Effect of Feeding on Bovine Milk Quality

Average milk yield was kg 7.2±1.53 vs 9.54±2.72 vs 16.20±2.12 kg, for EG, SG and FC respectively Milk chemical composition was unaffected by treatment (Table 2).

Table 2:Milk chemical composition (g/kg).

CP: crude protein; NDF: neutral detergent fiber; ADF: acid detergent fiber; UFL: net energy for lactation

Milk fatty acid profile

Table 3:Milk saturated fatty acids (SFA) profile (g/100 gfat).

EG: Exclusive Grazing; SG: Supplemented Grazing; FC: Full Confinement

Myristic (C14:0), margaric (C17:0) and stearic (C18:0) acids, as well as total SFA, were significantly.

(P<0.05) higher in milk from FC than SG and EG. Group EG showed the lowest value of palmitic acid

(C16:0) (28.12 g/100g) statistically different (P<0.05) from both SG (30.00 g/100g) and FC (32.13g/100g) . The other SFAs were not significantly different among the breeding systems (Table 3).

Milk from SG showed the highest concentration, even if not significantly different, of unsaturated fatty acids (UFA): 35.76g/100g vs 35.09g/100g vs 34.62g/100g, for SG, EG and FC, respectively. concerning the Monounsaturated Fatty Acids (MUFA), milk from EG had the highest concentration (32.3g/100g) compared to FC (31.42 g/100g) and SG (32.27 g/100g), but, again, the differences were not significant. Similar results were found for the Polyunsaturated Fatty Acids (PUFA) concentration with no statistical difference among the breeding systems. The most representative acid in milk from all the systems was the oleic acid (C18:1) followed by linoleic acid (C18:2) and palmitoleic acid (C16:1) (Table 4). The ω6/ω3 ratio was significantly (P<0.05) different among the systems: group FC had the highest value (6.21:1) followed by SG (3.35:1) and EG (2.07:1). This result was mainly due to the different linolenic acid (C18:3) concentration among the groups. Concerning ω6 FA, a significant lower concentration (P<0.05) was found for linoleic acid (C18:2) in milk from EG compared to those from to other systems (Table 4).

Table 4:Milk Unsaturated Fatty Acids (UFA) profile (g/100g).

EG: Exclusive Grazing; SG: Supplemented Grazing; FC: Full Confinement

The ω6/ω3 ratio was significantly (P<0.05) different among the systems: group FC had the highest value (6.21:1) followed by SG (3.35:1) and EG (2.07:1). This result was mainly due to the different linolenic acid (C18:3) concentration among the groups. Concerning ω6 FA, a significant lower concentration (P<0.05) was found for linoleic acid (C18:2) in milk from EG compared to those from to other systems (Table 4). The ω6/ω3 ratio was significantly (P<0.05) different among the systems: group FC had the highestvalue (6.21:1) followed by SG (3.35:1) and EG (2.07:1). This result was mainly due to the different linolenic acid (C18:3) concentration among the groups. Concerning ω6 FA, a significant lower concentration (P<0.05) was found for linoleic acid (C18:2) in milk from EG compared to those from the other systems (Table 4). MUFA: monounsaturated fatty acids; PUFA: polyunsaturated fatty acids; UFA: unsaturated fatt acids; ω6/ω3: omega6/omega3 ratio.

Means with different letters indicate differences (p<0.05) among breeding systems. Both the Atherogenic (AI) and Thrombogenic (TI) indexes were higher for FC than EG and SG, but a statistical difference (P<0.05) was seen only for TI (Table 5). Means with different letters indicate differences (p<0.05) among breeding systems.

Table 5:Milk Atherogenic (AI) and Thrombogenic (TI) index.

EG: Exclusive Grazing; SG: Supplemented Grazing; FC: Full Confinement

The breeding system significantly affected milk yield which increased with the increase of concentrate in the animals’ diet. Concerning milk chemical composition, fat percentage was higher when animals had access to pasture but the differences with the full confinement system were not significant. By contrast, milk fatty acid profile was significantly healthier in the grazing than in the full confinement systems. Indeed, Park WY, et al. [21], Jensen RG [22], Chapkin RS [23], and Banskalieva V, et al. [24] discussed that fat and cholesterol have worldwide increased in human’s diet, thus becoming a serious health risk due to coronary and vascular problems. According to these authors, the consumption of saturated fatty acids, particularly lauric (C12:0) myristic (C14:0) and palmitic (16:0), are related to hypercholesterolemia due to an increase in plasma Low Density Lipoproteins (LDL) while stearic (C18:0) and oleic acid (C18:1) decrease LDL and increase High Density Lipoproteins (HDL), favoring liver formation of Very Low Density Lipoproteins (VLDL) that allows cholesterol to be transformed to gall bladder salts. Data in the present trial confirmed this low potential hypercholesterolemic effect of milk from grazing animals; in fact, milk from exclusive grazing had significantly lower contents of both myristic (C14:0) and palmitic (16:0) acids, and milk from supplemented grazing only of palmitic acid than that from full confinement system.

