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The ruminant trophoblast produces pregnancy-associated glycoproteins (PAG) that can be detected in the blood of pregnant animals. The objective was to determine the accuracy of a rapid ELISA PAG-based test for the purpose of pregnancy detection in cattle. Blood was sampled from dairy cattle (539 Holstein cows, 173 Holstein heifers, 73 Guernsey cows, 22 Guernsey heifers, and 12 Jersey heifers) and crossbred beef cattle (145 cows and 46 heifers) that were >or=25 d after insemination (range = 25 to 45 d for dairy and 29 to 56 d for beef). Cattle were examined by ultrasonography for detection of pregnancy within 2 d of blood collection. Whole blood or plasma was incubated in a polystyrene tube coated with a monoclonal PAG antibody for 15 min. The tubes were then washed and subjected to sequential incubations with a biotinylated polyclonal PAG antibody (15 min, followed by wash), a horseradish peroxidase-streptavidin solution (15 min, followed by wash), and a peroxidase substrate. Tubes were visually assessed for color after 15 min (clear solution = PAG negative, not pregnant; blue solution = PAG positive, pregnant). Total assay time was approximately 90 min. The ultrasound examination was used as the standard for pregnancy diagnosis. The sensitivity (99.8 +/- 0.2%), specificity (91.7 +/- 1.4%), and negative predictive value (99.7 +/- 0.3%) for the PAG test used in dairy cattle were similar for different breeds and for cows and heifers. The positive predictive value for the test was greater in dairy heifers than in dairy cows (96.5 +/- 1.4% vs. 90.5 +/- 1.7%, respectively). In beef cattle, the sensitivity (100%), specificity (92.3 +/- 3.0%), positive predictive value (95.0 +/- 2.0%), and negative predictive value (100%) for the PAG test were similar for cows and heifers. The accuracy of the test was not different for dairy and beef cattle. In conclusion, the rapid ELISA pregnancy test based on PAG was highly sensitive and specific for pregnancy detection in dairy and beef cattle.

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Cattle that are not pregnant to first fixed-time artificial insemination (TAI) may be resynchronized for a second TAI if they are found nonpregnant at pregnancy diagnosis. The specific interval between first and second TAI ranges from 4 to 8 wk. The selected interval depends on the available method of pregnancy diagnosis and the efficiency of the resynchronization program. The objective of this experiment was to evaluate a pregnancy diagnosis and resynchronization system that achieved a 21-d interval between TAI. This 21-d interval approximates the natural return-to-service interval. It also enables resynchronization to be implemented within the same estrous cycle in which cattle are first inseminated. Holstein heifers were randomly assigned to a 21-d resynchronization program (21d_resynch; n = 40) or a control group in which estrus was observed for the purpose of re-insemination (control; n = 29). The 21d_resynch heifers were diagnosed for pregnancy on d 18 after a TAI (d 0) by using predetermined cut-off values for 2'-5' oligoadenylate synthetase 1 (Oas1) gene expression in leukocytes and plasma progesterone concentration. Heifers that were not pregnant to first TAI had greater expression of Oas1 at the time of PGF(2α) (d -3) than pregnant heifers, but this relationship was reversed on d 18 after TAI: the heifers that were pregnant to first TAI had almost 5-fold greater expression of Oas1 compared with nonpregnant heifers. Nonpregnant heifers in the 21d_resynch group were injected with a luteolytic dose of PGF(2α) on d 19 and were injected with GnRH on d 21 and submitted to TAI. The pregnancy per AI after first insemination was similar for 21d_resynch (50.0%; pregnancy diagnosis on d 18) and control (51.7%; pregnancy diagnosis on d 27). Likewise, no difference was detected in second insemination pregnancy per AI for 21d_resynch (36.8%; nonpregnant heifers TAI on d 21) and control (35.7%; nonpregnant heifers inseminated at return to estrus or after nonpregnant diagnosis on d 27). The interval between first and second insemination was shorter for 21d_resynch compared with control (21.0 ± 0 and 27.5 ± 2.1 d). The conclusion is that a TAI resynchronization can be programmed within 21 d of previous TAI when a d 18 pregnancy test and a rapid resynchronization are used.