Induced lactation in prepubertal Holstein heifers.

Lactation was hormonally induced in six prepuberal Holstein heifers by seven daily injections of estrogen and progesterone and three injections of dexamethasone on d 18, 19, and 20, followed by twice daily hand milking beginning on d 21. Heifers were about 6 mo old and weighed 162 kg at the beginning of the experiment. Secretions were obtained from five of six of heifers, and twice daily milking continued for 75 d in three of five heifers. The volume of milk obtained on d 7 ranged from 32 to 500 ml and averaged 4.7, 4.1, and 3.7% lactose, protein, and fat, respectively. In the first natural lactation, milk yield and composition were nearly identical for controls and induced heifers. Serum alpha-lactalbumin was increased in induced heifers after treatment with dexamethasone and was highest on d 10 after onset of milking. Our data suggest that sufficient secretions for extensive biochemical testing can be obtained following hormonal induction of lactation in a majority of prepubertal heifers. Moreover, hormonal induction of lactation had no apparent effect on reproduction or first natural lactation. While it is unlikely that hormonal induction of lactation in prepubertal heifers is practical from a dairy production viewpoint, the advent of biotechnology for production of therapeutic recombinant proteins in the mammary gland of transgenic livestock has made early detection of these transgenic proteins very desirable. We conclude that induction of lactation in prepubertal heifers is a viable technique for testing the expression of mammary-linked gene constructs in transgenic cattle.

Regulation of the interferon system: evidence that Vero cells have a genetic defect in interferon production.

A clone of Vero cells was isolated and shown to be totally unable to synthesize interferon and insensitive to the toxic effect of poly(rI).poly(rC) treatment. Cells of this clone and mouse L cells were fused by treatment with polyethylene glycol or Sendai virus. Hybrid cell clones were isolated following selection in medium containing hypoxanthine, thymidine and ouabain. The hybrids were sensitive to the antiviral effect of poly(rI).poly(rC) and synthesized mouse, but not primate, interferon. It is proposed that in Vero cells, the gene for interferon synthesis is defective or absent.

Susceptibility of various cells treated with interferon to the toxic effect of poly(rI).poly(rC) treatment.

Various cells were treated with interferon and then exposed to polyriboinosinic-polyribocytidylic acid complex [poly(rI).poly(rC)]. With mouse L cells, there was a marked cytotoxic effect from low doses of interferon and poly(rI.poly(rC), whereas chick embryo cells showed an effect only after high doses. When primate cells (LLC.Mk2,BSC.B, Vero and human embryo cells) were treated with human or monkey interferon, poly(rI).poly(rC) was not cytotoxic.