Effect of body condition on reproductive efficiency of lactating dairy cows receiving a timed insemination

Body condition may influence pregnancy rates to a timed insemination (Ovsynch/TAI) protocol and affect the economical performance of dairy farms. The objectives were to compare pregnancy rates using the Ovsynch/TAI protocol for the first service of lactating dairy cows with body condition scores < 2.5 (scale: 1 to 5, low BCS group) versus > or = 2.5 (control group) and to estimate the economic impact of the effect of body condition on reproductive performance. At 63 +/- 3 d post partum, cows were assigned to 2 experimental groups (low BCS = 81; control = 126), and were treated with GnRH at d 0 and with PGF2alpha 7 d later. At 48 h after PGF2alpha, cows received an injection of GnRH and were inseminated 16 h later. Pregnancy rates to the Ovsynch/TAI protocol were lower for the low BCS group than for the control group at 27 d (18.1 +/- 6.1% < 33.8 +/- 4.5%; P<0.02) and at 45 d (11.1 +/- 5.4% < 25.6 +/- 4.1%; P<0.02) after insemination. Economic analysis indicated that reducing the percentage of the herd in low body condition increases net revenues per cow per year. Body condition influenced pregnancy rates to the Ovsynch/TAI protocol.     

Strategic use of gonadotrophin-releasing hormone (GnRH) to increase pregnancy rate and reduce pregnancy loss in lactating dairy cows subjected to synchronization of ovulation and timed insemination

The objective of this study was to determine the effect of GnRH (100 microg i.m.) treatment 5 and 15 days after timed insemination (TAI) on pregnancy rate and pregnancy loss in lactating dairy cows subjected to synchronization of ovulation. The study included 831 lactating dairy cows subjected to a Presynch-Ovsynch protocol for first service. On the day of TAI (Day 0), cows were randomly assigned to one of four experimental groups. Cows in Group 1 (n = 214) were treated with GnRH on Day 5; cows in Group 2 (n = 209) were treated with GnRH on Day 15; cows in Group 3 (n = 212) were treated with GnRH on both Day 5 and Day 15; cows in Group 4 (n = 196) were not treated. Pregnancy rate was evaluated at Day 27 and Day 45 after TAI. The interestrus interval and the proportion of cows diagnosed not pregnant based on expression of estrus and insemination before pregnancy diagnosis on Day 27 were determined. The results of this study are: (1) GnRH treatment on Day 5 or Day 15 did not increase pregnancy rate, or reduce pregnancy loss between Day 27 and Day 55 after TAI; (2) cows treated with GnRH on both Day 5 and Day 15 had a lower (P < 0.01) proportion of cows diagnosed not pregnant based on expression of estrus before ultrasonography on Day 27 (26.5%) compared to control cows (52.9%), and these cows had an extended (P = 0.05) interestrus interval (23.4 days vs. 21.5 days); and (3) GnRH treatment on both Day 5 and Day 15 after TAI reduced pregnancy rate on Day 27 (36.8% vs. 44.4% for control cows; P < 0.03) and Day 55 (28.3% vs. 36.2% for control cows; P < 0.01). Therefore, strategies to stimulate CL function using multiple doses of GnRH during the luteal phase need to consider potential negative effects.     

Timed artificial insemination plus heat I: effect of estrus expression scores on pregnancy of cows subjected to progesterone–estradiol-based protocols

Expression of estrus near timed artificial insemination (TAI) is associated with greater fertility, and estrus detection could improve TAI fertility or direct TAI management, although accurate estrus detection can be difficult and time-consuming using traditional methods. The aim of this study is to evaluate influence of estrus on pregnancy (artificial insemination pregnancy rates (P/AI)) and to validate an alternative method to classify estrus/heat expression using tail chalking (HEATSC) in postpartum Bos indicus cows subjected to TAI in progesterone–estrogen-based protocols. In experiment 1 (Exp. 1), cows (5491) were subjected to visual observation of estrus after progesterone device removal, before TAI, and P/AI was evaluated according to estrus and body condition score (BCS). Cows received a progesterone device and 2 mg estradiol benzoate (EB). After 8 days, the device was removed and 150 μg of d-cloprostenol and 300 IU equine chorionic gonadotrophin was given. Later, animals in Exp. 1 received 1 mg EB and TAI 44 to 48 h. In the Exp. 2 – 3830 cows using similar protocol, received different ovulation inducers: 1 mg EB (n=1624) or 1 mg estradiol cypionate (EC; n=2206) on day 8 (D8). Cows were then marked with chalk, and HEATSC evaluated at TAI on D10 (HEATSC1 – no chalk removal=no estrus expression; HEATSC2 – partial chalk removal=low estrus expression; HEATSC3 – near complete/complete chalk removal=high estrus expression). In Exp. 1, cows showing estrus presented greater P/AI (48.4% v. 40.2%, P<0.05). In Exp. 2, P/AI (HEATSC1 – 40.0%; HEATSC2 – 49.7%; HEATSC3 – 60.9%; P<0.001), and larger follicle timed artificial insemination (LFTAI) (<0.001) varied according to HEATSC. There was no difference in P/AI (P=0.41) or LFTAI (P=0.33) according to ovulation inducer. Cows with greater BCS showed greater P/AI in both experiments (P<0.05). Estrus presence and greater HEATSC improved P/AI, and EC v. EB used promoted differential estrus manifestation (cows showing HEATSC2 and HEATSC3: 79.5% with EB v. 69.98% with EC use, P<0.001), however, with similar P/AI. The use of HEATSC in B. indicus cows subjected to TAI is useful to identify cows with greater estrus expression and consequently improved pregnancy rates in TAI, allowing the cows with low HEATSC to be targeted for additional treatments aimed at improving P/AI.     

