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 x4 Latin square design with 21-d periods and a 2 x2 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 xF: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.

Influence of particle size on the effectiveness of the fiber in barley silage.

We used eight multiparous Holstein cows in a 4 x 4 Latin square design to evaluate the effects and possible interactions between silage particle size and concentrate level on chewing activities and productivity of cows fed barley-based total mixed rations (TMR). Diets were designed with two forage-to-concentrate ratios (low forage, 45:55, high forage 55:45), combined with two theoretical chop lengths of barley silage (short = 4.68 mm and long = 18.75 mm). Diets were formulated to provide similar and above-minimum neutral detergent fiber recommended for cows in early lactation. Increasing silage particle size of the forage did not affect dry matter intake. The 3.5% fat-correct milk and fat yields trended higher for increased particle size. Percent milk protein was higher for short particle size. Increasing the concentrate levels in the diets increased proportions of milk protein and lactose, but not milk fat. Cows fed short silage spent 90 min less per day chewing and ruminating than did those on long silage. Total chewing activity per kilogram of forage intake was higher for cows on long silage compared with those on short silage diets. Although a reduction in silage particle size did not depress milk fat, rumination and chewing activity were significantly reduced. These results suggest that particle size of the silage may have dominant control over chewing activity despite adequate neutral detergent fiber intakes.

Effects of flaxseed supplementation on milk production, milk fatty acid composition and nutrient utilization by lactating dairy cows.

Twelve multiparous Holstein cows at 72 +/- 20 days in milk were used in a switch-back design with 14-d periods to determine the effect of replacing barley grain into a dairy total mixed ration with micronized or raw flaxseed on nutrient digestibility, milk yield, milk composition. Total mixed diets were (DM basis) 50% barley silage, 50% concentrate mix mainly rolled barley grain and canola meal. Diets were supplemented with 1 kg raw (RF) or micronized (MF) flaxseed to substitute 1 kg of rolled barley grain (C). Neutral detergent fibre, ADF and CP digestibility of the diets were not significantly affected by supplementation; however, calcium digestibility was reduced by 62% and 46% when raw and micronized flax were fed, respectively. Milk yield (38.3, 39.6, and 38.4 kg/d for diets C, RF and MF, respectively) was similar for all diets. Milk fat (3.50, 3.48, and 3.52%) and protein (3.31, 3.34, and 3.31%) for diets C, RF and MF, respectively, were not affected by treatment diets. Concentrations of c9, t11 conjugated linoleic acid (CLA; 0.51, 0.72 and 0.76 g/100 g fatty acids) in milk fat increased (P<0.05) similarly among the two flaxseed supplemented diets. The RF and MF diets significantly increased the C18:1, C18:1 trans-11, C18:2 cis-9, cis-12 and C18:3 in milk fat however, C12:0, C14:0 and C16:0 were significantly reduced compared with control. Replacing barley grain with flaxseed in the diet of lactating cows increased the beneficial fatty acids in milk without depressing nutrient digestibility. Micronization of flaxseed did not reveal any advantage over raw flaxseed.