Autumn Lambing Research Articles

Effect of sward surface height on the performance of ewes and Iambs continuously grazed on grass/clover and nitrogen‐fertilized grass swards

AbstractIn three successive years, sward height was maintained at 3, 5, 7 or 9 cm on grass swards receiving a total of 300 kg N ha−1 in six equal monthly dressings from April, and on grass/clover swards receiving 50 kg N ha−1 as a single dressing in early spring. From turnout in April until weaning in July, 64 ewes and their lambs (mean litter size 1·5) were continuously grazed at the four sward surface heights on the two sward types. White clover content of grass/clover swards remained low throughout the experiment ranging from 0·2 to 7·4% of the herbage mass. During the first two years, lamb gains averaged over sward types were 204, 260, 285 and 308 g d−1 up to weaning, while in the third year gains were 238, 296, 296 and 260 g d−1 on 3, 5, 7 and 9 cm swards respectively. Ewes lost live weight on 3 cm swards but apart from this sward height had little effect on performance. During the autumn, weaned lambs gained — 27, 87, 147 and 167 g d−1 on 3, 5, 7 and 9 cm swards respectively. Sward type had only a small effect on the performance of lambs up to weaning but in the autumn, mean gains of weaned lambs were lower on grass/N swards (73 g d−1) than on grass/clover swards (115 g d−1). Relative to 3 cm swards, carrying capacities of 5, 7 and 9 cm swards were 0·76, 0·57 and 0·52 respectively from turnout to weaning and 0·66, 0·52 and 0·44 respectively during autumn. Grass/clover swards carried 0·67 of the ewes carried by grass/N swards from turnout to weaning and 0·51 of the live weight carried by grass/N swards during autumn.The reaction of the two sward types to sward height did not appear to differ but in the third year there was evidence of a reduction in white clover content when swards were grazed at 9 cm. The data suggest that lamb growth rates will increase as sward height increases up to 9 cm and the evidence for this was stronger with weaned lambs in autumn than with suckling lambs in spring.

Resumption of ovarian activity in post-partum ewes: Role of the uterus

The effect of the involuting uterus on luteal life span and pattern of secretion of progesterone was studied in suckled ewes and in ewes with lambs removed on Day 1 after an autumn lambing (breeding season). Total hysterectomy, performed the day of parturition or the day after, resulted in all cases within two weeks in the formation and development of persistent (more than 65 days) and actively progesterone-secreting corpora lutea immediately after the first post-partum LH surge. However, during the early post-partum period, progesterone secretion increased at a slower rate than later at the time of resumption of cyclic ovarian activity in control ewes. It may be inferred from these results that frequent short duration of first post-partum ovarian cycles results from: (1) the luteolytic influence of the involuting uterus due to an increased and prolonged release of prostaglandin F 2α as found by other workers; (2) an incompleted restoration of LH release leading to insufficient follicular growth and maturation.

Melatonin and light treatment of ewes for autumn lambing.

Forty spring lambing adult, and 24 unbred yearling, Suffolk crossbred ewes were allocated to 3 groups. Group I and II were maintained on 18L: 6D and Group III on Local light (51 degrees 42' N) during 24 Feb-13 April. During 13 April-11 July Group I changed to 9L: 15D and Groups II and III were group fed a diet containing melatonin and providing 3 mg/ewe at 16.00 hrs daily. A further 20 adult ewes, Group IV and V were maintained on Local light during 24 Feb-13 April; Group IV was transferred to 9L: 15D and Group V remained on Local light during 13 April-11 July. The ewes were exposed to vasectomised rams from the time of weaning on 3 June. All ewes were housed until 11 July and then remained at pasture thereafter. The performance of the yearling ewes was as follows - % Keel-marked during 11-28 follows: Group I - 90.0; Group II - 100.0: Group III 92.3; Group IV - 50.0; Group V - 10.0. There were no significant differences between Groups I, II and III. The following percentage of adult ewes lambed during 3-23 December - 66.7; 85.7; 69.2; 20.0 and 0.0 for Groups I - V respectively. Groups I, II and III were significantly higher than Group V. The performance of the yearling ewes was as follows - % keel-marked during 11-28 July: Group I - 100.0; Group II - 66.7; Group III - 22.2. The following percentage of yearling ewes lambed during 3-23 December - 50.0; 44.4 and 11.1 for Group I - III respectively. An assessment of these data in relation to autumn lambing is presented in the paper.

Out-of-Season Breeding in Adult Suffolk Ewes following Light and Melatonin Treatment

Photostimulation is an effective means of manipulating reproductive activity in most British breeds of sheep. Short term light treatment can initiate oestrus cycles during June/July and thus provides the opportunity for autumn lambing (Williams, 1977). The most effective light treatments comprise a period of supplementary light followed by a period of long nights which requires controlled environmental housing. Recent investigations have demonstrated that melatonin treatment may replace the long night phase thus simplifying management (Williams, 1985). Attempts to dispense with the period of supplementary light by transferring Spring lambing Welsh Mountain ewes abruptly to long nights during early Spring were not as successful as the conventional type of light treatment (Williams, 1967). This investigation was undertaken to compare the response of adult Suffolk crossbred ewes given melatonin in the Spring with or without a priming period of supplementary light.