Effect of one or three timed artificial inseminations before natural service on reproductive performance of lactating dairy cows not observed for detection of estrus

The objectives were to determine the effects of one or three timed artificial insemination (AI) before natural service (NS) in lactating dairy cows not observed for detection of estrus on hazard of pregnancy, days nonpregnant, and 21-days cycle pregnancy rate. A total of 1050 lactating Holstein cows were subjected to a double Ovsynch program for their first postpartum AI. On the day of first AI (78 ± 3 days in milk), cows were blocked by parity and randomly assigned to receive either one timed AI (1TAI, n = 533) or three timed AI (3TAI, n = 517) before being exposed to NS. Cows assigned to 1TAI were exposed to bulls 7 days after the first AI. Nonpregnant cows in 3TAI were resynchronized with the Ovsynch protocol supplemented with progesterone twice, with intervals between AI of 42 days, before being exposed to NS 7 days after the third AI. Cows were evaluated for pregnancy 32 days after each timed AI, or every 28 days after being exposed to NS. Pregnant cows were re-examined for pregnancy 28 days later (i.e., 60-day gestation). Exposure to heat stress was categorized based on the first AI being performed during the hot or cool season, according to the temperature-humidity index. Body condition was scored at first AI. All cows were allowed a period of 231 days of breeding, after which nonpregnant cows were censored. Pregnancy to the first AI did not differ between 1TAI and 3TAI on Day 60 after insemination (30.8 vs. 33.5%). Cows receiving 3TAI had a 15% greater hazard of pregnancy and a 17% greater 21-days cycle pregnancy rate than 1TAI and these benefits originated from the first 84 days of breeding. These changes in rate of pregnancy reduced the median and mean days nonpregnant by 9 and 10 d, respectively. Despite the long inter-AI interval in cows subjected to 3TAI, reproductive performance was improved compared with a single timed AI and subsequent exposure to NS. In dairy herds that use a combination of AI and NS, allowing cows additional opportunities to AI before onset of breeding with bulls is expected to improve reproductive performance.     

Reproductive responses following postpartum suppression of ovarian follicular development with a deslorelin implant during summer heat stress in lactating dairy cows

The objective was to evaluate pregnancy rate to a timed artificial insemination (TAI) protocol in the autumn for cows treated with a non-degradable GnRH agonist implant (Deslorelin [DESL], 5mg) during the summer heat stress period compared with non-treated controls (CON). Cows were randomly assigned to receive or not a DESL implant within 1-4 days postpartum (dpp) twice weekly, from 25 June through 8 August 2001. All cows in DESL implant and CON treatments were injected with PGF(2alpha) 7 days after enrollment. Ultrasonography (US) monitored numbers of ovarian follicles and corpus luteum (CL) at approximately 10, 30, 35/36, 45/44, 56/55 and 66/63dpp, while DESL implants were in situ and concurrently CON, respectively. DESL implants were removed at two specific days, 28 August and 4 September. Cows had DESL implant in situ for a range of 28-67 days, depending on date of enrollment and implant removal. Within 61-100dpp, 31 days after implant removal, DESL implant and CON cows were initiated in a Presynch-Ovsynch and TAI protocol. Pregnancy was evaluated by US and palpation per rectum at 28 and 46 days after TAI, respectively. Plasma concentrations of progesterone were analyzed for sets of blood samples collected during the Presynch-Ovsynch and at TAI day followed 8 days later. Cows in the DESL-implant treatment had more (P<0.01) Class 1 (3-5mm) follicles, less (P<0.01) Class 2 (6-9mm), Class 3 (> or =10mm) follicles and CL compared with CON cows. Proportion of cows having initiated estrous cycles after calving was less (P<0.01) in the DESL-implant treatment (52.2%, 58/111) compared with CON (93.7%, 104/111) at the beginning of Ovsynch. Pregnancy rate to TAI was less (P<0.01) in the DESL implant (27.5%, 33/120) compared with CON (53.9%, 69/128). Pregnancy rate to TAI was less (P<0.01) in DESL-implanted cows that had initiated estrous cycles after calving (30.6%, 19/62) compared with CON (53.7%, 65/121) cows having initiated estrous cycles after calving. Furthermore, pregnancy rate was less (P<0.01) for cows having ovulations that had initiated estrous cycles after TAI in the DESL implant (39.1%, 18/46) compared with CON (62.1%, 54/87) treatments. Pregnancy losses from day 28 to day 46 of pregnancy did not differ between DESL implant (15.1%, 5/33) and CON (13.0%, 9/69) treatments. The DESL implant induced a delay in initiation of a new wave of follicular development during the postpartum-heat stressed period. The lesser pregnancy rate in the DESL-implant treatment group may be due to a pool of heat stress damaged follicles that were depleted in the control group with re-occurring follicle waves.     

