Biomedical subjects

K L Macmillan

Publications and source records attributed to K L Macmillan.

At least 55 records · Page 3Linked to original sources

PubMed2000

Use of a small dose of estradiol benzoate during diestrus to synchronize development of the ovulatory follicle in cattle.

We tested the hypothesis that a small dose of estradiol benzoate (EB) at the midstage of the estrous cycle in cattle would synchronize the subsequent pattern of ovarian follicular development, estrus, and ovulation. Nonlactating Friesian cows received either 1 mg of EB i.m. on d 13 of the estrous cycle (T; n = 12; estrus = d0) or served as untreated controls (C; n = 12). Their ovaries were examined daily with transrectal ultrasonography from d 7, and blood samples were collected 0, 2, 4, 8, 24, and 48 h after treatment on d 13. Plasma concentrations of estradiol-17beta were elevated to 12 pg/mL during the initial 24 h following treatment, compared with a baseline of 1 pg/mL in untreated controls (P < .001). Progesterone concentrations in cows of the T group declined between 24 and 48 h after treatment (-3.2 +/- .5 ng/mL) compared with little change in concentrations of progesterone in cows of the C group at this time (P < .01). This difference was coincident with an earlier time to regression of the corpus luteum in cows of the T group. Disregarding treatment groups, the second dominant follicle of the estrous cycle (DF2) emerged on d 10.6 +/- .3 and was 9.4 +/- .4 mm in diameter on d 13. Further growth of the DF2 was halted by EB treatment on d 13. Cessation of growth occurred irrespective of whether the DF2 was in the early or late growth phase, and a new follicular wave emerged 4.5 +/- .2 d later. The dominant follicle from this wave (DF3) ovulated 5 d after emergence in most cases. During the estrous cycle of every cow in the T group, there were three waves of follicular development (3-wave), whereas the ratio of 2:3 waves of follicular development in cows of the C group was 1:3. Consequently, the interval from emergence to ovulation of the ovulatory dominant follicle in cows of the C group ranged from 3 to 11 d. The dynamics of ovarian follicular wave development during the estrous cycle can be strategically manipulated by treating with a small dose of EB to synchronize proestrous development of the ovulatory follicle.

Animals↗

PubMed2000

The strategic use of estradiol to enhance fertility and submission rates of progestin-based estrus synchronization programs in dairy herds.

Two experiments were performed to evaluate the efficacy of a progestin-based estrus synchronization program that incorporated the use of estradiol at the initiation of progestin treatment and at 48 h after progestin withdrawal (Exp. 2). In Exp. 1, cyclic, lactating dairy cows (n = 112) were assigned to receive either 1 (1mg) or 2 (2mg) mg of estradiol benzoate via an i.m. injection on d -9 (d 0 = initiation of the breeding season). All cows received an intravaginal progesterone-releasing insert (IPI; CIDR-B) on d -9. On d -2, the IPI was withdrawn and all cows were administered 500 microg of cloprostenol sodium. Beginning on d 0, cows were bred by AI upon detection of estrus. Estrus was observed in similar proportions of cows in each treatment during the first 6 d of AI (90% across treatments), but the interval to estrus was shorter (P < .05) in 1mg (1.26 +/- .18 d) than in 2mg (1.77 +/- .18 d). Conception and pregnancy rates did not vary among treatments; however, cows in estrus on d 0 tended to be less fertile (P = .11) than those in estrus on d 1. In Exp. 2, 408 cyclic cows from three herds were assigned to receive either no synchrony treatment (Control, n = 214) or the treatments described in Exp. 1 (1mg, n = 100; 2mg, n = 94). Anestrous cows from all herds received an IPI from d -9 to -2 (n = 143; Anestrus). All cows in the 1mg, 2mg, and Anestrus groups, with the exception of those detected in estrus between d -1 and 0, also received 1 mg of estradiol benzoate on d 0. Greater than 90% of cows that received an IPI were in estrus between d -1 and 3, and 92.1% of cows in the Control group were in estrus by d 21. Conception rate to first service in 2mg (61.7%) was similar to Control (57.0%), tended to be higher (P = .06) than 1mg (49.0%), and was greater (P < .05) than Anestrus (39.9%). The mean day of conception was earlier (P < .05) in the 2mg (d 13.1 +/- 2.0) than the Control (d 23.2 +/- 1.6) and Anestrus (d 22.4 +/- 1.9) groups. Conception occurred earlier in 1mg (d 17.4 +/- 2.1) than in Control. The proportion of cows that were pregnant at the end of the breeding season tended (P = .09) to be greater in the 2mg and Anestrus groups. This regimen of estrus synchronization improved reproductive competence in cyclic cows and resulted in similar reproductive performance in anestrous cows and untreated cyclic cows inseminated at a spontaneous estrus.

