 หัวเรื่อง:ไม่มีชื่อไทย (ชื่ออังกฤษ : Genotype by Environment Interaction Effect on Lactation Pattern and Milk Production Traits in an Ethiopian Dairy Cattle Population) ผู้เขียน: Gebregziabher Gebreyohannes,  ดร.ศกร คุณวุฒิฤทธิรณ, รองศาสตราจารย์ , Mauricio Aguirre Elzo, ดร.ธนาทิพย์ สุวรรณโสภี, รองศาสตราจารย์ สื่อสิ่งพิมพ์:pdf AbstractThe genotype by environment interaction (GEI) was evaluated for lactation milk yield (LY), initial milk yield (IY), peak milk yield (PY) and average milk yield per day (YD) in an Ethiopian multibreed dairy cattle population. Analyses used 4,488 lactation milk records from 1,320 cows collected at the Bako and Holetta research centers from 1979 to 2010. Breeds were Horro, Boran, Friesian crossbreds, Jersey crossbreds and Simmental crossbreds. The GEI for each trait was evaluated using estimates of cow breed group by environment (Bako and Holetta) interactions (univariate fixed models) and Spearman’s rank correlations between sire-predicted values for the same trait measured in both environments (bivariate mixed models). Friesian crossbreds had higher (P < 0.0001) least squares mean (LSM) values for LY, IY, PY and YD than Simmental and Jersey crossbreds at Holetta, whereas Friesian and Simmental crossbreds had higher (P < 0.0001) LSM values for LY, PY and YD than Jersey crossbreds at Bako. Correlations between sire rankings at Bako and Holetta were 0.86 for LY and IY and 0.87 for YD indicating that substantial re-ranking occurred across locations. Thus, multiple-trait models with phenotypic information from Bako and Holetta would be needed to accurately select the most appropriate sires for each location. |
หัวเรื่อง:ไม่มีชื่อไทย (ชื่ออังกฤษ : Estimation of genetic parameters using a random regression monthly test-day model in an Ethiopian dairy cattle population) ผู้เขียน:Gebregziabher Gebreyohannes, ดร.ศกร คุณวุฒิฤทธิรณ, รองศาสตราจารย์, Mauricio A. Elzo, ดร.ธนาทิพย์ สุวรรณโสภี, รองศาสตราจารย์ สื่อสิ่งพิมพ์:pdf AbstractMonthly test-day milk records (n ? 50,839) from 2045 cows born from 312 sires and 1169 dams in Bako, Debre Zeit and Holetta (Ethiopia, 1977 to 2010) were used to estimate the variance components and genetic parameters for monthly test-day milk yield. Cows were Horro (H), Boran (B), Friesian (F) crossbreds, Jersey (J) crossbreds, and Simmental (S) crossbreds. Lactations were modeled with a logtransformed, modified, incomplete, gamma function. The random regression, animal repeatability model considered herd-year-test-day subclass, parity, H, B, F, J, and S cow fractions, F B, F H, J B, J H, S B and S H cow heterozygosities as fixed effects. Random effects were additive genetic, permanent environmental and residual. Variance components were estimated using restricted maximum likelihood procedures. Additive genetic, permanent environmental and phenotypic variances, heritabilities (0.17e0.42) and repeatabilities (0.84e0.94) for test-day milk yields increased as lactation progressed. Additive genetic, permanent environmental and phenotypic correlations were higher between adjacent than non-adjacent monthly test-days, and decreased as interval between test-days increased. The results suggested that a random regression, animal repeatability model using a modified, incomplete, gamma function would be appropriate for genetic evaluation in this multibreed population. |
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หัวเรื่อง:ไม่มีชื่อไทย (ชื่ออังกฤษ : Fitness of Lactation Curve Functions to Daily and Monthly Test-Day Milk Data in an Ethiopian Multi-Breed Dairy Cattle Population) ผู้เขียน:Gebregziabher Gebreyohannes, ดร.ศกร คุณวุฒิฤทธิรณ, รองศาสตราจารย์, Mauricio A. Elzo, ดร.ธนาทิพย์ สุวรรณโสภี, รองศาสตราจารย์ สื่อสิ่งพิมพ์:pdf AbstractThe objectives of this study were to identify the lactation curve function that had the best fi t to daily and monthly test-day milk data and to evaluate the factors affecting parameters of the best fi t lactation curve function for an Ethiopian dairy cattle population. An incomplete gamma (IG), a modifi ed incomplete gamma (MIG; b = 1) and an inverse polynomial (IP) function were compared using 6,717 lactation milk records of 2,064 cows from the Bako, Holetta and Debre Zeit Research Centers, Ethiopia. Breed groups were Horro (H), Boran (B), B ? Friesian, H ? Friesian, B ? Simmental, H ? Simmental, B ? Jersey and H ? Jersey. The MIG and IG were log-transformed to linear form before fi tting. The functions were compared based on the least squares means (LSM) of R2 (LSM R2) and adjusted R2 values and on the accuracy of lactation milk yield prediction. The statistical model included herd-year-season of calving, parity, data type, breed group, lactation curve function, and the interactions of data type ? function and breed ? data type ? function as fi xed effects, and the residual as a random effect. The MIG, IP and IG functions ranked from the best to the worst fi t based on LSM R2 and adjusted R2. The LSM R2 and adjusted R2 were signifi cantly (P < 0.001) different among all classes of fi xed effects considered in the model. The LSM R2 and adjusted R2 for the MIG function were 0.90 and 0.89, respectively. All functions fi tted to monthly test-day better than to daily milk data. The MIG function had the best fi t (P < 0.001) to daily milk data, but both the MIG and IP functions had a similar fi t to monthly test-day milk data based on the LSM of adjusted R2. The ln(a) and c from the MIG function with daily and monthly test-day milk data, and the A0, A1 and A2 from the IP function with monthly test-day data were different among breed groups, parities and herd-year-season classes (at least P < 0.05). The MIG function predicted the lactation milk yield from the monthly test-day milk with the lowest prediction error (P < 0.001) compared to the IP and IG functions. Thus, the MIG function could be recommended to model lactation milk data from monthly test-day milk in the studied dairy cattle population. |
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