The effects of aspirin on pregnancy rates and pregnancy specific protein B in lactating dairy cows during the summer

Abstract Text: The occurrence of embryonic loss in cattle may be due to a hormonal imbalance and untimely secretion of PGF_2α around the time of maternal recognition on days 14-16 after fertilization. The objective of this study was to examine the effect of aspirin, a non-steroidal anti-inflammatory drug, on pregnancy rates (PR) and blood pregnancy specific protein B (PSPB) in lactating dairy cows bred more than once and during the summer months. On day 14 after two or more AI, 556 cows, from a commercial drylot herd in the Pacific Northwest, were assigned randomly to aspirin (total of 187.2 g; n=277) or control (n=279) treatment groups. Aspirin was administered orally with a balling gun 24 hours apart on day 14 and 15 (93.6 g/dose) after AI, whereas the control group was subjected to oral stimulation. On day 25 following AI, blood samples were collected from a subset of cows (n=192) and measured for PSPB concentrations. Pregancy status was determined by palpation per rectum between day 32 to 40 post-AI. The maximum daily ambient temperature ranged from 27 to 39.4°C during the trial period. To estimate the effect of aspirin on PR/AI, a logistic regression model was used. Concentrations of PSPB were analyzed using the analysis of variance. There were no differences in PR/AI (P>0.05) between aspirin (21.7%) and control (27.6%) groups. There was no effect of parity (primiparious 26.2% vs. multiparous 23.8%) or number of inseminations (TBRD) (2^nd and 3^rd 26.2% vs. ≥4 21.5%) on PR/AI. There was also no effects of treatment or treatment by pregnancy status on PSPB concentrations (P>0.05). Blood PSPB concentrations were 122.8 ± 8.1  and 127.8 ± 6.4 pg/mL for the aspirin and control groups, respectively. However, PSPB concentrations tended to be greater in multiparous cows compared with primiparous cows (132.7 ± 5.7 vs. 118.1 ± 7.3 pg/mL, P=0.07). In addition, PSPB concentrations tended to be greater (P=0.07) for 2^nd and 3^rdTBRD (133.1 ± 5.3 pg/mL) than ≥4 TBRD (117.6 ± 7.8 pg/mL). These results indicate that aspirin may not have an effect on PR/AI or PSPB concentrations in lactating dairy cows subjected to two or more AI during hot summer months in the Pacific Northwest.

Keywords: aspirin, dairy cow, fertility