M.-J. Thatcher

Conception rates after artificial insemination or embryo transfer in lactating dairy cows during summer in Florida.

The objective was to compare conception rates to embryo transfer relative to AI, during summer heat stress, in lactating dairy cows. Holstein cows (n = 180; 50 to 120 d postpartum) were allocated randomly to 1 of 3 groups: artificial insemination (AI, n = 84), embryo transfer using either embryos collected from superovulated donors (ET-DON, n = 48), or embryos produced in vitro (ET-IVF, n = 48). Embryos from superovulated donors were frozen in 10% glycerol and were rehydrated in a 3-step procedure, in decreasing concentrations of glycerol in a sucrose medium before transfer. Embryos produced in vitro were frozen in 1.5 M ethylene glycol, thawed and transferred without rehydration. Blood samples were collected from AI and ET recipients on Days 0, 7 and 22 for measurement of progesterone in plasma. Conception rate was estimated for the three groups at Day 22 (progesterone > 1 ng/mL) and confirmed at Day 42 by palpation per rectum. Conception rate estimates at Day 22 did not differ among groups (AI, 60.7%; ET-DON, 60.4%; ET-IVF, 54.2%), but conception rates at Day 42 differed (AI, 21.4%; ET-DON, 35.4%; ET-IVF, 18.8%; AI versus ET: P > 0.10 and ET-DON versus ET-IVF: P < 0.05). In cows considered pregnant at 22 d but diagnosed open at 42 d, the interestrous intervals were 28.8 +/- 2.2, 35.2 +/- 3.5 and 31.6 +/- 2.9 d, respectively, for AI, ET-DON and ET-IVF groups. Transfer of embryos collected from nonheat-stressed superovulated donors significantly increased conception rates in heat stressed dairy cattle. However, transfer of IVF-derived embryos had no advantage over AI. Where appropriate mechanisms are in place to attenuate the effects of heat stress, embryo transfer using frozen-thawed donor embryos increases conception rates.

Fetal survival in the cow after pregnancy diagnosis by palpation per rectum

It is desirable to determine whether a cow has failed to become pregnant as early as possible, preferably prior to 50 d after insemination. Although palpation per rectum has been the generally accepted method of pregnancy diagnosis in cattle, the procedure may be a significant iatrogenic cause of fetal attrition. In a study conducted at a North Florida dairy from January through June 1982, pregnancy was determined in 192 Holstein-Friesian cows by measuring low milk progesterone (P4) content on day of insemination (Day 0) and elevated P4 on Days 21 and 24. Pregnant cows were randomly assigned to a treatment and a control group. Cows in the treatment group (n=85) were palpated per rectum twice between Days 42 and 46 after insemination. Cows in the control group (n=107) were not palpated until both groups were palpated at Day 90. Palpation, done by two experienced clinicians, consisted of palpation of fetal fluid fluctuation, identification of the amniotic vesicle, and slipping of the chorioallantoic membranes. In both groups of cows fetal viability was monitored by milk P4 content. Last milk (5 to 15 ml) was collected from one front quarter on Days 0, 21, and 24 and twice weekly thereafter through Day 63. Milk was defatted by centrifugation and the fat-free milk progesterone content measured by a radioimmunoassay without extraction. The milk P4 test was 80.0% accurate in determining pregnancy in the palpated and nonpalpated cows. In the cows palpated on Days 42 to 46, pregnancy rates declined by 7.5% as determined by palpation at Day 90, or by 11.4% as determined by milk P4 content through Day 63 (both values P<0.05). Cows that were not palpated on Days 42 to 46 showed a 1.9% increase or a 4.3% decline in pregnancy rates as determined by the same criteria. Before palpation, at Days 42 to 46, pregnancy rates were better in cows that were inseminated in winter (January to March) than in spring (April to June) (82.3% vs 61.6%; P<0.05); P4 content was higher (winter>spring=2.13 ng/ml vs 1.38 ng/ml; P<0.05). First-lactation cows had higher P4 values on Days 21 and 24 than older cows (P<0.01).

