Silage chop length and hay supplementation on milk yield, chewing activity, and ruminal digestion by dairy cows.

The effects of whole-plant corn silage (CS) particle size and long unprocessed grass hay (LH) supplementation on milk yield, chewing activity, and ruminal digestion in dairy cows were evaluated in 2 experiments. In Experiment 1, corn silage harvested at fine (6 mm; FCS) or coarse (23 mm; CCS) theoretical cut length were fed to 22 lactating Holstein cows. Treatments were 2 total mixed rations containing 58% of dry matter (DM) as FCS or CCS. Diet DM intake tended to be higher in cows fed FCS than those fed CCS (23.4 vs. 22.1 kg/d). However, milk yield and composition, body condition score, and plasma metabolite concentrations were not affected by the dietary treatments. In the second experiment, 5 cannulated Holstein cows were used in a 5 x 5 Latin square design to evaluate the effects of the addition of LH to the diets evaluated in Experiment 1 on chewing activity and ruminal digestion. Treatments were 5 total mixed rations: FCS-based diet plus the addition of 0, 5, or 10% LH (DM basis) and CCS-based diet plus 0 or 5% LH. Long hay addition linearly decreased DM intake in cows fed FCS-based diets (25.0 to 21.7 kg/d), but increased DM intake in those fed CCS-based diets (22.7 to 27.1 kg/d). The intake of neutral detergent fiber (NDF) increased with LH addition in CCS-based diets (7.6 vs. 9.4 kg/d). Rumination time increased (16.8 to 21.0 min/kg of DM intake) when LH was added to FCS-based diets, but it decreased when included in CCS-based diets (18.8 vs. 12.9 min/kg of DM intake). Ruminal pH was higher (5.9 vs. 5.7) and lag-time for in situ NDF disappearance was shorter (3.5 vs. 8.7 h) for cows fed CCS compared with cows fed FCS. The rate of NDF disappearance tended to be higher for the CCS-based diet with 5% LH than for the diet with 0% LH (2.0 vs. 4.4 %/h), but solids passage rate was not affected by the treatments. These results suggest that addition of LH to FCS-based diets does not affect ruminal environment or digestion, but depressed DM intake. In contrast, addition of LH to CCS-based diets may improve ruminal NDF digestion, increasing DM intake by reducing filling effect and time needed for rumination.

Ruminal digestion by dairy cows grazing winter oats pasture supplemented with different levels and sources of protein.

Six Holstein cows fitted with ruminal cannulae were used in two simultaneous 3 x 3 Latin squares to study the effects of protein supplements on ruminal fermentation and in situ crude protein degradability. Cows rotationally grazed a winter oats (Avena sativa L.) pasture and were supplemented with one of three concentrate supplements: 1) low protein sunflower meal (L-SM); 2) high protein sunflower meal (H-SM); or 3) high protein feather meal (H-FM). Concentrates (6.5 kg/d) were offered in equal portions twice daily during milking. Ruminal pH and total volatile fatty acids concentration were unaffected by treatments. Supplementation with L-SM and H-FM decreased ruminal NH3-N concentration compared with H-SM. The concentrate with feather meal had lower effective rumen degradability of crude protein than concentrates containing sunflower meal. Effective rumen degradability of crude protein of pasture averaged 82.7%. Thirty-six multiparous Holstein cows (71 d in milk) were used in a complementary experiment to study the effect of treatments on intake, milk yield, and milk composition. Pasture (13.2 kg/d) and total (19.6 kg/d) dry matter intake (estimated using Cr2O3 as fecal marker) and milk yield (20.5 kg/d) were unaffected by level or source of protein supplemented. Intake of rumen undegradable protein in grazing dairy cows was higher when the amount of sunflower meal was increased or when feather meal was used in the supplement. However, higher rumen undegradable protein intake did not increase milk production, suggesting that rumen undegradable protein was not limiting for cows on pasture producing less than 22 kg of milk.

Sites of digestion and bacterial protein synthesis in dairy heifers fed fresh oats with or without corn or barley grain.

Six Holstein-Friesian heifers fitted with ruminal, duodenal, and ileal cannulas were used in a replicated 3x3 Latin square to study the effects of partial replacement [1:1 dry matter (DM) basis] of fresh winter oats (WO) by ground corn (C) or barley (B) on digestion and bacterial protein synthesis. Supplemented diets contained 24% starch, and all diets were fed indoors at 2.5% of body weight (DM basis). Ruminal and total tract digestibilities of organic matter and neutral detergent fiber were similar for all treatments. Ruminal and total tract starch digestibility was similar for C and B diets. Nitrogen intake was greater for WO than for supplemented diets. However, duodenal flows of nonammonia N and bacterial N did not differ among treatments. The efficiency of bacterial protein synthesis was similar for the three diets, suggesting that the fermentation of high quality fresh forage DM provided sufficient energy for the microorganisms in the rumen. Ruminal ammonia-N concentration was greater for WO than for supplemented diets, and for C than for B diet. Ruminal fluid pH and concentrations of total volatile fatty acid were not different among diets, but concentration of acetate was higher and that of propionate was lower for WO than for supplemented diets and for C than for B diet. Supplementation of WO with barley rather than with corn decreased C2:C3 ratio without affecting fiber digestion. Supplements increased N utilization relative to N intake but did not increase duodenal nonammonia N flow.

Dietary fiber and milk yield, mastication, digestion, and the rate of passage in goats fed alfalfa hay.

Two experiments were conducted to study the effect of intake of fiber on productive performance of high producing dairy goats during early to midlactation. Four dietary treatments were isonitrogenous and consisted of combinations of chopped alfalfa hay and concentrate, yielding 14, 18, 22, and 26% ADF. In Experiment 1, 40 multiparous Alpine does were used in a completely randomized block design. Milk fat content and total chewing time increased, and milk yield tended to decrease, as dietary ADF intake increased. Chewing efficiency [min/(g x kg BW.75)] for DM decreased, whereas that for ADF increased as ADF intake increased. Prediction equations were the following: milk fat yield, g/d = 115.78 - .128 x ADF intake, g/d + .00021 X (ADF intake)2 (r = .55); total chewing time, min/d = 345.33 + .32 x ADF intake, g/d (r = .60). In Experiment 2, 20 does were used in a completely randomized design. Apparent digestibilities of DM and energy decreased as dietary ADF intake increased. Rumen turnover rate and transit time of liquid were affected by ADF intake. Transit time of hay decreased as ADF intake increased. Intake of ADF affected pH and ammonia, acetate, and butyrate concentrations in the rumen. Acetate to propionate ration increased with ADF intake. No apparent trends were observed in whole blood beta-hydroxybutyrate or in plasma NEFA concentrations related to ADF intake. It appeared that DMI and milk fat yield leveled at 22% ADF or 43% NDF. For lactating dairy goats producing more than 3.5 kg/d of milk, calculated fat output reached a plateau when they consumed 587 g/d of ADF and spent 512 min/d chewing.