Characteristics and retention of luteal structures, extended postinsemination cycle, progesterone, and pregnancy-specific protein B in serum after human chorionic gonadotropin treatment of dairy cows

Abstract

Our objectives were to determine characteristics (size, number, and stayability) of luteal structures formed in response to human chorionic gonadotropin (hCG) administered on d 7 after timed artificial insemination (AI) and the influence of hCG on returns to estrus and pregnancy outcome. Holstein cows (n=328), milked 3 times daily, previously inseminated at first service were assigned randomly to a completely randomized design consisting of 2 treatments when at least 1 corpus luteum (CL) was detected on d 7 after AI. Treatment consisted of 1,000 IU hCG or 1 mL of saline (control) administered i.m. Blood was collected and luteal structures were mapped and sized by transrectal ultrasonography on d 7, 14, 21, 28, and 32 after AI. Blood also was collected on d 60 in all pregnant cows. Treatment with hCG induced new luteal structures in 70% of cows, regardless of pregnancy status or number of pretreatment CL. Cows producing greater than the median 46 kg of energy-corrected milk per day were less likely to respond to hCG. The number of total luteal structures per cow, original CL volume, and total luteal volume (original CL + new luteal structures) were increased by hCG. Progesterone concentration was greater in pregnant than nonpregnant cows on d 14 unless cows responded to hCG by forming new luteal structures. Concentrations of progesterone were greatest in pregnant, hCG-treated cows. Pregnancy per AI at d 32 or 60 after first AI was less in hCG- than saline-treated cows because pregnancy outcome for hCG cows that had only 1 pretreatment CL and failed to respond to hCG was only 55 to 61% of that observed in controls. Proportions of cows returning to estrus from 18 to 25 d after AI were less in hCG than control cows but greater for cows returning >25 d. Regardless of treatment, 25% of cows in both treatments retained at least 1 original CL to d 28 after AI and were not pregnant on d 32. Progesterone concentrations in these nonpregnant cows with retained CL between d 14 and 28 after AI were intermediate between nonpregnant cows that returned to estrus by d 25 and all pregnant cows. Concentrations of pregnancy-specific protein B were elevated in some of these nonpregnant, CL-retained cows, indicating early pregnancy loss. Retention of original luteal tissue in nonpregnant cows to d 28 after AI indicated that pregnancy had been initiated but failed, as verified by concentrations of progesterone and pregnancy-specific protein B.

Effect of 2 corpora lutea on blood perfusion, peripheral progesterone, and hepatic steroid-inactivating enzymes in dairy cattle

“…In the current study, response rates using Ovsynch were well below expected outcomes (63.3 vs. 87%). Success rates in previous reports using hCG to cause a spontaneous ovulation and induce an acces-sory CL were approximately 70% (Wallace et al, 2011;Stevenson and Pulley, 2012). The observed response in the current study to hCG to induce an accessory CL (36%) was also less than expected.…”

The Induction of a Secondary Corpus Luteum on Day 12 Post‐Ovulation can Delay the Time of Luteolysis in High‐Producing Holstein Cows

“…In addition to the extended duration of the ovulation to luteolysis interval, the formation of a CL2 also increased circulating P4 concentrations between 2 and 6 days after hCG injection. Significant increases in plasma or milk P4 were observed in most studies after hCG injection on Days 2-7 (Helmer and Britt 1986;Diaz et al 1998;Santos et al 2001;Stevenson and Pulley 2012), or Day 14 of the oestrous cycle. This increase may be related to a direct luteotropic effect of hCG on the primary CL (Fricke et al 1993) and/ or to the increase in amounts of luteal tissue (linked to CL2 formation) (Schmitt et al 1996a).…”

“…; Santos et al. ; Stevenson and Pulley ), while ovulation was only achieved in four cows of nine treated on Day 14 (Rajamahendran and Sianangama ) and seven of 23 treated on Days 8–13 of the oestrous cycle (Price and Webb ). Similarly, only 21% of high‐producing dairy cows exhibited an additional CL after a GnRH treatment at the time of AI and 12 days later (Lopez‐Gatius et al.…”

“…; Santos et al. ; Stevenson and Pulley ), or Day 14 (Sianangama and Rajamahendran ) of the oestrous cycle. This increase may be related to a direct luteotropic effect of hCG on the primary CL (Fricke et al.…”

“…The global rate of CL induction after hCG treatment on Day 12 was 55%, that is lower than results obtained by others when hCG was injected at earlier stages of the oestrous cycle (Days 4-7), but globally higher than those evaluated after later administration (Days 14-18). Indeed, 70-100% of the cows formed accessory corpora lutea after hCG administration on Days 4-7 (Schmitt et al 1996b;Kerbler et al 1997;Diaz et al 1998;Santos et al 2001;Stevenson and Pulley 2012), while ovulation was only achieved in four cows of nine treated on Day 14 and seven of 23 treated on Days 8-13 of the oestrous cycle (Price and Webb 1989). Similarly, only 21% of highproducing dairy cows exhibited an additional CL after a GnRH treatment at the time of AI and 12 days later (Lopez-Gatius et al 2006).…”