Angus-sired heifers were allotted by age (mean=4 mo), BW (mean=135 kg), and sire (n=4) to either a control (n=10) or infected group (n=11; 600 metacercariae of Fasciola hepatica, intraruminally) to test our hypothesis that puberty is delayed by experimental fascioliasis. Blood samples were collected biweekly for analysis of steroid hormone concentrations. At 2-wk intervals, BW was recorded, and samples were collected for analysis of liver enzymes and serum proteins and fecal egg counts. A radiotelemetry system (HeatWatch??) was used to detect estrus and ovulation was confirmed by an elevation in serum progesterone (P4) after estrus. Heifers were artificially inseminated (AI) at the second observed estrus. Serum &#947;-glutamyl transpeptidase (GGT) and aspartate aminotransferase (AST) increased (p<0.0008) between day 0 and 112 in the infected group. Serum estradiol (E2) and P4 concentrations did not differ (p>0.1) between treatment groups. Mean age at puberty was 10 days later (p>0.1) in the infected group. Conception rate did not differ between control and infected heifers. The HeatWatch?? data were used to compare mounting activity during estrus in pubertal and gestating heifers. Mean duration of estrus was longer (p<0.01) for the second than for the pubertal estrus, though total mount duration and number of mounts did not differ. Number of mounts at second estrus was greater (p<0.05) for heifers that conceived (n=9). Mean duration of estrus and total mount duration at second estrus were not associated with pregnancy outcome. Estrus events were detected in all nine heifers during pregnancy (total=73). A majority (75%) of the interestrus intervals during gestation was <17 d. Number of mounts (p=0.035) and total duration of mounts (p=0.022) at second estrus were predictive of number of mounts during gestation. Experimental infection of Fasciola hepatica did not alter serum steroid hormone concentration or delay pubertal development in heifers. Estrus duration was longer for the second estrus compared to the pubertal estrus, and the number of mounts received during the second estrus was greater in heifers that did conceive to AI. Estrus events were detected in each heifer during pregnancy; however, a normal interestrus interval occurred in only 10% of the estrus events.

The objective of the study was to compare three systems for detection of estrus and combinations of these systems on a large commercial dairy (1000 lactating cows) during stress of summer heat. At 37 to 45 days in milk (DIM), 266 cows were fitted with a HeatWatch (HW) device (HeatWatch; DDx Inc., Boulder, CO), an activity (A) sensor (ALPRO; DeLaval Inc., Kansas City, MO), and observed visually (V) twice daily. Pregnancy status was determined by uterine palpation 35 to 49 d following artificial insemination (AI). The effects of DIM, parity, physical activity, standing events, months, AI technician, and interval between onset of estrus and AI on conception rate were determined using linear contrasts and logistic regression. Efficiencies for detection of estrus, determined by comparing detected periods of estrus with a theoretical total of 707 periods, were 45.8% (V), 33.2% (A), 40.3% (HW), and 71.6% for all three systems simultaneously. Conception rates (LSM ± SE) by method of detection were 16.7 ± 4.9 for HW, 19.8 ± 5.5 for A, 7.9 ± 3.4 for V, 16.3 ± 6.0 for V + A, 27.6 ± 4.6 for V + HW, 21.1 ± 4.9 for A + HW, and 21.9 ± 4.5 for V + A + HW. Conception rate and number of mounts decreased for cows in first versus second and third parity (P < 0.05). For periods of estrus detected by A, the lowest conception rate (P < 0.05) occurred >18 h after the onset of estrus (16.7 ± 7.9). The highest conception rate occurred with the combination of V + HW, which confirms the premise that combination of multiple systems enhances both the efficiency and accuracy of detection. / Master of Science

Estrus detection programs practiced on most U.S. dairy farms are not intense enough to provide the information needed to accurately time insemination, thus preventing AI from obtaining its full conception rate potential. Herds (n = 17) participated in a trial designed to evaluate percent pregnant relative to various characteristics of estrus. Herds utilized HeatWatch® electronic estrus detection system to detect and record mounting activity for cows in estrus. Inseminations were performed daily during a three hour interval for all cows identified in estrus the previous 24 h. Model characterizing percent pregnant for cows (services = 2661) included effects of interval from first mount to AI (P < 0.01), mounts per estrus (P < 0.01), DIM at insemination (P < 0.01), herd (P <0.05), and season of AI (P < 0.05). As mounts per estrus and days in milk increased, percent diagnosed pregnant increased. Interval affected probability of pregnancy with highest odds ratios for percent pregnant occurring >4 to 16 h following onset of estrus. Model for heifers (n = 306) included linear effects of interval (P < 0.01), season (P < 0.05), and herd (P < 0.01). In dairy heifers, as interval from first mount to AI increased, percent pregnant decreased. Timing of insemination in dairy cows can now be performed relative to first mount of estrus, with highest probability of pregnancy occurring between >4 to 16 h after onset. If onset of estrus is not known, insemination should be performed at the next most convenient time within 3 h. / Master of Science