Three breeds of Javanese sheep are described briefly and data suggesting the segregation of a gene with large effect on ovulation rate and litter size are presented. The three breeds are Javanese Thin Tail (JTT), Javanese Fat Tail (JFT) and Semarang (SEM), the last possibly a substrain of JTT. All three breeds have mean mature ewe weights under 30 kg. Ovulation rate and litter size did not differ significantly among the three; all had litter sizes of up to 4 or 5 with a mean for mature ewes of approximately 2. Ovulation rate ranged from 1 to 5 and had an average within-breed repeatability of .8 within season and .65 between seasons. Within-breed repeatability of litter size was .35 +/- .06. Prenatal survival in pregnant ewes with two, three and four or more ovulations averaged 93, 88 and 86% over two seasons. Dams that had at least one ovulation rate or litter size record greater than or equal to 3 produced two groups of daughters in approximately equal numbers: one group with many records greater than or equal to 3 and mean ovulation rate and litter size of 2.73 and 2.31, respectively, and one group with ovulation rates and litter sizes of 1 or 2 and corresponding means of 1.39 and 1.38. Dams with ovulation rate or litter size records of only 1 or 2 produced daughters in which over 90% had records of only 1 or 2. Estimated heritabilities for the mean of approximately three ovulation rate or litter size records from these daughter-dam comparisons exceeded .7. These results suggest segregation of a Booroola-type gene, one copy of which increases ovulation rate by about 1.3 and litter size by .9 to 1.0. Relationships between duration of estrus and ovulation rate, and between timing of release of luteinizing hormone and number of eggs shed, resemble the pattern in Booroola Merino more closely than that in Finnish Landrace or Romanov, supporting the hypothesis of a major gene.

The effects of dose of oestrogen and season on the expression of oestrous behaviour was studied in 60 spayed and 16 intact ewes.In progesterone-primed spayed ewes the incidence and duration of oestrous behaviour increased and the interval between injection of oestrogen, and onset of oestrous behaviour decreased as the dose of oestrogen was increased. The linear regression of duration of oestrus on log dose of injected oestrogen provided the most precise measure of the effect of changing dose level of oestrogen on oestrous behaviour.The sensitivity of spayed ewes to constant levels of oestrogen increased to a maximum near the middle of the breeding season and then declined to a minimum during the non-breeding season. In progesterone-synchronized intact ewes the interval between the end of progesterone treatment and onset of oestrus was at a minimum, and duration of oestrus at a maximum, near the middle of the breeding season. By bioassay it was estimated that endogenous oestrogen production was greater near the middle ofthe breeding season than at either the beginning or end.It is concluded that seasonal variation in the expression of oestrous behaviour in intact ewes is controlled by changes in both the production of endogenous oestrogen and the sensitivity of ewes to it.

Peripheral plasma concentrations of LH, oestradiol-17\g=b\ and progesterone were measured in 13 mature swamp buffalo cows at 4-h intervals from 36\p=n-\40h before until 36\p=n-\40h after the onset of oestrus. Mean LH concentrations increased sharply to a peak of 35 ng/ml and returned to basal levels of 5 ng/ml within a 12-h period beginning soon after the onset of oestrus. Mean oestradiol-17\g=b\ concentrations were within the range 9\p=n-\13pg/ml from 36\p=n-\40h before until 12\p=n-\16h after the onset of oestrus, and within the range 7\p=n-\9 pg/ml thereafter. Progesterone concentrations remained around 0\m=.\1ng/ml throughout the sampling period. There were no significant differences in hormone concentrations or changes between cows that conceived and those that did not conceive to artificial insemination 12\p=n-\24h after onset of oestrus.

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