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Graduate Student Supervision
Doctoral Student Supervision (Jan 2008 - Nov 2019)
Automated technologies have been developed to improve dairy cattle reproductive efficiency, yet there is still need for better understanding of how these technologies can be used and determine how the information collected relates to key events important for fertility. The aims of this thesis were to determine 1) if automated activity monitors (AAM) can predict estrus and be used within reproductive management, and 2) the interrelationship between estrous expression, ovulation and fertility. In Chapter 2, I provide evidence that AAM can be successfully incorporated into reproductive management without impeding the outcomes of an AI protocol and that increased estrous expression is associated with improved fertility. Chapter 3 investigates if changes in rumen-reticular temperature can be used to detect ovulation. Rumen-reticular temperature is shown to increase at the time of estrus and then declines near the time of ovulation, but the magnitude increase at estrus is dependent on the intensity of estrous expression as well as temperature and humidity at the onset of estrus. In Chapter 4 I demonstrate that the intensity of estrous expression is associated with the timing and failure of ovulation, where cows with lesser estrous expression had shorter intervals from estrus alert to ovulation and lower ovulation rates. Finally, in Chapter 5 I summarize work that investigated if the administration of GnRH at the moment of AI could increase fertility of cows with reduced estrous expression by increasing ovulation rates and modifying progesterone concentrations post-AI. The administration of GnRH increased fertility of cows with lesser estrous expression, but did not affect ovulation or progesterone profiles. Future research is merited to further understand the relationship between estrous expression and fertility of dairy cows.
Detection of estrus in dairy cows is challenging, partly because of poor behavioural expression. Automated activity monitors allow quantification of estrus expression based on restlessness. The main goals of this thesis were to use automated measurements and visual observation of behaviour to increase understanding of estrus characteristics, variation among animals, risk factors for poor expression, and its association with fertility. In the first study, the behaviour of heifers was video-recorded and activity peaks were identified from accelerometer data; estrus was validated by ovarian ultrasonography. Chin rest, sniff, back mount, crossover, and follow had the largest increase in frequency during estrus. Estrus relative increase in walking activity (290 ± 160%) and duration (14 ± 4 h) varied greatly and were affected by estrus order, season and time of the day. The second study investigated how estrus affected automated measurements of lying and standing behaviour, a less explored aspect of estrus. At estrus, bout frequency was lower, daily standing time was greater, and heifers stood uninterruptedly for twice longer than at baseline. Relative changes in standing behaviour at estrus were smaller for estrus starting between 1200 h and 0300 h. The third experiment investigated the agreement between estrus characteristics in heifers fitted with two accelerometers. Both systems were precise (PPV = 84.7% [Heatime] and 98.7% [IceTag]) and provided similar characterization and timing. Plasma estradiol was not correlated with follicle diameter, duration, intensity, or presence of estrus signs. Finally, estrus lying behaviour of lactating cows and its associations with fertility were studied. Daily lying time and bout frequency were reduced at estrus (65 ± 21% and 65 ± 24% of baseline). Ovulation and pregnancy at d 32 after AI were 4.9 and 1.6 times more likely if estrus lying time was
Master's Student Supervision (2010 - 2018)
The objective of this study was to determine the effect of vaginal temperature on levels of physical activity expressed by lactating Holstein cows following induced estrus. Lactating Holstein cows (n = 641; 41.5 9.4 kg milk/d) were fitted with a leg-mounted pedometer resulting in 843 evaluated activity episodes of estrus. Vaginal temperature was monitored using thermometers, attached to an intravaginal device that recorded vaginal temperature every 10 min for 3 d. Ambient temperature and relative humidity were monitored using an external thermometer placed in the center of each pen. Milk production and BCS were collected at the time of thermometer insertion. All statistical analysis was performed in R. Heat stress (HS) was calculated based on the percentage of time the cow spent with a vaginal temperature ≥39.1°C (PCT39) 9-11 d prior to Timed Artificial Insemination (TAI), and was classified as high or low (median: 22.9%). The mean vaginal temperature was 38.9 ± 0.2°C, whereas the mean maximum and minimum vaginal temperatures were 39.7 ± 0.5°C and 38.0 ± 0.8°C, respectively, with an average amplitude 1.71 ± 0.9°C. Mean relative increase (RI) of steps/hr at estrus was 237.0 ± 160 %. Animals with low BCS were associated with lower RI compared to cows with medium BCS (260.31 ± 17.45% vs. 296.42 ± 6.62%). Lower temperature and humidity (THI) values (≤ 65) were associated with greater RI compared with medium (> 65 -
