MILK PRODUCTION AND CHARACTERISTICS OF LACTATION CURVE IN DAIRY SHEEP AND THEIR CROSSES IN MEXICO
The use of appropriate genotypes for milk production in dairy sheep herds allows maximizing the use of natural resources, obtain adequate milk yields and promotes their economic viability. The aim of this study was analyze the milk yield and the characteristics of the lactation curve of sheep of local breeds, dairy breeds and their crosses. Lactation records used were obtained from dairy herd located in Mexico. We used 863 weekly milk records of sheep of six genotypes: 12 East Friesian (EF), 12 Native (Nt), 6 EF½Native½ (EF50Nt50), 16 EF¾Native¼ (EF75Nt25), 15 Suffolk½Native½ (SF50Nt50), and 8 Corriedale sheep. Sheep were milked mechanically and milk production was recording weekly from the fourth day after lambing; the first sixty days of lactation, sheep were milked once a day with a partial weaning, lambs were separated from sheep during the night and milked in the morning (08:00h). At day 60 post-lambing full weaning was complete and sheep began to be milked twice daily (08:00 and 18:00h). For analysis of the lactation curve and their parameters, we used the Wood (WD) model: Yt=atbect. Where Y is the milk production at time t, and a, b and c are the parameters describing the curve shape, these were estimated individually for each lactation using a nonlinear regression. Using WD model, we calculated total milk yield observed (TMYobs) and adjusted to 180 days (TMY180), peak yield (PY), peak time (PT) and persistence (Per). Genotype influenced significantly (P<0.05) in the TMYobs and TMY180, where EF50Nt50 sheep had the best performance. With respect to parameters of WD model, differences between genotypes were observed only in the parameter b, being higher (P<0.05) in SF50Nt50, EF50Nt50, and EF sheep. PY was higher (P<0.05) in sheep EF50Nt50, also PY showing a positive correlation with TMY (r=0.582) and negative with Per (r=-0.176). PT was positively correlated (P<0.01) with TMY180 and Per (r=0.479 and 0.525 respectively). There was a positive effect on the TMYobs, TMY180 and shape of the lactation curve in EF50Nt50 sheep. EF and EF75Nt25 sheep showed lower TMY compared with EF50Nt50, who show the best productive performance, which may be associated with better adaptation to the agroclimatic conditions and the lower adaptation to the environmental conditions of animals with a higher proportion of EF genes. The crossing EF50Nt50 is a viable option in dairy sheep herds with similar climatic conditions to those of the present study.
Keywords: Dairy sheep, Crossbreeding.