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Title: VISCERAL TISSUE GROWTH AND PROLIFERATION DURING THE BOVINE LACTATION CYCLE

Author
item Baldwin, Ransom - Randy
item MCLEOD, KYLE - UNIV. KENTUCKY
item Capuco, Anthony

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/18/2003
Publication Date: 9/1/2004
Citation: Baldwin, R.L., Mcleod, K.R., Capuco, A.V. 2004. Visceral tissue growth and proliferation during the bovine lactation cycle. Journal of Dairy Science.87:2977-2986.

Interpretive Summary: Twenty one multiparous, nonpregnant, lactating dairy cows were used to assess the impact of stage of lactation on visceral tissue mass and small intestinal cell proliferation. Four to six cows were slaughtered at each of four stages of lactation: 14, 90, 120, and 240 d of lactation and visceral organs were removed, separated, and weighed. Additionally, intestinal lengths were determined and tissue sections were sampled for composition analysis and immunohistochemical analysis of proliferation (Ki-67 and BrdU incorporation). Duodenal mucosa was obtained by scraping with a glass slide and incubated for 1 h in the presence of tritiated-thymidine to assess proliferative activity. Dry matter intake by the cows increased with stage of lactation through d 90 and thereafter remained similar through d 240 (quadratic; P < 0.01). Conversely, carcass weight and empty body weight declined with stage of lactation through d 120 and increased thereafter (quadratic; P < 0.01). When corrected for cow size by dividing by empty body weight, rumen, small intestine, and liver weights increased with increasing stage of lactation, increasing from 14 to 120 d and declining through 240 d. However, stage of lactation did not have a measurable affect on reticulum, omasum, abomasum, or large intestine weights when corrected for cow size. Visceral adipose tissue mass as a percentage of empty body weight declined with stage of lactation to a minimum at 120 d and had increased by 240 d. Concentrations of RNA and DNA of digestive tract organs were largely unaffected by stage of lactation with the exception of the liver DNA concentration through d 120. Although mitotic indicies (Ki-67) was unaffected by stage of lactation, BrdU incorporation in jejunal segments exhibited a response with stage of lactation. Tritiated thymidine incorporation by duodenal epithelial tissue increased with stage of lactation through d 120, declining thereafter. These data demonstrate that dairy cattle visceral tissues increase in mass, as a percentage of empty body weight, as a result of hyperplastic growth in order to meet the energetic demands of lactation.

Technical Abstract: Twenty one multiparous, nonpregnant, lactating dairy cows were used to assess the impact of stage of lactation on visceral tissue mass and small intestinal cell proliferation. Cows were housed in tie stalls with 12 h of light/dark and were milked twice daily at 0700 and 1800 h. Cows had ad libitum access to water and a common corn silage based total mixed ration. Four to six cows were slaughtered at each of four stages of lactation: 14 d (n = 4), 90 d (n = 5), 120 d (n = 6) and 240 d (n = 6) of lactation. Following exsanguination, visceral organs were separated and weighed. Additionally, intestinal lengths were determined and tissue sections were sampled for composition analysis and immunohistochemical analysis of proliferation (Ki-67 and BrdU incorporation). Duodenal mucosa (100 mg) was obtained by scraping with a glass slide and incubated for 1 h in the presence of tritiated-thymidine to assess proliferative activity. Dry matter intake increased with stage of lactation through d 90 and thereafter remained similar through d 240 (quadratic; P < 0.01). Conversely, carcass weight and empty body wt. (EBW) declined with stage of lactation through d 120 and increased thereafter (quadratic; P < 0.01). As a percentage of EBW, ruminal and small intestinal and liver weights increased with increasing stage of lactation (quadratic; P < 0.01), increasing from 14 to 120 d and declining through 240 d. However, stage of lactation did not have a measurable affect on reticular, omasal, abomasal, or large intestinal weights as a percentage of EBW (P > 0.1). Visceral adipose tissue mass as a percentage of EBW declined with stage of lactation to a minimum at 120 d and had increased by 240 d (quadratic; P <0.05). Concentrations of RNA and DNA of digestive tract organs were largely unaffected by stage of lactation with the exception of the liver DNA concentration through d 120 (quadratic; P < 0.05). Although mitotic indicies (Ki-67) was unaffected by stage of lactation, BrdU incorporation in Jejunal Crypts exhibited a cubic response (P < 0.05) with stage of lactation. Tritiated-thymidine incorporation by duodenal epithelial tissue increased with stage of lactation through d 120, declining thereafter (quadratic, P < 0.01). These data demonstrate that dairy cattle visceral tissues increase in mass, as a percentage of EBW, as a result of hyperplastic growth in order to meet the energetic demands of lactation.