Feed intake
There was no effect of treatment on DM, OM, CP, EE, aNDF and energy intake, because the diets were formulated to be similar in protein, energy and fiber. When added fat in the form of calcium salts in the diet of lactating cows, depressive effects on consumption can be observed (NRC, 2001), and are associated with low palatability, unsaturation and chain length of acids fatty, as well as metabolic effects to the release of cholecystokinin (Allen, 2000). None of these possible effects was observed in our study. Results about nutrient intake are varied, but Kennelly (1996) suggested that fat addition in ruminants diets like whole oil seeds, proved to have less detrimental effect on dry matter intake, due to the slower release seed oil than the same amount, fed as free oil, resulting in no effect on dry matter intake. Petit et al. (2009) also observed that cows in early lactation fed with the highest level of linseed (150 g/kg of dry matter) did not reduce dry matter intake.
In studies with calcium salts of fatty acids, although there was a lower dry matter intake, Jenkins (1993) report that the energy intake did not fall because it increase in energy density or metabolic efficiency, without affecting milk production. Onetti & Grummer (2004) confirmed this hypothesis in a review at that the author compiled data from 41 trials that assessed supplementation from different sources and levels of fat to lactating cows. From 23 experiments evaluated, using calcium salts of fatty acids as the fat source, it observed a reduction in dry matter intake of 0.97 kg/d. However, when analyzing the milk production of 21 of these studies, the average milk production was increased by 1.29 kg/d. Thus, it is assumed that the net energy intake was maintained or increased with lipids supplementation. That is one of the main objectives of the use of fat in diets of lactating cows, to increase the energy density, particularly avoiding non-fiber carbohydrates, in order to avoid acidosis risks in high producing animals.
The lack of effects on feed intake confirms our hypothesis, that oilseeds can be used as lipid sources to replace commercial protected fat, probably because they are processed at different parts of digestive tract. Besides that, there was no effect on net energy intake, that depends how and where the diet is metabolized. Probably, the slow release of oil in the rumen, leads to a partial protection, as suggested by Kennelly (1996).
The use of oil like whole grains, especially LI and SY provided a significant reduction in soybean meal use at diet, major proteic ingredient of livestock feeding, which has a high cost when compared to grain used.
The lower intake of NFC in SF and SY was not enough to reduce milk yield corrected to energy and milk solids production, therefore the diets were appropriate.
Apparent Digestibility
The absence of differences in DM, OM and aNDF ensures that lipid sources LI, SF and SY not causes negative effects on the digestive process.
Other results about digestibility of nutrients in dairy cows are quite heterogeneous. Martin et al., (2008) observed reductions, while Gonthier et al. (2004) found increase and Doreau et al. (2009) not found effect.
The main determinants of these effects are the amount of lipids and how they are fed (free oil or seed). In our study, these two factors contributed to the results and the few differences observed, since the inclusion of fat from LI sources, SF and SY occurred at an intermediate level, less than 35 g/kg of DM intake, maintaining low ruminal availability.
The digestibility of protein was less in SY. This is associated with a higher protein inclusion coming from soybean grain. In the other treatments was used soybean meal, with higher protein digestibility. Another associated factor may be related to reduced digestibility of soybean seed, occurring loss in feces.
The CS showed higher digestibility of EE, probably because that is composed of fat free saponified that solubilizes widely in the abomasum (Naik, 2013). Chouinard et al. (1998) observed an increase in digestibility of DM, CP, and aNDF in diets with AG calcium salts when compared to a control diet. In LI, SF and SY, the way the fat is arranged in the grains, there may be some limitations, due to the presence of fibrous exospermas in grain, or the association of that fat to protein grain matrix (Ekeren et al., 1992), that can affect negatively both the access of ruminal microflora, as digestive enzymes in the small intestine. Supplementation with vegetable oil in free form (rich in unsaturated fatty acids) could be a trouble to ruminal fermentation, however when this is from oilseeds these disorders be reduced by slower fat release, without losses on nutrient digestibility (Coppock & Wilks, 1991), that seems to be confirmed in this study.
Production, milk composition and milk fatty acid profile, feed efficiency and energy balance
The higher milk production observed in CS may be related to the specific characteristics of this diet, because although it was not found effects of treatments on the digestibility of OM, the higher digestibility of EE and the highest intake of NFC may be responsible for increased lactose production, that has high correlation (0.9742; r<0.0001) with milk production. However, it did not affect the energy corrected milk production and feed efficiency, that qualifies all diets as effective to input high energy densities and should be considered the availability. The costs of different oil sources may be important to decision about which will be used.
The absence of changes in milk fat and protein reinforces the theory of natural protection in whole grains as well as the uniformity of the diets because these milk components are variable, both as a result of dietary lipids, or microbial growth, either for lack of fermentable carbohydrates or deficiency in protein intake. The lower production of lactose observed in SY treatment may be related to reduced intake of NFC, however, is not considered a limiting factor, because no effects were observed in the ECM nor in solids.
The milk urea nitrogen (MUN) was above to the standards (10 - 16 mg/dL) proposed by Jonker et al. (1998) in LI and SF treatments, however, acceptable to the high protein levels of these diets (209 g/kg OM). So we can infer that the inclusion of lipids not depressed energy from NFC into rumen, with mean concentration of 368 g/kg OM.
Blood profile
No effects on blood profile (P>0.05) confirmed the similarity of diets and the potential of lipid sources. Blood glucose (62.1 mg/dL), triglycerides (3.34 mg/dL) and NEFA (0.30 mmol/L) are consistent with the physiological values described by Kaneko et al. (2008).
The concentration of blood urea was 39.3 mg/dL, within the range 15-42 mg/dL described by Wittwer (2000), but lower than those described by Kaneko et al. (2008), that accept values between 42.8 and 64.3 mg/dL.
Serum cholesterol, although not reflected treatment differences, was higher than 120 mg/dL, described by Kaneko et al. (2008). The increase occurred in response to intake of high levels of lipids (Wittwer, 2000). Elliott et al. (1993), showed that the elevated cholesterol levels in diets with oil may be related to greater need to transportation of long chain fatty acids.
The NEFA means were 0.30 mmol/L (Table 6), that combined with energy balance data (Table 5) show that no BEN during the trial, due the effectiveness of the diets. The absence of effects on AST and GGT concentrations confirms that did not liver damage by the fat sources used.
It was observed that higher levels of CLA cis 9 trans 11 for CS, however, in the same way, also found, despite low, values of CLA cis 12 trans 10, its isomerized form. Several factors influence biohydrogenation in the rumen and can change the amount and composition of unsaturated fatty acids, both those destined for deposition in adipose tissue and those secreted in milk. Biohydrogenation can happen completely or with the formation of intermediate products, such as C18: 2c9t11, these compounds being absorbed in the ruminal walls and, in blood flow, can be absorbed by the mammary gland and incorporated into milk. Into the bloodstream, they can be absorbed by the mammary gland and incorporated into milk. However, when we observed the MUFA values, SY presented higher values than the other treatments. Unlike the other diets evaluated, where MUFA content was around 20% of the total fatty acids, SY presented values of 83.52%. This high content of MUFA in the composition of SY and its higher values in the final composition of milk compared to other diets evaluated, demonstrates that for total efficiency of biohydrogenation, a balance is needed between the fatty acid compounds present in the feed.