Thesis - Open Access
Master of Science (MS)
cattle, disease, nutrition, reproduction, resynchronization
The beef industry is a unique community of operations that employ different management techniques to accomplish a similar goal. Like other facets of animal agriculture, profitability of the beef industry is heavily reliant upon the implemented management practices. Reproductive efficiency is an area of management that has great potential to positively influence the success of beef production. Through the use of reproductive technologies such as estrus synchronization and AI, a greater percentage of females can become bred to superior sires, breeding and calving seasons can be shortened, calf uniformity increased, and economic return maximized (Odde, 1990; Rodgers et al., 2012; Bó et al., 2016). In recognizing the merit of utilization of these reproductive technologies, the possibility of extending these benefits past an initial synchronization and AI can be appreciated. Implementation of estrus resynchronization and additional inseminations has been adopted by the dairy industry, but is slow to be utilized by beef producers. Evaluating the efficacy of estrus resynchronization and a second insemination offers the potential to maximize the previously mentioned benefits in a defined breeding season. Additionally, if reproductive efficiency is to be optimized, disease and nutrition management are also aspects that require consideration. It is understood that appropriate biosecurity practices against reproductive diseases, such as Bovine Viral Diarrhea Virus (BVDV), are required to allow for maximal production efficiency (Newcomer et al., 2017). In order to mitigate the negative effects of this disease in the breeding herd, there is room for scientific evaluation of the effects BVDV has in herds that employ vaccination schedules. Further, nutrient partitioning in the beef animal limits the prioritization of reproduction over other metabolic functions (Short et al., 1990). Nutrient intake changes shortly prior to, and following insemination, have the potential to greatly influence pregnancy success through alteration in estrus expression, steroidogenic activity, uterine environment, and embryo development (Lamond, 1970; Short and Adams, 1988). Therefore, in considering these areas of management that allow for improved reproductive efficiency, the objectives of the following studies were to evaluate the necessity of a controlled internal drug releasing device (CIDR) in a fixed-time AI resynchronization protocol (Chapter 2), the effect of Bovine Viral Diarrhea Virus infection on reproductive success (Chapter 3), and the influence of plane of nutrition before and after AI on estrus expression, steroid concentrations, and thus uterine environment and embryo development (Chapter 4). In Chapter 2, beef cows and heifers over a two year period from sixteen herds were inseminated using the 7-day CO-Synch + CIDR protocol. On d 21 following the first insemination, the protocol was repeated, with animals either receiving a CIDR or no CIDR. Pregnancy status was determined on d 28 by both transrectal ultrasonography and the IDEXX Rapid Visual Pregnancy Test. Non-pregnant animals by both methods (n = 373 cows, n = 453 heifers) received an injection of PGF2 and were time inseminated 52 to 56 (heifers) or 60 to 66 (cows) h later or bred following detection in estrus. Corpora lutea (CL) number and largest follicle diameter (LF) were recorded on a subset of non pregnant animals (n = 229) from each herd and treatment at time of pregnancy diagnosis. Estrus expression was recorded at time of insemination. Pregnancy status was determined a minimum of 28 d following the second AI. Statistical analyses were performed using the GLIMMIX procedure of SAS for estrus, and pregnancy, including age and year in the model. The final model was obtained following stepwise removal of insignificant interactions. The MIXED procedure was utilized for analyses of CL number and LF. There was no