NADIS disease bulletins
are written specifically for farmers, to increase awareness of prevalent
conditions and promote disease prevention and control, in order to benefit
animal health and welfare.
Farmers are advised to discuss their individual farm
circumstances with their veterinary surgeon.
Management
of Replacement Rams
The basic requirements of breeding rams are that they can confer the
physical characteristics of ease of lambing, growth rate, conformation, body
fat distribution, wool production, resilience or resistance to disease and
hardiness to their progeny. The relative
importance of these characteristics depends on the production system in which
they are used. Rams need to be free from
physical defects and production limiting diseases, and should be immune to
those diseases which are endemic within the flock. They must be sound for breeding purposes,
which requires sound limbs and freedom from abnormalities and diseases of the
reproductive organs.
Management of purchased rams
Replacement rams should be acquired at least 8 weeks before the start of
the breeding season, to allow them to adapt to their new environment and
diet. Introduced rams should be dosed
with moxidectin or a combination of two anthelmintic groups on arrival and housed or placed in an
area not intended for subsequent sheep grazing for 48 hours, to reduce the risk
of introduction of anthelmintic resistant helminth parasites. Introduced rams should also be treated for sheep scab on arrival, or
shortly after arrival along with the whole flock. If rams are brought in from potential fluke
areas, they should be treated with triclabendazole to
remove adult and immature flukes. Ideally, introduced rams should be separated from the main flock for
about 4 weeks, during which period they should be closely monitored for signs
of disease. Problems such as lameness
and skin diseases should be managed during this period to avoid spread to the
main flock. Introduced animals should be
vaccinated against clostridial diseases. Where flock vaccination against pasteurellosis and louping ill is
required, the introduced rams should also be included in these vaccination
programmes.
To avoid temporary infertility associated with louping ill and tick borne fever, replacement rams for use in tick-infested areas
should be sourced from other flocks within tick areas which experience a
similar incidence of these diseases. If
this is not possible, homebred ram lambs should be selected and retained, or
replacements purchased as ram lambs to allow a period of natural exposure to
the tick borne diseases, before using as shearling rams.
Contusive injury to the brain and fractures of the neck vertebrae of
rams are common, particularly during the autumn months. Such injuries occur least frequently in
established groups of rams, but can prove difficult to avoid following the
addition of introduced animals. Penning
the ram group in a small area for a period after mixing may reduce the
incidence of serious injury by reducing the momentum of any impact. Groups of rams should also be penned tightly
after shearing or plunge dipping until they recognise each other and
re-establish their order of dominance.
A WIDE-BASED AND ‘WOBBLY’ STANCE DUE
TO FIGHTING INJURY TO THE NECK
Ram sales are an integral and very important part of sheep farming
life. However, many of the practices
which are required to ensure a reasonable sale price are not conducive to
subsequent optimal breeding soundness. Sale rams are sometimes over-fat and struggle to acclimatise to a new
harsher environment and feeding regime, while feeding of large quantities of
oestrogenic cabbages and heat stress may reduce fertility. Furthermore, differences in feeding regimes
and in the skill of preparation of rams for sale make between flock comparisons
difficult. Ram sales also provide an
opportunity for the spread of diseases such as sheep scab and caseous lymphadentis. The alternative strategy of selling rams
directly from the farm of origin on the basis of their estimated breeding values
for liveweight gain overcomes most of these problems,
and has the added benefit of enabling purchasers to assess the environment in
which the replacement rams were reared. While this strategy remains impractical for most UK flocks, it is
important to ensure that the disease and production risks associated with
traditional ram sales are minimised.
OVER FAT RAMS OFTEN STRUGGLE TO
ADAPT TO A NEW HARSHER ENVIRONMENT AND MAY BE TEMPORARILY UNSOUND FOR BREEDING
Selenium deficiency has been associated with poor fertilisation rates
due to a role of selenium enzymes in testis metabolism and semen membrane
quality. Where selenium deficiency is
recognised within a flock, rams should therefore be supplemented at least 8 weeks
before the start of the mating period.
Ram breeding soundness
The importance of ram breeding soundness should not be
underestimated. Overseas, where for
several decades breeding soundness has been as important a ram selection index
as conformation and growth rate, satisfactory flock reproductive performance is
commonly achieved with a ratio of less than one ram to 100 mixed-aged
ewes. Ratios of more than one ram to 40
ewes are commonly employed in UK flocks to overcome the problem of between 3.5
and 10 percent of rams being unsound. Furthermore, the use of unsound rams generally reduces the lambing
performance of ewes and may result in a protracted lambing season. These problems may be compounded when an
unsound ram is the dominant animal in a group.
YOUR VET CAN CHECK YOUR RAMS FOR BREEDING SOUNDNESS
Ram breeding soundness is particularly important where groups of ewes
are single sire mated, or where a high ratio of rams to ewes is required
following synchronisation with intravaginal sponges.
Neil Sargison BA VetMB DSHP FRCVS