Factors affecting body tissue mobilization in early lactation dairy cows. 2. Effect of dietary fat on mobilization of body fat and protein.

Twenty-two multiparous Holstein cows were fed either a control diet or a control diet plus 3% added fat (dry matter basis) to determine the effect of added dietary fat on body tissue mobilization and milk production. Body composition measurements were taken using the D2O dilution technique at -2, 5, and 12 wk postpartum. Cows fed added fat produced 2.7 kg/d more milk than did those fed the control diet alone, but milk production, milk composition, and dry matter intake were not affected by diet. The maximum amount of body tissue loss occurred between -2 and 5 wk postpartum when cows fed both diets mobilized 46 kg of body fat and 12 kg of body protein. Between 5 and 12 wk postpartum, only small changes in both body protein and body fat were observed. Even though cows fed added fat showed a tendency toward reduced body fat mobilization (66 kg for cows fed the control diet vs. 37 kg for cows fed the control diet plus added fat) and increased body protein mobilization (4.8 kg for cows fed the control diet vs. 19.5 kg for cows fed the control diet plus added fat), the differences were not significant. Apparent differences in fat mobilization between diets might have been due to initial body fat stores (159 kg for cows fed the control diet vs. 126 kg for cows fed the control diet plus added fat). Across diets, one unit of change in body condition score corresponded to about 55 kg of empty body fat. Supplemental dietary fat did not reduce body tissue mobilization in early lactation.

Factors affecting body tissue mobilization in early lactation dairy cows. 1. Effect of dietary protein on mobilization of body fat and protein.

Twenty Holstein cows were fed diets that were formulated with 16 or 19% crude protein (CP) that contained, respectively, 6 and 9% ruminally undegradable protein (RUP) (dry matter basis) to study the effect of increased RUP on tissue mobilization and production parameters. Cows were enrolled in the study from -14 to 114 d postpartum. Body composition measurements using the D2O dilution technique were made at -2, 5, and 12 wk postpartum. Maximum loss of body tissue occurred between wk 2 prepartum and wk 5 postpartum during which time cows fed both treatments mobilized a mean of 54 kg of body fat and 21 kg of body protein. Cows continued to mobilize 18 kg of body fat through wk 12 postpartum, but the amount of body protein was unchanged. One unit of change in body condition score corresponded to about 40 kg of empty body fat. Partitioning of empty body energy between empty body fat and protein indicated that, for each unit of change in body energy, 93% was lost or gained as body fat, and body protein accounted for only 7%. Increasing RUP in the diet had no effect on the postpartum amounts of empty body protein, empty body fat, or empty body energy. Milk production was 39.8 kg for cows fed the 16% CP diet and 42.4 kg for cows fed the 19% CP diet. There was an interaction of treatment by week postpartum. Both dry matter intake and milk production were lower during the first 6 wk postpartum but were greater thereafter for cows fed the 19% CP diet than for cows fed the 16% CP diet. Milk CP percentage was higher (3.08% vs. 2.89%), and milk CP yield tended to be greater (1.29 vs. 1.15 kg/d), for cows fed the 19% CP diet.

Structural organization and mammary-specific expression of the butyrophilin gene.

Butyrophilin is a glycoprotein of the immunoglobulin superfamily that is secreted in association with the milk-fat-globule membrane from mammary epithelial cells. As a first step towards determining the possible function(s) of this protein in lactation, the mouse butyrophilin gene (Btn) has been cloned from a 129-ES cell genomic library. Over 14 kb of DNA was sequenced, including the entire transcriptional unit of the gene, and 4.6 kb and 1.1 kb of the 5' and 3' flanking region, respectively. In addition, the overall structure of the bovine gene (BTN) was determined by amplification of genomic DNA by the polymerase chain reaction. Both Btn and BTN comprise seven exons and six introns. The signal sequence and two immunoglobulin-like folds of the exoplasmic domain and the membrane anchor are encoded by separate exons, and the cytoplasmic domain is encoded by two short exons and a large terminal exon that also includes 3' untranslated sequence. The butyrophilin gene appears to have evolved from a subset of genes in the immunoglobulin superfamily and genes encoding the B30.2 domain, which is conserved in a family of zinc-finger proteins. Murine butyrophilin mRNA was detected specifically in the mammary gland by RNase protection analysis. Expression increased during the last half of pregnancy and was maximal during lactation. The 5' flanking region of Btn was analyzed for putative regulatory elements and is different from the promoters of other mammary-specific genes. Btn should be useful for determining the mechanisms underlying mammary-specific gene expression and potentially for the production of heterologous proteins in the milk of transgenic animals.