6,502
edits
Changes
Jump to navigation
Jump to search
Subacute Rumenal Acidosis (view source)
Revision as of 21:00, 26 August 2010
, 21:00, 26 August 2010→Risk Factors
===Risk Factors===
===Risk Factors===
Insufficient long fibre in the diet
Long fibre is essential both for rumen mat formation and
to stimulate cudding. It is usually defined as fibre longer
than 2-5 cm. However, if it is longer than 10 cm, it is
possible for cows to 'sort' the ration and avoid eating the
fibre. Consequently, long fibre for inclusion in a TMR
should be chopped to between 2-5 and 10 cm. Provision
of long fibre in modem diets is problematic as there is an
increased tendency for silages to be chopped very short
in the belief that better compaction and fermentation will
result. Furthermore, there is an inverse relationship
between fibre content and the 'D-value' (or digestible
organic matter digestibility [DOMD]) which is correlated
with the metabolisable energy (ME value). Farmers
tend to concentrate on making high energy silage at the
expense of fibre quantity and quality. In the case of
maize silage, fibre length is often so short that it is best
to assume that its peNDF content is minimal and additional
long fibre may be required (eg, 1 to 2 kg of
chopped hay or straw per cow).
Inaccurate fodder dry matter estimation
If the dry matter content of fodder is overestimated, insufficient
fodder may be provided, thereby leading to SARA.
Excessive mixing of a TMR diet
If a diet is overmixed in the TMR mixer wagon, long
fibre will become less effective. The long fibre (forages)
should always be placed in the mixer wagon last to
ensure minimal degradation.
Excessive feeding of starches and sugars
Excessive feeding of starches and sugars is a common
problem, especially soon after calving. Maize silage is
a rich source of starches and sugars and this property,
together with its lack of effective fibre, means that it is
frequently implicated as a factor in the development of
SARA. A common scenario is for a farmer and his advisors
to counter poor yields or an excessive loss of body
condition score during early lactation by feeding additional
concentrates in order to supply additional energy.
However, often the problem is one of SARA, and feeding
additional energy actually makes the situation worse
- although a temporary increase in milk yield may be
observed, probably as a result of small intestinal carbohydrate
digestion.
Poor dry cow management
As mentioned earlier, feeding a suitable transition diet is
essential for rumen papillar development and the acquisition
of a suitable rumen microflora capable of dealing
with the lactation diet.
Feeding post-calving
While most farmers appreciate the need for a pre-calving
transition diet, they frequently fail to appreciate the fact
that the transition period is properly defined as three to
four weeks pre-calving to three to four weeks post-calving.
The rumen is not capable of handling high energy
density diets until this period is complete. Cows should
be fed a relatively low energy diet during this postcalving
period. Ideally, the energy density of the diet
during this time should be no more than 10 per cent
greater than the transition diet. In practice, this means
that freshly calved cows should remain on a diet suitable
for M+25 to M+28 litres during this period. This will
encourage a maximal dry matter intake and avoid
SARA. All too often, post-calving cows are fed a diet
with too high an energy density in the mistaken belief
that they would otherwise develop negative energy balance.
Many cows and their lactations are ruined during
this critical period.
The objective during the post-calving period is to
maximise dry matter intake rather than keep up with the
daily energy requirements of the cow.
Sorting of long fibre
If the fibre in a TMR is longer than 10 cm, cows are likely
to sort the food and only consume small particles and
short fibres, leaving the long fibre alone (Lammers and
others 1996). Cows which sort food in this manner will
be at risk of developing SARA. If feed barrier space is
restricted, dominant cows may sort the food and thus
develop SARA. Subordinate animals, such as heifers and
lame animals, will then consume the sorted diet and
so obtain a diet of lower energy but greater fibre content
than is intended. The net result is that both groups are
at risk of negative energy balance, although for different
reasons. Ensuring that fibre length in a TMR is adequate
to prevent SARA, but not too long such that sorting
occurs, is problematic. Many mixer wagons will not cut f0o1age to an appropri ate leng-Ith (25 to 10() cm1) and thet e
is eur-r-elItIx no suitaSlic for-age choppei- on the UK miarket,
althouLgh sonic. but 1ot 1all, stli\ax clioppers Wxill Cut to a
suLitahble length. OneoCptioll is to nSe a stationiarx foIagce
hair-\cstel fromil xxhich blades cani he reni-oved it' reqUoired
to enlsui e the conICCt Chop leingth. Hoxxcxeri, the nise ot'
suLICh miachineiv inI this 1manIler is not xxithout risk to the
oper-atoi- a1njid appr-oprialtc safectV guLardl-CIs illust be eni1ployed.
Slug feeding of concentrates in the
milking parlour
It' giealtei- th.an 3 to 4 kg-, of co-ceniiti ates arc fed at a timlie.
I-Lillmen IpH is likelx to tall anid i-emiiain loxW fol- mnLIchI of
the time. The pi-ohlemi is comI)pounided if cox\x7 aIre receCixinc
a TMR at the Itcd bhai-i iei- that is hiTh inI en-erx
coni-pari-ed to gri-ass silalc. It mIulst he remicemicber-ed that
suIbstitution effects xvill also he oCCurlrine so that, the
miore cake is fed, the less foraoc xxill be coIlsumLIed. In
the conitext ol' 1K ag1i cuIltuIre, tIlC aIthor- considers this
pr-actice of hxhl-id TMR feedii-Ig to bc a miajoi factoIr iII
thIe dex elopmenlet o(fSARA.
Food deprivation and irregular feeding
InI oidel- to naiilalisc dr- illattei intake, a TMR should be
axllablc at all times. It is gen1erall recomimiiciided that
5 to 11) pei cenit of the ationi should be left ox er each daxl
anid remiosved befoi-c t'frcshi food is ot't'ered. It is comImIIIonto
ftind situation-s xxheci ther-c is 0o f'ood in frouit of the
coW s. su(estinSt it ian out )A thin the last fcxx flurs.
AlteiratxVcly f(oodI ilay he Pliscilt, but unlax ailable to
the cox s since it Ilas not benCI puLshed uip to tile barl--icr SO
that thex cani eat it. Peliods ot' food deprixvatioil mia disrLipt
the riLiIeillniicrobial pOpu-lation. aIld tencd to caulse
coxs to oxvercat xvhleu food is cintioduced. Both of thesc
factol S ilneealse the i-isk of SARA dcx eloping. Most
tfaric- s tccd a TMIR oil-ce daIilvx, elerallx, iil the illoiilillg
t im.av be adxaitagLeouLs to feedl the TMR ii the
afterilooni, tllerbhy CilsuIr-lgtl tilat fooCd is il tfr(lilt of the
cox S aIt iiglit (XxV1lCl tilexC arC ilMatteilded). DuLingt the
dax!' food cain casily bhc psiledC uIP to tile barrier as tai-ll
staff arec ceilerallN, illiattendalnlce.
Poor cow comfort
Pooi covx coilltort xxi -Csuilt in lcss tinle beint spceit
1uillila.1til-L xxith ani associated r-eduLctioll in saliaa produLIctionI
anIdi runlinaiial hbfl't'clrilng
Miscellaneous factors
Lailileiless. pooi tfeedl hbianci-s. aildtc so olil. ill.a all play a
Phart il tlic dcx\cloPi-ille-it of'SARA.
==Signalment==
==Signalment==