Administration, Intravaginal↗

PubMed1999

The inter-ovarian distribution of dominant follicles is influenced by the location of the corpus luteum of pregnancy.

The objective was to characterise the distribution of dominant ovarian follicles in the early post-partum period in relation to the side of the preceding pregnancy and its relationship with the left and right ovaries. Primiparous cows were enrolled over a 2-year period (n = 33 in Year 1 and n = 28 in Year 2). Ovarian follicles were observed daily by trans-rectal ultrasonography commencing within 9 days of calving. Dominant follicles (DF) were described as occurring on the ovary ipsilateral to the CL of preceding pregnancy (ipsilateral ovary of pregnancy, IOP) or contralateral to the CL of the preceding pregnancy (contralateral ovary of pregnancy, COP), and as occurring on the left or right ovary. Results in Year 1 were analysed for the effect of breed (Friesian n = 15; Jersey n = 18). There was a bias towards the COP for the first DF post-partum in both breeds (DF1; 70%; p<0.05). A breed interaction was observed with the second DF post-partum with a bias towards the COP in the Friesian (93%; p<0.05); but not the Jersey animals (50%). In Year 2, all cows were Friesians, and there was again a biased distribution of the DF1 towards the COP (89%; p<0.05) and for the combined distribution of the first three DF post-partum (76%; p<0.05) as well as the first ovulatory follicle (71%; p<0.05). A comparison of the pooled data for the location of the DF1 from both years showed that only one DF1 was observed on a left ovary in the 29 cases where the preceding pregnancy was also on the left side. This study demonstrated a bias in the distribution of DL in the early post-partum period towards the ovary on the side opposite that of the preceding pregnancy as well as towards the right side.

Animals↗

PubMed1999

Treating cattle with progesterone as well as a GnRH analogue affects oestrous cycle length and fertility.

Initiating the chronic administration of progesterone to cattle during metoestrus will produce shortened oestrous cycles containing one or two wave-like sequences of ovarian follicle development. Conception rates are reduced to inseminations at the oestrus preceding these shortened cycles. In contrast, a single injection of the GnRH analogue, buserelin, around mid-dioestrus can lengthen the oestrous cycle by increasing the proportion of cycles with three waves of follicular development and may also increase conception rates. A series of trials was conducted to test the hypothesis that the adverse effects of progesterone on oestrous cycle length and conception rate could be prevented with a strategic injection of GnRH. In Trial 1, progesterone was administered per vaginum to heifers for 10 days from Day 2 or 3 (Oestrus = Day 0) and with (n = 42) or without (n = 46) an injection of a GnRH analogue (10 microg buserelin) on Day 12 or 13. Other heifers (n = 44) served as an untreated control group. The average inter-oestrous interval (IOI) for those heifers treated only with progesterone was 17.0 days and was less (p<0.05) than the average intervals for those also receiving GnRH (20.2 days) or in the control group (20.0 days). In Trial 2, 45 heifers were inseminated following a synchronised oestrus. Progesterone was administered as in Trial 1 to 22 of the heifers. Their conception rate was 45.4% and this was less (p<0.05) than the 73.9% obtained with their 23 untreated contemporaries. Trial 3 was completed using 530 cows in commercial dairyherds. The 259 cows receiving progesterone and GnRH (buserelin) after their first inseminations had a conception rate of 68.3% compared to 56.1% for their 271 untreated herdmates (p<0.05%). Heifer calves born to treated cows had heavier birthweights (33.4 vs. 31.1 kg; p<0.05), but birthweights of bull calves were unaffected (35.5 vs. 35.8 kg). Gestation lengths for cows conceiving to first inseminations were similar for treated and control groups (280.9 vs. 280.5 days). The results of these trials confirmed the hypothesis that a strategic injection of the GnRH analogue, buserelin, could prevent the reductions in oestrous cycle length and conception rate associated with the chronic metoestrous administration of progesterone.

