are enhancing rumen health and feed
efficiency.
REFERENCES
James B. Russell. 2002. Rumen Microbiology and
its Role in Ruminant Nutrition.
Alex Bach, Sergio
Calsamiglia. 2002. Manual de Racionamiento para el Vacuno Lechero. Editorial
Servet.
W. Z. Yang, K. A. Beauchemin, and L.M. Rode.
2002. Effects of Particle Size of Alfalfa-Based Dairy Cow Diets on Site and
Extent of Digestion. J. Dairy Sci. 85:1958-1968
K. A. Beachemin, B. I. Farr, L. M. Rode and G.
B. Schaalje. Effectos of Alfalfa Silage Chop Length and Supplementary Long Hay
Chewing and Milk Production of Dairy Cows. J. Dairy Sci. Vol 77. No 5. 1994
Q. Zebeli, J.R. Aschenbach, M. Tafaj, J.
Boguhn, B. N. Ametaj, and W. Drochner. Role of physically effective fiber and
estimation of dietary fiber adequacy in high-producing dairy cattle. J. Dairy
Sci. 95:1041-1056
Your
comments and suggestions are welcome.
