A study of lactation as affected by heredity and environment.

摘要: 1. A review of the existing knowledge regarding inheritance milk yield indicated need for a more extensive investigation subject, particularly with reference to (i) various components lactation yield, and (ii) differentiation hereditary from environmental variations. 2. In present thesis an account is given such investigation, requisite data being obtained six prominent herds tuberculin tested pedigree Ayrshire cattle. The Official records all recorded cows in these were used as basis study, (i.e. was not limited published therefore selected data). available comprised total over 2,800 period records. portion curve studied between 15 days eight half months after calving production each record successive 30-day intervals this computed. 3. first step find satisfactory mathematical expression describe shape curve. After reviewing previous work, use exponential decided upon. As result preliminary however, it discovered that, although gave good fit. some lactations, fit extremely poor others. parabolic next tried found that most addition extra constant considerably improved work became clear individual curves satisfactorily, two constants required: linear (exponential), which measures average slope curve, parabolic, describes how on rate varies period. With lactations former term was, have preponderating influence graduating time-change view fact very high variability exhibited by term, latter included subsequent (except study effect time calving). 4. Because maximum fitted theoretical different observed maximum. It therefore, instead value measure any lactation. 5. special made factors are known quantitative available, namely month age. 6. Two methods adopted studying calving, one based lumped other confined intra-cow comparisons. results discussed text explanation offered Correction worked out persistency, yield. 7. age investigated corrected alternative again employed. selection allowed working correction also correlation cow at ages. bearing question predictability future performance cow, cow's genetic constitution, method standardisation indicated. 8. her earlier multiple regression. during immediately preceding be predicted gives nearly estimate probable lactations.