SUMMARY: Most Chilean sheep stock comprises different degrees of crossbreeding over Corriedale breed. A common absorbent crossbreeding has been Australian Merino over Corriedale which, in many cases, has not been complete. The aim of this study was to evaluate the process of morphology differentiation and structural functionality of Corriedale ewes undergoing incomplete absorbent crossbreeding which was carried out in order to create an animal with a new morphology. A total of four hundred adult ewes were measured; two hundred belonging to the incomplete crossbreeding, and two hundred from the two original breeds (one hundred Corriedale and one hundred Australian Merino ewes). All measured ewes were randomly selected. Fourteen body measurements were recorded and nine body indexes were calculated for each ewe. Results show that a new biotype has been created from the absorbent crossbreeding of Corriedale by Australian Merino, which produced ewes with a clear morphological and structural functionality differentiation as compared to the two original breeds. The new body format shows morphostructural variability coefficients that are similar to those found on other formally recognized sheep breeds.

Morphological traits of the whole udder (circumference, width, height, and length), teats (angle, length and width), udder cistern (teat opening and cistern height), and milk yield were measured over one lactation in a total of 18 ewes (nine Chilota and nine Suffolk Down sheep) belonging to the same experimental flock (Centro Experimental INIA Butalcura, Chiloé, Chile). Analysis of variance showed significant effects for breed, sheep within breed, and stage of lactation. Chilota ewes evidenced greater udder circumference (433 mm), udder length (86 mm), teat opening (96º), and milk yield (947 mL d -1 ) than Suffolk Down ewes (410 mm, 77 mm, 93º, and 559 mL d -1 , respectively). Udder circumference, udder width, udder length, cistern height and teat size significantly decreased throughout lactation. Repeatabilities of all traits were between 0.17 and 0.60; the highest repeatability was for udder circumference. This trait is easy to measure and had a discriminatory value for breed differentiation. In conclusion, Chilota sheep had a dairy aptitude greater than Suffolk Down sheep and similar to Spanish and Mediterranean dairy sheep breeds at beginning of their breeding programs.

SUMMARY:The aim of this study was to evaluate the stability and harmony of the morphostructural format of the Marin Magellan Meat Merino breed in order to contribute to knowledge about the differentiation of sheep populations. In summer 2010, evaluation on a sheep population coming from an incomplete absorbent crossbreeding of Corriedale by Australian Merino breeds was done in Magallanes Region, Chile. All three and five year-old ewes (62 and 50, respectively) were measured. Fourteen body measurements were taken and nine body indexes were calculated. Results show that the evaluated sheep population does not show significant intergenerational differences in most of the morphostructural variables. At the same time, there is a high between-age similarity in the correlations between zoometric indexes. Therefore, it can be stated that the morphostructural model of Marin Magellan Meat Merino ewes shows a high degree of stability and harmony. INTRODUCCIÓNThe census of Chilean sheep livestock indicates that there is about two and a half million head of sheep. Most of this animal stock corresponds to Corriedale breed, which hold a marked aptitude to the production of medium-fineness wool. Value addition to production has led many producers to a crossbreeding process with Merino breed, in order to produce a finer wool withhigher commercial value (Bianchi et al., 2006;Cardellino & Müeller, 2008). One of the most widespread crossbreedings has been the absorption of Corriedale by Australian Merino, process that, in many cases, has not been complete, leading to the appearance of animal populations which differ from the breeds on which the crossbreeding was based, and favoring the appearance of a new genetic resource. In this regard, the characterization of the morphological attributes is the first step for the management of a genetic resource (Azor et al., 2008;Traoré et al., 2008;Duchev & Groeneveld, 2006;Salako, 2006). By characterizing the animal population resulting from the incomplete absorbent crossbreeding of Corriedale by Australian Merino, it was evidenced a significant morphostructural differentiation in relation to the breeds that originated the crossbreeding, with a high degree of homogeneity within the population itself (Latorre et al., 2011); this allowed the official registration of a new breed, the Marin Magellan Meat Merino, and the opening of the respective genealogical register (Sánchez et al., 2011).The definition of a breed clearly involves the differentiation of this new population from others, and at the same time, a delimited variability among the members of the population itself (Sierra, 2001;Herrera & Luque, 2009). Nevertheless, when the new breed is the result of a crossbreeding process, is essential to determine if the morphostructural format keep its characteristics from one generation to the next, as it depends that the characteristic attributes of the population are sustained over time (Herrera et al., 1996;Legaz et al., 2011).Therefore, the aim of this study was to evaluate the stability and h...

SUMMARY:Chilota sheep are typical of the Chiloé archipelago in southern Chile. The objectives of this study were: 1) To describe the development of the morphostructure of Chilota lambs in their first months of life using some variables that determine lamb meat value (zoometric traits and body weight) and 2) To determine the optimum slaughter age. Measurements were taken from 12 male single-born lambs. Body weight, Withers height; Perimeter of thorax, Chest depth, Shoulder point width and Body length were measured in each animal. The first measurements were taken at 7 days old, and the rest at 37, 67, 97, 127, 157 and 187 days old. The body weight variables and zoometric traits developed allometrically throughout the growth phase. The correlation coefficient between all the traits was very high, varying between 0.91 and 0.98. The zoometric variable that best predicted body weight was Perimeter of thorax (r2=0.93), which was fully developed in 90% of the animals at 97 days old. Maximum growth was recorded in all the studied variables during the first control month, days 7-37, but then it decreased gradually. This decrease was moderate until day 127, becoming very low from then on until end of the study. The optimum age for slaughtering fattened lambs is approximately four months, as from day 127 the daily growth rate slows down considerably, to 61.81 g/day, in comparison with the previous stage, which is 220.00 g/day. Therefore, the maintenance of lambs after four months is not productively efficient.

In this paper, the degree of differentiation and morphostructural variability reached by the type of animal resulting from sustained directional selection, in addition to its implications for the emergence of a new sheep breed are analyzed. Twenty-five rams and 200 ewes from a sheep flock submitted to directional selection since 1987 were measured. Thirteen body measurements were taken in other to evaluate the structural morphology and sexual dimorphism. These measurements were compared with identical measures taken in Australian Merino and Marin Magellan Meat Merino sheep breeds. The intrapopulation homogeneity was assessed using the coefficients of variation of the average percentage of body measurements. It is concluded that sustained directional selection has generated the differentiation of the morphostructural format of the subject population compared to the main Merino-type breeds in the Chilean Patagonia. The population shows a similar (and in some cases lower) morphostructural variability than those found in recognized sheep breeds in Chile, so it is possible to state that this population behaves like a different animal group, with breed characteristics.