Administration, Intravaginal↗

PubMed1999

Ovarian responses to progesterone and oestradiol benzoate administered intravaginally during dioestrus in cattle.

This study examined the effects of administering progesterone and oestradiol benzoate (ODB) during mid-dioestrus, on ovarian follicular dynamics in cattle. Twelve cycling cows were used in a 4 x 4 latin square design, with the 4 treatments being initiated on Day 13 of the cycle (oestrus = Day 0) and comprising intravaginal insertion for 5 days of: (i) a progesterone releasing device (CIDR; 'P4'); (ii) a CIDR device with a gelatin capsule containing 10 mg ODB and 1 g lactose (CIDIROL; 'P4/ODB') attached; (iii) a placebo CIDR device with the 10 mg ODB capsule (ODB); and, (iv) a placebo CIDR device alone (CTRL). The ovaries of each cow were examined daily by transrectal ultrasonography from Day 7 of the cycle until subsequent ovulation. Blood samples were collected daily from Day 11, and at intervals of 2-4 h during the 24 h period either side of treatment initiation. The second dominant follicle (DF2) emerged on Day 10.7 +/- 0.2 (mean +/- SEM), and was 8.5 +/- 0.2 mm in diameter by Day 13. The DF2 developed through to ovulation (2-wave cycles) in half of the animals in the CTRL group; while in the other half of cases, the ovulatory follicle originated from the third follicle wave that emerged on Day 17.2 +/- 0.4. Administration of a CIDR device alone (P4 group) did not alter the 1:1 ratio of 2 and 3-wave cycles, but the third dominant follicle (DF3) in those cows with 3-wave cycles emerged earlier on Day 15.6 +/- 0.2. In contrast, the DF2 of every animal in the ODB and P4/ODB groups became atretic and was replaced by a DF3 which emerged 4.0 +/- 0.3 days later. The effects of ODB on luteal function were limited to an earlier decline in plasma progesterone concentrations from 2 to 4 days after device insertion and a reduction in diameter of the corpus luteum when administered concurrently with progesterone. Intravaginal administration of 10 mg ODB on Day 13 of the oestrous cycle, with or without progesterone, was effective in promoting follicle wave turnover. In the absence of ODB, progesterone administration alone (P4 group) did not alter the ratio of animals with 2 or 3-wave cycles from that observed in animals in the CTRL group, but did advance the timing of subsequent follicle wave emergence in those animals with 3-wave cycles.

Administration, Intravaginal↗

PubMed1999

Insemination at the second of two induced oestrous periods in anoestrous dairy cows increases conception rates to first service.

