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Ram selection can really improve flock genetics

Fall is when sheep and goat farmers breed their flocks. This year we made sure we weren’t going to have lambs in February. We didn’t pick up our new ram until we were ready for him.

Before shopping for a new ram we spent time deciding what we wanted to improve in our flock. The key features our family would like to improve are:

  • Quality of fleece.
  • Parasite resistance.
  • Hardiness of ewes and lambs.

Clean fleece weight and fibre diametre are highly heritable traits in sheep, according to the Queensland government in Australia. The ram we have chosen is from a flock that values their wool production. It is exciting to learn that our management program can enhance his genetic potential and improve our fleece.

We started raising sheep to produce both wool and meat. Until now meat has been more of our focus, and we have made only some progress in improving wool quality. We love the fine texture and softness of our Rambouillet crosses and really wanted to improve this with our new ram.

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photo: Premier 1 livestock supplies

Characteristics with moderate heritability are staple strength, lean meat yield, eye muscle depth, fat depth, weight, and parasite resistance. The reproductive traits such as birth weight and number of lambs born/weaned are actually low in heritability.

Although the heritability is low we can still use genetics to improve our production. Research in both sheep and cattle has indicated that daughters from sires with a larger testicle circumference are more fertile than females sired by males with a smaller circumference. This makes the measuring of scrotal circumference an important part of a breeding soundness exam. When measuring scrotal circumference it is important that both testicles are fully descended. The measurement should be taken at the point of greatest circumference. Guidelines from the University of Illinois relative to age and testis size are as follows:

When measuring the circumference take note of attachment of the scrotum to the body. There is a high correlation between scrotum attachment and the attachment of their future daughters’ udders.

The repeatability of reproductive traits is considered 15 to 20 per cent heritable, which is why they are considered low in heritability. Therefore, improving reproduction by genetic selection takes many generations. The following guidelines can be used, hopefully to speed up success, when selecting replacement lambs:

  • Select replacements from multiple births that are born early in the lambing season.
  • Select from multiple births from young ewes.
  • Keep triplet ewe lambs. When they get into production they will usually have twins.
  • Select replacements from dams that have a high lifetime productivity in your environment.
  • Select replacements from ewes that are less seasonal in their breeding ability. Don’t keep replacements from rams that are infertile during hot weather.
  • Save ewe lambs from rams that have large, well developed, problem-free testicles.

Crossbreeding

Crossbreeding increases heterosis (hybrid vigour) more dramatically in traits such as reproduction which is low in heritability. Therefore, commercial sheep producers usually increase reproductive rate, milking ability, and lamb vigour by utilizing crossbred ewes. This is the other reason for us switching back to a Rambouillet ram. We have been breeding Suffolk for many years and are starting to lose the effect of hybrid vigour.

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photo: Premier 1 livestock supplies

Another consideration for increasing productivity of our ewes is earlier breeding. There is mounting evidence that ewe lambs that cycle/breed to lamb at or near their first birthday are more fertile in their lifetime. There are considerations though, such as size, before one can breed ewe lambs. This chart from Premier 1 Livestock Supplies is a handy reference tool. It is also a consideration that ewe lambs will need a higher amount of feed to grow themselves and fetuses so separate penning should be a consideration.

Increasing productivity without fine-tuning management skills will not result in increased profit. From our experience ewes with multiple lambs need a higher level of quality feed. The more lambs they are milking for, the more a ewe will eat. They also require more shelter space when storms come in. There is also the problem with triplets coming from ewes without enough milk to feed twins.

This is where very good lambing records and culling are important. Over the years we have had ewes that had singles in years when we have had drought and quadruplets in years of plenty. Thankfully these girls also were able to mother the quads. We did supplemental bottle-feed them but the ewe raised them. These are the ewes that make our work easier.

Then there has been the odd lamb that just doesn’t understand it has to eat off the ewe and would prefer to try and suck off of a tree or our knee caps. This happened one year and after two weeks of making him eat we gave up and let the ewe go to pasture. She tried but the lamb had other ideas. We don’t consider this the ewe’s fault, but we also don’t give a ewe that blatantly refuses a lamb a second chance. Lambing is much more enjoyable when a ewe can mother her own offspring.

We are anxiously awaiting the arrival of our new ram. It will be an interesting next couple of years to see if our planning actually turns out.

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