Efficacy and production benefits following use of eprinomectin extended-release injection in pastured dairy heifers.

A study was conducted in grazing dairy heifers to assess anthelmintic efficacy and production responses in dairy heifers treated with a single injection of eprinomectin in an extended-release formulation over a 123 day-period. The study was conducted on a pasture-based dairy in the Southeastern United States (North Carolina) over the summer months. Sixty crossbred dairy heifers were weighed and randomly allocated into 2 groups. One group (n = 30) was given 5% eprinomectin subcutaneously in the cervical region while the other group (n = 30) was given an equivalent volume of saline. Calves were weighed every 30 days throughout the trial for calculation of average daily gain and differences in overall weight gain. In addition, fecal samples were collected at days 0, 30, 60, 90 and 123 for worm egg count and coproculture. Both groups of cattle had similar worm egg concentrations at the start of the study. However, the control group had increasing concentrations of fecal worm eggs throughout the summer months while the heifers that received eprinomectin had minimal fecal worm eggs. The primary parasite species identified in this study were Haemonchus placei, Cooperia species and Ostertagia. The heifers that received eprinomectin gained 105 + 2.8 kg during the 123-day study period, representing an average daily gain of 0.85 kg/day compared to 78.3 + 4.1 kg (0.64 kg/day) for the control group. This represented a 33 % increase in average daily gain associated with deworming. The results of this study indicate that a single dose of extended-release eprinomectin was sufficient to control parasites through a 123-day summer grazing season and that administration of the anthelmintic had a significant impact on weight gain.

A two-injection prostaglandin F2α presynchronization treatment decreases pregnancy rates of cycling replacement beef heifers.

Improving artificial insemination (AI) pregnancy rates in replacement heifers improves the genetic advancement within a herd. Heifers that have completed at least three estrous cycles prior to breeding have greater pregnancy rates compared to acyclic females. Therefore, it was hypothesized that a presynchronization treatment program consisting of two injections of prostaglandin F2α (PGF2α) prior to the start of the CO-Synch + 5 d CIDR protocol would initiate earlier attainment of puberty and more estrous cycles prior to AI, thus increasing AI pregnancy rates. All heifers were managed the same at two locations over the course of 2 yr. Heifers were randomly assigned to receive either the two-injection PGF2α presynchronization treatment (PreSynch; n = 105) or no presynchronization (Control; n = 106) prior to the start of estrous synchronization. On the first day of the trial, reproductive tract scores (RTSs), pelvic areas, body condition scores, and weights were collected on all heifers. All heifers were synchronized with the CO-Synch + 5 d CIDR protocol and fixed-time artificially inseminated with semen from a bull of known fertility. Blood samples were collected three consecutive times at 7 d intervals starting 45 d prior to estrous synchronization to determine the onset of puberty via analyzing progesterone concentrations. Pregnancy status to AI was assessed using ultrasonography diagnosis at approximately 30 and 60 d post insemination. Data were analyzed using PROC MIXED of SAS and reported as least square mean. The PreSynch treatment decreased AI pregnancy rates (52.2% vs. 38.1 ± 6.3% for Control vs. PreSynch, respectively; P = 0.06) and did not result in earlier attainment of puberty in beef heifers (P > 0.05). The PreSynch treatment did not impact pregnancy rates in heifers with an RTS of 3 or 4 (P > 0.05). However, PreSynch heifers with an RTS of 5 had decreased pregnancy rates (68.3% vs. 46.9 ± 10.1% for Control vs. PreSynch, respectively; P < 0.05). Finally, PreSynch heifers with increased body condition of 6 had decreased pregnancy rates when compared to Control heifers (37.5% vs. 62.5 ± 11.6%, respectively; P < 0.05). On the basis of these data, implementation of heifer breeding soundness examination at least 3 wk prior to the start of the breeding season may be beneficial for selecting replacement females; however, presynchronization with prostaglandins immediately prior to estrous synchronization will negatively affect AI pregnancy rates in cycling pubertal heifers.