Six defective calves and a bull with poor daughters

Reading the evidence

• Six affected calves from one bull, with two defects of the same developmental field (fused digits, cleft palate), make the bull the one common factor.
• A carrier's dam looks normal, so the normality of the bull's dam and half-sib sister proves nothing: a recessive carrier's dam need only carry one copy herself, and half her offspring by an unrelated sire are non-carriers anyway.

Candidate models

1. Autosomal recessive with the bull heterozygous and all six dams also carriers. This is unlikely if the dams are genuinely unrelated, because the allele frequency in the population would have to be high.
2. Autosomal recessive in a closed herd, where the dams are in fact related to the bull (the herd retained 9 of his sons, so mating back is likely).
3. A dominant mutation with germline mosaicism or incomplete penetrance; rarer, but it fits ‘unrelated’ dams.

The first thing to check is not another test but the dams' pedigrees. If any dam traces to the bull's sire, model 2 explains everything and needs no further proof.

What follows

• If he is a carrier, about 50% of his 22 daughters and 9 sons carry the allele, so the sons must not be used.
• A test cross needs a mate that can reveal the allele. Mating him to non-carrier females gives only normal calves and proves nothing. Mated to known carrier dams, one quarter of calves are affected, so about 11 calvings give 95% confidence that he is not a carrier. Mated to his own daughters (each 50% carrier), the risk per calving is 1/2 × 1/4 = 1/8, so about 23 calvings are needed.
• Cheapest and fastest: a DNA test on the bull if one exists for syndactyly in Murrah, or the pedigree check. Test mating takes two years.

Judgement Stop using the bull now; the cost of a replacement is trivial against six dead calves and a herd full of carriers.

Reliability first 22 daughters is workable but not large; a bull's proof firms up towards 30-50 daughters. More important, the comparison must be with contemporaries - daughters of other bulls calved in the same season under the same feeding - not with a herd average that includes the best older cows kept and the worst culled. The herd-mate comparison should be demanded before the numbers are believed.

What the numbers say

• Daughters at 4.1 kg FCM against a herd average of 5.6 kg is a deviation of about -1.5 kg. A sire's transmitting ability is roughly twice the daughter deviation from herd-mates, so his predicted transmitting ability is around -3 kg. He is a negative transmitter, and with 22 daughters the chance that this is pure luck is small.
• First calving at 38-42 months against a normal Murrah target of about 30-34 months says the daughters are also late maturing. Both milk and age at first calving are lowly heritable (h² around 0.25-0.30), which is exactly why a progeny test is needed: single records cannot tell you this, 22 daughters can.
• The AI bull offered has 8 daughters averaging 6.2 kg; that is a better figure but a much weaker proof, so it should be treated as promising rather than proven.

The teat abnormality One daughter with a chronic teat defect is not evidence on its own; a single case can be injury, mastitis or a badly shaped quarter. It becomes relevant only if more daughters show the same defect or if the defect is a known inherited trait in his pedigree.

Verdict The bull carries a lethal allele and transmits below-average milk and late maturity. Cull him from breeding, do not retain the sons, keep the daughters as milk animals, and screen their heifer calves before retention.

Cost of the AI option At 42% conception, each pregnancy takes about 1 ÷ 0.42 ≈ 2.4 doses, i.e. roughly ₹840 per conception plus inseminator charges. For 60 buffaloes calving once in about 15-18 months this is affordable, and the genetic gain, once fixed in the herd, is permanent.

Cost of a bull A breeding bull costs feed and labour every day of the year, serves only about 30-40 females in a season, and his faults are discovered only after three seasons of calves - exactly the situation now. With 60 females and one sire the effective population size is very small (roughly 4), so inbreeding and the chance that a recessive defect becomes fixed rise every generation.

Recommendation

1. Stop using the present bull; do not retain his sons. Keep his daughters for milk, but mate them only to a bull known clear of the defect.
2. Use AI with the unrelated progeny-tested bull for the next two to three generations, keeping a register so no female is mated to a bull related to her sire.
3. Alternate at least two AI bulls to keep the population wide, and record conception rate, calving difficulty and 305-day milk so that the next choice is made on data, not on a single advertisement.
4. Keep one young bull only as a standby if AI logistics fail, and progeny-test him on 15-20 first-calvers before wide use.
5. Consider a DNA test on retained heifer calves if the defect has a known marker; if not, avoid mating any female to a bull with affected calves in his pedigree.

Decision rule Choose AI unless conception falls below about 30% or the herd is more than 15 km from an inseminator. At 42% AI is still far cheaper than the loss from a defective bull, and the six dead calves are the evidence.