Relationships between body condition score, body weight, and some nutritional parameters in plasma and resumption of ovarian cyclicity postpartum during pre-service period in high-producing dairy cows in a subtropical region in Japan

The objective of this study was to investigate the relationships among body condition score (BCS), body weight and plasma metabolite concentrations, and resumption of ovarian cycles postpartum in high-producing dairy cows in a subtropical region in Japan. The study was conducted between May 2001 and January 2003 in a commercial dairy farm in Hiroshima. Cows were kept in free-stall barns with sawdust and wood shavings for bedding, and fed a total mixed ration consisting of alfalfa, timothy and oat hay, corn, tofu ground-wet, beet pulp, cottonseed and soybean. Milk samples were collected twice weekly from 2 to 11 weeks postpartum, and progesterone concentrations in skim milk were determined by ELISA. At 8 and 2 weeks before calving and 3, 5, 7, 9, and 11 weeks after calving, both BCS and body weights were determined and blood samples were collected to determine plasma concentrations of total cholesterol (T-cholesterol), non-esterified fatty acids (NEFA), total protein, and urea nitrogen. The average 305 days milk yield was 10,422 kg. Out of 110 cows, 44.5% had normal resumption (ovulation occurred < or =45 days after calving, followed by regular ovarian cycles), 33.6% had a prolonged luteal phase (luteal activity >20 days), 12.7% had delayed first ovulation (no ovulation until < or =45 days after calving), 4.6% had a short luteal phase (luteal activity <10 days, except in the first cycle), and the remaining 4.6% had cessation of cyclicity (no luteal activity > or =14 days between cycles). The BCS of cows with delayed first ovulation were lower than the BCS of cows with normal resumption and prolonged luteal phase at 5 weeks (2.9+/-0.1 versus 3.1+/-0.1 and 3.2+/-0.1; P<0.05), 7 weeks (2.8+/-0.1 versus 3.1+/-0.1 and 3.2+/-0.1; P<0.01), 9 weeks (2.7+/-0.1 versus 3.0+/-0.1 and 3.2+/-0.1; P<0.01) and 11 weeks (2.6+/-0.1 versus 3.0+/-0.1 and 3.2+/-0.1; P<0.01) after calving. None of the plasma parameters differed (P>0.05) among different groups of cows. Cows loosing > or =1 unit BCS after calving had a prolonged interval to commencement of luteal activity, and were at greater risk of having delayed first ovulation. Poor postpartum nutritional status was associated with delayed first ovulation postpartum. Regular monitoring of BCS before and after calving would be useful in nutritional management, and help in preventing delayed first ovulation in high-producing dairy cows.     

Resumption of postpartum ovarian cyclicity in high-producing Holstein cows

The objective of this study was to investigate the resumption of ovarian cyclicity postpartum in high-producing dairy cows in commercial dairy farms under subtropical conditions. The cows were kept in a free-stall or tie-stall barn. Milk samples were collected from cows twice weekly, and progesterone in the skim milk was assayed by double-antibody ELISA. Cows were examined rectally and vaginoscopically at 2-week intervals after calving. Body condition score (BCS) and body weights were taken before and after calving. A cow was considered to have resumed ovarian cyclicity on the day of ovulation if followed by regular ovarian cycles. Thirty seven percent (n=20/54) of the cows had normal resumption of ovarian cyclicity (resumption within 45 days after calving), and 63% (n=34/54) had delayed resumption (resumption did not occur until >45 days after calving). Delayed resumption Type I (one or more ovarian cycles with luteal phase >20 days, i.e. prolonged luteal phase; 31.5%) and delayed resumption Type II (first ovulation did not occur until > or =45 days after calving, i.e. delayed first ovulation; 24.1%) were the most common types of delayed resumptions. Almost half (46.3%) of the cows did not resume their ovarian cyclicity until >65 days postpartum. Cows with delayed resumption Type I had a higher incidence of abnormal cervico-vaginal discharge (64.7%) and incomplete uterine involution (94.1%) compared to cows with normal resumption (P<0.01). The BCS of cows with delayed resumption Type II were lower than those of normal resumption cows at 5 weeks and later in the postpartum period (P<0.05). Approximately two-thirds of high-producing cows had delayed resumption of ovarian cyclicity postpartum. Prolonged luteal phase and delayed first ovulation were two important ovarian dysfunctions that delayed postpartum resumption of cyclicity in high-producing dairy cows.     

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.     

