Submitted to: Joint Abstracts of the American Dairy Science and Society of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: March 18, 2004
Publication Date: July 29, 2004
Citation: Meyer, M.J., Capuco, A.V., Van Amburgh, M.E. 2004. Effects of energy intake and time to puberty on mammary growth of prepubertal Holstein heifers [abstract]. ADSA/ASAS/PAS Joint Meeting, St. Louis, MO, p. 47.
In the bovine, early postnatal mammary growth is thought to occur at an allometric rate and return to an isometric rate after puberty. Elevated energy intake prior to puberty has been shown to retard mammary parenchymal (PAR) DNA content at puberty, however, a causative relationship between PAR DNA at puberty and future milk yield has yet to be substantiated. Our objectives were to describe effects of increased energy intake from shortly after birth on 1) total PAR and fat pad (FP) DNA, 2) PAR DNA accretion rates, and 3) timing of the prepubertal allometric growth phase. Holstein heifers (n = 78) were fed from 45 kg either elevated (E) or restricted (R) levels of energy to achieve divergent rates of gain (E 950 g/d; R 650 g/d). Six heifers per treatment (TRT) were slaughtered at 50kg increments from 100 to 350kg. Six were slaughtered at birth, at which time PAR was difficult to discern and present as a small cord of tissue. FP weights were similar between TRT up to 200kg but were heavier from 250 through 350kg in E-heifers (P < 0.05). However, FP DNA content was similar between TRT until 350kg, at which point FP DNA was greater in E- than R-heifers (P < 0.05). PAR DNA was similar between TRT up to 200kg. From 250 through 350kg, R- had more PAR DNA than E-heifers (P < 0.05). Interestingly, daily PAR DNA accretion rates, calculated between consecutive slaughter points, were not influenced by energy intake (P = 0.98). This rate reached a peak of 5.4 mg PAR DNA per day between 200 and 250kg and declined precipitously during the peripubescent period. A plot of the log BW vs. log PAR DNA indicates that mammary growth rate, independent of TRT, was allometric by 100kg BW and became isometric shortly before puberty (puberty occurred at 280kg independent of TRT). These data demonstrate that reductions in mammary PAR DNA associated with elevated rates of gain result from reduction in time to puberty rather than impairment of epithelial cell proliferation and PAR DNA accretion.