Correctly entering BT and RT information
We know that whether an animal was born as a single or as a twin has a lasting impact on its performance for different traits. Similarly, being raised as a single or as a twin also has an impact.
For example, twin-born lambs tend to be smaller (on average) than single-born lambs. They also cut less wool that has a broader fibre diameter. This is not because they have poorer genes for growth, fleece weight or fibre diameter, but because they have had to share nutrition pre-birth. Their environment has not been (on average) as good as that experienced by single lambs.
Accounting for these differences by correctly recording Birth type (BT) and Rear type (RT) plays an important role in the calculation of reliable breeding values, especially early life traits such as BWT and WWT. Due to the importance of these traits, it is critical that if you are going to the effort of recording Birth types and Rear types, that it be recorded into your software system correctly. The following examples can be used as a guide to help you understand how to correctly record a birth and Rearing type.
A Ewe has 2 lambs born. Of these 2 lambs, Lamb 1 is dead at birth (DAB) and Lamb 2 is live.
Lamb 1, will have a Birth type that reflects the number at birth, in this case 2. As the Lamb was Dead at Birth, it should have a Rear Type of 0.
Therefore; BT=2, RT=0.
Lamb 2, was born as a twin, so is given a Birth type of 2. Provided it survives to weaning, it will then get a Rear type of 1, as it has had the same opportunities through rearing as a single lamb.
Therefore; BT=2, RT=1
2 different ewes lamb on the same day, Ewe 1 has twins at Birth (Lamb1 and Lamb 2), Ewe 2 has a single at Birth (Lamb 3). But Lamb 1 is left behind by Ewe 1, and Ewe 2 who lambed nearby, fosters Lamb 1.
In this situation, Lamb 1 and Lamb 2 both get a BT of 2. While Lamb 3 gets a BT of 1.
However, as Lamb 1 was fostered by Ewe 2, this lamb should have a RT of 2, as will Lamb 3 who has been reared as a twin with Lamb 1. An important process to do now is to make sure Lamb 2 is recorded as having a RT of 1, as it was raised by Ewe 1 as a single.
Lamb 1; BT=2, RT=2
Lamb 2; BT=2, RT=1
Lamb 3; BT=1, RT=2
What is of similar importance is to also ensure that Ewe 2 is now listed in your software program as the Foster Dam for Lamb 1. Recording this correctly will have a significant effect on maternal traits (such as MWWT) for both individual ewes and flow on effects will be seen in the Ewe’s pedigree and relatives. If you have a query about how to record a scenario that may be different to above, please contact Sheep Genetics and we will discuss the best practice for your situation. Contact your software provider if you are uncertain where you would record certain information such as a Lamb’s Foster Ewe.