Reproductive responses of early postpartum dairy cattle to continuous treatment with a GnRH agonist (deslorelin) for 28 days to delay the resumption of ovulation

An experiment was conducted to investigate the potential of chronic delivery of a potent GnRH agonist (deslorelin) via subcutaneous implants to delay the resumption of ovulatory cycles in postpartum dairy cattle. Cows received either a single deslorelin implant (n=40; DES) within 7 days of calving or were untreated (n=24; CON). Blood samples were collected thrice weekly during the period the implants were in place. Plasma concentrations of progesterone (P4) and 17beta-oestradiol (E2) were measured along with selected serum metabolites. Implants were removed after 28 days and cattle monitored daily for behavioral oestrus. Serial weekly blood samples were collected to detect the occurrence of ovulation. Cows were artificially inseminated as they were detected in oestrus from 30 days after implant removal. Pregnancy status was subsequently determined by manual palpation of uterine contents at strategic intervals.Insertion of implants induced ovulation in 3/40 cows as determined by a rise in progesterone 7 days later. Deslorelin implants delayed the onset of ovulatory cycles compared with untreated herdmates (mean 43.4+/-4.2 versus 57.3+/-1.6 days postpartum; P<0.001). A noticeable delay of at least 12 days was observed between implant removal and the first animals ovulating. Mean plasma E2 concentrations during the period the implants were in place were similar for DES and CON cows that experienced a prolonged spontaneous postpartum anoestrus (low P4 >60 days), although both groups had concentrations only 20% of CON cows that had ovulated prior to 30 days postpartum.The patterns of recovery following implant removal were highly variable. A number of DES cows showed a low and transient rise in plasma progesterone around 21 days after implant removal. Some cows displayed oestrus but did not appear to form a fully functional corpus luteum with this phenomenon being more prevalent among DES cows (7 of 37 versus 1 of 21; P<0.05). Overall, significantly more DES cows were detected in oestrus without ovulating compared to CON cows. Final pregnancy rates did not differ between DES and CON groups. The mean time to conception for DES cows was longer (21.2+/-5.6 versus 41.1+/-7.4 days, CON versus DES; P<0.01). This difference was not present if the time from first ovulation to conception was compared (50.5+/-5.3 versus 43.5+/-9.3 days, CON versus DES; P>0.05). Deslorelin implants provided a reliable method of inducing anoestrus when treatment was initiated prior to 3 days postpartum. A variable pattern of recovery was observed which delayed conception but did not ultimately reduce the final proportion pregnant at the completion of mating. The study demonstrates the potential of GnRH agonists to control postpartum reproductive function to manipulate the fertility of dairy cows.     

The effect of strain of Holstein-Friesian cow and feeding system on postpartum ovarian function, animal production and conception rate to first service

Three strains of Holstein-Friesian (HF): high production North American (HP), high durability North American (HD) and New Zealand (NZ) cows were assigned, within strain, to one of three pasture-based feeding systems: (1) the Moorepark (control) system (MP), (2) a high concentrate system (HC), (3) a high stocking rate system (HS). Ovarian function was assessed using milk progesterone samples, collected from 117 cows in each of two successive years, with 81 animals being common to both years. Milk samples were collected thrice weekly, beginning day 5 post-calving and continued to day 26 after first AI. Data from animals subsequent to reproductive hormonal treatment were removed from the analysis. Feed system and strain of HF by feeding system interaction had no significant effect on re-establishment of ovarian activity and subsequent conception rate to first AI. Strain of HF had no significant effect on interval to commencement of luteal activity (CLA). The mean interval to CLA was 32.9 days (S.E. 1.18), ranged from 6 to 100 days, with 42 and 85% of cows ovulating by day 26 and 60, respectively. The HD (62%) and NZ (57%) strains had a higher conception rate to first AI than the HP strain (40%), (P < 0.05). Retrospective analysis categorised all cows into four quartiles based on interval to CLA (< 20 days, 20-26 days, 27-44 days and > 44 days). Cows in the first and fourth CLA quartiles had a longer calving to conception interval (P < 0.05). Cows with abnormal progesterone profiles (38.4%) had an earlier mean calving date, with a similar submission rate and conception rate to first service compared to cows with normal hormonal profiles. There was no significant difference in luteal activity or reproduction performance, apart from calving to conception interval, between cows that conceived or did not conceive to first service. These results indicate that while conception rate to first service differed between strains of HF cow, this was not associated with differences in the onset and pattern of luteal activity post partum.     