AIM: To determine whether mating previously anoestrous cows on their second, rather than first, oestrus post pm-turn could increase conception rates to that service. METHODS: Cows diagnosed as anovulatory anoestrus were allocated to two groups, starting treatment on Day -17 (OES2) or on Day -7 (OESI) where the date of the planned start of mating = Day 0. All cows were treated with intravaginal progesterone (CIDR device) for 6 days and an injection of 1 mg oestradiol benzoate 24 h after removal of the device. Cows in the OES2 group were also injected with prostaglandin F2alpha on Day 0. RESULTS: During the first 7 days of mating, 61.8% (207/335) and 88.2% (328/372) of cows in the OES2 and OESl groups, respectively, were inseminated on detection of oestrus (p <0.001). Oestrus without ovulation occurred in 1.5% of cows in the OES2 group and 6.2% of cows in the OESl group during this period (p <0.01). Of those cows inseminated in the first week of mating, conception rates were 54.0% in the OES2 group and 45.5% in the OESl group (p = 0.05). There was no significant difference in median interval from start of mating to conception between the two groups (24 and 22 days for OES2 and OESl, respectively, p >0.05). CONCLUSION: Mating previously anoestrous cows on their second, rather than first oestrus post partum increased conception rates to that service. However, median intervals from start of mating to conception were not altered.

Journal Article↗

PubMed1998

Fertility regulation in cattle.

This paper reviews the physiological, endocrinological and pharmaceutical literature pertaining to the design, development and optimisation of subcutaneous and intravaginal progestogen-containing drug delivery systems used in the control of synchrony and ovulation in cattle.

Administration, Cutaneous↗

PubMed1998

Controlled-release products for the control of the estrus cycle in cattle, sheep, goats, deer, pigs, and horses.

This paper describes the estrus cycles of a number of livestock breeds and reviews the controlled-release drug delivery systems that are currently available for the purpose of controlled breeding. The bovine estrus cycle is reviewed in detail, and the estrus cycles of other species are described in a manner that highlights similarities and differences between species. Pertinent formulation and pharmacokinetic information about current drug delivery systems is presented and discussed, and recent advances in this area are also described.

Animals↗

PubMed1997

Reproductive performance of lactating dairy cows following estrus synchronization regimens with PGF2alpha and progesterone.

The objective of this study was to evaluate the reproductive performance of lactating cows in seasonal dairy herds after estrus synchronization with PGF2alpha (PG) with or without supplementation with progesterone (P4). In Trial 1, synchronized cows (S1; n = 521) were compared with untreated control cows (C; n = 518) in 5 herds. Estrus of cows in the S1 group was synchronized with 2 treatments of PG (Lutalyse) 13 d apart. The breeding season started 2 d after the second PG. Cows were first bred by AI for 7 wk and then herd sires were used. Compared with C cows, estrus synchronization in the treated cows reduced the conception rate to first AI (61.1 vs 70.5%; P < 0.01) and the intervals from start of the breeding season to conception for cows conceiving to AI (11.0 vs 14.6 d; P < 0.05) or to both AI and natural mating (16.5 vs 18.4 d; P < 0.05). There was no effect on conception rate to second AI (68.8%), on pregnancy rate by Day 24 (72.3%) or Day 49 (86.3%) of the breeding season, or on the percentage of cows not pregnant at end of the breeding season (5.0%). In Trial 2, effects of P4 supplementation before the second PG on reproductive performance were evaluated in 4 herds. Estrus of each cyclic cow was synchronized with PG as in Trial 1. Half of the cows in each herd were treated with an intravaginal P4 device (CIDR) for 5 d before the second PG (S2+P4, n = 608), whereas the remaining half received no CIDR treatment (S2, n = 593). Compared with S2 cows, P4 treatment increased the estrous response rate to the second PG (89.6 vs 82.9%; P < 0.01), the conception rate to first AI (65.1 vs 59.7%; P = 0.07), the pregnancy rate by Day 6 of the breeding season (59.3 vs 49.0%; P < 0.001), and reduced the intervals from start of the breeding season to conception for cows conceiving to AI (8.6 vs 10.4 d; P < 0.10) or to both AI and natural mating (12.7 vs 16.4 d; P < 0.01). Treatment with a used CIDR from Days 16 to 21 after start of breeding to re-synchronize returns to service had no effect on conception rate to first or second AI but may decrease the conception rate to second AI in cows previously treated with CIDR. In conclusion, estrus synchronization with the double PG system can reduce fertility, while P4 supplementation for 5 d before the second PG can improve estrous response and overall reproductive performance. Stage of the estrous cycle at the time of the second PG can affect fertility following synchronization.

