Kheirabadi Khabat
Independent Researcher, Sanandaj, Kurdistan, Iran.
Trop Anim Health Prod. 2024 Sep 27;56(8):294. doi: 10.1007/s11250-024-04150-4.
The objectives of this study were to evaluate the influence of environmental effects on growth curve traits of Zandi lambs and estimate their genetic parameters with the best-fit animal model. For this purpose, live body weight (BW) records (n = 10,607) of 2,519 individuals (which were progeny of 278 rams and 1,485 ewes) were used to estimate genetic effects on growth curve traits from birth to yearling age of Zandi lambs. Using the Stochastic Approximation Expectation Maximization (SAEM) algorithm the growth curve parameters of five different mixed functions (i.e., Brody, Richards, Von Bertalanffy, Gompertz and Logistic) were obtained, then for the most appropriate model the genetic parameters were estimated using a Bayesian approach fitted multivariate animal model and ignoring or including maternal genetic effect. Except Richards model, all other mixed functions used here closely fitted actual BW records (R > 0.96). However, the Logistic function provided the best fit in every type. So, studied growth curve traits were estimated asymptotic weight which considered as mature weight (a), rate parameter (b), rate of maturing (k), and age (Ai)/weight (Wi) at the point of inflection. Of the fixed effects studied (i.e., gender, birth type, dam age, season and year of birth), the only non-significant relationship was the effect dam age on b and Ai. Based on the best-fitted model, posterior means of heritability estimates for a, b, k, Wi and Ai were 0.142 ± 0.036, 0.094 ± 0.029, 0.143 ± 0.063, 0.149 ± 0.039 and 0.029 ± 0.013, respectively. Posterior means of genetic correlations between mentioned traits ranged from -0.018 ± 0.069 (b-k) to 0.959 ± 0.029 (a-b), whereas the phenotypic correlation varied from -0.047 ± 0.014 (b-k) to 0.836 ± 0.007 (a-b). It was concluded that the model including only direct additive effect was sufficient to explain the variation in all investigated growth traits of Zandi lambs, selection for these traits results in slow genetic gain (due to the lack of sufficient genetic variation), but it would not be difficult to improve their mature weight and rate of maturing jointly. The results indicate that although the rate of genetic change for mature weight has been small (0.008 ± 0.003 kg year; P < 0.05) but in the favorable direction for this breed.
本研究的目的是评估环境因素对赞迪羔羊生长曲线性状的影响，并使用最佳拟合动物模型估计其遗传参数。为此，利用2519只个体（278只公羊和1485只母羊的后代）的活体体重（BW）记录（n = 10607）来估计赞迪羔羊从出生到一岁龄生长曲线性状的遗传效应。使用随机近似期望最大化（SAEM）算法获得了五种不同混合函数（即布罗迪、理查兹、冯·贝塔朗菲、冈珀茨和逻辑斯蒂）的生长曲线参数，然后对于最合适的模型，使用贝叶斯方法拟合多变量动物模型并忽略或包含母体遗传效应来估计遗传参数。除理查兹模型外，这里使用的所有其他混合函数都与实际BW记录拟合良好（R > 0.96）。然而，逻辑斯蒂函数在每种类型中拟合效果最佳。因此，所研究的生长曲线性状估计为渐近体重，将其视为成熟体重（a）、速率参数（b）、成熟速率（k）以及拐点处的年龄（Ai）/体重（Wi）。在所研究的固定效应（即性别、出生类型、母羊年龄、季节和出生年份）中，唯一不显著的关系是母羊年龄对b和Ai的影响。基于最佳拟合模型，a、b、k、Wi和Ai的遗传力估计后验均值分别为0.142±0.036、0.094±0.029、0.143±0.063、0.149±0.039和0.029±0.013。上述性状之间的遗传相关后验均值范围从-0.018±0.069（b - k）到0.959±0.029（a - b），而表型相关则从-0.047±0.014（b - k）到0.836±0.007（a - b）。得出的结论是，仅包含直接加性效应的模型足以解释赞迪羔羊所有研究生长性状的变异，对这些性状进行选择会导致遗传进展缓慢（由于缺乏足够的遗传变异），但同时提高其成熟体重和成熟速率并不困难。结果表明，虽然成熟体重的遗传变化率较小（0.008±0.003千克/年；P < 0.05），但对该品种而言是朝着有利方向变化的。