Factors affecting the occurrence of postpartum prolonged luteal activity in clinically healthy high-producing dairy cows

The objective was to characterize risk factors affecting the occurrence of prolonged luteal phase (PLP) in postpartum, clinically healthy, high-producing dairy cows. Transrectal ultrasound examinations of the reproductive tract were performed twice weekly, from the 1st to 8th wk after calving in 151 multiparous clinically healthy lactating Holstein cows (mean ± SD of peak milk yield = 56.7 ± 7.4 kg). Serum samples were collected twice weekly to measure progesterone and every 2 wk to detect β-hydroxybutyrate (βHB), and α1-acid glycoprotein (AGP). Body condition score (BCS) was recorded weekly after calving. Based on the serum progesterone profile, 52 (34.4%) cows had normal ovarian activity (NLA), whereas 36 (23.8%) cows had a prolonged luteal phase (PLP), the most prevalent type of abnormal pattern of luteal activity. Furthermore, 63 cows with short luteal activity, delayed first ovulation, or cystic ovaries were excluded from this study. Serum AGP concentrations, as an indication of postpartum chronic endometritis, were not different (P > 0.05) between cows with NLA and PLP. Categories of peak milk yields (kg) were positively correlated with the incidence (%) of cows with PLP (r = 0.87, P = 0.02). Furthermore, milk yield peak, day of milk yield peak, mean milk yield (8 wk in milk), and milk yield on the expected day of luteolysis were higher (P < 0.05) in cows with PLP than NLA, and cows with PLP had greater loss of BCS (P = 0.007) than those with NLA. The likelihood of cows with PLP decreased by 0.9-fold for every 1 d delay of commencement of luteal activity (C-LA). Moreover, the likelihood of cows with PLP increased by 1.8-fold for each 1 mmol/L increase in the 1st wk serum βHB concentrations. In conclusion, higher mean of milk yield, greater BCS loss, earlier C-LA, and later peak milk yield were the major risk factors affecting the occurrence of postpartum PLP in clinically healthy, high-producing dairy cows.     

Influence of parity on follicular dynamics and resumption of ovarian cycle in postpartum dairy cows

The present study examined ovarian changes preceding the resumption of the ovarian cycle in postpartum dairy cows with different parities under similar body nutritional conditions. In postpartum primi- (n=6), bi- (n=4), and multiparous (n=6) Holstein dairy cows, ovarian ultrasonographic observations starting at 7 days after calving were performed every other day and then daily after the confirmation of clinical signs of oestrus for the detection of postpartum first ovulation. Blood samples were collected at the same time as ultrasonography and analyzed for oestradiol and progesterone to monitor ovarian activity. To evaluate the nutritional condition of the cows, body weight and body condition score (BCS, 1=emaciated to 5=obese) were measured weekly and blood samples for the analysis of glucose, insulin, and non-esterified fatty acid (NEFA) were collected at the same time until postpartum second ovulation. Dominant follicles (>8mm in diameter) of the first follicular wave were detected at 7 days after calving in all cows. The first wave follicle ovulated in five of six multiparous cows, whereas no first wave follicle ovulated in any of the primiparous cows. The days to first ovulation after calving in primiparous cows (31.8+/-8.3 days) were significantly greater (p<0.05) than those in multiparous cows (17.3+/-6.3 days), but were not significantly different from biparous cows (28.8+/-8.6 days). There was a significant relationship between parity and days to first ovulation after calving (p<0.05). BCS was maintained at a level of more than 2.5 during the postpartum period in all cows and there was no influence of parity on postpartum changes in BCS, glucose, insulin, or NEFA throughout the experiment. The present study demonstrated a negative relationship between parity and number of days from calving to first ovulation in dairy cows under similar body nutritional conditions. It is possible that the influence of parity on the resumption of ovarian cycle is modulated by the factors different from the nutrition-related changes during the postpartum period in dairy cows.     

Resumption of ovarian function in autumn lambing Dorset, Rambouillet and Finnish Landrace ewes

The establishment of ovarian activity during lactation was studied in the postpartum period of Rambouillet, Dorset and Finnish Landrace ewes following lambing during the month of October (1981). The mean postpartum intervals to first ovulation and first estrus were 22.7 and 53.0 for Rambouillets, 25.2 and 51.0 for Dorsets, and 22.5 and 49.7 days for Finnish Landrace ewes. Estrus was not associated with the first ovulation postpartum in any breed. The number of silent ovulations prior to the first estrus was highest in the Rambouillet and lowest in Finnish Landrace breeds. Of the 18 ewes in the project, 14 had normal luteal phase lengths, 1 had a possible short luteal phase and 3 had prolonged luteal phases following the first ovulation postpartum. The first service conception rate of all ewes bred was 82% (14 17 ) at an average of 52 days postpartum. The lambing rate following the autumn breeding was higher (2.14 +/- 0.14) than the lambing rate which followed the previous spring breeding (1.28 +/- 0.11).     

