The effects of different fat sources during late pregnancy and early lactation on apparent digestibility, rumen parameters, and milk fatty acid pattern of Afshari ewes

Negative energy balance in pregnant ewes during last of gestation could result in fatal pregnancy toxemia and affects ewe and lamb health. Fat supplementation of the diet is an efficient mean to increase energy concentration of diet and modify body weight, body condition score, milk yield, fat content and fatty acid composition in lactating ruminants. Addition of fats to ruminant diets provides preformed fatty acids (FA) which are directly available for milk fat synthesis in dairy cows and small ruminants. Much of the research attempted to obtain milk fat with healthier properties by increasing milk concentration of specific human health promoting fatty acids. Although mechanisms of action are unclear and its use in humans is controversial, CLA is still of particular interest because of its speculated role in preventing human health problems and increasing the nutritive and therapeutic value of milk. Therefore, this study contacted to investigate effects of different fat sources and CLA during late-pregnancy and early lactation on DMI, rumen metabolites and milk fatty acid pattern of Afshari ewes.

Fifty Afshari ewes were assigned randomly to one of the five experimental diets with ten replicates in a completely randomized design; 1- control (without fat supplement), 2- 3% protected fat powder of saturated fatty acids (palm oil), 3- 3% Ca salt of  omega-6 fatty acids (soybean oil), 4- 3% Ca salt of omega-3 fatty acids (fish oil), 5- 2% protected fat powder of saturated fatty acids (palm oil) and 1% CLA in a completely randomized design. Diets were fed between 14 days before and 45 days after lambing. Dry matter intake was measured daily, feed compound and milk composition was measured weekly. Milk fatty acid profile was determined using Gas Chromatography. Feeding behaviors were recorded every 5 minutes in 40 day of experiment. Rumen samples were taken directly from the rumen fluid through the esophagus and concentration of volatile fatty acids determined using a gas chromatography. Data were analyzed using SAS statistical software and MIXED procedure.

In prepartum, the addition of saturated fat, omega-6, and omega-3 significantly reduced the dry matter intake, but this effect was not observed in CLA containing treatments (P <0.01). In the postpartum period, the addition of fat resources caused a significant increase in dry matter intake (P <0.01). NDF digestion decreased significantly by adding protected fat powder of saturated fatty acids (P <0.05), but not affected by other treatments. It has been reported that the effect of different fat sources on the dry matter is not constant and depends on various factors such as palatability, amount, source and degree of saturation, chain length and fatty acid stile (triglyceride and free fatty acid). The results showed that adding different sources of fat supplementation to 3% in diet did not have a significant effect on feeding behaviors of Afshari sheep. Animal-derived data showed that ewes were in good condition in terms of comfort. Rumen volatile fatty acid profile and pH after lambing were not affected by feeding different fat sources. In agreement with the results of this study, most studies no reported a significant effects on rumen pH with the addition of fat supplement. Adding protected fat powder of saturated fatty acids alone and, along with conjugated fatty acids, increased a significant increase in milk fat percentage. The addition of omega-6 fatty acids resulted in a reduction in the short, medium, and saturated fatty acid fatty acids, and the increase of medium chain fatty acids. The addition of omega-3 fatty acids did not have a significant effect on the fatty acid model of milk compared to the control treatment. The addition of conjugated fatty acids resulted in a significant increase in the concentration of conjugated linoleic acid in milk. It has been reported that the pattern of milk fatty acids can be affected by the amount and type of fatty acids in the diet.

Dry matter was reduced by fat supplementation resources before lambing and increased afterward. Reduction in dry matter digestibility and dietary fiber was observed with saturated fat sources. Rumen pH and Volatile fatty acids (VFA) were not affected by feeding different fat sources. Adding conjugate fatty acids in the diet, increased the conjugate linoleic acid (CLA) concentration in the milk. In general, supplementing fat sources to the prepartum diets increased dry matter intake (DMI) after parturition and conjugated fatty acids resulted in a significant increase in the concentration of conjugated linoleic acid in milk.