El-Tarabany MS, El-Tarabany AA
Theriogenology 2015 Dec;84(9):1523-9
PMID: 26324113
エジプトにおいて、ホルスタイン、ブラウンスイス 、ホルスタインとブラウンスイスのF1の3群でTHI別（<70、70-75、75<）に繁殖成績をまとめている。耐熱性がブラウンスイス 、ホルスタインとブラウンスイスのF1にある分、繁殖成績は上昇していた（妊娠率の上昇、空胎日数の短縮、胎児死滅率の減少、流・死産率の減少）。
暑熱ストレスというと、早期の胚死滅への影響ばかり頭にあったが、授精後28日以降の影響も大きいことがよく分かる。
この論文には乳量と産次のデータが無いのが残念。F1は耐熱性あるのは直感的に分かるのだが乳量の違いはどれほどなのであろうか？エジプトでは暑熱対策としてF1を生産して搾る傾向にあるらしい。
Abstract
Heat stress in hot environments is one of the major factors that can negatively affect milk production, reproduction, and the health of dairy cows. The aim of this study was to evaluate the impact of maternal heat stress at insemination on the subsequent reproductive performance of the pure Holstein (HO), Brown Swiss (BS), and their F1 crossbred (BF) cows, under subtropical Egyptian conditions. The influence of temperature-humidity index (THI) on the pregnancy rate, fetal loss rate, calving traits, and reproductive indices were investigated. Fetal loss rate of pure HO was significantly increased from 17.1% at low THI to 24.9% at greater THI (odds ratio = 2.09; P = 0.032). Furthermore, abortion and stillbirth rates of pure HO were significantly increased from 3.6% and 3.8%, respectively, at low THI to 7.2% and 5.9%, respectively, at greater THI (odds ratio = 2.17 and 2.58; P = 0.037 and 0.031, respectively). In contrast, BS and BF cows can tolerate the heat stress, as there were no differences in the fetal loss, abortion, and calving difficulty rates at the different levels of THI. Pure HO cows had a significant longer calving interval and days open at high THI (449 and 173 days, respectively), compared with low THI (421 and 146 days, respectively). On the contrary, BS and BF cows had no difference in the calving interval at the different levels of THI. Our results indicate that pure BS and BF cows have a better adaptability and competent reproductive performance than pure HO under subtropical conditions.