Effect of body condition score and reuse of progesterone-releasing intravaginal devices on conception rate following timed artificial insemination in Nelore cows

Evaluation of strategies to maximize fixed-time artificial insemination efficiency in Bos taurus indicus ("Nellored") females in Brazilian savannah environment by a real-life study

This study aimed to identify factors and technologies that could enhance the pregnancy rate of "Nellored" females by evaluating the animal category, number of progesterone-releasing intravaginal device (DP4) uses and day of its removal, equine chorionic gonadotropin (eCG) dosage, time of fixed-time artificial insemination (FTAI), melengestrol acetate (MGA®) supplementation (before FTAI in heifers and after artificial insemination in cows), vaccination against reproductive diseases, body condition score (BCS, on a 1-5 scale), month of last calving before FTAI, and estrus expression intensity. Data from 15,618 FTAI procedures conducted across three breeding seasons (October to February of 2016/2017, 2017/2018, and 2018/2019), were evaluated. Multiparous cows showed higher pregnancy rates (45%), compared with primiparous cows (39%) and heifers (29%) (p < 0.05). Pregnancy rates decreased with lower estrus expression scores (51% for score 3, 36% for score 2 and 27% for score 1). The month of last calving before FTAI, period of the day when FTAI was performed, DP4 removal day and vaccination against reproductive diseases did not affect pregnancy rates (p > 0.05). MGA® supplementation before FTAI increased pregnancy rates in heifers from 19 to 34% (p < 0.05). The use of DP4 affected pregnancy rates (p < 0.05); however, its reuse did not have a negative impact. Higher pregnancy rates for FTAI protocols were observed in multiparous cows, animals with high estrus intensity, and a BCS of 2.5 to 3.0. Administering at least 200 IU eCG and supplementing heifers with MGA® through 26th to 13th days before FTAI is recommended.

Presynchronization with a progesterone device and prostaglandin F2α enhances ovulatory response to first GnRH, estrus expression and tended to increase fertility in beef heifers submitted to a 5-day CO-Synch protocol

The main objectives of the present study were to determine the effects of presynchronizing with a 1.0 g intravaginal progesterone device (IVPD) and prostaglandin F2α and to assess the effects of re-utilization of IVPD in a 2x2 factorial design, on the ovulatory response to first GnRH, ovarian status at different protocol stages, estrus expression and fertility in beef heifers submitted to a 5d-CO-Synch + Progesterone (P4) protocol. Beef heifers (n = 564) were assigned to 1 of 2 treatments at D-15: Pres5 (n = 283), where heifers received a (IVPD) for 5 days and administration of prostaglandin F2α (25 mg of dinoprost) at D-10; and Control (n = 281), where heifers received no treatment. At D-8, all heifers received 100 μg of GnRH (gonadorelin acetate) and were assigned to 1 of 2 IVPD-use treatments: new-IVPD (n = 279), where animals received a new IVPD for 5 days, and once-used IVPD (n = 285), where heifers received a once-used IVPD for 5 days (used previously for 5 days). On D-3, IVPD was removed and 50 mg of prostaglandin F2α was administered. All heifers were timed artificially inseminated (AI; D0) 62 h after IVPD removal concomitant with an administration of 100 μg of GnRH. Estrus detection patches were placed on heifers at D-3 and evaluated at the time of AI. In a subset of heifers (n = 278), transrectal ultrasonography of the ovaries was carried out at D-8 and D-3 to assess presence and diameter of CL and largest follicle diameter (LFD). A blood sample was collected on D-3 to determine serum P4 concentration. Heifers with a once-used IVPD had a greater (P = 0.01) pregnancy per AI (P/AI) than heifers treated with a new-IVPD [62.8 % (179/285) vs 51.2 % (143/279)]. There was a lower percentage of animals (P = 0.002) having a corpus luteum (CL) on D-8 in Pres5 group compared to Control [16.4 % (22/134) vs 69.4 % (100/144)]. Similarly, a greater percentage of Pres5 heifers had a dominant follicle on D-8 (P < 0.0001) than Control heifers [97.7 % (131/134) vs 75.7 % (109/144)]. At D-3, Pres5 heifers had a greater ovulatory response to D-8 GnRH (P < 0.0001) compared to Control animals [82.8 % (111/134) vs 49.3 % (71/144)]. In addition, Pres5 heifers had a greater estrus expression behavior [87.6 % (248/283) vs 72.9 % (205/281); P < 0.0001] and tended to have (P = 0.10) a greater P/AI [61.8 % (175/283) vs 52.3 % (147/281)] than Control heifers. In conclusion, the tendency for a greater fertility observed in Pres5 heifers (∼10 %) justifies the extra animal handling required for presynchronization. A once-used IVPD represents a viable strategy to enhance P/AI and reduce the cost in beef heifers submitted to timed AI.

