Abstract
It is desirable to control the sex of embryo transfer offspring in the dairy industry. The relationship between estrous behavior, superovulatory response, and embryo sex ratio after superovulation has not been investigated. The objective of the present study was to compare estrous behavior, superovulatory response, and sex ratio of embryos resulting from superstimulated donors in herds in which the female ratio was naturally high (>50%, FR-H, n = 9) or low (d50%, FR-L, n = 7). Holstein heifers (14 to 18 months of age, n = 16) were given decreasing doses of FSH IM (total of 28 Armour units, Antrin R-10; Kawasaki-Mitaka, Kanagawa, Japan) twice daily for 4 days between Days 8 and 10 of the estrous cycle. Five (25 mg) and 3 (15 mg) mL of dinoprost (PGF; Veterinary Pronalgon; Pfizer Animal Health, Tokyo, Japan) were administered IM with the seventh and eighth FSH treatments, respectively. The length of estrus and numbers of standing mounts were determined by an electric heatmount sensor (HeatWatch; Comtec Co. Ltd., Miyazaki, Japan), which was attached to the tailhead of the animals. Heifers received 50 �g of GnRH IM (fertirelin acetate; Conceral; Schering-Plough Animal Health KK, Tokyo, Japan) 48 h after the first PGF treatment, and were inseminated with frozen–thawed semen into the uterine body 12 and 24 h later. Seven-day embryos were recovered nonsurgically and Grade 1 embryos (IETS classification) were selected for this study. Male and female embryos were identified using the loop-mediated isothermal amplification procedure (Hirayama et al. 2004 Theriogenology 62, 887–896). The data (mean � SEM) were compared with Fisher's protected least significant difference test following ANOVA. Mean values for female sex ratio in FR-H and FR-L embryos were 72.2 � 4.6% (32/46) and 30.6 � 7.1% (23/68), respectively (P < 0.01). The duration of estrus in the FR-H group (13 h 10 min � 3 h 51 min) was shorter than that of the FR-L group (24 h 51 min � 6 h 32 min; P < 0.05). Moreover, the numbers of standing mounts in the FR-H group (27.8 � 5.9) were less than in the FR-L group (75.0 � 18.5; P < 0.05). Although the mean number of ova/embryos collected from FR-H heifers (8.4 � 1.0) was significantly less than from FR-L heifers (19.7 � 3.1; P < 0.05), the percentage of Grade 1 embryos did not differ (63.7 � 8.2%, 46/76 vs. 54.5 � 8.3%, 68/138, respectively; P > 0.05). In summary, superstimulated heifers from the FR-H herd had a shorter duration of estrus, a lower superovulatory response, and a higher proportion of female embryos than heifers from the FR-L herd. However, data do not demonstrate a cause and effect relationship.
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