Review: genetic background of milk fatty acid synthesis in bovines

Milk fat composition is an important trait for the dairy industry as it directly influences the nutritional and technological properties of milk and other dairy products. The synthesis of milk fat is a complex process regulated by a network of genes. Thus, understanding the genetic variation and molecular mechanisms regulating milk fat synthesis will help to improve the nutritional quality of dairy products. In this review, we provide an overview of milk fat synthesis in bovines along with the candidate genes involved in the pathway. We also discuss de novo synthesis of fatty acids (ACSS, ACACA, FASN), uptake of FAs (FATP, FAT, LPL), intracellular activation and channelling of FAs (ACSL, FABP), elongation (EVOLV6), desaturation (SCD, FADS), formation of triglycerides (GPAM, AGPAT, LIPIN, DGAT), and milk lipid secretion (BTN1A1, XDH, PLIN2). The genetic variability of individual fatty acids will help to develop selection strategies for obtaining a healthier milk fat profile in bovines. Thus, this review will offer a potential understanding of the molecular mechanisms that regulate milk fat synthesis in bovines.

Role of Fatty Acids in Milk Fat and the Influence of Selected Factors on Their Variability-A Review

Fatty acids (FAs) of milk fat are considered to be important nutritional components of the diets of a significant portion of the human population and substantially affect human health. With regard to dairy farming, the FA profile is also seen as an important factor in the technological quality of raw milk. In this sense, making targeted modifications to the FA profile has the potential to significantly contribute to the production of dairy products with higher added value. Thus, FAs also have economic importance. Current developments in analytical methods and their increasing efficiency enable the study of FA profiles not only for scientific purposes but also in terms of practical technological applications. It is important to study the sources of variability of FAs in milk, which include population genetics, type of farming, and targeted animal nutrition. It is equally important to study the health and technological impacts of FAs. This review summarizes current knowledge in the field regarding sources of FA variability, including the impact of factors such as: animal nutrition, seasonal feed changes, type of animal farming (conventional and organic), genetic parameters (influence of breed), animal individuality, lactation, and milk yield. Potential practical applications (to improve food technology and consumer health) of FA profile information are also reviewed.

The effect of adding herbs to the summer diet on the fatty acid profile of the lipid fraction of sheep milk

The study was carried out on bulk milk samples collected at two-week intervals during the summer (June-August) and individually from ewes at the end of the experiment. The milk was obtained from ewes of the Koluda prolific dairy breed, housed indoors and fed green alfalfa forage and hay with a mixture of concentrate feeds. Three diet groups were established: group I – control (without the addition of herbs to the concentrate feed) and groups II and III, in which an herbal mixture was added to the concentrate feed in the amount of 10 and 20 g/sheep/day, respectively. The effect of the herb supplement in the sheep diet on the fatty acid profile of the milk fat was analysed. The results showed that the fat composition changed in all groups during the three-month milking period. In the first two months, an improvement was noted in the health-promoting properties of the milk fat (a decrease in SFA and an increase in MUFA and PUFA), but in the final period of the experiment they deteriorated. The unfavourable changes were smaller where the proportion of herbs in the diet was higher. As a consequence, in the final stage of research, lower SFA content was noted in the fat of the group III sheep than in the control group and II, by 6.0% (P≤0.01) and 4.1% (P≤0.05), respectively, lower content of OFA by 9.1% (P≤0.01) and 5.6% (P≤0.05), and higher content of UFA by 17.7% (P≤0.01) and 11.8%. (P≤0.05), including MUFA by 20.1% (P≤0.01) and 11.3% and PUFA by 11.7% (NS) and 15.0% (P≤0.05), as well as CLA, by 26.0% (P≤0.01) and 17.9% (ns) and DFA by 23.8% (P≤0.01) and 13.0% (P≤0.05). This also meant favourable changes in the UFA/SFA, PUFA/SFA and DFA/OFA ratios. The milk fat of group III also had higher content of n-3 PUFA (by 25.3%) than in group II, and thus a lower n-6/n-3 ratio.

The effect of adding herbs to the winter diet on the fatty acid profile of the lipid fraction of sheep milk

The study was carried out on bulk milk samples collected at two-week intervals during the winter (February-April) and individually from ewes at the end of the experiment. The milk was obtained from ewes of the coloured variety of Polish Merino, housed indoors and fed conserved bulky feeds and a mixture of concentrate feeds. Three diet groups were established: group I – control (without the addition of herbs to the concentrate feed) and groups II and III, in which an herbal mixture was added to the concentrate feed in the amount of 10 and 20 g/sheep/day, respectively. The effect of the herb supplement in the sheep diet on the fatty acid profile of the milk fat was analysed. The results showed that in the period from 69 to 137 days of lactation the content of SFA increased in the milk fat of sheep fed without the addition of herbs, while the content of UFA decreased. The addition of the herbal supplement to the concentrate feed in the amount of 10 or 20 g/sheep/day improved the fatty acid profile from the 97th day of lactation. As a result, at the end of the experiment, the milk fat of sheep in groups II and III contained more MUFA acids than that of group I (6.7%; P≤0.05 and 10.6%; P≤0.01, respectively), more PUFA (by 11.1% and 12.5%; P≤0.01), and more DFA (by 6.3%; P≤0.05 and 11.8%; P≤0.01). The addition of herbs in the amount of 10 or 20 g/sheep/day (groups II and III) increased the content of n-3 PUFAs in the milk fat (by 17.5%; P≤0.01 and 7.9%; P≤ 0.05, respectively,), n-6 PUFA (by 9.7% and 11.4%; P≤0.01) and CLA (by 11.9% and 28.6%; P≤0.01), and decreased the content SFA (by 1.75% and 2.8%, respectively; P≤0.01) and OFA (by 2.9%; P≤0.05 and 5.2%; P≤0.01). In both experimental groups, beneficial changes were also noted in the health quality indicators of the milk, calculated on the basis of the UFA/SFA, DFA/OFA and PUFA/SFA ratios.