reproduction

• in female sheep, puberty occurs between 6 months and a year old. Ewe lambs born early in the season will hit puberty earlier, those born late will mature the following year
• Ewes are approximately 60% of their mature weight at puberty
• sheep are seasonally polyoestrus. Their cycle length is 16-18 days (follicular 3-4 days, luteal 13 days) Ovulation occurs shortly before the end of oestrus
• in sheep, the first post-partum oestrus is the following season. the first ovulation is silent with no progesterone priming in the behaviour centres
• the sheep breeding season begins when days get shorter. decreasing daylight causes the pineal gland to release more melatonin which reduces negative feedback of oestrogen. peak fertility is October to November
• the duration of the sheep breeding season varies by type:

  • hill sheep - 2-4 months
  • down breeds - 5-6 months
  • dorset horns can breed 8 months of the year
• in sheep, oestrus lasts 36 hours.

  Anatomical signs: vulval hypertrophy / hyperaemia with clear mucus discharge

  Behavioural signs: tup seeking, tail wagging, standing for tup, reduced food intake
• oestrus ewes will seek a tup and vice versa. coitus is short but a ewe may be served several times
• sheep gestation is 145 to 152 days depending on breed, parity and litter size. The placenta takes over progesterone production from the CL from day 56.
• in sheep, real time ultrasound can establish if pregnant from 45 days and foetal numbers from 80 days.
• a raddled vasectomised tup can be sent to run with ewes after mating to identify late returns
• the lambing % equation is: lambs weaned / 100 ewes put out to tup

  Another measure of reproductive performance is duration of lambing for the flock. Causes of low lambing % include high barren rate, low litter numbers, abortion and high perinatal lamb mortality
• ovulation can be controlled through:

  • body condition scoring and flushing (nutritional management)
  • PMSG (synthetic follicle developing hormone)
  • FSH
• the most popular tup breeds are texel and suffolk
• Tup puberty occurs at 6 months old and can breed out of season. Typically 10% of tups are identified as infertile and 30% as subfertile
• Why might a subfertile or infertile tup reduce ewe fertilisation rates even in a multi-sire group with fertile tups?

  Tups demonstrate dominance behaviour and may reduce ability for fertile tups to sire
• the ideal ewe/tup ratio is 1-2 per 100 however on lowland farms this is often 3 per hundred, 1 per hundred in hill farms and 1 per 20-30 for tup lambs
• Goats kept for dairy will have kids every second year and lactate for approximately 22 months. Goats kept for meat will be bred annually with a 200% kidding target
• in goats, puberty occurs at 6-8 months old. Spring born females will show oestrus in autumn of the same year. Pygmy goats may show oestrus from 3 months old
• Goats are seasonally polyoestrus and have 8-10 cycles per season (August to March). Oestrus onset is triggered by decreasing daylight, presence of buck and is influenced by nutrition
• Dairy goat cycle length is 19-21 days
• pygmy goat cycle length is 18-24 days
• goat oestrus lasts 1-2 days (up to 5), with ovulation 12-36 hours after onset
• Goat's first post-partum oestrus is after at least 3 months but often in the following autumn
• Signs of oestrus in goats: (increased by presence of buck)

  • Anatomical: vulval swelling and hyperaemia, clear discharge which thickens and greys towards the end of oestrus
  • Behavioural: cleating, dominant behaviour between does (and even towards humans) and upturned tail. Does will seek out and urinate near bucks. Reduced food intake and short pre-oestrus milk yield increase
• detection of pregnancy in goats:

  -Real time ultrasound: must see a foetus and placentomes. In a pseudopregnancy only fluid will be present.

  -Milk or blood oestrone sulphate: possible from 50 days gestation.

  -Observation: possible from 18-21 days but cannot differentiate true and pseudopregnancy
• Goat gestation is 145-154 days (150), usually yielding twins or triplets. milk yield falls from 8 weeks post-service. A doe will be dry for the last 5/6 weeks of pregnancy. Can induce using progesterone from 144 days
• pseudopregnancy in goats occurs in unmated does or following resorption. There is a persistent CL and anoestrus with a closed cervix. The endometrial glands secrete fluid and the uterus distends. Eventually the distension leads to PGF2a release, luteal tissues regress and the fluid contents are expelled. It is a recurring problem in some individual, particularly high-yielding dairy goats
• hermaphroditism and pseudo-hermaphroditism is common in goats. It is a recessive linked gene to a dominant polled gene so one parent is usually horned to reduce risk.
• Buck puberty occurs at 5-6 months old, but well-grown bucks may be used sparingly until their second year
• controlled breeding in sheep and goats can be achieved by advancing the breeding season through:

  • artificial light subjection for increased darkness hours
  • ram effect: introducing rams again after 4-6 weeks apart (often vasectomised teaser then fertiles after)
  • melatonin implants
  • progesterone sponges to synchronise flock, acts like CL and when removed stimulates follicular development
• when using artificial insemination is goats and sheep, they should be synchronised with sponges or PMSG, fresh semen cervically, can use frozen intra-uterine
• lambs are viable from 135 days gestation
• cows are non-seasonal polyoestrus. They achieve puberty at 7-12 months old, with a first-calving target usually at 2 years old
• A heifer's onset of cyclicity is linked to weight not age. Ideally, a heifer should be at 65% her mature weight by 15 months for her first pregnancy
• Cow cycle length is 21 days. pro-oestrus 3-4 days, oestrus 18 hours, metoestrus 3-4 days, dioestrus 10-14 days
• In cows, there are 2-3 waves of follicular development per cycle(typically 2 for high-yielding dairy cows, 3 for beef cows and heifers)
• cow ovulation occurs 30 hours after the onset of oestrus
• In cows, the main sign of oestrus is standing to be mounted. (cows in pre-oestrus will mount cows in oestrus) Other signs include ruffled tail head, clear mucus vaginal discharge, swollen vulva, restlessness, reduced feed intake and milk yield
• cows in metoestus will have bloody vaginal discharge