Lambing date and lamb production of spring-mated Rambouillet, Dorset and Finnsheep ewes and their F1 crosses.

The reproductive performance of 255 Rambouillet (R), Dorset (D), Finnsheep (F) and F1 ewes born in 1978-1979 (group I) and 1979-1980 (group II) and managed in a semiconfinement fall/winter lambing system was evaluated through 4 yr of age of all ewes and through 5 yr for a portion of group I ewes. Ewes were with rams from approximately May 1 to late September each year, with a 2-wk break late in July/early August. Traits considered were fertility (ewes lambed/ewes exposed), lambing date, litter size, lamb survivial and 70-d lamb weights. Breeds and crossbred groups differed significantly in lambing date, with DR crossbred ewes earliest and F ewes latest. Repeatabilities for groups I and II were .31 and .22, .24 and .24 and .11 and .07 for lambing date, fertility and litter size, respectively. There was no significant heterosis in lambing date, although DR ewes in both groups I and II were superior to (D + R)/2, by about 1 wk on average. There was significant positive heterosis for fertility and traits of which fertility is a component in FR ewes in group I, but none in group II. The FD ewes showed negative heterosis for litter size, -.23 (P less than .05) for group I and -.09 for group II. The results indicate: F and FD ewes are not well adapted to the Mediterranean climate where this experiment was conducted; there is little, if any, useful heterosis in crosses among these three breeds for lambing date or other reproduction traits and RD and R ewes are most suitable of the groups tested, while late onset of the breeding season limits the usefulness of even 50% Finnsheep ewes for an autumn lambing system in this environment.

AUTUMN AND WINTER LAMBING STRATEGIES IN NORTHLAND

Progress in the development of autumn and winter lambing systems in Northland is described. Both involve split flock lambing in which 30 or 15% of ewes lamb in autumn or winter respectivelv, the remainder in spring. Using progesterone priming, a high ram to ewe ratio (10%) and ram management, 80.90% of ewes joined lamb over 2 cycles. Winter lambing using cull ewes is simple and does not require a breeding programme. Ewes and their lambs can be sent to the meat works from September. For low cost lamb production with present breeds, autumn lambing requires a breeding programme to develop spring mating ability. Heavyweight(18kg)carcasses can be produced early in the killing season. Autumn born replacement ewe lambs consistently averaged 40kg before their first summer. Both systems offer more flexibility in sheep production on farms and in processing and marketing. Keywords: Autumn lambing, winter lambing, split lambing, management options, extending killing season, heavyweight lambs production

Variations in the plasma levels of gonadotrophin and testosterone and in Leydig and Sertoli cell populations between birth and adulthood in Romanov lambs born in spring or autumn.

Plasma gonadotrophin and testosterone levels during the prepuberal period have been compared in spring and autumn-born Romanov lambs; the somatic and germ cell populations of these lambs have also been compared at birth and at adulthood. At 1 and 3 months of age, the number of LH pulses per hour and mean plasma LH levels were significantly higher in spring than in autumn lambs. In adults, no such differences were observed. Similarly, at 1 and 3 months of age, the number of testosterone pulses per hour was higher in spring than in autumn animals. In the prepuberal period, the ratio of the levels of mean plasma testosterone to LH was higher in autumn than in spring lambs. The highest ratio was observed in adults but there was no variation according the season of birth. At 1 month of age, mean plasma FSH levels were higher in autumn than in spring lambs; this difference did not persist later on. Despite these endocrinological differences, testis weight, total Sertoli and Leydig cell numbers per testis, total number of gonocytes per testis at birth and daily production of round spermatids per testis in adult rams were similar in spring and autumn-born animals.

Effect of stocking rate, time of lambing and inclusion of lucerne on prime lamb production in north-east Victoria

