Ad justment factors for lamb weaning weight

Jury, K. E.; Johnson, D. L.; Clarke, J. N.

doi:10.1080/00288233.1979.10430764

Cited by 6 publications

(6 citation statements)

References 3 publications

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“…These relationships allowed the prediction of flock-specific adjustment factors to be extended to larger numbers of flocks, because derivation of flock-specific factors required only an estimate of the mean weights of lambs in the reference class for each flock. These results conflict, in part, with those observed in 12 large New Zealand Romney flocks [15, 16]. In those flocks, significant variation was observed among flocks and years in adjustment factors for effects of lamb sex, birth-rearing type and dam age, but no association was reported between resulting factors and flock means for weaning weights.…”

Section: Discussioncontrasting

confidence: 56%

Effects of birth-rearing type on weaning weights in meat sheep are systematically associated with differences in mean performance among flocks

Notter

Brown

2015

Genet Sel Evol

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BackgroundAdjustment of body weights for systematic environmental effects such as dam age and litter size is essential for accurate prediction of breeding values in meat sheep and often accomplished by pre-adjusting records using simple multiplicative adjustment factors, which are derived as ratios of least-squares means of weights of lambs in target and reference classes. However, increasing use of multibreed genetic evaluations that incorporate data from both purebred and commercial flocks has generated concerns regarding the ability of simple additive or multiplicative adjustment factors to properly correct for environmental effects in flocks that differ widely in mean performance. Thus, consistency of adjustment factors across flocks and systematic effects of the level of flock performance on these factors were evaluated using data from the US National Sheep Improvement Program.MethodsWe used birth and weaning weights of lambs from 29 flocks that had at least 500 records per flock and represented several terminal-sire sheep breeds. Effects of lamb sex, dam age class and litter size on birth weights, and of dam age class and combined effects of type of birth and rearing on weaning weights were evaluated. Interactions between these effects and flock were assessed. Bias associated with different adjustment protocols was evaluated for high- and low-performance flocks.ResultsEffects of litter size and differences between yearling and adult dams varied (P < 0.001) among flocks. For weaning weights, additive adjustment factors were not associated with the level of flock performance, but multiplicative adjustment factors were strongly and inversely related to flock means for weaning weights (W). Flock-specific adjustment factors (F = αWβ) reduced bias in adjusted weaning weights associated with differences in flock performance. By contrast, simple multiplicative adjustment factors were appropriate to adjust birth weights.ConclusionsDifferences in weaning weights among single, twin, and triplet lambs were inversely related to the level of flock performance. Use of simple multiplicative adjustment factors led to adjustment bias when applied across flocks with large differences in mean performance. This bias was reduced by using additive adjustment factors or multiplicative factors that were derived as simple exponential functions of flock means for weaning weight.

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Section: Discussioncontrasting

confidence: 56%

Effects of birth-rearing type on weaning weights in meat sheep are systematically associated with differences in mean performance among flocks

Notter

Brown

2015

Genet Sel Evol

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“…The data used are the adjustment factors derived from the least-squares analysis of Jury et al (1979). These adjustment factors were calculated by taking differences between particular least-squares means within each flock and year.…”

Section: Methodsmentioning

confidence: 99%

“…respectively. Jury et al (1979). If sej6 denotes the standard error of the adjustment factor when 6 years of data are pooled within the jth flock then an estimate of u€ is given by 1 12 where MIj and M2j are the average annual number of lambs in flock j belonging to the two classes appropriate to the particular adjustment factor and s,?j, is the residual mean square from the analysis offlockj.…”

Section: Methodsmentioning

confidence: 99%

“…Significant flock X year interactions are present for all adjustment factors. Referring to the least-squares analysis of Jury et al (1979), this result represents a three factor interaction between flock, year, and each of sex, birth-rearing rank, and age of dam.…”

Section: Analysis Of Variance Of Adjustment Factorsmentioning

confidence: 99%

“…Analysis of data from the New Zealand National Flock Recording Scheme has indicated significant variation among flocks and years in the magnitude of adjustment factors for weaning weight of New Zealand Romney lambs (Jury et al 1979). Presence of such variation suggests that adjustments should be carried out on the basis of the particular flock X year data.…”

Section: Introductionmentioning

confidence: 99%

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Adjustment factors for lamb weaning weight

Eikje

Johnson²

1979

New Zealand Journal of Agricultural Research

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Sources of variation in adjustment factors for weaning weight of New Zealand Romney lambs were studied. Data from 12 flocks and 6 years were used. Adjustment factors for sex differences were affected significantly by flock, year, and interactions between flock and year. Birth-rearing rank factors were affected mainly by interactions between flock and year, and age-of-dam adjustments seemed to be affected by flock and interactions. Only a small proportion of the variance in adjustment factors could be explained by flock level for weaning weight. It is concluded that some sort of flock X year specific adjustment should be carried out in flocks weaning more than about 150 lambs per year. An exception is adjustment of lambs l)orn as twins and reared as singles, where considerably larger flocks are required before flock X year specific adjustment will be better than overall adjustment.

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Hormonal induction of twinning in farmed red deer (Cervus elaphus): comparative mortality and growth of twins and singles to weaning

Fennessy¹,

Moore²,

Littlejohn³

1990

Anim. Sci.

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Multiple births were induced in 20 hinds subjected to a progesterone plus gonadotropin treatment to advance the breeding season by about 4 to 5 weeks. In total, over 2 years, 92 hinds were treated and run with melatonin-treated stags. Of the 59 hinds that calved to the induced oestrus, 39 produced single calves, 19 produced twins and one produced triplets. Birth weight, gestation length, perinatal mortality and growth rate to weaning at ca. 20 weeks of age were compared for singles and twins. There was a significant effect of birth type on birth weight with twins being proportionately 0·30 lighter than singles (6·27 and 8-94 kg; P < 0·001), with a significant interaction between the birth weight of a calf and the sex of its co-twin (P < 0·05); males born as co-twins to females were proportionately 0·18 heavier than their co-twin females (P < 0·06), while in contrast twin male sets were substantially lighter than twin female sets. Gestation lengths were similar for both singles and twins, with significant negative relationships between gestation length and birth weight for both singles and twins, with a 2-day decrease in gestation length for a 1-kg increase in mean birth weight. There was a strong quadratic relationship between perinatal survival and birth weight; the expected mortality rates at 5, 8 and 11 kg birth weight derived from the relationship were 0·39, 0·11 and 0·39 respectively, indicating reduced probability of survival at both low and high birth weights. The regression relationships between weaning weight or growth rate to weaning and birth weight indicate that at the same birth weight, twin-reared calves were about 5 kg lighter than singles at 20 weeks, while an extra 1 kg weight at birth was associated with an extra 2 kg weight at 20 weeks.

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Ad justment factors for lamb weaning weight

Cited by 6 publications

References 3 publications

Effects of birth-rearing type on weaning weights in meat sheep are systematically associated with differences in mean performance among flocks

Effects of birth-rearing type on weaning weights in meat sheep are systematically associated with differences in mean performance among flocks

Adjustment factors for lamb weaning weight

Hormonal induction of twinning in farmed red deer (Cervus elaphus): comparative mortality and growth of twins and singles to weaning

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