Effect of time lapse from the onset of estrus detected by pedometer until insemination and synchronization for artificial insemination on calf sex ratio in Japanese Black Cows

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  • 歩数計測による発情開始から人工授精までの時間と発情同期化が黒毛和種子牛の性比に及ぼす影響
  • ホスウ ケイソク ニヨル ハツジョウ カイシ カラ ジンコウ ジュセイ マデ ノ ジカン ト ハツジョウ ドウキカ ガ クロゲ ワシュ コウシ ノ セイヒ ニ オヨボス エイキョウ

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Abstract

Effect of time lapse from the onset of estrus detected by data transmissible pedometer (Gyuho, Comtec, Miyazaki, Japan) until artificial insemination (AI) and estrous synchronization on calf sex ratio was investigated in Japanese Black Cows. A total of 80 Japanese Black Cows were installed with pedometers, which store the number of steps per hour and transmit the date for 24 hours. The onset of estrus was defined when the number of each hour steps in cows exceeded more than double of the maximum steps in recent 15 days. Cows were randomly assigned to either timed AI program with estrus synchronization using progesterone-releasing intravaginal device (PRID®) (n = 33) or AI using AM/PM rule (n = 47). Cows were subdivided into three groups retrospectively based on the time lapse from the onset of estrous until AI ; 0-8h (n = 8), 9-16h (n = 43), 17-24h (n = 29). Estimating the onset of estrus using pedometers revealed that only a small number of cows showed estrus during daytime hours (08:00～18:00), whereas many cows commenced estrus at night-time (18:00～08:00) (daytime 23.7 % vs. night-time 76.3 % : P<0.01). There was no significant difference between groups in conception rate (timed AI 45.5 % vs. estrus AI 63.8 % : P=0.10), which showed estrus synchronization using PRID® could be useful to improve reproductive performance in Japanese Black Cows. Male calf ratio was lower in early AI group (0 % in 0-8 h, 75.0 % in 9-16h and 46.7 % in 17-24h), which indicated calf sex ratio might be affected by the time lapse from the onset of estrus until AI. However, there was no such tendency in the synchronized timed AI cows.

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