effect (P > 0.55) of treatment on AI 1 pregnancy (CIDR; 45.30 ± 1.8%, no CIDR; 47.48 ± 1.8%) AI 2 pregnancy (CIDR; 28.54 ± 5.2%, no CIDR; 29.56 ± 4.9%), or overall pregnancy (CIDR; 58.7 ± 7.3%, no CIDR; 58.6 ± 7.4%). Treatment influenced (P < 0.0001) estrus expression prior to AI 2 (CIDR; 56.1 ± 5.5%, no CIDR; 36.4 ± 5.2 %). There was an effect of treatment x age on AI 2 pregnancy (P = 0.007), with heifers receiving a CIDR having higher AI 2 pregnancy (CIDR Heifers; 34.9 ± 5.8%, CIDR Cows; 22.9 ± 6.0%), and cows without a CIDR having higher pregnancy than heifers without a CIDR (no CIDR Heifers 24.7 ± 4.9%, no CIDR Cows; 34.8 ± 6.4%). Estrus expression impacted AI 2 pregnancy success (41.0 ± 5.9% estrus vs. 19.43 ± 3.9% no estrus; P < 0.001), as well as the interaction of treatment, age, and estrus expression (P = 0.04). Heifers not exhibiting estrus had increased AI 2 pregnancy rate with CIDR inclusion (CIDR; 28.2 ± 6.8%, no CIDR; 17.9 ± 4.8%), while cows not exhibiting estrus had decreased AI 2 pregnancy rate with CIDR inclusion (CIDR; 9.3 ± 4.2%, no CIDR; 27.7 ± 6.8%). There was no effect of treatment on embryonic loss (P = 0.62), CL number (P = 0.18), follicle diameter (P = 0.93). There was a tendency for age to influence the presence of ≥ 12 mm size dominant follicles (P = 0.08), with a greater percentage observed in cows (Cows; 63.1 ± 6.9%, Heifers; 48.2 ± 10.6%). Further, there was a tendency for an effect of treatment x age interaction on follicle size (P = 0.07). In conclusion, the use of a CIDR in this resynchronization protocol increased estrus expression, increased AI 2 pregnancy for heifers, but reduced AI 2 pregnancy in cows that failed to show estrus, and did not influence overall pregnancy or embryonic loss. In Chapter 3, vaccinated cows (n=370) and heifers (n=528) from nine different herds were synchronized using the 7-day CO-Synch + CIDR protocol and were fixedtime AI (FTAI). On d 28 following insemination, blood samples were collected and pregnancy status was determined. Non-pregnant animals were resynchronized and FTAI occurred a second time. In six herds bulls were comingled with females beginning 10-15 d after the second AI. Final pregnancy status was determined 33-80 d following the first pregnancy diagnosis. Blood samples were tested for the presence of BVDV antigen using the IDEXX BVDV PI X2 Kit. Animals that tested positive were considered infected with BVDV at the time of blood collection. Herds were determined to be BVDV infected by the presence of at least one animal having a positive test for antigen (n = 4 infected herds, n = 5 non-infected herds). Statistical analyses were performed using the GLIMMIX procedure of SAS with herd as a random variable. Herds that had evidence of BVDV infection at d 28 following insemination had significantly decreased (P < 0.01) first service AI conception rates compared to herds that had no evidence of infection (34 ± 2.3% vs. 54 ± 2.3%). Additionally, breeding season pregnancy rates were decreased (P < 0.01) in BVDV infected herds compared to non-infected herds (69 ± 3.4% vs. 80 ± 3.6%). There was no significant effect of BVDV infection status on embryonic loss (P = 0.42) or percentage of animals which lost a pregnancy and rebred by the end of the breeding season (P = 0.63). In conclusion, BVDV infection in well vaccinated herds had a significant negative impact on both first service AI conception rate and overall breeding season pregnancy success. In Chapter 4, seventy nine Angus cross beef heifers were randomly divided into one of two diet treatments (High or Low) a maximum of 45 days prior to AI (d 0 as AI). Diets were sampled before and after AI and evaluated for nutrient analysis. The Low diet provided 90 and 81% of maintenance, while the High diet provided 162 and 148% of maintenance before and after AI, respectively. Estrus synchronization (PG 6-d CIDR protocol) was initiated on d -12. Estrus expression was monitored and recorded, and heifers detected in estrus were inseminated 8 to 