This experiment was conducted to determine the optimal dose of estradiol benzoate (EB) to induce and synchronize estrus. More heifers and cows displayed estrous behavior within 45 to 57 h after insert removal, but only in the heifers was their a tendency for a linear and quadratic dosage effect. For both the heifers and cows, the pregnancy rates after breeding were not different between the estrous cycling and the anestrous females. In conclusion, an injection of 4 mg of EB in the cows resulted in a higher, but not significant, pregnancy rate than any other dose of EB, with 92% of the cows detected in estrus over a three day period. The heifers' response to EB was not as vigorous as that of the cows and no dosage can be recommended.

Five hundred and forty-three postpartum beef cows were administered norgestomet and estradiol valerate (Syncro-Mate B®; SMB) to synchronize estrus. MGA feeding increased synchronization rates in the estrous-cycling females; however, MGA feeding did not improve pregnancy rates. In summary, MGA may be used to improve synchronization rates of estrus-cycling females, but the improvement is likely not warranted unless higher pregnancy rates are observed.

This study was conducted to determine if the uterus was necessary for SMB to induce luteolysis. SMB-induced luteolysis required the involvement of the uterus. The luteolysin, prostaglandin F_2alpha, is probably the secretion from the uterus that mediates the SMB-induced luteolysis. SMB treatment, however, required 7-8 days to induce luteolysis.

This trial is designed to evaluate the effects of Angus and Wagyu breeding on feedlot performance and the deposition of marbling and rib fat for heifers managed differently post-weaning. Additionally, these data were used to relate feed efficiency to marbling and rib fat deposition. Twenty-four heifers, 12 Angus and 12 Wagyu-cross (1/2 Wagyu, ½ Angus) were weaned at 180 d of age and grown on endophyte-infected tall fescue for 16 months prior to entering the feedlot. An additional 20 head of heifers, 11 Angus and 9 Wagyu-cross (1/2 Wagyu, ½ Angus) were early-weaned (140 d of age) and immediately adjusted to a high concentrate diet. As 2-year-olds, Angus and Wagyu heifers performed similarly in the feedlot. However as yearlings, Wagyu heifers gained less efficiently (P < 0.01) than Angus heifers. Twelfth rib fat of 2-year-old heifers increased linearly (P < 0.01) with increased days in the feedlot. In contrast, 12th rib fat for yearling heifers behaved quadratically (P < 0.01) over time in the feedlot. Twelfth rib fat was thicker for Angus 2-year-old heifers relative to Wagyu 2-year-olds. However, differences in 12th rib fat that resulted from breed were not significant for yearling heifers. Marbling scores increased quadratically (P < 0.01) for 2-year-old heifers. However, marbling score increased linearly (P < 0.01) for yearling heifers.

(Refer to Part I)

The purpose of this experiment was to determine if exogenous progesterone administered to cows from d 5 to d 14 post-insemination, via an intravaginal progesterone insert (IPI; aka CIDR), would improve the d 28 pregnancy rate. IPI treatment improved pregnancy rates in estrus-cycling cows, but there was a tendency for pregnancy rates to be lower in treated cows that were previously anestrous.

In this experiment, induction of a new CL to maintain pregnancy to term in cows that experienced premature regression of the CL was investigated. Eighteen of the 65 cows were determined to be pregnant without a CL, and 12 of the eighteen were maintained on norgestomet treatment. Of those 12 cows 42% (5) had prolonged pregnancies and 8% (1) maintained pregnancy to term.