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Abstract Milk production reccrds of the Friesian herd, located at Sakha Expe]C-:.i.>~:.talStation, Animal Production Research Ins~itute, Ministry of Agricu1- ture were used. These records included data tor imported cowa from the Netherlands between 1960 and 1961, in addition to ’:~heir descendents up till 1979. First and second l~~tation records (1794 and 1389 records, respectively) oGtained through the period from 1l)bU to 11)7Y Wl\8 une u to inveat1gate the nongenetic factors that 1.r..1: __..•e• nced 305-day mUle production and to evaluate phenot;:;i-c, envirDDDl8ntal aDd genetic trends of change in -:’~ .’_ ;:05-day milk yield. The least squares procedures were :ollowed •. Results obtained are sl,..;::.r.;;,eriZed as fol101J8: Non-genetic factors: ’lhe overall mean 29.67 months. It ShOWf the age at first calving was on-signi:ficant effect on 305-day milk yield. Autumncalvers recorded the highest milk prod..u.c’tion compared with calvers of the other seasons of the yea:r. The differences due to season of oalving in 305-day milk yield were non-significant. Year or calving c:”:’;itituted U considerable highly significant (P 0.01) source of variation in 305-day milk product i”’ll of either the III or the 2-nd lactations. Trends of change: ~oDltive phenotypic change was observed in )05-d~ milk yield of both tbe III and 2nd lactations. The average annual phenotypic change ranged between 22.C17 and 44.05 Kg. Bnvironmental change in J05-day milk yield of either the 1-st or the 2.-rU laotation was indioated to - ~4 be positive. The averu.L. amount of this change, obtained by the 2 methods used, ranged between 45.09 and 65.75 Kg per year. Genetic change in the 305-day milk yield of the 1ll and 2Ee, lactatiorj.~ was found to have a negatiTe diroct ion. The overage annual genetlo ohange, oaloulated by the three methods of analysis used, ranged between _ 1.03 and _ 36.17Kg. The average genetic change per generation ranged betw$en - 31.25 and - 49.68 Kg. |