Influence of carbohydrate source and buffer on rumen fermentation characteristics, milk yield, and milk composition in late-lactation Holstein cows.

The effects of concentrate-to-forage ratio and buffer on rumen fermentation and production parameters were examined in four rumen-cannulated cows (240 +/- 18 d in milk) fed a total mixed ration ad libitum in a 4 x 4 Latin square design. The treatments were a 50:50 concentrate to forage ratio with [1.2% of dry matter, (DM)] and without (0% of DM) buffer and a 75:25 concentrate to forage ratio with (1.2% of DM) and without (0% of DM) buffer. Rumen pH declined in response to increased concentrate but was not influenced by buffer. In the absence of the buffer, rumen acetate declined and propionate was elevated at the higher level of concentrate inclusion. The milk fat concentration was lower for cows fed the high concentrate diet without buffer; however, the addition of buffer to the diet prevented the milk fat depression. Milk fat depression was associated with elevated trans-C18:1 fatty acids in milk, which provides additional support for an inhibitory effect of these fatty acids on mammary fat synthesis. We concluded that the potential of nutrition as a tool to alter milk composition is greater in later lactation as these animals are better able to cope with the negative effects of high grain diets, and the treatment response is greater than in early lactation.

Effects of forage source and amount of concentrate on rumen and intestinal digestion of nutrients in late-lactation cows.

The objectives of this study were to determine the effects of dietary forage source with two concentrate concentrations on dry matter (DM) intake, rumen fill, ruminal and intestinal digestibility of nutrients, and duodenal N fractions in lactating cows. Four rumen and duodenal cannulated Holstein cows in late lactation were used in 4 x 4 Latin square design experiment with 21-d periods. Diets were 1) 65% first-cut alfalfa silage and 35% concentrate, 2) 50% alfalfa and 50% concentrate, 3) 65% bromegrass silage and 35% concentrate, and 4) 50% bromegrass and 50% concentrate. Dry matter intake was not affected by forage source but tended to be (P = 0.08) higher for cows fed diets with 50% concentrate. Rumen fill was greater (P < 0.01) for cows fed bromegrass compared with those fed alfalfa silage. Ruminal and intestinal digestion of DM was not affected by dietary forage source or concentrate level. Total N intake was greater for cows fed alfalfa-based diets, reflecting the higher crude protein content of alfalfa. However, total N flow at the duodenum was not affected by either forage source or concentrate in the diet. Although forage source influenced the site of digestion of some nutrients no significant effects on total tract digestibilities were observed.

Effects of substituting barley grain with corn on ruminal fermentation characteristics, milk yield, and milk composition of Holstein cows.

The influence of corn or barley, or the equal mixture of both, on digestion characteristics and dairy cow performance was evaluated in metabolic and production experiments. Three rumen-cannulated early-lactation cows were used in a 3 x 3 Latin square design experiment to study the effect on ruminal fermentation characteristics and whole-tract digestion of substituting barley grain with corn. Production responses were determined by the use of 27 early-lactation Holstein cows. Cows in the production study were fed the test diets for 12 wk after a 2-wk covariate period. Results from the metabolic study indicated the effects of grain source on ruminal and total-tract digestion to be minimal. Total ruminal volatile fatty acids and acetate concentrations decreased linearly, butyrate increased linearly, and pH and lactic acid concentration were not affected by increasing levels of corn. Apparent digestibility of DM and organic matter showed a quadratic response with increasing the corn level in the diet, with no dietary effect on neutral detergent fiber, acid detergent fiber, and cellulose digestion. Ruminal fermentation characteristics suggest that substitution of barley grain with corn may alter the site of digestion and the end products of digestion that are absorbed by the animal. Multiparous cows failed to respond to treatment, whereas primiparous animals showed the greater response in milk yield and milk-component yield to diets that contained an equal mixture of corn and barley. These results probably reflect a more optimal synchronization of dietary protein and energy for dairy cows fed the 50:50 barley/corn diet.

Influence of carbohydrate source and buffer on rumen fermentation characteristics, milk yield, and milk composition in early-lactation Holstein cows.

