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

Abstract

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.

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

“…Research on this topic has examined various milk recording plans based on recording only one milking a day, their evaluation being usually carried out on the basis of twice-a-day monthly measures and under an intensive production system (three lambing times in 2 years). There are few reported studies using more informative data sets (with reduced recording intervals), as a more accurate comparative basis for milk yield (Gonzalo et al 2003) or milk composition (Othmane et al 2006a). Both studies reported high errors when comparing yields from simplified monthly plans with yield based on records collected weekly (A1).…”

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.…”

“…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). This is not the case with test-day data sets that override the use of lactation data sets in many genetic improvement programmes in ewes.…”

“…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.…”

contrôle de croissance des ovins allaitants en Tunisie. ii. Perte de précision sur le calcul des performances à âge type selon un protocole simplifié alternatif au protocole officiel

“…Pour alléger les charges, de nombreux travaux de recherche ont envisagé de simpli fier les protocoles de contrôle laitier (1,6,8,11) et de croissance (2, 13) des ovins. En Tunisie, le contrôle de croissance des ovins allaitants nécessite au moins cinq à six visites d'un technicien à 21 jours d'intervalle, ce qui est très onéreux.…”