Effects of calving-related disorders on prostaglandin, calcium, ovarian activity and uterine involution in postrartum dairy cows

Postpartum ovarian activity, uterine involution and plasma concentrations of calcium and 15-keto-13, 14 dihydro-prostaglandin F2alpha (PGFM) were assessed in dairy cows with retained fetal membranes (n=10) and milk fever (n=10) at parturition. In addition, calcium and PGFM were evaluated in dairy cows affected with uterine prolapse (n=10) and pyometra (n=14). Cows with retained fetal membrane averaged 24.2+/-3.7 d until their first postpartum ovulation, while controls averaged 29.0+/-3.7 d (P>0.10). In cows with retained fetal membranes, the difference in follicular activity between the contralateral and ipsilateral ovaries in relation to the previously gravid uterine horn was appreciably greater post partum when compared with that of the controls. Cows with milk fever had an average of 30.8+/-3.1 d until their first postpartum ovulation, while control cows had an average of 20.4+/-3.3 d (P<0.05). The mean diameter of the uterine horns in cows with milk fever was greater (P<0.05) compared with that of the controls between Days 15-32 post partum. Concentrations of plasma calcium were lower in cows with retained fetal membranes within 24 h after parturition and during the first week post partum than in the controls (6.27+/-0.18 vs 7.40+/-0.18 mg/100ml, P<0.05). Concentration of calcium was lower (P<0.05) in cows with milk fever on Day 1 prior to treatment (4.68+/-0.40 < 5.8+/-0.45 mg/100ml) than in control cows; however, the calcium (Ca) level was not different during the subsequent 7 d post partum after treatment. Cows with uterine prolapse had lower concentrations of Ca during the first 7 d post partum than the controls (6.10+/-0.15 vs 7.33+/-0.12mg/100ml; P<0.01). Cows with pyometra had higher (P<0.05) concentrations of plasma PGFM than the controls (208.+/-13.2 > 138.1+/-15.2).

Application of one injection of prostaglandin F2α in the five-day Co-Synch + CIDR protocol for estrous synchronization and resynchronization of dairy heifers

The objective was to determine if the 5-d Co-Synch+CIDR (controlled internal drug releasing insert) protocol can be used in dairy heifers for a synchronized timed artificial insemination (TAI) with one injection of PGF(2alpha) for first and second services. In experiment 1, heifers were assigned randomly to receive 1 (n=295) or 2 (n=298) injections of PGF(2alpha) in the 5-d Co-Synch+CIDR protocol. Corpus luteum (CL) regression was measured in one replicate (n=218). No difference in pregnancy per TAI (P/TAI; 46.1 and 48.6%) or CL regression (86.9 and 92.8%) was detected for 1 versus 2 injections of PGF(2alpha), respectively. In experiment 2, nonpregnant heifers (n=86) were assigned to a resynchronized 5-d Co-Synch+CIDR with 1 PGF(2alpha)/TAI or insemination at detected estrus. There was no difference in P/TAI (52.2 and 55%) between groups. In experiment 3, nonpregnant heifers (n=110) were assigned randomly to receive a CIDR (n=54) or no CIDR insert (n=56) in the 5-d Co-Synch protocol for resynchronization of TAI. Pregnancy per TAI was lower without the CIDR device (39.3 vs. 51.8%). In a commercial field evaluation, 416 heifers were synchronized for the first and resynchronized TAI with the 5-d Co-Synch+CIDR protocol with 1 injection of PGF(2alpha). Pregnancy per TAI on d 60 was 58.2 and 47.5% for first and second TAI, respectively; there was a sire effect to the second TAI. In conclusion, the 5-d Co-Synch+CIDR protocol with 1 injection of PGF(2alpha) is an effective reproductive management program for first and second TAI in dairy heifers.

Comparison of reproductive performance in lactating dairy cows bred by natural service or timed artificial insemination

