CENID Fisiología Animal, INIFAP. Apartado Postal No. 5, Colón Qro, CP 76270, México.
Theriogenology. 2010 Oct 15;74(7):1107-14. doi: 10.1016/j.theriogenology.2010.05.007. Epub 2010 Jul 1.
The primary objective was to compare various mathematical models to describe scrotal circumference (SC) and paired testis volume development in Blackbelly ram lambs. The study was conducted in the state of Querétaro, México (20° 43' N, 100° 15' W). Spring-born Blackbelly ram lambs (n = 41) were housed outdoors and fed alfalfa hay and concentrate. Body weight, SC, and testis length, diameter, and volume were recorded every 2 wk from 24 to 172 d of age (June 18 to November 3). The following mathematical functions were used to model SC-age and testis volume-age relationship: Von Bertalanffy, Brody, Gompertz, Logistic, and Richards. The suitability of the models was evaluated based on parameter values and standard errors, residual mean square, the coefficient of determination (R(2)), and the average prediction error (APE). All models, except for Brody's, had good fit to SC (R(2) > 0.98) and testis volume (R(2) > 0.95), and produced similar growth curves in the range of ages studied. The logistic model predicted SC at maturity quite well, 33.6 ± 0.6 cm as compared with 33.9 ± 0.5 cm observed in adult animals; all models had APE's smaller than ± 7% between 56 and 168 d of age. The Bertalanffy model predicted testis volume at maturity quite well, 513 ± 22 cm(3) as compared with 488 ± 20 cm(3) calculated for adult animals. The logistic model had a good fit to testis volume during the period of study, but underestimated the volume at maturity by 28%. All models, except for Brody's, had APE's smaller than ± 14% between 98 and 168 d of age. The logistic and Bertalanffy models predicted the inflection point for SC at 83 and 59 d of age, and testis volume at 116 and 109 d of age, respectively. In conclusion, all models, except for Brody's, had good fit to actual SC and testis volume data in the range of age evaluated, whereas the logistic and Bertalanffy's models made the best predictions for adult SC and testis volume, respectively.
主要目的是比较各种数学模型来描述黑腹绵羊羊阴囊周长（SC）和配对睾丸体积的发育。该研究在墨西哥的克雷塔罗州（20°43'N，100°15'W）进行。春季出生的黑腹绵羊羊（n=41）被安置在户外，喂食苜蓿干草和浓缩饲料。从 24 日龄到 172 日龄（6 月 18 日至 11 月 3 日），每 2 周记录一次体重、SC 和睾丸长度、直径和体积。使用以下数学函数来模拟 SC-年龄和睾丸体积-年龄的关系：Von Bertalanffy、Brody、Gompertz、Logistic 和 Richards。根据参数值和标准误差、残差均方、确定系数（R(2)）和平均预测误差（APE）来评估模型的适用性。除了 Brody 模型之外，所有模型都很好地拟合了 SC（R(2)>0.98）和睾丸体积（R(2)>0.95），并且在研究的年龄范围内产生了相似的生长曲线。Logistic 模型很好地预测了成熟时的 SC，为 33.6±0.6cm，而成年动物观察到的为 33.9±0.5cm；所有模型在 56 到 168 日龄之间的 APE 都小于±7%。Bertalanffy 模型很好地预测了成熟时的睾丸体积，为 513±22cm(3)，而计算出成年动物的为 488±20cm(3)。Logistic 模型在研究期间很好地拟合了睾丸体积，但低估了成熟时的体积，低估了 28%。除了 Brody 模型之外，所有模型在 98 到 168 日龄之间的 APE 都小于±14%。Logistic 和 Bertalanffy 模型分别预测了 SC 的拐点在 83 和 59 日龄，以及睾丸体积的拐点在 116 和 109 日龄。总之，除了 Brody 模型之外，所有模型在评估的年龄范围内都很好地拟合了实际的 SC 和睾丸体积数据，而 Logistic 和 Bertalanffy 模型分别对成年 SC 和睾丸体积做出了最佳预测。
