A note on the effects of previous photoperiod exposure and gradual transitions of light intensity at dawn and dusk on growth in Holstein heifers

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Abstract
Long-day photoperiods of 16 h light (L) and 8 h dark (D) stimulate a proportional increase in live-weight (LW) gain of peripubertal Holstein heifers of 0·08 to 0·17 compared with heifers exposed to short days of less than 12 h L per day (Peters, Chapin, Leining and Tucker, 1978; Peters, Chapin, Emery and Tucker, 1980; Petitclerc, Chapin, Emery and Tucker, 1983; Zinn, Chapin and Tucker, 1986). One factor that could account for some of this variation in the magnitude of the growth response to long days is that the previous photoperiod exposure may influence the response to a subsequent different photoperiod (Moore-Ede, Sulzman and Fuller, 1982). For example, exposure to 13L: 11D induced pulsatile activity of serum luteinizing hormone (LH) in ewes previously exposed to 16L: 8D, but reduced serum LH to undetectable levels in sheep previously exposed to 8L: 16D (Robinson and Karsch, 1987). Thus, sheep exposed to identical photoperiods exhibited different responses depending on previous photoperiod exposure.