Journal Article↗

PubMed1997

Selected times of insemination with microencapsulated bovine spermatozoa affect pregnancy rates of synchronized heifers.

This experiment was designed to test whether spermatozoa encapsulated in an alginate poly-L-lysine matrix had an extended fertile life in vivo after insemination. Estrus was synchronized in 417 primiparous Friesian and Jersey heifers with a system based on a CIDR-B intravaginal device before the heifers were inseminated either during proestrus (24 h after device removal) or at estrus (48 h after device removal). Pregnancy rates to first inseminations did not differ between the 24 and 48 h inseminations (61 vs 60.6%) with liquid semen diluted in Caprogen (control) but differed with encapsulated semen (45.1 vs 68.6%). The difference in pregnancy rates between the 2 types of semen was more pronounced (P < 0.08) in the animals that were visually detected in estrus. The mean survival time of spermatozoa in the female reproductive tract following insemination at the 24-h insemination time was estimated to be 50 +/- 7.5 h. The increased pregnancy rate with insemination of encapsulated spermatozoa at 48 h could have been due to this process predisposing spermatozoa to capacitate soon after insemination.

Journal Article↗

PubMed1997

Treatment of post-partum anoestrous dairy cows with progesterone, oestradiol and equine chorionic gonadotropin.

Anoestrus in lactating dairy cows at the start of the breeding season is a major form of reproductive wastage for seasonal dairy production based on pasture. The objective of this study was to compare the reproductive performance of anoestrous cows that were treated with a combination of progesterone, oestradiol and equine chorionic gonadotrophin either 10 days before (T-10, n = 2 19) or 16 days after (T+16, n = 229) the start of the breeding season. A higher percentage of cows in the T-10 group were detected in oestrus and inseminated during the first 6 days of breeding than those in the T+16 group (69.4% v. 26.2%. p <0.001). However, the percentage of cows detected in oestrus by Day 16 was similar between the two treatment groups (T10 v. T+ 16; 77.7% v. 76.7%). There was no difference between treatment groups in conception rate to the first (51.2% v. 59.0%) or the second insemination (50.8% v. 57.6%), in pregnancy rate over the first 49 days (74.0% v. 75.1%), in empty rate (10.0% v. 10.5%) or in the mean day of conception from the start of the breeding season (24.0 v. 25.7 days). These results suggest that, under favourable environmental conditions, treatment of anoestrous cows with the programme used in this trial can be performed 16 days after the start of the breeding season with similar results to that performed 10 days before the start of the breeding season. Further studies are needed to determine if this is the case under different environmental conditions or for other treatment programmes.

Journal Article↗

PubMed1997

Impact of exporting dependence on livestock production systems, industry structure, and research.

From 84 to 93% of New Zealand's annual production from livestock is exported to over 100 markets throughout the world. This export dependence has produced production systems that are low-cost because the Mediterranean maritime climate allows animals to graze outdoors throughout the year without provision for housing and with minimal requirements for cropping, harvesting, and forage storage. These systems exploit the inherent tendencies for ruminants to have annual production cycles that can be synchronized to use the seasonal availability of pasture, but this means that processing facilities must handle peak supply for brief periods. Processing technology can reduce the impact of peaks in supply that may not match market demand. The disadvantages of seasonality in processing costs are outweighed by lower production costs, as well as by the opportunity to manage large numbers of animals per labor unit. Cooperative structures that are owned by livestock producers are a common feature, especially in New Zealand's dairy industry. This continued preference for cooperatives may reflect the need to have a guaranteed processor for a perishable product such as milk, as well as sharing the risk in an export industry that has scant control over prices received. In addition, management systems for ruminant livestock can only respond slowly to changes in market demand because their production cycles last at least 12 mo and only one or two offspring are produced in each cycle. Export marketing of livestock products is complicated by trade barriers and by dumping of subsidized surpluses. Negotiations to eliminate these practices may mean that livestock production systems in many countries will have to adopt some principles similar to those developed in New Zealand, not because of export dependence but because this dependence has created low-cost systems.

