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J. M. SREENAN

Summary.

A total of 273 Hereford cross heifers were treated with intravaginal progestagen pessaries to determine some of the factors affecting oestrous response and fertility following long-term (20-day) and short-term (10-day) treatments. Oestrous response and degree of synchronization were high after treatment for 20 days, but the fertility rate was lower than that of control heifers. There was no difference in the fertility of heifers inseminated artificially and those mated naturally. When the treatment period was reduced to 10 days and 900 mg progesterone and 5 mg oestradiol valerate given intramuscularly at the start, a high oestrous response and a low degree of synchronization resulted, but the conception rate was similar to that of the control animals. Reducing the dose of progesterone to 250 mg resulted in a high oestrous response and a high degree of synchronization. The stage of the cycle at the start of the 10-day treatment did not affect the oestrous response. Retention of the progesterone pessary was low (79·9%) in heifers treated for 20 days, but was 100% in those treated for 10 days.

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M. Grealy and J. M. Sreenan

The effects of direct and indirect activation of adenylyl cyclase on the production of intracellular and extracellular cAMP and cGMP by 13- to 16-day-old cattle embryos were determined. Embryos were incubated for 2 h in a Krebs Ringer bicarbonate medium containing the phosphodiesterase inhibitor isobutyl-methylxanthine, to which stimulating agents forskolin (100 μmol l−1), cholera toxin (2 μg ml−1), or both were added. Total (intraand extracellular) basal cAMP and cGMP concentrations ranged from 6.65 ± 0.895 to 3.4 ± 0.708 fmol μg−1 protein in 13-day-old embryos and from 4.05 ± 1.151 to 0.19 ± 0.041 fmol μg−1 protein in 16-day-old embryos. Forskolin induced an increase (P < 0.001) in cAMP that ranged from 5.4-fold on day 13 to 2.7-fold on day 16, whereas cholera toxin induced an increase (P < 0.001) that ranged from 30-fold at day 13 to 21-fold at day 16, similar to the effect of forskolin and cholera toxin combined. Individually, forskolin and cholera toxin had no effect on cGMP concentrations, but together they induced an increase (P < 0.05). cAMP (P < 0.01) and cGMP (P < 0.001) concentrations decreased with embryo age from day 13 to day 16 for all treatments; the decrease was greater for cGMP than cAMP (5-24-fold versus 1.6-3.3-fold, respectively). It is concluded that inducible adenylyl cyclase is present in 13- to 16-day-old cattle embryos and that the embryos secrete cAMP and cGMP into the incubation medium. In addition, basal and inducible concentrations of cAMP and cGMP decrease with embryo age from day 13 to day 16. These observations indicate that cAMP and cGMP may have a role in the rapid embryonic cell proliferation that occurs at this time or in signalling to the endometrium.

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J. M. Sreenan and D. Beehan

High pregnancy and egg survival rates can be achieved following surgical egg transfer techniques in the cow (Rowson, Lawson & Moor, 1971; Sreenan, Beehan & Mulvehill, 1975). The application of such techniques under farm conditions requires the development of simple non-surgical transfer techniques, but attempts to develop such procedures have so far resulted in pregnancy and egg survival rates much lower than those achieved by surgical techniques (Rowson & Moor, 1966; Sreenan, 1975; Lawson, Rowson, Moor & Tervit, 1975; Boland, Crosby & Gordon, 1975), perhaps because of egg expulsion or the introduction of uterine infection (Rowson, Lamming & Fry, 1953; Rowson, Bennett & Harper, 1964). More recent work indicates a trend towards improved pregnancy rates when non-surgical transfers are carried out between Days 6 to 9 of the oestrous cycle rather than earlier (Lawson et al., 1975; Sreenan, 1975).

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J. M. SREENAN and P. MULVEHILL

Summary.

Progestagen-impregnated pessaries were inserted into 205 heifers on eight farms. Treatments were either pessaries only for 20 days or pessaries for 10 days combined with an intramuscular injection of 250 mg progesterone+ 7·5 mg oestradiol benzoate on the day of insertion. Pessary retention was low (86·7%) over the 20-day period, but high (93·6%) during the 10-day period. Calving rates of heifers inseminated in oestrus following the 20-day treatment were low, while those of heifers inseminated on a fixed-time basis with the 10-day treatment were slightly higher than those of control heifers.

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J. M. Sreenan and D. Beehan

The Agricultural Institute, Belclare, Galway, Ireland

In sheep, embryonic loss is higher after multiple ovulation than single ovulation (Casida, Woody & Pope, 1966; Edey, 1966; Mackenzie & Edey, 1975). Among twin-ovulating sheep, mortality is greater if both ovulations occur from the same ovary (Baier & Russe, 1968; Scanlon, 1972). Few data are available on the incidence of multiple ovulation in cattle and the extent of prenatal loss in multiple pregnancies is unknown. The development of egg transfer techniques in cattle (Rowson, Moor & Lawson, 1969) has permitted the establishment of twin pregnancies (Rowson, Lawson & Moor, 1971; Sreenan, Beehan & Mulvehill, 1975), and the embryonic survival and development in heifers becoming pregnant after bilateral surgical transfers were therefore examined.