Reproductive performance of repeat breeders in dairy herds

The objectives were to characterize repeat breeding in dairy cows, including reproductive performance and risk factors. Data from 613 Holstein Friesian cows in nine dairy herds across Japan were enrolled. A repeat breeder was defined as a cow that did not become pregnant after three inseminations, despite no clinically detectable reproductive disorders. In contrast, cows that became pregnant within three inseminations were considered to have normal fertility. Of the 613 cows, 87.3% eventually became pregnant after repeated AI (maximum calving to conception interval was 435 d). Mean (±SEM) first AI conception rate, days in milk at first AI, calving to conception interval and service per conception were 38.3%, 82 ± 2 d, 125 ± 3 d, and 2.0 ± 0.1 times, respectively. Normal fertility cows (n = 479) required only 114 ± 3 d to conceive and 1.7 ± 0.1 inseminations per pregnancy, whereas repeat breeders (n = 86) required significantly more days to conceive (211 ± 10) and more inseminations per pregnancy (4.7 ± 0.2). Based on survival analysis, it took 94 d after calving for 50% of normal fertility cows to become pregnant, compared to 155 d for repeat breeders. For repeat breeders, 31.4, 50.0, and 58.1% became pregnant within 210, 300, and 435 d after calving, respectively. The risk factors for repeat breeding were parity (relative risk [RR] = 0.809; P = 0.058), resumption of postpartum ovarian cycles (RR = 1.928; P = 0.009), and days in milk at first AI (RR = 0.991; P = 0.039). In conclusion, repeat breeder dairy cows had very poor reproductive performance. Lower parity, abnormal resumption of postpartum ovarian cycles, and shorter days in milk at first AI were risk factors for repeat breeding.     

Photoperiodic alteration of postpartum reproductive function in suckled cows

Three experiments were conducted using a total of 41 cows to determine if photoperiod modulates the establishment of postpartum estrous cycles and conception. Cows calving in the autumn and winter were exposed to either 18 hr light/day (18L:6D) or natural photoperiods. In Exp. 1, cows receiving 18L:6D had shorter (P<0.025) intervals from calving to estrus (61 +/- 3.8 days) than cows not receiving supplemental light (154 +/- 23.9 days). The same was true for primiparous cows in Exp. 2 (76 +/- 5.5 days vs 153 +/- 38.0 days; P<0.06) but not for the multiparous cows in Exp. 2 (56 +/- 5.2 days vs 40 +/- 7.4 days) or for all cows in Exp. 3 (60 +/- 10.1 days vs 70 +/- 13.5 days). Because conception rate was higher for cows exposed to 18L:6D for the multiparous cows in Exp. 2 and all cows in Exp. 3, interval to conception was significantly shorter for animals exposed to 18L:6D in all experiments. Generally, interval from calving to uterine involution was also reduced by exposure to 18L:6D. No effects of photoperiod were observed on body weight changes, serum levels of luteinizing hormone (LH), follicle stimulating hormone (FSH) or estradiol or on estradiol-induced release of gonadotropins. It was concluded that in certain situations day length can hasten estrus and conception in postpartum cows. The effect of photoperiod interacts with other conditions, one of which is parity. The endocrine basis for these effects are not known.     

A Survey of the Postpartum Reproductive Performance of Dairy Cows with Fertility Problems in Southern Iceland

