# Utilization of Wool Integral Lipids to Determine Milk Fat Content in Suffolk Down Ewes
## 4 Discussion
The authors consider that the DI results are related to the activity of the desaturase enzyme. In this sense, DI is probably altered due to the mobilization of reserves and the inhibition of lipogenic enzymes, such as SCD, which occur in animals with a negative energy balance [34]. The lipid composition is affected by the release of non-esterified FA (NEFA), C16:0, C18:0, and, particularly, C18:1n9c. Thus, a major release of C18:1n9c, together with a further possible conversion of C18:0 to C18:1n9c through the enzymatic activity of SCD [28], can explain the high DI C18 observed in wool collected at 30 days when the milk fat increased. As described above, several factors affect the wool FA composition, and the energy status of ewes probably plays an important role. Stress can also affect the FA composition of blood and hair or wool and can inhibit complete de novo FA synthesis [14]. Thus, to establish a relationship between wool FAs and milk fat, we calculated the correlations in milk collected at 30 and 60 days. The FAs C18:1n9c, C18:2n6c, and C22:2 were the FAs that maintained a positive correlation in both periods. Various FAs demonstrated different correlations in each period or were not correlated with milk fat content. In the case of C18:1n9c, the current study showed a high concentration of C18:1n9c in wool when the milk fat content increased and a positive correlation with the milk fat variable. Another study determined that, in milk fat, C18:1n9c is a useful diagnosis and early warning marker for cows suffering from a severe negative energy balance, but the positive correlation shown by C18:1n9c between blood NEFA concentration and milk C18:1n9c was only modest (R\({}^{2}\) = 0.383) [28]. However, we determined a strong positive correlation between C18:1n9c and milk fat content (Table 3). Furthermore, the FAs C18:2n6c and C22:2 exhibited the same trend as C18:1n9c, i.e., increasing when the milk fat was high and with a positive correlation in both periods. C18:1n9c, C18:2n6c, and C22:2 exhibited a greater stability in the classification according to milk fat content variable and presented a positive correlation in both periods. Our focus was to evaluate the concentration of FAs in wool in the discriminant analysis, to determine FAs that represent candidate positive markers of high milk fat concentration. Discriminant analysis of the concentrations of the FAs C18:1n9c, C18:2n6c, and C22:2 in wool fat, used to classify ewes with high milk fat contents, demonstrated an accuracy of 79.17% with the FA C18:1n9c, and a maximum of accuracy of 87.50% when the FA C18:2n6c was included. As mentioned above, the FA C18:1n9c is released from body reserves and is a product of SCD activity, thus, it reflects the mobilization of body fat. However, the other preformed FAs of interest, i.e., C18:2n6c and C22:2, originate from the diet and are not synthetized by ruminant tissue. Considering the origin of the FAs, it is difficult to consider C18:2n6c and C22:2 as candidates with which to discriminate milk fat content, because their concentration in wool fat depends on diet. Thus, we suggest analyzing these FAs in different production systems and diets, because this function was evaluated in the conditions of the present study. The authors consider C18:1n9c concentration in wool fat in the period of the current study to be a positive marker for milk fat content. Although milk fat content can be directly determined, the utilization of wool FAs as markers of milk fat can also be used to determine ewe status during lactation and be decisive in matters of nutritional supplementation during this period. Moreover, the FA C18:1n9c in wool fat may be conveniently included in routine analyses when testing milk FAs.