Lipid Supplementation of Dairy Cows’ Diets: Effects on Milk Fat Composition Giovanna Contarini,* ,† Piero M. Toppino, † Riccardo Leardi, § Franco Polidori, ‡ Giovanni Savoini, ⊥ and Luigi Bertocchi | Istituto Sperimentale Lattiero-Caseario, via Lombardo 11, 20075 Lodi, Italy, Istituto di Analisi e Tecnologie Farmaceutiche ed Alimentari, Universita ` di Genova, Via Brigata Salerno, 16147 Genova, Italy, Facolta ` di Medicina Veterinaria, Universita ` di Camerino, Via Fidanza 15, Camerino (MC), Italy, Istituto di Zootecnica, Facolta ` di Medicina Veterinaria, Via S. Cecilia 30, 98100 Messina, Italy, and Istituto Zooprofilattico Sperimentale della Lombardia e dell’Emilia, Via Bianchi 7, 25100 Brescia, Italy The influence of supplementation of diets with some lipid sources (i.e., whole cottonseeds, flaked whole soybean seeds, and calcium soaps) on the composition of milk fat from dairy cows, bred in 50 farms of the Brescia province, was evaluated; 117 bulk milk samples were collected, and the lipid fraction was analyzed. Considerable variations in the composition of both fatty acids and triglycerides were detected, and these variations showed a good correlation with the amount of crude lipids in diets. The application of ratios between fatty acids as an index for butterfat purity is ineffective due to the modifications of the fatty acid composition. Keywords: Fatty acids; butterfat; milk fat; dairy cows INTRODUCTION The use of supplemental fat for the diet of ruminants, especially dairy cows, arises from various reasons, which can be summarized as follows: (1) The energy concen- tration of diets may be increased. This is particularly interesting since it may reduce the negative energy balance in early lactation and have a positive effect on fertility (Buttler and Elrod, 1991). (2) An adequate energy level can be maintained even when a low dry matter concentration is administered as, for instance, during hot periods (Knapp and Grummer, 1991). (3) The use of energy for milk production is more efficient (Savoini, 1993). (4) Lipid supplementation has a posi- tive effect on the ovarian activity since it increases the plasmatic cholesterol content and, consequently, the precursor of both estradiol and progesterone (Buttler and Elrod, 1991). However, the use of supplemental fat for diets of dairy cows shows some difficulties since fat, particularly unsaturated fatty acids, reduces the fermentative activ- ity of the ruminal bacteria and protozoa (Palmquist and Jenkins, 1980; Savoini, 1993). Therefore, the diet of cows should be supplemented with either saturated fatty acids or protected lipids, which do not affect ruminal fermentation. Oily seeds, such as cottonseeds and soybean seeds, are a natural source of partially protected fat. In recent years, fatty acid calcium salts have been widely used as protected fat (Bondioli et al., 1989; Ohajuruka et al., 1991). Lipid supplementation to the diet of dairy cows resulted in an increase in production and showed varying effects on milk quality (Polidori et al., 1986; Bondioli et al., 1989; Savoini et al., 1992; Grummer, 1993; DePeters, 1993). One of these effects is the variation in the acidic composition of milk fat as well as a decrease of the medium-chain fatty acids content and an increase of the long-chain fatty acids content (DePeters, 1993). This may result in improper evaluations of butter purity (Toppino et al., 1988). This product, as stated by the EEC Regulation (No. 985/68, Article 1), must be obtained exclusively from cow’s milk or cream. At present, using ratios between fatty acids, it is difficult to determine whether variations in the acidic composi- tion of milk fat depend on food factors or on possible adulterations, such as addition of foreign fat during butter- or cheesemaking. The aim of this research was to detect variations in the quality of the lipid fraction of bulk milk as a result of the supplementation of dairy cows’ diets with flaked whole soybean seeds, whole cottonseeds, and calcium soaps. MATERIALS AND METHODS In order to evaluate the lipid fraction, 117 bulk milk samples from dairy cows bred in 50 farm of the Brescia province and the data on the dry matter intake and on the composition of the corresponding cow’s diets were collected a whole year through. Some diets (55%) were supplemented with exogenous fat as flaked whole soybean seeds, whole cottonseeds, calcium soaps, or mixtures of these. Crude protein, crude lipid, and crude fiber contents were calculated from tables (NRC, 1989) taking into account, for the commercial concentrates, the composition labeled. Fat was extracted from milk by the Rose Gottlieb procedure (FIL-IDF Standard Method, 1987) and analyzed by gas chromatographic methods to evaluate the acidic (Toppino et al., 1982) and triglyceride (Lund, 1988) compositions. This evaluation was carried out to check whether the triglyceride composition was subject to the same changes as the fatty acid composition, due to the presence of fat in the diet. Statistical Analysis. Data on diet composition were classified according to the presence of supplemental fat in the diet, and the average and standard deviation have been calculated. Multivariate statistical analyses were applied by PARVUS package (Forina et al., 1988) to evaluate the influ- ence of supplemental fat on the composition of the lipid fraction of milk. † Istituto Sperimentale Lattiero-Caseario. § Universita ` di Genova. ‡ Universita ` di Camerino. ⊥ Facolta ` di Medicina Veterinaria. | Istituto Zooprofilattico Sperimentale della Lombar- dia e dell’Emilia. 3507 J. Agric. Food Chem. 1996, 44, 3507-3511 S0021-8561(96)00022-2 CCC: $12.00 © 1996 American Chemical Society