The purpose of this survey was to evaluate the reproductive performance of dairy cows on problem farms in southern Iceland. In all 229 cows on 6 farms were studied. The animals were examined clinically by rectal palpation, once a month. Blood samples were taken 2–5 and 7–10 weeks after calving. The blood samples were analysed for the contents of glucose, urea, inorganic phosphate, calcium and magnesium. Milk samples for progesterone profiles were taken, by the farmer, every 4th day from day 10 postpartum until first oestrus. Because of this sampling method, 128 cows had no rise in progesterone levels, when milk sampling was stopped. These 128 animals were excluded from the study. The results are based on 101 animals. There was a large variation between cows in postpartum reproductive performance. In the total material 1st ovulation occurred later than reported in many other countries. Fifty percent of the cows had ovulated 35 days after calving and 90 percent 70 days after calving. The first luteal phase was short in about 60 % of the cows. The progesterone values assayed from those short cycles were lower than the values assayed from the following cycle. First artificial insemination (ai) was on the average 77 days postpartum (pp). The conception rate to first service was 49 %. Of 100 milk samples taken at the time of ai, 20 had high progesterone value. This indicates a high frequency of luteal phase inseminations. Clinical ketosis was diagnosed in 35 cows. Of these, 31 had a low glucose value. Cows with clinical ketosis ovulated, on the average, later than other animals and 24 ovulated later than 40 days pp. The results indicated that the fertility problems of these cows studied were late ovulations, low conception rate, probably in part, due to luteal phase inseminations, and a high frequency of ketosis which could be caused by low quality feedstuff.     

Luteal competency during the resumption of ovarian cyclicity in postpartum Brahman cows

Twenty pluriparous, spring-calving Brahman cows were used to determine luteal competency, as measured by serum progesterone concentrations, during the first and the second postpartum estrous cycles. Prior to and after calving, all cows were maintained in good body condition on Coastal bermudagrass pasture (IFN 1-00-703). The calves were allowed to suckle ad libitum, and sterile marker bulls were maintained with the cow herd as an aid in estrus detection throughout the trial. Cow weight and body condition score were recorded within 24 hours after calving and again at the first behavioral estrus observed. From day 1 through day 14 (day 0 = estrus) of both the first and the second postpartum estrous cycles, blood samples were collected from each cow, processed to yield serum and analyzed by radioimmunoassay for progesterone concentrations. There was a higher incidence of abnormal estrous cycles following the first postpartum estrus (35%) than following the second (5%) postpartum estrus (P<0.05). The abnormal first estrous cycles were characterized by either a short luteal phase (four cows) or by standing estrus behavior without luteal tissue formation (three cows). When serum progesterone concentrations were compared for all cows during the first estrous cycle with those during the second estrous cycle, there was less progesterone released during the cycle (P<0.05) and lower peak progesterone concentrations (P<0.10) during the first estrous cycle. However, if the abnormal cows were excluded from the analyses, there was no difference (P>0.10) in either progesterone concentrations through the 14 days measured or in peak progesterone concentrations between the first and the second postpartum estrous cycles. It can be concluded from this study that the higher incidence of abnormal luteal function following the first postpartum estrus may contribute to the decreased conception rates observed when cows are bred at their first postpartum estrus.     

Progesterone concentration, follicular development and induction of cyclicity in dairy cows receiving intravaginal progesterone inserts

Objectives were to evaluate progesterone concentrations after cows had initiated estrous cycles following calving and induction of estrous cycles in postpartum anovular high-producing Holstein dairy cows treated with controlled internal drug releasing (CIDR). In experiment 1 (EXP1), 62 cows that had initiated estrous cycles received a new CIDR (NCIDR) containing 1.38 g of progesterone or a 7-d used autoclaved CIDR (UCIDR) 48h after luteolysis for 7 d. Ovaries were examined by ultrasonography, and plasma analyzed for concentrations of progesterone. In experiment 2 (EXP2), 515 cows diagnosed as anestrus were randomly assigned to untreated control, NCIDR or UCIDR for 6d. Plasma was analyzed for concentration of progesterone 12 d after CIDR removal to determine ovulation. In EXP1, milk yield and body condition did not influence progesterone concentrations. Concentration of progesterone tended to increase faster (P=0.10) in cows receiving UCIDR than NCIDR, but both treatments reached a plateau at 90min. Cows receiving the NCIDR had greater (P=0.04) concentrations of progesterone during the 7-d treatment, but they were mostly subluteal (<1.0 ng/mL) after d 2. After removal, concentrations of progesterone were greater for NCIDR than UCIDR for the first 45 min, and were similar thereafter. Multiparous cows had lesser (P=0.004) concentrations than primiparous cows throughout the study. The pattern of ovarian follicular development was not affected by treatment. In EXP2, induction of onset of estrous cycles increased (P<0.01) with progesterone treatments, but was similar between NCIDR and UCIDR. Proportion of cows experiencing shorter than typical length estrous cycles after first AI tended to be greater (P=0.09) for control cows than those receiving the CIDR, and for cows remaining anestrous than those in which onset of estrous cycles was induced. Pregnancy per AI and pregnancy loss were similar among treatments. Cows that resumed estrous cyclicity prior to first AI had greater (P=0.01) pregnancy per AI. Treatment of high-producing Holstein cows that had previously initiated onset of estrous cycles with CIDR resulted in subluteal concentrations of progesterone, but in anestrous high-producing cows increased induction of estrous cycles with no effect on fertility at first insemination.     

