Department of Animal Sciences, University of Florida, Gainesville 32611.
Department of Animal Sciences, University of Florida, Gainesville 32611.
J Dairy Sci. 2019 Jun;102(6):5647-5656. doi: 10.3168/jds.2018-15721. Epub 2019 Apr 17.
Cooling during the entire dry period abates the negative effects of heat stress postpartum, yet the temporal relationship of cooling (i.e., early or late dry period) to performance is unknown. We evaluated the effect of heat stress early, late, and for the entire dry period on subsequent performance. Cows were selected based on mature-equivalent milk yield and dried off 45 d before expected calving. Cows were blocked by parity, previous 305-d mature equivalent milk yield, and body weight (BW) and randomly assigned to cooling (shade, fans, and soakers; CL) or heat stress (shade; HT). Treatments included CL (n = 20) or HT (n = 18) during the entire dry period, HT during the first 3 wk dry and then CL until calving (HTCL, n = 21), or CL during the first 3 wk dry period and then HT until calving (CLHT, n = 19). Heat stress increased rectal temperature (RT; CL, 38.8; HT, 39.1 ± 0.04°C) and respiration rate (RR; CL, 52.9; HT, 70.5 ± 1.9 breaths/min) during the early dry period. In the late dry period, HT increased RT and RR relative to CL cows (RT = CL, 38.7; HT, 39.1; CLHT, 39.1; HTCL, 38.9 ± 0.05°C; RR = CL, 47; HT, 64; CLHT, 66; HTCL, 53 ± 2.1 breaths/min). During the early dry period, HT decreased dry matter intake (CL, 11.8; HT, 10.5 ± 0.35 kg/d) but dry matter intake did not differ among treatments during late dry period (HT, 10.7; HTCL, 11.1; CL, 11.2; CLHT, 10.1 ± 0.55 kg/d). Cows exposed to prepartum cooling during the entire dry period had increased dry matter intake compared with cows exposed to heat stress during the late dry period (CL vs. CLHT, 11.2 ± 0.55 and 10.1 ± 0.55 kg/d, respectively). Heat stress at any time reduced gestation length compared with cows under prepartum cooling during the entire dry period (CL, 277 vs. HT, 274; CLHT, 273; and HTCL, 274 ± 1.17 d). Dry period length decreased by approximately 4 d if cows were exposed to HT at any time. During the early dry period, HT decreased BW, whereas CL increased BW relative to that at dry-off (CL, 6.9; HT, -9.4 ± 3.7 kg). In the late dry period, we detected no differences in BW gain among treatments, but cows exposed to prepartum cooling for the entire dry period tended to have increased BW gain compared with HT and HTCL. Prepartum cooling during the early or late dry period alone partially rescued milk yield only in the first 3 wk of lactation (CL, 32.9; HT, 26.6; CLHT, 29.7; HTCL, 30.7 ± 1.37 kg/d). Cooling for the entire dry period increased milk yield up to 30 wk into lactation compared with all other treatments. Thus, HT at any time during the dry period compromises performance of cows after calving.
在整个干奶期进行冷却可以减轻产后热应激的负面影响，但冷却（即早期或晚期干奶期）与性能之间的时间关系尚不清楚。我们评估了热应激早期、晚期和整个干奶期对随后性能的影响。根据成熟当量奶产量选择奶牛，并在预计产犊前 45 天停奶。根据胎次、前 305 天的成熟当量奶产量和体重（BW）对奶牛进行分组，并随机分配到冷却（遮荫、风扇和喷淋；CL）或热应激（遮荫；HT）组。处理包括整个干奶期的 CL（n = 20）或 HT（n = 18）、干奶前 3 周的 HT 然后是直到产犊的 CL（HTCL，n = 21）或干奶前 3 周的 CL 然后是直到产犊的 HT（CLHT，n = 19）。在早期干奶期，热应激增加了直肠温度（RT；CL，38.8；HT，39.1 ± 0.04°C）和呼吸频率（RR；CL，52.9；HT，70.5 ± 1.9 次/分钟）。在晚期干奶期，与 CL 奶牛相比，HT 增加了 RT 和 RR（RT = CL，38.7；HT，39.1；CLHT，39.1；HTCL，38.9 ± 0.05°C；RR = CL，47；HT，64；CLHT，66；HTCL，53 ± 2.1 次/分钟）。在早期干奶期，HT 降低了干物质采食量（CL，11.8；HT，10.5 ± 0.35 kg/d），但在晚期干奶期，不同处理之间的干物质采食量没有差异（HT，10.7；HTCL，11.1；CL，11.2；CLHT，10.1 ± 0.55 kg/d）。与晚期干奶期暴露于热应激的奶牛相比，整个干奶期暴露于产前冷却的奶牛干物质采食量增加（CL 与 CLHT，分别为 11.2 ± 0.55 和 10.1 ± 0.55 kg/d）。任何时候的热应激都比整个干奶期的产前冷却缩短了妊娠期（CL，277 比 HT，274；CLHT，273；和 HTCL，274 ± 1.17 d）。如果奶牛在任何时候都暴露于 HT，干奶期会缩短约 4 天。在早期干奶期，HT 降低了 BW，而 CL 相对于停奶时增加了 BW（CL，6.9；HT，-9.4 ± 3.7 kg）。在晚期干奶期，我们没有发现不同处理之间 BW 增加的差异，但整个干奶期暴露于产前冷却的奶牛 BW 增加趋势高于 HT 和 HTCL。单独在早期或晚期干奶期进行产前冷却仅在泌乳的前 3 周部分恢复了产奶量（CL，32.9；HT，26.6；CLHT，29.7；HTCL，30.7 ± 1.37 kg/d）。与所有其他处理相比，整个干奶期的冷却使泌乳 30 周内的产奶量增加。因此，在干奶期的任何时候，热应激都会影响产后奶牛的性能。