Follicular Dynamics and Pregnancy Rate in Nellore Heifers Submitted to Fixed-Time Artificial Insemination Protocols (FTAI)

This study aimed to evaluate follicular dynamics and pregnancy rates in Nellore heifers submitted to fixed-time artificial insemination (FTAI) protocols associated with equine chorionic gonadotrophin (eCG) or follicle stimulating hormone (FSH). Nellore heifers (n = 259) were used, divided into two studies. Experiment I evaluated the ovarian follicular dynamics in 64 Nellore heifers submitted to different FTAI protocols (n = 32/group) using either FSH or eCG. In Experiment II, the pregnancy rate was evaluated in 195 heifers submitted to FTAI protocols and divided into two groups: FSH (n = 97) and eCG (n = 98). In Experiment I, the ultrasound examination showed that the maximum diameter of the dominant and preovulatory follicles and the ovulation time were similar between the FSH and eCG groups (p > 0.05). However, the ovulation rate was higher in the eCG group when compared to FSH (p = 0.014). In Experiment II, females that received eCG presented a higher pregnancy rate (58.1%) when compared to FSH (40.2%) (p = 0.012). The use of eCG in the FTAI protocol in Nellore heifers promoted a higher ovulation rate and increased pregnancy rate and may be the most suitable alternative to increase conception rates in animals that are raised in an extensive system under tropical conditions in the Amazon.

Influence of Days after Calving and Thermal Stress on the Efficacy of a Progesterone-Based Treatment in Acyclic Italian Mediterranean Buffalo

Simple Summary

“Mozzarella di Bufala Campana DOP” (mozzarella cheese) is mainly produced and marketed during the spring and summer months. The buffalo is a seasonal species that increases its reproductive activity when daylight hours decrease. Therefore, to increase milk production in the favourable period, the so-called “Out of Breeding Season Mating” technique is applied. It consists of the interruption of sexual promiscuity during the naturally occurring breeding season and concentrating calving and milk production during periods of increasing daylight length. However, the application of this technique increases the incidence of anoestrus, as animals are forced to breed outside of their natural and favoured period of the year, although other factors can also increase the incidence of anoestrus, such as climate. A reduction of seasonal anoestrus can be achieved by using some hormonal treatments. In this study, primiparous acyclic buffaloes were selected and divided into three classes according to their days in milk. Animals were synchronized using P₄ vaginal implants, and artificial insemination (AI) was performed according to protocol. The temperature–humidity index (THI) was recorded to evaluate its influence on anoestrus. Statistical analysis showed that the implemented P₄-based treatments were highly effective in removing the anoestrus condition in buffaloes. On the contrary, no influence of the THI on the efficacy of the P₄ synchronization treatment was observed.

Abstract

The aim of this study was to evaluate the efficacy of a progesterone-based treatment on anoestrus in buffaloes. Primiparous acyclic buffaloes (n = 276), were divided into three classes according to their days in milk (DIM): from 50 to 90 (Class I; n = 86), from 91 to 150 (Class II; n = 102) and from 150 to 200 (Class III; n = 88). Animals were synchronized using P₄ vaginal implants, followed by timed artificial insemination (TAI). They were then allowed to enter into a larger group of buffaloes for natural mating 15 days after AI was performed, and pregnancy status was monitored from then on at 15-day intervals. Finally, the temperature–humidity index (THI) was calculated. Statistical analysis was performed by ANOVA by means and both multiple and linear regression. The total pregnancy rate (PR) was 87.7%, with no differences among DIM classes (88.0, 92.4, and 80.0% in Classes I, II, and III, respectively). However, the PR at TAI tended to be higher (p = 0.07) in buffaloes in Class II. The follicle (FL) area in Class II buffaloes was larger (p < 0.01) than that of the other classes. No influence of the THI on the total PR was recorded. The pregnancy outcome at TAI was affected by the FL area (odds ratio = 2.237; p < 0.05) and body condition score (BCS) (odds ratio = 1.256; p < 0.05). In conclusion, treatment with vaginal P₄ optimizes pregnancy rates in anoestrus buffaloes, particularly when the animals are in mid-lactation and show an optimal BCS. Furthermore, the THI does not seem to affect the efficiency of the progesterone treatment.

