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Pech C.I.V.M.,Campo Experimental Mococha | Vazquez J.A.T.,CENID Fisiologia y Mejoramiento Animal | Zepeda A.B.,Sitio Experimental El Verdineno | Utrera A.R.,Campo Experimental la Posta | And 4 more authors.
Revista Mexicana De Ciencias Pecuarias

Genetic parameters for growth traits of Katahdin lambs were estimated using six variants of the animal model. Data on birth weight (BW; n= 13,099), weaning weight adjusted to 75 d (WW; n=11,509) and postweaning weight adjusted to 120 d (AW; n=6,886) were collected for seven years (2004-2010) in 20 states across Mexico. Analyses were carried out by ignoring or including maternal effects. The simplest model included the direct additive genetic effect as the only random effect. The most complete model included direct and maternal genetic effects, their covariance, and the maternal permanent environmental effect. Selection of the best model was based on likelihood-ratio test. When maternal effects were not taken into account, estimates of direct heritability and direct genetic variance were overestimated for all traits. Direct heritability estimates for the best model were 0.18 ± 0.03, 0.30 ± 0.04, and 0.20 ± 0.05 for BW, WW and AW, respectively. Maternal heritability estimates also varied depending on the model; estimates ranged from 0.05 to 0.23, 0.00 to 0.12, and 0.09 to 0.25 for BW, WW and AW. Ignoring maternal effects in the model would result in inaccurate genetic evaluation for growth traits in Katahdin sheep. Source

Alcaraz Romero R.A.,Campo Experimental Mococha | Quintal Franco J.A.,Campo Experimental Mococha | Hernandez Sanchez D.,Colegio de Mexico | Sanchez Torres T.,Colegio de Mexico | And 5 more authors.
Livestock Science

Seventy crossbred ewe lambs, born from Pelibuey (PB) dams mated with five sire breeds: White Dorper×PB (WD×PB), Black Head Dorper×PB (BHD×PB), Ile de France×PB (Ile×PB) Katahdin×PB (KT×PB) and Pelibuey (PB×PB), were used to determine age and weight to puberty, follicular populations during prepubertal development, ovulation rate at first ovulation and function of the first corpus luteum (FCL). Ewe lambs were maintained under grazing conditions and were supplemented with 300ghead-1day-1 of a concentrate with 14% CP and 3.0McalMEkg-1 of DM. From 145days of age, monthly observations were performed by endoscopy to monitor follicular populations and luteal structures. Ovarian follicles were classified according to size into small (≥1 and <3mm), medium (≥3 and ≤4mm) and large (>4mm). Additionally, weekly observations by ultrasonography were performed in four ewes per genotype to assess follicular populations. Luteal function from first ovulation was determined by circulating concentrations of progesterone. Ovulation rate was not affected by genotype (P>0.05). All breed groups had the same pattern of follicular populations, where most of follicles were small, followed by medium and a small proportion of large follicles. Maximum diameter of follicles was similar for all genotypes during prepubertal development (P>0.05), with an average range of 3.9±0.20 to 4.4±0.20mm. The BHD×PB reached puberty at the youngest age of 240.9±13.0days, compared to all other genotypes (P<0.05), 259.1±11.7 for WD×PB, 279.3±9.6 for KT×PB and 289.0±15.3days for PB×PB and 308.6±11.9days for Ile×PB ewe lambs. Ile×PB had greater weight to first ovulation (31.5±1.19kg) as compared to other breed groups (P<0.01). The largest percentage of FCL was for KT×PB ewes (100%) (P<0.05), followed by BHD×PB (88.9%), PB×PB (83.3), WD×PB (78.6%) and Ile×PB (77.8%). There were no differences in ovulation rate attributable to type of lambing from which ewe lambs came from (P>0.05). BHD×PB ewe lambs reached puberty at an earlier age than other in this study. KT×PB ewe lambs had the highest percentage of FCL in their first ovulation. Breed of sire Ile de France increased weight to puberty and decreased FCL at first ovulation. In conclusion, the BHD×PB ewe showed puberty at an earlier age than other genotypes, while the KT×PB had the highest percentage of functional corpus luteum in their first ovulation. Ewe lambs coming from single lambings reach puberty at a heavier weight than those coming from multiple lambings. The ovulation rate in the first ovulation of ewe lambs is not affected by genotype and type of lambing. © 2011 Elsevier B.V. Source

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