Onset of oestrus and fertility in lactating dairy cows injected with an analogue of prostaglandin F2α, cloprostenol

Prostaglandin responses in dairy herd breeding programmes

A re-evaluation of results from ten trials conducted in commercial dairy herds between 1974 and 1981 in which lactating dairy cows were injected once or twice with either of two forms of prostaglandin F2alpha (PGF) showed that: the variation in the post-injection interval to oestrus was influenced by the stage of the oestrous cycle at which treatment was administered; this variation was sufficient to reduce pregnancy rates to set-time inseminations; an accurate aid for oestrus detection, such as tail painting, should be used routinely with PGF; if PGF-treated cows were detected in oestrus before being inseminated, the pregnancy rates to first insemination were usually 10% higher than in untreated herd mates. The results show that PGF systems in dairy herds should not be used as au alternative to accurate oestrus detection. These systems can be used to condense the breeding programme and increase pregnancy rates to first insemination. The exploitation of this fertility effect justifies the reassessment of PGF usage in New Zealand dairy herds.

Associations between the manipulation of patterns of follicular development and fertility in cattle

The wave-like patterns of ovarian follicular development in cattle can be manipulated by shortening the luteal phase with prostaglandin F2alpha (PGF), lengthening the period of follicle dominance with progesterone or curtailing follicle development with GnRH or oestradiol as 17beta, benzoate or cypionate. These hormones can also be used to synchronise ovulation allowing timed inseminations without detected oestrus. Progesterone, PGF, GnRH and oestradiol benzoate have each been used to increase conception rates in some situations, but their use has reduced them in others. For example, inseminations made within 96 h of a single injection of PGF administered during the luteal phase were associated with increased conception rates in dairy cows whereas double injection protocols reduced conception rates. The three forms of oestradiol and GnRH have greater effects on follicular development following divergence and dominance than following wave emergence. This can mean that follicles of differing maturity will be present about 7 days later and can result in varied intervals to the onset of oestrus following a PGF injection. The consequent variation in ovulation time can be reduced by injecting GnRH or an oestradiol during pro-oestrus. This means that some less mature follicles will ovulate, forming corpus luteum (CL) associated with a slower rise in plasma progesterone and lower mid-luteal concentrations. The lower conception rates recorded with single timed inseminations with synchronised ovulations have been associated with increased prevalences of short cycles in lactating dairy cows (with GnRH), with long luteal phases in cows and heifers (with oestradiol benzoate) and with embryo loss following positive pregnancy diagnosis (as with Ovsynch in lactating Holstein cows). Extensive Canadian studies have demonstrated that these same hormones can be successfully used without these limitations and reliably obtaining conception rates over 50% and up to 70% in beef cattle that have been supplemented with a progestin during the period of ovarian follicle synchronisation. The inherently lower fertility of Holstein cows during early lactation may be contributing to the reduced effectiveness of hormonal treatments for synchronised follicle development and ovulation. The role of reduced dose rates of GnRH in compromising this effectiveness needs to be determined if the potential of these treatments realised with beef cattle is to be achieved with lactating Holstein cows.

Recent advances in bovine reproductive endocrinology and physiology and their impact on drug delivery system design for the control of the estrous cycle in cattle

When methods of drug intervention are being developed to control estrous cycles, a thorough understanding of the endocrine and functional changes together with the reproductive behavior of the animals are essential. This review presents our current knowledge on reproductive endocrinology, physiology and behavior, and the methods of drug intervention to control estrous cycles. It also describes current efforts to develop advanced drug delivery systems that meet the animal scientist's demands to control the estrous cycle in cattle.

Use of ultrasonography to help to predict observed oestrus in dairy cows after the administration of prostaglandin F2 alpha

A total of 76 cows from seven herds with an ultrasonographically visible corpus luteum at routine herd fertility examinations were treated with prostaglandin F2 alpha. The sizes of the cavities of all the follicles on both ovaries with a diameter greater than 5 mm were measured. The cows were observed for signs of oestrus over the following six days and the time to onset of oestrus was recorded. Milk samples collected when the prostaglandin was administered and at oestrus were assayed for milk progesterone concentration. The herd of origin, lactation number, body condition score, days after calving at the time of examination and the total number of follicles when the prostaglandin was administered were not found to have any correlation with time to oestrus. Seventy-three of the 76 cows had milk progesterone concentrations consistent with active luteal tissue when the prostaglandin was administered, and 33 of them were observed in oestrus and had low milk progesterone concentration within six days. The mean time to the onset of oestrus was significantly and inversely related to the size of the cavity of the smallest follicle with a diameter of more than 5 mm.