Factors affecting pregnancy loss from gestation Day 38 to 90 in lactating dairy cows from a single herd

The present study was designed to establish whether factors such as previous estrus synchronization, corpus luteum and embryo number at the time of pregnancy diagnosis, changes in body condition score, milk production, clinical disease (mastitis or lameness) and the inseminating bull affect pregnancy loss from 38 to 90 days of gestation. We derived data from 601 pregnant lactating dairy cows from a single herd. Pregnancy diagnosis was performed by ultrasonography between Day 38 and 44 following insemination. We also recorded corpus luteum and embryo number at this time. Pregnancy loss was defined as a negative pregnancy diagnosis on the second palpation per rectum undertaken between 90 and 96 days after insemination. Data were analyzed using multiple logistic regression methods. Cows that had an additional corpus luteum were eight times less likely to miscarry. The risk of pregnancy loss was 3.1 times higher in cows bearing twins. A one unit reduction in body condition score from previous partum to 30 days postpartum resulted in a 2.4-fold increase in pregnancy loss. We noted a higher incidence of pregnancy loss in cows inseminated using semen from one of the six bulls used. This particular bull led to a 3.4-fold increase in the rate of pregnancy loss. Logistic regression analysis showed no significant effects of previous estrus synchronization, milk production, clinical disease, body condition at previous partum or at pregnancy diagnosis, or body condition change between previous partum and pregnancy diagnosis. Our findings indicate a positive relationship between the presence of an additional corpus luteum and the maintenance of gestation. Risk factors for pregnancy loss were twin pregnancy, reduced body condition after previous parturition and the inseminating bull.     

Use of AI technician scores for body condition, uterine tone and uterine discharge in a model with disease and milk production parameters to predict pregnancy risk at first AI in Holstein dairy cows

Technicians recorded body condition score (BCS) and several parameters related to estrus and/or metritis for 1694 first insemination cows on 23 farms. Additional variables for modeling the adjusted odds ratios (OR) for pregnancy were data on disease prior to or within 21 days of AI and test day milk yields. Significant predictors for pregnancy were farm, year and season, BCS, uterine tone, contaminated insemination gun after AI, fat-protein corrected kilograms milk (FPCM), days in milk (DIM), and diseases. Vaginal mucus, ease of cervical passage, and lameness were not significant predictors for pregnancy. Pregnancy risk at AI increased with increasing DIM, reaching a near optimum after 82 days. Lack of uterine tone was associated with a lowered pregnancy risk (OR = 0.69) as was contaminated insemination gun (OR = 0.67), first-parity lactation, FPCM >33 kg (OR = 0.71), BCS 2.5 at AI (OR = 0.65), clinical mastitis (OR = 0.53), cystic ovarian disease (OR = 0.53), and metritis (OR = 0.74). It was concluded that data on BCS and uterine findings, as collected by AI technicians, are significant predictors of AI outcome. Dairy producers and veterinarians should jointly examine the potential costs and value of such AI technician-based data to improve herd fertility.     

Risk factors for resumption of postpartum estrous cycles and embryonic survival in lactating dairy cows

The objectives of this study were to evaluate factors associated with resumption of postpartum estrous cycles and embryonic survival in lactating dairy cows. Holstein cows, 6396 from four dairy farms were evaluated to determine the relationships among parity, body condition score (BCS) at calving and at AI, season of year when cows calved, and milk yield on resumption of postpartum estrous cycles by 65 days postpartum, and all the previous variables, estrual or anestrus and AI protocol on conception rates and embryonic survival at the first postpartum insemination. Cows had their estrous cycle pre-synchronized with two PGF_2α injections given 14 days apart and were inseminated between 69 and 82 days postpartum following either an estrous or ovulation synchronization protocol initiated 12–14 days after the presynchronization. Blood was sampled and analyzed for progesterone twice, 12–14 days apart, to determine whether cows had initiated onset of estrous cycles after calving. Cows were scored for body condition in the week after calving, and again at AI, between 69 and 82 days postpartum. Pregnancy was diagnosed at 30 ± 3 and 58 ± 3 days after AI. Farm influenced all reproductive outcomes evaluated. More (P < 0.0001) multiparous than primiparous cows had initiated estrous cycles. Onset of estrous cycles was also influenced (P < 0.01) by BCS at calving and at AI, BCS change, season, and milk yield. More (P < 0.001) cows that had initiated estrous cycles than anestrous cows were pregnant at 30 and 58 days after AI, but anestrus did not affect pregnancy loss. Conception rates were also influenced (P < 0.01) by parity, BCS at calving and AI, BCS change, and season; however, milk yield and insemination protocol were not associated with conception rates at 30 and 58 days after AI. Factors that reduced conception rate on day 30 after AI also increased pregnancy loss between 30 and 58 days of gestation. Improving BCS at calving and AI, minimizing losses of BCS after calving, and hastening onset of estrous cycles early postpartum are all expected to increase conception because of enhanced embryonic survival.     