Effects of work and diet on progesterone secretion, short luteal phases and ovulations without estrus in postpartum F1 crossbred dairy cows

The effects of work and diet supplementation on progesterone secretion and on incidence of short luteal phases and ovulations without estrus was investigated in 40 postpartum F(1) crossbred dairy cows. These cows were allocated to 1 of 4 treatment groups: Group SPNW, supplement-nonworking; Group SPW, supplement-working; Group NSNW, nonsupplement-nonworking; and Group NSW, nonsupplement-working. After calving, working cows pulled sledges with a load of 300 to 450 Newtons(N); 4 hours per day 4 days per week, for a total of 100 days over a 1-year period. All cows were fed natural grass hay ad libitum while the supplemented cows were fed 3 kg of concentrate per head per day. The proportion of cows which showed behavioral estrus by 1 year post partum was 100, 100, 60 and 20% for Group SPNW, SPW, NSNW and NSW cows, respectively. Based on plasma progesterone concentrations, ovulation started 62 days earlier than onset of behavioral estrus. A total of 73 ovulations occurred by 1 year post partum. Forty-nine (67.1%) and 26 (32.9%) ovulations occurred in the supplemented and nonsupplemented cows while 33 (45.2%) and 40 (54.8%) ovulations occurred in the working and nonworking cows, respectively. Of the total ovulations, 26 (35.6%) were not associated with behavioral signs of estrus and occurred in 13 (32.5%) cows. The incidence of ovulation without estrus was higher (P<0.05) in working (42.4%) than in nonworking (30%) cows and in nonsupplemented (41.7%) than in supplemented (32.7%) cows. Short luteal phases occurred in 32.5% of the cows before the establishment of normal estrous cycles. In working cows, diet supplementation off-set the negative effect of work on the onset of estrus and conception. However, a relatively higher number of cows in Group SPW had ovulations without estrus before a normal estrous cycle was established. The incidence of short luteal phases or ovulations without estrus did not influence the pregnancy rate in subsequent normal estrus periods. In conclusion, in the supplemented cows, work did not influence the proportion of cows showing estrus and conceiving, but it significantly delayed the postpartum anestrus interval. In the nonsupplemented cows, reproductive activity was impaired in both working and nonworking cows, but was pronounced in working cows. However, once pregnancy was established there was no effect of work on the maintenance of pregnancy. Our study shows that with appropriate feeding regimens lactating crossbred cows could be used for draught purposes without any detrimental effects on fertility, but calving intervals would be extended. Finally, the physiological mechanisms involved in anestrus and ovulations without estrus and the significance of such phenomena in affecting postpartum reproductive performance and fertility in working cows require further investigation.     

Assessment of the post partum Reproductive Performance of the Icelandic Dairy Cow During a 3 Year Period

The time of ovulation, artificial insemination (AI), conception and conception rate were studied in 412 Icelandic dairy cows from 2 different areas during a period of 3 years. To assess these parameters the progesterone level was measured in sequential samples of milk and the status of the genital organs evaluated by monthly rectal palpations. The time and number of AI was recorded and the conception rate calculated and compared with the other parameters. Furthermore, the length of the calving interval and gestation period were determined. The effects of year, season, area, age, herd and parity on these parameters were evaluated. The overall mean for the time of first post partum ovulation was 42 days and varied from 29 to 49 days between herds. This is a considerably longer time than recorded for many other breeds of dairy cows. The effects of season, area and herd were significant for the time of first post partum ovulation. The overall time of first post partum AI and conception were 74 days and 97 days, respectively. In spite of late onset of ovarian activity in Icelandic dairy cows, these two pararmeters are comparable to those of other breeds of cattle. The effects of season, parity and herd were significant for these two parameters. The conception rate to first post partum AI was 59% and the number of AI per conception was 1.6. The time of conception correlated closely (r = 0.5) with the time of first post partum AI, but the conception rate to first AI increased and the number of AI per conception decreased with increasing time of first post partum AI. The calving interval was 382 days and the gestation period was 287 days.     