Pharmacologic manipulation of fertility

The professional application of agents to the manipulation of fertility of cows requires basic and applied knowledge of the physiologic mechanisms that are affected and of the pharmacologic agents that are used. In all areas of the pharmacologic manipulation of fertility, the achievement is less than the ideal, and further research is required to improve the efficiency of treatments. The induction of estrus in acyclic animals can involve a reduction in the depth of anestrus, pretreatment with progestagen to ensure estrous behavior and the formation of a normal corpus luteum, and then treatment with exogenous gonadotropin. Responsiveness to treatment can be variable and reflects the depth of anestrus of the animals. Improved treatment regimens require a knowledge of the basic mechanisms involved with the depth of anestrus, a means of assessing the depth of anestrus, and an understanding of the hormonal requirements of ovarian follicles for development and maturation in animals at different depths of anestrus. The optimal precision in the synchronization of estrus (and ovulation) in cyclic animals requires the synchronization of both follicular waves and the end of progestational phase. The end of progestational phase can be synchronized effectively using prostaglandin F2a (or analogs), or by treatment with progestagens with or without luteolytic agents. Procedures to synchronize follicular waves need to be established. The induction of superovulation can be achieved readily using gonadotropins prior to estrus synchronization using prostaglandin F2a. The responses to standard treatments in terms of ovulation rates and yield of transferable embryos are highly variable. The development of procedures to reduce this variability requires an understanding of the intra-ovarian mechanisms involved in recruitment of follicles for a wave of follicular growth, in the selection of dominant follicles for further development, and in the mechanisms controlling follicular atresia. Cystic ovarian disease can be treated effectively using HCG or GnRH (follicular cysts) or prostaglandin F2a (luteal cysts). The basic mechanisms resulting in failure of estrogen positive feedback on LH secretion (that results in cystic follicles) remain to be determined. Small but significant increases in pregnancy rates can be achieved treating cows with prostaglandin during the post-partum period, with prostaglandin to induce estrus for insemination, with GnRH or HCG at estrus, and with GnRH or progestagen treatment during diestrus. Beneficial effects of treatment have been shown in some trials but not in others.(ABSTRACT TRUNCATED AT 400 WORDS)

Comparison of Melengestrol Acetate-Prostaglandin F2α to Syncro-Mate B for estrus synchronization in beef heifers

Three hundred and ten yearling heifers of various breeds were used in five trials to compare two estrus synchronization treatments. Treatment 1 consisted of Melengestrol Acetate-Prostaglandin F(2)alpha (MGA-PGF(2)alpha). Heifers were fed 0.5 mg MGA/head/d for 14 to 16 d. Sixteen or 17 d after the final MGA feeding, heifers were injected i.m. with 25 mg PGF(2)alpha. Treatment 2 consisted of Syncro-Mate B (SMB). Heifers were given a 9-d norgestomet implant plus an injection containing 3 mg norgestomet and 5 mg estradiol valerate i.m. at implant insertion. Heifers were observed for estrus at 6-h intervals for 120 h after the end of treatments and were artificially inseminated 12 to 18 h after observed estrus. Heifers synchronized with MGA-PGF(2)alpha and SMB had a similar (P > 0.10) estrous response (83.4 vs 90.2%) and a similar (P > 0.10) degree of synchrony (71.8 vs 79.0%) following treatment. However, the synchronized conception rate (68.7 vs 40.6%) and the synchronized pregnancy rate (57.3 vs 36.6%) were higher (P < 0.01) in MGA-PGF(2)alpha than SMB heifers. Breeding season pregnancy rates were similar in both treatment groups. Heifers in both groups that were classified as cycling prior to initiation of treatment had improved reproductive performance following synchronization compared with those classified as noncycling. Based on higher synchronized conception and pregnancy rates and lower labor requirements and drug costs, the MGA-PGF(2)alpha system appears to be a better method to synchronize estrus in beef heifers than the SMB system.

Enhanced precision of estrus and luteinizing hormone after progesterone and prostaglandin in heifers

Objectives were to determine if low progesterone and increased basal luteinizing hormone for 3 d after injecting prostaglandin F2 alpha would affect precision of preovulatory surges of luteinizing hormone and onset of estrus in Holstein heifers. In experiments 1 and 2, heifers received progesterone devices for 10 d and prostaglandin F2 alpha on the 7th d after inserting progesterone device. For controls, progesterone devices were removed when prostaglandin F2 alpha was injected, and control devices were installed for 3 d. In experiment 1, jugular blood was sampled every 2 or 4 h from injection of prostaglandin F2 alpha until 108 h after removing progesterone to determine basal and peak secretion of luteinizing hormone. In treatment heifers, basal luteinizing hormone tended to increase, and intervals to peak secretion of luteinizing hormone were shorter and more precise than for controls. In experiment 2, heifers were observed for estrus for 30 min every 4 h for 96 h after removing progesterone devices. Intervals to onset of estrus for experimental heifers were shorter and more precise than for controls. After exogenous prostaglandin F2 alpha, 1 to 2 ng of progesterone per milliliter of serum for 2 to 3 d allows increased basal luteinizing hormone and is associated with increased precision of preovulatory secretion of luteinizing hormone and onset of estrus. This may be an acceptable method to control ovulation precisely for fixed time insemination of cattle.