Fertility-associated antigen on Nelore bull sperm and reproductive outcomes following first-service fixed-time AI of Nelore cows and heifers

The objective was to determine whether the presence of fertility-associated antigen (FAA) on sperm collected from Nelore (Bos indicus) bulls can be used to assess potential fertility of sperm for use at first-service fixed-time AI (TAI). Six Nelore bulls were selected based on FAA status (FAA-negative: N = 3; FAA-positive: N = 3) and the ability to produce neat semen with ≥ 70% morphologically normal sperm and 60% estimated progressive motility before cryopreservation. In Experiment 1, suckled multiparous Nelore cows (N = 835) were evaluated for body condition score (BCS) and received an intravaginal progesterone device (CIDR) and 2.0 mg of estradiol benzoate (Day 0). On Day 9 the CIDR was removed, 12.5 mg of PGF_2α and 0.5 mg of estradiol cypionate were administered, and calves were removed for 48 h. All cows received TAI on Day 11 (48 h after CIDR removal). Pregnancy per TAI (P/TAI) was not different between FAA-positive and FAA-negative bulls (41.5% vs. 39.3%, respectively). There was an effect of AI technician on P/TAI (36.0% vs. 43.9%; P < 0.05) and BCS tended to affect P/TAI (P = 0.09), as cows with BCS ≥ 2.75 were 1.4 times more likely to become pregnant compared with cows with BCS < 2.75. In Experiment 2, nulliparous Nelore heifers (N = 617) were evaluated for BCS and received a CIDR and estradiol benzoate (2.0 mg) on Day 0. On Day 7, all heifers received PGF_2α (12.5 mg). On Day 9, CIDR inserts were removed and all heifers received estradiol cypionate (0.6 mg) and 200 IU eCG. All heifers received TAI on Day 11 (48 h after CIDR removal). Pregnancy/TAI was different (P = 0.04) between FAA-positive and FAA-negative bulls (33.7% vs. 40.7%, respectively). Presence of FAA on sperm was unsuccessful in assessing the potential fertility of sperm for use in TAI.     

Factors affecting conception and expression of oestrus in anoestrous cows treated with progesterone and oestradiol benzoate

Nutrient balance affects the resumption of ovarian cyclic activity following calving in dairy cattle. However, few data are available about the relationships between nutrient balance and expression of oestrus or conception. It was hypothesised that previously anoestrous cows that conceived to first insemination and cows that expressed oestrus at the subsequent expected return to oestrus would be less likely to be in negative energy balance (i.e. would have higher body condition score, higher glucose, insulin-like growth factor (IGF), leptin or insulin concentrations, and lower non-esterified fatty acids (NEFA), blood urea nitrogen (BUN), beta hydroxy butyrate (BOH) concentrations 12-15 days after insemination) than herd mates not conceiving or expressing oestrus. Anoestrous cows were treated with progesterone and oestradiol benzoate (Day 0 = end of treatment period) and retrospectively categorised as conceiving (n = 108) or not conceiving (n = 108) to insemination. A subset of cows not conceiving to insemination were categorised as expressing (n = 44) or not expressing (n = 44) oestrus between Days 14 and 28 after initial insemination. Cows conceiving had a lower NEFA concentration (P = 0.014) than non-conceiving cows. Cows subsequently detected in oestrus had higher body condition scores (P = 0.016), IGF concentrations (P = 0.008) and milk protein percentages (P = 0.038), and lower BOH concentrations (P = 0.018) than cows not expressing oestrus. No difference in concentrations of leptin, insulin, glucose, blood urea nitrogen or milk yield were found between cows conceiving or not conceiving and those detected in oestrus or not detected in oestrus (P > 0.1). It is concluded that some measures of metabolic status at the time of pregnancy recognition affects the probability of pregnancy and of subsequent expression of oestrus in those treated, anoestrous cows not conceiving.     

Inferences of body energy reserves on conception rate of suckled Zebu beef cows subjected to timed artificial insemination followed by natural mating

