Suitability of simplified methods for monthly and twice-monthly milk recording, and new prediction factors for the alternate a.m./p.m. method in dairy ewes under a low-input production system

Abstract

Sicilo-Sarde dairy flock test-day data were analysed (1) to check predicting ability of ten milk recording procedures, based on information from a single monthly or bimonthly milking and (2) to look for the best pair of factors for predicting daily milk yield from either morning or afternoon milkings for the alternate testing method (AT). Prior to analyses, data were adjusted for variation factors with known significant effect. Number of test-day observations was 4755 from 458 lactations of 288 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 2-weekly intervals and in the official A4 milk recording (monthly recording of the two daily milkings). Ranking of simplified plans based on their accuracy was still the same under either monthly or twice-monthly frequency. Estimates of lactation yields showed more lack of precision when the usual monthly designs were compared with twice-monthly sampling of both a.m. and p.m. milkings. Losses of precision ranged from 5.1%, for the A4 plan, to 14.6%. Thus, milk production should be estimated from both mikings when their measurement is economically feasible. When only one milking is weighed, designs based on-or beginning with-the a.m. milking were more accurate. There was no evidence of improvement in sampling accuracy by adjustment for milking interval or production level. For practical and economic reasons, the design alternating a.m. and p.m. milkings, without adjustment, is suggested for ovine milk recording. In such a case, new factors for estimating daily production from the measured milking (1.7, 2.3) should be used rather than the factors currently in use (2, 2) because they improved the loss of precision by more than 13% in a monthly recording system.

Feasibility of using alternate control as a dairy control system in goats

“…Liu et al (2000) demonstrated that AM milking records are more reliable, and that less precise estimations are carried out with data from PM milkings. Othmane and Trabelsi (2007) obtained similar results in dairy ewes. Using seven statistical models, they determined daily milk production based on one of two daily milkings.…”

Impact of simplified methods of monthly and twice monthly milk recording on genetic parameter estimates and genetic evaluation in dairy ewes under a low input production system

“…The alternate methods had been reported to be the most efficient simplified milk recording designs to estimate milk yield and composition (Gabiña et al, 1986;Gonzalo et al, 2003;Othmane et al, 2006;Othmane and Trabelsi, 2007;Othmane et al, 2011); but there was no available information on the impact of their adoption on genetic parameters and animal genetic evaluation allowing them to be judged as milk recoding designs for genetic improvement programs. In our study, the genetic variance component estimation showed that the adjusted alternate methods seemed more accurate; they had the lowest residual variances which were the closest to that observed with the reference method in both monthly and bimonthly milk recording designs.…”

“…The rest of recorded flocks in the Sicilo-Sarde population are on the standard A 4 plan of testing, and all ewes are milked twice daily. Daily milk production level in the entire population ranges from 0.6 to 0.8 l (Othmane and Trabelsi, 2007).…”

“…However, costs of supervised recording of the two daily milkings are especially high in dairy ewes compared to other dairy species (Othmane and Trabelsi, 2007) and ovine milk recording simplification is still a necessity. For this very reason, several studies have been carried out on this topic (Gabiña et al, 1986;Barillet et al, 1987;Gonzalo et al, 2003;Othmane et al, 2006;Othmane and Trabelsi, 2007); evaluating and suggesting simplified milk recording designs, based on recording only one milking a day, with high phenotypic precision levels. In such cases, daily milk production has to be estimated from the available information on only the recorded milking.…”

“…Usual alternate a.m.-p.m. testing systems are in use in several countries as a simplified milk recording method for dairy ewes, where the same weight is accorded to a.m. and p.m. milkings when estimating daily milk production from one milking, by using the pair of factors (2, 2), respectively. Investigation after implementation of new factors for the alternate plan in use indicated that the adoption of the pair of factors (1.7, 2.3) may remove by more than 13% the lack of fit associated to old factors (Othmane and Trabelsi, 2007). On the other hand, accuracy of these alternate methods, as simplified milk recording designs, is usually evaluated using lactation data sets where variation in a.m.-p.m. milk production would be compensated from one test-day to another, provided the number of test-days is sufficient (Othmane et al, 2006).…”