Understanding the phenotypic and genetic background of the lactose content in Sarda dairy sheep

Lactose, the principal carbohydrate found in milk, plays an important role in the physiological processes of milk production because it is related to milk volume, and it is responsible for the osmotic equilibrium between blood and milk in the mammary gland. In this study, factors affecting lactose content (LC) in sheep milk are investigated. For this purpose, 2,358 test-day records were sampled from 509 ewes (3-7 records per animal). The LC and other main milk traits were analyzed using a mixed linear model that included days in milk (DIM) class, parity, lambing month, and type of lambing as fixed effects and animal, permanent environment, and flock test day as random effects. The pedigree-based approach was used to estimate the heritability and re-peatability of LC. Moreover, the genomic background of LC was investigated through a GWAS. The LC was affected by all tested factors (i.e., DIM class, parity, lambing month, and type of lambing). Low heritability (0.10 +/- 0.05) and moderate repeatability (0.42 +/- 0.02) were estimated for LC. High negative genetic correla-tions were estimated between LC and NaCl (-0.99 +/- 0.01) and between LC and somatic cell count (-0.94 +/- 0.05). Only 2 markers passed the chromosome-wide Bonferroni threshold. Results of the present study, al-though obtained on a relatively small sample, suggest the possibility to include LC in the breeding programs, particularly because of its strong relationship with NaCl and somatic cell count.

Automated summary

This study investigated the factors affecting lactose content in sheep milk and found that it is influenced by several factors, suggesting the possibility of incorporating lactose content into breeding programs.