The influence of body condition score (BCS), rump fat thickness (RFAT), and live weight (LW), and the changes in these parameters during the interval from 165 of prepartum (i.e., 125 days of prior gestation) to 112 postpartum on first service conception and pregnancy rates were investigated in suckled Zebu (Bos indicus) beef cows (n = 266) subjected to timed artificial insemination (TAI) followed by natural mating. The aforementioned parameters were recorded at 165 ± 14 days (mean ± standard error) prepartum (concurrent with the weaning of previous calf), at parturition, and at 42 ± 7 days (at the onset of the synchronization of ovulation protocol), 82 ± 7 days (30 days after TAI), and 112 ± 7 days (60 days after TAI) postpartum. At the start of the breeding season (BS), cows were subjected to a synchronization of ovulation program for TAI. Bulls were placed with cows 10 days after TAI and remained until the end of the study (112 days postpartum). Cows with the highest BCS at parturition had an increased probability of first service conception rate at 60 days after TAI (P = 0.02) and a reduced probability of occurrence of pregnancy loss (P = 0.05). Also, cows had a greater likelihood of conceiving postpartum if they had greater RFAT and BCS at 165 ± 14 days prepartum (P = 0.01 and P = 0.03, respectively) and at parturition (P = 0.0007 and P = 0.003, respectively). Cows that had an increase in RFAT and BCS during the dry period (i.e., interval from weaning of the previous calf to parturition) also had a greater likelihood of conceiving (P = 0.03 and P = 0.06, respectively) during the BS. Among the different time points, RFAT and BCS at parturition had the largest impact on risk of conception during the BS. The LW was a poor predictor of conception during the BS (P = 0.11–0.68) except for LW at 165 ± 14 days prepartum (P = 0.01). Collectively, the findings indicated that the likelihood of conception during the BS was highest in cows that had an improvement in RFAT and BCS during the dry period. Therefore, assuring a good nutritional status in the dry period (BCS ≥ 3.0 at 165 ± 14 days prepartum and ≥3.25 at parturition) is an important aim to optimize the postpartum conception rate of suckled Zebu beef cows subjected to TAI followed by natural mating.     

Effect of presynchronization strategy before Ovsynch on fertility at first service in lactating dairy cows

The aim of this study was to evaluate the effect of presynchronization with or without the detection of estrus on first service pregnancy per artificial insemination (P/AI) and on Ovsynch outcome in lactating dairy cows. A total of 511 cows were divided randomly but unevenly into 3 treatment groups at 44 to 50 days in milk (DIM). Ovsynch was started at the same time (69 to 75 DIM) in all three groups. Cows in the Ovsynch group (CON, N = 126) received no presynchronization before Ovsynch, and all cows were bred by timed AI (TAI). Cows in the presynchronization with estrus detection (PED) and the presynchronization with only TAI (PTAI) groups received two doses of prostaglandin F_2α (PGF) 14 days apart, starting at 44 to 50 DIM. Ovsynch was initiated 11 days after the second PGF treatment. Cows in the PED group (N = 267) received AI if estrus was detected after either PGF injection. Cows that were not determined to be in estrus after PGF injection received Ovsynch and TAI. Cows in the PTAI group (N = 118) were not inseminated to estrus, with all cows receiving TAI after Ovsynch. The ovulatory response to the first GnRH injection administered as part of Ovsynch differed (P = 0.002) among treatment groups (83.1% in PTAI, 72.6% in PED, and 62.7% in CON). However, the ovulatory response to the second injection of GnRH during Ovsynch did not differ among treatment groups. Of the 267 PED cows, a total of 132 (49.4%) exhibited estrus and were inseminated. The P/AI at the 31-day pregnancy diagnosis was similar between the cows in the PED group with AI after estrus detection (37.9%; 50/132) and those bred with TAI (34.1%; 46/135). The P/AI in the CON group (46.8%; 59/126) was greater (P < 0.05) than that in the PED group (36.0%; 96/267). In addition, the P/AI in the CON group was greater (P = 0.04) than that in the PED cows receiving TAI (34.1%; 46/135) but less than that in the PED cows bred to estrus (37.9%; 50/132) (P = 0.16). At the 31-day pregnancy diagnosis, the cows in the PTAI group had greater P/AI (55.9%; 66/118) than both those in the PED group (P < 0.01; either estrus or TAI) and those in the CON group (P = 0.08). Thus, presynchronization with PGF (PTAI) increased the ovulatory response to Ovsynch and improved P/AI in dairy cows. Interestingly, the breeding of cows to estrus during presynchronization reduced fertility to the TAI and overall fertility, including cows bred to estrus and TAI. These results indicate that maximal fertility is obtained when all cows receive TAI after the presynchronization protocol.     

Relationship of parity and body condition score to pregnancy rates in Florida beef cattle

Pregnancy rates, determined by per rectum palpation, were analyzed with respect to cow parity (range 1 to >8 calvings) and body condition score (BCS, 1=thin to 9=fat) at pregnancy examination for 3734 beef cattle females on 3 commercial beef operations (8 herds) in 3 Florida counties in 1989 and 1990. The means and standard deviations for the herds were the following: pregnancy rate, 81.3 +/- 39% (range 62.1 to 91.5%); BCS, 4.7 +/- 0.6 (range 4.3 to 4.9); and parity, 3.9 +/- 2.3 (range 2.8 to 4.8). Significant associations were found between pregnancy rate, parity, BCS and herd (P < 0.001); and between the variable interactions, parity with BCS, herd with BCS, and herd with parity (P < 0.001). Cows with a BCS /=5 had a pregnancy rate of 90%. Cows having a parity of <4 had a PR of 80%, while cows having a parity >/=4 had a PR of 85%. The interaction of parity with BCS was significant, resulting in pregnancy rates as follows; parity <4 and BCS /= 5 was 88%; parity >/=4 and BCS /=5 and BCS >/= 5 was 93%. Body condition, parity, and the interaction of body condition and parity play important roles in the reproductive performance of commercial beef cows in Florida.     