Agriculture↗

PubMed1997

Adrenocortical responses to an adrenocorticotropic hormone in bulls and steers.

We hypothesized that the sexual status of male cattle would influence adrenocortical responses to exogenous ACTH. Eight male Holstein-Friesian cattle, four intact and four castrated at 4 mo of age, were submitted to adrenal response tests using .01 mg ACTH(1-24)/100 kg live weight at 6, 8, 10, and 15 mo of age. At 11 mo of age, a dose-response study using three dose rates of ACTH (.01 to .04 mg/100 kg live weight) with an intensive blood sampling regimen was also carried out. In the longitudinal study, the responses to exogenous ACTH were similar in the bulls and steers at 6 mo of age. By 8 mo, the responses of the bulls had declined (P < .01), and they remained less than those of the steers thereafter (P < .01). This difference was confirmed in the dose-response study. Plasma cortisol concentrations at 50 min and at peak were 1.5 times greater in the steers than in the bulls at equivalent dose rates of ACTH (P < .001). The results of these studies clearly indicate that adrenocortical function of male dairy cattle, after the age of puberty, is influenced by the presence of the testicles. The observed changes may be a result of direct modulation of steroidogenesis by androgens, changes in negative feedback to the pituitary, inhibition of the hypothalamo-pituitary adrenal axis from higher centers, or a combination of these factors.

Adrenal Cortex↗

PubMed1996

Oestradiol potentiates a prolonged progesterone-induced suppression of LH release in ovariectomised cows.

Our working hypothesis was that the negative feedback effect of progesterone on LH secretion in ovariectomised cows is greatly enhanced by oestradiol when both hormones are administered intravaginally. Each of eight ovariectomised cows had a progesterone releasing device ('CIDR-1'; Eazi-breed CIDR-B. InterAg, Hamilton, New Zealand) inserted into the vagina for 3 days, followed by an injection of 1 mg oestradiol benzoate (ODB) in peanut oil 24 h after device removal. The timing of this injection was designated as Day 0. The CIDR-1 was reinserted concurrently with an injection of 0.4 mg ODB on Day 5. An additional device ('CIDR-2') was inserted 4 days later (Day 9). In four of the cows, an ODB capsule (CIDIROL), Douglas Pharmaceuticals. Auckland, New Zealand) was placed into a groove on the surface of CIDR-2 preceding insertion. CIDR-2 was withdrawn after 5 days (Day 14) and CIDR-1 was withdrawn 2 days later (Day 16). The treatment regimen was repeated in a cross-over design where each cow received CIDR-2 with or without an ODB capsule. Blood samples were collected at intervals of 15 min for a period of 16 h beginning 8 h before insertion of CIDR-2 to determine changes in LH secretion pattern, and then at intervals of 8 h until 48 h after removal of CIDR-1 to determine mean LH and steroid concentrations. Concentrations of progesterone in plasma reflected the effects of inserting and removing each CIDR device. The insertion of CIDR-2 elevated progesterone from 2.0 +/- 0.1 ng ml-1 to 4.9 +/- 0.1 ng ml-1 within 30 min (P < 0.01) and maintained levels > 3 ng ml-1. Withdrawal of CIDR-2 produced a new baseline level of 1.8 +/- 0.1 ng ml-1 within 4 h (P < 0.01). Concentrations of oestradiol-17 beta in plasma increased from a baseline of < 1 pg ml-1 to-a-maximum of 12.6 +/- 2.2 pg ml-1 at 22 h after insertion of an ODB capsule. Initial pulse frequency of LH (1.2 +/- 0.05 pulses h-1) and mean concentration of LH (1.6 +/- 0.1 ng ml-1) declined (P < 0.05) to 0.2 +/- 0.1 pulses h-1 and 0.5 +/- 0.1 ng ml-1 during the period from 2 to 8 h following insertion of CIDR-2. Mean concentrations recovered to pre-treatment levels (> 1 ng ml-1) within 48 h if CIDR-2 was inserted without an ODB capsule. In contrast, LH levels remained less than 0.7 ng ml-1 for 5 days following this form of ODB treatment. A subsequent increase in mean LH of 1.4 +/- 0.2 ng ml-1 (P < 0.05) was inversely synchronised with the precipitous decline in progesterone of 1.2 +/- 0.1 ng ml-1, following removal of CIDR-2. The inclusion of an ODB capsule with insertion of CIDR-2 reduced concentrations of FSH from 166 +/- 17 ng ml-1 to a new baseline of 105 +/- 16 ng ml-1 within 24 h (P < 0.05). In conclusion, an acute increase in progesterone induced a transient suppression of LH lasting less than 48 h. This suppression was prolonged to 5 days by the concurrent insertion of a capsule containing 10 mg ODB. The subsequent recovery of LH was coincident with the decline in progesterone following removal of CIDR-2.

