Effects of corn silage particle length and forage: Concentrate ratio on milk fatty acid composition in dairy cows fed supplemental flaxseed

This study aimed to evaluate the effects of length of chop of corn silage and forage: concentrate ratio ( F: C) on performance and milk fatty acid profiles in dairy cows supplemented with flaxseed. Our hypothesis was that decreasing forage particle length and F: C ratio would increase unsaturated fatty acid flow to the small intestine and subsequent transfer of these unsaturated fatty acids into milk. Eight Holstein cows (648.1 +/- 71.5 kg body weight; 109.6 +/- 43.6 days in milk) were used in a replicated 4 x 4 Latin square design with 21-d periods and a 2 x 2 factorial arrangement of dietary treatments. Dietary factors were: 1) F: C ratios ( dry matter basis) of 55: 45 and 45: 55; and 2) corn silage particle lengths of 9.52 and 19.05 mm. All experimental cows received 1 kg of flaxseed to substitute for 1 kg of a rolled barley grain-based concentrate daily. Diets were fed twice daily as a total mixed ration. Corn silage particle length and F: C ratio had no effect on dry matter intake, milk yield, and milk composition; however, feeding short cut corn silage depressed milk protein yield. Significant particle size x F: C ratio interactions were observed for milk fat proportions of C-16: 0, C-18: 1 cis-9, and C-18: 2 cis-9, trans-11 ( a conjugated linoleic acid isomer). At short corn silage particle size, decreasing F: C ratio depressed milk fat proportion of C-16: 0. Conversely, feeding short corn silage at high F: C ratio increased the proportion of C-18: 1 cis- 9 and C-18: 2 cis-9, trans-11 in milk fat. The milk fat proportion of C-18: 2 trans-10, cis- 12, a conjugated linoleic acid isomer that is associated with milk fat depression, was not affected by dietary treatment. Our results show that corn silage particle length and F: C ratio influence milk fatty acid profiles in dairy cows fed supplemental flaxseed as a source of polyunsaturated fatty acids.