Pregnancy rates to timed artificial insemination in dairy cows treated with gonadotropin-releasing hormone or porcine luteinizing hormone

We compared the effects of porcine luteinizing hormone (pLH) versus gonadotropin-releasing hormone (GnRH) on ovulatory response and pregnancy rate after timed artificial insemination (TAI) in 605 lactating dairy cows. Cows (mean ± SEM: 2.4 ± 0.08 lactations, 109.0 ± 2.5 d in milk, and 2.8 ± 0.02 body condition score) at three locations were assigned to receive, in a 2 × 2 factorial design, either 100 μg GnRH or 25 mg pLH im on Day 0, 500 μg cloprostenol (PGF) on Day 7, and GnRH or pLH on Day 9, with TAI 14 to 18 h later. Ultrasonographic examinations were performed in a subset of cows on Days 0, 7, 10, and 11 to determine ovulations, presence of corpus luteum, and follicle diameter and in all cows 32 d after TAI for pregnancy determination. In 35 cows, plasma progesterone concentrations were determined 0, 3, 4, 5, 6, 7, and 12 d after ovulation. The proportion of noncyclic cows and cows with ovarian cysts on Day 0 were 12% and 6%, respectively. Ovulatory response to first treatment was 62% versus 44% for pLH and GnRH and 78% versus 50% for noncyclic and cyclic cows (P < 0.01). Location, ovulatory response to first pLH or GnRH, cyclic status, presence of an ovarian cyst, and preovulatory follicle size did not affect pregnancy rate. Plasma progesterone concentrations after TAI did not differ among treatments. Pregnancy rate to TAI was greater (P < 0.01) in the GnRH/PGF/pLH group (42%) than in the other three groups (28%, 30%, and 26% for GnRH/PGF/GnRH, pLH/PGF/GnRH, and pLH/PGF/pLH, respectively). Although only 3% of cows given pLH in lieu of GnRH on Day 9 lost their embryo versus 7% in those subjected to a conventional TAI using two GnRH treatments, the difference was not statistically significant. In summary, pLH treatment on Day 0 increased ovulatory response but not pregnancy rate. Cows treated with GnRH/PGF/pLH had the highest pregnancy rate to TAI, but progesterone concentrations after TAI were not increased. In addition, preovulatory follicle diameter did not affect pregnancy rate.     

Hormonal induction of ovulation and artificial insemination in suckled beef cows under nutritional stress

The objective was to develop a program for inducing estrus (followed by insemination) of suckled beef cows under nutritional stress (poor body condition). A total of 123 cows, from 60 to 75 days postpartum, were classified according to their body condition score (BCS; range from 1 to 5, in increments of 0.5) and allocated into two groups. On Day 0 (without regard to stage of the estrous cycle), cows (n = 59) in the hormone induction (HI) treatment group were given an intravaginal device (IVD) containing 250 mg of medroxiprogesterone acetate (MAP) and an i.m. injection of 2.5 mg estradiol benzoate (EB). On Day 6, these cows were given 500 IU eCG i.m. and calves were weaned for 96 h. The IVD were removed on Day 7. Cows detected in estrus by 45 h after IVD removal were inseminated 12 h after standing estrus; cows not in estrus by 45 h after IVD removal received an i.m. injection of 100 microg gonadorelin (GnRH) and were inseminated 16-18 h later. In the control group (C), cows (n = 64) only had their calves weaned at Day 6 (for 96 h), with estrus detection and AI from Days 6 to 11. Overall, the BCS ranged from 2.0 to 3.0. In the treatment group, estrus and pregnancy rates in cows with BCS 2.0 (20 and 30%, respectively) was lower (P < 0.05) than those with BCS 3.0 (50 and 66.6%, respectively), but did not differ (P > 0.05) from BCS 2.5 (23.3 and 47.6%). In C group, only 2 of 66 cows were detected in estrus and bred (neither was pregnant). In conclusion, the program for induction of ovulation using MAP, EB, eCG and GnRH increased the pregnancy rate in beef cows in poor body condition, enabling AI to be done in a 63-h interval.     

Incorporation of a rapid pregnancy-associated glycoprotein ELISA into a CIDR-Ovsynch resynchronization program for a 28 day re-insemination interval

The objective was to compare two resynchronization programs; one that used a blood-based ELISA for pregnancy-associated glycoproteins (PAG) for pregnancy diagnosis so that non-pregnant cows were re-inseminated at 28 d after first TAI, and another that used transrectal ultrasonography for pregnancy diagnosis so that non-pregnant cows were re-inseminated at 35 d after first TAI. The PAG_resynch cows (n = 103) began CIDR-Ovsynch resynchronization on Day 18 after first TAI (Day 0). On Day 25, the CIDR was removed and pregnancy diagnosis with a PAG ELISA was performed. If a cow was not pregnant on Day 25, she was treated with PGF_2α, treated with GnRH 2 d later (Day 27), and TAI on Day 28. Control cows (n = 99) were observed for estrus until Day 25, when they began an identical CIDR-Ovsynch program with pregnancy diagnosis by transrectal ultrasonography on Day 32. If a cow was not pregnant on Day 32, then she was treated with PGF_2α, treated with GnRH 2 d later (Day 34), and TAI on Day 35. There was no difference in pregnancy per AI (P/AI) for either group at first or second insemination. For cows without pregnancy loss, the interval between first and second (P < 0.001) or second and third (P < 0.016) TAI was shorter for PAG_resynch cows compared with Control cows. The interval between first and second or second and third TAI was not different if pregnancy loss cows were included in the analysis. Plasma progesterone concentrations were similar at PGF_2α treatment, and plasma estradiol concentrations increased similarly after PGF_2α treatment for PAG_resynch and Control cows. In conclusion, the 28 d CIDR-Ovsynch resynchronization protocol was comparable to a 35 d CIDR-Ovsynch resynchronization protocol that also included estrus detection. Shortened resynchronization protocols that do not require estrus detection may improve reproductive efficiency in dairy cattle.     

