The aim of these experiments was to determine whether the presence of a dominant follicle affects the developmental competence of oocytes from small antral follicles of cattle. In Expt 1, oocytes or follicular fluid samples were collected from follicles 2–7 mm in diameter before (day 3 of the oestrous cycle; n = 4) or after (days 6 and 7 of the oestrous cycle; n = 6) emergence of the first wave dominant follicle (verified by rectal ultrasonography). Five to ten follicles were aspirated for the determination of individual follicular fluid concentrations of oestradiol, progesterone, testosterone and dimeric inhibin; oocytes from the remaining follicles from each cow were pooled and developmental capacity assessed by in vitro fertilization and maturation. In Expt 2, ovaries containing a young corpus luteum and with or without a large oestrogen-active follicle were collected from the abattoir. Follicular aspirates from small follicles in each pair of ovaries were pooled, and oocyte quality and steroid concentrations were determined. In Expt 1, small follicles obtained before emergence of the dominant follicle contained significantly more oestradiol than they did after emergence (19.5 ± 1.5 versus 0.7 ± 1.1 ng ml−1, respectively; P < 0.05), but there were no significant differences in concentrations of progesterone, testosterone or dimeric inhibin. The percentage of blastocysts obtained from oocytes collected before (12.1 ± 9.0) or after emergence (11.8 ± 7.0) of the dominant follicle did not differ significantly (P > 0.05). In Expt 2, follicular steroid concentrations did not differ in small follicles taken in the presence versus the absence of a large oestrogen-active follicle, and there were no differences in the developmental capacity of the oocytes. There were significant negative correlations between follicular oestradiol concentration and the percentage of blastocysts formed from two-cell (r = −0.90; P < 0.01) and eight-cell embryos (r = −0.65; P < 0.05). These data suggest that in cattle the developmental competence of oocytes from small antral follicles is not adversely affected by the presence of a dominant follicle.

The main aim of the present study was to examine the effects of long-term supplementing diets with saturated or unprotected polyunsaturated fatty acids from two different plant oils rich in either n-3 or n-6 fatty acids (FAs) plus docosahexaenoic acid (DHA)-rich algae on mammary gene expression and milk fat composition in lactating dairy cows. Gene expression was determined from mammary tissue and milk epithelial cells. Eighteen primiparous German Holstein dairy cows in mid-lactation were randomly assigned into three dietary treatments that consist of silage-based diets supplemented with rumen-stable fractionated palm fat (SAT; 3.1% of the basal diet dry matter, DM), or a mixture of linseed oil (2.7% of the basal diet DM) plus DHA-rich algae (LINA; 0.4% of the basal diet DM) or a mixture of sunflower oil (2.7% of the basal diet DM) plus DHA-rich algae (SUNA; 0.4% of the basal diet DM), for a period of 10 weeks. At the end of the experimental period, the cows were slaughtered and mammary tissues were collected to study the gene expression of lipogenic enzymes. During the last week, the milk yield and composition were determined, and milk was collected for FA measurements and the isolation of milk purified mammary epithelial cells (MECs). Supplementation with plant oils and DHA-rich algae resulted in milk fat depression (MFD; yield and percentage). The secretion of de novo FAs in the milk was reduced, whereas the secretion of trans-10,cis-12-CLA and DHA were increased. These changes in FA secretions were associated in mammary tissue with a joint down-regulation of mammary lipogenic enzyme gene expression (stearoyl-CoA desaturase, SCD1; FA synthase, FASN) and expression of the regulatory element binding transcription factor (SREBF1), whereas no effect was observed on lipoprotein lipase (LPL) and glycerol-3-phosphate acyltransferase 1, mitochondrial (GPAM). A positive relationship between mammary SCD1 and SREBF1 mRNA abundances was observed, suggesting a similar regulation for these genes. Such data on mammary gene expression in lactating cows presenting MFD contribute to strengthen the molecular mechanisms that govern milk fat synthesis in the mammary glands. In purified MEC, the dietary treatments had no effect on gene expressions. Differences between mammary tissue and milk purified MEC gene expression were attributed to the effect of lipid supplements on the number of milk purified MEC and its RNA quality, which are determinant factors for the analysis of gene expression using milk cells.