Inbreeding in Sheep and Goats: How Pedigree Records Prevent It

Inbreeding means mating related animals: a ram with his daughters, sisters or granddaughters. Over time it lowers fertility and lambing rate, slows growth, raises losses and brings out genetic defects. To prevent it, record the dam and sire of every animal, change the ram before his daughters reach breeding age, and buy rams from unrelated flocks.

In small and medium flocks inbreeding usually happens by accident. One ram stays for years and his daughters grow up and are mated to him, or the ram's son is kept to replace him and serves his own sisters. Because the effect builds slowly, the farmer sees the flock weakening without knowing why. The fix is not complicated, but it depends on one thing: knowing who the mother and father of each animal are.

Why inbreeding causes harm

Every animal carries two copies of each gene, one from its dam and one from its sire. Many harmful traits are recessive: they only show when the animal inherits the harmful copy from both parents. Relatives share more of the same genes, so the chance that a lamb gets two harmful copies goes up.

The result is called inbreeding depression. Common signs include:

• Lower fertility, repeat cycles and fewer twins.
• Weaker newborns and higher losses in the first days.
• Slower growth and lighter weaning weights.
• Birth defects such as jaw, limb or testicle abnormalities, although these can have other causes too.
• Weaker immunity and recurring health problems.

How close is too close?

Specialists measure relatedness with the inbreeding coefficient: the expected share of genes a lamb inherits identically from both sides. These are standard calculated values for common matings:

For a commercial flock the simple rule is: never mate an animal with its parent, sibling, offspring or grand-offspring. Deliberate line-breeding to fix a trait is work for specialist stud breeders, not for a production flock.

Practical rules to avoid inbreeding

1. Change the ram on time. A ram's daughters reach breeding age in roughly one to one and a half years in sheep and goats. Either replace the ram before then, or separate his daughters and mate them to another ram.
2. Do not keep the ram's son to serve his sisters. If you like your ram's son, use him on a different group that does not include his sisters.
3. Buy rams from unrelated flocks. A ram from a neighbour who originally bought stock from the same source as you may be related to your flock. For selection criteria see how to choose a breeding ram.
4. Use more than one ram in larger flocks and assign females to defined mating groups, so you know the sire of every lamb.
5. Swap rams with trusted breeders once their health is checked, with quarantine before they join.
6. Watch shared grazing. On communal range, other flocks' rams may serve your ewes, or yours theirs, and sire information is lost.

Pedigree records: the only tool that reveals relatedness

Nobody remembers the pedigree of two hundred head over five generations, and relatedness cannot be seen: two half-sisters may look nothing alike. Records are the foundation:

• A fixed identity for every animal: a number and tag colour that never repeat. See livestock numbering and ear tag colours.
• Record dam and sire at birth, not weeks later.
• Record the mating group and ram for each female, so the sire is known even if you did not see the mating.
• Review relationships before every mating season: who are each ram's daughters and granddaughters?

In Throf every animal's card holds its dam and sire, and mating is recorded with the ram and date. From a ram's card you can see his sons and daughters; from a ewe's card you can see her ancestry. When you set up mating groups, you move the ram's daughters into a separate group served by another ram. Older records can be imported from Excel, so you start with what you already have rather than from zero.

If you already see signs of inbreeding

• Start recording now, even if older records are incomplete; the next generation is what counts.
• Bring in a ram from a distant source with no relationship to your flock.
• Remove animals with birth defects from breeding, and their parents if defects repeat in their offspring, after your vet has ruled out other causes.
• Track the indicators: conception rate, twinning rate, losses and weaning weight before and after the change.