Accuracy of simplified sampling procedures for estimating milk composition in dairy ewes.

Simplified designs of milk-composition recording, based on information from a single monthly milking, adjusted or not for interval between milkings and for milk yield, were simulated and evaluated for 2553 ewe-test-day records belonging to 155 lactations of Churra dairy ewes. Accuracy of simplified methods was evaluated by comparing estimated trait values (fat, protein, casein and total solid yields) with those observed both in a reference plan, where the two daily milkings were recorded at weekly intervals (A1), and in the official A4 milk recording (monthly records of the two daily milkings). Trait yields per lactation were estimated and adjusted to the only milking period (days in milk 30-120). Estimates of milk component traits were less precise when monthly designs, including the A4 design, were compared with a weekly sampling of both a.m. and p.m. milkings, with fat yield being the most difficult trait to estimate. 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. Adjustment for the preceding interval between milkings or milk yield did not improve sampling accuracy. The design alternating a.m. and p.m. milkings every month, without adjustment, is suggested for recoding milk component traits in dairy ewes.

Effects of selective and complete dry therapy on prevalence of intramammary infection and on milk yield in the subsequent lactation in dairy ewes.

The study was carried out in a commercial flock on 286 Churra breed ewes (566 half-udders) assigned to three lots depending on the type of antibiotic dry therapy received in the lactation previous to the one studied. One-hundred-and-four ewes were given complete therapy in all udders, 103 received selective therapy of infected half-udders, and 79 received no therapy at all. Half-udders of all animals were sampled for bacteriological study at < or = 72 h (lambing), 60 d, 120 d, and 155 d (drying-off) post partum. Dry therapy, parity number, lactation stage and therapy x parity interaction contributed significantly to variation in intramammary infection prevalence. Antibiotic dry therapy had the most significant effect. Prevalence during the whole of the subsequent lactation was significantly lower in lots receiving complete (18.8%) and selective (15.6%) dry therapy than in the untreated control lot (48.3%). Coagulase-negative staphylococci and streptococci (in particular Streptococcus agalactiae) were the organisms most significantly affected by dry therapy. In untreated ewes, prevalence increased noticeably from the 2nd to the 6th and subsequent lactations, but no significant changes were observed in the treated lots. Milk yield in the dry treated lots was 6.9% higher that in the untreated one. It was concluded that complete and selective treatments of ewes at drying-off were efficient and comparable methods of reducing the intramammary infection prevalence, improving bacteriological quality of milk, and increasing milk yield.

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.