EFFECT OF PLANE OF NUTRITION BEFORE AND AFTER 200 KILOGRAMS OF BODY-WEIGHT ON MAMMARY DEVELOPMENT OF PREPUBERTAL HOLSTEIN HEIFERS

Twenty Holstein heifer calves at 138 d of age and 118 kg of BW were as signed randomly to one of four treatments in a factorial design. Heife rs were fed for low (0.7 kg/d) or high (>1.0 kg/d) gain during two per iods. Period 1 was from start to 200 kg of BW, and period 2 was from 2 00 kg of BW to slaughter, which occurred in the middle of the luteal p hase following the third estrus. Calves on the high plane of nutrition during period 2 were heavier at the end of trial and gained more BW b etween puberty and the end of trial. Those calves also had heavier mam mary glands, which had more fat and dry fat-free tissue. Heifers that had been raised on the low plane of nutrition throughout the trial had greater concentrations of DNA and RNA but did not have greater protei n in the dry fat-free tissue. Low plane of nutrition during either per iod increased DNA and RNA concentration in the dry fat-free tissue. To tal mass of DNA and RNA did not differ among treatments. Protein mass was increased by the high plane of nutrition during period 2. This stu dy indicated that dietary manipulation affects mammary dry fat-free ti ssue, protein, and adipose mass in the period up to and including pube rty.