The influence of seasonal variation on fertility and early body growth in sheep

Land, R. B.; Dickinson, A. G.; Read, J. L.

doi:10.1017/s0003356100026866

Cited by 10 publications

(5 citation statements)

References 3 publications

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“…The annual variation in response was similar to that reported by Palsson (1962) and Newton and Betts (1968). The smaller litter sizes resulting from later conceptions possibly resulted from the occurrence of conception later in the breeding season and an associated decline in ovulation rate (Land, Dickinson and Read, 1969). It would be of considerable advantage to be able to assess the level of naturally occurring gonadotrophic hormone in ewes and supplement accordingly, or in more practical terms to associate hormone administration with the body condition of the ewe.…”

Section: Discussionmentioning

confidence: 99%

Some consequences of high flock prolificacy in an intensive grassland sheep production system

Boaz

Tempest

1975

Anim. Sci.

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An intensive sheep production system using flocks of 100 Scottish Halfbred (SHB), 100 Welsh Speckleface (WSF) and 100 Finn Blackface (FBF) ewes maintained by 8, 4 and 6 ha grassland respectively for a 5-year period, was investigated to establish the consequences of high flock prolificacy and the measures taken to achieve it, including PMS administration. Mating occurred in late October/ November at ewe : ram ratios of 25 or 33 : 1. Ewes were housed in winter and fed silage, with supplementary cereals in late pregnancy. Lambs in excess of 2 (SHB) and 1 (WSF and FBF) per ewe were artificially reared and fattened indoors; ewes and lambs at grass were rotationally grazed (with forward creep grazing by the lambs). Prolificacy in the SHB breed was 225 lambs born per 100 ewes mated for untreated ewes and 237 for hormone-treated ewes; 119 and 155 respectively for WSF ewes; and 255 for FBF ewes (all untreated). Lambs sold per 100 ewes mated were: for SHB, 200 and 177; WSF, 102 and 107; FBF, 201. Good ewe condition and heavy live weights at mating were associated with appetite problems on silage in late pregnancy; PMS injection with a failure to secure conception rates above 80% at the critical oestrus and a markedly lower prolificacy for ewes conceiving at later oestruses; mating in the middle of the breeding season and March/ April lambing with slow lamb growth rates on grass in July and August. Hormone-induced high prolificacy was associated with a greater proportion of large multiple litters than natural high prolificacy, and consequent smaller lamb birth weights and more perinatal mortality. There was a significant negative regression relating fleece weight with litter size. The results suggest the existence of an optimal level of prolificacy for the system employed. 20/2D

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Section: Discussionmentioning

confidence: 99%

Some consequences of high flock prolificacy in an intensive grassland sheep production system

Boaz

Tempest

1975

Anim. Sci.

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“…grass growth and quality of pasture, which in turn are related to changes in the climate throughout the season. Seasonal influence on body growth has been illustrated in Clun Forest lambs reared under British conditions (Land, Dickinson & Read, 1969;Lees, 1969).…”

Section: Discussionmentioning

confidence: 99%

Puberal development of Clun Forest ram lambs in relation to time of birth

Dýrmundsson¹,

Lees

1972

J. Agric. Sci.

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Some aspects of sexual development and the attainment of puberty in Clun Forest ram lambs were studied during the two seasons 1970-1. Strong correlations existed between parameters of penial, scrotal and testicular development. Sexual development in general appeared to be more closely associated with the body growth than the chronological age of the ram lamb.Nevertheless, marked variation existed in both age and body weight at puberty. Although the majority of the lambs attained this stage of development at 4-5-5 months the age-range extended from 99 to 176 days. The mean body weight at puberty was 32-5 kg, ranging from 24-5 to 38-0 kg. There appeared to be an interaction between chronological age and general body development in relation to the appearance of sperm in the epididymides. Not only did it seem that a certain degree of body growth and testicular size was required before spermatozoa could be released, but also a limit of chronological age below which puberty was not attained. Large differences existed between individual lambs in both testicular and epididymal weights at puberty. There was a high degree of symmetry in growth between the left and the right testes and epididymides.Time of birth influenced the pattern and rate of body growth and sexual development. This seemed to be largely due to seasonal fluctuations in nutritional conditions during rearing but the results obtained do not preclude the possibility that other seasonal factors, such as the daylight environment experienced by the ram lamb, might have a certain limited influence on sexual development. INTRODUCTIONMATERIAL AND METHODS

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“…The latter approximates to maximum fecundity under field conditions (Land, Dickinson and Read, 1969). Thereafter the light period is reduced by 3i min per day.…”

Section: Intensive Unit For Controlled Breedingmentioning

confidence: 81%

“…The above values are however only flock means and the large within-breed variation has been used as a means of selecting for improved prolificacy (Owen, 1969). Both the within-and between-ewe variation in prolificacy are at best crude estimates, influenced by age (Bichard and Cooper, 1966), mating time within the normal breeding season (Land, Dickinson and Read, 1969;Hendy and Bowman, 1971;Tempest and Boaz, 1973), and body condition at mating (Gunn, Doney and Russel, 1969). Add to these factors the use of exogenous hormone in the form of pregnant mare's serum gonadotrophin (PMSG) to boost litter size and its known interaction with genotype (Newton, Betts and Large, 1970;Bradford, Quirke and Hart, 1971) and it is apparent that there are many methods for the control of litter size.…”

Section: Factors Affecting Litter Sizementioning

confidence: 99%

Intensifying ewe productivity

Robinson¹

1974

Proc. Br. Soc. Anim. Prod (1972)

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Calculations on the relative efficiencies of cattle, sheep and pigs as meat producers indicate that the main factor limiting the energetic efficiency of sheep meat production is the low average fecundity of the ewe (Blaxter, 1968). Nevertheless with an estimated ‘biological ceiling’ of five lambs per ewe per pregnancy, and a potential mean lambing interval of 6 months (Wilson, 1968), the sheep industry is much further from achieving its biological ceiling than any other form of domestic livestock production. Because these estimates are based on the performance of specific individuals one must question their attainment on a flock basis. Furthermore, even if the necessary technical information were available, its adoption on a commercial scale may be prohibitive on economic grounds. These uncertainties should not deter us from seeking a greater understanding of the basic factors controlling ewe productivity, nor from attempting to integrate this knowledge into existing production systems.

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The influence of seasonal variation on fertility and early body growth in sheep

Cited by 10 publications

References 3 publications

Some consequences of high flock prolificacy in an intensive grassland sheep production system

Some consequences of high flock prolificacy in an intensive grassland sheep production system

Puberal development of Clun Forest ram lambs in relation to time of birth

Intensifying ewe productivity

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