Mighty Good Advice
For Your Heifers
(From SELECTIONS Dairy Newsletter)
By Mel Dejarnette, Reproductive Specialist
For any animal breeding operation with progressive
genetic goals, the youngest animals in the herd should
be the most valuable animals. This is especially true
for the dairy or beef producer who is currently using
artificial insemination.
Unfortunately, in many dairy operations, the heifers
tend to be overlooked and undervalued. Because they’re
not producing milk to contribute to the cash flow,
they’re often looked at as simply an expense item on
the balance sheet; a necessary evil of the operation.
Additionally, due to the limitations in space, heifers
are often reared in facilities distant to the milking
operation. Here they often receive less than optimal
management attention. All too often the job of getting
heifers bred is turned over to an unproven herd bull
because no one has time to watch them for heat. This
creates what I refer to as a "genetic stumbling block."
I’m sure you’re familiar with the age old saying;
"one step forward, then two steps back." Using A.I.
on your cows is taking a genetic step forward. However,
allowing an unproven herd bull access to the most valuable
animals you own is taking two genetic steps backwards.
Synchronizing your heifers with MGA and prostaglandins
and breeding them to proven calving ease sires, can turn
your genetic stumbling block into a genetic launching pad.
MGA stands for Melengestrol Acetate, a synthetic form of
the naturally occurring hormone, progesterone. Prostaglandin
is also a naturally occurring hormone produced by the uterus
and commercially available under the trade names Lutalyse
and Estrumate.
The MGA-PGF system (Figure 1) works as follows: MGA is fed
to all animals at a rate of 0.5mg/head/day for 14 days. The
progesterone activity of MGA will block the expression of
estrus in the cycling animals during the feeding period.
This hormonal stimulation will also induce or "jump start"
many of the non- cycling animals. Within three to six days
after the last day of MGA feeding, most animals will display
a standing heat. DO NOT breed at this heat as conception
rates are usually compromised. Wait 17 to 19 days later
and inject heifers with a single dose of prostaglandin.
Watch for heats for the next five to seven days and breed
animals eight to 10 hours after detection of initial
standing heat.
The MGA-PGF system has numerous benefits. Compared to
using prostaglandin alone, the MGA system results in a
higher estrous response rate and higher conception rates
(figure 2). That’s right! Higher conception rates! Not
only does MGA induce many anestrous heifers to cycle,
but the progesterone stimulation during the 14 day feeding
period appears to stimulate higher fertility in all animals
at the prostaglandin induced heat. That’s something no
herd bull can do for you.
Although not close enough to allow for fixed time A.I.,
the synchrony or "tightness" of estrous response is somewhat
closer for the MGA-PGF system compared to using PGF alone.
This allows you to focus heat detection labor into a shorter
time period.
Traditionally, the recommended interval between MGA feeding
and PGF injection has been 17 days. However, more recent
research data suggests estrous response and synchrony may
be slightly improved with a 19 day interval. This also
lends flexibility to the protocol should labor or scheduling
problems arise at the last minute.
For optimum success with the MGA-PGF system:
- Feed heifers to reach at least 65% of their
projected mature weight by 14 months of age.
- If heifers are not accustomed to eating at
the feed bunk, start feeding a grain supplement
two weeks prior to MGA feeding.
- MGA can be top dressed, but proper consumption
rates are facilitated by thorough mixing of MGA
into a grain supplement or a silage based TMR ration.
- MGA usually comes in the form of a pelleted protein
supplement. Read the label to determine the actual
concentration of MGA/lb of pellet (usually 1.0 mg/lb)
and mix pellets with grain or feed to ensure
that each heifer is getting .5 mg of MGA/head/day.
The MGA-PGF system is ideal for many dairy operations
because the heifers are already being fed in a feedlot
situation. Implementation is basically hassle free.
Although the MGA-PGF system also works great on beef
cows and heifers where feeding facilities are available,
MGA is not approved for use in lactating dairy cows.
Most large feed suppliers will have access to MGA if
they don’t already have it in stock. Should you have
trouble locating a source, call your Select Sires sales
representative or your member headquarters office and
we can readily assist you in locating a supplier.
Although MGA actually stands for a reproductive hormone,
I prefer to think of MGA as an abbreviation for
"Mighty Good Advice." In fact, I don’t think I can come
up with any better advice for breeding age heifers than MGA-PGF.
To order product contact:
Select Sires Inc., 11740 U.S. 42 North, Plain City, Ohio 43064 / Phone: (614) 873-4683 Fax: (614) 873-5751
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