Estrus synchronization systems involving prostaglandin F2α and progesterone pretreatment in beef heifers

Two trials were conducted to evaluate treatments combining progesterone pretreatment and prostaglandin F(2alpha) (PGF(2alpha)) on estrus response, pregnancy and calving rate in heifers. Treatments in Trial 1 were 1) control (T(1); n=59), 2) 25 mg PGF(2alpha) on Day 0 (T(2); n=58), 3) 150 mg progesterone (P(4), i.m.) in corn oil on Day -24 plus PGF(2alpha) (T(3); n=61), and 4) 150 mg P(4) on Day -5 plus PGF(2alpha) (T(4); n=59). Trial 2 had T(2) and T(4) only. Heifers were artificially inseminated 8 to 16 h after detection of estrus for 10 and 5 d in Trials 1 and 2, respectively. In Trial 1 more heifers in T(3) and T(4) showed estrus by 72 h compared to T(1) and T(2). In T(3), percentages were greater at 84 and 96 h than in T(1) and T(2). There were no differences between T(3) and T(4) or T(1) and T(2) over time. Cumulative distributions of responses showed that more heifers in T(3) and T(4) were in estrus by 84 h after PGF(2alpha) than after other treatments, while T(3) showed the greatest total number of heifers in estrus by 84 h; this difference persisted for 180 h. In Trial 2, percentages of heifers observed in estrus for T(1) and T(4) were not different. Average interval from PGF(2alpha) to estrus was shorter in Trial 1 for T(3) heifers compared to other treatments. No difference was observed in interval to estrus for T(2) and T(4) in Trial 2; this interval averaged 58 h. Artificial insemination pregnancy rates were not different among treatments in either trial and averaged 67.4%. In Trial 1, a greater proportion of heifers in T(2), T(3) and T(4) calved by 35 days into the calving season compared to T(1), but in Trial 2 calving rates for T(2) and T(4) were not different. Progesterone pretreatment combined with PGF(2alpha) appeared to enhance estrus synchronization without influencing either pregnancy or calving rates.

Prostaglandin F2 alpha for lactating dairy cows with a palpable corpus luteum but unobserved estrus

Two experiments in 17 dairy herds were for the effectiveness of prostaglandin F2 alpha (treatment) in reducing luteolysis and inducing intervals to conception of 308 cycling lactating dairy cows. Cows with unobserved estrus before first insemination (Experiment 1) and nonpregnant cows with unobserved estrus after insemination (Experiment 2) were eligible for treatment. Cows in Experiment 1 were assigned alternately either to an untreated control group of 85 or to a group of 138 that received 25 mg prostaglandin F2 alpha after detection of a corpus luteum by ovarian palpation. Cows were inseminated either at estrus or at 72 and 96 h posttreatment in the absence of detected estrus. Intervals from treatment to estrus, to first service, and to conception were longer for controls than for treated cows. Conception at first service was similar for controls (39%) and for treated (43%) cows. Procedures were similar for Experiment 2. Intervals from treatment to estrus and treatment to first service were longer for control cows, and treatment to conception tended to be longer for 39 controls than for 46 treated cows. Conception at first service was similar controls (52%) and treated (44%) cows. Prostaglandin F2 alpha was 91% effective for inducing luteolysis based on progesterone concentrations in blood serum. Successful treatment was dependent upon accurate diagnosis of a functional corpus luteum. Days from treatment to conception were reduced for cows with unobserved estrus if treated cows were inseminated at estrus or by appointment in the absence of detected estrus.

Prostaglandin F2α — A fertility drug in dairy cattle?

Lactating dairy cows were injected once or twice with the Tham salt or an analogue of prostaglandin F(2alpha) (PGF) in a series of nine trials. In specific comparisons involving only those cows observed in estrus during the 24 h before they were inseminated, the average pregnancy rate to first insemination for over 2000 PGF treated cows was 69%, compared to 60% in a comparable number of untreated herd mates. The one trial in which this fertility effect did not occur was one in which semen of low fertility was used only with PGF treated cows. Exploitation of this fertility effect associated with the use of PGF requires accurate diagnosis of estrus. This is necessary because of variation in the interval from injection to estrus and can be achieved by the use of tail paint. This simple technique also allows single PGF injection regimens to be successfully used. The fertility advantages associated with the use of PGF have also been reported by others but may not have received due recognition because of the quest for a procedure which dispensed with the need for estrus detection.