Effects of dry period length and dietary energy source on lactation curve characteristics over 2 subsequent lactations

This study evaluated the effects of dry period (DP) length and dietary energy source on lactation curve characteristics over 2 subsequent lactations. It also evaluated the relationships of energy balance or metabolic status in early lactation with lactation curve characteristics in dairy cows. Holstein-Friesian dairy cows (n = 167) were assigned randomly to 1 of 3 DP lengths (0-, 30-, or 60-d) and 1 of 2 early-lactation diets (glucogenic or lipogenic) for 2 subsequent lactations. In the second lactation following DP length treatments, 19 cows in the 0-d DP group were assigned to a 0→67-d DP group (actual days dry: 67 ± 8 d). Cows were allocated to this new group when they had a milk yield of 2 cows, total FPCM yield and average daily FPCM yield throughout 2 lactations did not differ among DP lengths. In addition, average energy balance in the first 4 wk after calving had a negative relationship with peak yield and FPCM305, and a positive relationship with lactation persistency. Average plasma concentrations of free fatty acids and β-hydroxybutyrate had a positive relationship with peak yield and FPCM305, and a negative relationship with lactation persistency. Shortening or omitting the DP affected lactation curve characteristics in both lactations after implementation of DP length treatments but did not compromise FPCM yield compared with a conventional DP of 60 d in parity >2 cows. Severe negative energy balance and poor metabolic status were related to greater peak yield, FPCM305, and lower lactation persistency.