Seasonal variation in oestrus and ovarian activity of Finnish Landrace, Tasmanian Merino and Scottish Blackface ewes

Abstract

The patterns of seasonal variation in reproductive activity were observed over a period of 15 mo for approximately 15 females of each of three breeds: Finnish Landrace (Finn), Tasmanian Merino (Merino) and Scottish Blackface (Blackface). The incidence of oestrus was measured by teasing with vasectomized rams, and the incidence and rate of ovulation were determined frequently by laparoscopy. Luteal function was assessed from peripheral venous blood progesterone concentration on days 7 and 11 of the oestrous cycle. Nutritional status was monitored by recording body weight and plasma-free fatty acid levels throughout the study.The breeding seasons differed significantly: Finn, October to May; Merino, September to February; and Blackface, October to February. Variation in the incidence of ovulation was similar to that in the incidence of oestrus for each breed. The incidence of silent ovulation varied with the breed, being greatest in the Merino and least in the Finn. The ovulation rate varied among breeds (Finn, 2-99; Merino, 1-08 and Blackface, 1-30), and during the breeding season (e.g. Finn: November, 3-5; March, 2-6). Follicles were observed in each breed throughout the period of study.The pattern of variation in progesterone concentration was similar for each breed despite their different breeding seasons. In addition to breed differences in ovulation rate and in onset and end of the breeding season, the sensitivity to oestrogen was apparently such that, with the Finn if oestrogen secretion was high enough to stimulate ovulation it would usually also stimulate oestrus, whereas with the Merino ovulation often occurred without oestrus; this suggests that in the Merino the centres controlling ovulation are more sensitive to oestrogen than those controlling behaviour.

Comparisons of the ovulatory and steroidogenic activities of the left and right ovaries of the ewe

“…Similarly, no differences were found in the durations of the oestrous cycles when the ovaries were observed during alternate cycles (?<72) = 0-0534, > 0-9). There was no bimodality in the distribu¬ tion of the durations of the oestrous cycles (Wheeler & Land, 1977).…”

“…The means of the progesterone concentrations in the peripheral plasma on Days 7 and 11 of the oestrous cycles (Table 2) were examined, for single CL in the left or right ovary, by using Student's t test on log-transformed data to normalize the skewed distribution (Wheeler & Land, 1977). No differences were found either within breeds or when all the data were combined (til68) = 1-630, 0-1 < < 0-2).…”

“…In the present investigation the sequential pattern of ovulatory activity has been studied in the sheep, and the ovulatory and steroidogenic activities of the left and right ovaries have been compared. Materials (Wheeler & Land, 1977 Scaramuzzi, Corker, Young & Baird (1975). The antiserum (91920/9) had cross-reactions of 100% with progesterone, 121 % with lla-hydroxyprogesterone, 78% with 11 ß-hydroxyprogesterone and 82% with 11-ketoprogesterone.…”

Seasonal variation in oestrus, the secretion of oestrogen and progesterone and LH levels before ovulation in the ewe

“…Four Finnish Landrace Tasmanian Merino ewes (aged about 2\ or 3^years in November 1972) with the left ovary autotransplanted to the neck (Goding, McCracken & Baird, 1967b) (Goding, Harrison, Heap & Linzell, 1967a), for up to 200 days before regression and ovulation occur spontaneously (Baird, Land, Scaramuzzi & Wheeler, 1976b (Wheeler & Land, 1977 (Collett, Land & Baird, 1973). Timed samples of ovarian venous blood (25 ml) were collected as previously described (Godinget al, 1967b).…”

Variations annuelles du comportement d'oestrus, du taux et des possibilités d'ovulations chez la brebis Peulh du Niger

“…La variation saisonnière de l'activité sexuelle est une caractéristique commune à plusieurs races ovines (Hafez, 1952 ;Wheeler et Land, 1977 ;Mauléon, 1980 (Land et al, 1973 ;Wheeler et Land, 1977 ;Valls et al, 1977 (Guerra et al, 1972) (Goodman, 1978). L'allongement de l'intervalle qui sépare deux phases lutéales peut être lié à un ralentissement de la maturation folliculaire et/ou à un retard de la décharge pré-ovulatoire de LH (Yenikoye et al, 1982 (Thimonier et Mauléon, 1969 ;Land et al, 1973. ;Wheeler et Land, 1977 …”