This experiment aimed to make a comparison between the effect of a mix of two energy preparations (a glucogenic preparation (G) and a free fatty acid preparation (F)), administered in the diet during the transition period over different periods of time (5 or 8 weeks), on the animal condition, feed intake, yield and composition of milk, and blood and urine parameters. The experimental additive was a mixture (1:1) of two energy preparations, namely, a loose mixture of propylene glycol and sodium propionate and a free fatty acid preparation in the form of rumen-undegradable pellets. The study included 50 Polish Black-and-White Holstein–Friesian dairy cows, allocated into five treatment groups, including one control (C) and four experimental ones (G1F1, G2F2, G2F1 and G1F2). The preparations were mixed at a 1:1 weight ratio (500 g per head, comprising 250G and 250F) and they were administered to all experimental groups of cows daily as a component of the experimental concentrate for 5 weeks (from the 2nd week before the expected calving and until the 3rd week of lactation). From the 4th until the 6th week of lactation, the supplementation in the experimental groups changed and animals received either no additive (G1F1), or were continuously supplemented with the G–F mix (G2F2), or received only G (G2F1) or only F (G1F2). The preparations used in the study had a long-term influence on the increase in the milk yield of cows, on the improvement of their health condition, and on the reduction of weight loss. The study results confirmed that prolongation of the supplementation until the 6th week of lactation may cause favourable changes in animal performance and milk quality. Due to different modes of action, the simultaneous supplementation of G and F reduced the negative energy balance in the cow and improved milk production and composition. The best results were obtained after administration of the mixture (1:1) of the G and F at the dose of 500 g/cow.day over the 8-week periparturient period.

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High-producing dairy cows require an appropriate management system, good care, and a tailored nutritional program that provides well-balanced feed rations. High yielders, especially during the periparturient period, normally show a reduced feed intake with a concomitant increased demand for nutrients for milk synthesis. Thus, the incidence of metabolic disorders may greatly increase, and consequently, a decrease in milk production is noted. Deterioration in milk composition is also observed (4). Although a range of energy additives to ruminant diets has been extensively investigated (7,48), an ongoing research focused on the negative energy balance of periparturient dairy cows is required (29,50). In this regard, much attention is given, among others, to the use of energy feed additives in dairy cow diets and to their impact on animal metabolism and performance, as well as on milk composition. Each of gluconeogenic precursors, such as glycerol (51), propylene glycol (28), sodium or calcium salts of propionate (30), has a different route for conversion to glucose. Depending on their type and administration period, energy supplements may contribute to reducing metabolic disturbances during the transition period. Propylene glycol may affect glucogenic action in different ways. A portion of this substance is metabolized in the rumen to lactic acid Klebaniuk R., Kochman G., Kowalczuk-Vasilev E., Grela E. R., Bąkowski M., Olcha M., Dunster F.Energy efficiency of diet for periparturient dairy cows supplemented with free fatty acids or glucogenic additives Summary The aim of the study was to compare the efficiency of two energy preparations used at fixed doses, but for different lengths of time: 1) a loose mixture of propylene glycol and sodium propionate, and 2) a granular formulation of free fatty acids produced from palm oil and palm nut, non-degradable in the rumen.A three-factorial experiment was carried out on 5 groups of Polish Black and White Holstein-Friesian cows (10 animals each) which were within the transition period. The aim of the experiment was to determine the effect of two energy preparations administered at a constant dose, but over different time periods, on the animals' performance, as well as on their milk yield and composition. The following treatment groups were formed: control group C, which received a standard diet; experimental groups G1 and G2, which received a dietary additive of a glucogenic preparation; and experimental groups F1 and F2, which received a free fatty acid preparation. The diet of the transition cows was supplemented with the full dose of the additives (500 g/ head/day) for 2 weeks before the expected calving and 3 or 6 weeks of lactation.The present research confirmed the benefits of dietary inclusion of energy supplements for transition cows. Supplementation with both glucogenic and free fatty acid preparations reduced the negative energy balance in the cow's organism and improved milk production and composition. The milk yield, higher by ca. 10% for the cows fed diets with...