Advancing the breeding season and increasing production in early lambing flocks

Date published: 1 July 2020

Obtaining a good lamb price is often associated with early lambing flocks. However achieving a good lambing percentage to drive high ewe output is perhaps more challenging without well planned use of a hormonal intervention programme. Achieving a compact lambing period is also key to reducing labour costs and having lambs ready for market at the target time.

Two of the key targets for an early lambing flock are:

• Litter size of 1.65 lambs reared per ewe
• 90 % of lambs sold within 16 weeks of age.

Sheep are seasonal breeders and begin to come into heat or oestrus as daylight hours decrease. While some specific lowland breeds will mate early in the year, most lowland breeds and cross bred ewes within the Northern Ireland flock need veterinary intervention to aid them to lamb early in the season and improve their prolificacy.

There are a number of different programmes that can be used to help ewes come into season early and produce a good crop of lambs. Two of the most common programmes are progestogen impregnated sponges with PMSG and secondly melatonin implants.

Sheep sponges and PMSG

Using progestogen impregnated sponges as part of the breeding programme allows a group of ewes to be mated as a batch on one day, and the use of a hormone injection PMSG will increase ovulation rates and in turn improve litter size.

The main benefits of sponging and PMSG to the early lambing flock are:

• Improvement in litter size;
• Compact lambing – ewes that hold to 1^st service will typically lamb within a 4-5 day period;
• Repeats - ewes mated to second or subsequent oestrus will lamb from 15 days onwards;
• Advances the breeding season around 6 weeks ahead of normal mating time.

A typical programme for synchronising ewes is suggested below in Table 1:

Table 1. Synchronisation programme for early lambing ewes.

Important points to note to improve performance include:

• Ewes should be weaned for at least 6 weeks before the start of the breeding programme.
• Ewes targeted for sponging should be body score 3.5-4.0
• Use 3 rams together per 20 ewes - have plenty of rams available.
• Ram lambs are not always recommended.
• Rams must be fit, active and ready for work.
• Order the sponges and PMSG well in advance from your Veterinary Surgeon and store the PMSG in the fridge, according to manufacturer’s instructions.
• Read the instructions carefully on the use of all the products used in the programme.
• PMSG is administered into the muscle and the amount given is breed and month dependant. Typical rates for an early lambing flock would be 500-700 international units (i.u.) per ewe.

Melatonin implant

This is a hormone administered at the base of the ear around 35 days prior to ram introduction to the flock. It works by releasing a small amount of melatonin into the ewe similar to what the ewe produces naturally as daylight hours decrease. It therefore has the ability to make the ewes come into season earlier in the year and produce a lambing percentage similar to a March lambing flock.

Table 2. Melatonin implant programme.

Brian Hanthorn concluded: “Lamb prices this spring have been encouraging, but it is still very important for early lambing flocks to produce at least 1.65 lambs per ewe. Either sheep sponging /PMSG or Melatonin implants are very useful programmes for early lambing flocks to bring forward the lambing season, make it more compact, and achieve their targets to improve output and profit.

“You should consult your veterinary surgeon about which programme is most suitable for your farm and your sheep, and follow veterinary advice at all times.”