While the 2014 crop of lambs are approaching weaning, if they are not already weaned, it is an opportune time to look toward the 2015 crop and how to maximise the lambing percentage.

One of the primary drivers of ewe reproductive performance is ewe nutrition. Ewes going to the ram should have a body condition score of between 3 and 3.5.

A rising plane of nutrition during the mating season and for three weeks afterwards will help increase ovulation rates among thinner ewes (body condition score between 2.5 and 3).

Ovulation rates will be reduced among over-conditioned ewe (score of 4 or more). Generally, ovulation rates are lower among hoggets than adult ewes.

Hoggets need to be more than 60% of their mature weights to achieve reasonable conception rates.

Parasite burdens, such as worms and fluke, have a negative impact on body condition score, and may need to be addressed to ensure optimal nutrition.

The presence of a ram can bring on oestrus (heats) behaviour in ewes.

This can be utilised by putting a vasectomised ram among ewes.

However, the ewes must have had no contact with any male sheep or goats in the previous three weeks. It is important the vasectomised rams used are sexually mature and have good libido.

The presence of such teaser rams synchronises oestrus in the ewes, therefore the ram to ewe ratio needs to be increased.

Similar to ewes, rams must be fit not fat to maximise their fertility. Generally, rams lose about half a condition score over the course of the mating season.

Typically, a ram to ewe ratio of one ram per 80 ewes is recommended in lowland flocks if mating is natural. The ratio needs to increase to 1 to 30 if ewes are synchronised with progesterone sponges.

Hoggets need more rams than mature ewes, and there needs to be a greater number of rams if mating is taking place outside the ewes’ natural mating season.

More rams will also be required if the terrain is steep. Rams need to be rotated after 17 days, or new rams introduced in case any of the rams are infertile.

Rams should be acquired eight weeks prior to the start of the mating season, to allow them to adapt to their new environment.

On arrival, they should be treated for worms, fluke and sheep scab, and given any vaccines used in the flock routinely.

Any condition which causes fever among the rams will cause infertility for up to eight weeks, which could have a profound effect on reproductive performance in the flock.

Therefore, the ram should be monitored for any signs of ill-health.

Particular attention should be paid to the feet, as lameness can have a significant effect on reproductive performance.

It is estimated that between 3.5% and 10% of breeding rams may be unsound, and this will have a negative impact on lambing percentage and may result in a protracted lambing season.

While the practice of pre-breeding soundness examinations for rams are quite common overseas, they are not widely used in Ireland.

*Damien Barrett is a veterinary research officer in Sligo Regional Veterinary Laboratory, one of six regional veterinary laboratories (RVLs). The RVLs carry out animal health surveillance within the Dept of Agriculture, Food and the Marine in association with veterinary practices.