The objective of this study was to compare reproductive performance of lactating dairy cows bred by natural service (NS) or timed AI (TAI). One thousand fifty-five cows were blocked by parity and enrolled to receive either NS or TAI. Cows in both groups were presynchronized with 2 injections of PGF(2alpha) given at 42 and 56 d postpartum. Fourteen days after the last PGF(2alpha) injection, cows in the TAI group were enrolled in an Ovsynch protocol (d 0 GnRH; 7 d later, PGF(2alpha); 56 h after PGF(2alpha) injection, second dose of GnRH; and 16 h after second GnRH cows were TAI). Cows in the TAI group were resynchronized with an intravaginal insert containing progesterone inserted 18 d after TAI and removed 7 d later when GnRH was given. Cows were examined by ultrasonography on d 32 after TAI; nonpregnant cows received PGF(2alpha) and GnRH 56 h later followed by TAI 16 h after the GnRH injection. Nonpregnant cows in TAI group were reinseminated up to 5 times using the same scheme. Cows in the NS group were exposed to bulls 14 d after the second PGF(2alpha) injection, and ultrasonography was performed 42 d after exposure to bulls to determine pregnancy status. Nonpregnant cows in the NS group were reexamined by transrectal palpation combined with ultrasound every 28 d until diagnosed pregnant or 223 d postpartum, whichever occurred first. Cows diagnosed pregnant in TAI or NS were reconfirmed 28 d later to determine pregnancy loss. All bulls underwent an evaluation of breeding soundness and were rested for 14 d after 14 d of cow exposure. Health disorders were evaluated up to 70 d postpartum, and body condition score was evaluated at d 70 postpartum. Blood was collected on d 56 and 65 postpartum and analyzed for progesterone to determine cyclicity. The proportion of pregnant cows in the first 21 d of breeding did not differ between groups. The overall 21-d cycle pregnancy rate (PR), which included a total of 8 and 5 service opportunities for NS and TAI, respectively, was not different between groups (25.7 and 25.0% for NS and TAI, respectively). The daily rate of pregnancy was 15% greater for NS than TAI because cows in NS had a greater PR, which resulted in fewer median days open (111 vs. 116 d). Proportion of pregnant cows at 223 d postpartum was greater in the NS than TAI group (84.2 vs. 74.8%, respectively). Cyclicity did not affect reproductive performance. Cows with body condition score >/=2.75 had greater proportion of pregnant cows in the first 21 d of breeding and daily PR in the first 223 d postpartum Primiparous cows had greater proportion of pregnant cows and daily PR than multiparous cows at 223 d postpartum. In conclusion, the greater proportion of pregnant cows in the NS group was attributed to more opportunities for breeding than in the TAI group.

Effects of Buserelin injection and Deslorelin (GnRH-agonist) implants on plasma progesterone, LH, accessory CL formation, follicle and corpus luteum dynamics in holstein cows

The influence of Buserelin injection and Deslorelin (a GnRH analogue) implants administered on Day 5 of the estrous cycle on plasma concentrations of LH and progesterone (P4), accessory CL formation, and follicle and CL dynamics was examined in nonlactating Holstein cows. On Day 5 (Day 1 = ovulation) following a synchronized estrus, 24 cows were assigned randomly (n = 4 per group) to receive 2 mL saline, i.m. (control), 8 micrograms, i.m. Buserelin or a subcutaneous Deslorelin (DES) implant in concentrations of 75 micrograms, 150 micrograms, 700 micrograms or 2100 micrograms. Blood samples were collected (for LH assay) at 30-min intervals for 2 h before and 12 h after GnRH-treatment from cows assigned to Buserelin, DES-700 micrograms and DES-2100 micrograms treatments and thereafter at 4-h intervals for 48 h. Beginning 24 h after treatment, ovaries were examined by ultrasound at 2-h intervals until ovulation was confirmed. Thereafter, ultrasonography and blood sampling (for P4 assay) was performed daily until a spontaneous ovulation before Day 45. A greater release of LH occurred in response to Deslorelin implants than to Buserelin injection (P < 0.01). Basal levels of LH between 12 and 48 h were higher in DES-700 micrograms group than in DES-2100 micrograms and Buserelin (P < 0.05). The first wave dominant follicle ovulated in all cows following GnRH treatment. Days to CL regression did not differ between treatments, but return to estrus was delayed (44.2 vs 27.2 d; P < 0.01) in cows of DES-2100 micrograms group. All GnRH treatments elevated plasma P4 concentrations, and the highest P4 responses were observed in the DES-700 micrograms and DES-2100 micrograms groups. The second follicular wave emerged earlier in GnRH-treated than in control cows (9.9 vs 12.8 d; P < 0.01). However, emergence of the third dominant follicle was delayed in cows of DES-2100 micrograms treatment (37.0 d) compared with DES-700 micrograms (22.2 d), Buserelin (17.8 d) or control (19.0 d). In conclusion, Deslorelin implants of 700 micrograms increased plasma P4 and LH concentrations and slightly delayed the emergence of the third dominant follicle. On the contrary, Deslorelin implants of 2100 micrograms drastically altered the P4 profiles and follicle dynamics.

