Milk fatty acid composition of cows fed a total mixed ration or pasture plus concentrates replacing corn with fat.

Thirty-one Holstein cows (six ruminally cannulated) were used to evaluate milk fatty acids (FA) composition and conjugated linoleic acid (CLA) content on three dietary treatments: 1) total mixed rations (TMR), 2) pasture (Avena sativa L.) plus 6.7 kg DM/d of corn-based concentrate (PCorn), and 3) pasture plus PCorn with 0.8 kg DM/d of Ca salts of unsaturated FA replacing 1.9 kg DM/d of corn (PFat). No differences were found in total (22.4 kg/d) or pasture (18.5 kg/d) dry matter intake, ruminal pH, or total volatile fatty acids concentrations. Fat supplementation did not affect pasture neutral detergent fiber digestion. Milk production did not differ among treatments (19.9 kg/d) but 4% fat-corrected milk was lower for cows fed the PFat compared to cows fed the TMR (16.1 vs. 19.5 kg/d) primarily because of the lower milk fat percentage (2.56 vs. 3.91%). Milk protein concentration was higher for cows fed the TMR than those on both pasture treatments (3.70 vs. 3.45%). Milk from the cows fed the PCorn had a lower content of short- (11.9 vs. 10.4 g/100 g) and medium-chain (56.5 vs. 47.6 g/100 g) FA, and a higher C18:3 percentage (0.07 vs. 0.57 g/100 g) compared with TMR-fed. Cows fed the PFat had the lowest content of short- (8.85 g/100 g) and medium-chain (41.0 g/100 g) FA, and the highest of long-chain FA (51.4 g/100 g). The CLA content was higher for cows in PCorn treatment (1.12 g/100 g FA) compared with cows fed the TMR (0.41 g/100 g FA), whereas the cows fed the PFat had the highest content (1.91 g/100 g FA). Pasture-based diets increased the concentrations of long-chain unsaturated FA and CLA in milk fat. The partial replacement of corn grain by Ca salts of unsaturated FA in grazing cows accentuated these changes. However, those changes in milk FA composition were related to a depression in milk fat.

Supplemental carbohydrate sources for lactating dairy cows on pasture.

Two experiments were conducted to evaluate steam-flaked corn and nonforage fiber sources as supplemental carbohydrates for lactating dairy cows on pasture. Cows were allotted to a new paddock of an orchardgrass (Dactylis glomerata L.) pasture twice daily in one group in both trials. In experiment 1, 28 Holstein cows, averaging 216 d in milk, were randomly assigned to either a cracked-corn (CC) or a steam-flaked (SFC) supplement in a split plot design. The supplement contained 66.7% of corn and a protein/mineral pellet. In experiment 2, 28 Holstein cows, averaging 182 d in milk, were randomly assigned to either a ground corn (GC) or a nonforage fiber (NFF)-based supplemented in a single reversal design. The GC supplement contained 85% ground corn plus protein, mineral, and vitamins. The NFF supplement contained 35% ground corn, 18% beet pulp, 18% soyhulls, 8% wheat middlings plus protein, mineral, and vitamins. In both experiments, cows were fed the grain supplement twice daily after each milking at 1 kg/4 kg milk. In experiment 1, milk production (24.3 kg/d) and composition did not differ between treatments; however, plasma and milk urea N were lower with the SFC supplement. In experiment 2, milk production (27.5 kg/d) was not affected by treatments, which may be related to the medium quality of pasture grazed. The GC supplement tended to reduce plasma and milk urea N and increased milk protein percentage (3.23 vs. 3.19%). Pasture dry matter intake, measured using Cr2O3, did not differ between treatments in either experiment 1 (15.1 kg/d) or experiment 2 (12.2 kg/d). Milk production did not differ when mid-late lactation cows on pasture were supplemented with SFC or NFF instead of dry corn.

Invited review: production and digestion of supplemented dairy cows on pasture.

Literature with data from dairy cows on pasture was reviewed to evaluate the effects of supplementation on intake, milk production and composition, and ruminal and postruminal digestion. Low dry matter intake (DMI) of pasture has been identified as a major factor limiting milk production by high producing dairy cows. Pasture DMI in grazing cows is a function of grazing time, biting rate, and bite mass. Concentrate supplementation did not affect biting rate (58 bites/min) or bite mass (0.47 g of DM/bite) but reduced grazing time 12 min/d per kilogram of concentrate compared with unsupplemented cows (574 min/d). Substitution rate, or the reduction in pasture DMI per kilogram of concentrate, is a factor which may explain the variation in milk response to supplementation. A negative relationship exists between substitution rate and milk response; the lower the substitution rate the higher the milk response to supplements. Milk production increases linearly as the amount of concentrate increases from 1.2 to 10 kg DM/d, with an overall milk response of 1 kg milk/kg concentrate. Compared with pasture-only diets, increasing the amount of concentrate supplementation up to 10 kg DM/d increased total DMI 24%, milk production 22%, and milk protein percentage 4%, but reduced milk fat percentage 6%. Compared with dry ground corn, supplementation with nonforage fiber sources or processed corn did not affect total DMI, milk production, or milk composition. Replacing ruminal degradable protein sources with ruminal undegradable protein sources in concentrates did not consistently affect milk production or composition. Forage supplementation did not affect production when substitution rate was high. Fat supplementation increased milk production by 6%, without affecting milk fat and protein content. Increasing concentrate from 1.1 to 10 kg DM/d reduced ruminal pH 0.08 and NH3-N concentration 6.59 mg/dl, compared with pasture-only diets. Replacing dry corn by high moisture corn, steam-flaked or steam-rolled corn, barley, or fiber-based concentrates reduced ruminal NH3-N concentration 4.36 mg/dl. Supplementation did not affect in situ pasture digestion, except for a reduction in rate of degradation when high amounts of concentrate were supplemented. Supplementation with energy concentrates reduced digestibility of neutral detergent fiber and intake of N but did not affect digestibility of organic matter or flow of microbial N.

