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Background. During lactation the mammary fat synthesis is increased compared to adipose tissue. Objective. This study evaluated the promoter specific gene expression of acetyl-CoA carboxylase alpha (ACACA) transcripts from promoters II and III, fatty acid synthase (FASN), sterol regulatory element binding transcription factor 1 (SREBF1) in mammary gland and adipose tissue and, peroxisome proliferator-activated receptor gamma (PPARG), fatty acid transporters acyl-CoA synthetase long chain family member 1 (ACSL1), solute carrier family 27 member 6 (SLC27A6), fatty acid binding proteins 3 and 4 (FABP3 and FABP4), CD36 molecule (CD36) and lipoprotein lipase (LPL) in the mammary gland. Methodology. Eight Lacaune lactating ewes at 15, 70, and 120 days in milk (DIM) were used. Results. There was no effect of tissue, lactation stage, or tissue by lactation stage interaction for PIII ACACA transcripts. Mammary PII transcripts changed according to stage of lactation with higher expression at 15 than 120 DIM. In adipose tissue at 120 DIM, expression of PII ACACA transcripts were higher than 15 and 70 DIM. Expression of FASN in adipose tissue was higher at 70 and 120 DIM when compared to mammary tissue at 120 DIM. The SREBF1 expression at 70 was higher than 15 DIM in mammary tissue and higher than 70 DIM in adipose tissue. In the mammary gland, the gene expression of LPL, CD36 and FABP3 was decreased from 15 to 120 DIM. Implications. Collectively, our results highlight the fact that in early lactation (15 to 70 DIM) milk fat synthesis is prioritized over adipose tissue in dairy sheep. Conclusion. This prioritization is managed through an orchestrated increase in mammary gene expression of ACACA transcripts, FASN, SREBF1, LPL, CD36, and FABP3.

Milk fat is the component responsible for the organoleptic and manufacturing characteristics of the dairy products and also the most variable and affected by the diet. This study was designed to evaluate the lipid supplementation with high concentration of palmitic acid on the milk production and composition. Thirty-nine multiparous Holstein cows weighting an average of 550 kg, with 79 ± 2 days in milk (DIM), producing 29.4 kg milk/day were randomly assigned to each one of the three treatments: 1) 320 g/day of high palmitic acid supplement (Palmitic); 2) 400 g/day of calcium salts of fatty acids rich in linoleic acid (Linoleic) and; 3) Control (no lipid supplementation). Palmitic supplement increased milk fat content in 8.6% (P=0.001) and yield 16.2% (P=0.001) compared to Control. Compared to Control, Linoleic supplement decreased milk fat content in 16.1% (P=0.001). There was an effect of treatment for bonus payment for fat (P=0.01), with the highest payment for Palmitic treatment. There was no effect on milk production and concentrations and yields for milk protein and lactose.

The objective of this study was to measure fecal n-alkane concentration variation and herbage intake in grazing lactating dairy cows fed with two sources of fat: conjugated linoleic acid (CLA) or Megalac (Control). Cows were dosed with n-alkanes using a controlled-release capsule. There was no difference in herbage dry matter intake between CLA and Control. In the first period, there were no differences in fecal concentration of both natural and synthetic n-alkanes from the capsules. For the second period, there was a difference in fecal concentration for time of collection for all natural, dosed, and alkanes ratios. In the third period, there was a difference for time of collection for natural n-alkanes and their respective ratios, with higher excretion values recorded in the afternoon. In addition, there was an effect of day of collection for all n-alkanes and ratios, with higher excretion values recorded on days 2 and 4. Overall, our results highlight the importance of strict control of grazing management and sward structure in studies where external markers are used. Monitoring herbage, sward and animal managements might have an influence on n-alkanes excretion, causing a change in the ratio of their fecal concentration. These modifications may result in erroneous estimates of intake.