Influence of dry period length on reproductive performance and productivity of Lacaune dairy sheep under an intensive management system

Intensive management is almost the only way to ensure dairy farm profitability. The dry period length (DPL) is a key factor in the productivity and health of dairy cows, but whether the same is true of dairy sheep is unclear. This study investigated the effects of DPL on the performance of Lacaune sheep under intensive management. We recorded 8136 lactations from 4220 ewes on one farm for the period 2005-2010, and data from a total of 6762 complete lactations 1-4 were included in the study. The length of the dry period following the current lactation was studied. The larger the total milk yield (MY) and daily milk yield (DMY), the shorter was the DPL before the next lactation. DPL correlated with MY (r=-0.384), DMY (r=-0.277) and the lambing-to-conception interval (LC; r=0.201, P<0.0001) in the global analysis of all lactations (lactations 1-4). The influence of previous-DPL (P-DPL), or the length of the period prior to the start of the next lactation, was studied for 4318 lactations. P-DPL was classified into five intervals: very short (P-DPL-XS), 1-30 d; short (P-DPL-S), 31-60 d; medium (P-DPL-M), 61-90 d; long (P-DPL-L), 91-120 d; and very long (P-DPL-XL), > 120 d. P-DPL positively correlated with lambing-to-next conception interval (LNC; r=0.095, P<0.0001) for lactations 1-4. LNC was significantly shorter for P-DPLs that were very short, short, or long (P-PDL-XS, 144.2 +/- 67.8 d; P-PDL-S, 149.1 +/- 57.2 d; P-PDL-L, 152.0 +/- 53.7 d) than for groups with very long or medium P-PDLs (P-DPL-XL, 161.5 +/- 62.9 d; P-DPL-M, 169.0 +/- 74.8 d; P<0.0001). Moreover, P-DPLs that were very short, long, or very long were associated with the lowest milk yields (P-PDL-XS, 377 +/- 215 l; P-PDL-l, 370 +/- 168 l; P-PDL-XL, 396 +/- 196 l). These yields were significantly lower than the yields for short and medium P-DPLs (P-DPL-S, 432 +/- 187 l; P-DPL-M, 436 +/- 191 l; P<0.0001) when averages of lactations 1-4 were analysed. These results indicate that lactations with larger MY are followed by a shorter dry period, and that a dry period of 30-90 d leads to larger yields in the next lactation. The best LNC was associated with the shortest Previous-DPL. Hence, 30-60 d should be the optimal dry period length for Lacaune sheep under intensive conditions.