The effects of concentrate to forage ratio and sodium bicarbonate (buffer) supplementation on intake, ruminal fermentation characteristics, digestibility coefficients, milk yield, and milk composition were examined in 4 cannulated Holstein cows (100 +/- 20 d in milk). A 4 x 4 Latin square design with 2 x 2 factorial arrangement of treatments was implemented for 3-wk experimental periods. The 4 treatments were a 50:50 concentrate to forage ratio with 1.2% of dry matter (DM) and without added buffer and a 75:25 concentrate to forage ratio with (1.2% of DM) and without (0% of DM) buffer. The forage component of the ration was a 50:50 mixture of alfalfa and barley and triticale silage, and diets were fed ad libitum as a total mixed ration. Although feed intake was not influenced by treatments, substantial treatment differences were observed for milk yield and milk composition. Cows fed high-concentrate diet had lower ruminal pH, ruminal acetate, and butyrate concentrations, whereas propionate concentrations were significantly elevated. The addition of buffer, at both levels of concentrate inclusion, resulted in elevated total volatile fatty acids and acetate concentrations. We concluded that altering the forage concentrate ratio in the diet of lactation cows influenced milk yield and milk composition, but the addition of buffer to the diet prevented the elevation in trans-C18:1 fatty acids in milk fat, and related milk fat depression, associated with feeding high-concentrate diets.

Effect of added dietary fat on performance, rumen characteristics, and plasma metabolites of midlactation dairy cows.

Effects of supplemental Jet-Sploded canola seed in the diets of dairy cows on milk yield and composition and blood metabolite concentrations were investigated. Twenty multiparous and 5 primiparous midlactation Holstein cows were assigned to treatments following a 3-wk covariate period; cows were then on the treatments for 70 d. Ten of the cows had previously been fitted with rumen cannulas. Five concentrate mixtures containing 0, 7.5, 15, 22, or 29% Jet-Sploded canola seed (Simons Feed Co., Quimby, IA) (equivalent to 0, 2.66, 5.33, 7.81, and 10.30% added fat, respectively) were formulated by substituting Jet-Sploded canola seed for barley and canola meal. Diets consisted of 25% alfalfa silage, 25% whole-crop oat silage, and 50% of one of the concentrate mixtures (dry matter basis). An increase in the amount of dietary fat from Jet-Sploded canola seed did not influence feed intake, milk yield or composition, or milk component yields. The inclusion of Jet-Sploded canola seed in the diet increased long-chain fatty acids and inhibited de novo synthesis of medium-chain fatty acids in milk. Mean total volatile fatty acids in the rumen and propionate concentration were reduced in a linear fashion by treatment. The inclusion of Jet-Sploded canola seed in the diets of mid-lactation cows altered rumen and blood metabolite concentrations; however, these changes had minimal effects on yield responses with the exception of milk fatty acid composition and milk protein content.

Site and extent of mineral absorption in lactating cows fed whole-crop cereal grain silage of alfalfa silage.

The site of apparent absorption of Na, K, Ca, P, Mg, and S in lactating dairy cows fed whole-crop barley, oats, triticale, or alfalfa silages was studied. Eight ruminally and duodenally cannulated Holstein cows with ad libitum access to a total mixed diet were assigned to one of four treatments as a replicated 4 x 4 Latin square design. All diets contained the same concentrate (50%, DM basis) plus one experimental silage. The concentrations of Na, K, Ca, P, Mg, and S in the concentrate were .84, .71, .85, .78, .27, and 38%, respectively. Dry matter intake was higher (P < .05) for cows fed alfalfa and barely silages than for cows fed oats and triticale silages (19.6, 18.6, 16.7, and 17.2 kg/d, respectively). Alfalfa silage contained a higher concentration of all minerals studied than the cereal silages, except Na. Sodium flow at the duodenum was substantially greater than dietary intake and apparent total tract digestibilities ranged between 74.5 and 85.2%. Secretion of P in the forestomach ranged from 34 to 61 g/d and the major site of absorption was in the intestine. The correlation between P intake and fecal excretion of P was significant (P < .001, r/ = .39) and linear. Potassium absorption occurred before the duodenum and in the intestine. Apparent digestibilities of K were lower for cereal silages (range 74.0 to 82.9%) than for alfalfa silage (88,7%). Apparent total tract digestibilities of Ca (28 to 32%), P(27 to 34%), and MG (17 to 24%) were similar for all diets so that Ca, P, and Mg absorption (g/d) reflected dietary Ca, P, and Mg levels. Data indicate that forage source can influence the site and extent of absorption, fecal output, and apparent digestibilities of macrominerals.

Forage source alters nutrient supply to the intestine without influencing milk yield.

