Crecimiento predestete de corderos en sistemas intensivos de pastoreo y manejo reproductivo en el altiplano central de México

Abstract

TO STUDY FACTORS AFFECTING BIRTH WEIGHT (BW), WEIGHT AT 30 DAYS AND 60 D, DATA FROM 917 COLUMBIA LAMBS WERE ANALYZED. LAMBS WERE BORN IN APRIL (N-B) FROM YEARLY BREEDING, OR IN APRIL-MAY (A-M), DECEMBER JANUARY (DJ) AND AUGUST-SEPTEMBER (A-S) FROM AN EVERY EIGHT MONTHS BREEDING PROGRAM (I-B). EWES AND LAMBS WERE GRAZED ON IRRIGATED GRASS-LEGUME TEMPERATE PASTURES; LAMBS HAD ACCESS TO CREEP FEEDING FROM 15 D OF AGE. FIXED EFFECTS IN THE VARIANCE ANALYSIS WERE: EWE AGE; SINGLE OR TWIN BIRTH; SEX AND YEAR OR SEASON OF BIRTH. SIMPLE CORRELATIONS WERE OBTAINED BETWEEN BW AND WEIGHTS AT 30D AND 60D AND OF THESE WITH EWE BODY CONDITION. THE BW (5.7 ± 0.06 KG) AND WEIGHT AT 30 D (15.0 ± 0.17 KG) IN I-B WERE HIGHER (P < 0.05) THAN IN N-B (5.5 ± 0.06 KG AND 13.8 ± 0.17 KG), WITHOUT DIFFERENCE AT 60 D (21.5 ± 0.25 KG VS. 21.4 ± 0.24 KG, RESPECTIVELY). SINGLE BIRTHS AND MALES WERE ALWAYS HEAVIER (P < 0.05) FROM BIRTH TO 60 D. YEAR DIFFERENCES IN N-B WERE NOT OBSERVED AT BIRTH OR 60D (P > 0.05), BUT WERE AT 30D (14.7 ± 0.22 KG VS. 13.2 ± 0.18 KG). I-B LAMBS BORN IN D-J WERE ALWAYS HEAVIER (P < 0.05): 6.2 ± 0.08 KG, 5.3 ± 0.10 KG AND 5.5 ± 0.09 KG; 16.2 ± 0.22 KG, 14.8 ± 0.27 KG AND 13.8 ± 0.25 KG; 22.2 ± 0.33 KG, 21.3 ± 0.39 KG AND 20.8 ± 0.36 KG FOR BW, 30 D AND 60 D IN D-J, A-M AND A-S, RESPECTIVELY. CORRELATIONS BETWEEN WEIGHTS WERE ALWAYS POSITIVE (P < 0.05), AND ONLY IN N-B WAS THERE NEGATIVE CORRELATION BETWEEN EWE BODY CONDITION AND WEIGHT (P < 0.05).