Our objective was to compare the effect of treatment with GnRH at the first treatment (G1) of the Breeding-Ovsynch portion of a Double-Ovsynch (DO) protocol with human chorionic gonadotropin (hCG) on pregnancies per artificial insemination (P/AI) in lactating dairy cows. In experiment 1, lactating dairy cows (n = 1,932) submitted to a DO protocol for first timed artificial insemination (TAI) on 2 commercial dairy farms were blocked by parity (primiparous vs. multiparous) and were randomly assigned to receive 100 µg of GnRH versus 2,500 IU of hCG at G1. Overall, P/AI 39 d after TAI for cows inseminated with sexed dairy semen was greater for cows treated with GnRH than for cows treated with hCG within each parity (primiparous: 42.6% vs. 38.2%; multiparous: 39.4% vs. 30.3%). Similarly, P/AI 39 d after TAI for multiparous cows inseminated with conventional beef semen tended to be greater for cows treated with GnRH than for cows treated with hCG (41.1% vs. 34.3%). In experiment 2, lactating Holstein cows (n = 43) were blocked by parity and were randomly assigned to the treatment protocols described for experiment 1. Ovaries were evaluated with transrectal ultrasonography immediately before treatment and 24, 28, 32, 36, and 40 h after treatment to assess time from treatment to ovulation, and blood samples were collected immediately before G1, at the first PGF 2α treatment, 8 and 16 h later, at the second PGF 2α treatment, 8 and 16 h later, at the second GnRH (G2) treatment, and at TAI to compare luteolysis based on serum progesterone (P4) concentrations. Although mean (± standard error of the mean) time from treatment to ovulation was approximately 2 h greater for cows treated with hCG than for cows treated with GnRH (33.7 ± 0.6 vs. 31.5 ± 0.6 h), P4 concentrations during luteolysis and the proportion of cows with complete luteolysis (P4 <0.4 ng/mL at G2) did not differ between treatments. We conclude that replacing 100 µg of GnRH with 2,500 IU of hCG at G1 of a DO protocol decreased fertility to TAI in lactating dairy cows but did not affect the rate or completeness of luteolysis despite the increased interval from treatment to ovulation.

This study evaluated the presence of polyunsaturated fatty acids in circulating blood and in the ovarian follicular fluid of mares, after supplementation of the diet with linseed oil. Six Mangalarga Marchador mares, weighing 397.00±31.89 kg, were kept on native pasture, and assigned to the current study. In a switch over design, mares were randomly allocated to receive 150 ml of vegetable oil daily, containing polyunsaturated fatty acids n3 (62.23 g ALA, 20.34 g LA, 2.27 g EPA, 2.32 g DHA), (n=3) or no supplementation (n=3) in two replicates. Blood and follicular fluid samples were taken on the first day (D0) and every 30 days until the end of the supplementation period (D60). After 60 days of supplementation, mares were switched across the treatments. Plasma concentrations of linolenic acid in total fatty acids were higher (P=0.006) in the supplemented compared to the control group (1.89±0.13 vs. 1.49±0.13%). There were positive correlations between plasma linoleic acid and follicular fluid arachidonic acid (P=0.0106; r 2 =0.13) and between plasma alpha linolenic acid and follicular fluid EPA (P=0.0004; r 2 =0.2544). Data indicated a low to moderate relationship between the dietary linseed-based oil supplementation studied and circulating and follicular fluid polyunsaturated fatty acids contents in mares.

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The objective was to determine the effect of hCG (3,300 IU) administered on days 0 and/or 5 of the estrous cycle on total luteal area (TLA) and circulating concentrations of progesterone (P4) in recipient heifers. All heifers (n = 232; BCS = 3.3 ± 0.2) were synchronized with a 5d CIDR-Synch protocol (d-8: used CIDR inserted; d-3: CIDR removed and PGF2α treatment; d0: 100µg GnRH or hCG). Heifers were randomly assigned to four treatments: control, hCGd0, hCGd5, and hCGd0&5. Controls were treated with GnRH on d0, while hCGd0 received hCG on d0. hCGd5 heifers were treated with GnRH on d0 and hCG on d5, while hCGd0&5 received hCG on d0 and 5. Ovaries were scanned by ultrasound on d0, 5, and 12. Blood was collected on d0, 5, 7, and 12. Synchronization rate (94%) did not differ (P = 0.94) by treatment. Treatment differences were only tested in synchronized heifers (n = 218). Proportion of heifers with 1 or 2+ CL on d5 did not differ (P = 0.10) for hCG d0 treatments (hCGd0 + hCGd0&5) vs. GnRH d0 treatments (controls + hCGd5). However, heifers treated with hCG on d0 had greater (P &lt; 0.01) TLA and P4 on d5 vs. treatments with GnRH on d0 (311 ± 13 vs. 257 ± 9 mm2; and 2.39 ± 0.15 vs. 1.90 ± 0.09 ng/mL). Ovulation rate for d5 hCG did not differ (P = 0.63) for hCGd5 vs. hCGd0&5 (93 vs. 84%). Controls had the lowest serum P4 on d7 and 12. In contrast, hCGd0&5 had the highest serum P4 on d7 (Table 1). Serum P4 on d7 did not differ for hCGd0 vs. hCGd5. On d12, serum P4 and TLA were not different for hCGd5 vs. hCGd0&5. These data indicate that hCG can be used on d0 to induce an increase in serum P4 on d5 compared to GnRH. However, only heifers treated with hCG on d5 achieved mean serum P4 &gt; 8ng/mL.