Administration, Intravaginal↗

PubMed1996

Effects of administering progesterone at selected intervals after insemination of synchronized heifers on pregnancy rates and resynchronization of returns to service.

In 3 separate trials at 2 locations, dairy heifers (n = 396) were treated with a Controlled Internal Drug Release (CIDR) progesterone device for 9 d. On Day 7 of CIDR treatment, all heifers were injected with PGF(2alpha). Synchronized estruses were detected using a tailpaint and chalk (TPC) scoring system. An animal's tailhead was painted at device insertion, and this strip was covered with a contrasting color of chalk at device removal. Over all trials, 85.1% of the heifers were detected in estrus and were inseminated at 48 or 72 hours after CIDR removal. These synchronized and inseminated heifers were divided into the following treatment groups: 1) untreated controls, receiving no further treatment (n = 138); 2) post-insemination progesterone supplementation with a new (n = 59) or used (n = 29) CIDR device for Days 1 to 8 or 2 to 9, respectively, following insemination; or 3) resynchronization of return to service with a used CIDR device for Days 17 to 22 after insemination (n = 112). The pregnancy rate to first insemination in the control and resynchronized groups (Groups 1 and 3) was 46.4%, but decreased to 18.2% with the post-insemination progesterone supplementation. Resynchronization of returns to service (estrus detected 1 to 4 d following removal of second CIDR) occurred in 58.9% of all nonpregnant heifers in Group 3. In summary, CIDR devices used in conjunction with PGF(2alpha) effectively synchronize estrus in dairy heifers. Progesterone supplementation within 2 d of first insemination for 7 d suppressed fertility. Used CIDR devices inserted for Days 17 to 22 after first insemination resynchronized heifers not pregnant to first insemination.

Journal Article↗

PubMed1996

Reproductive performance of lactating dairy cows following oestrus synchronisation with progesterone, oestradiol and prostaglandin.

