No abstract

Heifers typically have a reduced ovulation rate following gonadotrophin-releasing hormone (GnRH) application at initiation of a CO-Synch + controlled internal drug release (CIDR) protocol. Thus, the objective of the present study was to determine whether increasing the dose of GnRH at initiation of a 5-day CO-Synch protocol in beef heifers would improve ovulation rate and therefore increase pregnancies per AI (P/AI). Angus yearling heifers (n=299) at five locations in Ohio (United States) were randomised to receive either 100µg (single; n=149) or 200µg (double; n=150) of gonadorelin acetate (Gonabreed, Parnell) at initiation of a 5-day CO-Synch. On Day −8, heifers received a new intravaginal progesterone-releasing device (1.38g of progesterone; CIDR, Zoetis) and either a single or double dose of GnRH as described above. Five days later (Day −3), devices were removed, 1000µg of cloprostenol sodium (Estroplan, Parnell) was administered, and an oestrous detection patch was applied (Estrotect, Rockway Inc.). Sixty hours after device removal, AI was performed concurrently with the administration of 100µg of GnRH. Pregnancy was determined using ultrasonography 35 days after AI. Ovaries from a subset of animals (n=178) were examined on Days −8 and −3 using ultrasonography to determine the presence of corpora lutea (CL) and the size of the largest follicle. Data were analysed using the GLIMMIX procedure of SAS ver. 9.4 (SAS Institute Inc.). Oestrous expression was similar (P=0.50) between heifers treated with a single (49.0%) or double (52.7%) dose of GnRH. Overall, P/AI was similar (P=0.35) between heifers receiving a single (43.6%; 65/149) or double (38.7%; 58/150) dose of GnRH at initiation of the protocol. However, increasing the dose of GnRH resulted in a greater (P=0.04) ovulation rate in heifers in the double-dose group (40.9%; 36/88) compared with those in the single-dose group (26.1%; 23/88). In addition, heifers with a CL at the time of treatment had reduced ovulatory response to GnRH treatment (16.0%) compared with heifers without a CL (53.7%; P=0.001); however, there was no treatment×CL presence interaction (P=0.69). Heifers that did not ovulate to the initial GnRH treatment had a greater (P=0.0008) diameter of the largest follicle on Day −3 compared with heifers that did ovulate (11.4±0.2 vs. 10.0±0.3). Furthermore, heifers that did ovulate after the initial GnRH had greater (P=0.04) P/AI (52.5%) than heifers that did not ovulate (40.2%), and heifers with a CL on Day −8 tended (P=0.07) to have greater P/AI (47.9%) than heifers without a CL (40.2%). In addition, heifers with a CL present on Day −3 had greater (P=0.04) P/AI (48.2%) than heifers without a CL (31.7%). In summary, increasing the dose of GnRH at initiation of a 5-day CO-Synch did not affect fertility to fixed-time AI but enhanced ovulation rate in beef heifers. Furthermore, heifers that did ovulate at initiation of the protocol or that had a CL at device insertion or removal had greater fertility to fixed-time AI. Thus, alternative strategies that maximise ovulation at initiation of the synchronisation protocol are needed.

