Analysis of production records from a lowland sheep flock 2. Flock statistics and reproductive performance

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SUMMARYPhenotypic and genetic parameters for reproductive performance in a flock of Clun Forest ewes have been estimated. Average litter size (ALS) appeared to be more repeatable than the number of lambs born per ewe mated and present at lambing (NLBEM), and the estimates obtained by regression (0·15 and 0·14) were slightly higher than those from the analyses of variance (0·12 and 0·09). The repeatability of barrenness was very low (0·05). It was concluded that little scope existed for the improvement of reproductive performance from a regular policy of culling.Estimates of heritability by analysis of variance and a method for all-or-none traits were 0·12 and 0·11 for ALS, and 0·15 and 0·10 for NLBEM, whereas barrenness was less heritable (0·07). An estimate of 016 was found for the heritability of ALS performance over two years. The phenotypic correlation between body weight and reproductive performance were positive yet small (ALS:+0·16; NLBEM:+0·10), while at the genetic level ALS was more strongly related to body weight (+0·21) than NLBEM (-0·04). The genetic regressions indicated that an increase of 5 lambs per 100 ewes lambing would accompany genetic gain of 5 kg in ewe body weight, while an increase of 1 lamb per ewe lambing would lead to a correlated response in body weight of 5 kg.Selection for ALS on the basis of dams' performance, within the flock studied, would be expected to yield a rate of progress of 2% per annum.

Section: Repeatabilitymentioning

confidence: 96%

Analysis of production records from a lowland sheep flock 3. Phenotypic and genetic parameters for reproductive performance

Forrest

Bichard

1974

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“…Conception and lambing rates, however, although depending to a large extent on breed, management and husbandry practices, are much more variable and usually lower in first-lambing female sheep than in older ewes (Dyrmundsson, 1973;Forrest and Bichard, 1974;Quirke, 1977). Conception and lambing rates, however, although depending to a large extent on breed, management and husbandry practices, are much more variable and usually lower in first-lambing female sheep than in older ewes (Dyrmundsson, 1973;Forrest and Bichard, 1974;Quirke, 1977).…”

Section: Introductionmentioning

confidence: 99%

Pre-puberal plasma luteinizing hormone concentrations and progesterone concentrations during the oestrous cycle and early pregnancy in Galway and Fingalway female lambs

Quirke

Gosling

1979

Twenty-four young female sheep, 12 Galways and 12 Fingalways, were used to study the effects of breed and level of nutrition on prepuberal plasma luteinizing hormone and progesterone concentrations throughout the oestrous cycle and during the first 35 days of pregnancy. The sheep were spring-born and were housed at the end of July when they weighed approx. 34 kg. Equal numbers of animals from each breed were fed on a concentrate diet either ad libitum or at a restricted level that was slightly above their estimated maintenance requirements. The Fingalways reached puberty 1 month earlier than the Galways (11 October ±4 days v. 10 November ±5 days). The restricted animals tended (P<0-10) to reach puberty later than those fed ad libitum (1 November ±5 days v. 20 October ±4 days). Breed differences in the mean level of plasma progesterone on any day of the oestrous cycle were not significant. The mean daily plasma progesterone concentration was similar for the animals on the two planes of nutrition throughout the cycle, with the exception of day 11 when those fed ad libitum had a significantly higher level (F<0-01). Plasma progesterone levels in the pregnant females between 5 and 35 days post mating were generally higher in Fingalways than in Galways and were not influenced by plane of nutrition. Plasma luteinizing hormone levels tended to be higher, during the 7 weeks before puberty, in Fingalways than in Galways and in animals fed ad libitum than in those on the restricted level of feeding.

“…Effect of rates are normally lower than those found in PMSG dosage on the reproductive performance of adult ewes(Gordon, 1967;Dyrmundsson, a d u l t e w e s a n d ewe lambs bred at a progestagen-Cumberland, 1974;Forrest and Bichard, 1974; Synchronization of estrus and reproductive performance Quirke, 1979b; Ainsworth and Wolynetz, of ewes treated with synthetic progestagens 1982; AINSWORTH, L., FISER, P. ' S., HEANEY, D .…”

mentioning

confidence: 99%

The reproductive performance of ewe lambs in a controlled environment

Ainsworth¹,

Shrestha²

1987

The effects of strain, season, type of birth, age and body weight at breeding on fertility and fecundity of ewe lambs raised in a controlled environment were evaluated. Data were derived from 2776 ewe lambs of a synthetic sire strain, two synthetic dam strains and two control strains (Suffolk and Finnish Landrace breeds) mated to 719 rams over 15 breeding periods during January, May or September over 9 years. The ewe lambs were exposed to rams at a synchronized and follow-up oestrus at 6-5 to 7-5 months of age. There were significant differences among strains. Fertility and fecundity were highest for lambs of the Finnish Landrace breed, intermediate for the two synthetic dam strains and lowest for the synthetic sire strain and the Suffolk breed. Although period of breeding and season had an effect on reproductive traits, the strain differences were not consistent. Type of birth did not affect performance of lambs at the synchronized oestrus. However, overall fertility and fecundity increased progressively as the type of birth of the lambs increased from singles to triplets and greater. Increased age and body weight at the synchronized oestrus had a significant and positive effect on fertility and fecundity.