The ability to synchronise onset of oestrus, and hence the time of breeding and calving, offers potential economic and management benefits to dairy farmers, especially in herds with seasonally concentrated calving patterns. A trial involving 2681 cows in 11 seasonal herds was conducted to evaluate the reproductive performance of lactating dairy cows following oestrus synchronisation with a combination of progesterone, oestradiol and prostaglandin. Cows were randomly assigned within herds to synchronised and control groups, balanced for age, date of calving, body condition and breed. Cows in the synchronised group were treated with an intravaginal progesterone-releasing device containing 1.9 g of progesterone and a gelatin capsule containing 10 mg of oestradiol benzoate 10 days prior to the planned start of the breeding season (Day 0). The device was removed 8 days later on Day -2 and a luteolytic dose of prostaglandin F2alpha was administered 2 days prior to removal of the progesterone-releasing device. Returns to service for cows in the synchronised group were synchronised by inserting a previously used intravaginal device during Days 16-21 after the start of the breeding season. Cows in the control group were left untreated. The percentage of cows being inseminated during the first 5 days was 89.0% for the synchronised group compared to 29.7% for the control group. Compared to cows in the control group, those in the synchronised group had a lower conception rate to the first insemination (52.9% v. 64.3%, p<0.001), a lower conception rate to the second insemination (51.8% v. 62.5%, p<0.001), a higher percentage of empty cows at the end of the breeding season (7.3% v. 5.1%, p<0.05), and more insemination services per pregnancy to artificial insemination (2.0 v. 1.6, p<0.001). There was no difference between the synchronised and control groups in the percentage of cows pregnant to artificial insemination (81.8% v. 85.5%, p>0.10). The mean day of conception from the start of the breeding season was advanced (p>0.0 1) by 1.3 days in synchronised cows (19.9 +/- 0.7 days; mean +/- SEM) compared to control cows (21.2 +/- 0.5 days). It is concluded that the oestrus synchronisation regime used in the present study caused a reduction in fertility, which reduced the potential gains from using such a programme to increase reproductive efficiency in dairy cows.

Journal Article↗

PubMed1996

The effects of lactation on the fertility of dairy cows.

Lactation has been negatively associated with fertility because pregnancy rates in maiden heifers exceed those obtained after first or subsequent calvings. The extent of this difference is less in pasture-fed dairy cows ( < 10%) than in American Holsteins ( > 20%) fed grain and conserved forages. The latter cows have pregnancy rates to first insemination and oestrus detection rates of only 40 to 45%. This suggests that the subsequent fertility of inherently fertile Holstein heifers may be severely compromised by high levels of milk production. International comparisons show that pasture-fed dairy cows may experience extended periods of anovulatory anoestrum but have normal fertility (60% pregnancy rate to first insemination) once cycling. The high-producing American Holstein may ovulate within 4 weeks postpartum but is more likely to continue ovulating without being detected in oestrus. Both situations are associated with negative energy balances (NEB) during early lactation. The severity and duration of this NEB may vary with body condition at calving, age or parity, ration formulation, production level and environmental factors. Relative daily milk yield is not an absolute indicator of NEB, because some lower producing cows within a herd have lower feed intakes and more severe energy deficits. NEB is not simple to measure; nonetheless, it is correlated with genetic improvement for milk yield. A positive energy balance, greater weight gain and higher body condition score have all been shown to be positively correlated with plasma progesterone concentrations in early lactation. No studies have investigated the possibility that the rapid increase in metabolic rate at this time may also alter steroid concentrations with consequent effects on oestrous behaviour and fertility. Studies to more precisely define the effects of increasing milk yields in early lactation, especially in Holsteins, may need to be completed in Australia and New Zealand. Oestrus detection rates and pregnancy rates for American Holsteins of less than 50% are accepted widely in the USA. Such low detection rates confound studies on fertility. The objective should be to increase these 2 rates to at least 80% and 60% respectively. This may involve the use of controlled breeding, especially if oestrous behaviour is less overt in high-producing Holstein cows.

Animals↗

PubMed1995

Some effects of feeding pasture silage as a supplement to pasture on reproductive performance in lactating dairy cows.

Supplementation of a ryegrass/white clover pasture diet with pasture silage is a common management practice in New Zealand dairy herds. The effect of this supplementation on reproductive performance has not been investigated. Five herds of 20 cows were formed before calving commenced on 1 June 1992. From 5 August to 4 September, two of these herds were fed 5 kg/cow/day of pasture silage in addition to the ryegrass/white clover pasture offered to all herds. Pasture silage supplementation did not alter the intervals from calving to first ovulation, first oestrus, or to conception. However, it reduced the first service conception rate (37.5% v. 53.3%; difference +/- sed = 15.8 +/- 10.0%, for pasture and silage and pasture only cows, respectively). A positive effect on reproductive performance of pasture silage supplementation was not demonstrated in this trial.

Journal Article↗