I'd always previously associated lambing season with the Easter period (late March and April), so I was surprised that it was happening so early (February) at the farm, but when I enquired, I discovered that they try and make lambing week coincide with the half term holiday, since the farm is open to the public. Other advantages of early-lambing include:
-higher availability of farm labourers in winter months
-meat can be sold in the Easter period, when lamb-prices tend to increase
due to demand
Sheep are seasonal breeders, so naturally they will mate in Autumn when
the photo period is shortest. The gestation period of a sheep is
generally around 150 days, so parturition (birth) takes place in spring to take
advantage of the abundance of grass and milder weather conditions which promote
survival. As day-length shortens, the pineal gland (located in the brain)
produces more of the hormone melatonin in response to the decreased exposure to
light, which triggers the release of the hormone GnRH and consequently FSH
(follicle stimulating hormone) and oestrogen, so oestrus occurs. As a side
note, the oestrus cycle (found in the majority of mammalian females) differs
from the menstrual cycle in that the endometrium (inner membrane of the uterus)
is reabsorbed if conception does not occur, rather than being shed.
During their fertile period, Ewes will come into oestrus around every 17
days, until they become pregnant, and the duration of oestrus is generally
24-36 hours. During oestrus, she will allow, and sometimes even encourage
through nuzzling, a ram to mount her.
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Top graph shows E2 (a form of oestrogen) levels
of a Ewe (and other short-day breeders) throughout the year
|
Rams are also affected by decreasing day-length, though to a lesser extent
than ewes. During winter, rams are more fertile, have greater sperm production
and produce fewer abnormal spermatozoa (sperm cells) than in summer. Rams have
receptors under their top lip, allowing them to detect a Ewe's hormonal
changes.
Different breeds exhibit these seasonal breeding patterns to various
extents (interestingly, it is thought that breeds which originate in areas
further from the equator are more likely to be strictly seasonal breeders),
which can be another factor in deciding whether to have an early or late
lambing season.
While there, I also learnt a bit about tupping season at the farm, which
had taken place in October. Each ram is fitted with a raddle; (a harness
with a coloured wax block attached to the chest), which marks each ewe during
mating. The wax block is replaced weekly with a darker coloured block, so that
the colour of the most recent mating will over-write any previous matings. Once
the ewe is pregnant, the ram will lose interest, so you can take the darkest
colour as the date of conception. This way you know which ewes are pregnant and
when their lambs are due. This is particularly important as there is limited
space in the lambing shed at Adam's farm and ewes are only brought inside when
they are within 3 weeks of their due date. It also helps allows you to alter
their diet during gestation to ensure healthy lambs.
The farm's commercial breeding stock consisted of a mixture of Lleyn and
Romney breeds, due to their easy-lambing and good maternal characteristics. At
Adam's farm, ewes are ultrasounded around 3 weeks before their expected
delivery date and marked according to the expected size of their litter, before
being sorted accordingly. Twins are the most common, though first-time mothers
are more likely to have single lambs and sheep tend to give birth to their
largest litters between the ages of 3 and 6. Generally, smaller lambs will be
found in bigger litters. In the case of litters having 3 or more lambs, lambs
will often be coated in the amniotic fluid of another ewe who only has one
lamb, to convince her to foster the extra lamb and provide it with milk.
Lambs are born in a group pen to allow more space and an average labour
lasts for around 30 minutes. If a labour is taking much longer than this,
intervention may be required. After birth, lambs are taken into separate pens
to give them the opportunity to bond with their mothers. Once bonded, they move
into the nursery pen before being finally turned out in a field, as long as the
weather's decent enough.
So it turned out to be a pretty fun and educational day out. Rescuing a
panicking goat which had got its head stuck in the fence was a definite
highlight for me!
