Estimation of daily milk yield from alternative milk recording schemes in dairy sheep
The objectives of this study were to develop and compare different models for estimation of daily milk yield from alternative milk recording scheme (single morning and evening milking records). In this study, 3.000 individual test-day milk yield records from Central data base of Agricultural institute of Slovenia were used. Data were collected from April 1999 to September 2002 on 565 sheep reared on 10 family farms in Slovenia. Daily milk yield as well as daily fat and protein content were estimated by several statistical models. Determination coefficients of models for estimation of daily milk yield as well as daily protein were slightly lower when estimation was based on evening milkings, while the determination coefficients of models were slightly higher when daily fat content was estimated from evening milking. With the complexity of the models the amount of explained variance increases and the bias between true and estimated daily yields decreases. Inclusion of other effects in models, beside single milking weights, like effects of breed, lactation stage and number of liveborns, did not significantly increase the amount of explained variance, so the differences between models used for estimation were minor and statistically insignificant, therefore we would recommend use of model A in practice. That model included only partial milk yield as linear regression so, because of its simplicity, the implementation in routine work is simple. Because in present research the information of the interval between successive milkings, which is the most important effect in estimation of daily yields, was not available there is a need for further investigation in which we would be able to take that effect into account.