Estrus Prediction Models for Dairy Gyr Heifers

Abstract

Technological devices are increasingly present in livestock activities, such as identifying the reproductive status of cows. For this, predictive models must be accurate and usable in the productive context. The aims of this study were to evaluate estrus-associated changes in reticulo-rumen temperature (RRT) and activity (ACT) in Dairy Gyr heifers provided by reticulo-rumen boluses and to test the ability of different models for estrus prediction. The RRT and ACT of 45 heifers submitted to estrus synchronization were recorded using reticulo-rumen boluses. The means of RRT and ACT at different time intervals were compared between the day before and the day of estrus manifestation. An analysis of variance of RRT and ACT was performed using mixed models. A second approach employed logistic regression, random forest, and linear discriminant analysis models using RRT, ACT, time of day, and the temperature-humidity index (THI) as predictors. There was an increase in RRT and ACT at estrus (p < 0.05) compared to the same period on the day before and on the day after estrus. The random forest model provided the best performance values with a sensitivity of 51.69% and specificity of 93.1%. The present results suggest that RRT and ACT contribute to the identification of estrus in Dairy Gyr heifers.

Keywords: Zebu; activity; body temperature; heat; reproduction; sensors.

Figure 1

Hormonal protocol for estrus synchronization and artificial insemination. i.m: intramuscular administration.

Figure 2

Time intervals (hour) during which mean reticulo-rumen temperatures were compared in relation to first observed mount acceptance (0). Scheme 1 (light gray)—2 h: Interval of 2 h before first observed mount acceptance was compared with the same daily hours the day before (−26 to −24 h) and the day after (22 to 24 h). 4 h: Interval of 4 h before first observed mount acceptance was compared with the same daily hours the day before (−28 to −24 h) and the day after (20 to 24 h). 6 h: Interval of 6 h before first observed mount acceptance was compared with the same daily hours the day before (−30 to −24 h) and the day after (18 to 24 h). 8 h: Interval of 8 h before first observed mount acceptance was compared with the same daily hours the day before (−32 to −24 h) and the day after (16 to 24 h). 12 h: Interval of 12 h before first observed mount acceptance was compared with the same daily hours the day before (−36 to −24 h) and the day after (12 to 24 h). Scheme 2 (dark gray)—2 h: Interval of 2 h after first observed mount acceptance was compared with the same daily hours the day before (−24 to −22 h) and the day after (24 to 26 h). 4 h: Interval of 4 h after first observed mount acceptance was compared with the same daily hours the day before (−24 to −20 h) and the day after (24 to 28 h). 6 h: Interval of 6 h after first observed mount acceptance was compared with the same daily hours the day before (−24 to −18 h) and the day after (24 to 30 h). 8 h: Interval of 8 h after first observed mount acceptance was compared with the same daily hours the day before (−24 to −16 h) and the day after (24 to 32 h). 12 h: Interval of 12 h after first observed mount acceptance was compared with the same daily hours the day before (−24 to −12 h) and the day after (24 to 36 h).

Figure 3

Time intervals (hour) during which mean activity per hour was compared in relation to removal of the progesterone implant (0). 6 h: Interval of 6 h after implant removal was compared with the same hours of the day before (−24 to −30 h). 12 h: Interval of 12 h after implant removal was compared with the same hours of the day before (−24 to −36 h). 18 h: Interval of 18 h after implant removal was compared with the same hours of the day before (−24 to −42 h). 24 h: Interval of 24 h after implant removal was compared with the same hours of the day before (−24 to −48 h).

Figure 4

Daily mean of reticulo-rumen temperature (RRT) and activity of Zebu heifers on a day.

Figure 5

Estimated least squares means of RRT by hour during estrus in Scheme 1 (hours before) and Scheme 2 (hours after). Means in the same color followed by different superscript letters differ significantly (Tukey test, 5% significance level).

Figure 6

(a) Observed mean reticulo-rumen temperatures (RRT) over the hours before and after first observed mount acceptance (0) on the day of estrus, on the day before, and on the day after. (b) Observed mean activity over the hours after removal of the progesterone implant (hour 0) and on the day before.