Fertility in Dairy Cows Managed for Calving Intervals of 12,15 or 18 Months

Effects on reproduction in a total of 135 dairy cows managed for calving intervals of 12, 15 or 18 months (72, 38 and 25 cows respectively) were studied. The cows were of the Swedish Red and White Breed (SRB) and the Swedish Freisian Breed (SLB) and were housed in 2 different herds with 3 different management systems (tied, loose, and tied but milked in a milking parlour; mixed). The cows in one of the herds (48 cows) were assigned for milking either 2 times or 3 times a day. When comparing conception rate at 1st insemination (AI) and the percentage of cows finally pregnant, we found no significant differences between the 3 calving interval groups, however, a tendency for a higher conception rate with a 15 months' interval compared with a 12 months' interval was found in one of the herds (50% vs 41.5%). The percentage of finally pregnant animals varied between 81% and 100%, but this variation was mainly attributed to the herd rather than calving interval group. A significantly higher percentage of cows was treated for anoestrous in the 12-month group than in the 15-month group in one of the herds (28.6% vs. 5.3%). The frequency of ovulations with external heat signs increased with ovulation number up to the 4th ovulation and thereafter remained stable. No significant difference was found in number of AIs required per conception with respect to calving intervals, breeds, or milking frequency groups. However, cows milked 3 times a day had a significantly longer interval from the 1 st AI to conception compared with cows milked 2 times a day (45.8 days vs 17.6 days, p<.01). Cows kept loose exhibited 1st ovulatory oestrous, approximately 2 weeks earlier (55.9 days vs 69.7 days, p<.05) than their herd mates kept tied. In conclusion, our study shows that lengthening the calving interval to 15 or 18 months may have a positive influence on reproduction in terms of less need for treatments of ovarian disorders and higher conception rates. Our results also indicate that milking 3 times a day may have negative effects, and keeping cows in a loose-housing management system may have positive effects on ovarian function. kw|Keywords|k]reproduction; k]extended calving intervals; k]cattle; k]milking frequency     

Effects of propylene glycol drenching on energy balance, plasma glucose, plasma insulin, ovarian function and conception in dairy cows

We postulated that daily drenching of propylene glycol to cows in early lactation would increase plasma glucose and insulin concentrations and improve fertility in postpartum cows. Thirty-six Holstein cows were assigned to treatment or control groups. Each treatment cow was given 500 ml of propylene glycol by drenching daily from 7 to 42 days of lactation. Blood samples for glucose, insulin, nonesterified fatty acids (NEFA), and plasma urea N were collected at 0, 30, and 90 min postdrenching once weekly during 1-6 weeks. Blood samples were collected for progesterone analysis and cows were palpated three times per week until 11 weeks to assess ovarian status. Propylene glycol did not affect dry matter intake (DMI), milk yield or energy balance in treatment cows. After drenching, propylene glycol increased (P<0.01) plasma glucose and insulin and decreased (P<0.01) NEFA; plasma urea N of the treatment group tended (P=0.07) to be higher than that of the control group through 90 min. Days to first service, days open, and services per conception were not different between groups. Conception rates to first insemination were 33% in the control group and 57% in treated cows, but these were not significantly different. First ovulation of treatment cows occurred earlier than that of control cows (32.3 versus 44.5 days, P=0.06) and the length of the first luteal phase was longer in treated cows (13.1 versus 7.3 days, P<0.05). These data are consistent with the hypothesis that insulin is important for normal ovarian function. During negative energy balance, treatment with propylene glycol, which induced small increases in plasma concentrations of insulin, prevented the short luteal phase characteristic of the first estrous cycle in control cows.     

The use of milk progesterone profiles to characterise components of subfertility in milked dairy cows

Milk progesterone (P₄) concentrations of 1682 postpartum (PP) dairy cows during 2503 lactations were used to define and quantify the incidence of atypical ovarian patterns and to assess their impact on reproductive performance. A total of 257 animals (10.94%) with their first significant luteal activity after day 44 PP were considered a result of delayed ovulation type I (DOVI). Prolonged luteal activity (P₄>3 ng/ml for at least 19 days) observed in 170 (7.3%) and 161 (6.35%) animals during first and subsequent cycles was considered a result of the presence of a persistent corpus luteum (CL), respectively denoted as PCLI and PCLII. Following the demise of an oestrous cycle CL, a total of 322 (12.85%) animals showed a delayed ovulation Type II (DOVII) with P₄<3 ng/ml for >12 days. In 238 inseminated animals (9.92%) prolonged luteal activity was followed by the CL demise which may indirectly indicate the incidence of a late embryo to early foetal mortality (LEM). In this study animals during 794 (31.7%) lactations had at least one atypical ovarian pattern before insemination that, in comparison to those with typical P₄ patterns, contributed to a delayed conception (88.2 vs. 106.2 days), higher number of services per conception (1.49 vs. 1.8), lower first service conception rate (60.9 vs. 43.7%) and a reduced total conception rate (92.6 vs. 82.1%), all of which were significantly different at P<0.001. The incidence of PCLI and PCLII before insemination resulted in a higher level of LEM. Milk progesterone monitoring offers an accurate and objective measurement of factors associated with PP ovarian activity which will assist in investigating the genetic and environmental factors affecting fertility.     