Resynchronization of ovulation and timed insemination in lactating dairy cows III. Administration of GnRH 23 days post AI and ultrasonography for nonpregnancy diagnosis on day 30

The objective was to compare pregnancy rates to resynchronization and timed AI (TAI) protocols in lactating dairy cows that received GnRH at 23 d and were diagnosed not pregnant at 30 d after the pre-enrollment AI. Nonpregnant cows (624) at ultrasonography on day 30 (study day 0) were classified as diestrus (74.8%), metestrus (5.6%) and without a CL (19.5%). Cows in diestrus were assigned either to the GnRH group (PGF2alpha on day 0, GnRH on day 2 and TAI 16 h later, n = 238) or the estradiol cypionate (ECP) group (PGF2alpha on day 0, ECP on day 1, and TAI 36 h later, n = 229). Cows in metestrus were assigned to the Modified Heatsynch Group (GnRH on day 0, PGF(2alpha) on day 7, ECP on day 8 and TAI on day 9, n = 35). Cows without a CL (n = 122) were classified either as proestrus (10.6%), ovarian cysts (7.5%) or anestrus (1.4%), and assigned to factorial treatments (i.e., use of GnRH versus CIDR) to either the GnRH group (GnRH on day 0, PGF2alpha on day 7, GnRH on day 9 and TAI 16 h later, n = 28), the CIDR group (CIDR insert from days 0 to 7, PGF2alpha on day 7, GnRH on day 9 and TAI 16 h later, n = 34), the GnRH + CIDR group (GnRH on day 0, CIDR insert from days 0 to 7, PGF2alpha on day 7, GnRH on day 9 and TAI 16h later, n = 32), and the control group (PGF2alpha on day 7, GnRH on day 9 and TAI 16 h later, n = 28). For cows without a CL, plasma P4 concentrations were determined on days 0, 7, 10 and 17 and ovarian structures determined on days 0, 7 and 17. Pregnancy rates were evaluated at 30, 55 and 90 d after the resynchronized AI. For cows in diestrus, there were no differences in pregnancy rates on days 30, 55 and 90 for cows in the GnRH (27.5, 26.5 and 24.2%) or ECP (29.1, 25.5 and 24.1%) groups. In addition, there were no differences in pregnancy losses between days 30 and 55 and 55 and 90 between the GnRH (7.0 and 8.6%) and ECP (9.8 and 5.4%) groups. For cows without a CL, GnRH on day 0 increased the proportion of cows with a CL on days 7 and 17 and plasma P4 concentration on day 17 in cows with ovarian cysts but not for cows in proestrus. The CIDR insert increased pregnancy rate in cows with ovarian cysts but reduced pregnancy rate for cows in proestrus.     

Synchronization and resynchronization of inseminations in lactating dairy cows with the CIDR insert and the Ovsynch protocol

Pregnancy per artificial insemination (AI) was evaluated in dairy cows (Bos taurus) subjected to synchronization and resynchronization for timed AI (TAI). Cows (n = 718) received prostaglandin F_2α (PGF) on Days –38 and –24 (Days 39 and 53 postpartum), gonadotropin-releasing hormone (GnRH) on Day –10, PGF on Day –3, and GnRH and TAI on Day 0. Between Days –10 and –3, cows received a progesterone intravaginal insert (CIDR group) or no CIDR (Control group). Between Days 14 and 23, cows received a CIDR (Resynch CIDR group) or no CIDR (Resynch control group), GnRH on Day 23, with pregnancy diagnosis on Day 30. Cows in estrus (between Days 0 and 30) were re-inseminated at detected estrus (RIDE). Nonpregnant cows received PGF on Day 30 and GnRH and TAI on Day 33. Plasma progesterone was determined to be low or high on Days –24 and –10. Pregnancy rates were evaluated 30 and 55 d after AI. The CIDR insert included in the Presynch-Ovsynch protocol did not increase overall pregnancy per AI for first service (36.1% and 33.6% for CIDR; 34.1% and 28.8% for Control) but did decrease pregnancy loss (7.0% for CIDR and 15.6% for Control). The CIDR insert increased pregnancy per AI in cows with high progesterone at the time the CIDR insert was applied. Administration of a CIDR insert between Days 14 and 23 of the estrous cycle after first service did not increase overall pregnancy per AI to second service (24.7% and 22.7% for Resynch CIDR; 28.6% and 25.3% for Resynch control). For second service, RIDE cows had lower pregnancy rates in the Resynch CIDR group than in the Resynch control group. Cows with a CL (corpus luteum) at Day 30 had higher pregnancy rates in the Resynch CIDR group than those in the Resynch control group.     

