Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/25/2005
Publication Date: 11/17/2005
Citation: Rius, A.G., Connor, E.E., Capuco, A.V., Kendall, P.E., Auchtung, T.L., Dahl, G.E. 2005. Long day photoperiod that enhances puberty does not limit body growth in Holstein heifers. Journal of Dairy Science. 88:4356-4365. Interpretive Summary: Whereas puberty can occur at 7 months of age, heifers are not bred until a later time when appropriate body weight is attained. Rapid body weight accretion, however, is associated with reduced mammary growth because of excess fat and lower parenchymal tissue accretion. Long day photoperiod treatment is known to promote lean growth and therefore may overcome negative consequences when accelerating growth in heifers. However, long day photoperiod also accelerates puberty which may ultimately limit body scale. In the present work, prepubertal heifers exposed to long day photoperiod grew faster and reached puberty sooner relative to heifers exposed to short day photoperiod, yet accelerating growth by long day photoperiod treatment did not limit body scale. Therefore, long day photoperiod treatment is a possible approach to speed the entry of dairy heifers into production without sacrificing future milk yield.
Technical Abstract: As extended photoperiod accelerates puberty, it may limit mature body size and be detrimental to ultimate milk yield during lactation. We hypothesized that the potential negative effects of rapid growth and puberty through long day photoperiod (LDPP) exposure could be overcome with a greater supply of metabolizable protein in dairy heifers fed rumen undegradable protein (RUP). In an initial slaughter study, we compared deuterium oxide (D20) and chemical methods to assess body composition at 5 and 7 mo of age in heifers (n=20) exposed to LDPP or short day photoperiod (SDPP). Before slaughter, D20 dilution was used to estimate body composition and results were compared to actual values determined by chemical analysis. In 5 mo-old heifers, the correlation between the two methods was 0.86 for protein content, 0.85 for water content, and 0.76 for minerals; however, fat content values were not correlated (r = - 0.068). In 7 mo-old heifers, we were unable to accurately estimate body composition using the D20 method. A second study was conducted to determine if LDPP, which hastens puberty, could be combined with RUP to promote lean growth without limiting body stature in prepubertal heifers. Thirty-two weaned heifers were assigned to LDPP or SDPP and RUP or control diet in a 2 ' 2 factorial arrangement until the onset of puberty. Relative to SDPP, LDPP increased prolactin (PRL) secretion (P = 0.026) and promoted lean growth. Exposure to LDPP also enhanced body weight (BW; P = 0.02), withers height (WH; P = 0.009) and heart girth (HG; P = 0.005). Furthermore, RUP supplementation increased WH (P = 0.06) and HG (P = 0.005). There was a significant interaction between LDPP and RUP (P = 0.001) for hip height (HH). Moreover, LDPP hastened the onset of puberty (P = 0.01). In summary, D20 was a feasible method to estimate lean composition in heifers at younger ages, however it failed to accurately estimate body composition in heifers around puberty. LDPP hastened puberty and accelerated lean growth without limiting skeletal growth in dairy heifers.