Superovulation, egg recovery and transfer were carried out as previously described (Sreenan et al., 1975). All recipient heifers were checked for return to oestrus with the aid of vasectomized bulls. Initial

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P. Mulvehill and J. M. Sreenan

Many studies have shown that suckling beef cows have an extended anoestrous period after parturition (Wiltbank & Cook, 1958; Foote & Hunter, 1964; Chupin, Pelot, Alonso de Miguel & Thimonier, 1976). The interval from parturition to first oestrus has been shown to be prolonged by low-energy intake before or after parturition (Wiltbank, 1970) and also by suckling (Oxenreider 1968; Graves, Lauderdale, Hauser & Casida, 1968; Wiltbank, 1970). Fertility following artificial insemination of nursing beef cows is lower than in non-nursing cows and in the former the fertility level increases with the interval from parturition (Graves et al., 1968). The use of exogenous steroids to induce oestrus in suckling cows has generally resulted in a decrease of the post-partum interval to oestrus but fertility levels have been low (Ulberg & Lindley, 1960; Foote, Weeth & Hunter, 1960; Foote & Hunter, 1964; Smith & Vincent, 1972). In cyclic animals, normal fertility has been obtained after administration of progestagen for oestrous cycle control (Wiltbank & Kasson, 1968; Wishart & Young, 1974; Roche, 1974; Sreenan & Mulvehill, 1975). Using progestagens, Sreenan & Mulvehill (1974) reported a calving rate of 48% in suckling beef cows following a fixed-time insemination. Stimulation of follicular growth following the use of PMSG has been reported to result in a higher oestrous response and improved degree of synchronization in heifers when administered in combination with a short-term oestrous synchronization treatment (Thimonier, Pelot & Chupin, 1976).

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J. M. SREENAN and D. BEEHAN

The Agricultural Institute, Beldare, Galway, Ireland

(Received 13th June 1974)

Apart from the results reported by Rowson, Moor & Lawson (1969), Rowson, Lawson & Moor (1971) and Rowson, Lawson, Moor & Baker (1972), no data are available on pregnancy rates following the surgical transfer of fertilized cow eggs. Rowson et al. (1969) recorded a pregnancy rate of 91 % in a group of eleven heifers, each of which received either two or three fertilized eggs transferred to the uterine horn adjacent to the ovary carrying the corpus luteum. No incidence of twinning was recorded following these transfers. Rowson et al. (1971) reported a twinning rate of 50% following the transfer of one fertilized egg to each uterine horn in eighteen recipients. The total egg survival in this study was 61·1 %. When both the donor and recipient were in oestrus on the same day, however, the corresponding rates were 71·4%

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J. M. Sreenan and T. McDonagh

Summary. In Exp. 1, embryo survival rates of 45 and 47% were recorded after artificial insemination and ipsilateral transfer respectively. In Exp. 2, pregnancy rates of 62 and 60% were recorded after artificial insemination and contralateral transfer to inseminated recipients respectively. In this experiment the contralateral transferred embryo survival rate was 44%. Transferred embryo survival was lower overall when donors and recipients were out of phase by 1 day than when exactly synchronous.

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M. G. Diskin and J. M. Sreenan

Summary. A total of 256 beef heifers, in 2 experiments, was used to establish fertilization rate and subsequent embryo survival rates. Fertilization rate following a single artificial insemination was 90%. Pooled estimates of embryo survival showed high survival rates up to Day 8 (93%) but markedly reduced (P < 0·001) survival at Days 12 (56%), 16 (66%) and 42 (58%). It is suggested that most embryonic mortality occurs between Days 8 and 16.

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J. M. Sreenan and M. G. Diskin

Summary. Uni- and bilateral twin embryo distributions were effected by the transfer of one embryo on Day 7 to the ipsi- or contralateral uterine horn of previously inseminated heifers (123, Exp. 1) or cows (95, Exp. 2). The embryo transfers were surgical in Exp. 1 and non-surgical in Exp. 2. Transferred and native embryos were distinguished by breed. Embryo survival rate was measured in a proportion (N = 40) of the heifers at Day 53 of gestation and in the remainder of the heifers and all of the cows at term. In the heifers (Exp. 1) overall pregnancy rates of 76% and 75% were recorded after uni- and bilateral twin embryo distributions respectively. Twinning rates of 55% and 60% at Day 53 of gestation and 60% and 60% at term were recorded for uni- and bilateral distributions respectively. In the cows (Exp. 2) calving rates of 61% and 63% and twinning rates of 33% and 38% were recorded following uni- and bilateral twin embryo distributions respectively. When the data from both experiments were combined, overall embryo survival rates were similar for both twin embryo distributions although the ipsilateral transfer of an embryo reduced the survival rate of the native embryo. It is concluded that the confinement of two embryos in one uterine horn on or after Day 7 does not depress pregnancy, twinning or overall survival rate to term.

Keywords: embryo distribution; twinning; survival rates; cow