Eight Holstein cows in early lactation and fitted with ruminal and duodenal cannulas were used in a 4 x 4 Latin square design experiment to determine the influence of forage source on microbial digestion in the rumen and nutrient supply to the intestine and to determine relationships between DMI, ruminal fill, and NDF content of silage. Cows were fed a TMR formulated to contain a 50:50 concentrate:forage ratio. A significant negative correlation was found between dietary NDF concentration (range 32.2 to 37.9%) and DMI (16.7 to 19.6 kg/d). In addition to forage NDF concentration, the lower DMI of cows fed oat or triticale silage (16.7 and 17.2 kg/d, respectively) relative to that of cows fed barley or alfalfa silage (18.6 and 19.6 kg/d, respectively) might reflect a lower true rate of NDF digestion (range 2.39 to 4.09%/h), higher ruminal turnover time (12.9 to 17.1 h), and lower rate of NDF intake (3.31 to 3.96%/h). However, differences in ruminal bacterial yield, ruminal metabolites, and nutrient supply to the intestine associated with different silages had no major effect on dairy cow performance. We concluded that the dairy cow can maintain similar milk yield despite marked differences in the type of end products arising from carbohydrate and protein digestion.

Response of early lactation cows to ruminally undegradable protein in the diet.

The objective of this study was to determine the response of dairy cows in early lactation to diets based on the recommendations of the Agricultural Research Council or the NRC for sustaining milk yield. Diets were formulated to satisfy the nutrient requirements of Holstein cows weighing 600 kg and yielding 35 kg of 3.5% fat milk/d according to either Agricultural Research Council recommendations or NRC recommendations for RUP. A third diet was a 1:1 (wt/wt) mixture of the Agricultural Research Council and the NRC diets. The same forage was fed in all diets at a forage to concentrate ratio of 40:60, and the RUP supply was altered by substituting fish and corn gluten meal for canola meal. The calculated effective degradabilities of CP for the TMR were 70.1, 66.1, and 62.1% for the Agricultural Research Council diet, the mixture of Agricultural Research Council and NRC diets, and the NRC diet, respectively. Milk composition was similar for the three dietary treatments. Multiparous cows showed a linear yield response (30.4, 31.6, and 33.7 kg/d) to increasing inclusion of the NRC concentrate in the diet. No response to additional RUP was observed for first lactation heifers. Agricultural Research Council recommendations for dietary RUP underestimated the requirements for multiparous cows in early lactation yielding > 25 kg of milk/d.

Effects of cereal grain silages versus alfalfa silage on chewing activity and reticular motility in early lactation cows.

Four early lactation Holstein cows fitted with ruminal and duodenal cannulas were used in a 4 x 4 Latin square design experiment to determine the effects of whole crop barley, oat, and triticale silages substituted for alfalfa silage in the forage portion of diets on chewing behavior and the relationships between attributes of reticular contractions and voluntary intake and digesta passage from the reticulorumen. Mean ad libitum DMI was 18.3 kg/d and was affected by diet. Duodenal flows of DM, NDF, and OM were not affected by diet. The frequency and duration of reticular contractions during eating, rumination, and resting were not influenced by diet. Amplitude of reticular contractions during eating was lower for cows fed alfalfa than for those fed barley silage. The NDF of alfalfa was transferred less efficiently than that of cereal silages at the duodenum. Cows fed alfalfa and barley silage diets transferred less NDF per unit of duration than cows fed oat and triticale silage diets. However, an equal amount of NDF was transferred per unit of amplitude of contraction, regardless of diet. Changes in DMI and digesta passage could be explained only partially by changes in chewing activity and attributes of reticular contractions required to transfer each unit of digesta from the reticulorumen.

Influence of dietary protein and starch on production and metabolic responses of dairy cows.

The effects of starch and CP degradability on ruminal digestion, milk yield, and milk composition were evaluated using a 4 x 4 Latin square design. Thirty-six Holstein cows (15 multiparous; 21 primiparous) and 4 ruminally cannulated cows were assigned randomly to four diets. The experiment was conducted during wk 4 through 16 postpartum. Diets contained 60% concentrate and 40% bromegrass hay. Treatments were barley plus canola meal and soybean meal; barley plus corn gluten meal, fish meal, and meat and bone meal; corn plus canola meal and soybean meal; and corn plus corn gluten meal, fish meal, and meat and bone meal. Intake of DM was not influenced by starch source, but CP intake was higher for diets based on corn than for those based on barley. Yields of milk, milk protein, and lactose were higher for diets based on fish meal than canola meal but were not altered by dietary starch source. Milk protein percentage and 4% FCM yield were not altered by dietary protein source. The 4% FCM and milk fat yields were higher for cows fed diets based on corn than for cows fed diets based on barley. Cows fed diets based on corn had significantly lower concentrations of most short- and medium-chain fatty acids and elevated concentrations of C18:0, C18:1, and C18:2 in milk. Protein source significantly influenced milk yield, and milk composition was altered by starch source. However, no interaction was observed between starch and protein sources.

