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## Estimation of Genetic Parameters for Lactation Curve Traits in Holstein Dairy Cows in Iran | ||

Iranian Journal of Applied Animal Science | ||

مقاله 4، دوره 7، شماره 4، زمستان 2017، صفحه 559-566
اصل مقاله (348 K)
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نوع مقاله: Research Articles | ||

نویسندگان | ||

F. Saghanezhad؛ H. Atashi ^{} ؛ M. Dadpasand؛ M.J. Zamiri؛ F. Shokri-Sangari
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^{}Department of Animal Science, Shiraz University, Shiraz, Iran | ||

چکیده | ||

The objectives were to estimate (co)variance components and genetic parameters for lactation curve traits in Holstein dairy cows in Iran. The used data were records on Holstein cows collected during January 2003 to December 2012 by the Animal Breeding Center of Iran (Karaj, Iran). In order to describe the lactation curve, an incomplete gamma function was fitted to 691200 test-day records on 96263 lactations, 377696 test-day records on 52168 lactations, and 182143 test-day records on 24951 lactations for the first three parities, respectively. Lactation curve traits that were analyzed included a scaling factor associated with initial yield, the inclining and declining slopes of the curve, peak time, peak yield, 305-d milk yield and a lactation persistency measure derived from the incomplete gamma function. The estimated heritability of lactation curve traits for the first, second and third lactation ranged from 0.012 to 0.29, 0.017 to 0.15, and 0.02 to 0.13, respectively. Genetic correlations among lactation curve traits for the first, second and third lactation ranged from -0.68 to 0.99, -0.84 to 0.98 and -0.90 to 0.94, respectively. The estimated repeatability of lactation curve traits ranged from 0.07 to 0.40. The moderate to large positive genetic correlations of 305-d milk yield with initial yield, peak yield and lactation persistency suggest that one of these traits could be used as a selection criterion to improve all four traits. However, the peak yield and 305-d milk yield were more heritable than lactation were persistency and initial yield. | ||

کلیدواژهها | ||

Holstein dairy cow؛ incomplete gamma function؛ lactation curve | ||

اصل مقاله | ||

The graphical representation of milk yield during lactating period is lactation curve. Typical lactation curve of a dairy cow shows a peak or maximum daily yield occurring during first weeks after calving, followed by a daily decrease in milk yield until the cow is dried-off (Keown
The used data were records on Holstein cows collected from January 2003 to December 2012 by the Animal Breeding Center of Iran (Karaj, Iran). The evaluated herds (n=261) were purebred Holsteins, managed under conditions similar to those used in most developed countries, and were under official performance and pedigree recording. The diet, fed as a
To describe the lactation curve, the incomplete gamma function proposed by Wood (1967) was used. The function was as follows: y Where: y t: length of time since calving. e: Neper number. a: parameter to represent initial yield. b and c: factors associated with the upward and downward slopes of the curve, respectively. In this study, the incomplete gamma function was transformed logarithmically into a linear form as: ln(y Typical lactation curves have positive
(Co)variance components for lactation curve traits (initial yield, upward and downward slopes of the curve, peak time, peak yield, lactation persistency, and 305- d milk yield were estimated using single and multiple-trait animal model. The linear model included fixed effects of herd-year-season (HYS), covariate effects of age at first calving (FCA) and total days in milk (DIM) in both linear and quadratic forms, as well as animal and residual random effects. The following repeatability animal model was used to estimate the repeatability of lactation curve traits: y Where: y HYS lac: fixed effect of j a pe The genetic analyses were carried out through restricted maximum likelihood (REML) method using WOMBAT software (Meyer, 2006).
A typical lactation curve has positive a, b, and c parameters, characterized by an initial phase that increases to a maximum and is followed by a declining phase. Lactation curve with negative values for a, b or c parameters is considered atypical. In this study, 21.48% of 96263 lactations in first parity, 20.71% of 52168 lactations in second parity and 19.91% of 24951 lactations in third parity were atypical. Rekik
The estimated heritability (±SE) (diagonal), genetic correlations (upper off-diagonal) and phenotypic correlations (lower off-diagonal) for lactation curve traits in the first, second and third parity are presented in Tables 1, 2, and 3, respectively. The heritability for lactation curve traits in the first, second and third parity ranged from 0.012 (downward slope of the curve) to 0.29 (peak yield), 0.017 (initial yield) to 0.15 (305-d milk yield), and 0.02 (lactation persistency) to 0.13 (305-d milk yield), respectively. Ferris
The genetic correlations among lactation curve traits in the first parity ranged from -0.68 (downward slope of the curve and peak time) to 0.99 (peak time and lactation persistency), while the phenotypic correlations ranged from -0.95 (initial yield and the upward slope of the curve) to +0.83 (peak time and lactation persistency). The genetic and phenotypic correlations among lactation curve traits in the second parity ranged from -0.84 (downward slope of the curve and peak time) to 0.98 (peak time and lactation persistency), and -0.94 (initial yield and the upward slope of the curve) to +0.85 (peak time and lactation persistency), respectively. The genetic correlation among lactation curve traits in the third parity ranged from -0.90 (initial yield and upward slope of the curve) to 0.94 (upward and downward slopes of the curve), while the phenotypic correlations ranged from -0.95 (initial yield and the upward slope of the curve) to +0.84 (peak time and lactation persistency). Similar results have been reported in earlier research (Rao and Sundaresan, 1979; Shanks
Tekerli
The lactation curves for first parity cows born in 2000 and for those born in 2009 are presented in Figure 1, which explain phenotypic trend of lactation curve shape in Holstein cows in Iran.
Phenotypic trends for lactation curve traits in first parity cows are presented in Figure 2.
In the period from 2001 to 2009, initial yield, upward slope of the curve, lactation persistency, peak yield and 305-d milk yield significantly increased (P<0.05), but downward slope of the curve and peak time did not significantly changed (P≥0.05). Phenotypic trends for 305-d milk yield and peak yield were more straightforward than those for initial yield, upward slope of the curve and lactation persistency.The additive genetic trends for lactation curve traits in first parity cows, given as average additive genetic solutions per birth year were presented in Figure 3.
In the period from 2001 to 2009, upward slope of the curve, lactation persistency, peak time, peak yield and 305-d milk yield increased and showed significant genetic trend (P<0.05), but initial yield and downward slope of the curve showed no significant genetic trend (P≥0.05). Initial yield, peak yield, and 305-d milk yield showed same phenotypic and genetic trends, because there are strong phenotypic and genetic correlations among these traits. Ferris
The genetic correlations between initial yield, downward slope of the curve, lactation persistency and peak yield with 305-d milk yield indicate that cows that have a higher initial level of production, higher peak yield, higher lactation persistency and decline at a slower rate would have a higher 305-d milk yield. The moderate to large positive genetic correlations of 305-d milk yield with initial yield, peak yield and lactation persistency suggest that one of these traits could be used as a selection criterion to improve all four traits. However, the peak yield and 305-d milk yield are more heritable than lactation persistency and initial yield.
The co-operation of the Animal Breeding Center (Karaj, Iran) for providing the data is greatly appreciated. | ||

مراجع | ||

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