Losses of precision associated with simplified designs of milk recording for dairy ewes

Simplified designs of milk yield recording based on the yield of a single monthly milking, adjusted or not for interval between milkings and for production level, were simulated and evaluated for 3173 ewe-test-day records belonging to 155 lactations of Churra dairy ewes. Losses of precision associated with simplified methods were evaluated by comparing estimated lactation yields with those observed both in a reference plan, where the two daily milkings were recorded at weekly intervals, and in the official A4 milk recording (monthly records of the two daily milkings). Estimates of lactation yields were less precise when the usual monthly designs were compared with a weekly sampling of both a.m. and p.m. milkings. The losses of precision were high at 9·4–36·2% including the A4 plan. The yield from only the milking period was more predictable than milk yield from the whole lactation (suckling and milking periods) and should consequently be adopted in dairy ewes. All options with one daily milking every month were more accurate when the corresponding plan was based on, or began with, the a.m. milking (loss of precision 14·9–15·8%). There was no evidence of improvement in sampling accuracy by adjusting for the preceding interval between milkings or production level. For practical and economic reasons, the design alternating a.m. and p.m. milkings every month, without adjustment, is suggested for ovine milk recording.