Follicular dynamics during postpartum anestrus and the first estrous cycle in suckled or non-suckled Brahman (Bos indicus) cows

Brahman (Bos indicus) cows, were selected at 28+/-10 days after calving and analyzed by real time rectal ultrasonography three times a week, in order to evaluate and compare follicular and corpus luteum development during postpartum (PP) anestrus and the first PP estrous cycle under sylvopastoril conditions. Suckling (S, n=11) or non-suckling (NS, n=5) cows were evaluated in a zone of tropical dry forest (450m of altitude, mean temperature=27 degrees C, annual rainfall=1000mm). Estrous detection was performed twice daily by direct observation. Progesterone was quantified using RIA. From 28+/-10 days postcalving to resumption of estrous cycles, there were no differences (P>0.05) between NS and S cows for diameter of the dominant or first subordinate follicle, follicular growth rate, or interdominance interval. Silent ovulation, corpus luteum formation and subsequent progesterone concentrations ranging from 0.3 to 9. 7ng/ml, were found in both groups. The first calving to ovulation and calving to standing estrus intervals were shorter (P<0.01) in NS (34.8+/-5.81 and 41.2+/-9.03 days) than in S (65+/-4.82 and 81+/-6. 21 days) cows. Follicular development and progesterone concentrations during the first PP estrous cycle did not differ (P>0. 05) between NS and S cows. These results suggest that Brahman cows could have an early PP resumption of follicular recruitment if fed under sylvopastoril system conditions. However, non-suckled cows did have an earlier standing estrus and ovulation than did suckled cows.     

Influence of a CIDR prior to bull breeding on pregnancy rates and subsequent calving distribution

We determined whether insertion of a CIDR for 7 days prior to the breeding season enhanced pregnancy rates and altered the date of conception in suckled beef cows mated naturally. Suckled beef cows (n=2033) from 15 locations were randomly assigned to one of two treatments: (1) cows received a CIDR 7 days prior to the breeding season for 7 days (CIDR; n=999); (2) cows received no treatment (Control; n=1034). On the first day of the breeding season bulls were introduced to herds at a rate of 15-25 cows per yearling bull or 20-30 cows per mature bull. Pregnancy status and the date of conception were determined via transrectal ultrasonography at 56 and 120 days after initiation of the breeding season. Overall pregnancy rates ranged from 59.3 to 98.9% among the 15 locations. The percentage of cows becoming pregnant during the first 30 days of the breeding season was similar between CIDR (68.2%) and Control (66.7%) cows, and overall pregnancy rates were similar between CIDR (88.9%) and Control (88.6%) cows. The average day of conception after initiation of the breeding season was shorter (P<0.01) for CIDR (20.1+/-0.8 days) compared to Control cows (23.2+/-0.8 days). Of cows conceiving during the breeding season, more (P<0.05) CIDR cows (35.9%) conceived during the first 10 days of the breeding season than Control cows (30.8%). Neither body condition score and nor parity affected pregnancy rates or days to conception, whereas pregnancy rates and days to conception were affected (P<0.01) by location and days postpartum. Days to conception were greater for cows that calved within 40 days (31.6+/-1.2 days) of initiation of the breeding season compared to cows calving between 40 and 50 days (25.3+/-1.2 days) prior to initiation of the breeding season, which were greater than those cows calving between 50-60 days (20.0+/-0.8 days) and 60-70 days (21.3+/-1.0 days) prior to initiation of the breeding season. Cows calving greater than 70 days (17.3+/-1.5 days) from initiation of the breeding season had the shortest interval to conception. We concluded that insertion of a CIDR prior to the breeding season failed to increase overall pregnancy rates, but did influence the average day of conception.