Intensity of estrus following an estradiol-progesterone-based ovulation synchronization protocol influences fertility outcomes.

The objective of this study was to examine the association between increased physical activity at the moment of timed artificial insemination (AI), detected by an automated activity monitor (AAM), and fertility outcomes. This paper also investigated factors affecting estrous expression in general. A total of 1,411 AI events from 1,040 lactating Holstein cows were recorded, averaging 1.3 ± 0.6 (±standard deviation) events per cow. Activity (measured as steps/h) was monitored continuously by a leg-mounted AAM located on the rear leg of the cow. Ovulation was synchronized by a timed AI protocol based on estradiol and progesterone. Ovarian ultrasonography was performed in all cows on d -11 (AI = d 0) and in a subset of cows on d 0 (n = 588) and d 7 (n = 819) to determine the presence of a corpus luteum and follicles. The body condition score (1 to 5 scale) was assessed on d 0 and a blood sample was collected for progesterone measurement on d 7. Using the AAM, an estrus event was determined when the relative increase (RI) in physical activity of the cow exceeded 100% of the baseline activity. The physical activity was classified as strong RI (≥300% RI), moderate RI (100-300% RI), or no estrus (<100% RI). Milk production was measured daily and averaged between d -11 and 0. Pregnancy was diagnosed at 32 and 60 d post-AI and pregnancy losses were calculated. The mean RI at estrus was 328.3 ± 132.1%. Cows with strong RI had greater pregnancy per AI than those with moderate RI and those that did not express estrus (35.1 vs. 27.3 vs. 6.2%). When including only cows that successfully ovulated after timed AI, those that displayed strong intensity RI still had greater pregnancy per AI than those with moderate intensity RI or those that did not express estrus (45.1 vs. 34.8 vs. 6.2%). Cows expressing strong RI at timed AI had greater ovulation rates compared with moderate RI and cows that did not express estrus (94.9 vs. 88.2 vs. 49.5%). Furthermore, pregnancy losses were reduced in cows with strong RI compared with cows expressing moderate RI (13.9 vs. 21.7%). Cows with a strong RI at estrus were more likely to have a corpus luteum at the beginning of the protocol and had greater concentration of progesterone 7 d post-AI. Multiparous cows expressed lower RI compared with primiparous cows. Cows with lower body condition score tended to have decreased RI at estrus. No correlation between estrous expression and pre-ovulatory follicle diameter was observed. Also, no correlation was observed between milk production at AI and RI. In conclusion, strong intensity RI of estrus events at timed AI was associated with improved ovulation rates and pregnancy per AI, and reduced pregnancy losses. These results provide further evidence that measurements of estrous expression can be used to predict fertility at the time of AI and possibly be used as a tool to assist decision making strategies of reproduction programs.

Daily lying behavior of lactating Holstein cows during an estrus synchronization protocol and its associations with fertility.

Objectives were to quantify lying behavior (LB) during an estradiol and progesterone-based synchronization protocol, to assess risk factors for ovulation, pregnancy per AI (P/AI), and degree of behavioral change at estrus, and to investigate the associations between estrus LB and walking activity. Holstein cows (43.6 ± 11.0 kg of milk/d) were fitted with leg-mounted accelerometers. Total lying time/d (L_time), bout frequency (bout_N), average lying bout duration, and relative increase in walking activity (ACT%) were evaluated for 1,411 timed artificial insemination events. The day with lowest L_time or bout_N among d -2, -1, and 0 (day of timed artificial insemination) determined the day of behavioral estrus. The variables L_time% and bout_N% represent relative ratios between lowest L_time and baseline (d -7), L_time, and lowest bout_N, and baseline (d -7) bout_N, respectively [e.g., (lowest L_time/baseline L_time) × 100]. Correlation coefficients between L_time% and bout_N% and ACT% were -0.38 and -0.31, respectively. Estrus LB change was considered large if <75% of baseline and small if ≥75% of baseline for both L_time% and bout_N%; average lying bout duration did not change with estrus. Lowest L_time% and bout_N% corresponded to, respectively, 65 ± 21% (mean ± standard deviation; 447 ± 157 min/d) and 65 ± 24% (8.5 ± 4.0 bouts/d) of baseline. The change in L_time% at estrus was smaller when cows had milk yield above average; the change in bout_N% was smaller among multiparous cows and for estrus occurring in the colder season. Likelihood of ovulation was greater when there was larger change in L_time% [odds ratio = 4.9; ovulation rate = 93 (large change) and 76% (small change)], as well as when a corpus luteum was present at start of protocol (odds ratio = 3.6; in the model with L_time%). Likelihood of pregnancy at d 32 was 1.6 times greater for estrus with large change in LB [L_time% or bout_N%; P/AI = 34% (large change in L_time%) and 26% (small change in L_time%)]. Among estrus events with ACT% ≥300% (high intensity), classification by small or large L_time% did not influence P/AI at 32 d. The magnitude of LB change at estrus and its association with fertility suggest potential application toward improved use of activity monitors (e.g., increased estrus detection, fertility prediction). The contribution of LB to accuracy of estrus detection when physical activity is known remains to be addressed. The relationship between intensity of estrus expression and fertility requires further investigations of its physiological rationale and on-farm applications.