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The current study sought to genetically assess the lactation curve of Alpine × Beetal crossbred goats through the application of random regression models (RRM). The objective was to estimate genetic parameters of the first lactation test-day milk yield (TDMY) for devising a practical breeding strategy within the nucleus breeding programme. In order to model variations in lactation curves, 25,998 TDMY records were used in this study. For the purpose of estimating genetic parameters, orthogonal Legendre polynomials (LEG) and B-splines (BS) were examined in order to generate suitable and parsimonious models. A single-trait RRM technique was used for the analysis. The average first lactation TDMY was 1.22 ± 0.03 kg and peak yield (1.35 ± 0.02 kg) was achieved around the 7th test day (TD). The present investigation has demonstrated the superiority of the B-spline model for the genetic evaluation of Alpine × Beetal dairy goats. The optimal random regression model was identified as a quadratic B-spline function, characterized by six knots to represent the central trend. This model effectively captured the patterns of additive genetic influences, animal-specific permanent environmental effects (c 2 ) and 22 distinct classes of (heterogeneous) residual variance. Additive variances and heritability (h 2 ) estimates were lower in the early lactation, however, moderate across most parts of the lactation studied, ranging from 0.09 ± 0.04 to 0.33 ± 0.06. The moderate heritability estimates indicate the potential for selection using favourable combinations of test days throughout the lactation period. It was also observed that a high proportion of total variance was attributed to the animal's permanent environment. Positive genetic correlations were observed for adjacent TDMY values, while the correlations became less pronounced for more distant TDMY values. Considering better fitting of the lactation curve, the use of B-spline functions for genetic evaluation of Alpine × Beetal goats using RRM is recommended., (© 2024 Wiley‐VCH GmbH. Published by John Wiley & Sons Ltd.)

The present study was aimed at optimizing the selection strategy for enhancing reproductive efficiency and milk productivity of Alpine × Beetal crossbred goats. The data set included 2949 milk trait records across parities and 1389 milk records from first parity and corresponding reproductive traits. The traits included for analysis were 150-day milk yield (150DMY), days in milk (DIM), peak yield (PY) and total milk yield (TMY). The litter size (LS) and litter weight (LW) were used for specifically formulating selection plan using indirect selection. The least squares mean for lactation traits during the first parity were 150DMY: 195.32 ± 2.09 kg, DIM: 236.42 ± 3.04 days, PY: 1.82 ± 0.02 kg, TMY: 269.62 ± 4.52 kg. Notably, Alpine × Beetal goats demonstrated genetic superiority pan India for milk productivity as compared to other native goat breeds. The least squares mean for 150DMY across all parities was 236 ± 3.13 kg. An animal model employing average information restricted maximum likelihood was used for (co)variance component estimation to get the genetic parameters. The analysis revealed total heritability estimates for 150DMY, DIM, PY and TMY as 0.18 ± 0.06, 0.04 ± 0.04, 0.12 ± 0.06 and 0.08 ± 0.05, respectively. Repeatability estimates for 150DMY, DIM, and TMY were 0.28 ± 0.04, 0.21 ± 0.03 and 0.37 ± 0.03, respectively. Bivariate analysis of 150DMY with reproductive traits revealed heritability for LS and LW as 0.05 ± 0.01 and 0.10 ± 0.01, respectively using Gibbs sampling. Strong and positive genetic correlations of 150DMY with other production and reproduction traits was observed, such as DIM (0.72), PY (0.98), TMY (0.88), LS (0.57) and LW (0.33). Moderate heritability and repeatability estimate of 150DMY, along with its positive correlation with production and reproductive traits suggested it as a suitable selection criterion for early selection and overall genetic progress of lactation traits. The genetic trend analysis showed an overall improvement in all these traits, with observed gain of 98.4 g per year for 150DMY, 0.04 days per year for DIM, 0.5 g per year for PY and 220.5 g per year for TMY. We observed that selecting based on 150DMY would lead to a favourable indirect improvement for LW as 79 g and LS 0.04 units per generation. We, therefore, recommend employing 150DMY as the single trait selection criteria to enhance both milk productivity and reproductive potential of Alpine × Beetal goats., (© 2023 Wiley-VCH GmbH.)

This study focused on the accurate genetic evaluation of a small dairy flock of crossbred dairy goats, specifically developed for high milk production in the Indian sub-tropical climate. The study was conducted on Saanen x Beetal (SxB) crossbred goats, which utilized 12,660 test day records for first parity. Additionally, complete lactation records (N=1283) across multiple parities and for the first parity (N=659) were analyzed separately for genetic evaluation. The main traits examined were 150-day milk yield (150DMY), days in milk (DIM), peak yield (PY), and total milk yield (TMY), with averages of 198.80±2.83 kg, 227.90±4.18 days, 1.17±0.02 kg, and 262.40±6.12 kg, respectively, highlighting the genetic superiority of SB goats over native Indian goats. Across parities, the estimates for 150DMY, DIM, and TMY were 230±6.16 kg, 210±7.0 days, and 277±11.82 kg, respectively. Given the moderate heritability (0.24±0.08) and repeatability (0.29±0.04) estimates of 150DMY, the study recommends using 150DMY as the primary selection criterion for genetic improvement in SxB goats. The single-trait random regression model (RRM) utilizing various orders of orthogonal Legendre polynomials (LEG) and B-spline (BS) functions with heterogeneous residual variances was also employed. The test day milk yield (TDMY) showed a least squares mean of 1.30±0.01 kg, with moderate heritability estimates across test days (0.26±0.08). The optimal model was identified as a quadratic B-spline function with six knots (BS6Q). Positive genetic correlations were observed between consecutive test-day milk yield values, while correlations decreased for more distant test days. The study demonstrated the superiority of the B-spline model in genetically assessing Saanen x Beetal dairy goats, highlighting its benefits in curve fitting, genetic parameter estimation, and higher breeding value prediction accuracy. Looking into the moderate heritability and desirable genetic correlation of 150 DMY with other lactation traits, we recommend using 150 DMY for further selection programs. As the concordance of ranking between different approaches for breeding value prediction was high, we recommend using the random regression test day model (RR-TDM) when data recording across lactation is costly. • Genetic evaluation shows potential for further selection in Saanen x Beetal goats in India's tropical climate. • Saanen x Beetal goats produce nearly twice the milk of indigenous breeds. • RR-TDM is optimal for genetic evaluation, maximizing resource use. [ABSTRACT FROM AUTHOR]