Relationships between antral follicle count, body condition, and pregnancy rates after timed-AI in Bos indicus cattle

An experiment was performed to evaluate the association between the antral follicle count (AFC) plus body condition score (BCS) and the pregnancy rate in Bos indicus undergoing timed artificial insemination (TAI). A total of 736 Nelore cows with BCSs ranging from 2 to 4 received a conventional protocol for TAI. On a random day of the estrous cycle (Day 0), all cows received an intravaginal P4 device and an intramuscular (i.m.) injection of 2.0 mg estradiol benzoate. On Day 8, the P4 device was removed, and 150 μg sodium D-cloprostenol, 300 IU equine chorionic gonadotrophin and 1.0 mg estradiol cypionate were administered by i.m. injection. TAI was performed 48 h after P4 device removal, and pregnancy diagnosis was performed by ultrasonography after 30 days. On Day 0, all cows were examined by ultrasonography to determine the AFC by counting the number of follicles >3 mm in diameter that were present in both ovaries and to evaluate the BCS (scale of 1-5). The cows were then classified based on their AFCs as those with low (≤10 follicles), intermediate (11-29 follicles) and high AFC (≥30 follicles). Furthermore, cows were classified as having low (≥2.0 to ≤ 2.9) and high (≥3.0 to ≤ 4.0) BCSs. The AFCs and BCSs were analyzed using the generalized linear model, and the pregnancy rate was assessed with the binary logistic regression model (P ≤ 0.05). The pregnancy rate was influenced (P < 0.05) by AFC and BCS classification and by interactions (P = 0.034) between these factors. Cows with a low AFC exhibited higher a pregnancy rate than did cows with a high or an intermediate AFC (57.7% ^a, 47.9% ^b and 49.7% ^b, P = 0.008). Low BCS resulted in a higher pregnancy rate than did high BCS (55.2% vs. 50.4%, P = 0.008). Cows with a high BCS and a low AFC had a higher pregnancy rate (P < 0.05) than did those with a high BCS and an intermediate or a high AFC (59.8%^a, 48.0%^b, and 38.0%^b, respectively). An interaction (P < 0.05) was observed between the AFC and BCS, and the pregnancy rate decreased significantly in cows with an AFC > 30 and a BCS between 3 and 4. In conclusion, AFC and BCS classifications influence the pregnancy rate of Bos indicus beef cattle subjected to TAI. In addition, an important interaction between these factors was observed, namely, the lowest pregnancy rates were found in cows with high BCSs and high AFCs.

Effect of oestrous resynchronization on the reproductive efficiency of zebu cows

The aim of this study was to develop a resynchronization strategy before the return of oestrus in cows diagnosed as not pregnant after fixed-time artificial insemination (TAI). A total of 839 cows, approximately 45 days post-partum, were synchronized using TAI. On day 0, intravaginal progesterone-releasing devices were inserted and 2 mg of oestradiol benzoate was administered. Eight days later (D8), the progesterone-releasing devices were removed and oestradiol cypionate (0.5 mg, eCG [300 IU]) and prostaglandin (7.5 mg) were administered. All cows were inseminated between 48 and 56 hr after device removal (D10). Thirty days after TAI, cows that were not diagnosed as pregnant by ultrasound were immediately resynchronized and again inseminated at a fixed time. The hormonal protocol used in the first and second rounds of TAI was the same. The pregnancy rate after the first TAI was 52%, and after the second TAI, it was 49%. The increase in the total pregnancy rate (synchronization + second oestrous synchronization) compared to a single synchronization was 23.5%. In conclusion, resynchronization of oestrus and ovulation in zebu cows that had previously undergone TAI protocols is effective in increasing the reproductive efficiency.