Colour Doppler ultrasonography (CDU) of the corpus luteum (CL) has the potential to be used for early pregnancy diagnosis in order to improve reproductive efficiency and increase the use of fixed-time AI (FTAI) in beef cattle. The objective of the present study was to determine the sensitivity and specificity of CDU of the CL for pregnancy diagnosis in beef heifers with or without a CIDR at different days after FTAI. Angus-cross beef heifers (n=84) were synchronized using a 5-day Co-Synch with AI at 60h after CIDR removal. On Day 15 post-AI, heifers were randomly assigned to receive a CIDR (Eazi-Breed CIDR, Zoetis, Parsippany-Troy Hills, NJ) for 9 days or remain as untreated controls. Heifers were evaluated by transrectal CDU (MyLab Delta, Esoate, Genoa, Italy; 7.5-MHz linear array probe, pulse repetition frequency=960Hz) at 15, 17, 20, and 22 days post-AI. Heifers were determined to be pregnant by CDU if colour pixels covered >10% of the periphery of the CL and contained at least 2 colour internal tracts penetrating toward the centre of the CL. Heifers were evaluated by B-mode ultrasonography on Day 28 to determine true pregnancy status. Differences between days and treatments were evaluated using generalized estimating equations. Pregnancies per AI at Day 28 after FTAI were 53.6% (45/84) and were not different between CIDR (52.4%; 22/42) and control (54.8%; 23/42) heifers (P=0.83). Sensitivity and specificity for CIDR and control heifers at different days are shown in Table 1. There was no effect of treatment (P=0.49), day (P=0.99), or treatment by day interaction (P=0.99) on test sensitivity. Specificity was different (P<0.01) between days; however, no treatment (P=0.91) or treatment by day interaction (P=0.82) was identified. Specificity was lowest on Days 15 and 17 and increased to reach its maximum at Day 22. Although no differences between treatments were observed, specificity on Day 22 was numerically greater in CIDR-treated heifers. Positive and negative predictive values for CDU at Day 22 were 84 and 94.1%, respectively, for CIDR-treated heifers and 79.3 and 100%, respectively, for control heifers. Cohen’s Kappa indicated slight (0.19), fair (0.27), moderate (0.50), and substantial (0.73) agreement between conventional ultrasound at Day 28 and CDU at Days 15, 17, 20, and 22, respectively. In summary, CDU showed excellent sensitivity between Days 15 and 22, indicating a very low rate of false-negative results. However, high specificity (low false-positive rate) was achieved only at Day 22. Thus, pregnancy diagnosis by CDU at Day 22 after FTAI coupled with the use of a CIDR may be an effective strategy to identify nonpregnant heifers and attempt their prompt resynchronization. Table 1.Sensitivity and specificity (%) for pregnancy diagnosis by CDU in beef heifers with or without a CIDR at different days after FTAI

No abstract

Colour Doppler ultrasonography of the corpus luteum (CL) can be used for early pregnancy diagnosis to improve reproductive efficiency and increase the use of AI in beef cattle. The objective of the present study was to determine the diagnostic performance of different Doppler ultrasonography settings for pregnancy diagnosis based on CL perfusion at 21 days after fixed-time AI in beef heifers and cows. Yearling Angus-cross heifers (n=25) and suckled Angus-cross cows (n=84) aged 2-13 years were submitted to a 5-day CO-Synch + controlled internal drug release (CIDR) and timed AI at 60 or 72h after CIDR removal for heifers and cows, respectively. Animals were evaluated by a single operator using colour Doppler ultrasonography (Esaote MyLab Delta) at Day 21. Three settings for colour flow mapping (720, 960, and 1500Hz) and one setting for power Doppler (960Hz), which differed in pulse repetition frequency, were evaluated. The other settings remained unchanged with a probe frequency of 6.3MHz, wall filter of 3, and gain of 61. The pregnancy status (pregnant or non-pregnant) of cows and heifers was determined at 21 days following insemination using colour Doppler ultrasonography. Cows and heifers were considered to be pregnant if the CL blood flow area covered >10% of the periphery of the CL and contained at least two colour internal tracts penetrating towards the centre of the CL. Cattle were evaluated using transrectal B-mode ultrasonography on Day 35 to determine actual pregnancy status. Differences between diagnostic performance variables were evaluated using logistic regression, and setting, category (heifer or cow), and the interaction were included as fixed effects. Pregnancies per AI at Day 35 after fixed-time AI were 47.7% (52/109). Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for pregnancy diagnosis at Day 21 for each setting are included in Table 1. There were no differences in sensitivity and NPV between settings (P>0.9), category (P>0.9), or the interaction (P>0.9). There was no effect of setting (P>0.5) or category×setting interaction (P>0.8) on specificity and PPV. There was, however, an effect of category (P<0.01). Colour Doppler ultrasonography had less specificity (59.1% compared with 90.2%) and PPV (75% compared with 89.3%) in heifers than in cows. In conclusion, colour Doppler ultrasonography settings that were evaluated did not affect the diagnostic performance for pregnancy diagnosis at Day 21 after AI, although, numerically the colour flow mapping at 960Hz appears to maximise diagnostic accuracy. In addition, the false-positive rate was greater in heifers, which warrants further research. Table 1.Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for pregnancy diagnosis for four colour Doppler ultrasound settings (colour flow mapping (CFM) at 720, 960, and 1500Hz and power Doppler (PWD) at 960Hz) at 21 days after fixed-time AI Item CFM720 CFM960 CFM1500 PWD960 Sensitivity,% 100 100 92.3 100 Specificity,% 80.7 87.7 87.7 80.7 PPV,% 82.5 88.1 87.3 82.5 NPV,% 100 100 92.6 100