Despite a similar content of oleic acid (C18:1), milk from EG and SG showed 50% higher content of linolenic acid (C18:3) than that from FC group. Some studies reported modifications of milk fatty acid profile as a function of animals diet: in particular, a decrease of C16:0 and an increase of C18:0 and C18:1 content were observed in cows grazing pasture compared to cows fed a total mixed ration [25,26]. Concerning ω6 and ω3 PUFA, it has been shown that milk contents of both linoleic acid (C18:2, ω6) and linolenic acid (C18:3, ω3) are affected by the feeding system [27]. Similarly, in the present study, the highest content of linoleic acid was in milk from FC while that of linolenic acid in milk from EG. Decreasing milk ω6/ω3 ratio showed several beneficial effects for human health [5,15], particularly with values lower than 4, since higher levels could modify the beneficial effects of ω3 [14,15]. In present trial, the relationship between breeding system and milk ω6/ω3 ratio was shown: feeding animals with higher quantity of concentrates increased milk yield and ω6/ω3 ratio. Similar results were reported by Salado EE, et al. [28], in a study aimed to evaluate the effects of diets with different levels of concentrate (3.5, 7.1 and 10.5kg/day) on milk yield and quality of grazing dairy cows in early lactation. These authors registered higher milk yield and protein in groups fed 7.0 and 10.5kg/day than in group fed 3.5kg of concentrate [28- 35]. In contrast, milk fat did not differ among the groups and, even if the potential hypercholesterolemic fatty acids of milk (C12:0 to C16:0) did not change by increasing concentrate intake, linolenic acid decreased and the ω6/ω3 ratio increased in groups fed higher amounts of concentrate. Corazzin M, et al. [35] evaluated the effect of concentrate supplementation (High: 3.0kg/head/d vs. Low: 1.5 kg/ head/d) on milk fatty acid profile of Italian Simmental dairy cows grazing on alpine pasture. Low milk showed higher concentration of linolenic acid and total PUFA than High milk. Recently, Santa- Ana A, et al. [29] and Galina MA, et al. [30] compared two breeding systems for goats, full confinement or grazing: milk from animals fed on pasture showed higher PUFAs and MUFAs and lower SFAs with a significant reduction of atherogenic index, thus presumably more beneficial for human health. Musco N, et al. [31] evaluated the effects of a feeding strategy (based on the use of outdoor paddocks; forage: concentrate ratio at least 70:30; forage including at least five different herbs; and no silages) in dairy cows on milk yield and chemical composition, and blood metabolic profile, including the evaluation of oxidative stress.

These authors reported that the proposed feeding system was able to increase milk quality, mainly in terms of fats quality, without negative effects of animal health. Animals fed higher forage: concentrate diet were able to maintain body homeostasis by changing metabolism despite the low energy diet and they showed a general improvement of oxidative status, probably due to an improvement of the biological antioxidant potential. All these results showed that, even considering the differences among ruminants, management on grazing is the key component to improve omega relationship. Finally, both Milk Atherogenic (IA) and Thrombogenic Index (IT) were affected by breeding system. They take into account the potential effect of each fatty acid on human health, and they were lower for grazing than full confinement animals. Thus, milk from grazing animals should have low probability of increasing the incidence of atheroma and/or thrombus formation [32]. The possibility of producing healthier milk by grazing may be of great importance in those areas, like Mexico, still plenty of natural grasses. Also, further studies in the same areas should confirm the hypothesis that grazing may be also beneficial for animals health, thus addressing the increasing concerns about animal welfare.

The breeding system resulted as a fundamental aspect to determine the nutritional quality of milk, mainly related to its fatty acid profile. Despite an increase of milk yield, the full confinement system showed a worsening of healthier parameters: ω6/ω3 ratio greater than 4:1 and increase of both atherogenic and thrombogenic indexes. Therefore, in response to the consumer demand for foods with high nutritional quality, the grazing systems has to be encouraged and milk from animals with free access to pasture has to be recommended.

Experimental cows were treated following the Ley Federal de Sanidad Animal (Federal Law for Animal Health [www.diputados. gob.mx/LeyesBiblio/ref/Ifsa.htm]).

Research was supported by PAPIIT IN IT202014 and Cátedra Faculty of Higher Studies Cuautitlan, National Autonomous University of Mexico.

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