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Abstract
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In the present study, test-day records of milk yield (TDMY), fat yield (TDFY), and protein yield (TDPY) of first-parity
Murciana-Granadina goats, collected from 2017 to 2024 in the southern part of Kerman province of Iran, were used. The
traits were analyzed by applying random regression models (RRMs) with the Legendre polynomials (LEG) and B-spline
(BSP) functions. The RRM with order 3 for direct genetic and animal permanent environmental effects under the LEG
function was the best for TDMY. The RRMs employing quadratic BSP functions with 5 and 4 knots were determined as
the most suitable models for TDFY and TDPY, respectively. The heritability (h2) estimates of TDMY across the lactation
period were low, varying from 0.15 ± 0.03 at days in milk (DIM) 5 to 0.03 ± 0.02 at DIM 275. For TDFY, the h2 estimates
were medium to low and varied from 0.22 ± 0.09 at DIM 5 to 0.01 ± 0.01 at DIM 245. The h2 estimates of TDPY were
low and ranged from 0.18 ± 0.07 at DIM 5 to 0.02 ± 0.01 at DIM 215. Genetic correlation estimates varied from 0.41 ± 0.18
(DIMs 5 and 203) to 0.99 ± 0.17 (DIMs 137 and 275) for TDMY, 0.41 ± 0.12 (DIMs 5 and 275) to 0.98 ± 0.16 (DIMs 203
and 275) for TDFY, and 0.18 ± 0.06 (DIMs 5 and 203) and also 0.18 ± 0.10 (DIMs 5 and 275) to 0.99 ± 0.17 (DIMs 137
and 203) for TDPY. The strongest genetic correlations were found between closely located DIMs, with these correlations
decreasing as the interval between DIMs increased. In general, early DIMs showed higher genetic variations relative to the
other stages of the lactation period with positive genetic correlations in late lactation. Therefore, there is an opportunity
for early selection practices to improve the traits in the later stages of the lactation period.
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