Protected palmitic acid to mitigate milk fat depression in grazing Holstein cows in the Mexican Highlands

The cis-9 trans-11 and trans-10 cis-12 isomers of conjugated linoleic acid (CLA) are associated with anticancer and lipolytic effects in tissues, respectively, but in lactating cows, the latter isomer reduces the milk fat concentration, a detrimental aspect for the dairy industry, as it reduces the yield of milk derivatives. Therefore, the objective of this study was to evaluate the effect of providing protected palmitic acid (PA) to grazing lactating Holstein cows supplemented with soybean oil as a source of conjugated linoleic acid, on milk production, fat concentration and mitigation of milk fat depression. Nine multiparous Holstein cows were used, distributed in three groups of three cows each, with initial means of days in milk, live weight, milk production, and number of calvings: 124 ± 16 days, 494 ± 53 kg, 20.9 ± 1.3 kg, and 3.2 ± 2.2, respectively. A crossover design with three treatments was used: control (base diet, BD, = grazing +4 kg concentrate without soybean oil + 2.5 kg corn silage), soybean oil (BD with inclusion of 300 g dry basis soybean oil cow^-1 day^-1), and soybean oil + PA (BD with inclusion of 300 g dry basis soybean oil and 412 g PA cow^-1 day^-1). The groups of cows were on rotational grazing in a mixed pasture of Alfalfa (Medicago sativa) and Orchard grass (Dactylis glomerata). The variables evaluated were as follows: dry matter intake (DM), milk production, concentration of protein, fat and lactose in milk, and milk fat profile. Statistical analysis was through PROC MIXED and comparison of means with Tukey's test (p < 0.05). There were no differences (p > 0.05) between treatments in dry matter intake, milk production or milk protein and lactose content. But the addition of PA in the cow diet increased fat-corrected milk production (p = 0.010), yield (p = 0.030) and fat concentration (p = 0.040), and improved the milk fatty acid profile, by increasing (p = 0.010) the concentration of cis-9, trans-11 CLA in milk fat. Soybean oil supplementation in the diet of grazing lactating cows showed no differences in productive variables, and did not cause the expected milk fat depression. However, combining soybean oil with PA improved the fatty acid profile, increasing the cis-9, trans-11 isomer CLA and palmitic acid in milk fat, with higher yield and fat concentration.