Results of a grazing study involving Border Leicester x Merino ewes and their progeny are reported for a 4-year period 1969 to 1972. The study was conducted at Rutherglen in north-east Victoria. The 1260 ewes observed throughout the study were allotted to 42 treatment plots with 30 ewes per plot. Thirty of the plots were located on annual pasture (subterranean clover, barley grass) involving three replicates of ewes stocked at 7.4,9.9 and 12.4 ewes ha-l for ewes joined over 7-week periods to commence lambing about May 5, June 23 or August 8. Additionally, an extra three plots with spring lambing were grazed at 14.8 ewes ha-1. A further 12 plots contained lucerne on one third of the plot area. The ewes on these plots also lambed for a 7-week period commencing August 8, and provided three replicates of 7.4 9.9, 12.4 and 14.8 ewes ha-1. First services were concentrated early in the joining period in the spring-lambing ewes, there were few returns to services and few ewes failed to mate. On the other hand, among ewes joined to lamb in autumn, first services were distributed over the entire joining period, and many ewes returned to service or failed to mate. The mating pattern of ewes joined to lamb in winter were intermediate between the autumn and spring lambing groups. Although the liveweight of spring-lambing ewes was lighter at mating, the number of lambs born per 100 ewes joined was greater than for winter lambing, and these in turn were greater than for autumn lambing ewes. The response to an additional 1 kg liveweight at mating was 1.7, 2.0 and 2.8 additional lambs born per 100 ewes joined for autumn, winter and spring lambing, respectively. Wool production per hectare increased linearly with increase in stocking rate; it was marginally affected by time of lambing and was greatest where lucerne was provided. The number of lambs reared per ha increased linearly with increase in stocking rate, albeit there was some decline in carcase weight and a small decline in numbers of lambs reared per ewe. Lambs born in autumn and winter were generally slaughtered in prime condition at 31 kg liveweight, except in the drought year of 1972, but more lambs were produced from a winter lambing than from autumn lambing. When lambing was in August-September there was a slight increase in the numbers of lambs reared above that of winter lambing, but the proportion of lambs marketed at less than 31 kg was greatly increased. Where lucerne was provided to spring-lambing ewes the greatest weight of meat per hectare was produced, and few lambs were less than 31 kg. In descending order of magnitude, the major factors affecting carrying capacity were season, year, stocking rate and time of lambing. Seasonal shortcomings in nutrition were alleviated by the provision of supplementary feed. At the lighter stocking rates of 7.4 and 9.9 ewes ha-1 the amounts of supplements fed were very low, even in the drought year of 1972. These two lowest stocking rates could be maintained indefinitely without excessive use of supplementary feed. Discernible changes in botanical composition with partial loss of productive grass and clover species, reduction in pasture growth rate, increased use of supplementary feed and lowered wool production of ewes, occurred with spring lambing without lucerne, particularly at 12.4 and 14.8 ewes ha-1. Pasture composition and growth details were very similar with either autumn or winter lambing.

Effects of grazing by lambs in autumn on a red clover‐perennial ryegrass sward

AbstractIn 1976, 1977 and 1978 a red clover‐perennial ryegrass sward was cut twice for silage, and in the autumn of 1976 and 1977 it was either grazed at low and high stocking rates, i.e. seventeen and thirty‐four lambs per ha respectively, or was cut with a forage harvester. The effects of grazing on yield in the following year were examined.Herbage growth in the grazing period was slow and did not differ significantly between the treatments. The yield of silage dry matter taken in May and July was highest in ungrazed plots (9·8 and 8·1 t ha‐1 in 1977 and 1978 respectively) and lowest in plots stocked at the high rate (5·9 and 5·7 t ha‐1 in 1977 and 1978 respectively). The aftermath yield for grazing in 1977 was slightly but significantly greater on treatments grazed in the previous year compared with ungrazed treatments.Red clover content decreased markedly during grazing, the high stocking rate treatment containing 2·4% clover and the ungrazed treatment 57·3% clover. The high stocking rate treatment also had the lowest red clover content in the first silage cut. Red clover content in grazed plots increased to a level similar to that in ungrazed plots by the start of the grazing period in the subsequent harvest year.Animal performance was higher at the low than at the high stocking rate but herbage consumption per head did not differ significantly between the two grazing treatments.Possible reasons for the adverse effect of grazing on the red clover are defoliation and treading. It is concluded that such experiments can form the basis of an economic assessment of red clover and help the farmer decide whether or not he should integrate the crop into his system.

The production of lambs in autumn from a commercial flock in England.

The production of lambs in autumn from a commercial flock in England.

The induction of pregnancy in the anoestrous ewe by hormonal therapy V. Progesterone-pregnant mare's serum therapy on Clun forest maiden sheep and general conclusions

This trial concerns the induction of pregnancy in two flocks of Clun maiden yearling ewes and involves seventy-six animals. Previous observations suggested that treatment of this particular category usually gives rise to a higher conception percentage than is found with drypost-partumor lactating sheep. The trial sought to elucidate some factors of animal and environment which may be associated with this response.In flock 45, during the period 10 February to 29 March, observations were made on the incidence of spontaneous breeding activity in forty-seven ewes; hormonal therapy was first applied at the latter date. Treatment for all ewes consisted of three doses of 50 mg. progesterone (in oil) given at 3-day intervals; a single dose of 750 i.u.p.m.s.was administered 2 days after final progesterone.Nineteen of the forty-seven ewes (40%) in flock 45 showed spontaneous oestrus in February or March. Three (16%) of those ewes previously mated came in oestrus after treatment; forty-nine of the fiftyseven unmated ewes (86%) showed oestrus 3–5 days after the end of injection. Of the nineteen sheep that mated spontaneously, ten (53%) produced autumn lambs. Twenty-six of the fifty-two sheep (50%) served in response to the progesterone-p.m.s.therapy conceived. 1·25 lambs were born per ewe that lambed. Some evidence for total embryonic or foetal loss in the ewes during pregnancy was obtained. Results indicate that conception in these maiden ewes may have been facilitated by the presence of corpora lutea or recent luteal activity, which maintained the oestrogen-progesterone balance necessary for providing an adequate uterine environment. For this reason, maiden ewes of breeds with short breeding seasons (e.g. Scotch Half-Breds) may not give such satisfactory response when injected at times comparable to long season breeds, such as the Clun.