Alejandro La Cruz Ju�?árez
Wool produced (kg of fleece/shearing) by 371 sheep from the genetic groups of Romney Marsh (31) Criollo Chiapas sheep (135) and their hybrids (205) was analyzed using repeated measures models and random regression analysis. One thousand one hundred and eight production records collected over a period of 12 years, under extensive production conditions in the region of the Altos de Chiapas, Mexico, were analyzed. The genetic groups displayed wool production differences (P < 0.0001), with Romney Marsh showing the highest performance (2.21±0.94 kg of fleece/shearing), the F1 animals were intermediate (1.397±0.07) and the Criollo sheep showed the poorest performance (0.881±0.07). Heterosis estimation for fleece weight (kg) per shearing was -0.1517±0.0543, P = 0.0055. Romney Marsh animals were the most affected by the environmental effect of animal age at shearing since its negative linear slope was four to ten times steeper than the linear slopes of the F1 and the Criollo animals, respectively. The Criollo Chiapas Sheep remained the longest period of time in the flock. The environmental effects of age of animal (P < 0.0001), gender (P = 0.037), number of shearing (P < 0.001) and year (P < 0.0001) were important on wool production. Wool production for the first four years of age was similar, and it decreased from the fifth year on; males were 6.9% superior to females; the first three shearings were similar between them (P > 0.06), but lesser than the last ones (P < 0.05). Criollo sheep showed remarkable environmental adaptation; therefore, the preservation of this animal genetic resource is extremely important for the indigenous community that makes use of it.
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