The dominant follicle exerts an interovarian inhibition on FSH-induced follicular development.

An experiment was conducted to evaluate the role of the dominant follicle (DF) of the first wave in regulating follicular and ovulatory responses and embryonic yield to a superovulation regime with FSH-P. Twenty normally cycling Holstein-Freisian heifers (n = 20) were synchronized with GnRH and pgf(2alpha) and randomly assigned to a control or a treated group (n = 10 each). Treated heifers had the first wave dominant follicle removed via transvaginal, ultrasound-guided aspiration on Day 6 after a synchronized estrus. All heifers received a total of 32 mg FSH-P given in decreasing doses at 12 h intervals from Day 8 to Day 11 plus two injections of pgf(2alpha) (35 mg and 20 mg, respectively) on Day 10. Heifers were inseminated at 6 h and 16 h after onset of estrus. Follicular dynamics were examined daily by transrectal ultrasonography from Day 4 to estrus, once following ovulation, and at the time of embryo collection on Day 7. Blood samples were collected daily during the superovulatory treatment and at embryo collection. Follicles were classified as: small, </= 5 mm; medium, 6-9 mm; or large, >/= 10 mm. Aspiration of the dominant follicle was associated with an immediate decrease in large follicles, and a linear rate increase in small follicles from Day 4 to Day 8 just prior to the FSH-P injections, (treatment > control: +0.33 vs. -0.22, number of small follicles per day; P < 0.10). During FSH-P injections, the increase in number of medium follicles was greater (P < 0.01) for treatment on Day 9-11 (treatment > control: Day 9, 3.2 > 1.8; Day 10, 9.2 > 4.7; Day 11, 13.1 > 8.3; +/- 0.56). Number of large follicles was greater in treatment at Day 11 (5.12 > 1.4 +/-0.21; P < 0.01). Mean number of induced ovulatory follicles (difference between number of follicles at estrus and Day 2 after estrus) was greater in treatment (13.4 > 6.3 +/- 1.82; P < 0.01). Plasma estradiol at Day 11 during FSH-P treatment was greater in treatment (32.5 > 15.8 +/- 2.6; P < 0.01). Plasma progesterone at embryo flushing (Day 7 after ovulation) was greater in treatment (7.4 > 4.9; P < 0.02); technical difficulties at embryo recovery reduced sensitivity of embryonic measurements. No changes in the distribution of unfertilized oocytes and embryo developmental stages were detected between control and treatment groups. Presence of dominant follicle of the first wave inhibited intraovarian follicular responses to exogenous FSH.

Use of a five-day progesterone-based timed AI protocol to determine if flunixin meglumine improves pregnancy per timed AI in dairy heifers

Two experiments were conducted to test the hypothesis that the 5 d Co-Synch + CIDR (Controlled Internal Drug Release insert containing progesterone) protocol could be applied as an efficient timed AI (TAI) protocol in dairy heifers, and that treatment with flunixin meglumine (FM) during the period of CL maintenance would increase pregnancy per TAI (P/TAI) and late survival of embryos. Objectives were: 1) in Experiment 1, to compare P/TAI with the 5 d Co-Synch+CIDR protocol to a PGF(2alpha)/GnRH protocol; and 2) in Experiment 2, to determine if FM administered 15.5 and 16 d after first TAI would increase P/TAI, using the 5 d Co-Synch+CIDR protocol with a new or previously used (5 d) CIDR insert. In Experiment 1, 248 heifers were assigned randomly to either the PGF(2alpha)/GnRH protocol (n=120) or the 5 d Co-Synch+CIDR protocol (n=128). Pregnancy per TAI did not differ between the 5 d Co-Synch+CIDR protocol (53.1%) and the PGF(2alpha)/GnRH protocol (45.8%; P=0.22). In Experiment 2, 325 heifers synchronized with the 5 d Co-Synch+CIDR protocol were assigned randomly to receive two injections of FM (FM group; n=158) at 15.5 and 16 d after TAI, or to remain as untreated controls (n=165). Pregnancy per TAI in Experiment 2 was 59.4 and 59.5% at 45 d for control and FM groups, respectively, with no differences between groups (P=0.83). The 5 d Co-Synch+CIDR protocol resulted in an acceptable P/TAI in dairy heifers. However, FM did not improve P/TAI in dairy heifers.

