Abstract
The effect of hCG administration on accessory corpus luteum (ACL) formation, CL area, and plasma progesterone (P4) concentration (ng/mL) seven days after breeding was studied in nulliparous Santa Inês sheep. Intravaginal 60 mg MAP sponges were inserted into ewes for six days and 300 IU eCG i.m. and 30 µg d-cloprostenol latero-vulvar were administered 24 h before sponge removal. Ewes were naturally bred and, seven days after first mating (Day 0; D0), were treated with either 250 IU hCG (hCG group; n = 7) or 1 mL saline solution (control group; n = 7). Blood was collected to determine plasma P4 concentrations and sonograms were performed on Days 7, 10, 13, 16, 19, and 22. Number of CL on D7 was similar (P > 0.05) between hCG (1.3 ± 0.5) and control (1.3 ± 0.5) groups; however, on D13, it was greater (P < 0.05) in the hCG group (2.3 ± 0.5) than in the control group (1.3 ± 0.5). A greater (P < 0.05) luteal tissue area was detected in hCG-treated ewes (n = 4) on Days 16 to 22 than in the animals in the control group (n = 7). Plasma P4 concentration on D13 to D22 was higher (P < 0.05) in hCG-treated animals than in control ewes. Administration of hCG seven days after estrus onset efficiently induced accessory CL formation in ewes, increasing luteal tissue area and plasma P4 concentration.
Highlights
Materials and MethodsExperimental animals and facilitiesThis research was reviewed and approved by the Animal Care Committee of Embrapa Dairy Cattle (Protocol 15/2014) and conducted across two trials during the nonbreeding season of Santa Inês (Balaro et al, 2014), between October and November, at the Experimental Campus of Embrapa Dairy Cattle, in the rural area of Coronel Pacheco, Brazil
Inês breed appeared to represent a good model for this type of study since the Santa Inês sheep is a breed of relative lower prolificacy (1.3; Mexia et al, 2004) and ovulation rate (1 to 1.3 ovulation per estrus induced ewe; Cavalcanti et al, 2012; Teixeira et al, 2016)
Previous study found that ovulation in estrus-induced Santa Inês ewes occurred at around 24 h after estrus onset (Cavalcanti et al, 2012) and that the first follicular wave emerged near to ovulation
Summary
This research was reviewed and approved by the Animal Care Committee of Embrapa Dairy Cattle (Protocol 15/2014) and conducted across two trials during the nonbreeding season of Santa Inês (Balaro et al, 2014), between October and November, at the Experimental Campus of Embrapa Dairy Cattle, in the rural area of Coronel Pacheco, Brazil (latitude 21° 35’ S, longitude 43°15’ W, and altitude of 435 m). A total of 14 nulliparous Santa Inês ewes aged between 12 and 14 months were kept in an intensive system, and were fed corn silage and Napier grass They were administered with a balanced concentrate supplement according to their nutritional needs (National Research Council, 2007). Mineralized salt and drinking water were available to the ewes ad libitum.
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