The aim of this study was to test the effect of expression of estrus at artificial insemination (AI) on the endometrium, conceptus and corpus luteum (CL) gene expression. Twenty-three multiparous non-lactating Nelore cows were enrolled on an estradiol (E2) and progesterone (P4) based timed-AI protocol (AI = d 0), then slaughtered for endometrium, CL and conceptus collection on d 19. Body condition score (BCS), blood samples and ultrasound examination was performed on d 0, 7 and 18 of the experiment followed by RNA extraction and quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis of 58 target genes. Data was checked for normality and analysed by ANOVA for repeated measures using proc GLM, MIXED and UNIVARIATE. Estrous expression had no correlation with parameters such as BCS, pre-ovulatory follicle and CL diameter, P4 concentration in plasma on d 7 and 18 after AI and IFN-tau concentration in the uterine flushing (P > 0.05); however, a significant increase was observed in conceptus size (P = 0.02; 38.3 ± 2.8 vs 28.2 ± 2.9). The majority of transcripts affected by estrous expression in the endometrium belong to the immune system and adhesion molecule family (MX1, MX2, MYL12A, MMP19, CXCL10, IGLL1 and SLPI) (P ≤ 0.05). Genes related to apoptosis, P4 synthesis and prostaglandin receptor were down-regulated (CYP11A, BAX and PGF2α receptor) (P
Dairy cattle are often challenged with stressful practices and conditions. Cortisol is often used as a biomarker to detect stress. Hair is a promising new medium to detect long- term changes of circulating cortisol. This thesis investigated methodologies for the collection and processing of hair for cortisol analysis, and determined associations of hair cortisol concentrations with health disorders and fertility in lactating Holstein cows.First, we investigated the effects of hair colour, sampling location, and processing method on the amount of cortisol extracted from hair samples of 18 black and white Holstein dairy cows. Second, we investigated the associations between hair cortisol with clinical and subclinical disease, and reproductive success. Hair samples were collected from the tail switch of lactating Holstein cows to determine the effects of clinical disease and fertility (n = 64), or subclinical disease (n = 54).White hair had greater cortisol concentrations than black hair (Geometric Mean [95% CI]) (7.8 [6.8, 9.2] vs. 4.2 [3.6, 5.0] pg/mg). When only white samples were analyzed, hair from the tail switch had more cortisol than the shoulder (11.0 [7.6, 16.0] vs. 6.2 [4.2, 9.2] pg/mg). Processing with a ball mill yielded greater concentrations of extracted cortisol than when using scissors (10.4 [5.8, 18.8] vs. 4.7 [2.6, 8.4] pg/mg). In Holsteins, the tail switch is always white and grows faster making it an ideal location for measuring hair cortisol.Animals with clinical disease presented higher hair cortisol concentrations than clinically healthy animals (8.8 [7.8, 9.9] vs. 10.7 [9.6, 12.0] pg/mg); however, animals diagnosed with subclinical disease did not differ (11.5 [9.7, 13.7] vs. 11.3 [9.6, 13.3] pg/mg for healthy and subclinical groups, respectively). Multiparous cows that became pregnant by 100 days postpartum had lower hair cortisol concentrations at 42 and 84 DIM.Overall, using standard and consistent methods to sample, cortisol in hair offers important insights into long-term changes of circulating cortisol. Hair cortisol concentrations appear to be associated with clinical disorders and have a direct association with pregnancy outcomes; however, hair cortisol concentrations may not be suited to differentiate situations of stress with lower magnitudes, such as subclinical disease.
- Can cover sheath model influence semen retention in AI-gun trials and pregnancy rates of cows inseminated at a fixed-time? (2020)
Semina: Ciências Agrárias,
- Influence of pathogens causing clinical mastitis on reproductive variables of dairy cows (2020)
Journal of Dairy Science, 103 (4), 3648--3655
- Short communication: Greater intensity of estrous expression is associated with improved embryo viability from superovulated Holstein heifers (2020)
Journal of Dairy Science, 103 (6), 5641--5646
- Automated and visual measurements of estrous behavior and their sources of variation in Holstein heifers. I: Walking activity and behavior frequency (2015)
Theriogenology, 84 (2), 312--320
- Automated and visual measurements of estrous behavior and their sources of variation in Holstein heifers. II: Standing and lying patterns (2015)
Theriogenology, 84 (3), 333--341