H.Ll. Williams

The influence of a low-nutrient intake after mating on gestation and perinatal survival of lambs.

Abstract The effects of a low-nutrient intake during the first trimester of gestation on inutero and perinatal survival of lambs were investigated in Blackface ewes. The ewes were all in good condition (score 3 to 3 1 2 ) at the start of the experiment. The treatment group (T, 15 ewes) was given about 15% of the recommended nutrient allowances for maintenance during 60 days post mating. The control group (C, 10 ewes) was given the full maintenance allowance for the same period. At other times ewes in both groups received equal and adequate levels of nutrients. The T group lost almost 9 kg live-weight on average during the restricted feeding period and lost 0·8 unit in condition. There was some compensatory weight gain after the regime finished, but the T ewes were still a little lighter than their original live-weight by parturition. There was no evidence of embryo mortality as a result of the restricted regime. However, lambs from the experimental ewes were less viable, had a lower birth-weight and showed evidence of intrauterine growth retardation. Plasma progesterone profiles showed evidence of elevated levels in the T ewes during days 20 to 25 post coitum , significantly higher than those of the C ewes.

The Reproductive Performance of British Breeds of Sheep in an Equatorial Environment. II. Lowland Breeds

SUMMARY The paper describes the reproductive performance of 44 Romney Marsh, 16 Dorset Down, 23 Hampshire Down and 16 Border Leicester ewes during two “seasons” following their arrival at Pasto, Colombia. In season I the percentage keel marked were 93.2, 87.5, 100.0 and 0.0, respectively, and the percentage lambed were 68.2, 50.0, 52.3 and 0.0. In season II the percentages were 97.7, 100.0, 100 0 and 56.3 keel marked and 79.5, 100.0, 100.0 and 37.5 lambed.

Ovarian activity and fertility during the first breeding season of friesland ewe lambs

The onset and duration of ovarian activity was assessed in 19 March-born, pure bred Friesland ewe lambs. Blood samples were collected for progesterone assay from 6 August-27 March when the lambs were 5-12 months of age. From 23 January a harnessed vasectomised ram was introduced. Colour marks on the rumps were taken as presumptive evidence of oestrus. During 1-25 March the vasectomised ram was replaced by a harnessed entire ram in order to assess fertility. The mean onset of the first normal luteal cycle, when progesterone levels exceeded 2 ng/ml-1 for two consecutive plasma samples, was on 7 October. The mean age and weight at this time were 29.9 +/- 2.73 weeks and 36.71 +/- 1.39 kg respectively. One ewe lamb became pregnant and lambed on 27 July. The mean date for cessation of ovarian activity (n = 18) was 1 March and the mean number of normal cycles monitored was 8.8 +/- 0.38. Few short luteal cycles were recorded (7/18 lambs) when only transient increases in progesterone levels were detected. The average duration of the breeding season was 142.6 +/- 4.95 days. It is concluded that pure bred Friesland ewe lambs, born during March, will reach puberty around 30 weeks of age and continue regular cyclic activity for approximately 5 months. Entire rams should be joined during January or February to ensure successful matings for lambing and milk production in late summer/early autumn.

The effects of 'adequate' and 'low' sodium intake on reproductive performance of Scottish Blackface ewes and growth of their lambs.

A low sodium diet was given to Scottish Blackface ewes over two reproductive seasons. It provided a total of 3–7 mmol sodium per day, except during lactation when the intake was about 11 mmol sodium per day. Control ewes were given the same diet supplemented with sodium chloride to Agricultural Research Council recommended concentration which was about ten times greater than that in the experimental diet. The ewes remained clinically healthy throughout the experiment. The length of gestation and the birth weight of lambs were unaffected by diet. The number of lambs born alive per ewe lambing was unaffected by year or diet. The percentage of ewes producing twins was similar in control ewes in both years at about 64; in treatment ewes this was 70% in year 1, and 50% in year 2. Lamb mortality was higher in both years in the treatment ewes than in control ewes. None of these differences reached significance.

The effect of light environment on post-partum reproductive activity and prolactin levels in two breeds of sheep

The onset of reproductive activity in Poll Dorset and North Country Cheviot ewes, kept in local (51 ° 43′N) and in equatorial (13L:11D) light was assessed following lambing in the autumn (n = 10) and in the spring (n = 12). The relationship between the levels of plasma and milk prolactin and the duration of post-partum anoestrus was also investigated. A clear seasonal variation in the duration of post-partum anoestrus and in the incidence of oestrus was observed in the local light environment. Ewes lambing in the autumn showed earlier and more ovarian and behavioural activity than those lambing in the spring. The mean prolactin levels in plasma and milk of ewes lambing in the local light, were significantly higher (P < 0·001) in the spring than in the autumn. In contrast, under equatorial light, prolactin levels did not show a significant seasonal change.

