Kok A, van Middelaar C E, Engel B, van Knegsel A T M, Hogeveen H, Kemp B, de Boer I J M
Animal Production Systems group, Wageningen University, PO Box 338, 6700 AH Wageningen, the Netherlands; Adaptation Physiology group, Wageningen University, PO Box 338, 6700 AH Wageningen, the Netherlands.
Animal Production Systems group, Wageningen University, PO Box 338, 6700 AH Wageningen, the Netherlands.
J Dairy Sci. 2016 Apr;99(4):2956-2966. doi: 10.3168/jds.2015-10559. Epub 2016 Feb 3.
To compare milk yields between cows or management strategies, lactations are traditionally standardized to 305-d yields. The 305-d yield, however, gives no insight into the combined effect of additional milk yield before calving, decreased milk yield after calving, and a possible shorter calving interval in the case of a shortened dry period. We aimed to develop a measure that would enable the comparison of milk yield between cows with different dry period (DP) lengths. We assessed the importance of accounting for additional milk yield before calving and for differences in calving interval. The 305-d yield was compared with a 365-d yield, which included additional milk yield in the 60 d before calving. Next, an effective lactation yield was computed, defined as the daily yield from 60d before calving to 60 d before the next calving, to account for additional milk yield before calving and for differences in calving interval. Test-day records and drying-off dates of 15 commercial farms were used to compute the 305-d, 365-d, and effective lactation yields for individual cows. We analyzed 817 second-parity lactations preceded by no DP, a short DP (20 to 40 d), or a conventional DP (49 to 90 d). Compared with cows with a conventional DP, the 305-d yield of cows with no DP was 7.0 kg of fat- and protein-corrected milk (FPCM) per day lower, and the 305-d yield of cows with a short DP was 2.3 kg of FPCM per day lower. Including additional milk yield before calving in the 365-d yield reduced this difference to 3.4 kg of FPCM per cow per day for cows with no DP and to 0.9 kg of FPCM per cow per day for cows with a short DP. Compared with cows with a conventional DP, median days open were reduced by 25d for cows with no DP and by 18d for cows with a short DP. Accounting for these differences in calving interval in the effective lactation yield further decreased yield reductions for cows with no DP or a short DP by 0.3 kg of FPCM per cow per day. At the herd level, estimated 365-d yield losses for cows with no DP or a short DP differed from effective lactation yield losses by 0.4 to -0.8 kg FPCM per cow per day. Accounting for additional milk yield before calving had a major and consistent effect on yield comparisons of cows with different DP lengths. The effect of correcting for calving interval was more variable between farms and will especially be important when calving interval is affected by DP length.
为了比较不同奶牛或管理策略之间的产奶量，传统上会将泌乳期标准化为305天的产奶量。然而，305天的产奶量无法反映产犊前额外产奶量、产犊后产奶量下降以及干奶期缩短时可能出现的较短产犊间隔的综合影响。我们旨在开发一种方法，以便能够比较不同干奶期（DP）长度的奶牛之间的产奶量。我们评估了考虑产犊前额外产奶量和产犊间隔差异的重要性。将305天的产奶量与365天的产奶量进行比较，365天的产奶量包括产犊前60天的额外产奶量。接下来，计算有效泌乳期产奶量，定义为从产犊前60天到下次产犊前60天的日产量，以考虑产犊前的额外产奶量和产犊间隔的差异。利用15个商业农场的测定日记录和干奶日期来计算每头奶牛的305天、365天和有效泌乳期产奶量。我们分析了817例二胎泌乳期，其之前的干奶期分别为无干奶期、短干奶期（20至40天）或常规干奶期（49至90天）。与具有常规干奶期的奶牛相比，无干奶期奶牛的305天产奶量每天低7.0千克脂肪和蛋白质校正乳（FPCM），短干奶期奶牛的305天产奶量每天低2.3千克FPCM。在365天产奶量中纳入产犊前的额外产奶量后，无干奶期奶牛的差异降至每头奶牛每天3.4千克FPCM，短干奶期奶牛的差异降至每头奶牛每天0.9千克FPCM。与具有常规干奶期的奶牛相比，无干奶期奶牛的平均空怀天数减少了25天，短干奶期奶牛减少了18天。在有效泌乳期产奶量中考虑这些产犊间隔的差异，进一步使无干奶期或短干奶期奶牛的产奶量减少量每天每头奶牛降低0.3千克FPCM。在牛群水平上，无干奶期或短干奶期奶牛的估计365天产奶量损失与有效泌乳期产奶量损失之间的差异为每头奶牛每天0.4至 -0.8千克FPCM。考虑产犊前的额外产奶量对不同DP长度奶牛的产奶量比较有重大且一致的影响。校正产犊间隔的影响在不同农场之间变化更大，当产犊间隔受DP长度影响时尤其重要。
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