The Use of Progestagens and Photoperiodism in Improving the Reproductive Rate of the Ewe

Abstract

SUMMARYA brief description of an intensive unit in which Finnish Landrace x Dorset Horn ewes are bred to Suffolk rams every 205 days, to produce lambs which are abruptly weaned at four weeks of age on to cereal-based diets, is given. The unit combines photoperiodism and hormone treatment for the induction and synchronisation of oestrus respectively. The photoperiod treatment consists of an abrupt increase in daylength to i8 hours at 6 0 days of gestation followed by a daily reduction of 3 r/z mn from 90 days of gestation. Hormone treatment is in the form of intravaginal pessaries impregnated with 30 mg 9 a-fluoro-i i-hydroxy-i 7 a-acetoxy progesterone (SC-9 88o, G. D. Searle) and 400 mg progesterone. The overall mean conception rate for five consecutive reproductive cycles was 8 7 .8 p. I oo and the mean litter size 2 . 1 resulting in an average annual production of 3 . 5 lambs per ewe. Despite the continuous careful control of the artifical daylength regime an innate natural seasonal effect on the onset of behavioural oestrus after pessary withdrawal was noted and is discussed.

Ovulation and embryo survival rates and plasma progesterone concentrations of prolific ewes treated with PMSG

“…Lamb production following matings within the breeding season is further limited by low ovulation rates (Hulet & Foote, 1967) and failures of fertilization and embryonic death (Edey, 1969(Edey, , 1976. Robinson, Fraser & McHattie (1975), using a combination of treat¬ ments, including controlled photoperiod, early weaning and pregnant mares' serum gonadotrophin (PMSG) injections, successfully eliminated seasonality and maintained a high level of lamb production from Finnish Landrace Dorset Horn ewes bred at 7-month intervals. How¬ ever, reproductive performance was measured only in terms of conception rates and lambing percentages, and the factors limiting production under these conditions could not be assessed.…”

“…How¬ ever, reproductive performance was measured only in terms of conception rates and lambing percentages, and the factors limiting production under these conditions could not be assessed. The aim of the present work was to investigate ovulation rates, the subsequent development of embryos and fetuses and the associated changes in the concentrations of progesterone in the peripheral plasma of the ewes that were used in the studies of Robinson et al (1975).…”

Effects of season, lactation and plane of nutrition on the reproductive performance and associated plasma LH and progesterone profiles in hormonally treated ewes

“…Studies in which Finnish Landrace Dorset Horn ewes were kept under artificial daylength conditions and weaned after 1 month of lactation (Robinson, Fraser & McHattie, 1975) showed that conception rates of about 90% and litter sizes greater than 2 could be obtained consistently in a breeding programme involving a 7-month interval between lambings. This interval was achieved by the synchronization of oestrus using intravaginal pessaries impregnated with pro¬ gestagen.…”

Reproductive Performance of Hormonally Treated Sheep Maintained Year-Round in a Controlled-Light Environment

“…In (Robinson et al 1975). Differences in prolificacy between the two lighting regimes were not significant. Fecundity followed the pattern of fertility (Table 4 …”

“…1918;Fairnie et aL l9l6, 1977;Fukui and Roberts 1977;Gordon 1910Gordon , 1913Gordon , 191 5 , 1911Hackett and Robertson I 980;Haresign 1976;Jennings 1975;Lightfoot et al 1976;Mauleon and Le Provost 1975;Robinson 1965;Thimonier and Cognie 1977;Trounson et al 1916). However, only limited information on the application of these procedures to sheep continuously maintained indoors year-round under controlled lighting is available (Hackett et al 1979; Hackett et al l98l; Hackett and Wolynetz l98l; Robinson et al 1975 (Heaney et al 1980 Although these variables are discrete and not normally distributed, probability levels obtained in this manner should approximate the correct probability levels (Gabriel 1963;Li 1964 (19) l5 (28) 29 (l-s) s2 ( l3) 7 11) 0 03) l 38 (37) 84 (17) 75 (15) 52 (20) 65 (l9) 21 (28) s4 (rs) 126 (13) l0 ( l7 (Gordon 1975). Other studies on our sheep flock have also shown that PMSG does not increase fertility in FGA-treated ewes bred by natural mating (Hackett and Wolynetz l98l , 1982 (Table 6) and 47o in the sixth experiment.…”