Dynamics of prostaglandin secretion, intrauterine fluid and uterine clearance in reproductively normal mares and mares with delayed uterine clearance

Two experiments were performed to investigate relationships between oxytocin, prostaglandin release, uterine emptying and fluid accumulation in the uterus. In Experiment 1, the effect of oxytocin on the pattern of prostaglandin release during uterine clearance of radiocolloid was measured in 5 normal mares and 5 mares with delayed uterine clearance. Uterine clearance was measured during estrus by scintigraphy at 0, 60 and 120 min after colloid infusion. After the 120-min reading, 20 IU, i.v., oxytocin were given, and the amount of colloid cleared was measured at 135, 150 and 180 min. Plasma was obtained prior to and during scintigraphy at 5- and 15-min intervals to measure concentrations of 15-keto-13,14-dihydro-PGF2 alpha metabolite (PGFM) by RIA. In Experiment 2, plasma PGFM levels were compared after administration of oxytocin in 8 normal mares and 6 mares with delayed uterine clearance to determine if intrauterine fluid stimulated prostaglandin release. Mares received 2 treatments in a cross-over design. Treatment 1 consisted of 20 IU, i.v., oxytocin during estrus. Treatment 2 consisted of an infusion of 10 mL, i.u., saline 15 min prior to oxytocin administration. Treatments were performed 4 to 6 h apart. Blood was collected and PGFM was measured as in experiment 1. Data were analyzed by least squares analysis of variance. In Experiment 1, regression analysis of scintigraphy and PGFM profiles indicated that time response curves differed between groups (P < 0.01). At 120 min, normal mares retained 40.4 +/- 4.9% (mean +/- SEM) of the radiocolloid while mares with delayed clearance retained 88 +/- 5%. Fifteen minutes after oxytocin administration (135 min), all normal mares and 4 of 5 mares with delayed clearance retained only < 6% of the colloid. During the first 120 min, plasma PGFM concentrations did not differ between the 2 groups. After oxytocin was given, plasma PGFM concentrations increased in 4 of 5 mares with delayed uterine clearance (80 to 3,096 pg/mL) but not in normal mares (13 to 46 pg/mL). In Experiment 2, plasma PGFM concentrations did not rise in normal mares but rose in 3 of 6 mares with delayed clearance (135 to 483 pg/mL) independent of treatment or period. The results suggest that intrauterine clearance of radiocolloid after oxytocin administration appears to be independent of PGF2 alpha release in normal mares during estrus. The difference in prostaglandin release response after oxytocin administration between the 2 groups was unrelated to the presence of intrauterine fluid.

Effect of housing type on health and performance of preweaned dairy calves during summer in Florida1

The objective was to evaluate the effect of housing type on health and performance of preweaned dairy calves. One hundred calves, Holsteins (HO) or Holstein-Jersey crosses (HJ), were randomly assigned to a Calf-Tel (L. T. Hampel Corp., Germantown, WI) polyethylene hutch exposed to direct sun light (n=25 for both HO and HJ) or a wire hutch with a plywood shade located under trees (n=24 and 26 for HO and HJ, respectively). Calf rectal temperature, respiratory rate, health scores, and weaning weight were compared by housing type. Rectal temperatures were higher in calves in Calf-Tel hutches compared with calves in wire hutches at 1500 h, at 40.1±0.28 and 39.1±0.22°C, respectively. Similarly, respiratory rates were higher in calves in Calf-Tel hutches compared with calves in wire hutches at 1500 h, at 90±15 and 65±10 breaths per minute, respectively. Frequencies of calves presenting abnormal ear scores did not differ between calves in Calf-Tel or wire hutches. Abnormal eye scores were less likely to occur for calves in the wire hutches. Frequencies of calves with signs of respiratory disease, such as nasal discharge and coughing, were higher in the wire hutches compared with the Calf-Tel hutches. No differences were noted in the incidence and time of first diarrhea event in calves between hutch types. Calves in wire hutches had 5.47 greater odds of receiving veterinary treatment compared with calves in the Calf-Tel hutches. Weaning weights were not different for calves in Calf-Tel or in wire hutches. The lower frequency of calves with abnormal health scores and receiving veterinary treatment in Calf-Tel hutches and the lack of difference in weight gain suggests that this housing system adapted well to the specific environmental conditions of this study.