Precision of Simplified Milk Recording for Zaraibi Goats

A total of 6604 test-day records belonging to 1651 lactations of 784 Egyptian Zaraibi goats were used to generate and evaluate several simplified milk yield recording plans based on the yield of a single monthly milking, adjusted or unadjusted for interval between milkings and for production level. Loss of precision associated with simplified designs was evaluated by comparing estimated lactation yields with actual milk yield, where the two daily milkings were recorded at daily intervals, and with the official A4 milk recording (monthly records of the two daily milkings) as reference methods. Actual milk yield included two traits: total suckled and milked milk (TSMM), i.e., milk yield from kidding to the end of lactation (210 d milk yield) and total milked milk (TMM), i.e., post weaning milk yield for 120 d. Breeding values from reference and simplified methods were predicted and compared. Simplified monthly plans were used to estimate both TSMM and TMM. The loss of precision in estimating TSMM was much lower (3.3-6.0%) than that for TMM (12.3-18.3%). Due to the essentially long suckling period during which peak lactation occurred for Zaraibi goats (almost 43% of the lactation period and 60% of milk yield), TSMM is better than TMM as a basis to evaluate simplified designs of milk yield recording. Therefore, TSMM is recommended to be used in genetic evaluation and managerial decisions. Most options with one daily milking every month were more accurate when the corresponding plan was based on, or started with, the a.m. milking. In most cases accuracy of estimation got worse by adjusting for interval between milkings or for production level. The design alternating a.m. and p.m. milkings, started with the a.m. milking and adjusted to the preceding interval between milkings gave the most satisfactory results with a slight advantage in precession (≤ 2.6%) over other simplified methods. Product moment and rank correlations between breeding values predicted from actual and simplified designs were very high (0.972-0.997) indicating that any of the simplified methods can be used as a precise alternative to actual milk production for breeding decisions. For practical and economic reasons, the unadjusted alternating a.m. and p.m. milk recording, started with the a.m. milking is suggested for milk recording of Zaraibi goats.