Influence of Roughages on Certain Biochemical Properties of Milk

Abstract

The evidence is presented to show that the roughages fed to cows and the physiological response of an animal to feed, influence both the fat-soluble vit. content of milk and its biochemical make-up that regulates the reactions which produce the oxidized flavors. Of the roughages studied, the early hay-crop silage was higher in tocopherol and carotene content than any other roughage. The late field-cured hay was uniformly lower in vit. and provit. content, whereas the late hay-crop silage and early barn-cured hay were intermediate. As an avg., the fat produced on early silage ration was highest in tocopherol, vit. A, and carotenoid content; and the fat produced on late field-cured hay was lowest. The differences in the avg. tocopherol, total vit. A value, and carotenoid content of the fat samples, as affected by the roughages fed to the cows, were statistically highly significant (P <0.01). Likewise, the differences in the avg. total vit. A value and carotenoid content of the fat samples, as affected by the physiological response of the individual cow to the feed consumed, were significant. Under the exptl. conditions descr., the cow and the period as a source of variance produced no significant effect on tocopherol levels of the fat. 53% of samples of milk produced on early silage,barn, and field-cured hays rations were unstable, and became unpalatable during the 1st 3-day storage in the presence of 0.1 mg./ 1. of added Cu; and 47% remained stable during 10-day storage tests at 0_5[degree]C. Data show that the late silage produced milk that efficiently resisted the oxidized flavors throughout the exptl. trial, even in the presence of 1.0 mg. of Cu/l., and yet contained 2614 [mu]g. tocopherols per 100 g. of fat, on the avg., as compared with 3090 [mu]g. vit. yield on the early silage. Observations indicate therefore, that in addition to tocopherols, some roughages fed to the cow contain other protective substances, influencing the path of oxidative processes, and that their excretion by the mammary gland is mainly responsible for the stability of milk with 3000 [mu]g. tocopherols and below, when both ascorbic acid and Cu act as the catalysts. The data suggest, that the prevention or practical postponement of the reactions, which result in the development of oxidized flavors, was effected in the late silage milk by the presence and preferential oxidation of the unknown substances, named non-flavor forming compounds. Apparently, some of the animals continued to excrete these substances long after the causative ration had been discontinued.