Correlation between reproductive efficiency, as determined by new mathematical indexes, and the body condition score in dairy cows

The aim of this work was to study a new mathematical model based on dynamic indexes designed to evaluate reproductive efficiency in dairy herds and to correlate the new index with the body condition score (BCS) in order to evaluate the reproductive state of the cows post partum. Four groups of dairy cows were used: 1) loose-housed Italian Friesian (loose Friesian, n = 190); 2) stanchioned Italian Friesian (stanchioned Friesian, n = 121); 3) stanchioned Italian Simmental (stanchioned Simmental, n = 120); and 4) loose-housed selected Italian Friesian cows (BCS test, n = 117). The first 3 herds were used to develop the new mathematical model while the fourth was used to correlate the method with the BCS. The new model was developed from the analysis of progesterone (P4) concentrations in whey and the frequency distribution of the cows in 3 reproductive states: cyclicity, acyclicity and pregnancy. The frequency distribution generated 3 curves, the intersections of which form a closed area. The barycenter of this closed area gives a simple static representation of the reproductive efficiency of each herd. We also studied the movement of the barycenter with time (dynamic index) for each reproductive status curve. The dynamic index allowed for evaluation of the reproductive efficiency of a group of cows at 40 d after calving, by analyzing the evolution of the different reproductive states post partum. A reproductive index called Cycle Time was characterized in a 240-d period of observation as the interval needed to bring all the animals from acyclic to pregnant status. The loose Friesian cows had the best reproductive efficiency. The BCS test was used to divide cows into 3 groups depending on the percentage loss of BCS due to the negative energy balance at 30 d post partum. Cows which lost more than 20% in BCS had the lowest reproductive efficiency. The following protocol was devised to monitor herds in order to identify cows that were likely to have reproductive problems: 1) measure BCS 10 d before calving; 2) monitor progesterone in whey starting 5 d after calving; 3) measure BCS 30 d after calving; 4) isolate cows that lost more than 20% of BCS; 5) measure progesterone only in the cows that lose more than 20% of BCS; 6) activate appropriate feeding strategies to help prevent excessive mobilization of body fat reserves.     

Timed artificial insemination plus heat II: gonadorelin injection in cows with low estrus expression scores increased pregnancy in progesterone/estradiol-based protocol

The use of tail chalk and estrus/heat expression scores (HEATSC) evaluation is instrumental in identifying cows with greater estrus expression and greater artificial insemination pregnancy rates (P/AI) in cows submitted to timed artificial insemination (TAI), and cows with low or no estrus expression present lower P/AI. It was intended in this study to improve the pregnancy rates in TAI for Bos indicus beef cows, and gonadotrophin-releasing hormone (GnRH) injection was hypothesized to increase pregnancy rates in a TAI program for cows submitted to progesterone–estradiol-based protocols with low or no estrus expression, evaluated by HEATSC. Cows (n= 2284) received a progesterone device and 2 mg estradiol benzoate, after 8 days the device was removed and 1 mg estradiol cypionate, 150 μg of d-cloprostenol and 300 IU equine chorionic gonadotropin was administered. All cows were marked with chalk and HEATSC evaluated (scales 1 to 3) at TAI performed on day 10. Animals with HEATSC1 and HEATSC2 (n= 937) received 100 μg de gonadorelin (GNRH group; n= 470), or 1 ml saline (Control group; n= 467), and cows with HEATSC3 (named HEAT group; n= 1347) received no additional treatment. The larger dominant follicle, evaluated on day 8and at TAI (day 10), was greater in HEAT group (P= 0.0145 and P <0.001, respectively). Corpus luteum (CL) area and progesterone concentration was evaluated on day 17, and CL area was larger in HEAT group, intermediary in Control and lower in GnRH group (Control= 2.68 cm², GnRH= 2.37 cm², HEAT group= 3.07 cm², P <0.001). Greater progesterone concentrations were found in HEAT group than in Control and GnRH groups (Control= 4.74 ng/ml, GnRH= 4.29 ng/ml, HEAT group= 6.08 ng/ml, P<0.001). There was a difference in ovulation rate, greater in HEAT group than GnRH and Control groups (Control= 72.5%; GnRH= 81.25%; HEAT group= 90.71%; P= 0.0024). Artificial insemination pregnancy rates was greater in HEAT group (57.09% (769/1347) than in Control and GNRH groups, with positive effect of GnRH injection at the time of TAI in P/AI (Control= 36.18% (169/467), GnRH= 45.95% (216/470); P<0.0001). In conclusion, GnRH application in cows with low HEATSC (1 and 2) is a simple strategy, requiring no changes in TAI management to increase pregnancy rates in postpartum beef cows submitted to progesterone–estradiol-based TAI protocols, without reaching, however, the pregnancy rates of cows that demonstrate high estrus expression at the TAI.