12 h later with semen from one of two sires. At time of AI, half of the heifers were randomly reassigned treatment to generate four final pre x post-AI treatments; High-High (HH, n = 20), High-Low (HL, n = 20), Low-High (LH, n = 19), and Low-Low (LL, n = 20). Heifers remained in their new diet treatment for 7 to 8 days following AI when embryo collection occurred. Blood samples were collected on d -3 to d 0, and d 1, 3, 5, 7 and 8 post-AI. Ultrasonography of dominant follicle diameter was evaluated on d -3 and d 0, while CL diameter was recorded at the time of uterine flush (d 7 or 8). Heifer body weight and plasma concentrations of nonesterified free fatty acids (NEFA), glucose, protein, estradiol, and progesterone were analyzed as repeated measures using the MIXED procedure of SAS. Estrus expression and embryo recovery were evaluated using the GLIMMIX procedure of SAS. The GLM procedure of SAS was used to analyze follicle size, growth of the dominant follicle, interval to estrus, interval to AI, CL size, embryo stage and embryo quality. There was a Pre-AI treatment by time interaction on heifer body weight (P < 0.0001). Heifers on the low diet lost 8.22 kg but heifers on the high diets gained 9.34 kg. There was also a post AI treatment by time interaction of body weight (P < 0.0001). Heifers on the low diet lost 5.21 kg but heifers on the high diets gained 6.33 kg between AI and uterine flush. There was also a Pre-AI treatment (P = 0.0003) and post-AI treatment (P < 0.0001) influence on NEFA concentrations, with low treatment heifers having increased concentrations compared to the high treatment heifers (Pre-AI treatment Low; 0.60 ± 0.03 mEq/L, High; 0.43 ± 0.03 mEq/L and Post-AI treatment Low; 0.61 ± 0.03 mEq/L, High; 0.42 ± 0.03 mEq/L). There was a tendency for both Pre-AI treatment (P = 0.06) and Post-AI treatment to impact circulating concentrations of glucose, with the High treatment having greater glucose than low during both periods. There was also a Pre-AI x Post-AI treatment interaction on glucose concentrations (P = 0.04). Heifers in the HH treatment had elevated concentrations (102.75 ± 3.13 mg/dL) of glucose compared to heifers in the HL, LH, and LL treatments which did not differ. There was an effect of time on estradiol concentrations (P < 0.0001), with concentrations increasing from d -3 (2.18 ± 0.15 pg/mL).to d 0 (6.05 ± 0.04 pg/mL). Pre-AI treatment also impacted post- AI concentrations of progesterone (P = 0.015), with the high heifers having greater concentrations of progesterone compared to the low heifers (High; 4.85 ± 0.37 ng/ mL, 3.53 ± 0.38 ng/mL); however, Post-AI treatment did not influence post AI concentrations of progesterone (P = 0.88). Pre-AI treatment also influenced estrus expression (P = 0.05) and size of the dominant follicle at AI (P= 0.0016). Heifers in the high treatment had increased estrus expression (80 ± 6.3% vs. 59 ± 7.9%), and larger dominant follicles (11.7 ± 1.42 mm vs. 10.68 ± 1.33 mm) compared to heifers in the low treat. There was no significant effect of pre, post or pre x post treatment on protein concentrations, estradiol concentrations, initial follicle size, growth rate of the dominant follicle, interval to estrus, interval to AI, CL size at flush, or on embryo stage, grade, or recovery rate (P > 0.10). In conclusion, findings from this study confirm the ability of nutrient restriction prior to and shortly following AI has the ability to impact ovarian function, steroidogenesis, and estrus expression. Further elucidation of these effects is needed to evaluate the effects of these changes on embryo development and pregnancy success.
Number of Pages
South Dakota State University
In Copyright - Educational Use Permitted
Epperson, Kaitlin M., "Optimization of Reproductive Success in Beef Cattle by Implementation of Estrus Resynchronization, Nutritional Management, and Evaluation of Disease Prevalance" (2019). Electronic Theses and Dissertations. 3643.
Available for download on Friday, December 18, 2020