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Data on 218 lactations of 127 Tharparkar cowl at the Govern-ment Livestock Farm, Raktt. Ghia!amen, District 1Bhakkar, were analyaed f or the influence of gelison and oomelLetation parameters on Forge, tenoy of lactation, Milk yield. averaged 1138 5+26-.8 kg with mean lactation period of 220,4 ± 3.2 days, Average- peak yield per roon.th and mean initial yield for fink 80 days were 235,6 ±-4.8 kg and 431,15 ± k8, respectively. The persistency of lactation averaged 66.2 2: 0,9 per cent and was not significantly affected by the season of calving. The correlation co-efficients between persistency and three other variables., namely, peak yield, irhitial yield 11,1341 ]notation length were 0,108, 0.121, and 0.824, respectively. Multiple corre• ration for the combined effects of the three variables was 0.820. The teat of significance of multiple correlation indicated. that, of three variables, the lactation length.after fitting peak yield and. initial yield, was the factor affecting persistency signi6.cantly.. The multiple regression equation co predict peraisteney (Y) from peak yield {Xi), initial yield (X2) and length of lactation (X3) W1116 y = 16.0795 _ 0.0s25 Xi 0.0219 X2 + 0.2239 X3 The standard partial regreission indicated that lactation lngth.
wag 4.157 and 3.6S times more important in influencing the perbiAtency than peak yield and initial yield, resPeetivelY. IN TRODUCTION Milk production in a particular lactation depends to a great extent upon *Department of Animal Brer.ding & Genetics, University of Agriculture, Faisalabad,.
Abdul Ghaffar, M, D. Ahmad. (1984) Studies on the persistency of lactation in Tharparkar cows, Pakistan Journal of Agricultural Sciences, Volume 21, Issue 3,4.
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