Forestomach and whole tract digestion in lactating dairy cows fed canola meal treated with variable levels of acetic acid.

Five Holstein cows in midlactation were fed four isonitrogenous (mean 2.76% N) mixed diets containing untreated canola meal or replaced with canola meal treated with 0, 33, 67, or 100% of acetic acid in a 12-wk 4 x 4 Latin square experiment. Diets were 50% barely-based concentrate, 12% canola meal, 30% whole crop oat silage, and 8% alfalfa silage (DM basis). Fore-stomach and whole tract apparent digestibilities of DM, OM, and its components, including fiber and CP, did not differ as proportions of treated canola meal increased. Rumen pool sizes of OM, NDF, and bacterial OM, as well as total NAN and bacterial N, were not influenced by treatment, although bacterial N pool size tended to decline as treated canola meal replaced untreated. This result was consistent with a trend for reduced flow of bacterial N at the duodenum. Duodenal flow of AA protein, and its profile, was not influenced by treatment. Results suggest that low level replacement of untreated canola meal with canola meal treated with acetic acid stimulated microbial growth by providing more sustained delivery of slowly degraded true protein. However, at higher substitution, the rumen microbial pool was reduced progressively, perhaps because of a shortage of readily fermentable N. This hypothesis, although not consistent with all data, seems to be the most plausible explanation for all observations, although it is clear that differences in both digestion and duodenal flow, particularly for protein, attributable to replacement of untreated canola meal by that treated with acetic acid were moderate.

Effect of whole crop cereal grain silage substituted for alfalfa silage on performance of lactating dairy cows.

Barley, oats, and triticale were planted at the University of Alberta Research Station May 22 to June 1, 1990, harvested August 5 to August 19, 1990, at the early to mid-dough stage, and ensiled. Second-cutting alfalfa was harvested at midbloom and ensiled. Twenty Holstein cows in early lactation and 24 in midlactation were subjected to a 21-d standardization period (covariate) and were fed a TMR (50:50, forage: concentrate). Forage was a combination of equal portions of silage of alfalfa, barley, oats, and triticale. Following the covariate period, cows were offered TMR for ad libitum intake for 12 wk in which the forage portion of the TMR was one of the four silages. Diets based on oat and triticale silages lowered DMI, but overall milk production was not significantly different across treatments. Digestibilities of DM, OM, CP, and ADF were highest for the alfalfa silage diet, intermediate for the barley silage diet, and lowest for diets based on oat and triticale silages. The high dietary NDF concentration in oat and triticale silage limited feed intake. However, forage source had no major effect on dairy cow performance when forage was fed for ad libitum intake; therefore, barley, oat, and triticale silages harvested at an early stage of maturity can be used effectively in dairy cow rations.

Effect of canola fat on ruminal and total tract digestion, plasma hormones, and metabolites in lactating dairy cows.

The effects of canola fat on digestion and metabolism were investigated by incorporating 0, 4.5, 9, 13.2, or 17.4% Jet-Sploded canola seed into a diet containing a 60:40 (DM) concentrate:forage ratio. The diets contained 16.5% CP, 30% alfalfa silage, and 10% whole-crop oat silage on a DM basis and were fed for ad libitum consumption as TMR to 10 ruminally cannulated Holstein cows in early lactation. Jet-Sploded canola seed supplementation did not change ruminal pH or NH3 N concentrations, but VFA concentrations declined with increasing level of inclusion. Apparent digestibilities of DM, OM, CP, NDF, and ADF were unaffected by level of inclusion of Jet-Sploded canola seed, but ether extract digestibility declined linearly, which resulted in similar ether extract absorption across the three diets supplemented with canola fat. Based on in sacco data, the percentages of ruminal digestion of OM and CP declined with increasing inclusion of Jet-Sploded canola seed. Plasma glucose and FFA concentrations tended to respond in a quadratic fashion, plasma insulin concentration declined linearly, and plasma glucagon and somatotropin concentrations were unaffected by dietary treatment. The results indicate that a positive productive response may be expected from dietary inclusion of about 5% Jet-Sploded canola seed, but the benefits of increased energy density associated with higher inclusion levels may be offset by reduced availability of energy in the rumen and decreased fat digestibility postruminally. The substantial effects of time postfeeding on ruminal fermentation and on concentrations of plasma hormone and metabolites in animals fed TMR demonstrate that infrequent sampling can result in misleading results and, thus, invalid interpretation of the influence of dietary fat on these parameters.

