GENETIC AND PHENOTYPIC PARAMETERS OF REPRODUCTIVE TRAITS IN YANKASA SHEEP
GENETIC AND PHENOTYPIC PARAMETERS OF REPRODUCTIVE TRAITS IN YANKASA SHEEP
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Date
1995
Authors
BEMJI, Martha Nchang
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Abstract
A study was conducted to determine genetic and phenotypic parameters of
reproductive traits from 2773 lambings of a semi-intensively managed breeding flock of
Yankasa sheep at the National Animal Production Research Institute (NAPRI), Shika,
situated within the subhumid zone of Nigeria.
Edited records of 2204, 2490, 1225, 1461, 1196, 1204 and 247 lambings were used to
analyse for environmental effects on litter size (LS), birth weight (BWT), litter birth
weight (LBWT), 90-day weaning weight (WWT), gestation length (GL), lambing interval
(LI) and age at first lambing (AFL), respectively.
Least-squares means (±SE) were 1.22±0.01 (LS), 2.48+0.01 kg (BWT), 3.57±0.03 kg
(LBWT), 10.58±0.11 kg (90-day WWT), 151.37+0.01 days (GL), 249.81+2.72 days (LI),
and 575.00±9.55 days (AFL). Litter size was significantly (P<0.001) affected by parity,
season and year of birth. Multiparous ewes and ewes lambing in the dry season were
superior in litter size to primiparous ewes and ewes lambing in the rainy season. Ram
lambs were consistently heavier than ewe lambs (P<0.001) by 0.12 and 0.78 kg
respectively at birth and at weaning. A similar trend was observed with single and twin
bom lambs, the difference (P<0.001) being 0.39 and 2.32 kg in favour of single born
lambs at birth and at weaning respectively. Lambs from multiparous ewes had higher body
weights than lambs from primiparous ewes, likewise rainy season born lambs than dry
season bom lambs. Gestation length was significantly affected by parity (P<0.05) and year
of birth (P<0.001), but not by litter size, sex and season of birth (P>0.05). Younger ewes
had shorter GL than older ewes, being 150.94 vs 151.70 days for primiparous and sixth
parity ewes. Parity, litter size and sex of lamb insignificantly (P>0.05) affected LI, while
the effects of season (P<0.01) and year of birth (P<0.001) were highly significant. Ewes
lambing in the rainy season had shorter LI than ewes lambing in the dry season (249.64 vs
249.99 days). AFL was significantly affected by type of birth (P<0.05), season and year of
birth of ewe (P<0.01). AFL was attained earlier in single than twin bom ewes.
Additive environmental adjustment factors for effects of parity of dam, type of birth,
sex of lamb and season of birth for LS, BWT, and 90-day WWT were derived.
Heritability estimates for LS from daughter-dam regression was 0.07. Using paternal
half-sib analysis. BWT, LBWT, 90-day WWT, GL as dam trait. GL as foetal trait, LI and
AFL were estimated at 0.41±0.08, 0.12±0.07, 0.59±0.12, 0.15±0.12, 0.21+0.08,
0.73+0.26 and 0.99±0.38 respectively. With the exception of low heritability estimate for
litter size, most values were moderate to high suggesting moderate to high genetic
responses to selection for these traits. Estimates for LI and AFL were, however,
considered inflated and attributed to dominance and epistatic effects. There were high
genetic and phenotypic correlations (0.69±0.16 vs 0.36) between BWT and 90-day WWT
indicating a high positive correlated response to selection for these traits. Genetic
correlations between LS and BWT, LS and 90-day WWT, LS and GL, and LBWT and
GL were -0.08±0.35, -0.25+0.33, -0.11±0.32 and 0.07+0.27 respectively. Corresponding
phenotypic correlations were -0.14, -0.34, 0.02 and 0.09. Generally, genetic and
phenotypic correlations for most traits were moderate to low, and /or negative
Description
A Thesis
submitted to the Postgraduate School, Ahmadu Bello University, Zaria in
partial fulfillment of the requirements for the degree of Master of Science in
Animal Science.
Department of Animal Science
Faculty of Agriculture
Ahmadu Bello University
Zaria, Nigeria
1995
Keywords
GENETIC,, PHENOTYPIC,, PARAMETERS,, REPRODUCTIVE,, TRAITS,, YANKASA,, SHEEP.