Abstract
This study aimed to determine changes in rumen-reticular temperature (RRT) at estrus or ovulation and determine if these changes are associated with the intensity of estrous expression. Cows were equipped with an automated activity monitor (AAM) and a rumen-reticular bolus thermometer. A total of 190 estrus episodes were used where physical activity data was recorded using the AAM and ovulation was determined via ultrasonography of the ovaries at alert and twice daily, for a maximum of 60 h. Estrous expression was assessed using the maximum activity and duration in which activity remained above the AAM threshold; both characteristics were categorized using the median. Temperature data was collected for the duration of estrus, as well as for the interval of time where ovulation was determined to occur. Three measures of temperature were calculated: (1) positive area under the curve (AUC), (2) maximum positive temperature change (PTC), (3) maximum negative temperature change (NTC) at estrus (AUCE/ PTCE/ NTCE) and around ovulation (AUCO/PTCO/ NTCO). Both AUC and PTC were greater during estrus than around ovulation (2.7 ± 0.2 and 1.1 ± 0.3°C2 for AUCE and AUCO; 0.55 ± 0.03 and 0.26 ± 0.04°C for PTCE and PTCO, respectively). In contrast, NTC was lower around ovulation than estrus (−0.28 ± 0.05 and −0.60 ± 0.06°C for NTCE and NTCO). Cows with greater estrous expression had greater AUC and PTC during estrus than around ovulation, but cows with lesser estrous expression had similar AUC and PTC. Increases in AUC [High THI (Temperature Humidity Index): High activity: 4.7 ± 0.5, Low activity: 1.5 ± 0.4; Low THI: High activity: 3.1 ± 0.2, Low activity: 1.4 ± 0.2 °C2] and PTC (High THI: High activity: 0.79 ± 0.08, Low activity: 0.36 ± 0.07; Low THI: High activity: 0.60 ± 0.04, Low activity: 0.47 ± 0.04°C) associated with estrous expression were found to be greater on days with higher THI. Alerts created using standard deviations from the mean were unable to detect estrus or ovulation with acceptable precision. Further research is required to determine how changes in RRT can be used successfully to predict estrus and ovulation.
Highlights
New technologies have been developed to improve dairy cattle health and reproductive efficiency on dairy farms
All measures of temperature change (AUC, positive temperature change (PTC), and negative temperature change (NTC)) were affected by sampling time; where area under the curve (AUC) and PTC were greater at estrus than around ovulation (2.7 ± 0.2 and 1.1 ± 0.3◦C2 for AUCE and AUCO, respectively; P < 0.001; 0.55 ± 0.03 and 0.26 ± 0.04◦C for PTCE and PTCO, respectively; P < 0.001) and NTC was more negative at ovulation than at estrus (−0.28 ± 0.05 and −0.60 ± 0.06 ◦C for NTCE and NTCO, respectively; P < 0.001)
This study demonstrated that positive changes in rumen-reticular temperature were higher at the time of estrus than around the time of ovulation while negative changes in rumen-reticular temperature were greater around ovulation than at estrus
Summary
New technologies have been developed to improve dairy cattle health and reproductive efficiency on dairy farms. The development of hormonal protocols such as the Ovsynch have greatly improved reproductive efficiency in lactating dairy cows by increasing insemination rates, but a growing body of research indicates that insemination programs based on the detection of estrus are effective at obtaining acceptable conception rates and days to conception [1,2,3]. The recent development of rumen-reticular thermometer technologies that monitor core body temperature provide continuous data collection and analysis in real time. The ability to automatically measure continuous body temperature expands the applicability for health monitoring, and has the potential to be used as a predictor of estrus and ovulation. The recent surge in interest and use of automated technologies for estrus detection requires that these technologies be validated in terms of their performance
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