Genetic aspects of Wood's lactation curve parameters in Jersey crossbred cattle using Bayesian approach.

The study was undertaken to estimate the genetic parameters of lactation curve parameters of Wood's function in Jersey crossbred cattle using the Bayesian approach. Data on 33,906 fortnightly test day milk yields of 1,718 lactation records of Jersey crossbred cows, maintained at the ICAR-National Dairy Research Institute in West Bengal, were collected over a period of 40 years. The lactation curve parameters including '' (initial milk yield after calving), '' (ascending slope up to peak yield) and '' (descending slope after peak yield) and lactation curve traits, peak yield (), time of peak yield () and persistency of milk yield () of individual cow for each lactation were estimated using the incomplete gamma function (Wood's model) by fitting the Gauss-Newton algorithm as an iteration method using PROC NLIN procedure of SAS 9.3. Variance components and genetic parameters of lactation curve parameters/traits were estimated by a repeatability animal model using the Bayesian approach. Estimates of heritabilities were found to be 0.18 ± 0.05, 0.09 ± 0.03 and 0.11 ± 0.04 for parameters '', '' and '', respectively and 0.24 ± 0.05, 0.12 ± 0.04, and 0.15 ± 0.05 for , and P, respectively. Repeatability estimates were 0.31 ± 0.03, 0.21 ± 0.04 and 0.30 ± 0.04 for parameters '', '' and '' respectively and 0.39 ± 0.03, 0.24 ± 0.03 and 0.37 ± 0.03 for , and , respectively. Genetic correlations among lactation curve parameters/traits ranged from -0.75 to 0.95. Existence of genetic correlations among lactation curve parameters/traits indicated substantial genetic and physiological relationships among lactation curve parameters/traits of Jersey crossbred cattle.

Rahman M ，Baneh H ，Gayari I ，Karunakaran M ，Raja TV ，Deb SM ，Mandal A ... -  《-》

Bayesian approach for genetic analysis of production and reproduction traits in Jersey crossbred cattle.

The knowledge of genetic parameters of performance traits is crucial for any breeding programme in dairy animals. The present study was conducted to use a Bayesian approach for estimation of genetic parameters of production and reproduction traits in Jersey crossbred cattle. Data of Jersey crossbred cattle maintained at Eastern Regional Station, National Dairy Research Institute, West Bengal spread over a span of 41 years were utilized. The marginal posterior medians of heritability for 305-day milk yield (305MY), total milk yield (TMY), peak yield (PY), lactation length (LL), calving interval (CI), total milk yield per day of lactation length (TMY/LL) and total milk yield per day of calving interval (TMY/CI) were 0.31 ± 0.07, 0.29 ± 0.07, 0.27 ± 0.06, 0.16 ± 0.05, 0.15 ± 0.05, 0.29 ± 0.06, 0.27 ± 0.06, respectively. Moderate heritability estimates for 305MY, TMY, PY and production efficiency traits indicate the presence of adequate additive genetic variance in these traits to respond to selection combined with better herd management. Repeatability estimates for 305MY, TMY, PY, LL, CI, TMY/LL and TMY/CI were 0.57 ± 0.08, 0.58 ± 0.08, 0.51 ± 0.07, 0.34 ± 0.06, 0.31 ± 0.06, 0.54 ± 0.07 and 0.49 ± 0.07, respectively. Repeatability estimates for 305MY, TMY and PY were high in the current study, suggesting the use of first lactation records for early evaluation of Jersey crossbred cattle for future selection. Genetic correlations varied from 0.21 to 0.97 and maximum genetic correlation was observed between 305MY and TMY indicating that consideration of 305MY instead of TMY in breeding programmes would suffice. Positive genetic correlations of CI with 305MY and TMY indicated the antagonistic association between production and reproduction traits.

Ratwan P ，Kumar M ，Mandal A 《-》

Bayesian analysis of lactation curves of Holstein-Friesian cattle using a nonlinear model.

Rekaya R ，Carabaño MJ ，Toro MA 《JOURNAL OF DAIRY SCIENCE》

Estimates of genetic parameters and genetic trend for Wood's lactation curve traits of Tunisian Holstein-Friesian cows.

This study was conducted to (1) estimate Wood's incomplete gamma function parameters (a, b and c) for individual registered Tunisian Holsteins in the 3 first lactations; (2) estimate persistency (Per), peak time (PT), peak yield (PY) and 305-day lactation milk yields (Y305); (3) estimate the genetic parameters of the predicted traits and (4) evaluate the genetic trend of the most heritable traits. Pedigree data and 380,709 test-day milk records of 20,758 Holstein cattle collected from 2008 to 2018 in 33 herds were analyzed. Initially, Wood's incomplete gamma function parameters were determined and subsequently along with some production characteristics (Per, PT, PY and Y305). Each estimated trait was subjected to a single trait animal model to estimate genetic parameters using MTDFREML program (Boldman et al. 1995). Multivariate animal model was used to estimate genetic and phenotypic correlations between the most heritable traits and their breeding values (EBVs). Genetic trends were defined using BREEDPLAN multi-trait EBVs by averaging the EBV of all animals born by year of birth. The resulting heritability estimates varied from 0.04 to 0.06 for Per, 0.01 to 0.02 for PT, 0.08 to 0.16 for PY and 0.09 to 0.16 for Y305. The greatest heritabilities were within the first lactation for PY and Y305 traits. Genetic and phenotypic correlations were very high between the most heritable two traits (0.91 and 0.83, respectively). Heritability estimates of PT and Per were close to zero indicating that these traits are more influenced by the management and the environment. The regression coefficients, relative to the genetic trend graph, mark an overall rate of increase of 13.18 kg/year and 0.056 kg/year in Y305 and PY, respectively, over 16-year period. A number of policies should be developed by the Tunisian government to attend better genetic progress.

Bakri NE ，Pieramati C ，Sarti FM ，Giovanini S ，Djemali M' ... -  《-》

Genetic analysis of persistency indices of milk yield in Jersey crossbred cattle.

The study reported in this Research Communication was conducted to estimate genetic parameters for different lactation persistency indices and their association with reproductive traits in Jersey crossbred cattle. Data on lactation traits (part lactation yields and 305-days milk yield) comprising all lactations as well as reproductive traits viz. calving interval, conception rate and gestation length of 378 Jersey crossbred cattle, maintained at National Dairy Research Institute, Kalyani, West Bengal, India, were collected over a period of 35 years (1982-2016). Five lactation persistency indices of animals (P21, P31, P32, P4 and P5) were calculated using ratio method. A total of six different animal models, ignoring or including maternal genetic or permanent environmental effects, were fitted for all persistency traits. The best model was chosen after testing the improvement of the log-likelihood values. The estimates of direct heritability were low in magnitude and ranged from 0.02 to 0.14 for the studied traits under the best fitted animal model. The permanent maternal environmental (c2) effects of different lactation persistency indices accounted for 2-9% of the total phenotypic variance in this study. Estimated genetic correlations of lactation persistency indices with all studied reproductive traits were low to moderate and negative (-0.11 to -0.68), except for calving interval. Phenotypic correlations of lactation persistency measures with studied reproductive traits were low (0.01 to 0.15). The low heritability estimates of all the persistency indices indicate some limited scope of genetic improvement of lactation persistency of animals through selection under the prevailing management conditions.

Koloi S ，Mandal A 《-》