The reproductive performance of two British breeds of sheep in contrasting photoperiodic environments

The reproductive performance of breeding and cyclic Welsh Mountain (WM) and Border Leicester (BL) ewes was compared in two contrasting photoperiodic environments during January 1971–April 1972. Treatment 1 consisted of natural daylength changes at latitude 51° 43’ N. There was no difference between the two breeds in onset of the breeding season, percentage exhibiting oestrus or percentage lambing. The breeding season of BL ewes terminated earlier (mean date, 31 January) than that of WM ewes (mean date, 9 March). The WM ewes had 8–12 oestrous periods and the BL ewes 7–11 oestrous periods. In treatment 2 a simulated equatorial photoperiod (13 h light: 11 h dark) was applied from January 1971 but was inadvertently interrupted by a short period of continuous light in June 1971. All WM ewes exhibited oestrus compared with 37·5% of BL ewes. The failure to show oestrus in the majority of BL ewes contributed to the marked difference between breeds in the percentage of ewes lambing: 88·9% in WM compared with 11·1% in BL ewes. In the cyclic subgroup, the WM ewes had 3–10 oestrous periods and the BL ewes, 2–7 oestrous periods. It is concluded that the breeds showed a differential response to the two treatments and that Treatment 2 had a marked adverse effect on the reproductive potential of the Border Leicester ewes.

Effects of shearing on the reproductive activity and plasma prolactin levels of Dorset ewes.

The effect of shearing on the reproductive activity and plasma prolactin levels were studied from the 15 April to 23 June in 32 Dorset ewes (polled and horned) under field conditions. The ewes were shorn during the previous December (group A), 7 May (group B), 29 May (group C) or 18 June (group D). After shearing there was a significant (P < 0·05) fall in plasma prolactin in each group shorn during the experimental period. This temporary decrease in plasma prolactin did not result in an increase in the number of ewes exhibiting oestrus or ovulating, as judged by their progesterone profiles. The timing of shearing during late spring/early summer is unlikely to improve reproductive activity in this breed.

A Study of Infertility in Scottish Blackface Sheep in Colombia, South America

SUMMARY The reproductive performance of a flock of 226 Scottish Blackface (SB) ewes in Colombia, lat. 5°N, alt. 3200 m, showed that 96·0% were keel marked and 42·4% lambed. Of the 56·7% served once, 66·7% lambed. Of the 43·3% returning to service only 14·9% lambed. More detailed investigations were carried out on a representative sub-group of 19 Blackface ewes and on 10 ewes of the local Criolla breed. Progesterone profiles indicated that barrenness in SB sub-group ewes was due to relapse into anoestrum following an ineffective service or termination of pregnancy before day 60.

The Short-Term Effects of a Simulated Transfer to Higher Latitudes on Breeding Ewes

SUMMARY Ten Clun Forest (CF) and ten Welsh Mountain (WM) ewes (Group I) were maintained on the normal local photoperiod for 51°43′N and a similar number of each breed were exposed to a simulated photoperiod for 70°N (Group II). The onset of the breeding season was earlier in ewes of both breeds in Group II. The majority of GF ewes exhibited oestrus during the period of continuous light. The mean dates of first oestrus for Group I ewes were: GF—30 Aug., WM—29 Sept.; and for Group II ewes were: CF—13 Aug., WM—10 Sept. Group II ewes yielded positive vaginal smears earlier than Group I. Group II treatment had no apparent effect on the interval from positive smear to first oestrus, duration of oestrous cycle and fertility. Corpora lutea were not found in all the ewes subjected to laparotomy soon after yielding positive smears.

The Effect of an Equatorial Light Environment on Reproduction in Sheep. I. The Breeding Season

SUMMARY Various aspects of the breeding seasonality of Welsh Mountain (WM), Border Leicester (BL), North Country Cheviot (NCC) and Scottish Blackface (SBF) ewes were investigated during two breeding seasons in housed and field ewes in the local light (LL) environment of Potters Bar (lat. 51°43′N) and in ewes housed in a simulated equatorial light environment (EL) (13L: 11D). Significant advancement of the onset of oestrous periods was observed in all breeds maintained in the EL environment and resulted in a rephased and shorter breeding season. Advancement varied according to breed and was greater in WM (62 days) and BL (42 days). There was no significant difference between NCC (30 days) and SBF (28 days) ewes. The level of oestrous activity in a breed over a sequence of 17-day periods and the duration of oestrus tended to be reduced in EL ewes. In the EL environment NCC and SBF ewes had significantly lower mid-cycle progesterone concentrations than ewes of the same breed in the LL environment. There was also a higher incidence of ovulation without oestrus and oestrus without ovulation in the EL environment. The plasma progesterone concentration at various stages of pregnancy did not show a significant difference between light environments. Plasma progesterone concentration on day 17 after mating had an accuracy of 92·5% as a diagnosis of pregnancy. The value of plasma progesterone determinations in the study of seasonal reproductive activity is discussed.