Influence of canola fat on yield, fat percentage, fatty acid profile, and nitrogen fractions in Holstein milk.

Effects of canola fat on feed intake, yield, and composition of milk of early lactation dairy cows were investigated. Concentrate mixtures containing 0, 2.5, 5.0, 7.3, and 9.6% added fat as Jet-Sploded whole canola seed (0, 4.5, 9.0, 13.2, and 17.4% of DM, respectively) were fed to 15 cows in diets containing 60% concentrate and 40% forage (DM basis). Diets contained 16.5% CP, 30% alfalfa silage, and 10% whole crop oat silage (DM basis). There was a trend for a cubic effect on DMI, a quadratic effect on milk yield, and a small, but significant, linear decrease in milk protein percentage with increasing level of canola seed; the decrease was primarily in the casein fraction. Although milk fat percentage was not altered, addition of Jet-Sploded canola seed caused a substantial reduction in some short- and medium-chain fatty acids and a concomitant increase of as much as 65% in the concentration of C18:1. Results suggest that canola fat from Jet-Sploded whole canola seed can be included up to 5% of dietary DM without negative effects on DMI and with a net positive effect on milk yield.

Digestion of soybean meal and canola meal protein and amino acids in the digestive tract of young ruminants.

Eight male Holstein calves (body weight 68 +/- 5 kg; age 75 +/- 6 d), each with a permanent re-entrant pancreatic cannula and T-type ileal and duodenal cannulas, were used in a crossover design with four animals per group to determine amino acid kinetics and digestibilities in the digestive tract of calves fed soybean meal (SBM) and canola meal (CM) protein. The SBM and CM diets were fed twice daily at a level of 900 g at each feeding time (air-dry basis). With the exception of methionine, crude protein and amino acid flows at the proximal duodenum, expressed as a percentage of intake, were not influenced by dietary protein source. Apparent ileal and total tract digestibilities of CP and amino acids were reduced (P less than .05) by feeding CM compared to SBM, but apparent ileal digestibility of methionine was not affected by dietary protein source. Except for methionine, net disappearance of all amino acids in the small intestine, relative to the amount fed, was higher for the SBM diet than for the CM diet. Net disappearance or synthesis of amino acids in the large intestine were not affected by dietary protein source. Similarly, dietary protein source did not affect (P greater than .05) the secretion of pancreatic juice or concentrations of protein, chymotrypsin and trypsin in pancreatic juice. Soybean meal protein has higher ileal and total gastrointestinal tract digestibility than CM protein for young, growing calves.

Substitution of milk protein with isolated soy protein in calf milk replacers.

The influence of replacement of milk protein by isolated soy protein on digestion and pancreatic enzyme secretion was determined in nine Holstein male calves. Calves (average weight 47 kg) were fitted with permanent re-entrant pancreatic and a T-type cannula in the distal ileum at 6 to 10 d of age. Following a 2-wk recuperation period, the calves were fed three milk replacers in a triplicated 3 x 3 latin square. Experimental diets consisted of a control, in which 100% of the CP originated from spray-dried skim milk powder (SM), and the test diets, in which 50% (SM/ISP) or 100% (ISP) of the skim milk protein was replaced by isolated soy protein. Each experimental period lasted 2 wk. Replacement of SM protein by ISP decreased (P less than .05) the digestibilities of protein and most amino acids. Ileal digestibilities of total indispensable amino acids for SM, SM/ISP and ISP diets were 82.1, 75.8 and 61.8%, respectively, and total tract digestibilities of total indispensable amino acids were 90.0, 82.6 and 74.0%, respectively. Including ISP did not affect (P greater than .05) the volume of secretion of pancreatic juice, protein or chymotrypsin; however, the secretion of trypsin decreased (P less than .05). Reduction in trypsin secretion may be responsible, in part, for the lower amino acid digestibilities in milk replacers containing isolated soy protein.