Submitted to: Journal of Dairy Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 14, 2006
Publication Date: May 20, 2007
Citation: Powell, A.M., Kerr, D.E., Guthrie, H.D., Wall, R.J. 2007. Lactation induction as a predictor of post-parturition transgene expression in bovine milk. Journal of Dairy Research. 74(2):247-254. Interpretive Summary: In an attempt to increase the efficiency of transgenic dairy cattle projects, by shortening the time between birth of an animal and assessment of transgene expression in their milk, we hormonally induced both heifer and bull calves to lactate before they reached puberty. All nine females and three of the eight males produced mammary gland secretions in response to the hormone treatment. The concentration of lysostaphin, the transgene product, in the induced lactation samples was on average higher then it was in normal milk samples collected after calving. However, the ranking of concentration of lysostaphin in the induced samples served was a moderately accurate predictor of the ranking of the animals based on lysostaphin values in their normal milk. It turned out that a measure of lysostaphin's biological activity, the ability to kill Staphlococcus aureus, in the induced samples was highly accurate at predicting the activity of lysostaphin in normal milk. Interestingly, the concentrations of a number of endogenous milk components, such as alpha-lactalbumin, beta-lactoglobulin, lactose and BSA, in the induced samples were more reminiscent of colostrum than mature milk. This project demonstrated that two to four years can be saved in evaluating the functionality of mammary specific transgenes in cattle by inducing them to lactate between five and eight months of age.
Technical Abstract: The bovine's long generation interval results in a delay of several years when evaluating mammary specific transgenes in genetically engineered animals. This experiment was conducted to evaluate the feasibility of reducing that waiting period. Lactation was induced in prepubertal bull and heifer calves as a means of predicting transgene behavior during subsequent post-parturient lactations in the heifers themselves, and in daughters sired by the bulls. The animals carry a lactation specific transgene encoding lysostaphin, an antimicrobial protein that kills Staphlococcus aureus, a mastitis causing pathogen. Estrogen, progesterone, and dexamethasone were administered as previously described (Ball, et al., J Dairy Sci. 83:2459, 2000) to nine heifers (transgenics = 5) ranging in weight from 80 to 145 kg. Eight bull calves (transgenic = 7) weighing 81 to 178 kg received additional estrogen and progesterone injection prior to dexamethasone treatment. All nine heifers responded to the milk induction scheme yielding between 19 ml and 4.5 liters over 5 days. Milk volume from the three responding males (100 microliter to 2.5 ml) was significantly less than that harvested from females (p = 0.025). Only bull calves over 150 kg had a positive response. Lysostaphin was detected in all transgenic prepubertal heifers and in two transgenic prepubertal bull calves induced. A moderately strong linear relationship between lysostaphin concentration in secretions from induced lactations and post-parturition milk was detected by ELISA, (r2 = 0.705, p = 0.018). A stronger relationship was observed when lysostaphin's stapholytic activity was compared in the two types of lactations (r2 = 0.907, p < 0.001). Interestingly, endogenous whey proteins, lactose, and serum albumin in induced samples were not predictive of post-parturition milk concentrations. Rather the concentrations of endogenous components were similar to those in colostrum. Lytic activity in induced lactation samples was a good predictor of subsequent lysostaphin expression in post-partum milk.