Submitted to: North Carolina Dairy Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 12/11/2002
Publication Date: 3/15/2003
Citation: Eun, J., Fellner, V., Burns, J.C. 2003. Effects of feeding eastern gamagrass with or without corn supplementation on lactation performance of holstein cows.. North Carolina Dairy Conference Proceedings. Interpretive Summary: Of particular interest to the breeding and molecular genetics community today, is determining how or if selection (evolutionary trend to maintain advantageous or beneficial genes and therefore traits) has affected the genetic diversity in agronomically important genes in crop plants. Variation in the underlying genes that influence starch and protein kernel content may offer insight into yield and quality of corn. By characterizing the natural variation and genetic diversity related to starch genes in maize (corn), we have characterized past and ongoing selection in terms of the overall pathway. Such a pathway approach has not been attempted in this manner until now. Our data demonstrate that three of the six genes we examined in particular have been highly selected and may have been important in the domestication process of maize. We were also able to conclude that most beneficial starch traits have been chosen in genes along the portion of the pathway that controls the formation of a specific type of starch called amylopectin. Amylopectin is important in the food processing industry for special properties such as pasting (influential in tortilla making) and heat stability. Very low genetic diversity was found in several maize starch genes as compared to the diversity in maize's wild relative, teosinte. This dramatic decrease in diversity suggests that maize breeding dedicated to altering kernel quality may require an infusion of genetic diversity from teosinte.
Technical Abstract: Lactating cows fed gamagrass hay(GH) or silage(GS) produced similar daily milk yields(27.3 vs 29.5 kg/d). Including supplemental corn with GS at 12.6 % of the diet did not increase daily milk production(29.5 vs 32.4 kg/d), but when corn supplementation was increased to 27.8 and 54.6 % of the diet it increased daily milk production to 33.6 and 37.7 kg/d,respectively. This response is similar to data obtained with cows fed similar corn silage based diets. Cows fed GS had a higher feed conversion efficiency (daily milk/daily intake) compared with cows fed GH. Adding low , medium or high levels of concentrate to GS did not improve feed conversion efficiency. Conversion of feed N to milk N was greater for GS vs GH and corn supplementation of silage failed to improve N use efficiency.