Make Sire Selection Part of Your Mastitis Control
Follow These Recommendations for Using
Genetic Evaluations for Somatic Cell Score
does genetics have to do with mastitis and milk quality? In the U.S.,
semen distributors and sire selection specialists in the artificial
breeding industry often give little thought to mastitis and milk quality.
Milk quality and animal health specialists generally give little thought
to genetics. Even producers are often unaware of the genetic tools available
for preventing mastitis. As a result, genetic evaluations for somatic
cell score (SCS) have not gained the attention they deserve among producers,
AI personnel, and other dairy professionals.
Milk quality specialists and veterinarians are naturally focused on
short-term management issues, so a genetic approach to controlling mastitis
is rarely considered. However, while day-to-day management has large
and immediate impacts on udder health, genetics can have important long-term
impacts. The genetic impacts can be favorable or unfavorable depending
on how the sires are chosen.
The objectives of producers, milk quality specialists, semen suppliers,
and yes -- even the cows! -- could be advanced by a well-reasoned approach
to bull selection. The following recommendations are provided to enable
all segments of the industry to make appropriate use of genetic evaluations
Include sire selection as a point on your checklist when
consulting with herds for mastitis and milk quality. Designate someone
on your milk quality teams who will evaluate your clients' mating sire
choices in terms of SCS, fertility, and survival. Red-line those bulls
with PTA-SCS 3.2 or higher; use them sparingly and only when they are
truly exceptional for other economically important traits. Around 5
to 10% of AI bulls have PTA-SCS of 3.2 or higher. Recognize that sire
selection is a long-term, not a short-term solution to improvement.
For this reason, sire selection will not be an immediate priority for
herds facing loss of their milk market, but it should be part of every
herd's long-term outlook. Because genetic improvement is a long-term
process, even herds with excellent udder health management should avoid
sires with high PTA-SCS.
Use a selection index, e. g., Net Merit or a production and
type index, as an initial screening for selecting AI bulls. This will
provide a moderate amount of selection emphasis on PTA-SCS. Selection
indexes consolidate the genetic evaluations for all traits into a single
quantity for each bull. Producers should create a 'long list' of candidate
bulls using their chosen index. Be sure the index chosen is most appropriate
for the business goals of the herd.
Include PTA-SCS among the criteria for selecting a 'short
list' of service sires from the 'long list', but do not overemphasize
SCS to the exclusion of other economically important traits. Make only
limited use or avoid altogether the 5 to 10% of bulls with the highest
(most undesirable) genetic evaluations for SCS. In Canada, the percentile
ranking for SCS is provided for every bull by the Canadian Dairy Network
Avoid bulls with PTA-SCS or EBV-SCS 3.2 and higher. Other traits to
consider in forming the short list include herd life, daughter fertility,
calving ease, stillbirth, genetic defects, type, and semen cost.
Herds with low average SCC should give the same attention
to PTA-SCS in sire selection as herds with high average SCC. Genetic
differences among bulls' daughters are expressed to the same extent
in both high and low SCC herds. This will promote continued genetic
improvement for SCS and enable producers to obtain milk quality premiums
even when a herd encounters milk quality problems.
Producers who can successfully manage artificial insemination
should use AI bulls. A wealth of genetic information and true genetic
superiority are available through AI that is not available for non-AI
bulls. Producers who cannot manage AI, should purchase bulls from dams
with high selection index values and sired by well-qualified AI bulls.
The same tools used for selecting AI bulls should be applied to selecting
the sires and dams for non-AI bulls.
References: NMC 46th Annual Meeting Proceedings (Shook, 2007) pp
49-67 and NMC 2006 Regional Meeting Proceedings (Shook) pp.25-37. Updated