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Treatment with Gonadotropin-Releasing Hormone After First Timed Artificial Insemination Improves Fertility in Noncycling Lactating Dairy Cows

R. A. Sterry^*, M. L. Welle and P. M. Fricke^*,1

^* Department of Dairy Science, University of Wisconsin, Madison 53706
Miltrim Farms, Inc., Athens, WI 54411

¹ Corresponding author: pmfricke{at}wisc.edu

Lactating Holstein cows were assigned randomly to treatments to improve fertility after first postpartum timed artificial insemination (TAI). In Experiment 1, cows received no treatment (control; n = 9), a controlled internal drug releasing (CIDR) insert from 5 to 12 d after TAI (CIDR; n = 9), or 100 µg of GnRH 5 d after TAI (G5; n = 7). Although treatments did not affect circulating progesterone (P₄) concentrations from 5 to 19 d after TAI, there was a tendency for CIDR cows to have greater P₄ compared with control or G5 cows within 24 h after treatment. In 2 field trials, cows received either control (n = 223), CIDR (n = 218), or G5 (n = 227) treatments (Experiment 2), or control (n = 160), G5 (n = 159), or treatment with 100 µg of GnRH 7 d after TAI (G7; n = 163; Experiment 3). Treatment did not affect pregnancies per AI (P/AI) in Experiments 2 or 3; however, when data were combined to compare control (n = 383) and G5 (n = 386) treatments, P/AI tended to be greater for G5 (49.1%) than for control (45.8%) cows. This effect resulted from a GnRH treatment x cyclicity status interaction in which P/AI for noncycling cows receiving G5 was greater than for noncycling control cows (45.5 vs. 31.1%). In conclusion, treatment with CIDR inserts after TAI had no effect on P/AI, whereas treatment with GnRH 5 d after TAI improved P/AI for noncycling, but not for cycling cows.

Key Words: cyclicity • dairy cow • controlled internal drug releasing insert • gonadotropin-releasing hormone

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