Performance of high producing dairy cows with three different feeding systems combining pasture and total mixed rations.

Forty-five Holsteins cows in early to mid lactation were used to compare three feeding systems combining pasture and total mixed rations (TMR) on animal performance in a 21-wk repeated-measures experiment. The three treatments were: 1) pasture plus concentrate (PC), 2) pasture plus partial TMR (pTMR), and 3) TMR (non-pasture). Total dry matter intake, using chromic oxide as a marker, was 21.6, 25.2, and 26.7 kg/d for PC, pTMR, and TMR, respectively. Milk production was highest for TMR (38.1 kg/d), lowest on PC (28.5 kg/d), and intermediate for pTMR (32.0 kg/d). Cows on pTMR and TMR had higher milk fat and true protein percentages than cows on PC. Cows on PC gained less body weight and lost more body condition compared with cows on pTMR and TMR. Initial concentrations of plasma nonesterified fatty acids were higher on PC (302 microeq/L) than on pTMR (130 microeq/L) and TMR (225 microeq/L). Plasma and milk urea nitrogen were lower on both pTMR and TMR than on PC. Combining pasture and TMR resulted in higher milk production, milk fat and protein percentage, and maintenance in body condition score compared to pasture plus concentrate. The TMR feeding system resulted in the highest total dry matter intake and milk production.

Ruminal digestion and fermentation of high-producing dairy cows with three different feeding systems combining pasture and total mixed rations.

Six multiparous Holstein cows fitted with rumen cannulas were used to study the effect of three feeding systems combining pasture and total mixed rations (TMR) on ruminal digestion in a 21-wk repeated measures experiment. The three treatments were: 1) pasture plus concentrate (PC), 2) pasture plus partial TMR (pTMR), and 3) TMR (nonpasture). Ruminal NH3-N concentration was lower on both the pTMR and TMR treatments (10.2 +/- 0.5 mg/dL) than on the PC treatment (19.9 +/- 0.5 mg/dL). Ruminal pH was not affected by treatments and averaged 5.87. Neither total volatile fatty acid concentration (137.5 mmol/L) nor individual volatile fatty acid proportions (63.1,20.6, and 12.0 mol/ 100 mol for acetate, propionate, and butyrate, respectively) differed among treatments. The pTMR treatment reduced the total potentially degradable fraction of dry matter (85.5 vs. 82.3%) and the potentially digestible fraction of neutral detergent fiber (82.1 vs. 74.9%) of pasture compared to the PC treatment. Ruminal NH3-N losses were reduced when combining pasture and TMR; however this combination decreased the ruminal digestion of pasture, indicating the presence of associative effects in the rumen.

Milk response to concentrate supplementation of high producing dairy cows grazing at two pasture allowances.

Twenty multiparous Holstein cows (four ruminally cannulated) in five 4 x 4 Latin squares with 21-d periods were used to study the effect of concentrate supplementation when grazed at two pasture allowances. The four dietary treatments resulted from the combination of two pasture allowance targets (low, 25 vs. high, 40 kg of dry matter/cow per day) and two concentrate supplementation levels (zero vs. 1 kg of concentrate/4 kg of milk). Concentrate supplementation decreased pasture dry matter intake 2.0 kg/d at the low pasture allowance (17.5 vs. 15.5 kg/d) and 4.4 kg/d at the high pasture allowance (20.5 vs. 16.1 kg/d). Substitution rate was lower at the low pasture allowance (0.26 kg pasture/kg concentrate) than at the high pasture allowance (0.55 kg of pasture/kg of concentrate). Total dry matter intake of both supplemented treatments averaged 24.4 kg/d. Milk production of both supplemented treatments averaged 29.8 kg/d, but was increased with higher pasture allowance in the unsupplemented treatments (19.1 vs. 22.2 kg/d). Milk response to concentrate supplementation was 1.36 and 0.96 kg of milk/kg of concentrate for the low and high pasture allowances, respectively. Concentrate supplementation reduced milk fat percentage but increased milk protein percentage. Rumen pH and NH3-N concentration were decreased with concentrate supplementation. Substitution rate was likely related to both negative associative effects in the rumen (reductions in rumen pH, rate of pasture digestion, and NDF digestibility) and reductions in grazing time. The latter was more important, quantitatively explaining at least 80% of the reduction in pasture dry matter intake observed.

Evaluating nitrogen management options for reducing nitrate leaching from northeast U.S. pastures.

Substantial amounts of nitrate nitrogen NO3-N can leach from intensively grazed pasture in the northeast U.S. where there is about 30 cm of groundwater recharge, annually. Management options for reducing NO3-N leaching were evaluated for this environment using the Cornell Net Carbohydrate and Protein System Model and a recently developed nitrogen leaching index. Management options utilizing energy supplementation of grazing dairy cows could improve nitrogen efficiency within the cow, but would not necessarily reduce NO3-N leaching at the pasture scale if stocking rate was not controlled. The management option of using white clover to supply nitrogen to the pasture decreased NO3-N leaching, but produced less dry matter yield, which in turn reduced stocking rate. The economic returns of reducing NO3-N with these options need to be evaluated in light of milk prices and commodity and fertilizer nitrogen costs. At current prices and costs, the economic benefit from the energy supplementation options is substantial.